FOURTH TOPICAL WORKSHOP ON PROTON-ANTIPROTON ...

CERN 84 -09 8 August 1984

O R G A N I S A T I O N E U R O P É E N N E P O U R LA R E C H E R C H E N U C L E A I R E

CERN E U R O P E A N O R G A N I Z A T I O N F O R N U C L E A R R E S E A R C H

FOURTH TOPICAL WORKSHOP ON PROTON-ANTIPROTON COLLIDER PHYSICS

Berne, 5-8 March 1984

PROCEEDINGS Editors: [ H . H ä n n i

J . Schacher

w r î T "

GENEVA 1984

CERN — Service d'Information scientifique — RD/64I - 2000 - août 1984

Universität Bern Physikalisches Institut Laboratorium für Hochenergiephysik

Previoui wotkihopi: Collège d* France 1979, Univeniryef Wltconiin 1981, Rami Uní

4th TOPICAL WORKSHOP ON PROTON ANTIPROTON COLLIDER PHYSICS

„„„.3 BERN, MARCH 5-8, 1984

I * I

G Brionti P. Darnulat 8 Hahn P. Minkowski i. Mulvey li Nanopgtilos C Rubb.a G. Salv.n. A Tollcstrup

TOPICS : - W ±and2°physscs — Jets and QCD — Heavy flavours, Higgs,... — Supersymmetry and substructure — Present and future pp and pp-colliders — Future pp-physics

LOCAL ORGANIZING COMMITTEE K. Borer J. Gasser H.Honn, fl. Hahn (Charm-P. Moni J. Schacher F. Stocker W. Zeller

ÚDRESS Mrs. I. Maní Laboratorium für Hochenergiephysik Sidlersrrasse 5 CH-30l?_Bern Switzerland

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ABSTRACT

T h e most e x c i t i n g top ic at t h ' s Workshop was c l e a r l y t h e exper imenta l h int f o r new u n e x p e c t e d phenomena, r e p o r t e d b y t h e UA1 a n d UA2 Col laborat ions: A t t h e C E R N SPS Co l l ider ( V s = 540 G e V ) , a few events w e r e o b s e r v e d w i t h h igh missing t r a n s v e r s e energy in associa'

t ion wi th an isolated e lectromagnet ic c l u s t e r o r one o r more h a r d je ts ( U A 1 ) o r an isolated e lec t ron and one o r t w o h a r d je ts ( U A 2 ) . Due to t h e enhanced data sample, t h e d iscovery of t h e in te rmedia te v e c t o r bosons W and Z in 1983 was u n d o u b t e d l y con f i rmed , a n d the nice agreement of t h e i r p roper t i es w i t h t h e pred ic t ions of t h e elect r o weak t h e o r y was s h o w n . In a d d i t i o n , many new resul ts on e x p e r i mental and theoret ica l j e t physics w e r e p r e s e n t e d . T h e T e v a t r o n Col l ider p ro jec t and its p lanned exper iments at Fermi lab w e r e d i s c u s s e d , a n d t h e r e were c o n t r i b u t i o n s a b o u t t h e possible f u t u r e developments in t h e o r y (compos i ten ess , s u p e r s y m m e t r y ) as wel l as in exper imenta l h igh e n e r g y physics ( S u p e r c o l l i d e r , J u r a t r o n ) . 5 c A W*IS

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FOREWORD

I t was wi th g r e a t p leasure t h a t w e , the members of the High E n e r g y Physics Lab of the U n i v e r s i t y of B e r n e ( S w i t z e r l a n d ) , have o rgan ized t h e 4 t h Topica l Workshop on P r o t o n - A n t i p r o t o n Col l ider Phys ics , which was held in t h e aula of t h e Berne U n i v e r s i t y on March 5-8 1984. We wou ld l ike to t h a n k e v e r y b o d y who has c o n t r i b u t e d to i t in one way or another to make i t successfu l . O u r special t h a n k s go to t h e speakers whose t a l k s formed t h e f lesh of t h e confe rence and who have been so k ind as to send us t h e i r w r i t t e n vers ions w i th in a reasonable t ime (w i th a few except ions , of c o u r s e ) .

T h e h igh l igh t of t h e prev ious Workshop held in Rome in J a n u a r y 1983 was c lear ly t h e presentat ion of t h e f i r s t candidates f o r t h e leptonic decay of t h e charged in termediate vector boson W wi th exac t ly t h e f e a t u r e s expected f rom the Gla -show-Salam-Weinberg model of t h e e lect roweak i n t e r a c t i o n . In th is respect , the Berne Workshop has b r o u g h t not on ly the conf i rmat ion of the ex is tence of the W boson and of Its neu t ra l p a r t n e r , t h e Z boson, b u t impressive ve r i f i ca t ion of t h e e lectroweak t h e o r y as a whole: T h e p r o p e r t i e s of t h e in termediate vector bosons measured b y UA1 and UA2 at the C E R N pp col l ider a re in exce l lent agreement w i th t h e pred ic t ions of t h e s t a n d a r d model .

However , whi le t h e so called "convent ional" phys ics seemed to be safer than e v e r , the a t tent ion of t h e par t ic ipants was d r i v e n to a few unexpected events which may well lead h igh e n e r g y physics b e y o n d the minimal model of the weak in te rac t ion ; UA1 has r e p o r t e d on events w i t h h igh missing t r a n s v e r s e e n e r g y containing an isolated e lectromagnet ic c lus te r o r one or more h a r d j e t s . UA2 in its t u r n has found a few events wi th high missing t r a n s v e r s e e n e r g y , an isolat ed e lectron and one or two h a r d j e t s . None of these events a re l ike ly to come f rom o r d i n a r y W o r Z product ion and d e c a y , o r f rom o t h e r known processes. T h e UA2 e v e n t s , of which one is compatible w i t h W - p a i r p r o d u c t i o n , suggest an unknown massive state well above the W and Z mass. A h in t of such a new massive object is also seen in t h e t w o - j e t mass d i s t r i b u t i o n of U A 2 . Whether alt these new phenomena wil l s tay and be conf i rmed at the 5th pp Workshop, which will be held at S a i n t - V i n c e n t in the Aosta va l ley f rom F e b r u a r y 25th to March 2nd 1985, we do not know. But s u r e l y w i th t h e nex t C E R N pp r u n at Vs=630 G e V s t a r t i n g in September of th is y e a r t h e r e is an exc i t ing time to come f o r t h e h igh e n e r g y physics community . In th is sense the Berne Work shop has j u s t s ignaled the s t a r t of a race into an "exot ic" land of new p h y s i c s .

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T h e exc i t ing a d v e n t u r e of e x p l o r i n g th is new land will be shared soon b y o u r

colleagues w o r k i n g at Fermi lab , as we learned f r o m var ious i n t e r e s t i n g ta lks

about t h e T e v a t r o n p p col l ider pro jec t and its exper iments C D F and DO.

Final ly we hope t h a t those who a t tended th is conference en joyed t h e i r t ime in B e r n e . O u r U n i v e r s i t y is p r o u d of h a v i n g been g i v e n t h e o p p o r t u n i t y to host th is W o r k s h o p , fo l lowing its t r ad i t ion as a place w h e r e revo lu t ionary physics has e vo fved .

We would l ike to t h a n k A . G ü n t h e r f rom C E R N as well as t h e C E R N A u t h o r i t i e s f o r t h e i r permission and s u p p o r t in b r i n g i n g these Proceedings o u t as a C E R N yellow r e p o r t .

Hans H ä n n i , U n i v . of B e r n e J i i r g Schacher , U n i v . of B e r n e

ACKNOWLEDGEMENTS

We would l ike to t h a n k Prof . F r i t z G y g i f o r t h e hospi ta l i ty he o f fe red in t h e new aula of t h e U n i v e r s i t y of B e r n e , as wel l as f o r his nice open ing speech of the conference .

We a re also g r a t e f u l t o t h e V i c e Pres ident of t h e Government of the Canton of B e r n e , D r . Hans K r ä h e n b ü h l , who not on ly p r o v i d e d a cocktai l p a r t y at t h e Berne R a t h a u s , b u t also d e l i v e r e d a welcome speech which was h igh ly a p p r e c i a t e d .

Special t h a n k s go to M r s . Ida Mani and to M r s . V e r a D v o r a k f o r t h e i r exce l len t secretar ia l w o r k . T h e y have been k ind ly assisted d u r i n g t h e conference b y M r s . Mirel la Kel ler of C E R N .

We g r a t e f u l l y acknowledge t h e f inancia l s u p p o r t of the Scient i f ic Ins t i tu t ions a n d o t h e r Author i t i es t h a t made th is Workshop possib le:

- C R I S M A T E C , G r e n o b l e , France

- Schweizer ischer Nat ional fonds z u r F o r d e r u n g d e r wissenschaf t l ichen Forschung

- Schweizer ische N a t u r f o r s c h e n d e Gesel lschaf t

- Bern ische K r a f t w e r k e AG

- Gfe l le r Telecommunicat ions, Bern

- Phi l - na t . F a k u l t ä t d e r U n i v e r s i t ä t B e r n

T h e O r g a n i z i n g Committee

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CONTENTS

Page Ko.

vii B, Hahn

Introduction

J e t Physich 5 W. Scott <UA1 Collaboration)

Jets in the UA1 experiment 6 J.R. Hansen (UA2 Collaboration)

High P T jets from pp collisions at /s = 540 GeV in UA2 20 R.D. Field

Jet topologies in hadron-hadron collisions 46 G. Sohierkolz

Comparison of quark and gluon jets 84 Z. Ximszt

Triple and quadruple jets 102 B. Humpert

Jets: what we can still learn ... 108 IV.iV. Geist

Recent results from high transverse momentum processes at the ISR 114

if. Jf. Ellis

Transverse momentum distributions of jets and weak bosons 132

H,Z Physics and Standard Model 141 J. Schacher (UA2 Collaboration) +

Production of high mass ev and e e pairs in the UA2 experiment at the CERN pp collider 142

W.J. Marciano

Electroweak interaction parameters 165 P. Minkowski

(\3~,Z): Production from pp and decay 181 M. Greco

QCD p^, effects in W/Z and jet production 202 F. Herzog

Testing the WWy coupling of the Glashow-Salam-Weinberg model at pp colliders 209

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The New Events

C. Rubbia ÍUA1 Collaboration) Experimental observation of events with large missing transverse energy accompanied by a jet or a photon(s) in pp collisions at fk = 540 GeV

A. Rouesarie (UA2 Collaboration) observation of electrons produced in association with hard j^ts and large missing transverse momentum in pp collisions at - 540 GeV

Heavy Flavours and Rela ted Topics

R. Frey (UAl Collaboration) D*- production at the CERN SPS collider

C. Jarlekog Weak mixing angles and heavy flavours

F. Holzen and A.D. Martin The search for new flavours

f / . J . Stirling The minimum mass technique for detecting new heavy states in high energy hadron collisions

UA5 Resul ts

P. Carleon (UA5 Collaboration) New results from UA5: strange particle (K°, A, E ) production and large fluctuation in multiplicities

pp and pp E l a s t i c S c a t t e r i n g

A. Martin Elastic scattering

E* Senzi

New shape-effects in proton-antiproton elastic scattering F. Cervelli

Mew measurement of elastic scattering and total cross-section at the CERN pp collider

LEAR Physics

K. Kilian Physics vith antiprotons at LEAR

Upgrading o f CERN pp C o l l i d e r and Experiments

B. de Rood The SPS pp collider. Present performance and future prospecta

R. Billings pp-source at CERN

H. Jiofftoœm UAl improvement programme

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P. Jenni (ÜA2 Collaboration) UA2 future

Fermilab pp C o l l i d e r and Experiments

M. Harrison The Ferrailab pp collider

D. Theriot The collider detector (CDF) at Fermilab - An overview

M.D. Marx The D0 project at Fennilab

J. Freeman Transverse energy physics w'.th the CDF calorimeter

G.E. Theodosiou D0: Missing-py physics and detector design considerations

K. Hondo CDF electromagnetic shower counters

Supercolliders

I. Hinchliffe Supercollider physics

G, Brianti Large hadron collider in the LEP tunnel

Beyond the Standard Model

D. Wyler Higgs scalars and alternatives

R.D. Pecaei Compositeness and the Fermi scale

G. Pancheri Excited fermions

A. Masiero

Gluino mass and CP violation in supersywmetric models

C. Kounnas

Low energy particle spectrum from eupergvavity

D. NanopouloB 3 upe rsyraniefc ry

Summary and Conclusions J. Ellis

New collider physics

L i s t o f p a r t i c i p a n t s

LIST OF CHAIRMEN

G . Br ian t i ( C E R N ) I . B u t t e n v o r t h ( C E R N ) P. D a r r í u l a t ( C E R N ) L. Di Leila ( C E R N )

G . Ekspong ( U n i v . of Stockholm) R. Gat to ( U n i v . of G e n e v a ) M. Jacob ( C E R N ) H . L e u t w y l e r ( U n i v . of Berne ) D . Nanopoulos ( C E R N )

G . Salv in i ( U n i v . of Rome) W. Selove ( U n i v . of Pennsy lvan ia ) A . T o l l e s t r u p ( F e r m i l a b )

Introduction

Hopefully more interesting things are to appear during this conference than I will be able to say in Lhis introduction. Therefore I limit myself to a few remarks which have to d o w i t h the efforts done exactly 20 years ago, when we were searching for the W at Brookhaven and at CERN with v-beams. At that time it was suggested by Lee, Yang and Yamaguchi, that w e should look for the W in the interaction v,A -»• W u X

I » e \>e or v v y

with the nice signatures of a u-pai.r o r a y-e pair. In the spark chamber group at CERN we were just 13 physicists, mostly P r o f e s sors, and we had a lot of fun since several u-u and u-e pair c a n didates showed up. At the Siena Conference in 1963 Louis Alvarez asked the authoritarian question: "When I go home to Berkeley can I say to my colleagues you have found the W, yes or no ?". T h e r e was a loud silence, from which he concluded that the answ; r was n o and he was right. A careful analysis showed that the inteiesting candidates must have been due to non interacting charged pions or to electron showers coming from neutral pions, the decay y's converting very close to the vertex. For general amusement, I should mention that in the 1964 publication it read at one p l a c e immediate boson instead of intermediate boson and indeed the W disappeared immediately. Only a lower limit for the W - m a s s of approximately 2 GeV could be quoted in the paper of the spark chamber experiment. The personal merit for the limit was 150 MeV per physicist.

Subsequently the limit was pushed up by Brookhaven to 8 GeV. Then a long time span elapsed until the Rome and Berne meeting with n e w discoveries inbetvrjen, in particular that of the w e a k neutral currents. T h e efforts increased with respect to machines, detectors, number of physicists, but not much on the financial side. Five years ago t h e experimentalists and the machine physicists and engineers got a difficult home work assignment given by a number of theoreticians. As you know, this task was not easy and I

consider the technical and experimental achievements a minor miracle, since they were accomplished in a style, which I call t h e pseudodemocratic collective style which is strongly contradictory to whab we would expect of scientists, w h o are by definition intro or extraverted individuals. But obviously it depends on the g o a l .

The situation is illustrated in the following p i c t u r e , which represents the climbing by more and more competitors of a mountain chain which becomes higher and higher. Some climbers must be pushed by their colleagues, some return and give up, some fall down and a few succeed t o be among the first g r o u p . I am furtlv tempted to compare the situation to a sport race, the difference being that in sport, you can be first and get a medal but in physics you can be first and have a discovery and a m e d a l . The personal merit per physicist in this marathon -s the discovery of 500 MeV each of the W and Z ° , which have been found in this p i c ture on the last m o u n t a i n , the one which looks like the Matter-horn.

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Where are we now at this workshop ? We are sitting in a comfortable bivouac at some altitude and are thinking. There is no big or bigger une limbed mountain in sight. Instead there is a predesert in view and there is already one man rushing away, whose name I prefer not to m e n t i o n . This time the m a c h i n e people and the experimentalists are taking the lead. There is only very vague guidance by the theoreticians as to where to g o , and in fact they take from the hands of t h e experimentalists each crazy event and rush to interpret it prematurely. I leave to John Ellis, w h o was so kind as to accept the job of drawing the conclusions at the end of the workshop, the task of forecasting the future.

To close my introduction I would like to say a. word on the B e r n e s e . They are internationally known to b e very slow but good natured and agreeable. I am from Basle. Anyhow, w e have nice weather here in Berne, and I recommend that you partake of this conference for your pleasure. I wish you a nice stay in Berne and maybe also some surprises in Physics.

Beat Hahn

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Jet Physics

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JETS IN THE UAl EXPERIMENT

W.G. Scott (UAl Collaboration)

~Í~11tS'AClíb D: 8 4 1 0 0 2 6 0 8 2

X. TWO-JET CROSS-SECTION

1.1 Introduction

P**" The UAl two-jet cross-section based on the 1982 data has been published already**". He review that data briefly here and make a few additional comments. I

1.2 Theory

A point we emphasize particularly Is the theoretical simplicity of the two-jet cross-section in OCD. In a very good approximation the entire bwo-

on cm.a. scattering angle 6 which is completely analogous to the Rutherford scattering formula, and a single pure flavour singlet structure function:

This approximate description becomes exact in the limit cos 6 -» 1, i.e. for small c.m.s. scattering angles.

1.3 Angular diptribufcions

The angular distributions for various I1

Ia intervals are shown in

Fig. 1. The combined angular distribution obtained on the assumption that the angular dependence is independent of x^ and x is shown in Fig. 2. The combined angular distribution (Fig. 2) uses all the available statistics but has the disadvantage that and x^ (and hence, for example, the relative contributions of the various subprocesses) are varying across the plot. In general we prefer the angular distributions separated la x^ and

x . s

In Fig. 2 the axes have been chosen to display a power law dependence <1 - cos e> n for cos 0 -» 1. The daba have a tendency to rise above the leading order predictions (n = 2) for large cos 6 end this is reflected in the fitted value of n (n = 2.38 ± 0.10 for cos 9 > 0.4).

jet cross-section may be described in terms of a (1 - cos 6) dependence

F(xï = G(x) + 4/9 [Q<x)+Q<xí] <li

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A similar effect has boon observed, previously in *n ISR experiment and was satisfactorily accounted for largely in termi of the variation of a ß

with Q 2 .

Figure 3 shows the combined angular distribution plotted versus the variable x = d + C O B 0)/<l - cos ©) [cot 2 6/2], defined by Coatbridge and Maxwell 3'. If the angular dependence follows the Rutherford law precisely then the x distribution will be flat. In Pig. 3 the solid curves represent the x. dependence predicted by leading order QCD and the broken curves indicate the expected modification due to the Q a dependence of c t & . tie conclude that it will be necessary to account properly for the Q a dependence of « before any attempt is made to distinguish the various subprocasses on the s basis of the angular distribution.

1.4 Factorization test

Figure 4 shows the test of factorization in z and x . We remark 1 2

that the factorization test is independent of the assumed value of K and largely independent of energy scale uncertainties and Btnearing corrections.

1. !i Structure functions

Figure 5 shows the structure function F<x) computed from the two-jet data assuming factorisation in x and x and K = 2. Note that the varia-l a tion of a with Q has been taken into account in the determination of the s structure function. The systematic error (due to the uncertainty in the jet energy scale) is estimated to be = ±30%.

Over most of the available range in x the data show a largely exponential x dependence suggestive of a statistical sharing of momentum between the partons 4 . The data are in fair agreement with measurements of F(x) extrapolated in Q 3 from fixed target (neutrino) e x p e r i m e n t s 9 w h e r e the gluon contribution has been inferred from measurements af the scaling violations .

As a final step we subtract from the two-jet data the quark and anti-quark contributions {as extrapolated from the fixed target experiments) in

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order to obtain the gluou structure function directly. The gluon structure function is shown in Fig. 6 where the plotted error» include the estimated systematic errors on the two-jet data. Two fits have been made to the data:

G(x) = (12.0 ± 3.2X1 - x )1 G - 0 ± 2 * * x a 0.05-O.B

Í2) = <7.9 t 1.8X1 - x ) 1 1 * 1 1 ' * x * 0-1-0.80 .

We conclude that for these values of Q 2 the gluon distribution is a very rapidly falling function of x and in particular for x i 0.3 the contribution of the gluons is unraeasurably small.

1.6 Jet charge asymmetry

Figure 7 shows some preliminary data on the mean charge of the leading track/jet as a function of the pseudo-rapidity of the jet. The data are based (in part) on 1983 jet data analysed with a high threshold (E T > 40 GeV). There is a marked preference for jets with positive heading tracks in the proton arm and jets with negative leading tracks in the antiproton arm» demonstrating clearly that not all the jets detected result from gluon-gluon scattering. It is possible that such an effect could serve as a basis for isolating a valence quark structure function in pp experiments.

2. JETS IK W/Z E7BMTS

2.1 Introduction In this section we report on a preliminary study of jets In events,

with an identified \T or Z° (WYZ) events), for example:

PP •* (W + jetíx . (3) »•» Q v

2.2 Data sample

The data is based on a sample of 75 V7Z events''*'. Jets have been defined using the UA1 jet algorithm. Table 1 lists the number of eventa with 0, 1, 2, etc. jets for the various W/Z channels.

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In Fis* 8 the histogram represents the spectrum of all jets in the W/Z sample. The spectrum extends to B z = 25 GeV. The effective threshold for jets defined by the jet algorithm ii - 5 GeV.

2.3 The W/Z net correlation

Figure 9 shows the transverse momentum of the W/Z plotted versus the B of the highest B jet for events with 2 1 jet. For W events the trans-

W va-se momentum of the W(p^) is measured by the vector sum of the trans/erse momantum in all the calorimeter cells. Clearly the transverse momentum of the W/Z and the of highest Ej, jet are strongly correlated.

In Fig. 10a the histrogram shows the difference in the azimuthal angle <t> measured around the beams between the transverse momentum vector of the W/Z and the highest E^ jet. Figure 10b shows the same histogram for additional jets apart from the highest jet. Clearly the highest E ? jet is predominantly back to back in $ with the W/Z while additional jets apart from the highest E^, jet are essentially uncorrelated with the W/Z.

We can conclude that for W/Z events with jets, the transverse momentum of the W/Z is locally compensated by the highest E^ jet.

2.4 W/Z jet c.m.s. angular distribution

Jet production in W/Z events is expected in QCD mainly as a result of initial state gluon bremsstrahlung by the annihilating quark or antiquark. Very naively we expect:

do » G M W a s 1 (4) * S* (1 - cos 0 )

d cos 6 - * where s is the W/Z jet c.m.s. energy ( M ^ ) squared and 0 is the angle of

the W/Z (or jet) momentum measured with respect to the beam in the W/Z jet * -i

c.m.B. system. The angular dependence (1 - cos 6 ) appearing in Eq. (4) is characteristic of bremsStrahlung and corresponds roughly (exactly in the limit cos 6 •+ 1) to a flat pseudo-rapidity distribution. We can test the bremsstrahlung interpretation by plotting the daba verBUB C O S 6 and and comparing with detailed theoretical predictions.

- l O -it

In this report we focus attention on the distribution in cos 0 . Since the acceptance for low E^ jets is necessarily somewhat uncertain we compare the W/Z jet data with a selected sample of multijet events. The multijet sample is selected such that - 70-90 GeV <- ^ / z * a n d t h e

c.m.s. scattering angle 6 (defined by the two highest jets) satisfies cos 0 < 0.2. The additional jets in the multijet events (apart from the two highest E T jets) are believed to be predominantly due to initial atnte bremsStrahlung processes. la Fig. 8 and Fig. 10 the data points with error bars represent the multijet data.

A

In Fig. 11a the histogram represents the distribution in cos 6 for the highest E^ jet in the rest frame of the WVZ and the highest E^ jet. Figure lib shows the same distributiun for additional jets (apart from the highest E T jet). For the additional jets cos 8 has been computed in the rest frame of the W/Z and the highest E T jet. In each case the data points with error bars represent the corresponding distributions defined from the multijet data. Beth histograms show a pronounced peaking at cos 6 = ±1 In fair agreement with the multijet data. In Fig. 12 we compare the overall yield of jets/event in W/Z events with the yield of additional jets/event

A

in the multijet events as a function of cos 6 . The solid curve shows a (1 - cos 6) 1 dependence normalized to the W/Z data in the region

A

cos Ô < 0.9. We conclude that the yield of jets in W/Z events and the yield of jets in multijet events are comparable and show a similar cos 0 dependence consistent with (1 - C O B 6 ) 2.5 Conclusion

Further studies should include an analysis of the W/Z jet mass plot. Provisionally we conclude that the majority of jets in W/Z events are probably due to initial state bremsStrahlung processes.

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Table 1

Number of events/jets for various W/Z channels

Channel Total Ï 1 jet 1 jet 2 jets 3 jets Total no. of jets

W -» ev 52 14 10 2 2 20

W •> vv 14 4 4 - - 4

Z -» eè 4 3 - 2 1 7

Z -> V» 5 3 1 - 2 7

TOTAL 75 24 15 4 5 38

BBFBBKHCgS

1) G. Arni8on et al., UAl Collaboration, P l i y i . Lett. 136B (1984) 29«.

2) A.L.S. Anteils et al., CCOR Kollaboration, Nucí. Phys. B 209 (1982) 2B4.

3) B. Combridse and C. Maxwell, Nucí. Phye. B238 (1984).

4) C. Angelini and B. Pazzi, Pbys. Lett. 113B (1982) 343.

5) H. Abramowicz et al., CDHS Collaboration, Z. Fhvs. c 12 (1982) 282. F. Bisele, private communication.

6) F. Bergsma et al., Phys. Lett. 123B (1983) 269. K. Winter, private communication.

7) G. ArniBOn et al., UAl Collaboration, Phys. Lett. 129B (1983) 213.

8) G. Arn i son et al., UAl Collaboration, Phys. Lett. 126B (1983) 398.

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Figure captions.

Fig. 1 : Angular distributions for various x x intervals.

Fig. 2 : The combined angular distribution computed assuming the angular dependence is independent of x^ and i^.

Fig. 3 : The combined angular distribution plotted versua x = cot a 9/2.

Fig. 4 : Tests of factorization in x and x . ° i a

Fig. 5 ; The UA1 structure function. The curves are based on measurements of structure functions in fixed target (neutrino) experiments extrapolated to Q a = 2000 GeV a.

Fig, 6 The gluon structure function G(x) obtained for the two-jet data by subtracting the quark and antiquark contribution measured (and extrapolated) from neutrino experiments.

Fig. 7 The mean charge of the leading track/jet plotted versus the pseudo-rapidity of the jet.

Fig. 6 : The spectrum of jets in W/Z evencs (histogram) compared to multijet data (data points).

Fir. 9 : Scatter plot of the E T of the highest jet veraus the transverse momentum of the W/Z. The 2° events are represented by the open circles.

Fig. 10 : a) The azimuthal angle 41 between the transverse momentum vector of the w/Z and the highest jet (histogram). The data points represent the multijet data. b> The same as for a) but for additional jets apart from the highest Ej jet. In a) and b) the shaded aren represents the contribution of the jets in Z° events alone.

- 13 -

Fis- 11 : a> The distribution in cos Ö* for the highest jet in W/Z events. b> For additional jets apart from the highest jet (histograms). The data points represent the corresponding plots for the nulti-jet data.

Fig. 12 : The overaíl vield of jets/event in W/Z events (closed circles) *

and in multiset events (open circles) as a function of cos 6 . The curve, shows a (1 - cos 0 ) dependence normalized to the data with |cos 6 | < 0.9.

F i g . 1 F i g . 2

I S -

CHS Angular uïsfnùufion of j e t pairs

Ido/dxi / W t r / d x l , . , V s X Expected effect of Q - variation of a ,

QCO ading order)

Rulhe'ford region [inverse - square law]

10 12

X 'Catg 8/2

F i g . 3

14 16 18 20

U A 1

Gluon structure function at

proton | d J = 2000 GeV 2 |

Fits: an-Ki (»:0i-o.ei

0 2 D.i. 0.6 : a

F i g . 4

S(x1,x2=0.0S-0.1)

S(x,,x2=0.1-0.2>

FACTORISATION TEST S ( x l l X 2 ) = Ftx 1)F(x 2J

0.8 SI>|,x;=0.2-0.3)

S(x,,x2=0.1-0.2)

0.1 0.2 0.3 0.4 0.5 0.6 0.7 O.I

x.

F i g . 5 F i g . 6

- 17 -

~ i r T r

0.3

0.2 0.1

0 -0.1 -0.2 -0.3

i ' L

-3 -2 -1

18

16

K -

12

10

e

6

i.

2

F i g . 7

~i i r- - i 1 1 1

W + Z ° EVENTS

38 JETS

- f

O U 8 12 16 20 2Í, 28

JET Tranverse energy IGeV)

F i g . 8

- IS -

I.V.B, Transverse momentum IGeV /c l

F i g . 9

tapiront, «Jígr.ís. AwpUnar i t , |Oc 9 r« ís l

F i g . 10

F i g . 11 F i g . 12

O: 8 4 1 0 0 2 6 0 9 0

- 20

H I G H P-j- J E T S FROM p p C O L L I S I O N S A T Vs = 540 G E V I N UA2

T h e UA2 Col laborat ion

ï - t N B - l ^ — e h v s a y - i L A L ) -P a v i a - - S a c r á y l C ' E Ñ T

Presented b y John R e n n e r Hansen

A B S T R A C T

I T h e p roduc t ion and p r o p e r t i e s of v e r y l a rge t r a n s v e r s e momentum / hadron jets has been measured in t h e UA2 exper iment a i t h e C E R N pp

Col l ider f o r V s = 540 G e V using a h i g h l y segmented ca lor imeter . Events wi th v e r y large t r a n s v e r s e e n e r g y deposit ions ( I E y up to 250 GeV in t h e p s e u d o - r a p i d i t y in te rva l -1 < q < 1) a re o b s e r v e d to be s t r o n g l y dominated by a t w o - j e t s t r u c t u r e . Some of t h e charac ter is t ics of par ton sca t te r ing and f ragmenta t ion a re d iscussed and cross-sect ions f o r inc lusive je t product ion is p resented f o r p T up to 150 G e V . T h e t w o - j e t i n v a r i a n t mass d i s t r i b u t i o n up to - 280 G e V is shown and t h e resul ts a r e compared w i t h t h e predictions of Q C D models. A search

- 21 -

1 . I N T R O D U C T I O N

T h e recent unambiguous ident i f icat ion of jets in had ron ic coll isions [ 1 - 4 ] at the C E R N pp Col l ider and at the ISR has r e v i v e d the i n t e r e s t in th is f ie ld a f t e r the f i r s t observa t ion of l a rge t r a n s v e r s e momentum (p-p) processes in ear ly ISR exper iments [ 5 ] . T h e p red ic t ion t h a t t h e hard sca t te r ing of hadron const i tuents should resu l t in the p roduc t ion of two hadronic jets hav ing the same large t r a n s v e r s e momenta as t h e sca t te red par tons [ 6 , 7 ] has been v e r i f i e d in a d i r e c t way at the C E R N pp Col l ider w i th the observat ion of a dominant t w o - j e t s t r u c t u r e in events deposi t ing v e r y farge t r a n s v e r s e e n e r g y into the c e n t r a l calor imeters of the UA1 [3] or UA2 [1 ] e x p e r i m e n t s . In fac t one of t h e most ou ts tand ing benef i ts of the v e r y successful operat ion of the C E R N pp Col l ider [8 ] at a c e n t r e of mass e n e r g y Vs = 540 GeV is t h e possibi l i ty f o r deta i led measurements of hadron ic j e t p roduct ion and t h e i r f ragmenta t ion proper t i es [ 9 - 1 1 ] in an e n e r g y domain w h e r e h a r d processes can be separa ted c lear ly f rom t h e soft hadron ic in teract ions [ 1 2 ] .

2 . A P P A R A T U S

T h e UA2 d e t e c t o r , F i g . 1 , has been descr ibed in deta i l e lsewhere [ 1 3 , 1 4 ] . A t t h e c e n t r e of the UA2 a p p a r a t u s a v e r t e x de tec tor consist ing of cy l indr ica l p ropor t iona l and d r i f t chambers measures

par t ic le t ra jec tor ies in a region w i thou t magnetic f i e l d . T h e v e r t e x detec tor is s u r r o u n d e d b y a h igh ly segmented e lectromagnet ic and hadronic calor imeter ( t h e cent ra ! ca lor imeter ) which covers polar angles 40° < 9 < 140° ( -1 < n < 1 ) . T h e f o r w a r d regions (20° < 9 < 3 7 . 5 ° and 142 .5° < 9 < 160° ) a re each ins t rumented w i t h t w e l v e toroidal magnet sectors fol lowed by d r i f t chambers , mul t i tube propor t iona l chambers an J e lectromagnet ic ca lor imeters .

T h e p resen t resul ts have been obta ined mainly w i th the cen t ra l ca lor imeter . I t is segmented into 240 ce l ls , each cover ing 75° in <f> and 10° in 6 and bu i l t in a tower s t r u c t u r e po in t ing to the c e n t r e of t h e in teract ion reg ion . T h e cells a re segmented long i tud ina l ly into a 17 radiat ion length th ick e lectromagnet ic compartment ( l e a d - s c i n t i l l a t o r )

- 22 -

followed b y two hadronic compartments ( i r o n - s c i n t i l l a t o r ) of two absorpt ion lengths each . Following an in i t ia l e n e r g y ca l ibrat ion of all cells in a 10 G e V e l e c t r o n , muon and pion beam f rom the CERN PS t h e c a l o r i r ü t e r response has been t r a c k e d w i t h a l ight f lasher sys tem, measurements of the d i r e c t - c u r r e n t induced b y a C o 6 0 rad ioact ive source and b y measur ing the a v e r a g e e n e r g y flow into each cell f o r unbiased pp col l is ions. T h e systematic u n c e r t a i n t y in the e n e r g y cal ibrat ion for t h e data discussed h e r e is less than ±1.5% f o r t h e e lectromagnet ic ca lor imeter and less t h a n i 3 , 5 % f o r the hadronic o n e .

T h e response of the ca lor imeter to e l e c t r o n s , single hadrons and mu I t i - h a d r o n s ( p r o d u c e d in a t a r g e t in f r o n t of the ca lor imeter ) has been measured a t the CERN PS and SPS machines using beams f rom 1 to 70 GeV. T h e e n e r g y resolution f o r e lect rons is measured to b t a ^ / E =

0 . 1 4 / V E (E in G e V ) whereas f o r hadrons i t va r ies f rom 32% at 1 GeV to - 1 / 4

11% at 70 GeV , approx imate ly p ropor t iona l l y to E

Details of t h e cons t ruc t ion , ca l ib ra t ion and per formance of t h e calor imeter a re r e p o r t e d in Ref . [ 1 4 ] .

1 m — FORWARO CALORIMETER

F i g . I . Schematic d e t e c t o r a s s e m b l y , showing U A 2 in a l o n g i t u d i n a l c u *

para l le l to the beams.

- 23 -

3 . D A T A T A K I N G A N D R E D U C T I O N

T h e data p r e s e n t e d in th is paper w e r e recorded d u r i n g the 1983 CERN pp Col l ider run wi th a t r i g g e r select ing pp collisions which deposited a l a rge tota! t r a n s v e r s e e n e r g y (XE-j-) into the cen t ra l ca lor imeter . T h e gains of the photomul t ip l ie rs w e r e ad justed such t h a t t h e i r response is proport ional to t r a n s v e r s e e n e r g y , and t h e i r signals were l inear ly a d d e d . T h e sum was r e q u i r e d to exceed a t h r e s h o l d , normally at about 40 G e V except f o r special low t h r e s h o l d data r u n s .

B a c k g r o u n d f rom sources o t h e r than pp collisions was suppressed at the t r i g g e r level b y r e q u i r i n g a coincidence of the Z E y condi t ion wi th two signals ("minimum bias" t r i g g e r ) obta ined f rom sc int i l la tor a r r a y s cover ing an a n g u l a r range 0 . 4 4 ° < 9 < 2 . 8 4 ° on both sides of the collision region [ 1 5 ] . T h e loss of genu ine large X E y pp events due to th is requ i rement was measured in special runs w h e r e th is condi t ion was removed. For Z E y > 40 G e V the loss is consistent w i th zero a n d < 5% at 90% conf idence l e v e l , independent of X E y . Background f rom cosmic rays was f o u n d to be negl ig ib le .

A sample of "minimum bias" events was recorded s imul taneously wi th the Z E y data to p r o v i d e a measurement of t h e luminosi ty . Data wi th X E y > 40 G e V w e r e recorded f o r a total i n tegra ted luminosi ty J i f d t = 1 Î2 n b " 1 . An u n c e r t a i n t y of ±20% was est imated f o r / i ? d t from t h e observed f luc tua t ions d u r i n g d i f f e r e n t r u n n i n g condi t ions and f rom the overa l l u n c e r t a i n t y in the cross-sect ion accepted by t h e "minimum bias" t r i g g e r [ 1 5 ] .

T h e fu l l data sample was used in the fol lowing analysis f o r Z E j > 60 G e V ; smaller samples and special runs w e r e used f o r lower thresholds [ 1 6 ] .

T h e events col lected with t h e Z E y t r i g g e r include a small (< 10%) b a c k g r o u n d contaminat ion. Beam halo par t ic les can e i ther sat is fy t h e t r i g g e r i n g condit ion d i r e c t l y o r appear as an accidental over lap wi th a "minimum bias" pp in te rac t ion . T h e b a c k g r o u n d events e x h i b i t a charac ter is t ic p a t t e r n in the de tec tor d i f f e r e n t f rom tha t of la rge Z E y pp e v e n t s . T h e y a re re jected f rom the data sample if any of the fol lowing condit ions is sat isf ied :

- 24 -

i ) if they a r e associated w i t h an e a r l y signal in the small ang le scint i l la tor a r r a y s ;

i i ) if they have an abnormal ly l a rge total t r a n s v e r s e e n e r g y f rac t ion in the hadron ic compartments (more than 60% in t h e second one or more than 95% in both t o g e t h e r ) ;

i i i ) if they contain only one c lus te r (as de f ined below) w i th more

than 90% of its e n e r g y in t h e hadron ic compar tments .

T h e s e requi rements reduce t h e b a c k g r o u n d contaminat ion in t h e data sample to < 5% independent of T h e loss of good events i n t r o d u c e d b y the cuts is negl ig ib le . T h i s has been v e r i f i e d by a p p l y i n g t h e t i m e - o f - f l i g h t requ i rement on minimum bias events and b y us ing test beam data f o r the e n e r g y deposi t ion c r i t e r i a .

A. T R A N S V E R S E ENERGY D I S T R I B U T I O N

T h e response of the e lect romagnet ic calor imeter compartments to e n e r g y deposi ted by photons ( o r e lec t rons ) d i f f e rs f rom t h a t of hadrons by typ ica l l y 20%, depend ing on e n e r g y . We have adopted a constant set of w e i g h t i n g fac tors ( 1 . 1 8 , 1 . 0 0 , 1 .06 ) for the t h r e e compartment energies (e lec t romagnet ic , f i r s t and second hadron ic ) t h a t opt imizes t h e resolution and l inear i ty of t h e ca lor imeter response to h igh e n e r g y h a d r o n s , as descr ibed in deta i l in Ref . (14].

T h o total hadronic e n e r g y in a cell of the ca lor imeter is measured as

the we igh ted sum of the energies in t h e t h r e e compartments w h e r e each

compartment c o n t r i b u t i n g to t h e sum must exceed 150 M e V , which is

well above pedestal f luc tua t ions .

T h e observed lE-j- d i s t r i b u t i o n , normal ized using the i n t e g r a t e d luminosi ty , is p resen ted in F i g . 2 f o r two p s e u d o - r a p i d i t y i n t e r v a l s ( -1 < n < 1 and - 0 . 5 4 < n, < 0 . 5 4 ) . T h e t r a n s v e r s e energies are summed over all cells in the fu l l az imuthal acceptance ûo> = 360° u n d e r t h e approx imat ion tha t t h e e v e n t v e r t e x is located at the c e n t r e of the de tec tor . T h e e v e n t v e r t e x has been recons t ruc ted for a sample of the

- 25 -

events used for t h e cross-sect ion measurement , its d is t r ibu t ion along the pp beam axis is well centered in t h e detector and has a r. m. s . spread of 10 cm. No acceptance correct ion has been appl ied to the data shown in F i g . 2 . We estimate t h a t t h e uncer ta inty in t h e e n e r g y scale of I E y due to systematic ef fects (150 MeV minimum compartment e n e r g y requ i rement , cal ibrat ion e r r o r s , neg lec t ing e v e n t v e r t e x pos i t ion ,e tc . ) is less than ±10%.

T h e I t j d is t r ibut ions of F i g . 2 show a clear d e p a r t u r e f rom exponent ia l when £ E y exceeds - 6 0 G e V . T h i s corresponds to t h e t r a n s v e r s e energy w h e r e the t w o - j e t product ion cross-sect ion begins to dominate o v e r soft hadronic in te rac t ions , as exp la ined below.

EE r HieV)

Fig. 1 . Ol.»erv«J tot..I t i ™ 3 vera* « I M H ? v IE- , <jc»ti ihiiliofi? (or two

- 26 -

5. T W O - J E T D O M I N A N C E

!n o r d e r to invest igate the p a t t e r n of e n e r g y d i s t r i b u t i o n in the events a s t r a i g h t f o r w a r d c l u s t e r i n g a lgor i thm has been adopted which takes a d v a n t a g e of t h e f ine g r a n u l a r i t y of t h e calor imeter segmentat ion . All cells which share a common side and have a cell e n e r g y

c c e l l > 400 MeV a re jo ined into a c l u s t e r . C lus te rs hav ing two or more local maxima separa ted b y a va l ley d e e p e r than 5 G e \ a re s p l i t . In each e v e n t the c lusters a re r a n k e d in o r d e r of decreas ing t r a n s v e r s e energies denoted by E y 1 > E y a > E - ¡ - 3 . . . . T h e c lus te rs contain t yp ica l l y 3 cells f o r E-j- = 2 G e V and 10 cells f o r E y = 40 G e V .

T h e f rac t ions h1 - E y V Z E y and h a ( Et E t

2 ) / Z E - T - descr ibe t h e t r a n s v e r s e e n e r g y accounted f o r in each e v e n t b y t h e c l u s t e r ( r e s p e c t i v e l y t h e two c lus te rs ) w i th the l a rges t t r a n s v e r s e e n e r g y . An event conta in ing on ly two je ts of equal t r a n s v e r s e e n e r g y would have h i = 0 . 5 a n d h 2 = 1 in an ideal d e t e c t o r . T h e mean va lues of hj, and h 2 a re shown in F i g . 3a as a f u n c t i o n of ZEy. T h e i r b e h a v i o u r i l lustrates t h e emergence of a dominant t w o - j e t s t r u c t u r e at l a rge Z E y , as p r e v i o u s l y r e p o r t e d [ 1 , 9 ] . T h e e f fec t becomes even more pronounced at t h e la rgest values of Z E y reached in th is e x p e r i m e n i . T h e dependence on X E y of the mean va lues of t h e rat io r 2 1 = E y V E y 1 and r 3 2 _ E y V E y 2 a re d isp layed in F i g . 3 b . T h e y show the same e f fec t : as Z E y increases , r2i approaches about 0 . 9 whereas r 3 2 decreases below 0 . 1 . A v e r y large f rac t ion of t h e total t r a n s v e r s e e n e r g y of large Z E y events is shared on average b y two c lusters on ly .

h, : It) - Eíl/IE,

Fly. 3. a) l l i ^ f r . - T C T L I W R I i , , w i l>, o' ihr m i * , ti-ansvii-sc eiur-qy IZ r

I J I 1 I I— 0 50 100 150 2O0 250

t E, IGeVI b) DupftntlL-NCB on JEy of the ratios r, , = E y V E y 1 and

ln o r d e r to g i v e a qua l i t a t i ve fee l ing of the b e h a v i o u r of a t h i r d j e t in high ZEy. e v e n t s , we d e f i n e the var iab les e¡ ~ Ej C m /ni j - j ( ¡ = 1 , 2 , 3 ) .

E ¡ c m is t h e c m - e n e r g y of je t * i ' w h e r e E i C m > E 2c m > E 3

c m , m-j- is t h e 3 - j e t i n v a r i a n t mass, T o de f ine a 3 - j e t event we r e q u i r e E j 3 > 3 G e V . No f iduc ia l cut is a p p l i e d . T h e two i n d e p e n d e n t var iab les a n c !

Q = (e^ - £ 2 ) / V 3 measure the f rac t ion of avai lab le e n e r g y c a r r i e d away b y the t h i r d j e t a n d t h e e n e r g y s h a r i n g between t h e t w o most energe t i c j e t s . T h e accepted region of the (Eg,Q) p lane is r e s t r i c t e d b y kinematics to a t r i a n g l e w i th its c o r n e r s at A = ( 0 , 0 ) , B = ( . 2 5 , 1 / V 4 8 )

a n d C = ( 1 / 3 , 0 ) .

T h e d i s t r i b u t i o n of events in th is k ind of Da l i t z plot , r i g . 4 , has t h e fo l lowing f e a t u r e s :

i ) t h e events near A a re charac te r ised b y a soft t h i r d je t and equal e n e r g y shar ing between t h e two dominat ing j e t s . T h e s e events a re t y p i c a l l y associated w i t h soft gluon b r e m s s t r a h l u n g f rom t h e je ts or w i th t h e u n d e r l y i n g e v e n t .

Ü) events near B a re of t h e col l inear t y p e , w h e r e two jets of equal s ize balance t h e major jet in t h e e v e n t .

- 28 -

i i i ) the region near C contains events wih 3 equa l ly s t r o n g j e t s .

F i g . 4 gives a good feel ing of t h e re la t i ve populat ion of t h e t h r e e reg ions, for even ts wi th m— > 50 G e V / c 2 . As expec ted f rom F ig . 3 b , t h r e e - j e t events a r e dominated by t h e soft g luon c o n f i g u r a t i o n s . T h e region of t h e d iagram f o r which Eg is g r e a t e r t h a n .15 contains of t h e o r d e r of 20% of t h e e v e n t s .

A s t u d y of the Dal i tz plot in smaller mass b ins does not show anv resonant s t r u c t u r e .

T i g . 4 . T h r e e - j e t Ha l i t z d i a g r a m .

- 29 -

6. C H A R G E P A R T I C L E M U L T I P L I C I T Y IN J E T S

T h e c h a r g e d par t ic le mul t ip l ic i ty is measured by the v e r t e x

d e t e c t o r , F i g . 1 , whose angu la r coverage is much la rger than t h a t of t h e

cen t ra l ca lor imeter : i t ex tends down to © = 2 0 D and o v e r the fu l l

azimuthal r a n g e . As a resu l t t h e c h a r g e d par t i c le mul t ip l i c i ty

measurement is almost f r e e of acceptance c o r r e c t i o n s . T h e main

uncer ta in t ies in th is measurement ar ise f rom two sources:

i ) t h e e f f ic iency of t h e v e r t e x de tec tor and of t h e associated

p a t t e r n recognit ion a lgor i thm especial ly in regions of h igh

par t i c le d e n s i t y ,

i i ) t h e p r o c e d u r e t h a t def ines which of t h e o b s e r v e d t r a c k s a re

to be associated wi th the je t and which a r e not .

In o r d e r to address these prob lems, o u r analysis is r e s t r i c t e d to t h e

t r a n s v e r s e p l a n e , w h e r e the t r a c k reconst ruc t ion e f f ic iency is h ighes t ,

and w h e r e par t ic les not associated w i t h the jets a r e expec ted to

c o n t r i b u t e a un i form azimuthal d i s t r i b u t i o n .

Events a re cons idered in which two c l u s t e r s , hav ing an i n v a r i a n t mass

in excess of 40 G e V / c 2 and a azimuthal separat ion g r e a t e r than 150° ,

are o b s e r v e d w i t h |n , |< -7 . p(A4>), the d i s t r i b u t i o n of the azimuthal

separat ion A(J> be tween each t r a c k in t h e v e r t e x d e t e c t o r and the

cent ro id of t h e h ighes t t r a n s v e r s e e n e r g y c l u s t e r a re shown in F i g . 5

f o r two in te rva ls of m^, t h e i n v a r i a n t mass associated wi th t h e two

h ighest e n e r g y c l u s t e r s . C lear peaks a r e seen a t átp=0 and A$=n, as

expected for two je t e v e n t s . T h e d i s t r i b u t i o n is more peaked f o r t h e

l a r g e r s l ice, showing t h a t h i g h e r e n e r g y je ts a re more col l imated.

T h e d i s t r i b u t i o n in Ad> is not symmetr ic about A<$>=TT/2. T h i s is p a r t l y

exp la ined b y t h e fac t tha t the two jets a re not exac t ly b a c k - t c - b a c k in

the t r a n s v e r s e p lane and p a r t l y b y the fact tha t a b road h igh

mul t ip l ic i ty jet wi l l t e n d to deposi t less e n e r g y in a leading calor imeter

c luster than a more coíl ímated lower mul t ip l ic i ty j e t . T h e r e f o r e in

select ing t h e h i g h e r t r a n s v e r s e e n e r g y c luster t h e r e is a bias f a v o u r i n g

the selection of t h e n a r r o w e r , lower mul t ip l ic i ty j e t .

T h e t r a n s v e r s e t r a c k f ind ing e f f ic iency of t h e v e r t t x de tec tor was

measured in the a n g u l a r range covered b y the toro id spec t romete r , b y

comparing the two detectors for f ie ld of f d a t a . T h e e f f ic iency was f o u n d

- 30 -

to be 9 4 . 8 % ± .8% and the f ract ion of spur ious t r a c k s was 21 %. T h e loss of t r a c k s f rom t h e f i n i t e t w o - t r a c k resolut ion was est imated f rom t h e d i s t r i b u t i o n of t h e azimuthal separat ion between pa i rs of ne ighbour t r a c k s , and eva luated to be in the range f rom 16 % to 31 % depend ing on local mu l t ip l i c i t y . T h e data was also c o r r e c t e d f o r v conversions and I T 0 Dal i tz d e c a y s . As a check on th is p r o c e d u r e t h e mean c h a r g e mul t ip l ic i ty was measured f o r minimum bias events and compared w i t h resul ts obta ined b y t h e UA5 col laborat ion [17 ] in t h e same pseudo - r a p i d i t y range (|n.l< 2 ) . T h e resul t 13 .4 ± . 3 , is in good agreement w i th the UA5 measurement , 13 .45 Î . 1 5 .

As i l l us t ra ted in F i g . 5 t h e t r a c k d e n s i t y is approx imate ly constant o v e r a la rge AoS r a n g e a r o u n d A4j=TT/2, w h e r e i t t akes a va lu p 0 . On the a v e r a g e p D is measured to be tw ice as largo as in minimum bias e v e n t s .

..fiO< H„ < 70 GeV 1U0* M.I -110 GeV

2'. -i

OA 0 0 12 ' 6 2 0 2 i . 2 8 ¿<t>

31 -

Particles not associated wi th the je ts a re assumed to make a un i form

c o n t r i b u t i o n , A p a , to p(Atj>). Th is assumption was checked b y

measur ing t h e t r a c k densi ty in t h e f o r w a r d spectrometers f o r e v e n t s

containing a je t near G=90° . T h e d i s t r i b u t i o n of Ao>, the az imuthal

separat ion between t h e f o r w a r d t r a c k a n d t h e h ighest t r a n s v e r s e e n e r g y

c lus te r is f l a t .

A pr ior i X may t a k e any va lue between 0 and 1 ; lacking knowledge of

X , we evaluate a lower bound of t h e mean t r a c k mul t ip l ic i ty in juts,

< n c h > , by se t t ing X s 1 . T h e values o b t a i n e d , as a f u n c t i o n of m.. , a r e

d isp layed in F i g . 6 . T o avoid t h e bias caused b y t h e asymmetr ic AíJj dis t r ibut ion d iscussed above we de f ine the je t mul t ip l ic i ty as t h e

a va raged mul t ip l ic i ty of the two j e t s . T h e results a r e compared w i t h

e *e" data [18] wh ich we t r e a t the same w a y as thf. col l ider data to f i n d

Pd , using t h e fac t t h a t X=0 in e*e" t w o - j e t f ina l s ta te .

h UA2

T TASSO

12

10

8

6

2

'10

/ s e . a - or Mjj IGeVJ

H g - 6. Lower b o u n d on mean c h a r g e d p a r t i c l e mul t ip l i c i t i es in je ts < n c | ) > as a funct ion of V s Q , ß - a n d of the i n v . r i d n t t w o - j e t mass m-- for p p . T h e two UA2 poin ts c o r r e s p o n d i n g to low masses, come f rom low t h r e s h o l d data a n d have f o r t h a t reason b i g

- 32 -

F i g . 6 indicates a l a rger charged p a r t i c l e mul t ip l ic i ty in jet even ts

from t h e col l ider t h a n in similar even ts o b s e r v e d in eê" collisions at

lower e n e r g i e s . Even if \ were equal to 1 , which would imply t h a t je t

f ragments do not popula te t h e region A ( | ) = T T / 2 ( the charged par t i c le

mul t ip l ic i ty of jets o b s e r v e d in o u r da ta would be at least as large t h a n

tha t of the ex t rapo la ted e*e" da ta . T h e s e resul ts a re consistent w i t h

expectat ions based on Q C D ca lcu la t ions, which p r e d i c t tha t at r e l a t i v e l y

low x- ] -=2Ej /v 's gluon jets hav ing h i g h e r mul t ip l ic i ty t ïuin q u a r k jet?

[ 1 9 , 2 0 ] t end to dominate [21] in pp col l is ions.

7 . TWO J E T CMS S C A T T E R I N G A N G L E , Q

T h e fundamenta l p a r t o n - p a r t o n s c a t t e r i n g process has been s tud ied

t h r o u g h the resu l t ing a n g u l a r d i s t r i b u t i o n of j e t .

Events were selected b y r e q u i r i n g t w o c lusters wi th E- j - 1 + E-p 2 >46 G e V .

T h e p-p of the t w o - j e t system is chosen to be smaller t h a n 20 G e V / c and

Aij>jj ( the angle be tween the two c l u s t e r c e n t r o i d s ) to be g r e a t e r than

160° . T h e two la t te r condit ions fo rce the two jets to be back to b a c k ,

not l e t t ing a t h i r d je t d i s t u r b the a n g u l a r measurement .

T h e sca t te r ing angle 0 is measured f rom the e x t e r n a l b isector of t h e

p and p momenta in t h e t w o - j e t cm-system ( C o l l i n s - S o p e r f r a m e ) . T h e

measurement was done in a way f r e e of acceptance c o r r e c t i o n s , b y

choosing increasing in terva ls of | x ^ | , each time e n s u r i n g t h a t t h e

maximum | Xp | and Ö * cor respond to f u l l y conta ined j e t s . T h e data

f rom each in terva l a r e normalized and a d d e d , w i th t h e e r r o r s ad jus ted

a c c o r d i n g l y . F i g . 7 shows the f ina l r e s u l t . T h e main Q C D

subprocesses resul t in cos© d is t r ibu t ions inside t h e shaded region of

F i g . 7 , leaving no chance , w i t h the p r e s e n t data sample, to

d isen tang le the ind iv idua l c o n t r i b u t i o n s .

I t is anyhow clear t h a t scalar gluons would r o t be able to descr ibe the

o b s e r v e d cos© d i s t r i b u t i o n on t h e i r o w n , i i nce all associated c u r v e s

are below the data points (not shewn in F ig . 7 ) .

F i g . 7 . CMS s c a t t e r i n g angle d i s t r i b u t i o n , cosO . T h e shaded region

indicates w h e r e the c o n t r i b u t i o n f rom most of the 8 Q C D

subprocceses will f a l l .

- 34 -

8. I N C L U S I V E J E T P R O D U C T I O N C R O S S - S E C T I O N S

For a measurement of the inclusive je t product ion cross-sect ions

p p -* je t + a n y t h i n g pp -* jet j . + j e t 2 * a n y t h i n g

( 1 ) ( 2 )

events a re selected conta in ing at least one c lus te r w i t h E y exceed ing the 2E-|- th resho ld f o r reaction (1 ) a n d wi th E-j-1 + E y 2 l a r g e r than t h e l E - r th resho ld (nnd E y 1 , E y 2 > 10 GeV) f o r react ion ( 2 ) , a f t e r inclusion of nearby c lus te rs rs exp la ined below. T h e je t d i rec t ion and t r a n s v e r s e e n e r g y a r e measures f rom t h e cen t ro id and e n e r g y of t h e associated c lusters wi th respect to t h e event v e r t e x .

T h e ind iv idua l c lusters a re taken to be massless [ 7 ] in the fo l lowing p r o c e d u r e , equat ing t h e r e f o r e p y and E y . A c t u a l l y , b y a t t r i b u t i n g a zero-mass momentum vec to r C[p[=E) to each cell which par t ic ipa tes to » c luster one observes a mean i n v a r i a n t "c lus te r mass" of 9 G e V f o r c lusters hav ing E y > 3 0 G e V , This va lue resul ts f rom the combined ef fects of shower and cell sizes a n d of actual je t masses, and is in agreement w i th a Monte Car lo simulation [22] descr ibed below. For jets hav ing p y > 30 GeV th is calculation p red ic ts a mean rat io | p y | / E y

= 0 . 8 6 , w h e r e ¡p"y| and E y a re summed o v e r all g e n e r a t e d f ina l state

In o r d e r to p a r t l y account f o r f ina l state gluon radiat ion e f f e c t s , as repor ted and discussed in Ref . [ 9 ] , t h e j e t momenta are de f ined b y add ing to the measured momentum v e c t o r of t h e selected c lus te r those of all c lus te rs hav ing E y > 3 GeV and separa ted b y an angle u> f rom the selected c luster momentum vector such t h a t costo > 0 . 2 . A b o u t 20% of the je ts with p y > 30 G e V include at least one such n e a r b y c lus te r wi th E y > 3 G e V . Note t h a t in this case t h e jet acqui res a mass and p y d i f f e rs f rom E y . T h e inclusion of these n e a r b y c lus te rs increases t h e observed t r a n s v e r s e momentum d i s t r i b u t i o n Cpy) f o r je ts b y about 15%, rough ly independent of p y .

T h e evaluat ion of t h e cross-sect ions for react ions (1 ) and (2 ) f rom these events requ i res t h e measurement of t h e i n t e g r a t e d luminosity f o r the normal izat ion and t h e determinat ion of t h e de tec tor acceptance

p a r t i c l e s .

U A 2 1983

1\

pp - jet - X / s = 540 GeV

this measurement UA2 ref (9) UA1 re f IS) UAt refOO)

. £ . a) Inclusive sysiemme

¡3,9, JD)

p T ICeV)

10*

cross-section. The additional Previous measurements are from

U A 2 1983 pp — jet + jet + X / s » 540 GeV 1-0.85 < tiÔ.85]

• this measurement . UA2 re t . 191

t t TOO 200 300

irijj IDeV)

b) Two-jet production cross-section with both jets in the pseudo-rapidity range -0 .25 ( T, < 0 .85. The additional systemitic uncertainty , s The orevious measurement is from Ref. [9] .

- 36 -

inc lud ing the ef fects of the e n e r g y smear ing on the steeply fa l l i ng p-p

spect ra - A Monte Car lo simulation of t h e detector is used to calculate

the acceptance . T h e Monte Car lo events a r e processed t h r o u g h t h e same

analysis chain as t h e d a t a . T h e simulat ion reproduces the detai ls of the

e v e n t con f igura t ion and of t h e d e t e c t o r response, using the same

w e i g h t i n g fac tors f o r the t h r e e ca lor imeter compartment energies as f o r

t h e d a t a . In p a r t i c u l a r , t h e d i s t r i b u t i o n of c luster size and both

hadronic f ragmenta t ion and shower development a re adequate ly

descr ibed [ 9 ] . T h e comparisc~ of t h e t r a n s v e r s e momentum (p-p) and

t h e two- je t i n v a r i a n t mass ( m j j ) d i s t r i b u t i o n s of the reconst ruc ted Monte

Car lo even ts w i t h those of the in i t ia l par tons used as i n p u t p rov ides

t h e acceptance funct ions E ( P - J - ) a n d E(rrijj) by which t h e o b s e r v e d

cross-sect ions must be d iv ided to ob ta in the c o r r e c t e d jet and t w o - j e t

c ross -sec t ions . T h e func t ion £(p-¡-) v a r i e s f rom about 0 . 8 to 1.Q o v e r

the range 3 0 < p T < 150 GeV and e ( m ^ ) f rom about 0 . 5 to 0 . 8 o v e r the

r a n g e 50 < m~ < 250 G e V . T h e u n c e r t a i n t y d u e to t h e model

dependence of t h d acceptance ca lculat ion has been s tud ied by us ing

d i f f e r e n t independent models [ 9 , 2 2 ] , b y changing t h e detai ls of t h e j e t

f ragmenta t ion and b y v a r y i n g re levant analysis p a r a m e t e r s , such as t h e

accepted r a p i d i t y r a n g e , the p a r a m e t e r s of the c l u s t e r i n g a l g o r i t h m ,

w e i g h t i n g fac tors f o r tVie ca lor imeter compartment energ ies e t c . . . T h e

systematic u n c e r t a i n t y on e is est imated to be ±35%.

T h e cross-sect ion f o r inc lusive j e t product ion d a a /dp- j -dn , at n. = 0 is

shown in F i g . 8a and the c ross -sec t ion f o r t w o - j e t p roduct ion d a / d m -

w i t h both je ts in t h e in te rva l - 0 . 8 5 < T) < 0 . 8 5 , is d isp layed in F i g . 8 b .

T h e quoted e r r o r s include t h e stat ist ical e r r o r s and an

e n e r g y - d e p e n d e n t systematic u n c e r t a i n t y on the acceptance f u n c t i o n s .

F u r t h e r uncer ta in t i es have to be cons idered in addi t ion to the

systematic e r r o r on t h e acceptance (±35%) . T h e normalizat ion is a f fec ted

b y the -20% systemat ic u n c e r t a i n t y in t h e knowledge of t h e i n t e g r a t e d

luminosi ty , and the systematic e r r o r on the ca lor imeter e n e r g y

ca l ibrat ion is c o n t r i b u t i n g another ±20%. T h e overa l l systemat ic

u n c e r t a i n t y on the cross-sect ions f o r t h e reactions (1 ) and (2 ) is

est imated to be ±45% a f t e r a d d i n g the t h r e e cont r ibut ions in q u a d r a t u r e .

Also shown in F igs . 8a and 8b a r e t h e cross-sect ions obta ined

p r e v i o u s l y b y t h e same exper iment [9 ] w i th a much smaller data sample

( f r o m the 1982 r u n n i n g p e r i o d ) . For these data an addi t iona l systemat ic

- 37 -

e r r o r of ±40% has been q u o t e d . T h e two measurements a re in v e r y good agreement . One should note though tha t t h e systematic uncer ta in t ies of the two resul ts have largely comrr ••• o r ig ins and t h e two eva luat ions a r e not i n d e p e n d e n t . T h e inclusive jet p roduct ion cross-sect ion r e p o r t e d b y the U A l exper iment [ 3 , 1 0 ] is also shown in F i g . 8a . T h e systemat ic u n c e r t a i n t y for th is measurement is g i v e n in [10] as a fac tor 1 .65 . Even though the U A l data points are about a fac tor 1.5 to 2 below t h e p r e s e n t measurement , both exper iments a re consistent in the region of o v e r l a p wi th in systematic e r r o r s .

I t is na tura l at th is stage to look for bumps in the j e t mass s p e c t r u m , h a v i n g in mind the s t a n d a r d - m o d e l p red ic t ions f o r heavy intermediate vec to r boson decay into q q .

For an event to e n t e r the masss d i s t r i b u t i o n , i t is r e q u i r e d to have at least two c l u s t e r s , each wi th t r a n s v e r s e e n e r g y in excess of 10 G e V . T h e cent ro id of t h e b iggest c lus te r must have |n.|< .7 and all o t h e r dusters cons idered in the maps determination must fu l f i l In) < -85 . O t h e r c lusters a re merged wi th . 1 of the two h ighest E j c lusters when t h e y sat isfy t h e c r i te r ia descr ibed e a r l i e r (E-j->3 G e V , cosco>.2) , t h u s reduc ing the e v e n t to two main j e t s , w i th tota l t r a n s v e r s e e n e r g y I E j C ' , and a remaining e v e n t h a v i n g t r a n s v e r s e e n e r g y

IE- , - = Z E y - I E T

c t . Events hav ing Î È j > 15 G e V , f o r which the def in i t ion of two je t system may be ambiguous , are re jec ted . We also re ject events hav ing more than 6 GeV t r a n s v e r s e e n e r g y measured in the F / B calorimeters ( w h e r e the acceptance is r e d u c e d ) .

In each re ta ined e v e n t we increase t h e t r a n s v e r s e momentum vec to r of the weakest of the two je ts to balance t h a t of t h e s t r o n g e s t . Monte Car lo calculations show tha t th is p r o c e d u r e par t i a l l y compensates f o r losses ( h e a v y f l a v o r decays into undetec ted lep tons , soft g luons at la rge angles to the j e t s ) , and for measurement e r r o r s , and resul ts in an improved resolut ion and a more accura te mass d e t e r m i n a t i o n . In th.? W region the mass resolution is of the o r d e r of 10 G e V / c 2 .

T h e Q C D b a c k g r o u n d , assumed to have a form e x p ( b m * c m 2 ) , was f i t t e d in the mass region 40 GeV to 68 G e V (low t h r e s h o l d ) , 56 G e V to 68 G e V and 108 GeV to 148 GeV ( h i g h t h r e s h o l d ) ( e x c l u d i n g the region 72 G e V to 104 G e V ) , resul t ing in a %2=W .5/1$ dof .

A l though t h e spect rum is well r e p r o d u c e d b y the exponent ia l Q C D b a c k g r o u n d d i s t r i b u t i o n , we t r i e d to super impose two gaussian

- 38 -

d i s t r i b u t i o n s w i t h a f i x e d w i d t h of 10 G e V / c 2 , d e s c r i b i n g t h e contr ibut ion f rom W and Z decays in to q q . T h e two gaussians a r e j inked t o g e t h e r , t h r o u g h the s t a n d a r d mode 1 , b y r e q u i r i n g the number of Z's re la t ive to t h e number of W's ( n z / n w ) to be . 4 1 , and m z = 1.15

m W T h e new f i t g ives x 2 = 2 2 / 3 2 dof . and m w = 7 9 ± 8 G e V / c 2 . From the

va lue and e r r o r ob ta ined in the f i t f o r the W c o n t r i b u t i o n we d e d u c e , a f t e r acceptance c o r r e c t i o n s , an u p p e r limit on t h e W" product ion cross section : c y , + < 9 nb ( 95 % cl ) .

A f u r t h e r search f o r mass bumps in t h e region above 100 G e V / c 2 us ing the same method , b u t th is t ime wi th on ly one gaussian and wi th t h e mass and w id th as f r e e p a r a m e t e r s , resu l ts in an excess of 50 ± 16 events above b a c k g r o u n d , at m = 147 G e V / c * a n d o - 13 G e V / c 2 . F i g . 9 shows the mass spect rum above 100 G e V / c 2 . indicates t h e p u r e b a c k g r o u n d f i t , t h e b a c k g r o u n d c o n t r i b u t i o n to the combined f i t and t h e f ina l f i t leading to a x a=n-7/20 dof .

A s t u d y of these h igh mass events in terms of their configurations is u n d e r way and more w o r k is needed t o assess t h e s igni f icance of th is enhancement .

9 . C O M P A R I S O N W I T H Q C D C A L C U L A T I O N S

T h e measurements of the inc lus ive je t p roduc t ion c ross -sec t ions , ' react ions ( 1 ) a n d ( 2 ) , can be compared d i r e c t l y w i t h Q C D p r e d i c t i o n s . In p r i n c i p l e such comparisons do not requ i re a n y assumption on the f ragmenta t ion mechanism: to the e x t e n t t h a t jets a r e c o r r e c t l y ident i f i ed t h e y c o r r e s p o n d d i r e c t l y to t h e h a r d sca t te red par tons [ 7 ] . T h e observa t ions [ 1 , 3 , 9 , 1 0 ] of the p r e d i c t e d increase of the y ie ld of je ts hav ing P T > 20 G e V at the C E R N pp Col l ider w i th respect to top ISR e n e r g y ( b y about f o u r o rders of magni tude [ 2 1 ] ) is a remarkab le success of the Q C D p a r t o n p i c t u r e .

Severa l Q C D calculat ions have since been r e p o r t e d . In the fo l lowing the da ta a re compared wi th those of Re fs . [ 2 3 - 2 5 ] . T w o major uncer ta in t ies a f fec t t h e theoret ica l p red ic t ions [ 2 6 ] : scale ambigui t ies (choice of Q 2 ) in t h e leading logar i thm calculat ions a n d , re la ted to i t , the choice of t h e A parameter in the s t r o n g coupl ing constant a s ( Q 2 ) ,

- 39 -

M (GeV)

. 9 . M u l t i - j e t mass spectrum a b o v e 100 l e V / c 2 . ind icates the pure, b a c k g r o u n d f i t , t h e b a c k g r o u n d c o n t r i b u t i o n to the combined f i t and the f ina l f i t lead ing to a x a - " - 7 / 2 0 dof .

1 0 3 r

- 40 -

and the parametr iza t ion used for the par ton densi t ies [ s t r u c t u r e funct ions) in the incoming p and p. F u r t h e r m o r e h igher o r d e r f in a g ) contr ibut ions to the je t product ion c r o s s - s e c t k . s ce not f u l l y inc luded . T h e in f luence of these theoret ica l ambigui t ies has been s t u d i e d , f o r example, in Refs . [ 2 3 - 2 5 ] . T h e calculat ions ignore f ragmenta t ion ef fects and assume massless p a r t o n s .

A comparison between data and a range of these pred ic t ions is indicated in F igs. 10a and 10b as a shaded band [ 2 7 ] . T h e solid c u r v e in F ig . 10a corresponds to the pred ic t ion of Ref . [21 ] and almost coincides wi th the resul ts of Re fs . [ 2 3 , 2 4 ] , not separa te ly shown, f o r the theoret ical assumptions l isted in [ 2 8 ] . T h e la t ter resul ts a re also d isplayed in F i g . 10b as a solid c u r v e . T h e data a re a t a level comparable to the QCD pred ic t ions .

It has been suggested tha t a possible s u b s t r u c t u r e of q u a r k s and leptons would manifest itself as a new contact in teract ion v is ib le at large momentum t r a n s f e r s [ 2 9 ] . T h e cross-sect ions for react ions (1 ) and (21 a re expected to dev ia te at la rge p-p or nijj f rom the Q C D behav iour depend ing on the e n e r g y scale Ç wh ich charac ter i zes the s t r e n g t h of this new interact ion ( a n d the physical size of t h e composite s t a t e s ) . For example , for 2; = 200 G e V , the cross-sect ion of react ion (1 ) is expec ted to be one o r d e r of magni tude l a r g e r than the Q C D pred ic t ion = co) at p-p > 100 G e V ( F i g . 1 0 a ) . A determinat ion of £ f rom t h e data is in p r inc ip le possible b u t the uncer ta in t ies a t tached to the Q C D calculat ions limit its accuracy . By comparing the measured cross-sect ion f o r react ion (1 ) to t h e Q C D calculations of Ref . [ 2 3 , 2 8 ] we f ind a f a i r agreement ( X 2 = f o r 29 degrees of f reedom) if we mul t ip ly the Q C D cross-sect ions b y a p-p independent scale fac tor of 1.9. T h e remaining deviat ion can be expressed in terms of a lower limit on Ç b y using the calculation of Ref . [ 3 0 ] . Th is method, which is model d e p e n d e n t , g ives Ç > 275 G e V (95% C L ) .

in conclusion it has been further demonstrated that t w o - j e t product ion is the dominant hadronic process at la rge t r a n s v e r s e energies at the CERN pp Col l ider . T h e jet p roduct ion cross-sect ions a re adequate ly descr ibed by Q C D models.

- 42 -

REFERENCES A N D F O O T N O T E S

1 . UA2 Col labora t ion , M. Banner et a l . , P h y s . L e t t . 118B (1982) 203. UA2 Col laborat ion , P. Bagnaia et a l . , P h y s . L e t t . 138B (1934) 430 .

2 . Axia l Field Spect rometer Co l labora t ion , T . Akesson et a l . , Phys . Le t t . 118B (1982) 185 and 193.

3 . UA1 Col laborat ion , G . Arn ison et a l . , P h y s . L e t t . 123B (1983)

115.

4 . COR Col labora t ion , A . L . S . Angel is et a l . , P h y s . L e t t . 126B (1983) 132.

5. For reviews see f o r example :

Jets in High E n e r g y Col l is ions, Physica Scr ip ta 19 ( 1 9 7 9 ) , edi ted by K. Hansen and P. H o y e r ; P. D a r r i u l a t , A n n . R e v . N u c l . P a r t . Se i . 30 (1980) 159.

6. R . P . Feynman , Photon Hadron I n t e r a c t i o n s , Benjamin , New Y o r k , 1972;

S . M . Berman and M. Jacob, Phys . R e v . L e t t . 25 (1970) 1683 S . M . B e r m a n , J . D . Bjorkon and J . B . K o g u t , P h y s . R e v . 4D (1971) 3388 .

7 . J . D . B j o r k e n , P h y s . Rev . D8 (1973) 4098.

8 . T h e Staf f of the C E R N pp Pro ject , Phys . L e t t . 107B (1981) 2 3 1 .

9 . UA2 Col laborat ion , P. Bagnaia et a l . , Z . P h y s . C 20 (1963)

117.

10. UA1 Col labora t ion , G . Arn ison et a l . , P h y s . L e t t . 132B (1983) 214.

- 43 -

1 1 . U A l Co l labora t ion , G . Arn lson et a l . , P h y s . L e t t . 132B (1983) 223, a n d C E R N - E P / 8 3 - 1 9 8 .

12 . T . Akesson and H. Bengtsson , p h y s . L e t t . 120B (1883) 133.

13. B. Mansoul ié , T h e UA2 appara tus at t h e C E R N pp Co l l ide r , proceedings 3 r d Mor iond w o r k s h o p on pp p h y s i c s , edi t ions F r o n t i è r e s , 1983, p. 6 0 9 ; M. Dial inas e t a l . , T h e v e r t e x d e t e c t o r of t h e UA2 e x p e r i m e n t , L A L - R T / 8 3 - 1 4 , O R S A Y , 1a83; C . Conta et a l . . T h e system of f o r w a r d - b a c k w a r d d r i f t chambers in t h e UA2 d e t e c t o r , C E R N - E P / 8 3 - 1 7 6 , submit ted to N u c l . I n s t r u m . Methods;

K. B o r e r e t a l . , M u l t i t u b e propor t iona l chambers for t h e localization of e lectromagnet ic showers in t h e U A 2 d e t e c t o r , C E R N - E P / 8 3 - 1 7 7 , submi t ted to N u c l . I n s t r u m . Methods .

14. A. Beer et a l . . T h e cen t ra l ca lor imeter of th UA2 exper iment at the C E R N pp Co l l ider , C E R N - E P / 8 3 - 1 7 5 , submi t ted to N u c l . I n s t r u m . Methods .

15. T h e cross-sect ion seen b y t h e "minimum b ias" t r i g g e r counters is 4 3 . 9 i 3 . 5 mb as measured b y :

UA4 Co l labora t ion , R. Bat t is ton et a l . , Phys , L e t t . 117B (1982) 126 and G . S a n g u i n e t t i , p roceedings 3 r d Morionc workshop on pp p h y s i c s , edit ions F r o n t i è r e s , 1983, p . 2 5 .

16. T h e i n t e g r a t e d luminosit ies f o r t h e data used a t low thresho lds are f i f d t = 0 . 5 6 n b " 1 f o r I E y f rom 30 to 4 0 G e V , 5 .8 n b " 1

f rom 40 to 50 GeV and 12 .3 nb"» f r o m 50 to 60 G e V .

17. UA5 Col labora t ion , K. A l p g a r d e t a l . , P h y s . L e t t . 115B (1982) 7 1 .

18. TASSO col laborat ion , M. A l thof f et a l . , DESY 8 3 - 0 1 0 .

19. B. R. W e b b e r , Cont r ibu t ion to t h e X V I I I Rencont re de Mor iond on P r o t o n - A n t i p r o t o n col l ider p h y s i c s , La P lagne, March

1 9 - 2 5 , 1083 and C E R N T H - 3 5 6 9 (1083)

- 44 -

20 . G . Sterman and S . W e i n b e r g , P h y s . R e v . Le t t . 39 (1977) 1436. K. Shizuya and S - H . H . T y e , P h y s . R e v . L e t t . 41 (1978) 787 . M . B . Einhorn and B . G . Weeks , Nuc í . P h y s . B146 (1978) 445 .

2 1 . R. Horgan and M. Jacob, N u c í . P h y s . B179 (1981) 4 4 1 .

2 2 . I S A J E T programme, w r i t t e n b y F. Paige and S. Protopopescu, B N L repor t 31987 ( 1 9 8 1 ) .

23 . B. H u m p e r t , Two-je'c p roduct ion in p"p col l isions. to be

p u b l i s h e d , and p r i v a t e communicat ion.

24 . N . G . Antoniou e t a l . , Hedron and jet p roduct ion at Col l ider and I S R , Mc Gill U n i v . p r e p r i n t ( 1 9 8 3 ) , and Phys . L e t t . 128B (1983) 257 .

25 . Z . Kunsz t and E. P i e t a r i n e n , P h y s . L e t t . 132!- (1983) 4 5 3 .

26 . G . A l t a r e l l i , Q C D at the Co l l ider , Ref . T h . 3 7 3 3 - C E R N , t ^ be pub l ished in the proceedings of the In te rnat iona l School of Subnuc lear Phys ics , E r ice , I t a l y , 3 -14 A u g . 1983.

27 . T h e upper bounds in F igs . 10a and 10b correspond to a calculation of Ref. [23 ] us ing A = 0 . 5 G e V , Q 1 = 2 s t û / ( s ! * t " u 2 ) and t h e s t r u c t u r e funct ions ( S F ) of R. Baier et a l . , Z . P h y s . C 2 (1979) 265 . T h e lower bound in F i g . 10a is f rom Ref . [25 ] w i t h A = 0 . 5 G e V , Q 2 = 4 p y

2 and SF f rom J . F . Owens and E. R e y a , Phys . R e v . D17 (1978) 3 0 0 3 . T h e lower bound in F i g . 10b uses t h e same SF and is f rom Ref . [ 2 5 ] .

28 . T h e calculations of Ref . [ 21 ] uses Q2 = p-,- 2 , A = 0 . 5 G e V and SF of t h e t y p e J . F . Owens et a l . , P h y s . R e v . D18 (1978) 1501 . T h e c u r v e shown f rom Ref . [23 ] uses the SF of H . Abramowicz et a l . , Z . P h y s . C13 (1982) 199 , A = 0 . 5 G e V and Q 2 as g i v e n in [ 2 7 ] . T h e c u r v e f r o m Ref . [24] is obta ined wi th A = 0 . 2 G e V , Q 2 = 2 p y

2 and SF f rom M. Glück et a l . , Z . P h y s . C13 (1982) 119.

- 45 -

3 0 . B. H u m p e r t , J e t - j e t product ion in t h e m u l t i - T e V r a n g e , Ref . T H . 3 8 1 7 - C E R N ( F e b . 1 9 8 4 ) .

2 9 . E. E ichten et a l . , Phys . Rev . L e t t . 50 (1983) 811 ;

M. Abel in s et a l . , proceedings of t h e DP F summer s t u d y on

e lementary par t ic le p h y s i c s , Snowmass, Colorado 1982, p . 2 7 4 .

- 46 -

JET TOPOLOGIES IN HADRON-HADRON COLLISIONS'

R. D. Field D . 8 4 1 0 0 * ° 1 Q * PaiLlcTe Theory Croup-Department of Physics University of Florida

Gainesville, Florida 32611

Abstract

_^ Event topologies in pp collisions at W-60 GeV and in "pp collisions at ^

W=540 GeV resulting from a QCD Monte-Carlo model are examined. The model

includes gluon radiation both in the initial and final states and the outgoing

hadrons are labeled according to whether they arise before or after the hard

parton-parton collision. Transverse energy flows and transverse energy grids

are studied with emphasis, not on "jet finding", but on the patterns of energy

deposition. These patterns are quantified by examining the multiplicity of

transverse energy clusters each of which has energy greater than some fixed

amount. At high transverse energy the model produces events that are slightly

less "two-jet" like than the UA2 data, Howsver, the predicted frequency of /

occurrence of three cluster events Is In good agreement. Í

Work supported in part by the D. S. Department of Energy under contract No. DE-AS-05-81-ER40008.

- 47 -

I. Introduction

In leading order QCD, mesons are produced at large transverse momentum In

hadron-hadron collisions as the result of a hard parton-parton collision; one

parton .':rom the beam and one from the target hadron. The resulting elastic

parton-parton scattering produces two outgoing partons which subsequently

"fragment" into jets of hadrons producing the familiar four jet event topology

shown in Fig. 1 (two large p T jets, a beam jet, and a target jet).

The effects of soft and collinear gluon emissions off the Incoming

partons are treated by assigning a Q dependence to the parton structure

functions. Similarly, the soft and collinear gluon emissions off the outgoing

partons results in a Q dependence of the parton fragmentation functions. The

Q dependences are prescribed by perturbation theory (e.g. the Altarelli-Parisi

equations [1]). However, since to leading order, one only need consider the

case where the gluon radiation is either soft or collinear, one is still left

with an effective two-to-two subprocess.

The first attempts to include noncollinear gluon emission in hadron-

hadron collisions were made by Fox and Kelly [2] and by Field, Fox and Kelly

13] and by Odorico [4]. Here one approximates the effects of 2 •*• N

subprocesses by including the noncollinear emission of gluons off bsth the

initial and final state partons in the "leading pole" approximation [5-7],

Final state partons have timelike invariant masses with the radiated partons

being kinematlcally constrained to have invariant masses less than their

parents with the difference being converted Into the transverse momentum of

the emitted partons. The radiated partons themselves radiate more partons

until all invariant masses haye been degraded to some cut-off mass, y A, thus

producing a "parton shower". Initial partons also form a shower, but in this

case the partons ù.ive spacelike invariant mass. The Initial partons are

- 48 -

Jet Towards Trigger

Towards

Away

Fig. 1. Illustration of the four jet event structure resulting from a beam

hadron (entering from the left along the dotted line) colliding with a target

hadron (entering from the right along the dotted line) in the CM frame: two

jets (collections of particles moving in roughly the satae direction) with

large transverse momentum, p T , and two with small p T that result from the

break up of the beam and target hadrons.

- 49 -2

evolved from an initial invariant mass of ~(u ß) to a maximum (negative) 2 A 2 *

invariant mass of Q = -4p T , where p^ is the transverse momentum nf the hard

parton-parton subprocess [8].

In order to compare with experiment one must have a model for the way the

outgoing partons turn into hadrons. The approach adapted Wolfram and myself

[9] involves keeping track of the color strings (or clusters). All gluons are

forceably split into qq pairs and color singlet clusters are formed with a

distribution of invariant mass. For e+e- annihilations we choose a small cut

off invariant mass, u A, and allowed all clusters to "decay" isotropically in

their rest frame according to a simple phase-space prescription. To get a

completely color neutral system in hadron-hadron collisions it is necessary to

include the clusters containing the color "hole" that remains after a parton is removed from the beam and target hadron ("holes" are assigned the full

-bo

remaining momentum after the parton is removed). In our contribution the

Erice workshop [10J Fox and I used the phase-space method for clusters of mass

less than 3 GeV. Larger mass clusters were parameterized by back-to-back

Field-Feynman (11] jets In the color string CM frame.

In the analysis presented here I do not keep track of color strings and

fragment each parton (and "hole") independently in the hadron-hadron CM frame

according to the Field-Feynman prescription. In addition, I take the

invariant mass cut-offs uA

= W g ™ 2 G e V a n <* t h e perturbative parameter

A-0.4 GeV. I do not believe that this Is the most sensible hadronization

procedure £10]. However, with this fragmentation scheme I can keep track of

where the outgoing hadrons came from. This is Illustrated In Fig. 2. Type 1

hadrons are those arising from the initial partons Aj, A 2, •*• etc* plus the

hadrons coming from the fragmentation of the "hole" h g . Similarly, type 2

hadrona arise from Initial partons Bj» ... etc. plus "hole" h^. Outgoing

- 50 -

Hard Scatter ing Event

Fig. 2 . Illustration of a hard scattering QCD parton-shower Monte-Carlo event

in which the hadrons are labeled according to where they originate. Type 1

hadrons arise from the fragmentation of Initial partons A^, A 2 , etc. plus

the fragmentation of the "hole" h a (which is assigned fractional momentum

l-x a). Similarly, type 2 hadrons arise from the fragmentation of initial

partons Bj, ... etc. plus "hole" h D« Type 3 and type 4 hadrone arise from

the fragmentation of outgoing partons C^ and Dj, respectively, with p^ being

the transverse momentum of the hard constituent scattering, ab + cd.

- 51 -

partons and fragment into hadronB of type 3 and type 4, respectively. T

have been careful not to call, for example, type 3 hadrons a "Jet". Type 3

hadrons may form several jets or no jets or type 3 and type 1 hadrons may

conspire to form one jet. The definition of a "jet" is at the discretion of

the experimenter. The motivation here is to see in the Monte-Carlo for

various triggers and energies not.only the event topology but where the

hadrons originated. I am not interested in fitting the data perfectly but

Instead in learning more about the underlying QCD dynamics.

In the naive four jet language of Fig. 1, type 1 and type 2 hadrons

represent the beam and target jets, respectively, while type 3 and type 4

hadrons constitute the two large p . jets. QCD as we shall see is not so

simple. Sometimes type 1 or type 2 hadrons will form a large p T jet.

Sometimes type 3 hadrons will split and form two or three jets, etc.

II. Proton-Proton Collisions at W=60 GeV

Fig. 3 shows the cross sections for various transverse energy triggers at

W=60 GeV resulting from the Monte-Carlo with P T > 2 GeV. The total cross

section for this p T range is 2.1 mb at this CM energy. At low values of the

total transverse energy, E T , the cross section depends simply on the solid

angle subtended and the back-to-back As)=45ö, the side-to-side A<(>=450, and the

single A<J>=90° triggers all result in roughly the same cross section. As E T

increases the back-to-back trigger dominates over the other two indicating a

two jet (really a two blob) topology. The large aperture A<}i=36O0 cross

section results are in rough agreement with the preliminary AFS data [12].

The AFS large aperture A<fr=360° data at W=60 GeV indicate a rapid change

in the event structure at &p values of about 30 GeV. Below this value of Ry

events are more spherical, whereas above this value events are more "two jet

- 52 -

ID

4

-i—i—i—i—i—i—i—r W= 60 SeV |ij[< 0.9

2 6 10 14 18 22 25 30 14 E T ( G e V )

Fig. 3. Total transverse energy, E^, cross section for pp collisions at W=60

GeV and pseudorapidlty range -0.9 < n < 0.9 resulting from the QCD Monte-Carlo

model integrated over the hard scattering region p T > 2 GeV which yields a

contribution to the total cross section of 2.1 mb. The solid dots are for a

large aperture A<p=360° trigger while the up and down pointing triangles are

for a A$=90° and a back-to-back A$=45° trigger, respectively. The squares are

for a side-to-side A*=45° trigger. Preliminary AFS data fI2J are indicated by

the shaded region.

- 53 -

Hadron Multiplicity and Circularity W = 6 0 GeV \y \ < 0.9

o

0.6

0.4

0.2

0.0,

4 0

30

2 0

10

2 t 4 5 6 T • • l_ "

10 2 0 3 0 E T(GeV)

A F S Data

- | — i 1 — i — i — i — r -

I 2 3 4 5 6 7 ' ' ' l I 1 J _

0 10 2 0 3 0 4 0 E r(GeV)

Fig. 4. Comparison of AFS dita [12] (solid dotsi and che QCD Monte-Carlo

model (asterisk and dashed lines) on the average circularity (upper graph) and

average hadron multiplicity (lower graph) for a large aperture Ao)=360u

calorimeter trigger versus the total transverse energy, E^t in pp collisions

at W=60 GeV. Also shown are the results of the QCD Monte-Carlo for the

average circularity and hadron multiplicity (open circles) plotted versus-the

maximum transverse momentum in the event, p

- 54 -

like" in nature. This is indicated by the rapid change in che average value

of the circularity shown in Îg* 4 113]. Different triggers preferentially

select different parton substructures. Large aperture calorimeter triggers

are biased in favor of parton subprocesses involving large amounts of gluon

Brems Strahlung [3,, 10], Higher and higher Ej. values are produced by a larger

and larger multiplicity of hadrons each having only a slightly increasing mean

p T . As seen in Fig. 4, as the E T Increases so does the total multiplicity of

hadrons.

Fig. 5 and Fig. 6 show the average transverse energy flow about the

circularity axis for large aperture ¿$=360° triggers in the range 10 < E.p < 15

GeV and 25 < E . < 30 GeV, respectively. The average circularity has decieased

from 0.57 to 0.46. Nevertheless, the transverse energy contribution from

hadrons of type 1 and 2 has increased (shaded region). The central core of

the energy flow pattern expands both in the direction of the circularity axis

(y-asis) and in th« perpendicular direction (x-axls) as the total E , increases

indicating large gluon Bremsstrahlung contributions. In spite of this, the

average circularity resulting from the Monte-Carlo does begin to decrease at

around E^,=30 GeV (Fig. 4 ) . It is not clear whether this change Is as rapid as

seen in the data since at present I do not have sufficient statistics to

produce a point at 40 GeV.

Single particle triggers, on the other hand, bias on against large

amounts of gluon radiation. Nature cannot afford to waste the energy. This

can be seen in Fig, 4 where the average circularity and hadron multiplicity is

also ploted versus the maximum p T in the event, p ^ 3 X . Fig. 7 shows that the

energy flow perpendicular to the direction of the maximum hadron (x-axis)

actually decreases slightly as p ^ a X increases which is in contrast to the

expanding central core for the large aperture calorimeter trigger (Fig. 5 and

Fig. 6).

- 55 -

Transverse Energy Flow

A <f> = 3 6 0 ° trigger 10 < E T < 15 GeV

< N n o a > = 2 l . 5 < C > = 0 . 5 7

1 + ~ H 1

• 4 G B V

\T]\< 0.9

- 3

-Z

4 GeV 3 2 1 V Ï i Ï 3 GeV 4

L < E r ( l + 2 ) > = 6.2 GeV < N n o t f C1 +2)> = 13.4

• 2

• 3

-A GeV

Fig. 5. Average transverse energy flow with respect to the circularity axis

(y-axf?) resulting from the Monte-Carlo model <?ith a large aperture ¿$=360°

calorimeter trigger for pp collisions at W=60 GeV for the rotal tran IVERSE

energy range 10 < E^ < 15 GeV. Each bin represents the total amount of

transverse energy in the range ¿$=18" and |n| < 0.9 with dj measured with

respect to the circularity axis on an event-by-event basis. The shaded region

Is the amount oí energy arising from hadrons of type 1 and type 2 (see Fig,2).

- 56 -


A d ) = 3 6 0 ° triggei 25 < E T < 30 GeV

< N(KM> = 35.5 < C > = 0 . 4 6

| ^ | < 0 .9

< E T ( l + 2 ) > = 9 . 9 GeV < N h o a ( l + 2 ) > = 18.3

Fig. 6. Same as Fig. 5 but for the total transverse energy range 25 < E . < 30

GeV.

- 57


— 5 < F}.""* < 6 GeV •6

2 < Pf™"< 3 GeV < E T > = I4.e CeV .5.5 GeV < E T > = 9 8 GeV < N h o l l > = l 6 . 7 •5 < N h o d > = 16.5 < C > = 0.11 < C > = 0 3 4

•4

•3

2.34 GeV ; 2

4 GeV 3 2 i SC. X i 2 3 G B V 4

PT

m™ h-igger ¿__

| i7|< 0 .9 -1-2 GeV

Fig. 7 . Same as Fig. 5 but for two different ranges for the maximum

transverse momentum particle in the event, p ^ 3 X » and where the y-axiB is now

the direction of that particle.

- 58 -

-M SeV

Fig. 8. Same as Pig* 5 but for two different ranges of a small aperture

¿$=45^ trigger and where the positive y-axis is now the center of the

trigger.

- 59 -

2 6 10 14 18 22 26 3 0

E T ( G e V )

Fig. 9. Average value of the transverse momentum of the hard scattering

parton-parton elastic subprocess, p ,, resulting for the QCD Monte-Carlo in pp

collisions at W=»60 GeV versus the total trigger transverse energy, Eq.. The

solid dots correspond to a large aperture A{j>=36u trigger. The solid squares

and the down pointing triangles correspond to a A$=45° and a ¿$=90** trigger

while the up pointing triangles refer to a baek-to-back A$=45fl trigger. The

open circles correspond to events in which the maximum single particle py is

labeled on the x-axis (not E T ) . In all cases the pseudorapidlty range is

|n| < 0.9. The hard scattering transverse momentum is, of course, not an

observable that is directly accessible experimentally.

- 60 -

Soadll aperture calorimeter triggers fall in bt.ti.een the extremes of a

large aperture trigger and a single particle trigger. As seen in Fig. 8,

demanding large transverse energies into a single A+™45^ trigger (positive y-

axis) reBults In event topologies that are considerably more two-jet like In

nature than the large aperture A$=360 0 results. Here the central core changes

very slightly as the trigger energy Increases.

Clearly each energy and each trigger favors a different underlying parton

substructure. In QCD the parton substructure Is more complicated (and more

fluctuating) than in the naive parton model. By comparing event topologies

for various triggers one can reveal the CCD substructure. Fig. 9 shows that

the hard scattering regime can be reached by any of the various triggers,

However, the energy of the trigger and the event shape may be quite

different. For example, if one would like to explore hard scatterings at

p ,=6 GeV, one can take single p-y events at p>p=6 GeV, small aperture A<t>=45°

triggers at E T=7 GeV, or large aperture AiJ)=360f) triggers at E T=22 GeV. All

should be explained equally well by a correct model cf CCD- The amusing thing

is that each have about the same cross section. As is now well known, the

Idea that one can examine the hard scattering perturbative regime with a large

cross section by coing to large aperture calorimeter triggers la not correct.

III. Antiproton-Proton Collisions at W-540 GeV

Fig* 10 compares data on the large aperture A$=360" total E , cross

section for p"p collisions at W=540 GeV with the QCD Monte-Carlo integrated

over the hard scatter range 10 < p^ < 38 GeV. The dashed curve represents

42,000 events, but unfortunately can only be compared with data over the

limited region 50 < E T < 100 GeV. To compare at higher E T values would

http://bt.ti.een

- ô l -

IO"

10°

•ä lo

UJ T3

b IÜ 1

KT'

- "QCD-MC"

I O < P T < 3 8 GeV

\ \

UA2 pp = 5 4 0 GeV

< I

AFS pp W = 6 0 GeV - 0 . 9 < 7] < 0.9

50 100 150 200 250 300

E T (GeV)

Flg. 10. Comparison of UA2 data [17] on the total transverse energy, E T ,

cross section for a large aperture A$=360" calorimeter trigger in pp

collisions at W=5A0 GeV and for a pseudorapidity range |n| < 1 (solid dots)

with the QCP Monte-Carlo model integrated over the hard scattering range 10 <

P T < 3B GeV (dashed curve). Also shown are the AFS data of Fig. 3.

- 62 -

require generating more events at large p , values. Below &j=50 GeV the cross

section receives significant contributions from the region p T < 10 GeV. Over

the range 50 < E T < 100 GeV the QCD Monte-Carlo agrees roughly with the

data. Also shown in Fig. 10 Is the AFS E T cross section of Fig. 3 which also

roughly agrees with the Monte-Carlo at W=60 GeV. This indicates that the

energy dependence of the large aperture ¿^=360^ E^ cross section is correctly

described by the model. It has previously been reported that QCD can

reproduce the observed energy dependence of the single jet cross section which

ia extracted from the data by "jet finding" algorithms [14,15]. This analysis

shows that the large aperture A£=360° total E-j. cross section is also in

agreement with expectations from QCD.

Complicated "jet finding" algorithms are useful if one wants to compare

the naive four jets structure of leading order QCD (Fig, 1) with data. As I

mentioned above algorithms have been used to extract single jet cross sections

that agree roughly with leading order QCD. On the other hand, the topological

structure of QCD seems to be quite rich and what we are really interested in

is how transverse energy is deposited. Here the idea is not to identify

"jets" as such, but to identify patterns of energy deposition. The problem

becomes one of pattern recognition and In finding observables that reflect the

patterns. One way to accomplish this 's to form a transverse energy grid

("lego plot") as is shown in Fig, 11 [16]. Following the analysis of UA2

[17], I divide the solid angle Into bins of A^=10° and A<fr=15° and Sum all the

transverse energy into each bin. A 4TT detector would contain 432 cells, but

with the UA2 pseudorapidity cut |n|<1.0 (i.e. 40° < 6 < 140°) one Is left with

240 cells» Cells with energy less than some minimum, E™ i n, are ignored and

clusters of cells are formed by including in a cluster all cells with a common

side* Clusters are then ordered according to the total of all the cells in

- 63 -

the cluster with cluster #1 having the highest E T . I do not split clusters

with a "valley" of E T greater than 5 GeV into two smaller clusters as does UA2

[17]. I am not interested in finding jets (after all a jet depends on ones

definition anyway), but in the patterns of energy deposition.

Figs. II, 1?, and 13 and Table 1 give the properties of the three larges

E T events resulting from the QCD Monte-Carlo with 10 < p T < 38 GeV. Event 1

in Fig. 1J might be labeled a "two cluster event", since the first two

clusters have E T valueB of 55.S and 28.2 GeV, respectively, while the

remaining clusters are all less than 10 GeV, However, as seen in Table I even

in the pseudorapidity region |n|<l the event contains 57 type 2 hadrons

yielding 67 GeV of transverse energy. Only 27% of the transverse energy of

cluster il arises from hadrons of type 3 and 4. Actually cluster ff2 and 3 are

really the "naive two-jets" of Fig. 1. (Type 3 and 4 hadrons make up 100% and

9¿% of the transverse energy of cluster 2 and 3, respectively.) Event 2 in

Fig. 12 has three clusters with energies greater than 20 GeV, with cluster ffl

coming entirely from type I hadrons. Event #3 in Fig. 13 also has three

clusters with transverse energies greater than 20 GeV. Cluster #3 consists of

one cell of energy 25.7 GeV which arose from an outgoing quark that radiated

no gluons and hence produced a narrow jet. Outgoing gluons tend to radiate

lots of additional gluons sometimes depositing their transverse energy in

several clusters. For example, cluster #3 and #4 In event #2 (Fig. 12) both

consist primarily of hadrons of type 4 (Table 1) which arose from an initial

gluon that spilt into many gluons.

Clearly anything can happen in a single ev^nt and these three events are

probably not typical. However, they do illustrate the rich structure of the

QCD Monte-Carlo. In particular, they demonstrate the Importance of Including

both initial and final state BremsStrahlung. Table 2 and Figs. 14-20

represent an attempt to quantify these findings.

- 64

TABLE 1 _ Some properties of three large EIJ. events In pp collisions at tf=540 GeV resulting from the QCD Monte-Carlo with Ai» 360° and the pseudorapidity, n, range as marked-

Event #1 Event #2 Event #3

Type 4 hadrons:

T i k i

"had E T(GeV) 53.9 52.9 36.2 32.0 50.8

"had E T(GeV) 37.2 31.2 60.5 57.4 27.3

Type 1 hadrons: N h a d 24 5 81 45 8 1 E T(GeV) 8.3 2.0 71.5 49.8 4.4 0.9

Type 2 hadrons: N h a d 100 57 39 7 116 66 E^GeV) 95.0 67.0 14.6 2.6 84.9 64.6

Type 3 hadronß: NhaA 39 35 49 35 30 27

49.2

N h o J 50 36 42 36 9 7 26.8

All hadrona: N h a d 213 133 211 123 163 101 E T(GeV) 194.4 153.1 182.8 141.8 167.4 141.5

65 -

Transverse Energy Grid W = 5 4 0 GeV 360'

# Er(GeVl R cells i 5 5 . 8 0 . 2 7 19 2 2 8 . 2 1.00 5 3 9 . 8 0 . 9 2 7 4 9 . 3 0 . 0 6 3 5 6 . 3 0 . 2 0 6 6 5 .2 1.00 1 7 4 . 0 1.00 1 8 4 . 0 0 . 5 9 4 9 4 . 0 1.00 1

10 3 . 6 1.00 3

30° 60" 90° 120° 150° 180° Theta

Fig. 11. Transverse energy grid for event #1 of Table I. The solid angle 40°

< 9 < 140° and 0° < $ < 360° is divided into cells of A6=10 Q and ¿$=15° and

cells with total transverse energy less than E™ i n=0.4 GeV are omitted.

Clusters are formed by including in a cluster all cells with a common side and

are ordered according to their total transverse energy. The top 10 clusters

are shown in the figure with the asterlck referring to cells which belong to

lower ranked clusters* The quantity R refers to the fraction of the total

energy of a given cluster that Is due to hadrons of type 3 and 4 (see Fig. 2),

- 66 -

Transverse Energy Grid HT

W= 5 4 0 GeV T r~

1 3 4 . 7 0 . 0 0 6 2 3 0 . 6 0 . 9 9 8 3 2 3 . 4 0 . 9 6 10 4 ( 5 . 4 0 . 9 3 6 5 5 .8 1.00 1 6 2 .5 0 . 0 3 7 2 .3 0 . 0 1 8 1.9 1 .0 1 9 1.9 0 . 4 4 2

10 1.7 0 . 7 8 2

180°

Fig. 12. Same as Fig. 11 but for evei.t 112 In Table 1 .

67 -

Transverse Energy Grid W = 5 4 0 GeV -i—i—i—i i i i i

# ET(GeV) R cells 1 4 4 . 9 1 .00 12 2 3 3 . 6 0 . 0 6 17 3 2 5 . 7 1.00 1 4 10.1 0 D 4 4 5 2 . 8 0 . 0 2 6 £ . 7 0 . 3 9 2 7 2 . 4 0 .0 1 S 2.1 0.71 2 9 2 . 0 0 . 0 1

10 1.7 0 .0 1

(50° 180°

Fig. 13. Same as Fig. II but for event #3 Ir. Table 1.

- 68 -

In the Erp range 50 - 100 GeV an .-.verage event contains mostly empty

cells. Table 2 shows that in the range 80 <, E T < 90 GeV on the ¡rverage 70

cells contain energy with 47 remaining with E™^ n < 0.4 GeV (out of a possible

240 cells). On the average only 20% of the cells contain transverse energy

greater than 0.4 GeV. The average cell multiplicity is compared with data

from UA2 [17] in Fig. 14. At E T=100 GeV the Monte-Carlo has a slightly higher

cell multiplicity (about 6 cells out of 240), but I do not feel that this

difference is significant. In the Monte-Carlo the 47 cells then combine to

form 24 clusters on the average, which is a clear indication of "clustering".

At these values of E T cluster #1, #2, and #3 contain on the average 8, 5, and

4 cells, respectively, with 90% of the transverse energy of cluster #1, 88% of

cluster i/2, and 52% of cluster ¡?3 arising from hadrons of type 3 and 4.

Fig. Ï5 shows the first real discrepancy between the QCD Monte-Carlo and

the UA2 data. The average values of h ¿ = E T (cluster ifD/E^, (total) and h l 2 = E r

(cluster fll + # 2 ) / E T (total) resulting from the Monte-Carlo are larger than

the data at ^ = 5 0 GeV and smaller than the data at 100 GeV. The difference at

the lower E T values might be due partially because I do not "split" large

clusters into smaller ones as does UA2. However, the discrepancy at the large

values Is genuine. Unfortunately, I da not have results from the Monte-

Carlo *.t higher E T , say 200 GeV, where the differences may be even greater.

Clearly at E T > 75 GeV the data contain more energy on the average In the

first cluster and the first two clusters than the results from the Monte-Carlo

while the average values of r2j=E T(cluster #2 ) / E T (cluster #1) and r 3 2 = E T ^ c l u s t e r ^3 ) /E T(cluster #2) roughly agree*

One might be tempted to say that the data is more "two-jet" like at high

E T than the QCD Monte-Carlo. I believe, however, that this Interpretation Is

- 69 -

TABLE 2 Average event properties for a large aperature A$»360°, |n|<l calorimeter trigger at W=540 GeV resulting from the QCD Monte-Carlo where the maximum number of cells N . x

n 2 4 0 and where £^.(3+4) refers to the total transverse energy resulting 'com hadrons of type 3 and type 4 contributing to a particular cluster, c£,

50<E T<60 GeV 80<E T<90 GeV

<Vd> 7 3 9 0

^ c e l l ^ T 1 " 3 0 » 6 1 7 0

<N ,-(E^ i n=0.4 GeV)> 37 «7 cell i

<N(cluster)> 23 24

<E T(cluster # 1 » 14 GeV 27 GeV

<E T(3+4)/E T(tot»cMl 0.83 0.90

<E T(3+4)/E T(tot)>cM/2 0.67 0.88

<ET(3+«)/ET(cot)>c)t#3 0.52 0.52

<N ,,>c«l 5 8 cell

<N ,,>ci#2 6 5 cell

<N ,,>c«/3 3 4 cell

a , c e l i < n - ° > / N m a : C > ° - 2 5 ° - 2 9

< N c e l l i E ? 1 U - 0 - 4 ^ ' \ ^ > ° - 1 5 ° - 2 0

- 70 -

Cell Multiplicity

5 0 -

— i 1 1 1 1 1 r

E" i n = 0.4 GeV

UA2 Dota

4 0 6 0 8 0 100 120 140 160 ISO 2 0 0

E T (GeV )

Fig, 14. Comparison of UA2 data [17] on the average cell multiplicity (see

Fig, 11) with E™ l n=0.4 GeV in pp collisions at W=540 GeV versus the total

transverse energy for a large aperture ¿$=360° calorimeter trigger with the

results of the QCD Monte-Carlo model. The pseudorapidity range is as in Fig.

ÍÍ (fn| < 1.0).

- 71 -

ICO 150 200 E T (GeV)

O 0 5

CE

+ T

UA2 Data l - f -

O SO I » ISO 2 0 0 250 E T (GeV)

Flg. 15. (upper) Comparison of UA2 data [17] (solid dots) on the average

fraction of the total transverse energy, E T , carried by cluster #1,

hjoE T ( c i i i H)/E T(tot), and the average fraction carried by the top two clusters,

h 1 2='E T(cHÍ íl+cl#2)/E T<tot) In pp collisions at W=540 GeV with the QCD Monte-

Carlo model (dashed curves), (lower) Comparison of UA2 data (solid and open

dots) on the ratio of the transverse energy of cluster #2 to that of cluster

#1, r2j=E T(cl#2)/E T(clíl) and the ratio of cluster Í 3 to cluster #2,

r 3 2=E T(cl#3)/E T(cl#2) with the results of the QCD Monte-Carlo model (dashed

curves). The pBeudorapidity range is as In Fig. 11 ( | n | < 1.0).

10.0 8 0 < E T < 9 0 GeV

- U A 2 Data

1.0

. c •D b

- o

0.1

0.0J ,¿ L5-

I

I

+

I -

À1 0.2 0.4 0.6

h l 2

0.8 1.0

Fig, 16. Comparison of UA2 data [171 (solid dots) on the distribution of the

fraction of total transverse energy, E^, carried by the top two clusters,

h 1 2=E T(cl#l+cl#2)/E T(tot) for the range 80 < E T < 90 GeV in ff collisions at

tf=540 GeV with the QCD Monte-Carlo model (dashed curve). The pseudorapldlty

range ia as in Fig. 11 (|n| < 1.0).

slightly misleading. Fig. 16 compares the distribution of hj2 from the Monte-

Carlo with the tTA2 data In the range 80 < E T < 90 GeV. Although the data have

a slightly higher average hj2 than the Monte-Carlo, the UA2 values of are

distributed over a broad range with 22% of the events, at this energy, having

hj^ < 0.5. (The experimental distribution of h ^ i s broader than that

produced by the Monte-Carlo.) So aJthough the Monte-Carlo contains a little

less transverse energy in the first two clusters, as ia indicated b/ the

model, there is a lot more structure in the data at this energy than just two

clusters !

It is very important to look for and to quantify the multiCluster

topologies for they result from the rich substructure of QCD. Ii. addition,

the QCD Monte-Carlo model indicates that these topologies are much more

prevalent than In e+e- annihilations at existing energies where i • clusters

(i.e. two jets) truly dominate. One way to quantify cluster patterns is to

observe the multiplicity of clusters each of which has transverse energy

greater than some value, E ^ a c n . Fig. 17 shows the average cluste.

multiplicities versus total E T for E ^ a c h = 0 (curve d ) , 1 GeV (curve e ) , 5 GeV

(curve f), 10 GeV (curve g), and 20 GeV (curve h ) . Fig. 18 givt the

probability of finding an event with clusters each of which has energy

greater than 5, 10, and 20 GeV for two different total E T bins resulting from

the QCD Monte-Carlo. Clearly the maximum number of clusters with E ^ a c ^

greater than, say, 20 GeV Is limited by energy conservation with the average

number Increasing rapidly near the kinematic threshold. In QCD, however,

these mean values become greater than 2 as the total transverse energy is

increased. (Curve h In Fig. 17 for E ¡ j j a c n > 20 GeV eventually crosses 2.0 a-

hlghe.r total E^. values.) In the naive parton model of Fig. I it would be very

unlikely to find more than two clusters with E^. greater than, say, 10 GeV,

- 74 -

0.2 I 1 1 ' ' 50 6 0 70 8 0 9 0 100

E T ( G e V )

Fig. 17. Average multiplicities resulting from the OCD Monte-Carlo model

for pp collisions at W=540 GeV for a large aperture A$=360° trigger versus the

total transverse energy, E^: (a) hadran multiplicity; Cb) cell multiplicity

with E ^ - D . O ; (c) cell multiplicity «Ith £^"=0.4 GeV; (d) cluster

multiplicity with E ^ - O . i GeV; (e) cluster multiplicity with E ^ n = 0 . 4 GeV

and where each cluster has E ^ a c h > 1.0 GeV; (f) same as (e) but with E ° a c h >

5.0 GeV; (g) same as (e) but with E " c h > 10.0 GeV; (h) Bame as (e) but with

Eeach > 2 ( ) a & v > c l u s t e c a a n d M l l s a r e d e f l n e d l n p l g . H and c h e

pseudorapldity range Is as in Fig. 11 (jnj < l .o) .

- 75 -

E j 0 1 " > 2 0 GeV

3 4

TD

"fe

1 1 il°a,'> 10 GeV

- -

> 0 1 2 3 4 5

1.0

0.8

0.6

0.4

0.2

0.0

1.0

0.8

0.6

0.4

0 2

0.0

1.0

0.8

0.6

0.4

0 2

0.0

Fig. 18. Prediction of :he QCD Monte-Carlo model in pp collisions at W=>540

GeV for the probability of finding in a given event with total E^. in the range

50 < Ej < 60 GeV (dashed lines) and 80 < P-j, < 90 GeV (solid lines) H

clusters » each of which has transverse energy greater than 20 GeV (top), 10

GeV (middle), and 5 GeV (lower). Clusters are defined in Fig. 11 and the

pseudorapidity range la 3 8 in Fig. 11 (|n| < 1.0).

Cluster Mul t ip l ic i ty

- 76 -

whereas the QCD Monte-Carlo gives a 10% probability of finding 3 clusters

with E ^ a c h > 10 GeV for the total transverse energy in the range 80 < E T < 90

GeV (Fig. 18).

The average multiplicity of clusters with E ^ 3 0 " > 10 GeV is compared with

UA2 data in Fig. 19. At lower total E T value-S the Monte-Carlo produces fewer

clusters with energy greater than 10 GeV than seen by 0A2. However, above

E T=75 GeV the agreement is good. This is seen more clearly in Fig. 20 where

the distribution of clusters with E ^ a c h > 10 GeV is displayed for the total E T

range 50 < E T < 60 GeV and 80 < E T < 100 GeV. The agreement in the higher E T

range is quite spectacular with both data and the Monte-Carlo yielding three

clusters with E ^ a c ï l > 10 GeV In abo.it 20% of the events. The agreement may be

fortuitous, however, since as seen in Fig. 18 this might be the precise point

where the model predictions croas the data. I must run off more events at

larger Ey before any definite conclusions can be made.

IV. Summary and Conclusions

Hadrons of type 1 and type 2 are quite often referred to in a derogatory

manner as "background" to the high p T event. However, as we have seen these

hadrons play an integral role in the overall high pj event topology. There is

an event-by-event dynamical correlation between these hadrons and the hadrons

of type 3 and type 4. It Is Incorrect to consider large pij- events as an

Incoherent superposition of two *arge p-j. jets plus a "minimum bias"

background. The great majority of minimum bias events contain no hard

scattering, whereas essentially all large Err. event occur as the result of a

hard parton-parton. collision. Given that a hard seafaring has occurred, one

should be able to approximate the complete event structure from QCD

perturbation theory including the "background" hadrons (i.e. type 1 and type

http://abo.it

- 77 -

Cluster Multiplicity

3

z

1 1 1 1 1 1 1

E^ K " > I 0 GeV

•

/ /

/ / -

UA2 Data • i i i * ' 1

4 0 6 0 8 0 100 120 140 160 180 £ 0 0

E T (GeV)

Fig. 19. Comparison of UA2 data [17] (solid dots) on the average multiplicity

of clusters each of which has transverse energy greater than 10 1eV versus the

total transverse energy, E^., for "pp collisions at W=540 GeV with the QCD

Monte-Carlo model (dashed curve). The pseudorapidity range is as in Fig. 11

- 78 -

Cluster Multiplicity 5 0 < E T < 6 0 GeV

UA2 Dato

Cluster Multiplicity 8 0 < E T I 0 GeV

UA2 Data

2 3 4

Net 2 3

Nci

Fig. 20. Comparison of UA2 data 117] (solid lines) on the probability of

finding clusters each of which has transverse energy greater than 10 GeV

in an event with total transverse energy in the range 50 < E T < 60 GeV (left)

and 80 < E T < 100 GeV (right) for pp collisions at W-540 GeV with the QCD

Monte-Carlo model (dashed lines). The pseudorapidlty range is as in Fig. 11

<|n| < 1.0).

- 79 -

2) . QCD perturbation theory telle us nothing about minimum bias events.

Complicated "jet finding" algorithms are not necessary in order to

observe the rich topological structure of large prj hadron-hadron scattering

expected from QCD. One needs only to examine and Identify the patterns of

transverse energy deposition. This can be done by comparing the average

transverse energy flow patterns for a variety of triggers or by defining a

transverse energy grid and looking at the cluster patters. At large E T the

UA2 group at the CERN collider [17] find that the two highest transverse

energy clusters carry most of the total transverse energy (80% for E T > 100

GeV). However, I believe it is somewhat misleading to say that "two-jets"

dominate since raulticluster topologies occur at a sizeable rate.

One way to quantify the multicluster patterns Is to examine the

multiplicity of clusters each of which has a transverse energy greater than

some value, E ^ a c f l , Although the QCD Monte-Carlo produces events which contain

less total transverse energy in the first and the first two clusters at, say,

E T=100 GeV, the model and data do agree on the probability of finding three

clusters with E ^ a c h > 10 GeV (about 20% for 80 < Ej, < 100 GeV). Since I have

not examined the B e n s i t i v i t y of the QCD Monte-Carlo to changes i n the

fragmentation scheme or to changes in the QCD perturbative parameter A [18],

it is difficult to judge the significance of the disagreement (and the

agreement) with the DA2 data. Also, i do not know how well models without

initial state gluon Bremsstrahlung (such as Isajet [19]) fit the CERN collider

data. Nevertheless, I believe that the QCD Monte-Carlo model presented here

is telling us something interesting about the dynamical interplay between what

has previously been referred to as "background" and the what has previously

been referred to has "high p T jets". In addition, multlcluster topologies

with N > 2 must occur In nature if QCD is correct (although they may not

- 80 -

occur at precisely the rate I have predicted here). It is important to

quantify and examine these multicluster patterns experimentally. Hadron-

hadron collisions provide an excellent place to study the dynamics of QCD,

ACKNOWLEDGEMENTS

Much of this paper could net have been presented without the cooperation

of the UA2 group which allowed me access to unpublished data. In particular,

I wish to thank Peter Jenni for providing me the UA2 results on cluster

multiplicities. I gratefully acknowledge useful discussions with P. Darriulat

of UA2; G. Thompson and J. Rohlf of UA1; and K. Hansen, H. Boggild, and R.

Moller of AFS concerning the data. In addition, I would like to thank K.

Hansen, the Niels Bohr Institute, and Nordita for the hospitality shown to me

during the summer of 1983 where the analysis of the AFS lata was carried

out. Finally, I congratulate B. Hahn and P. Minkowski on a most enjoyable and

stimulating workshop.

- 81 -

FOOTNOTES AND REFERENCES

1. G. Altarelli and G. Farisi, Nucl. Phys. B126, 298 (1977).

2. G. C. Fox and R. L. Kelly, Caltech preprint CALT-68-890 and AIP

Conference Proceedings No. 85, "Proton-Antiproton Collider Physics

(1981).

3. R. D. Field, G. C. Fox, ard R. I. Kelly, Phys. Letters H 9 B , 439 (1982).

4. R. Odorico, Nucl. Phys. B199, 189 (1982); Phys. Letters I18B, 151 (1982);

University of Bologna preprint 1FUB 82120 (1982).

5. G. C. Pox and S. Wolfram, Nucl. Phys. B168, 285 (1980); G. C. Fox and S.

Wolfram, "A Gallimaufry of e+e- Annihilation Shapes", Caltech preprint

CALT-68-723 (1979), unpublished. G. C. Fox, lectures presented at the

1981 SLAC Summer School, CALT-68-863.

6. R, D. Field, "Jet Formation in QCD", invited talk presented at the XIII

International Symposium on Multlparticle Dynamics, Volendam, The

Netherlands, 6-11 June 1982, University of Florida preprint UFTP-82-28

(1982).

7. G. Marchesini and B. R. »ebber, CERN preprint TH-3525 (1983); B. R.

Webber, CERN preprint TH-3569 (1983), Marchesini and Webber have

improved the parton shower generation method to include, in an

approximate way, higher order perturbatlve effects.

8. To leading order, there is an ambiguity in the choice of the energy

scale, Q. All choices that increase linearly with the parton-parton

transverse momentum, p^,, jre equivalent. This choice of q saves a

considerable amount of computer time as is discussed in Ref. [2[.

9. R. D. Field and S. Wolfran, Nucl. Phys. B213. 65 (1983). R. D. Field,

"The Production of Partons and Hadrons In e+e- Annihilations - Quark and

Gluon Jet Models", University of Florida preprint UFTP-81-12 and proc.

conf. on perturbative QCD, Florida State University (March 1981), AIP

Conference Proceedings No. 74 (Particle and Fields Subserles No. 24).

10. R. D. Field and G. C. Fox, "QCD Monte-Carlo Models for e+e- Annihilations

and Hadron-Hadron Collisions", invited talks presented at the Europhyslcs

Study Conference on Jet Dynamics In Quark and Lepton Interactions, Erice,

Sicily, 12-17 Sept. 1982, CALT-6B-965 and UFTP-82-30.

11. R. D. Field and R. P. Feynman, Phys. Rev. D15, 2590 (1977); Nucl. Phys.

B138, I (1978),

12. T. Akeeson et al. (AFS Collaboration), "The Dominance of Jets at Large

Transverse Energy In a Full-Azimuth Hadron Calorimeter at ISR Energies",

CERN preprint CERN-EP/83-71.

13. The circularity, C, 1B a measure of the event shape. It is equal to I-P

where P is the planarity (two dimensional analogue of sphericity) defined

by P = (E(max)-E(mln) j/[E(aax)+E(mln)), where £(max) and £(mln) maximize 2

and minimize, respectively the sum of p^, In the transverse ( p f ) x a n d

( P T ) y plane.

14. G. Ami8on et al. (UAl Collaboration), "Hadronic Jet Production at the

CERN Proton-Antiproton Collider", CERN preprint CERN-EP/83-118.

15. M. Jacob, "Collider Physics - Present and Proapects", talk presented at

the SLAC Topical Conference, 27-29 July 1983, CERN preprint TH-3693.

16. I apol igize for not being able to produce the usual three dimensional

"lego plots", but at present my computer graphic capabilities are

limited*

17. F. Bagnaia at al. (UA2 Collaboration), "Measurement of Very Large

Transverse Momentum Jet Production at the CERN pp Collider", CERN

preprint CERN-EP/84-I2; and P. Jenni private communication.

10. To leading order the choice of the QCD perturbative parameter A is

arbitrary and no one knows the best leading order effective A to uBe in

hadron-hadron collisions. Reducing A wov.ld reduce the overall amount of

wide-angle gluon Bremsstrahlung. If it Indeed turns out that the CERN

collider data at high transverse energy is "cleaner" than the QCD Monte-

Carlo (i.e. more two-jet like) than it may simply be an indication that

one should use a smaller effective A.

19. F. E. Paige and S. D. Protopropescu, BNL 29777 (1980).

- 84 -

Comparison of Quark and Gluon Je ts

Ot 8 4 1 0 0 2 6 1 1 2

by

G. Schierholz

Deutsches Elektronen-Synchrotron DESY, Hamburg

Abstract

r ~ i If QCD is the underlying theory of the strong interactions, quark

and gluon jets should appear to be rather different in nature. In

this talk I s4«44*discuss the (theoretical) roots of this difference

and to what extent it has been borne out experimentally.

1 . Introduction

Quarks and gluons play quite a different role in QCD. While quarks are mainly flavour labels and sources of colour perturbation in the vacuum, gluons are largely responsible for confinement, i.e. the QCD vacuum, and dominate the particle production mechanism. This leads us to expect the fragmentation patterns of quark and gluon jets to be rather diverse.

- 85 -

The purpose of my talk is to illuminate this issue. So far we are not able to derive the fragmentation functions from first principles. But in the last years a vast amount of experimental information on the fragmentation mechanisms of quark and gluon jets has accumulated (and I believe there is a lot more to come from the pp collider) which will compensate for this weakness.

2. Space-Time Picture of Quark and Gluon Jets

To begin with let me review our current understanding of the process of hadroni-zation in quark and gluon jets.

Quark Jets

As a quark leaves the interaction region it trails behind it a colour (triplet) flux tube. At some point the gain in diminishing the flux tube length outweighs the cost of exciting a qq pair from the vacuum, and the flux tube will break into a string bit of perhaps a mass of 83> 1 GeV (length ßjl fermi, given a string tension of 1 GeV/fermi) and a "heavy" string consisting of the original (energetit quark and the newly created antiquark. As the leading quark and the antiquark move apart, the "heavy" string will break repeatedly until eventually the system has totally decayed into string bits of the aforementioned size:

>

.. • — • o • •

- 86 -

The string bits are strongly ordered in rapidity. The lengths of the arrows represent (pictorially) the velocities of the bits. If not originally so, the string bits will evolve into strongly interacting systems, bags, containing a qq pair:

The (Feynman) graphical description of the quark jet evolution

... >

leads in the limit = large Co more or less the saine strong ordering in rapidity. In the following I shall employ both notations.

The validity of thn string picture has only recently been verified experimentally by comparing the fragmentation properties of charm jets with those of the average jet. According to this picture the two jets should only differ in the leading particle spectrum, and that is exactly what has been found ^ .

Gluon Jet

An energetic isolated gluon will trail a colour (octet) flux tube behind it. In a world without dynamical triplets of colour the flux tube would break up into a sequence of gluon-string bits in the same way the quark flux tube decays

2) into string bits. The masses of the lowest-lying glueball states range from 0.7 to 5& 2 GeV, ai"?, hence the mass of a gluon-string bit is expected to follow some distribution centered on a mean in the range 1.5 to 2 GeV (lengthj£ 1 fermi,

- 87 -

givea a string tension more than twice that of the triplet flux). Including dynamical quark triplets is not expected to alter these numbers very much. In the real world with quarks the flux tube may. however, also break by exciting two qq pairs (in the octet representation) from the vacuum as shown (e.g.) below:

*9 r

-» —»

9 f \ \

The gluon-, mixed- and diquark-string bits will evolve iní.o three topologically distinct physical systems:

& O O giving rise to glueballs, so-called mixed (qqg) states and four-quark resonances, respectively. The masses of the lowest-lying mixed states are expected to lie in the range 3 ) 1.5-2 GeV.

The (Feynman) graphical description of the gluon jet evolution

err

does not obviously agree with the string picture. Presumably this can be achieved to some extent by taking proper care of quantum interference phenomena.

Topological Properties

From the discussion so far it is apparent that the gluon jet has a much richer particle spectrum than the quark jet. But more about this later. A further striking difference is that the particle flow in the gluon jet depends crucially on its history, while in the quark jet it appears to be more universal. To give an example consider (i) two back-to-back gluon jets as they arise (e.g.) from heavy para-quarkonium decays or pp-* gg + X

and £ii) a qqg three-jet event as it appears (e.g.) in e +e annihilation

- 89 -

The three-jet configuration shown is only one of many possible final states. Its particular feature is that the gluon (colour octet) flux tube has broken initially and repeatedly by qq pair creation. Furthermore, it assumes that the

4 p interaction between overlapping string bits ^ ^ is small so that the two resulting triplet flux tubes ervolve more or less independently (as indicated). Accordingly the gluon jet here will be oblate and much broader (in the event plane) than in case of the back-to-back jet (i). The JADE group has confirmed that the fragmentation proceeds to soce extent along the colour flux lines rather than stricrly along the parton axes. Below

4) I have transcribed their data into an event-shape plot

- 90 -

which clearly shows the effect. (In this p l o t ^ p ^ ^ i s zero when the particles fall on the jet axes.)

In general the gluon flux tube may also break by forming gluon-string bits

and the overlapping string bits in (ii) may interact (e.g. to give baryons as I will discuss later on), which then will fragment more or less along the parton axes. How much this is so can only be answered by the experimentalists at the moment. But it is conceivable that the Lund fragmentation model ^ \ which treats the gluon string as a superposition of two naninteracting quack strings, is as far from the truth as the independent parton fragmentation models.

It is interestins to note that Webber's model ^ for jet fragmentation, which follows the graphical description including some soft-gluon interfertnce, also reproduces the string effects, and I am sure that this will shed some more light on this issue.

3. Longitudinal Evolution

I like to discuss now the single particle distributions in quark and gluon jets. Let me begin (for a change) with the perturbative aspects of it.

(a) Perturbative

The longitudinal development of quark and gluon jets is believed to be governed by the evolution equations ^ :

- 91 -

This set of coupled equations can be solved for z f¡¿ 1 r and we obtain

J

? a - * / * ,

C (t) = C4f0> -r -iL. í

for the fragmentation function of the quark and

? a-» /

Ca«; = c,(o> + 2 - A - *

for the fragmentation function of the gluon (jf^ is Euler's constant). The derivation assumes that c ^ ^ c^ - 1 which, if not originally so, will become true at least at large t.

Because quark and gluon jets lose momentum by gluon bremsstrahlung, the single 2

particle distribution in the jets becomes softer as Q increases. Moreover, we see that the ratio between the rate of softening of gluon and quark jets is 9/4 = N / C , which is a consequence of the higher colour charge of the gluon. c ¥ For Q = 10 GeV, Q = ICO GeV and N = 5 we obtain (/I- = 200 MeV) o 1 MS

C Ct) = C (o) + 0.30,

Cg(t) = C gCo) + Û.6B

which might be just enough of a change to be detectable experimentally. To draw any firm conclusions one will, however, have to know c Co), C (o) (e.g. from

rr q s

measurements on and off the X resonance) rather accurately. I shall discuss the experimental situation after I have presented the nonpertur-bative aspects of the longitudinal distributions at the end of this section.

where t = 1*¿<ZV«S<£>7 , i = l«¿AWÂI.

- 92 -

Multiplicities

The zeroth moments of the quark and gluon fragmentation functions give the mean multiplicities in quark and gluon jets

* <

The evolution equations for the 2ßroth moments develop, as they stand, some divergences associated with the emission of a divergent number of soft gluons. But if the gluon is very soft it cannot fragment into hadrons. So we integrate only over those gluons t'^t which are capable of fragmenting ^ . This gives

which has the asymptotic solution

f i « ft; - «í -pí. e '

Again there is a factor 9/4 between the asymptotic multiplicities in gluon and quark jets due to the greater colour charge of the gluon.

To tell how far we are from asymptotic one has to go beyond the presentation given here. Webber has done this and he finds for the ratio«in ^/<n (which is of most interest to us here) the following energy dependence :

- S3 -

E(GeV) 111 I—i r-

Ul O Q2 at, 0.6

(In E/Al"2

(the points show the Monte Carlo results and the line is a linear fit). The outcome is that the asymptotic predictions are so asymptotic as to be useless. But the difference of quark and gluon jet multiplicities is still big enough to be conclusive.

The experimental data and the (Monte Carlo) predictions are summarized in the figure below

20

.9- 10 3 E

T—j ) ) IJJJ'i i—I Til n i j —ri—TT

• UA2(pp) I / I • CERN-Saclay(ppl , j\ MASSOl .4— / -

(e*e-) / / J

/ /

íI / Á v CLEO o MARK I

OL i I i i i i i n i l — i — XJ0 W1 X)2

E(GeV)

- 94 -

where E is the c m . energy of the two-jet system. The dashed line is the prediction for the quark jet multiplicities, the dashed-dotted line that for the gluon jet multiplicities ^ \ The TASSO data ^ , which proceed dominantly from quark jets, fall (at their highest energies) close to the quark curve while the UA2 data ^ \ which are dominated by gluon jets, fall on the gluon curve. This nicely confirms the predictions. One can also say that the QCD prediction of a rapidly increasing multiplicity is in accord with the data.

(b)Nonperturbacive

According to the string picture the fragmentation function of the quark is

given by the iterative equation

where dP/d^ is the probability to find a meson containing the original quark at 1-y. The most natural choice for the probability function is dP/dy » 1, apart from may be the boundaries. This implies the large-z behaviour D**(z)iyconst. For the fragmentation function of the gluon we find analogously

In case the gluon flux tube breaks into a sequence of noninteracting (triplet)

string bits

..._P« —» tí—• <*—"fcd fctf

we expect, except perhaps for y^, y^ fi¡ O,

< C ?

= 4 1 o i l = /

At large z this gives D^(z) »v (1-z), which has an extra power of ( 1 - z ) . Note

al¿o that < n ^ ^ $»-2 <n^V i n this picture.

The Lund group has studied the quark and gluon fragmentation functions in the context of this simplified model in great details. The result of their cal-

95 -

culation is given below ^ zD(z) 15r

z We see that the glupn fragmentation function comes out to be very much softer

than that of the quark.

This difference (if true) should become visible if we compare the jet fragmentation at PETRA (mostly quark jets) to that of the pp collider (mostly giuon jets) what I have done below

100

10

z|n T3TO

0.1

QUI

- 1 — I — 1 — I — 1 — I — 1 — I -I-UA1 E t(>t)>30G»V • TASSO 34GeV

Q2 0.6 06 06 z

Ic looks as if the quark and gluon fragmentation functions are almost the same contrary to the model. This appearance is, however, deceptive. In the UA2 data events with z 0.05 have been discarded. If one applies the same cut to the

- 96 -

Lund gluon fragmentation function (and rescaler.) one obtains the dotted 12)

curve in the figure before , and a lot of the difference has gone away. This will be further washed out by also including charra quark jets (which at PETRA energies are much softer than u and d quark jets ^ ) in the model calculations. But there is also the possibility, as I said before, that the gluon flux tube decays into gluebalLs and that the overlapping (triplet) string bits interact which will obviously modify the predictions for the quark and gluon fragmentation functions.

4. Transversal Evolution

The intrinsic transverse momenta in jets are proportional to A , the only scale parameter in OCD (in the chiral limit), and hence they are nonperturbative in origin.

Let us consider now (e.g.) two back-to-back quark-antiquark and gluon jets, respectively. As the quark and antiquark (thu two gluons) separate he transversal width of the field energy distribution (flux tube) increases due to

13) quantum fluctuations :

(It increases without bound when the qq (gg) separation goes to infinity.) The . 13)

chromo-electric field energy density above the vacuum is

>

where O - , , is the string tension and A is some constant. In momentum space q(g)

this gives

A* ¿/A i-

The partons that break the flux tube (while expanding) will now be created with an intrinsic transverse momentum

so that the mean transverse momentum of hadrons in quark and gluon jets is

The string tensions G~ and can and have been calculated on the lattice, q g

What will interest us here is only the ratio / <P. By dimensional reduction 15) 8 q

techniques (which have been verified in SU(2) by lattice Monte Carlo calculations ' ^ ) we arrive at <S~ / U~ = 9 / 4 , so that

S q

The JADE group finds a significant difference in the mean transverse momentum A)

out of the three-jet plane :

<Bl"" > IGeV/c)

0.2

— r — 1 1 1 1 , , , 1 , , , , 1 ,

• I f * * » «• * % -• J E T # 1 _

• • JET#2 : • , , 1 ... 1 • . J ^ T J ? Í :

) 5 10 15

- 98 -

The probability that trie fastest jet (0 1) is the quark or antiquark is 88 7.

and that the lease energetic jet (Ü 3) is the gluon is 51 %, Taking this into account I obtain (at E. = 10 GeV) jet

e ratio which gives for the ratio

which is close to what one expects

5. Particle Yields

In the gluon jet (at least) the leading string bits should remember that they are fragments of a (iso-singlet) gluon. This is to say that we expect glueballs, mixed (qqg) states, , Q, $ , etc. to be produced abundantly (for a model calculation involving the conventional mesons see (e.g.) ref. 16). So far the JADE group has found some evidence that the *J? yield is larger for three-jet events than for two-jet events supporting this picture. For a further test and for our further understanding of the fragmentation mechanism it is important now to also trace the glueballs and mixed states.

The four-quark states in the gluon jet, having a mean mass of 0(2 GeV), may

In case the two (triplet) string bits would not interact (Lund model) only the top mode would be present. To gain same insight into the dynamics of the decay one may look at low energy pp annihilations. At |Aj ft 2 GeV the relative kinetic energy is low enough that the intermediate state will at some point consist of

- 99 -

two quarks and two antiquarks mixed together in a strongly interacting region of total mass ft" 2 GeV. The annihilations correspond to the case when this

+ 19) system decays into mesons. The cross section is 77 — 3 tnb . The cross section for producing a baryon-antibaryon pair may be estimated by taking pp-*pp or

19) nn and subtracting the pp value. This gives 38 tnb . Thus there appears to be no particular suppression of this mode, and our best guess is that the decay of the gluon flux tube into baryon, antibaryon will also not exhibit any marked dynamical suppression. This contradicts obviously the (naive) Lund model to the extent that we observe abundant baryon production in gluon jets. (But at present we can also not totally deny that there are other mechanisms within the context of QCD that might lead to substantial baryon production in jets. For a further discussion see ref. 18).

Let me now turn to the data. The DASP II group has found that antiprotons on the ^ (presumably three gluon jets) are produced at a rate about six times

20) 21) ** higher than on the neighbouring continuum . At PETRA the p/meson and A /meson ratios increase with x and become large. In deep inelastic processes,

22) and in particular the EMC data , the ratio of protons to mesons increases with increasing pj_ (t 'iree-jettiness) as shown below:

- 100 -

We conclude that the recent high-energy data does not only reveal substantial baryon production but also indicates that the (dominant) source of all these baryons is glue.

6. Miscellaneous

In this last section I like to mention very briefly a couple of other features that further mark the different nature of quark and gluon jets.

KNO Scaling

We expect the shape of the KNO scaling curve ^ nc n ^ p i n

c h ^ v e r s u s nc ^ ^ n

c ^ tot gluon jets at large n^/î^^} to be much flatter than for quark jets. This follows naturally from the (simplified) Lund model and should be true in general though maybe in a weaker form. Experimentally there are some indications that this is indeed the cast .

Prompt Photons

The QCD vacuum is a highly nontrivial setup of fluctuating colour fields. Nachtmann and Reiter have put forward the idea that energetic quarks traversing

23) . these fields will produce soft photons (and soft gluons) similar to synchrotron radiation of energetic electrons passing through a magnetic field.

This would lead us to expect more prompt' photons in quark 1jets than in gluon jet

Charge Retention

Measurements of the net charges oí quark jets in neutrino and antineutrino 24)

interactions have appeared recently . It has been found that the net charge of the jet closely reflects the charge of the parent quark. Moreover, it has been shown that the energy dependence of the net charge of the quark jets bears

25) some information about the charge exchange properties of isolated quarks It will be important now to repeat the analysis for gluon jets at the pp collide

- 101 -

7. Conclusions

Quark and gluon jets, that seems to be established, are different. As far as one can tell, the differences are in qualitative (and in some cases even semi-quantitative) agreement with our theoretical expectations based on QCD. However, we cannot make precise tests of QCD yet because of substantial uncertainties in the theoretical calculations.

References

1. TASSO Collaboration, M. Althoff et al.: DESY preprint 83-114 (1983). 2. K. Ishikava, A. Sato, G. Schierholz, M. Teper: Zeitschr. f. Physik C21,

167 (1983); B. Berg: DESY preprint 84-012 (1984). 3. F. Close in Few Body Problems in Physics, Proceedings of the Tenth Inter

national Conference on Few Body Problems in Physics, 1983, ed. B. Zeitnitz, Vol. 1, p. 55c (North-Holland, 19B4).

4. JADE Collaboration, W. Bartel et al.: Zeitschr. f. Physik C21, 37 (1983). 5. B. Andersson, G. Gustafson, G. Ingelman, T. Sjostrandî Phys. Reports 97,

31 (1983). 6. B.R. Webber: CERN preprint TH.3713 (1983). 7. J.F. Owens: Phys. Lett. 76B, 85 (1978); T. Uematsu: Phys. Lett. 79B, 97

(1978). 8. E.g. B.R. Webber: Phys. Scripta 25, 198 (1982). 9. TASSO Collaboration, R. Brandelik et al.: Phys. Lett. 89JS, 418 (1980). 10. UA2 Collaboration, P. Bagnaia et al.: CERM preprint EP/83-94 (1983). 11. UA1 Collaboration, G. Arnison eï al.: Phys. Lett. I32B, 223 (1983). 12. T. Sjöstrand, private communication. 13. M. Lüscher, K. Symanzik, P. Weisz: Nucl. Phys. BI73, 365 (1980). 14. M. Lüscher, G. Münster, P. Weisz: Nucl. Phys. 8180, 1 (1981). 15. J. Ambjfirn, P. Olesen, C. Peterson: Niels Bohr Institute preprint

NBI-HE-84-06 (1984). 16. C. Peterson, T.F. Walsh: Pfcys. Lett. 9YB, 455 (1980). 17. JADE Collaboration, W. Bartel ït al.: DESY preprint 83-063 (1983). 18. G. Schierholz, M. Teper: Zeitsctir. f. Physik C13, 53 (1982). 19. V. Flaminia et al.: CERN-HERA 79-03 (1979); 0. Benary et al.: UCRL-20000 NN

(1970) . 20. DASP II Collaboration, H. Albrecht et al.: Phys. Lett. I02B, 291 <198 1). 21. TASSO Collaboration, R. Brandelik et al.: Phys. Lett. 94B, 444 (1980);

JADE Collaboration, W. Bartel et al.: Phys. Lett. 104B, 325 (1981). 22. European Muon Collaboration, J.J. Aubert et al.: CERN preprint EP/83-164

(1983). 23 0. Nachtmann, A. Reiter: Heidelberg preprint THEP-83-28 (1983). 24. J.P. Berge et al.: Phys. Lett. 9M3, 311 (1980); N. Schmitz: Lectures at the

XX Krakow School, Zakopane, 1980. 25. M. Teper: DESY preprint 81-007 (1981).

- 102 -

TRIPLE ÄND QUADRUPLE JETS

O: 8 4 1 0 0 2 6 1 2 0

Z. Kunszt *

Institut für Theoretische P\ysik Universität Bern

Sidlerstrasse 5 , CH-BERN, Switzerland

A b s t r a c t T h e p a r t o n m o d e l d e s c r i p t i o n o f t h r e e a n d f o u r j e t p r o d u c t i o n i n

I p r o t o n - a n t i p r o t o n c o l l i s i o n s i s s h o r t l y r e v i e w e d . P o u r h e a v y q u a r k p r o d u c t i o n i

i s a l s o d i s c u s s e d .

1 . T H R E E J E T P R O D U C T I O N

l)-4) T h e v e r y l a r g e r a t e o f j e t p r o d u c t i o n i n p r o t o n - a n t i p r o t o n c o l l i s i o n s

r e q u i r e s t h e q u a n t i t a t i v e s t u d y of m u l t i j e t p r o d u c t i o n r a t e s .

+ - 5) I n e e a n n i h i l a t i o n t r i p l e a n d q u a d r u p l e j e t s h a v e b e e n s t u d i e d b y

c a l c u l a t i n g t h e c r o s s s e c t i o n s o f t h e p a x t o n p r o c e s s e s e + e •*• q q g ,

e + e -+ q q g g + q q q ' q * . T h e s e c r o s s s e c t i o n s a r e s i n g u l a r w h e n t h e f i n a l p a r t o n s

h a v e c o l l i n e a x o r s o f t m o m e n t a , t h e r e f o r e t h e y c a n b e c o m p a r e d w i t h t h e d a t a

o n l y f o r w e l l s e p a r a t e d h a r d j e t s . S u c h a c o m p a r i s o n c a n b e p e r f o r m e d e i t h e r

w i t h t h e a p p l i c a t i o n of a j e t - f i n d i n g a l g o r i t h m t o t h e d a t a o r u s i n g a m o d e l

t o h a d r o n i z e t h e f i n a l j e t s . E x p e r i e n c e a i ; PETRA a n d P E P h a s s h o w n t h a t b o t h

» P e r m a n e n t a d d r e s s . C e n t r a l R e s e a r c h I n s t i t u t e f o r P h y s i c s r

B u d a p e a t i H u n g a r y

- 103 -

P o u t ^ J 2 l p i , o u t l U )

i

As we c a n s e e o n F i g . 1 t h e a g r e e m e n t b e t w e e n t h e m e a s u r e d d ~ - ^ r i b u t i o n and t h e

QCD c a l c u l a t i o n i s r e m a r k a b l y g o o d , a l t h o u g h 4 - j e t p r o d u c t i o n and h a d r o n i z a t i o n

e f f e c t s h a v e n o t b e e n i n c l u d e d .

9) Fox and Wolfram h a v e p r o p o s e d a b r a n c h i n g a p p r o x i m a t i o n i n w h i c h an

a r b i t r a r y number o f j e t s a r e p r o d u c e d b u t t h e m a t r i x e l e m e n t s a r e a p p r o x i m a t e d

by t h e l e a d i n g l o g summation o f t h e c o l l i n e a r s i n g u l a r i t i e s . In t h i s a p p r o x i m

a t i o n m u l t i j e t p r o d u c t i o n c a n b e i m p l e m e n t e d b y Monte c a r l o method n a t u r a l l y ,

s i n c e b o t h t h e m u l t i p a r t ! c l e p h a s e s p a c e and t h e m a t r i x e l e m e n t s a r e c a l c u l a t e d

by a b r a n c h i n g p r o c e d u r e .

The P o u t d i s t r i b u t i o n a s m e a s u r e d b y t h e UAl e x p e r i m e n t h a s b e e n c a l c u l a t e d

a l s o i n t h i s a p p r o x i m a t i o n ^ ^ ' . A g a i n t h e a g r e e m e n t i s a c c e p t a b l e a l t h o u g h t h e

t h e o r e t i c a l v a l u e i s s l i g h t l y a b o v e t h e d a t a .

A t v e r y h i g h e n e r g y t h e b r a n c h i n g a p p r o x i m a t i o n t e n d s t o p r o d u c e l a r g e j e t

m u l t i p l i c i t y " * " ^ w h i c h may i n d i c a t e t h a t t h e mode l t e n d s t o o v e r e s t i m a t e t h e

m u l t i j e t p r o d u c t i o n r a t e s .

2 . FOUR JET PRODUCTION

An e x p l i c i t c a l c u l a t i o n o f 4 - j e t p r o d u c t i o n i s s t r a i g h t f o r w a r d b u t v e r y

l e n g t h y . The number o f Feynman d i a g r a m s o f t h e v a r i o u s s u b p r o c e s s e s a r e a s

f o l l o w s :

m e t h o d s a r e p r a c t i c a l and t h e i r i n h e r e n t a m b i g u i t i e s a r e c o m p a r a b l e . The f i r s t

method h a s t h e a d v a n t a g e o f s i m p l i c i t y , t h e s e c o n d method i s c a p a b l e t o accom

modate more d e t a i l e d f e a t u r e s o f t h e f i n a l s t a t e h a d r o n s .

I n h a d r o n c o l l i s i o n s we c a n p r o c e e d s i m i l a r l y , h o w e v e r * t h e c a l c u l a t i o n s

a r e more c o m p l i c a t e d . E . g . t h e 2 -+ 3 s u b p r o c e s s e s a r e d e s c r i b e d by more t h a n

50 Feynman d i a g r a m s . N e v e r t h e l e s s t h i s c a l c u l a t i o n h a s b e e n p e r f o r m e d ^ ' and

B e r e n d s e t a l . ^ h a v e s u c c e e d e d t o f i n d s u r p r i s i n g l y s h o r t f o r m u l a e f o r t h e

o r i g i n a l q u i t e l e n g t h y e x p r e s s i o n s .

UAl h a s a n a l y z e d t h r e e j e t e v e n t s ' 1 - ' . They m e a s u r e d p ,_ d i s t r i b u t i o n and com-

p a r e d i t w i t h t h e o r e t i c a l p r e d i c t i o n i n t h e l a r g e P o u t . r e g i o n w h e r e a s i m p l e

two j e t mode l c l e a r l y f a i l s t o d e s c r i b e t h e d a t a . P Q U t i s t h e t r a n s v e r s e momentum

o u t o f t h e p l a n e g i v e n by d i r e c t i o n s o f t h e t h r e e momenta o f a t r i g g e r j e t and

t h e beam:

104 -

gggggg 205 diagrams (2a) ggggqq 123 diagrams (2b)

ggqqqq 72 diagrams (2c)

ggqqQQ 36 diagrama (2d) qqqqqq 42 diagrams (2e>

qqqqßQ 14 diagrams (2f)

qqQQS'Q' 7 diagrams (2g)

The calculation of these diagrams appears to be feasible with a completely numerical procedure, although the computer time becomes non-negligible. However, a reasonable! estimate of the 4-jet production rates can be obtained also with a partial calculation. It is well known that both for two and three-jet production the dominant subprocesses are of the scattering processes

gg + gg gg ggg + gqq (3a)

gq •* gq gq -* ggq + QQq (3b)

qq' •* qq' qq 1 qq'g (3c)

It has been found numerically that when flavour blind jet properties are calculai

ated the subprocesses (3a)-(3c) give very similar distributions . Furthermore 12)

their normalizations satisfy approximately the relation

dD : da : da 4/9 : 1 : 9/4. (4) qq gq gg

12) The advantage of this relation has been recently emphasized . Also it has

It has also been found that identical flavour effects in flavour blind jet

production are always negligible.

It seems naturel to assume that the relation £4) will hold approximately also in case of 4-jet production and that idential flavour effects remain negligible. With this assumption it is sufficient to calculate only the 36 diagrams of type <2d) and the 7 diagrams of type (2g). I have performed this calculation^ *.

TO il lu: utions for 3-jet and 4-jet production ic. ~-e rapidity interval [n[ < 1-5. The jets have been required to be well separated in the lego plot and to have

* The cross section of the six quark subprocess has been calculated both by a completely numerical program and by REDUCE. The matrix elements of the 4q2g subprocesses have been calculated only numerically.

- 105 -

reasonably large transverse momenta. The size of the 4-jet rate is non-negligible but it remains a reasonable radiative correction. With the cuts applied the 4-jet rate is larger at higher energy.

3 . PRODUCTION OF TWO PAIRS OF HEAVY QUARKS

The subprocesses of type (2d) and (2g) represent also the loading order

QCD processes for the production of two heavy quark pairs*^. Four heavy flavour production e.g. gives the background to the associated production of heavy

14) (ŒJJ ^ 3 0 - 1 5 0 GeV) standard Biggs boson with a pair of heavy quarks . In order to illustrate the magnitude of the background I summarized some cross section values in Table 1 . The result is negative, the direct QCD production of four heavy quarks has overwhelmingly 1 0 0 times) larger cross section than the associated production of two heavy quarks and a heavy standard Higgs boson which decays predominantly into the heaviest quark pair allowed by the kinematics..

References

1) UAl Collaboration, G. Arnison et al., Phys.Lett, 132B (1983) 214. 2 ) UAl Collaboration, G. Amison et al.. Phys.Lett. 132B (1983) 294. 3) UA2 Collaboration, P. Bagnaia et al., Z.Phys. C2Q (1983) 117. 4) UA2 Collaboration, P. Bagnaia et al., CERN-EP/84-12 (1984). 5) G. Wolf, talk given at the XIV International Symposium on Multiparticle

Dynamics, Granlibakken, Lake Tahoe, USA, DESY-83-096 (1983). 6) z. Kunszt and E. Pietarinen, 2.Phys. Ç2.(1979î 355 and Nucl.Phys. B164

(1980) 45. T. Gottschalk a n d D . Sivers, Phys.Rev. D2l (1980) 102.

7) F.A. Berends, R. Kleiss, P. De Causmaecker, R. Gastmanaf and T.T. Wu, Phys. Lett. 103B (1981) 124.

8) Z. Kunszt and E. Pietarinen, Phys.Lett. 132B (1983) 453. 9) G.C. Fax and S. Wolfram, Nucl.Phys. B168 (1980) 287. 10Í R. Odorico, Ref.Th.3744-CERN (1983).

11) F.E. Paige, preprint BNL-33952 (1983). 12) G. Cohen-Tannoudji et al., preprint SPh. T/70 (198').

B. Cambridge and C. Maxwell, preprint EL-83-095 (1983). F. Halzen and P. Hoyer, Phys.Lett. 130B (1983) 326.

13) Z. Kunszt, to be published.

14) J. Ellis and H. Kowalski, private comraurjication.

- 106 -

T a b l a 1 : C r o s s s e c t i o n v a l u e s f o r t t t t p r o d u c t i o n a n d t t H p r o d u c t i o n , w i t h m t = 3 5 GeV a n d = 1 2 0 G e V

/ s a ( t t t t ) a ( H t t ) ( T e V ) ( p b a r n ) ( p b a r n )

2 1 7 0 . 0 1 4

5 2 6 0 . 2 1

1 0 1 3 0 1

2 0 6 2 0 3 . 6

4 0 1 ^ 0 0 1 1

F i g u r e C a p t i o n s

F i g . 1 :

a 2 - j e t m o d e l a n d a p e r t u r b a t i v e QCD c a l c u l a t i o n .

p d i s t r i b u t i o n s g i v e n b y 3 - j e t a n d 4 - j e t f i n a l o u t

f e r e n t e n e r g i e s , a n d w i t h s u i t a b l e c u t - o f f t o m a t c h e x p e r i m e n t a l j e t

r e s o l u t i o n a n d a v o i d c o l l i n e a r a n d s o f t s i n g u l a r i t i e s , / s d e n o t e s t h e

c e n t r e o f m a s s e n e r g y o f t h e p r o t o n a n t i p r o t o n c o l l i s i o n s , n. i s t h e

p s e u d o r a p i d i t y

I5~ I - P H

n = 0 . 5 I n — I? I

T R ( i ) , E i s t h e t r a n s v e r s e e n e r g y E = 2 p j ^ ' , Û i s t h e d i s t a n c e i n

T R 2 T R . T R

t h e k e g o - p l o t A ^ = U^n,^,.} + <Ad>^_. > | , w h e r e Ad>^^ d e n o t e s t h e a z i -

n i u t h a l a n g l e d i f f e r e n c e b e t w e e n t h e t r a n s v e r s e m o m e n t a o f t h e j e t s i

a n d j .

- 107 -

: il ill teilt j -V.^. — H«l MC

* + to it's r _ i-„| MC • . V 2= 3-j«l ÛCD

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\ + \ v t ' \ +

\ ~*~ • \ \ 1

MV » 10 » w » I S K U p-1 lGcV/f.1

F i g . 1

F i g . 2

O: 8410026139 - 108 -

J E T S : W H A T WE C A N S T I L L L E A R N . . .

B . H u m p e r t ' I ns t i tu t d e Phys ique Nuc léa i re

U n i v e r s i t é de Lausanne CH-1000 L A U S A N N E

A b s t r a c t : / A shor t overv iew is g i v e n about ongo ing theore t ica l analyses concern ing l a r g e - and I o w - p t j e t ( j ) p r o d u c t i o n . A new class of ( 4 - p a r t o n ) processes , w i th two s h o r t - d i s t a n c e processes t a k i n g place s imul taneously , is i n t r o d u c e d , and cross-sect ion est imates a r e g i v e n f o r ; ( 4 j ) - , ( W * j j ) - , and ( W W ) - p r o d u c t i o n . T h e size of t h e ( 2 - p a r t o n ) 2 j - , . . , 6 j - cross sections (also w i t h W , Z ) is d e t e r m i n e d . T h e importance of coincidence measurements between l a r g s - and I o w - p t j e ts is s t r e s s e d .

T h e au thor t h a n k s t h e C E R N Theore t i ca l Physics Div is ion f o r its k ind h o s p i t a l i t y .

a n d

R. Odorico

Dipar t imento di Fisica deH ' U n i v e r s i t é d i Bologna

I . N . F . N . , Sezione di Bo'oona

J-40126 BOLOGNA

G e n e v a , A p r i l 2 7 , 1984

- 109 -

Jets resul t e i t h e r f rom ¡arge-p^ h a r d scattering or from a less u n d e r stood l o w - p t in teract ion process , In th is p a p e r we p r e s e n t ongoing d e v e l opments . We f i r s t g i v e deta i ls on the large-p^. j e t - j e t i n v a r i a n t mass d i s t r i b u t i o n . Al lowing f o r t h e simultaneous in te rac t ion of two p a r t o n p a i r s , we a r e led to a new class of processes c o n t r i b u t i n g to ( 4 j ) - , ( W * j j ) - a n d ( W W ) - p r o d u c t i o n . In t h e second p a r t , w e e v a l u a t e t h e i r i n t e g r a t e d c ross -sect ions , and we de te rmine the size of similar ( 2 - p a r t o n ) m u l t i - j e t c o n t r i b u t ions ( w i t h o u t / w i t h W , Z ) . F ina l ly , coincidence measurements be tween l a r g e - p ^ and low-p^ je ts can g i v e new ins ights into t h e l o w - p t dynamics .

L a r g e - p ^ j e t - j e t p roduct ion has in t h e r e c e n t pas t been s t u d i e d b y t h e pp col l ider exper iments UA2 [1 ] and U A l [ 2 ] , and a systematic ana lys is of t h e theoret ica l expecta t ions [3 ] was completed . In F i g . 1 we show der/dM ( f a t solid c u r v e ) and indicate t h e size of the re levant subprocesses (so l id c u r v e s wi th subprocess n u m b e r s ) . For calculat ion detai ls we r e f e r to Re f . [ 3 ] . A t smaller ( l a r g e r ) M values q g ( 7 ) ( q q ( l ) , q q ( 4 ) ) s c a t t e r i n g dominates whereas the g g ( S ) process is of neg l ig ib le in f luence . We have also l imited the r a p i d i t y region to l y I < 0 . 8 5 , as is at p resen t the case f o r the UA2 de tec tor , and show t h e enormous loss in ra te ( f a t dashed l i n e ) . How sensi t ive a re these resul ts if the Q C D paramete rs are c h a n g e d ? Us ing a v a r i e t y of scale d e p e n d e n t momentum d i s t r i b u t i o n s , we not ice a f a c t o r - 2 spread in the mass spect rum if parametr iza t ions wi th an excess ive ly ' h a r d ' g luon spect rum a r e ignored [ 3 ] . A t la rge M v a l u e s , the g luon ' q u a r k ) subprocesses reveal a c ross-sect ion spread of severa l o rders of m a g n i t u d e (of a fac tor 2 - 5 ) w h i c h , a t small M v a l u e s , is however much less. Since in t h e f o r m e r e n e r g y region t h e q u a r k subprocesses dominate, t h e c r o s s - s e c t ion spread in t h e tota l sum is modera te . V a r y i n g the scale pa ramete r w i th in 0 . 1 GéVÍAíO.1 GeV reveals at small ( l a r g e ) M values almost no (a fac tor - 3 ) cross-sect ion v a r i a t i o n , ma inly d u e to t h e s t r u c t u r e f u n c t i o n s . Similar fea tures a re o b s e r v e d in the s ing le - je t q^ d is t r ibu t ion [ 3 ] .

A l lowing for the possib i l i ty of two simultaneous s h o r t - d i s t a n c e processes [ 4 ] , we a re led to a new class of processes

which cc-r.tribute to ( 4 j ) - , ( W + j j ) - and ( W W ) - p r o d u c t i o n . T h e c ross - section reads

- H D -

V j TW.* da-- is t h e d i f fe ren t ia l p a r t o n c r o s s - s e c t i o n . n - R 2 = o , -40mb estimates the

ij el f lux of par tons in a h a d r o n , and V(xi,x3) is the t w o - p a r t o n momentum d i s t r i b u t i o n . For f u r t h e r detai ls we re fe r to R e f s . [ 4 ] .

T h e r e is l i t t le theoret ica l u n d e r s t a n d i n g of the s i n g l e - or m u l t i - p a r t o n momentum d i s t i b u t i o n s . T h e ear l ies t a t tempt dates back to 1971 [ 5 ] , and since t h e n - almost no progress I

T h e Kut i -Weisskopf model [51 assumes an i n f i n i t y of par tons in the nuc león , w h i c h , a p a r t f rom momentum conservat ion (-* C ( X ) , X = x 1

+ . . * x ^ ) , a re u n c o r r e l a t e d ; the conf inement ef fects on each const i tuen t t y p e a re descr ibed b y the 'p r im i t i ve ' s t r u c t u r e funct ions (-» f ( x j ) ) . In the small Xj region , th is form is wel l approx imated b y a p r o d u c t of the 'usua l ' s ingle p a r t i c l e s t r u c t u r e funct ions w h e r e b y t h e Q C D cor rec t ions a re also t a k e n into account .

We have determined the in f luence of the analogous ( 2 - p a r t o n ) ' b a c k g r o u n d ' processes b y us ing the Odor ico M o n t o - C a H o p r o g r a m [tí] f o r the mul t i - j e t e v e n t g e n e r a t i o n . T h e incoming par tons w i t h pr imord ia l t r a n s v e r s e momentum u n d e r g o a s ingle ' h a r d ' s c a t t e r i n g p rocess ; init ial and f ina l (so f t ) g luon radiat ion does occur accord ing to t h e A l t a r e l l i - P a r i s i ( l e a d i n g -log) sp l i t t ing p robab i l i t i es . T h e remain ing e n e r g y is d i s t r i b u t e d among the s p e c t a t o r - j e t hadrons according to a longi tud ina l phase -space model w i t h a

c u t - o f f and exper imenta l informat ion on t h e r e l a t i v e importance of the i n d i v i d u a l hadroná .

In F i g . 2 we show the i n t e g r a t e d cross-sect ions f o r 2 - , . . . , 6 - j e t p r o d u c t ion (sol id l i n e s ) . T h e t r a n s v e r s e momentum of all jets is l imited to q ^ > P ç u ^ - | 5 GeV. We have v a r i e d the Q C D paramete rs and found l i t t le cross-sect ion change . In the same f i g u r e we p r e s e n t t h e in f luence of the process: p p - ( 4 p a r t o n s ) — 4 - j e t s + X ( d a s h e d l i n e ) . As p c u t increases its c ross-sect ion fal ls f a s t e r than t h e analogous 2 - p a r t o n p rocess . In F i g s . 3 and 4 t h e in tegra ted cross-sect ions f o r W , Z * n j p roduc t ion ( n = 0 , . . , 4 ) a re shown (sol id l i n e s ) . T h e s t r o n g cross-sect ion r ise of t h e analogous 4 - p a r t o n processes (dashed l ines) is p a r t i a l l y d u e to the W , Z t h r e s h o l d onset and par t i a l l y follows f rom t h e simultaneous g luon sca t te r ing process . A b o v e Vs=2 T s V t h m e c h a n i s m dominates o v e r the analogous 2 - p a r t o n p r o cess . All these p r e d i c t i o n s , however , depend on t h e par ton f lux in t h e nucleón which implies a l a r g e ( b u t well d e f i n e d ) u n c e r t a i n t y . In F i g . 5 we compare the 2nd o r d e r S U 3 x U j . pred ic t ions invo lv ing only two ini t ia l s tate

- Ill -

. ¡2 I

d i s t r i b u t e d among t h e l a r g e - p t par ton ( x a ) and the spec ta to r - j e t p a r t o n

( X j = 1 - x z ) resu l t ing in the e x t e n d e d X j - d i s t r i b u t i o n ( in F i g . 6 ) .

In this shor t note we have in t roduced new ideas in the f ie ld of j e t - p h y

sics which awai t to be tested b y e x p e r i m e n t .

REFERENCES

[ 1] UA2 C o l l a b o r a t i o n , C E R N : M . B a n n e r et a l . , P h y s . L e t t .

U 8 B (T982) 203; P .Bagnaia et a l . , Z e i t s c h r . f . Phys ik C20

(1983) 117; P. Bagnaia e t a l . , " M e a s u r e m e n t of V e r y L a r g e

T r a n s v e r s e Momentum Jet Product ion at the C E R N pp Co l l ider" ,

C E R N - E P / 8 4 - 1 2 ( 1 9 8 4 ) .

par tons [ 7 ] , w i t h t h e analogous 4 - p a r t o n process . T h e s t rong d isc repancy resul ts f rom t h e la rge W , Z masses.

T h e product ion mechanism of t h e spec ta to r - j e ts is f a r f r o m being u n a n i mously c lear and severa l models f o r 'sof t ' hadron product ion have been p r o p o s e d . T h e recombinat ion model [8] assumes s e a - q y recombinat ion to fo rm a f ina l s ta te meson. In t h e D T U - m o d e l [ 9 ] , t u b e - l i k e co lo r -s ing le t systems a r s c rea ted consist ing of 3 a n d 3 colour charges which s t re tch t h e connect ing colour f l u x - l i n e and thus lead to hadron production. T h e L u n d model [10 ] is based on the space- t ime p i c t u r e of a ' Y o Y o ' , on the cjq c r e a t ion p r o b a b i l i t y , a n d en an Ansa tz f o r t h e q u a n t u m number d i s t r i b u t i o n on t h e s t re tched s t r i n g . Severa l o t h e r models ex is t [ 1 1 ] .

In o r d e r to f i n d more s t r i n g e n t d is t inct ion c r i t e r i a between these schemes, we s t ress the importance of coincidence measurements among the l a r g e - and l o w - P t j e t s ; a possib i l i ty which so f a r has been mostly i g n o r e d . With such purposes in mind we have c a r r i e d o u t a f i r s t

analysis [ 12 ] of t h e p rocess : X , ^ Í Í * * * 9 P P - Y J + J S

+ X a n d p r e s e n t in F i g . 6 the

spec ta to r - j e t momentum (X j ) d i s t r i b u t i o n f o r y^=0 and q t ^ 1 0 G e V . I n t e g r a t i o n o v e r all o t h e r kinematical var iab les has been c a r r i e d o u t . Using 2 - p a r t o n momentum d i s t r i b u t i o n s V ( x 2 , x : ) at the lower

v e r t e x (of t h e c lose -by g r a p h ) we admit t h a t p a r t of the e n e r g y is d i s t r i buted among the i n f i n i t y of par tons in t h e nucleón - t h e r e f o r e the rap id X j -decrease . In t h e L u n d m o d e l , i n s t e a d , all e n e r g y at t h e lower v e r t e x is

- 112 -

U A l C o l l a b o r a t i o n , C E R N : G . A r n i s o n e t a l . , P h y s . L e t t . 123B

(1983) 115; G . A r n i s o n et a l . , P h y s . L e t t . 132B C9B3) 214;

G . A r n i s o n et a l . , P h y s . L e t t . 132B (1983) 223 .

B . H u m p e r t / ' T w o - J e t Product ion in pp Col l is ions"( to a p p e a r ) ; P r e p r i n t , R e f . T H . 3 8 1 7 - C E R N 1 1 9 8 4 ) ( P h y s . L e t t , t o b e p u b l . ) .

B . H u m p e r t , P h y s . L e t t . 131 B(1983)461 ; N . P a v e r and D . T r e l e a n i ,

N u o v . C i m . 7 0 A ( 1 9 8 2 ) 2 7 5 ; i b i d . 7 3 A ( 1 9 8 3 ) 3 9 2 ; P r e p r i n t , I S A S - 6 0 / 8 3 / E . P . ,

T r i e s t e ( 1 9 8 3 ) .

Ear l ie r re ferences a r e :

P .Landshof f and J . Pol k ing h o m e , P h y s . R e v . D12 (1975 )3738 ; M .Jacob ,

R e f . T H . 3 5 1 5 - C E R N ( 1 9 8 3 ) ; G . G o e b e l et a l . , P h y s . R e v . D22( 1980) 2789;

F. Ta!<agi, Phys . R e v . L e t t . 4 3 ( 1979) 129G.

J . K u t i and V . F . W e i s s k o p f , Phys . R e v . D 4 0 9 7 1 1 3 4 1 8 ; H . R . G e r h o l d ,

N u o v . C i m . 5 9 A ( 1 9 8 0 ) 3 7 3 ; E . T a k a s u g i et a l . , P h y s . R e v . D 2 0 ( 1 9 7 9 ) 2 1 1 .

R . Q d o r i c o , N u c l . Phys . 8 2 2 8 ( 1 9 8 3 ) 3 0 1 , Ref . T H . 3 7 6 0 - C E R N , R e f . T H .

3 7 6 1 - C E R N ( 1 9 8 3 ) ; B . H u m p e r t and R . O d o r i c o , in p r e p a r a t i o n .

B . H u m p e r t , Phys . L e t t . 135B( 1 9 8 4 ) 1 7 9 .

K . P . D a s and R . C . H w a , P h y s . L e t t . 6 8 B ( 1 9 7 7 ) 4 5 9 .

A . C a p e l l a . U . S u k h a t m e and J . T r a n T h a n h V a n , Z . P h y s . 3 ( 1 9 8 0 ) 3 2 9 ;

P . A u r e n c h e , F . W . B o p p and J . R a n f t , Annecy P r e p r i n t L A P P - T H - 8 3

( Z . P h y s . , t o be p u b l . ) .

B .Andersson et a l . , P h y s . R e p . 9 7 ( 1 9 8 3 ) 3 1 ; H . - U . Bengtsson and G . l n g e l m a n , P r e p r i n t Ref . T H . 3 8 2 0 - C E R N ( 1 9 8 4 ) .

W. K i t t e l , Nijmegen U n i v . R e p o r t , HEW 203 ( 1 9 8 1 ) ; B . H u m p e r t , P r o c .

4 t h Warsaw Symp. on Elem. Part ic le Phys ics , Kaz imierz , 1981

( e d s . Z . A j d u k and K. Do roba,Warsaw U n i v . P ress , 1981 ) .

B . H u m p e r t and G . Inge lman, I n t . C o n f . ' H a d r o n S t r u c t u r e ' 83 ' ,

Smolenice ,Czechoslovak ia ,1983; a n d in p r e p a r a t i o n .

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0: 8410026147

ABSTRACT

f Various aspects of three XSR experiments on deep inelastic phenomena / are discussed. New data on inclusive production at high transverse / momentum of protons give first experimental evidence for hard d i quark, scattering. Measurements of deep inelastic production of single kaons and jets and rather detailed analyses of jet structures and of correlations between jets are presented. The experimental findings are consistently explained in terras of hard scattering of quarks and gluons. Finally, it is shown that a precise measurement of central particle production in these hard scattering events could reveal the prevailing frasmentation

. mechanism of systems of coloured partons.

RECENT RESULTS PROM HIGH TRANSVERSE MOMENTUM PROCESSES AT THE ISR

W.M. Geist

CERN, Genev«, Switzerland

- 1 1 4 -

- I I S -

1. INTRODUCTION! Experiments dea l ing with high t r a n s v e r s e momentum phenomena in

hadron-hadron c o l l i s i o n s elm p r imar i ly a t an unders tanding of par too s c a t t e r i n g dynamics. The s c a t t e r e d colored pa r tons fragment In to two j e t s a t l a r g e angles r e l a t i v e t o t he beam d i r e c t i o n . The n o n - i n t e r a c t i n g colored c o n s t i t u e n t s fragment in to two l o n g i t u d i n a l ( s p e c t a t o r ) j e t s . Hence the parton s c a t t e r i n g mecïianism can be i n f e r r e d from d e t a i l e d s t u d i e s of a l l j e t s .

The r a r e 4 - j e t events a re separa ted from the more numerous sof t hadronic i n t e r a c t i o n s by; (a) e i t h e r t r i g g e r i n g on a U r g e t r ansve r so energy E^ de tec ted in c a l o r i m e t e r s (E^ t r i g g e r ) , or (b) bj t r i g g e r i n g on those sideways j e t s in which one s i n g l e p a r t i c l e c a r r i e s a o s t of the j e t energy ( s i n g l e p a r t i c l e t r i g g e r ) . H i s t o r i c a l l y s i n g l e p a r t i c l e t r i g g e r experiments a t t he ISR gave f i r s t evidence for s t rong i n t e r a c t i o n s among p a r t o n s . New r e s u l t s from an experiment of t h i s type are given in s e c t . 2 . Recent da ta f ron two t r i g g e r experiments a r e presen ted in s e c t . 3 . Measurements of c e n t r a l p a r t i c l e product ion in deep i n e l a s t i c events a re d i scussed in s e c t . 4 .

2 . INCLUSIVE SINGLE PARTICLE PRODUCTION AT HIGH P T

The measurements p resen ted in t h i s s ec t ion come from the ABCDHW Col labora t ion working a t the S p l i t F i e ld Hagnet (SFM) De tec to r . The d a t a were taken with a s i n g l e p a r t i c l e t r i g g e r a t a po la r angle 6 away from 90° .

I t i s known s ince q u i t e some time t h a t events wi th a s i n g l e p a r t i c l e t r i g g e r of high t r a n s v e r s e momentum p^ Bhow the expected 4 - j e t s t r u c t u r e [ 1 ] .

A somewhat d i f f e r e n t r e p r e s e n t a t i o n of the r e s u l t s from ref, [ l e i i s given in f i g . 1 , where tha r a t i o F of the t r a n s v e r s e momentum flow in events with P T > 4 GeV/c t o the flow observed in normal i n e l a s t i c events i s d i sp l ayed as funct ion of c m . s r a p i d i t y y and azimuthal angle (<p ( t r i g ) -* 0 ) . The t r i g g e r p a r t i c l e i s not Included. In a d d i t i o n t o the l o n g i t u d i n a l s p e c t a t o r j e t s , a j e t of p a r t i c l e s along the t r i g g e r p a r t i c l e i s observed ( t r i g g e r j e t ) as we l l as a l a r g e r e l a t i v e momentum flow due t o the "away j e t " a t <p - 160* ± 30*. No t r i g g e r requirement i s imposed on the away j e t .

116 -

More than 75% of the t r i g g e r j e t energy [ 2 ] , however, Ifl c a r r i e d by the

t r i g g e r p a r t i c l e s . One expects the re fo re t h a t t he t r i g g e r j e t i s slimmer

than the away j e t s as observed in f i g . 1. A mare q u a n t i t a t i v e support of

t h i s reasoning comes from e*e da ta in f i g . 2 [ 3 ] . The i n c l u s i v e y i e l d of

charged j e t p a r t i c l e s i s shown as funct ion of the fragmentat ion v a r i a b l e z

in a d d i t i o n to the d i s t r i b u t i o n s for charged p a r t i c l e s produced in those

j e t s where the f a s t e s t charged p a r t i c l e ( t r i g g e r ) has z ( t r i g ) > 0.5 or

z ( t r i g ) > 0 . 7 . Also given are d i s t r i b u t i o n s for p a r t i c l e s In t r i g g e r j e t s

fronjpp ..111.1... with p T , « OeV/c and P j > 6 GeV/c W , I . . .

<z(t?is)> * 0.72 or 0.78 [ 2 a ] . Both s e t s of da t a e x h i b i t c o n s i s t e n t

t r e n d s , i . e . the p a r t i c l e y i e l d decreases with inc reas ing z ( t r i g ) . From

neu t r ino i n t e r a c t i o n s one knows [5] t h a t ~ 80% of the pions produced a t

z > 0.7 conta in the fragmenting quark. This s u g g o . s t ha t in pro ton-pro ton

c o l l i s i o n s high - P T T + ( u d ) and K + (us) mesons a r e mainly produced as l ead ing

fragments of s c a t t e r e d u-qu&rks wheeoas * <ud> s e r o n s cone mainly From d-quarks . A recen t d e t a i l e d study [6] suppor ts t he se simple i d e a s . K

t r i g g e r s oa the o the r hand, which do not share any valence quarks wi th t he

p r o t o n s , are shown to be predominantly l ead ing fragments cf f l a v o u r l e s s ,

sof t par tons such as gluons [ 7 ] . A t e s t of t h i s simple p i c t u r e i s

provided by the r e l a t i v e c ro s s sec t ions for i n c l u s i v e K~ and *~ product ion

shown in f i g . 3 as funct ion of i j s ? • PT'i/s [ 8 ] . The fac t t h a t both K*

and • * a re mainly produced by s c a t t e r i n g and subsequent fragmentat ion of

u-quarfcs t r a n s l a t e s in to a cons tan t r a t i o of cease flections. The

decreas ing r a t i o K / T in f i g . 3 is c o n s i s t e n t with K mesons being

produced by gluons which have a so f t e r s t r u c t u r e function [91 than the

d-quarks fragmenting i n t o % . QCD p r e d i c t i o n s in f i g - 3 a l so under l ine the

noed for a l a r g e gluon c o n t r i b u t i o n to K product ion [81 . Whereas one has

reached a cons i s t en t p i c t u r e of meson product ion a t high p^ the s i t u a t i o n

i s l e s s c l ea r in case of ( an t i )ba ryon product ion . In f i g . 4 r ecen t

measurements [10] of the i n c l u s i v e r a t i o s p/h* and p/h are d i sp layed as

funct ions of the polar angle 6 a t > 3 .8 GeWc. I f both ( a n t U p r o t o n s

and mesons of the same charge are produced by fragmentat ion of the same

type of s c a t t e r e d pa r tons one expects i n c l u s i v e r a t i o s independent of

kinematic v a r i a b l e s . This expec ta t ion is borne out exper imenta l ly for p

product ion on ly . The r a t i o p / h + does depend on (not shown, [10])

and on 0 ( f ig- 4 ) . This observat ion can be q u a l i t a t i v e l y expla ined by

hard s c a t t e r i n g of d iquarks which should f requen t ly frngmeot i n t o baryons .

1 1 7 -

Since diquarks are extended objects a form factor F(Q a) in the hard process tendB to suppress the cross section ab fixed as function of decreasing polar angle 0, i.e. increasing momentum transfer Q. Further detailed correlation measurements will be dono in order to verify this hypothesis. For a comparable kinematic configuration the EMC Collaboration has measured relative (anti)proton yields [111 in parton jets from deep inelastic rauon interactions. A comparison of the data of ref. [11] with those of fig. 4 (0 ~ SO") is given In fig. 5, good agreement is found.

3. INCLUSIVE JET PRODUCTION AMD JET PROPERTIES

At the ISR two experiments made use of triggers to select jet-like events. The transverse energy was measured in a solid angle ÛQ = üy.üfp ~ 2 * 2*. The CHOR Collaboration triggers on large electromagnetic energy E£ which is mainly due to the "neutral" jet component U . c . w°) [12]. The relative event yields in pp and pp Interactions are shown in fig. 6 as function of E£ at /s = S2.4 GeV/c. The value of the ratio is close to 1 and does not strongly depend on the "jettiness" of the events [13). The AFS Collaboration uses a large total energy E T as signature for jet production. They determine the invariant jet cross sections at v*s = 63 and 45 GeV from an analysis of event shapes measured in one quadrant of the full calorimeter. The invariant cross section [141 is displayed in fig. 7 as function of x T = Zp^/Vs. It was multiplied by P^'^ assuming that E * dtf/dp « p^° * f{x^, 6 ) . The UAl data [IS] are in reasonable agreement with the AFS measurements and justify thus a posteriori the assumed factorizable form. A compilation of measurements of the power n for inclusive production of jets» pions [16] and protons 117} is given ia fig. 8. Pointlike scattering corresponds to n = 4. fnj

dependence of the cross section on a length or momentum scale tends to raise n. In case of jet production there is a dependence on the intrinsic transverse momentum of partons and on Q S due to structure functions [91 and Í Q 2 ) ; for pion production one expects in addition t>3 dependent fragmentation functions and, finally, for proton production a further q z

dependence is caused by the diquark form factor.

- 118 -

For a mora complete understanding of hard process** a detailed study of jet properties was performed. It should be noted here that the jet energy E ^ t is roughly given by B j e t £ 0.5 * R^¡ B T - e J + 7 CeV for the CMOR data [22]. Both experiments state that only for & T 2 30 GeV more than 50% of all events are jet-like [18,19,22]. First, the jet axes were determined from charged and neutral particles in both experiments [12,18). The AFS Collaboration thon measured for charged particles the average transverse momentum q relative to the jet axis as function of z. The data

T are shown in fig. 9(a) for & T > 33 GeV [IS,19]. Good agreement is found with a Monte-Carlo calculation using <9.T> ~ O.SS CeV/c and including detector simulation, similar results were obtained by the UAl Collaboration [21]. Measurements of <lj^l> = <q T> by the CHOR Collaboration are given as function of z and E ^ t in fig. 9(b) 122]. In fig. 9(b) <IJ TI> is significantly smaller than in fig. 9(a) but is in rough agreement with e +e ' results at Ys ~ 2 * E, [23]. The large difference between the two sets jet of ISR data can hardly be attributed to instrumental effects or to the different method of determining the jet axes [12,18]. It may be a consequence of the fact that ~ 70% of B j e ^ recorded in the CHOR experiment is carried by the neutral jet component [22] triggered upon. This large percentage happens to be similar to <z(trig)> in the single particle experiment of sect. 2 such that in both cases only ~ 30% of E ^ e t is available to produce additional charged particles. For charged trigger jet secondaries fig. 9(c) shows = <q_> versus p <z = p./E, . >, the

perp x il il jet momentum component parallel to the jet axis. The data were obtained by the ABCDHV Collaboration with a single particle trigger [4]. Agreement with the CHOR data is found.

The longitudinal jet structure was investigated by the AFS Group. For charged jet particles tho distribution in x =2 * p/W was determined.

P

The invariant two-jet energy W was calculated from all particles associated to the jets. The resulting distribution is at variance with e +e~ results [23] (not shown [241). A refined determination of W based upon Monte-Carlo corrections to truncated jets gives rise to the nodified distribution in fig. 10 [18,19]. It is now consistent with UAl data [21] and also with e +e data [23] except for an excess at x < 0.10 (sect. 4 ) .

- 119 -

One nay a n t i c i p a t e d i s s i m i l a r j e t s due to t h e i r d i f f e r e n t par ton composition in e + e " i n t e r a c t i o n s < u , c , d , s , b ) and in pro ton-proton c o l l i s i o n s (probably u, d, g luons ) . Experimental evidence for the expected par ton composition of j e t e from pp i n t e r a c t i o n s , i . e . for valence quarks and g luons , was a l ready found in s e c t . 2 . Charge r a t i o s in j e t s which are not a f fec ted by the presence of a l ead ing ( t r i g g e r ) p a r t i c l e support t h i s p i c t u r e as demonstrated below. F ig . 11 shows the r a t i o s of p o s i t i v e to nega t ive p a r t i c l e s as funct ion of z from j e t s obta ined by the AFS (181 and CHOR [22] C o l l a b o r a t i o n s . The ABCDtfW charge r a t i o s as funct ion of x g - z * < z ( t r i g ) > obta ined from away j e t s r e c o i l i n g a g a i n s t a s i n g l e charged t r i g g e r p a r t i c l e a re given as wel l [ 6 , 7 ] . J e t p a r t i c l e s with z > 0.7 are p o t e n t i a l cand ida tes for s i n g l e p a r t i c l e t r i g g e r s ( s e c t . 2 ) , bence i t i s j u s t i f i e d to include in f i g . 11 the measured i n c l u s i v e r a t i o of p o s i t i v e and nega t ive hadrons, i . e . the r a t i o [o(w +) + a{K*) + a ( p ) ] / [ ö U " > + t»(K*> + <x(p)l [8 ,10 ,16] as funct ion of z (where z = z ( t r i g ) = f ( p T ) [ 2 a ] ) . Al l s e t s of da ta a re c o n s i s t e n t . A r a t i o bigger than 1 and r i s i n g with z (x^) supports the idea of a l a r g e c o n t r i b u t i o n of u quarks as expected from the proton composit ion.

Making use of the asymmetric t r i g g e r conf igura t ion <0 ( t r i g ) ~ 50") the ABCDHW Col labora t ion has obta ined evidence for j e t s from n e u t r a l pa r tons in the following way. Consider f i r s t quark-quark s c a t t e r i n g for which the momenta of the s c a t t e r e d quarks a r e equal and oppos i te on the average in the pp r e s t system. In t h i s case the t r i g g e r p a r t i c l e and the away j e t should be c o l l i n e a r (back- to -back) . This i s supported by f i g . 12 [6 ] where a l a r g e charge r a t i o for the away j e t s (from valence quarks) i s found in the back-to-back conf igura t ion for * + and K+ t r i g g e r s . Note t h a t the K*" and « + t r i g g e r s come dominantly from u-quarfc fragmentat ion ( s e c t . 2 ) . I f , however, (hard) u-quarks y i e l d i n g *•* and K+ t r i g g e r s s c a t t e r off ( s o f t ) g luons , the fragments of the gluons should f r equen t ly popula te the same l o n g i t u d i n a l hemisphere as the t r i g g e r p a r t i c l e (back- to -an t iback) due to a boost from the quark-gluon c m . s to the pro ton-proton c .m.s . This expec ta t ion i s supported by the small charge r a t i o [101 for t h i s conf igura t ion in f i g . 12. For K t r i g g e r s , however, t he charge r a t i o in the b a c k - t o - an t iback conf igura t ion i s much l a r g e r than for * + and R + t r i g g e r s ( f i g . 12 ) . This i s expected i f gluons y i e l d the K t r i g g e r s ( s e c t . 2) such t h a t the away j e t s a re dominantly due to valence quark j e t s .

- 1 2 0 -

4. CENTRAL PARTICLE PRODUCT10W

The transverse energy flow in jeb events obtained by the APS Collaboration (IS,19] at Vs = 63 GeV is shown in fig. 13 for lyl < 1 as function of the azimuthal angle Atp relative to one jet axis; an estimate of the flow in normal inelastic events (minimum lúas) is included. In addition to the clear jet structures at ~ 0° and 180* one notices an increase of a factor R ~ 3.0 of the flow at nip - 90* in jet events relative to inelastic events. Similar results were obtained by the UA2 Collaboration (253. In fig. 14 the measured ratio R' of particle densities in events triggered by a single particle with p y > 4 and 9 (trig) ~ 5C* 1eV/c to normal inelastic events is given as function of y for an> = 90* ± 20° {26]. For lyl < 1 the yield in high P t events is again larger (by a factor R' - 2). The observed effects may be caused by a superposition of two jet-jet systems with particle densities p. (2B. )

J jet from the system of sideways jets and <Vs' = Ys - 2E^ e^) from the spectator jets. Approximating p, (2E. ,) by -p (y ~ o) from e*e~ collisions at J jet - ay W = 2 E j e t {27] and p g (v*s') by -gç (y ~ o) from non-diffractive pp collisions at Ys\ one finds R* (E. > = (p, (2E. t ) + p Wsl))/p (Vs) - 2 - 2.S, jet j Jet s where p (/s) is taken from inelastic pp collisions . The ratio R' should be close to the recio R of energy flows, hence the data in fig. 3 and 4 are roughly consistent with a superposition of (at least) two fragmenting jet-jet systems.

Possible superpositions of two or more jet-jet systems are being studied in more detail by the ABCDHV Collaboration [28]. The idea is the following: the four coloured partons or parton systems emerging from a hard interaction may fragment e.g. either independently or the fragmentation may occur along strings connecting the coloured parton (system)s. In the latter case one expects a rather large particle density at medium transverse momentum relative to both neighbouring jet axes due to a Lorentz boost from the string c.m.s. to the proton-proton c.m.s <see sketch).

(*) p (non-diffr.) - 1-25 p (inelastic) at y - 0.

1 2 1

t r igger , y=0 ,7

away j e t

t he secondary p a r t i c l e d e n s i t y tp = 0 ° ± 2 0 * ( « ( t r l g ) = o*} and p^(sec) > 1 GeV/c was c a l c u l a t e d for the s t r i n g conf igura t ion given in the diagram which should occur mainly for quark-quark small angle s c a t t e r i n g [ 2 9 ] . The c a l c u l a t e d d e n s i t y was normalized to the dens i ty p r e d i c t e d for independent fragmentat ion and the r a t i o r i s shown in f i g . 15(~) as funct ion of y . Fragmentation was genera ted in t he r e s p e c t i v e r e s t system according to measured e + e d i s t r i b u t i o n s . In f i g . 15(a) one f inds indeed a l a r g e r e l a t i v a y i e l d from the s t r i n g p i c t u r e for - 3 < y < 0 . 0 and P T ( s e c ) > 1 GeVYc, i . e . ou t s ide the cores ' of t he t r i g g e r and the s p e c t a t o r j e t s . The experimental r a p i d i t y d i s t r i b u t i o n in f i g . 15(b) for the cu t s defined above i n d i c a t e s t ha t the p r e d i c t e d e f fec t i s measurable with s u f f i c i e n t p r e c i s i o n . This ana lys i s i s in p r o g r e s s . I t should be poin ted out , however, t h a t more than one s t r i n g conf igura t ion [291 c o n t r i b u t e s gene ra l ly t o a given experimental con f igu ra t i on .

5. CONCLUSIONS

Experimental evidence i s found for a s u b s t a n t i a l con t r i bu t ion of bard diquark s c a t t e r i n g t o bigh P t proton produc t ion . Data on i n c l u s i v e product ion at high p^ of mesons aad of j e t s , on j e t s t r u c t u r e s end on c o r r e l a t i o n s between j e t s a re c o n s i s t e n t l y desc r ibed by quark and gluon s c a t t e r i n g and f ragmenta t ion . A d e t a i l e d study of p a r t i c l e product ion in a k inemat ica l reg ion where j e t s merge haß been s t a r t e d . I t should c o n t r i b u t e to a b e t t e r understanding of f ragmentat ion mechanisms.

- 122 -

Acknowladita wants

I an g r a t e f u l t o the o rgan ize rs for i n v i t i n g « to t h i s vs ry i n s p i r i n g

meet ing, thanks t o fly co l l eagues Marking a t the ISK for d i scuss ions and,

e s p e c i a l l y , t o T. Akesson, T. Cox, H.G. F i s c h e r , ch. von Gagera and

I . Lohse for supplying ne with unpublished d a t a .

REFERENCES

(11 (a) K. Del ia Negra e t a l . , Nucl. Phys. B127 (1977) 1;

(b) H.G. Albrow e t a l . , Nucl. Phys. B14S <197S) 305;

(c) A. Breakstone e t a l . , CSBrt/KP 83-18?, t o be publ ished in Z e i t s c h r . für Phys. c .

[2) H.C. F i s c h e r , Proc . of the EPS Conference, Lisbon (1981) 897; C D . Buchanan, Proc. XVIIth Rencontre de Horiond (1982) v o l . I I , 139; J . L . Alonso e t a l . , z e i t s c h r . für Phys. C6 (1980) 21.

[3] G. Hanson e t a l . , Phys. Rev. D26 (1982) 991 .

(41 A. Breakstone e t a l . , CERN/EP 83-186, to be publ ished in Z e i t s c h r . für Phys. C.

[SI P. Alleu e t a l . , Nucl. Phys. 8214 (1983) 369.

(61 A. Breakstone e t a l . , CERN/EP 84-53, submitted t o Z e i t s c h r . für Phys. C.

[7) A. Breakstone e t a l . , Gluon tagging in hard pro ton-proton i n t e r a c t i o n s a t t he ISR, to be publ i shed .

[81 A. Breakstone e t a l . , phys. L e t t 1350 (1984) 510.

(91 H. Abranowicz e t a l . , Z e i t s c h r . für Phys. C12 (1982) 289;

F. Bergsma e t si., Phys. L e t t . 123B (1983) 269.

(10) A. Breakstone e t a l . , CERN/EP 81-2 , submitted to Phys. Rev. L e t t e r s .

(11) J . J . Aubert e t a l . , Phys. L e t t . 135B (1984) 225.

[121 A.L.S. AngeliB e t a l . , Phys. L e t t . 126B (1983) 132.

[13] CMOR Col l abora t ion , Ch. von Cagern, p r i u . conuiunlcatlon.

»

REFERENCES (Cont'd)

[14] I. Akesson et al., Phys. Lett. 123B (1933) 133.

[IS] H. Banner et al., Fhys. Lett. 118B (1982) 202.

[16] A. Breakstone et al., Phys. Lett. 13SB (1984) 505.

[17] ABCOHW Collaboration, T. Lohse, prlv. communication.

[18] T. Akesson, CERN/EP 83-130 (1983).

[19] T. Akesson et al., CERH/EP 84-56 (1984).

[20] t. Akesson et al., Phys Lett. 128B (198-1) 354.

[211 G. Arnison et al., Phys. Lett. 132B (1983> 223.

(22] A.L.S. Angelis et al., CERN/EP 84-46 and T. Coz, priv. comunlcation.

[23] H. Althoff et al., DESY 83-130 (1983).

[24] X. Akesson et al.. Contribution to the International Europhysics

Conference on High Energy Physics, Brighton, England, July 1983.

[25] P. Bagnaia et al., CERN/EP 83-94 (1983).

[26] ABCHW Collaboration, unpublished.

[271 P. Soding, Proceedings of the International Europhysics

Conference on High Energy Physics, Brighton, England, July 1983.

[28] ABCDHW Collaboration, to be published.

[29] e.g. H.U. Bengtsson and C. Ingelman, CERN/TIt 3820 (1984).

- 123 -

1 2 4

FIGURE CAPTIOUS

Fig- 1 Transverse momentum flow in events witti a trigger particle wltb Pj > 4 GeV/c produced at 6 - 50" relative to that in normal inelastic events.

Fig. 2 Inclusive ^-distribution of charged jet particles obtained at Vs = 6.B Gov by Hkl. Also given are z~distributions for charged particles In trigger jets from a SFM experiment using a single particle trigger at = 62 GeV.

+• f

Fig. 3 Relative cross sections for K" and »~ production versus s r ; also given are QCO predictions with and without gluon contributions.

Fig. 4 Relative proton and antiproton yields versus O at «'s = 62 GeV.

Fig. 5 -Relative proton and antiproton yields from SMC compared to SFH data obtained at P T i 4 GeV/c and 6 - 50* [101.

Fig. 6 Relative event yields versus E^ from pp and pp collisions.

UAl experiments.

of Inclusive cross sections {« p_ * f (x_,©)> for jets, plons \ T T

and protons.

Fig. 9 Measurements of average transverse momenta relative to jet u e s : (a) data from the .'-fS Collaboration and a Monte-Carlo simulation; (b) data from the CHOR Collaboration; (c) trigger jet data obtained by the ABCDHW collaboration.

Fig- 10 Inclusive distribution versus x p = 2p/W from jets obtained by the AFS Collaboration.

Fig. 11 Charge ratio (4-/-) in jets front the AFS and CHOR Collaborations, the charge ratio in jets recoiling against a single charged high P t particle and the ratio of inclusive cross section for positive and negative hadrons from the ABCDHW Collaboration are also shown.

Fig- 12 Charge ratio (+/-) from away jets in the back-to-back or back-to-antiback configuration for * + / K h and K~ triggers

Fig. 13 Transverse energy distribution as function of the azimuthal angle tip relative to one jet axis (AFS Collaboration, •s = 63 GeV).

Fig. 14 Ratio of parcele densities in high p T events (p^ > 4 GeV/c)

and normal inelastic events for <p = 90" ± ¿Q* as function of rapidity (ABCDHW Collaboration).

Fig. 15 (a) Ratio r of predicted particle densities from the string mod?l and from the independent fragmentation model as function of rapidity.

(b) Measured rapidity distribution for particles produced with P T (sec) > 1 GeV/c and with 9 = 0 ¿ 2 0 A in events with a single particle trigger with P R > 4 GeV/c, (p - 0* and 6 ~ 50" (ABCDHW Collaboration).

- 126 -

Fig. 2

- 127 -

- 128 -

i fi. iSCtV *fS

Fig. 6 Fig. 7

- t t C D n* - a c D i r iSFM n* rSFM i r 7 [COR J I °

. ABC n " AFS j e t s I SFM protons, prelim.

0.1 0.2 0.3

F1g. 8

- 129 -

1.0 i

0.5 "S t

<PT > IGeV/d V/s=62GeVl • 4.7 J

= 3.2 j./s=44G«V|

(CeV/c) Fig. 9

- 130

AFS ÎASSO

1/N„ , iti/ái, K.= 2¡»/W <W>= IS GtV 1,1.1 6S*-«Qj,,-e11S-0I«Pr<1S QeV/[

1/20, dJdx, V P ' * " *

/ s * JO GrV

0 0.1 0.Î 0.3 0.4 0.5 0.Í 0.7

Z.X E

Fig. 10 Fig. 11

2

SFM, p r e l .

/ s = 6 2 G e V

1 1

-

. t T

i • > o

\ i i * T

• K" trigger o K V n" [rigger \ back-to

1

antiback

J I i

* KVn'trigger b a c k - to - b a c k

0 2 0.4 0 6 O.B

Fig. 12

- 1 3 1

Fig. 13

?rM, prelim. <T = 6 2 G e V

• P , > 4 G e V / r .

- 4 - 3 - 2 - 1 0 1 2 3 4

Ï

Fig. 14

SFM : preliminary, ß~= 62CeV

trigger : p T » 4 G e V A , ys0.7, ipso"

secondaries: P t > I G e V / c . i f = n B i 2 0 g

Fig. 15

- 132 - , s , * 1 0 0 2 * 1 5 5

Transverse Momentum Distribute . of Jeta and Weak Bosons.

R, K. Ellis

Fermi National Accelerator Laboratory, Batavia, IL. 60510

The theoretical description of processes leading to events at large transverse momentum is reviewed. Numerical estimates are given for jet cross-sectioi.s and for W and Z production cross-sections. The influence which uncertainties in the input parameters have on the theoretical Dredictions is also discussed. ^

1 . Jet Cross-Sections The observation of clearly identified Jets at the CERN Spí collider 1* a^

opens a new era in the study of hadron structure. For the first time using hadronio probes we have irrefutable evidence for the parton substructure of the proton. The observed constituents scatter as the quarks and gluons of QCD should. Of course,In the interactions of objects as complicated as protons there are uncertainties, both theoretical and experimental, some of which will be described below. But before entering into these details it is important to remember that the gross features of the data are clearly in agreement with QCD.

The jet cross-section observed at the collider is four or more orders of magnitude bigger than the large p T cross-section at the ISR. Despite this big change,the predictions'^ of the QCD improved parton model describe the data well, both in 3hape and in normalisation. This agreement with data requires the inclusion of a scale breaking gluon distribution. In addition to the p T

spectrum, the angular distribution of the observed Jets la consistent with the exchange of a single massless vector gluon in the t channel K Apart from the scale breaking logarithms of QCD, the constituents cf the proton appear to behave as point-like particles.

The cross-section for jet production is calculate ' using the parton model formula.

F ä c h -I n f o r r n a ä o n s -z e n t r u m

Energie • Physik • Mathematik • GmbH

INPUT SHEET FOR SUBJECT ANALYSIS

(ArtMitsbtattfür inhaltliche ErschHe6ung)

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Sachtitel und Starrtert: Zeltschrift Vol/Nr.: Reportnummar:

(GeslmtSahmo) D l°™saloriseh bal: Rez. Expl.; PB-BilHiarn/Proceed.; Loading Abstracta)

EDS D E Q A T Q C H Q 0 0 • X E f J

COAL Q BIOMASS • ASSET Q

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Title in English (200): (engl. Titel) •

• Title in French (240) (.rant. Titel) • Title Augmentation In Engl. (620) (TitelErgänzung in engl.) n Title Augmentation in German (623) (Titeiergan. ung in dtsch.) • Tille Augmentation In French (623) -1—¡ (Titelerganzung in franz.) I I

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¡ T " 4 1 . 1 ° , %M U *>\ ira j r Desc

/Ih-lO-Y^j- I Bale: Descriptive Cataloguer-^ -

COAL, BIOMASS. ASSET onfy together with E08. ENERGIE, COAL, BIOMASS, ASSET must have EDB subject categories. Only non-nuclear energy in EDB ATVCH/DD/XE.

DE = Fédérai Republic of Germany AT = Austria CH = Switzerland DD = German Democratic Republic XE = Commission at the European Communities (CEC) XC = European Organization for Nuclear Research (CERN)

Links Descriptors (800) Data Base M/OJD

J e T MOOf.L A I

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e £ V P l w « . / I f b - inn (')

Compiled Data D O Evaluated Data D 0 Experimental Data 0 O Statistical Data D O Theoretical Data D O

- 1 3 3 -

where the sum on I,j runs over different types of partons. The parton cross-sections are calculable in perturbation tlieory î.nd in lowest order are given by

' d 3 r -VP)' (2)

where M is the invariant natrix element. The contribution of the various sub-processes to the total cross-section is dependent on the size of the matrix element and the value» of the distribution for the incoming partons. The influence of the former factor can be judged from Table 1 where the analytic forras of the matrix elements and their numerical values at £0° in the parton parton centre of mass are given. On the basis of the parton cross-sections alone it is clear that processes involving initial state glucns are favoured.

TARTON PKOCKSS l « l a

qq •> qq q q ' * q q '

qq -> qq

qq -> q ' q '

qq -*• qq

qq •* sr.

9 ( t a + u 1 5 " 27 st

* t'a+u* 9 s 2

(«liïïî + u ' ) 8 iL 9 t2 s ï ~ 2 7 St 3?. _ 8 27 ut " 3 s*

1 uf + tf; _ 3 u 2 + t 2

6 ut 6 s 2

i % u 2 * s 2

1 Ü 2 +S 2

9 us t 2

9 ( 3 HÍ - — —)

2,22

3.26

0.22

2.59

1.04

O . l i ,

J L -

Table 1. Parton matrix elements [averaged (summed) over initial (final) colours and spins]. F M is the value of |MJ Z In the parton parton centre of mass at 90°, ( 3 - -t/2 - -u/2).

Clean jets are observed at /S = 5^0 GeV for values of the transverse energy between 20 and 150 GeV. The parameter x T there Tore ranges between

( 3 )

- 1 3 4 -

The variable x T provides a good estimate of the value of x at which the parton distributions are probed. At lower values of x T even the softer parton distributions such as gluona or antiquar-ks are important. Flg.1,taken from ref.<5), shows the contribution of ':he various subprocesses to the total Jet produotion cross-seotion. Below E T of 80 GeV the dominant processes are gluon initiated. Above this value of E T the harder valence quark distribution makes the quark-quark scattering diagrams dominate. Low x T jets thus provide an ideal place to study gluon jets.

Ignorance of the gluon distribution function, which is poorly determined from deep-inelastic scattering, does not lead to a large uncertainty in the jet cross-section, because of a correlation between the shape of the measured gluon distribution and the value of A. This is illustrated in Fig.2 where two phenoraenalagically acceptable gluon distribution functions taken from ref.(6) are shown at Q 2 = iJGeV2 and Q 2 = 2000GeV 2. The narrower gluon distribution function (denoted DOt) has A =.2 GeV, whereas the broader gluon distribution (D02) has A => .4 GeV. Despite the large differences at law Q 2,at higher values (e.g. Q 2 = 2000GeV 2, the approximate scale relevant for high p T jets) the two gluon distributions are practically Identical. This Is particularly true of the

low x region in which the gluon distribution is most important. A theoretical issue, related to the value of A. is the choice of Q, the

scale in the parton distribution functions (eq.(T)) and in the running coupling constant (eq.(?)). In theory, this question could be resolved if an 0(a s3) calculation had been performed. Different choices for the scale Q modify the form of the 0(o 33) terras. Because the parton cross-section begins in order

0 ( a s2 ) the truncated result without 0(a 3^) terms ir quite sensitive to the

choice of scale. Without an 0<a g^) calculation we can at best make an educated guess of the correct scale using the only fragment of the complete calculation

7 B \ which has been performed • '.

<u+ ii — x+1¿ «• Q „, This calculation suggests that the most appropriate scale ia

With this choice of scale the corrections to the process in eq.í1*) are small for most values of x T . The complexity of the calculation of the radiative corrections to other partonic sub-processes, especially gluon-gluon scattering,

- 1 3 5 -

makes it probable that eq.(5) is the best estimate we shall have for some time. Furthermore our information on fhe gluan distribution is gleaned froii. deep inelastic scattering where it first entera at 0 ( a 3 ) . This information ia not sufficient to provide a meaningful determination of the gluon distribution function including the 0(a s) terms. It i3 precisely these correction terms which are needed to give meaning to the 0(rx 33) terms in gluon-gluon scattering. So even if the calculation of radiative corrections to gluon-gluon scattering were technically feasible,it would still be hard to interpret.

2. q«p Distributions of W and Z Bosons. The production of W and 2 bosons proceeds via the Drell-Yan quark

anti-quark annihilation mechanism. The total cross-section is calculated from,

where N is an overall normalisation and H is the product of quark and anti-quark distribution functions evaluated at scale C^t and weighted with the appropriate coupling factors. The Q(o¡3) terms have been calculated and give rise to a positive correction of about H0% for both W and 2 production at /S = 5f0 CeV. Because the correction is large there is some uncertainty in the prediction for the total cross-section. However the 0(a 3) correction is much smaller than it was for M - pair production at lower energies,(because the coupling constant is smaller),and therefore the ambiguity in the overall normalisation of W and Z production (the so called K-factor) i3 reduced. The best theoretical values for the total production crass-sections at /S = 540 GeV are \

Multiplying these numbers by the branching ratios into electrons,

corresponding to rat = 40 GeV and a 3/n = .04 the predictions for the observed decay channels are, ^ _

The transverse momentum distribution of the intermediate vector bosons ia theoretically more complicated than the total crosa-section. In the lirait in which the transverse momentum q T is of the same order as the mass of the vector boson, Q, the transverse momentum should be well described by recoil against one

- 136 -

raassless parton and the maximum transverse momentum A . ig controlled by the kinematics of the one parton emission diagrams.

v2

Decreasing q T introduces a second scale into the problem and for small q-f we find that large terms are generated and must be resummed if we are to have a valid perturbative prediction. The emission of many gluons changes the form of the q-j. distribution out should leave the total cross-section, which is quite reliably calculated in 0(a 3), unchanged. The resumniatlon was first attempted by D D T 1 0 ) and subsequently modified and consolidated* 1^. A consistent framework for going beyond the leading double logarithmic approximation has been indicated by Collins and Soper* 2). The work reported here 9) whl-^h was used to generate the numerical results has the following features.

a) At large q T we automatically recover the 0(a s) perturbative distribution coming from one gluon emission, without ad hoc Introduction of matching procedures between hard and soft radiation.

b) In the region q ><< Q the soft gluon resummation is performed at leading double logarithmic accuracy.

c) Only terras uorresponding to the emission of soft gluons for which the exponentiation can be theoretically justified are resummed.

d) The Integral of the q--. distribution reproduces the welJ known results for the 0(u 3) total cross-sections exactly.

e) The average value of q2. is also identical with the perturbative result at 0 ( a s ) .

f) All quantities are expressed in terms of precisely defined quark distribution functions as measured in deep inelastic scattering.

g) The results constitute the first term in a systematic expansion. The result contains a resummation of logarithmic terms in impact parameter space. This allows exact conservation of the transverse momentum of the emitted gluons. The form of the result is,

4k • ft *• '"*[•»•<)«** Y»,») „„ where the form factor (including only terms which can&ededuced from an 0(a s) calculation),Is

- 1 3 7

O S ) swtfj.í "J[*)-i]SfK-5) The complete 0(a s) expressions for ï and R are given in ref.(9) and are too complicated to reproduce here. The zeroth order terra in R involves the parton distribution functions evaluated at a b-dependent scale

( 1 3 )

The function ï is completely finite as q T tends to aero. This result for the form factor is in agreement with the general form of

Collins and Soper. Their result is written in terms of arbitrary parameters and c 2 which be used to modify the scale at which the separation between hard and soft contributions is made. After soma manipulation their result for the form factor can be written as,

taking the natural choices for the parameters,

ie obtain in the R5 scheme,

( 1 1 )

(15)

The term D is the higher order correction which is dominant in the low q T region and is given by,

( 1 7 )

Eq.(l4) is readily shown to be in agreement with eq.(12) in the approximation in which we replace the Bessel function by a 0 function. 1 5

The numerical consequences of eq.(ll) are shown in Fig. 3 . Also shown is a histogram of the 52 UA, W events suitably normalised. The parton distributions used are those of ref.(6), which have two different choicas for A. Both sets are compatible with low energy data. The principal uncertainty in eq.(ll) is associated with the choice of A. From Fig. 3 we see that this leads to a variation of about 15?. The form of the parton distribution functions leads to a small uncertainty,since quark distributlons.well determined in deep inelastic scattering, are most important. The behaviour of the strong coupling

- 1 3 8 -

3. References 1) G. Arnlson et al., Phys. Lett. 123B (1983) 115. 2) M. Banner et al., Phys. Lett. 118 (198 2) 203.

P. Bagnaia et al., 2. Phys. C20 (1983) 117. 3) R. Horgan and H. Jacob, Nucl. Phys. B179 (1981 ) 1*M1 . 1) W. Scott, these proceedings. 5) E. Eichten, I. Hinchliffe, K. Lane and C. Quigg, Fermilab preprint 81/17-T. 6) D . Duke and J.F, Owens, Florida preprint FSU-HEP-831115 (1983). 7) R.K. Ellis, H.A. Fuman, H.E. Haber and I. Hinchliffe, Nuol. Phys. B173

(1980) 397. 8) W. Furmanskl and W. Slominski, Krakow preprint Tpju 11/31 (1931). 9) G. Altarelll, R.K. Ellis, H. Greco and G. Martineiii, CERN preprint

TH (1981). 10) ïu. L. Dokshitzer, 0.1. Dyakonov and S.I. Troyan, Phys. Lett. 78B (1978)

290, Phys. Rep. 58 (1980) ÍÍ9. 11) G. Parlsl and R. Petronzlo, Nucl. Phys. B151 (1979) 127.

P. Chiappetta and M, Greco, Nucl. Phys. B221 (1983) 269 and references therein.

12) J.C. Collins and D.E. Soper, Nucl. Phys. B197 (1982) 116 and references therein.

13) J. Kodalra and L. Trentadue, Phys. Lett. 112B (1982) 335. Hl) C.T.H. Davies and W.J. Stirling, CERN preprint TH3853 (1981). 15) S.D. Ellis, N. Fleiahon and H.J. Stirling, Phys. Rev. D21 Í1981) 1386.

constant in the very low momentum region has only a minor effect above q T of 2 GeV. The influence of higher order corrections can estimated by including the only term which has been calculated (eq.(17)) in our numerical analysis. The effect of the inclusion of D Í3 numerically approximately equivalent to a rescaling of A by a factor of about 2. Thus the effect of higher order corrections cannot be distinguished from the uncertainty in A.

The differential c;'oss-section for W + + W" production at zei » rapidity is.

The corresponding result for Z production is,

£j lb'0 ^ ' S l v l ) (19) The shape of the q T distribution for Z production 13 very similar to the plot for W production shown in Fig.3. Here again the main uncertainty comes from the choice of A.

1 3 9 -

P T GeV

F i g . 1 S u h p r o c e s e

s c a t t e r i n g ; d a s h e d

s o l i d l i n e , t o t a l )

a n d A - - 2 G e V .

c o n t r i b u t i o n s t o t h e j e t c r o s ? - s e c t I o n ( d a s h e d l i n e , q q

- d o t t e d l i n e , g g s c a t t e r i n g ; d o t t e d l i n e , q g s c a t t e r i n g ;

. T h e s c a l e Q, ( c f . e q s . ( 1 , 2 ) ) i s c h o s e n s o t h a t Q = pT/-¡

R = / Í 2 . at rapidity y-0 dq Tdy f dy

- 1 4 1 -

W,Z Physics and Standard Model

1 4 2

P R O D U C T I O N O F H I G H MASS cv A N D e'e' PA IRS IN T H E

UA2 E X P E R I M E N T A T T H E C E R N p p C O L L I D E R

T h e UA2 Col laborat ion

( B e r n e , C E R N , CopenhagenT O r s a y ; " Pav ía , Sacïay)

Dî 84100S6163

presen ted by

J . S C H A C H E R

U n i v e r s i t y of B e r n e , S w i t z e r l a n d

A B S T R A C T

We p r e s e n t new resul ts on in termedia te vector boson product ion at the C E R N

p p co l l ider . A comparison is made wi th t h e pred ic t ions of t h e s t a n d a r d model

of t h e un i f ied e lect roweak Glashow-Sa lam-Weinberg t h e o r y .

- 143 -

1 , I N T R O D U C T I O N

We repor t here the resul ts from a search f o r e lect rons wi th > 15 G e V / c

p roduced at the C E R N pp col l ider (Vs = 540 G e V ) d u r i n g its 1982 a n d 1983

per iods of o p e r a t i o n .

Following a genera l discussion of t h e topology of t h e events conta in ing an

e lectron cand ida te , we shall compare t h e da ta w i t h expectat ions in the

f ramework of the e lect roweak s t a n d a r d model [ 1 ] f o r t h e react ions

p + p - W~ + a n y t h i n g ( 1 )

- e" • v (? )

p • p - Z ° + a n y t h i n g ( 2 )

-* e* + e" o r e* + e" + y

w h e r e W~ and Z° a r e t h e postulated c h a r g e d and neut ra l In te rmedia te V e c t o r

Bosonc ( I V B ) , r e s p e c t i v e l y ,

Accord ing to t h e amount of data col lected we a re now in t h e posit ion to

s t u d y some detai ls of the I V B p r o d u c t i o n , e . g . t h e inf luence of emission of

g luon radiat ion on the d i s t r i b u t i o n of t h e W t r a n s v e r s e momentum ( F i g . 1 ) .

F i g . l T y p i c a l d iagram for W a n d Z p r o d u c t i o n , t a k i n g into account

emission of gluon ( g ) rad ia t ion . 7T : par ton in p o r p.

- 1 4 4 -

Pre l iminary resul ts f rom t h e s t u d y r e p o r t e d h e r e have a l r e a d y been

p r e s e n t e d e lsewhere [2 ] and a more complete discussion can be found in a

recent publ ica t ion [ 3 ] .

2 . T H E D E T E C T O R

T h e exper imenta l a p p a r a t u s , shown in F i g . 2 , has been descr ibed in deta i l

e lsewhere [ 4 ] . A t t h e c e n t r e of t h e a p p a r a t u s a system of cy l indr ica l

chambers ( t h e v e r t e x de tec tor [ 5 ] ) measures charged par t i c le t ra jec to r ies in a

region w i t h o u t magnetic f i e l d . T h e v e r t e x d e t e c t o r consists of : a ) f o u r

m u l t i - w i r e propor t iona l c h a m b e r s , ( C I to C 4 ) , h a v i n g cathode s t r ips wi th

pulse h e i g h t r e a d - o u t at ±45° to t h e wires ; b ) two d r i f t chambers w i t h

measurement of the c h a r g e d iv is ion on a tota l of 12 w i res p e r t r a c k . T h e

d r i f t chambers a r e used to obta in both t r a c k i n g informat ion and to eva lua te

t h e most l i ke ly ionisation 1 0 associated w i t h each t r a c k . From t h e

r e c o n s t r u c t e d t r a c k s t h e posit ion of t h e e v e n t v e r t e x is de te rmined wi th a

prec is ion of ±1 mm in all d i r e c t i o n s .

Fig.2 A view of the UA2 detector in a plane containing the beam line.

- 1 4 5 -

T h e v e r t e x detector is s u r r o u n d e d b y an e lectromagnet ic and hadron ic

calor imeter ( c e n t r a l calor imeter [ 6 ] ) , wh ich covers t h e fu l l az imuth and a

polar angle i n t e r v a l 40° < 6 < 140° . T h e calor imeter is segmented into 240

independent ce l ls , each c o v e r i n g 10° in 6 and 15° in 4> a n ¿ bu i l t in a tower

s t r u c t u r e po int ing to the c e n t r e of the in teract ion r e g i o n . T h e celfs a r e

segmented longi tud ina l ly into a 17 radiat ion lengths t h i c k e lectromagnet ic

compartment ( l e a d - s c i n t i l l a t o r ) fo l lowed by two hadron ic compartments

( i r o n - s c i n t i l l a t o r ) of = 2 absorpt ion lengths each.

In the a n g u l a r region c o v e r e d b y t h e cent ra l ca lor imeter a cy l indr ica l

t u n g s t e n c o n v e r t e r , 1.5 radiat ion lengths t h i c k , fo l lowed b y a cy l indr ica l

propor t iona l chamber ( C 5 ) , is located j u s t a f t e r t h e v e r t e x d e t e c t o r . T h i s

device localises e lectromagnet ic showers in i t ia ted in t h e t u n g s t e n wi th a

prec is ion of ±3 mm, as v e r i f i e d using tes t -beam e lec t rons .

For the f i r s t 15 n b - 1 of i n t e g r a t e d luminosi ty , col lected d u r i n g t h e

A u t u m n of 1982, t h e azimuthal coverage of t h e cent ra l calor imeter was only

3 0 0 ° . T h e remain ing in te rva l ( ±30° a r o u n d the hor izonta l p lane ) was cohered

b y a magnet ic spectrometer which included a lead-g lass a r r a y to measure

c h a r g e d and neu t ra l par t ic le p roduct ion [ 7 ] .

T h e two f o r w a r d regions (20° < 8 < 3 7 . 5 ° and 1 4 2 . 5 ° < 9 < 160°) a r e each

e q u i p p e d wi th twe lve toroidal magnet sectors wi th an a v e r a g e b e n d i n g power

of .38 T m . Each sector is i n s t r u m e n t e d w i t h

a) t h r e e d r i f t chambers [ 8 ] located a f te r t h e magnet ic f ie ld r e g i o n . Each

chamber contains t h r e e planes w i t h wires at - 7 ° , 0 ° a n d * 7 ° w i t h respect to

t h e magnetic f i e 'd d i r e c t i o n .

b ) a 1.4 radiat ion lengths t h i c k l e a d - i r o n c o n v e r t e r , fo l lowed by a

p r e s h o w e r c o u n t e r which consists of two pa i rs of layers of 20 mm diameter

propor t iona l tubes ( M T P C ) , s t a g g e r e d b y a t u b e radius and equ ipped w i t h

pulse height measurement [ 9 ] . T h i s dev ice localises e lectromagnet ic showers

in i t ia ted in the c o n v e r t e r w i th a precision of ±6 mm.

c ) an electromagnet ic ca lor imeter consist ing of l ead-sc in t i i l a tor counte rs

assembled in ten independent ce l ls , each cover ing 15° in $ and 3 . 5 ° in 6 .

Each cell is subd iv ided into two independent longi tudinal sect ions, 24 a n d 6

radiat ion lengths t h i c k , r e s p e c t i v e l y , t h e l a t te r p r o v i d i n g reject ion against

h a d r o n s .

- 146 -

T h e systematic u n c e r t a i n t y in t h e e n e r g y ca l ib ra t ion of t h e e lectromagnet ic

calor imeters f o r t h e data p r e s e n t e d h e r e amounts to an a v e r a g e va lue of

±1.5%. T h e ce l l - to -ce l l ca l ibrat ion has a d i s t r i b u t i o n wi th a r . m . s . of 2 .2%.

T h e e n e r g y resolution f o r e lectrons is measured to b e c ^ / E = 0 . 1 4 / V E [6 ] in

the cen t ra l calor imeter and 0 . 1 7 / V E in t h e f o r w a r d ones (E in G e V ) .

3 . D A T A T A K I N G A N D D A T A R E D U C T I O N

In o r d e r to implement a t r i g g e r sensi t ive to e lec t rons of h igh t r a n s v e r s e

momentum, the photomul t ip l ier ga ins ¡n all ca lor imeters were ad justed so t h a t

t h e i r s ignals were propor t iona l to the t r a n s v e r s e e n e r g y .

Because of t h e cell d imensions, e lectromagnet ic showers in i t ia ted b y

e lectrons may be shared among adjacent ce l ls . T r i g g e r thresholds w e r e

app l ied , t h e r e f o r e , to l inear sums of signals f rom matr ices of 2 x 2 ce l ls ,

r a t h e r t h a n to ind iv idua l cel ls . In t h e centra l ca lor imeter , all possible 2 x 2

matr ices w e r e cons idered ; in t h e two f o r w a r d o n e s , we included only those

consist ing of cells be longing to the same sector .

A W t r i g g e r signal ( f o r Z° t r i g g e r : see R e f . 1 2 ) was genera ted w h e n e v e r

the l inear sum from a t least one such matr ix e x c e e d e d a t h r e s h o l d which was

typ ica l ly set a t 8 G e V . T o suppress background from sources o t h e r than p p

col l is ions, we r e q u i r e d a coincidence wi th t w o signals obta ined f rom

sc int i l la tor hodoscopes c o v e r i n g the polar angle i n t e r v a l 0 . 4 7 ° - 2 . 8 4 ° w i t h

respect to t h e beams on both sides of t h e collision r e g i o n . T h e s e

hodoscopes, which w e r e p a r t of an exper iment to measure the pp tota l

c ross-sect ion £ ï 0 ] , g a v e a coincidence signal in more than 98% of all

n o n - d i f f r a c t i v e pp col l isions.

Approx imate ly 7 x 1 0 s W t r i g g e r s w e r e recorded d u r i n g t h e 1982 and 1983

r u n s , c o r r e s p o n d i n g to an integrated luminosity SÛ - 131 n b " 1 ,

A f i r s t data reduct ion is made b y r e q u i r i n g t h e presence of an e n e r g y

c lus te r w i th a t r a n s v e r s e e n e r g y g r e a t e r than 15 G e V . In the cent ra l

ca lor imeter , c lusters a re obta ined b y jo in ing all e lectromagnet ic cells which

share a side and contain at least 0 . 5 G e V . A halo cont r ibu t ion f rom t h e cells

hav ing at least one side in common w i t h a c luster is also a d d e d . T h e f o r w a r d

calor imeter c lusters consist of a t most two adjacent cells hav ing t h e same

azimuth ( t h e cells a r e f a r f rom t h e in teract ion po in t a n d are much l a r g e r than

147 -

t h e latera l extension of an e lectromagnet ic shower - t h e dead region be tween

cells at d i f f e r e n t az imuth does no i allow c l u s t e r i n g across i t ) .

In t h e s u r v i v i n g e v e n t s , a search is .made f o r conf igura t ions consis tent

w i th t h e presence of a high-p-j. e lectron among t h e collision p r o d u c t s . A n

e lec t ron is ident i f ied from t h e observa t ion of

a) t h e presence of a c lus te r of e n e r g y deposit ion in t h e f i r s t compar tment

(e lec t romagnet ic ) of t h e ca lor imeters w i t h a small la tera l size and only a small

e n e r g y leakage in t h e hadronic compar tment .

b ) the presence of a reconst ruc ted c h a r g e d par t i c le t r a c k which pe ints to

t h e e n e r g y c lus ter . T h e p a t t e r n of e n e r g y deposi t ion must agree w i t h t h a t

expec ted f rom an isolated e lec t ron inc ident along t h e t r a c k d i r e c t i o n .

c ) t h e presence of a hi t in t h e preshower c o u n t e r w i t h an associated pu lse

he igh t l a r g e r than t h a t of a minimum ionis ing p a r t i c l e ( m . i . p . ) . T h e d is tance

of t h e hi t f rom t h e t r a c k must be consistent w i t h the space resolut ion of t h e

c o u n t e r i tse l f .

A set of cuts has been de f ined according these r e q u i r e m e n t s . A deta i led

descr ip t ion of these cuts can be f o u n d in R e f . 3 .

T h e eff iciencies of the simultaneous appl icat ion of these cuts a re 76% and

80% in the centra l and f o r w a r d r e g i o n s , r e s p e c t i v e l y .

4 . T O P O L O G Y O F E V E N T S C O N T A I N I N G A N E L E C T R O N C A N D I D A T E .

A f t e r appl icat ion of the e lect ron cuts the sample is reduced to 225 e v e n t s ,

conta in ing genuine electrons and stil l f a k e e lec t rons r e s u l t i n g f rom

misident i f icat ion of hadrons . T h e p^. d i s t r i b u t i o n is shown in F i g . 3 .

T h e b a c k g r o u n d of f a k e e lectrons can be shown to fal l main ly into two

ca tegor ies . In approx imate ly 70% of the cases we a r e deal ing w i t h " o v e r l a p s " ,

i . e . jets f r a g m e n t i n g into a h a r d TT° w i t h a c h a r g e d pion n e a r b y in ang le .

T h e rest of the b a c k g r o u n d resu l ts f rom n°s u n d e r g o i n g Da l i t z decays o r

convers ions in t h e beam-p ipe .

From studies of hadron jets [11] we e x p e c t t h e f a k e e lect rons to be

accompagnied b y o t h e r h i g h - p ^ . je ts a t approx imate ly opposite a z i m u t h . We

shall thre fore search f o r h i g h - p ^ . je ts b y g r o u p i n g t o g e t h e r adjacent cells

w i t h e n e r g y into c lusters us ing an a lgor i thm descr ibed e lsewhere [11 ] .

C l u s t e r s wi th more than 3 G e V of t r a n s v e r s e e n e r g y a re re ta ined and cal led

j e t s . For minimum bias t r i g g e r s such c lusters o c c u r :n on ly 15% of t h e e v e n t s .

- 148 -

Electron camMates/GeV/c

Threshold SO

30 1,

20 -

10

S 10 15 35 ¡.0 45 SO 55 PT ICeV/c)

F i g . 3 T r a n s v e r s e momentum d i s t r i b u t i o n of t h e 225 e lect ron candidates

sa t i s fy ing t h e e lectron c u t s .

We f i n d t h a t 45 even ts contain no j e t , t h e e lec t ron cand idate be ing the

o n l y h i g h - p T pa r t i c le o b s e r v e d . T h e i r Pj d i s t r i b u t i o n is shown in F i g . 4 a .

Such events conta in e i t h e r a n e u t r i n o , as in the case of W — ev d e c a y , or

o t h e r h igh -p . j - par t ic les h a v i n g escaped de tec t ion . In t h e l a t te r case we would

expect a r a p i d l y fa l l ing p- j . -spectrum t y p i c a l of the j e t p-j. d i s t r i b u t i o n [ I T ] .

T h e remaining ISO events contain a t least one / e t (acnording to our

d e f i n i t i o n ) , and F i g . 5 shows t h e az imuthal separat ion of t h e h ighest p ^ je t

f rom t h e e lec t ron cand ida te . T h e e v e n t s in t h e peak a t A4> = 180° a re l ike ly

to be b a c k g r o u n d . Hence we sum all t r a n s v e r s e momenta of c lus te rs hav ing

A(b > 120° and de f ine

p o p p = ~ ^ T e " I f 5 T , j e t / | f 5 T e | ( 3 )

w h e r e p i j . e and p ^ a r e two-dimensional

pY . on a p lane p e r p e n d i c u l a r to the beams.

a r e two-dimensional vec tors ob ta ined p r o j e c t i n g p"*" and

, > ^ . n . P, ' ß 20 25 30 35 i*Q

pf ( G e V / c l

F i g . 4 a ) T r a n s v e r s e momentum d i s t r i b u t i o n of the e lec t ron candidates in

events w i t h no addit ional j e t . b ) T r a n s v e r s e momentum d i s t r i b u t i o n of t h e

e lect ron candidates in events hav ing p > 0 . 2 . D a r k points cor respond to opp

e lectrons f rom 2 ° decays , c ) T r a n s v e r s e momentum d i s t r i b u t i o n of e lec t ron

candidates in events wi th addit ional jets hav ing p < 0 . 2 .

Ä* (degrees)

F i g . 5 D i s t r i b u t i o n of t h e azimuthal separat ion ¿<p between t h e e lectron

cand idate and t h e associated j e t h a v i n g t h e h ighes t p^.. C u r v e : est imated

b a c k g r o u n d .

T h e d i s t r i b u t i o n of p is shown in F i g . 6 . We re jec t t h e 156 events opp

hav ing P o p p ' 0 - 2 - T h e i r p ^ 0 d i s t r i b u t i o n is shown in F i g . 4 b . T h i s sample

contains t h e e ight Z n — e*e" ( o r e*e~v) even ts recent ly r e p o r t e d [ 1 2 ] .

T h e p T

e d i s t r i b u t i o n of the remaining 24 e v e n t s is shown in F i g . 4 c . T h e s e

events do c o n t a i n , in addi t ion to t h e e lect ron c a n d i d a t e , jets which do not

c a r r y a s ign i f icant t r a n s v e r s e momentum in t h e d i r e c t i o n opposi te to the

e lect ron (p < 0 . 2 ) . O D D

15 - tut

F i g . 6 D i s t r i b u t i o n of P Q o p f ° r even ts conta in ing an e lect ron candidate

and at least one associated j e t . C u r v e : est imated b a c k g r o u n d .

- 1 5 1 -

5 . B A C K G R O U N D T O T H E E L E C T R O N S P E C T R A

For t h e p r e s e n t we shall r e g a r d t h e 148 events conta in ing a j e t back to

back w i t h the e lectron candidate as a b a c k g r o u n d sample of f a k e e lectrons

( a f t e r removal of t h e e ight Z° e v e n t s ) .

T h e s e events occur at a ra te lower t h a n t h a t of j e t product ion b y a f a c t o r

of 3 . 6 * 10* f o r t h e centra l de tec tor and 2 . 6 » 1 0 5 f o r t h e f o r w a r d ones .

T h e b a c k g r o u n d s to t h e two event samples of F i g . 4 a and 4c a re now

est imated as fe l lows . We consider a sample of events conta in ing a mani fest ly

fake e lec t ron not s u r v i v i n g the c u t s . T h e s e events a r e now d i v i d e d into

t h r e e classes of d i f f e r e n t topologies, cal led samples A , B a n d C , c o r r e s p o n d i n g

to the t h r e e classes of e lect ron candidates of Fig.A.

We assume t h a t the P j d i s t r i b u t i o n s of t h e samples A , B and C a re similar

to these of t h e b a c k g r o u n d events conta ined in t h e cor respond ing e lect ron

samples. We can check th is assumption f o r t h e 148 e lec t ron candidates wi th

p > 0 . 2 w h i c h , as mentioned a b o v e , a r e taken as a p u r e b a c k g r o u n d K o p p

sample, and we do indeed f i n d t h a t t h e y have t h e same p-j. d i s t r i b u t i o n as t h e

fake e lect rons of sample B. T h e b a c k g r o u n d cont r ibu t ions to t h e 69 e lectron

candidates in t h e o ther two topologies (45 wi th no add i t iona l je ts and 24 wi th

jets h a v i n g P Q p p < 0 - 2 ) a r e then est imated d i r e c t l y f r o m t h e p^. d is t . ^butions

of samples A a n d C , mul t ip l ied b y a f a c t o r equal to t h e rat io of t h e tota l

number of e lec t ron candidates w i t h p > 0 . 2 (148 e v e n t s ) to the tota l opp

number of even ts in sample B. T h e s e b a c k g r o u n d estimates a re shown as

smooth c u r v e s in F i g . 4a and 4 Q .

6 . T H E W - ev E V E N T SAMPLE

T h e combined p^. e d is t r ibu t ion of t h e 69 events f r o m F ig .4a and F ig .4c is

shown in F i g . 7 t o g e t h e r With t h e b a c k g r o u n d est imate. T h e presence of a

s ign i f icant signai above t h e b a c k g r o u n d is t a k e n as ev idence t h a t most of t h e

e lect ron candidates shown h e r e a r e indeed e lectrons a n d associated w i t h a v W e

h igh-p- j . neu t r ino ( pîj. = pj - pij- ) . T h e r e is a c lear accumulat ion of

events near p^. 6 = 40 G e V / c , which is d is t inc t ive of t h e Jacobian peak as

expected f o r W — ev decay. For p . . 6 > 25 G e V / c t h e d i s t r i b u t i o n contains 37

events w i t h an est imated b a c k g r o u n d ^f 1 .5 ± 0 . 1 e v e n t s .

- 152 -

30 35 40 pf IGeV/c)

F i g . 7 T r a n s v e r s e momentum d i s t r i b u t i o n of t h e e lec t ron candidates in t h e

W — ev e v e n t sample. Full c u r v e : b a c k g r o u n d est imate . Dashed c u r v e : sum

of all t h e cont r ibut ions as discussed in Section 7 .

W We estimate the t r a n s v e r s e momentum pîj. of t h e W b y

_ W , ( 4 )

w h e r e t h e sum ex tends o v e r all o b s e r v e d je ts and P ^ . s p is the total p-j. of all

o b s e r v e d part ic les not be longing to j e t s . In an ideal de tec tor the correct ion

fac tor Ç would be 1 . For an incomplete coverage some f rac t ion of the

par t ic les in t h e e v e n t is lost ( t y p i c a l l y among t h e low t r a n s v e r s e momentum

p a r t i c l e s ) . We es t imate ,us ing t h e e i g h t Z ° e v e n t s , t h a t Ç should be 2 . 2 t 0 . 5

in o r d e r to sat isfy E q . ( 4 ) on t h e a v e r a g e . W

T h e d i s t r i b u t i o n of Pj is shown in F i g . 8 a and 8 b , us ing Ç = 1 and

Ç = 2 . 2 , r e s p e c t i v e l y . T h e mean va lue ( f o r Ç = 2 . 2 ) is < P 6 . 9 t 1.0 G e V / c . Q C D pred ic t ions [ 1 3 ] , i l l us t ra ted b y the c u r v e in

F i g . 8 , a r e consistent w i t h the o b s e r v e d d i s t r i b u t i o n . T h e event w i th the W

h ighest va lue of P T , 2 9 . 6 G e V / c , is i n t e r p r e t e d as a W recoi l ing against a

h igh -p— je t . Among t h e W candidates w i t h p T

e < 2 5 G e V / c we f i n d two events

- 1 5 3 -

a) Uncor rec ted d i s t r i b u t i o n of t h e W t r a n s v e r s e momentum ( E q . ( 4 ) : Ç=1)

b ) Cor rec ted d i s t r i b u t i o n ( E q . ( 4 ) : Ç = 2 . 2 ) . C u r v e : Q C D pred ic t ion [ 1 3 ] .

- 1 5 4 -

T h e mass M... of the W is de termined from t h e W - ev candidates w i t h W

p-j-ß > 25 G e V / c by per fo rming a maximum l ikel ihood f i t to t h e i r

two-dimensional d is t r ibu t ion d 2 n / d p _ e d ß , where 6 is the measured e lectron

T e e polar ang le . In the Monte Car lo p rogram which is used to genera te t h e d is t r ibu t ion d a n / d p - , . e d 9 for d i f f e r e n t values of M. , we make t h e fol lowing

i e w

assumptions:

a) t h e W longi tudinal momentum d is t r ibu t ion is ob ta ined using t h e q u a r k

s t r u c t u r e funct ions of t h e proton ( a n t i p r o t o n ) wi th scal ing v io la t ion , as g i v e n

by Glück et a l . [ 1 5 ] . W

b ) t h e p-j- d is t r ibu t ion is t a k e n f rom Ref . 13 a l lowing for var ia t ions of

W

<p^. > in o r d e r to take into account uncer ta in t ies of Q C D pred ic t ions .

c) t h e W — ev decay angu la r d i s t r i b u t i o n is descr ibed by t h e s t a n d a r d

V - A coup l ing .

d ) t h e M w d is t r ibu t ion is genera ted according to a B r e i t - W i g n e r c u r v e

with a fixed value of the W width, F... = 2 . 7 C e V / c 2 . W

T h e detec tor response is taken into account .

T h e sample of 37 measured events wi th P T

e > 25 G e V / c is contaminated b y

t h r e e b a c k g r o u n d sources:

a) mis ident i f ied e lectrons f rom two je t b a c k g r o u n d : 1.5 ± .1 e v e n t s .

b ) e lectrons from Z° — e*e~ decay w i t h one e lect ron u n d e t e c t e d : 2 . 5 Î . 9

e v e n t s . T h i s cont r ibut ion is eva luated b y Monte Car lo t e c h n i q u e normal iz ing

the resu l t to the total number of Z ° — e*e~ detec ted in this exper iment

(8 e v e n t s , Re f . 1 2 ) .

W

with even h igher values for p T ' c lear ly separa ted from the res t of the

even ts . T h e s e events a re discussed e lsewhere [ 1 4 ] .

We note t h a t the level of a c t i v i t y in the W events is about twice as h i . ih

as t h a t in minimum bias e v e n t s . Th is f e a t u r e is re f lec ted in t h e average

observed sum of the t r a n s v e r s e energies of all par t ic les o ther than t h e

electron and je ts ( i f a n y ) < Z E T > = 14.1 i 1.7 GeV and t h e average va lue of

the charged mul t ip l ic i ty <^ c ^> = 19 .3 +- 1.9 in t h e rest of t h e e v e n t . T h e

cor respond ing values for minimum bias events a r e <IE.p> = 8 . 8 GeV and <n , > = 1 4 . 7 .

ch

7 . D E T E R M I N A T I O N O F T H E W MASS

- 1 5 5 -

c ) e lectrons f r o m W — T V , T - e3 v decay chain : . 9 ± .1 . T h e de tec tor e T 7

acceptance for e lectrons from W -* T — e decay chain has been eva lua ted by

Monte Car lo t e c h n i q u e , and assume a b r a n c h i n g rat io B t = 0 .17 f o r t h e

decay T — ev v [ 1 6 1 . 1 e T

T h e sum of all cont r ibut ions is shown as a dashed c u r v e in F i g . 7 . A f t e r

subt rac t ion of the background e v e n t s , we a r e left w i th a sample of 3 2 . 1 ± 6 . 0

2 e

W — ev d e c a y s . T h e best f i t to the exper imenta ! d n /dp^ . d 6 ß d i s t r i b u t i o n

inc lud ing the mentioned b a c k g r o u n d cont r ibu t ions gives

My = 83 .1 i 1.9 ( s t a i . ) ± 1 .3 ( s y s t . ) G e V / c 2 ,

2 W An u n c e r t a i n t y of ±1 G e V / c , wh ich resul ts f rom the e f fec t of v a r y i n g <p-p >

between 4 and 10 G e V / c in the f i t , is a d d e d in q u a d r a t u r e to t h e stat ist ical

e r r o r . T h e systematic e r r o r ref lects t h e u n c e r t a i n t y in the overa l l mass scale

a r i s i n g f rom the absolute ca l ibra t ion of the ca lor imeter (±1 .5%) a n d from smali

d i f f e rences in the re la t ive ca l ibra t ion of var ious cells of t h e ca lor imeter .

With in t h e quoted e r r o r s th is va lue agrees wi th the resu l t of the U A l

e x p e r i m e n t [ 1 7 ] , M w = 8 0 . 9 i 1 . 5 ( s t a t . ) ± 2 . 4 ( s y s t . ) G e V / c 2 .

8 . CROSS S E C T I O N FOR I N C L U S I V E W P R O D U C T I O N

T h e cross section a ^ e f o r t h e inc lus ive process p + p — W~ * a n y t h i n g ,

fol lowed by t h e decay W -* ev , a t v"s=540 G e V is obta ined f r o m t h e re lat ion

N w

e = * V , n

w h e r e N ^ e = 3 2 . 1 ± 6 .0 is t h e number of W -* ev decays ob ta ined b y

s u b t r a c t i n g from t h e electron sample t h e b a c k g r o u n d events as descr ibed in

t h e p rev ious sect ion , a? = 131 n b " 1 is the i n t e g r a t e d luminos i ty ,

e = .60 - .01 is t h e detector acceptance which includes t h e e f fec t of t h e p^_e

t h r e s h o l d and 17 = .77 ¿ .05 is t h e overa l l e f f i c iency of t h e e lect ron

ident i f ica t ion c r i t e r i a averaged o v e r t h e centra l and f o r w a r d d e t e c t o r s . T h e

e f fec t of the cut pQ^<.2 p r e v i o u s l y descr ibed is taken into account in t h e

acceptance e v a l u a t i o n . We f ina l l y obta in

a ® = .53 ± .10 ( s t a t . ) t .10 ( s y s t . ) nb

- 156 -

w h e r e t h e systematic e r r o r ref lects a ±20% u n c e r t a i n t y in t h e knowledge of <£.

T h i s v a l u e is in agreement w i t h Q C D predic t ions [ 1 3 , 1 8 ] a n d w i t h t h e resul ts

of the U A l exper iment [17] .

9 . C H A R G E A S Y M M E T R Y

I t is known t h a t , as a consequence of the V - A c o u p l i n g , t h e W is always

p r o d u c e d wi th fu l l polar isat ion along the d i rect ion of t h e inc ident p beam and

a d i s t i n c t i v e c h a r g e asymmetry can be o b s e r v e d in t h e decay W — ev . In the * W rest f r a m e t h e angu la r d i s t r i b u t i o n has the form (1 * cosO ) 2 f o r electrons * * and (1 - cos9 ) 2 f o r p o s i t r o n s , w h e r e 8 is t h e angle be tween the momentum

of t h e c h a r g e d lepton and t h e d i rec t ion of the inc ident p r o t o n s . However ,

p rec ise ly the same conf igura t ion would resu l t f rom V + A coupl ing because in

th is case ail hel ici t ies change s i g n . In o r d e r to maintain fu l l genera l i t y and

allow f o r d i f f e r e n t amounts of V and A coup l ings , w e w r i t e t h e angu la r

d i s t r i b u t i o n in the fo rm

d n / d ( c o s 6 * ) <* ( 1 - q c o s e * ) 2 + 2 q a c o s 6 * ( 5 )

w h e r e q is -1 f o r e lectrons and + 1 f o r posi trons and a depends on the rat io x

between t h e A and V coupl ings ( t ime reversa l i n v a r i a n c e requ i res x to be

r e a l ) . U n d e r the assumption t h a t x is t h e same f o r both Wqq and Wev

c o u p l i n g s , a is g i v e n b y

a = [ ( 1 - x 2 ) / ( T x 2 ) ] 2 ( 6 )

wh ich g ives a = 0 for | x | = 1 .

In t h e UA2 detector a determinat ion of t h e charge s ign is only possible in

the f o r w a r d deter.tors w h e r e a magnet ic f i e ld is p r e s e n t .

We cons ider t h e 8 events h a v i n g an electron wi th pjG > 2 0 G e V / c in the

f o r w a r d d e t e c t o r s . T h e est imated b a c k g r o u n d is 0 . 2 e v e n t s . A comparison

be tween t h e e lectron momentum p a n d e n e r g y E is made in F i g . 9 , which shows

the posit ion of these events in t h e p lane ( p - 1 , E ~ a ) , w h e r e p is t h e e lectron

momentum wi th the sign of t h e p r o d u c t q c o s 8 e [Q^: l a b o r a t o r y angle of the

e lec t ron momentum with respect to t h e proton d i r e c t i o n ) . T h e hor izonta l e r r o r

b a r s in r i g . 9 represent t h e u n c e r t a i n t y on p - 1 , which is 0 .01 ( G e V / c ) " 1 .

- 157 -

1/E G e V 1

-O.06 -0.05 -0.0 í, -0.03 -0.02 -0 01 0 0.01 0.02 0.03 0.04 0.05 0.06

m = 1/p « sigtilq.cosö,) (GeV/cT 1

F i g . 9 Plot of 1/E vs 1 /p f o r t h e e ight W — ev candidates wi th

p^. e > 20 G e V / c de tec ted in the f o r w a r d reg ions. T h e q u a n t i t y p is t h e

e lect ron momentum wi th t h e sign of the p r o d u c t q cos8 [ q = + l ( - 1 ) f o r e * ( e " ) ] .

A c lear asymmetry is v is ib le in F i g . 9 : all even ts lie on one side of the

p l o t . In o r d e r to e x t r a c t a va lue of x f rom t h e s e d a ; a we compute

two-dimensional d is t r ibu t ions f ~ ( p y 6 , 9 g ) for posi t rons and electrons

s e p a r a t e l y , us ing Eqs .C5) and (6 ) and t a k i n g into account t h e W longi tudinal

mot ion. T o each e v e n t we assign a l ikel ihood Q. = f*n,* * f~n,~, w h e r e n,*(n.")

is the p r o b a b i l i t y d e n s i t y t h a t t h e o b s e r v e d par t i c le was a posi t ron (an

e lec t ron) of momentum p. T h e funct ions f~ a re ca lculated a t t h e observed

values of and 0 g . T h e probab i l i t y densi t ies n," re f l ec t the u n c e r t a i n t y in

the determinat ion of the c h a r g e s ign resu l t ing f rom t h e e r r o r in t h e momentum

measurement . Maximiz ing the l ikel ihood n. Q. we obta in | x | = 1 . 0 + ^ f o r

t h e rat io between the s t r e n g t h s of the A and V c o u p l i n g s .

We remark t h a t our e v e n t sample consists of seven p a î t r o n s de tec ted in

one hemisphere a n d one e lect ron detected in t h e opposi te o n e . T h e p r o b a b i l i t y

to o b s e r v e no more than one electron in o n e of t h e t w o hemispheres is = 7%.

- 1S8 -

10. T H E D E C A Y Z ° - e * e '

T h e observa t ion in th is exper iment of seven Z ° - e*e" decays and one

2 ° — e*e"y decay has a l r e a d y been r e p o r t e d [ 1 2 ) . Following a recent

reca l ib ra t ion of t h e ca lor imeters , the i n v a r i a n t mass values of these events

and t h e i r e r r o r s have been s l igh t ly modi f ied . T h e updated v a l u e of t h e Z °

mass based on a we ighted a v e r a g e [3 ] is

M z = 9 2 . 7 i 1 . 7 ( s t a t . ) ± 1 . 4 ( s y s t . ) G e V / c 2 . ( 7 )

We recal l t h a t th is v a l u e is obta ined us ing only t h e f o u r events f o r which

t h e e n e r g y of both e lectrons ( a n d tha t of t h e photon in the e*e"v e v e n t ) is

unambiguously d e t e r m i n e d . With in e r r o r s , th is r e s u l t agrees w i t h the Z° mass

v a l u e d e t e r m i n e d in the U A l exper iment [ 1 9 ] .

In o r d e r to e x t r a c t an est imate of t h e Z ° w i d t h , T^ , f rom these f o u r

e v e n t s , w e f i r s t note t h a t the r . m . s . dev ia t ion of t h e f o u r mass values f rom

t h e va lue of g iven b y E q , ( 7 ) is 2 . 0 G e V / c z , wh ich is almost t h e same as

t h e w e i g h t e d average of t h e e r r o r s a - 2 . 1 G e V / c 2 . T o obta in an u p p e r limit

to f ^ , we use a Monte Car lo p r o g r a m which genera tes a l a rge number of

e v e n t samples, each consist ing of f o u r Z ° — e*e~ d e c a y s , accord ing to a

B r e i t - W i g n e r shape and t a k i n g into account t h e e n e r g y resolut ion of the

d e t e c t o r . As an est imate of t h e u p p e r limit t o at t h e 90% conf idence l e v e l ,

we use t h e va lue which g ives an r . m . s . of less t h a n 2 . 0 G e V / c 2 in 10% of the

e v e n t samples . T h i s va lue is < 6 . 5 G e V / c 2 a t t h e 90% conf idence l e v e l .

Wi th in t h e s t a n d a r d model , th is u p p e r limit can be re la ted to t h e number

of add i t iona l l ight neut r inos A N y . We f i n d A N y < 22 at the 90% conf idence

l e v e l , assuming s i n 2 0 ^ - 0 . 2 2 and a v a l u e of the t - q u a r k mass m^ > M ^ / 2 .

An i n d e p e n d e n t est imate of can be obta ined w i th in the s t a n d a r d model

b y m e a s u r i n g the rat io R - a ^ ^ a \ ^ & r w h e r e a ^ 6 is t h e cross-sect ion for

inc lus ive Z° p roduct ion fo l lowed b y t h e decay Z ° — e*e" [ 2 0 ] . We obta in

a f t e r cor rec t ions which t a k e into account t h e de tec tor acceptance and t h e

e f f i c i ency of the e lectron ident i f icat ion c r i t e r i a . In t h i s case we use all e i g h t

e v e n t s , f o r which a t least one e lect ron 'asses all c u t s , and we f ind

o - 2

e = 0 .11 t 0 . 0 4 ( s t a t . ) ± 0 . 0 2 [ s y s t . ) nb (8)

- 1 5 9 -

which is approx imate ly twice as l a rge as t h e va lue p r e d i c t e d b y Q C D [ 1 3 , 2 1 ] .

For compar ison, we quote the resu l t found b y the U A l e x p e r i m e n t :

o z

e = 0 . 0 5 0 ± 0 . 0 2 0 ( s t a t . ) ± 0 . 0 0 9 ( s y s t . ) nb [ 1 9 ] .

T h e e r r o r on R is dominated b y s ta t is t i cs , because t h e va lue of t h e total

i n t e g r a t e d luminosity cancels o u t . We f i n d R = 0 .21 t 0 . 0 8 , and R > 0 . 1 1 6 at

the 90% conf idence leve l . Q C D estimates of the rat io between Z° and W

produc t ion cross-sect ions [20] p r o v i d e a relat ion be tween R and t h e rat io

V r z :

r v / r z = i 9 - 3 ± ° ' 9 ) R C 9 )

w h e r e t h e e r r o r ref lects the u n c e r t a i n t y of the Q C D calculat ions. Us ing the

s t a n d a r d model va lue of (~w , r w = G e V / c 2 ( w h i c h cor responds to a

t - q u a r k mass m t = M ^ / 2 ) , we f i n d l~ z < 2 . 6 G e V / c 2 a t the 90% conf idence

l e v e l .

As b e f o r e , we can e x t r a c t u p p e r limits to the number of addi t iona l l i gh t

neut r inos A N . We f i n d A N Í 0 at t h e 90% conf idence level ( f o r more v v de ta i l s , see Ref . 3 ) .

1 1 . T H E D E C A Y Z ° - e*e"v

We have r e p o r t e d [12] a Z D - e*e~y e v e n t conta in ing a photon wi th an

e n e r g y k = 24 G e V and an 11 G e V e lec t ron separa ted by an angle u | a b = 3 1 ° ,

e x c l u d i n g , t h e r e f o r e , e x t e r n a l b r e m s s t r a h l u n g . In R e f . 1 2 we est imated t h e

p r o b a b i l i t y to be s 5 x 1 0 " 3 per e v e n t , t h a t in a Z° — e*e" decay a photon at

least as h a r d as the observed one is emit ted as a resu l t of r a d i a t i v e

cor rec t ions [22] and t h e e *e" open ing angle is equal to or smaller than the

measured one . T h i s ca lcu la t ion , which was per fo rmed in t h e Z ° res t f r a m e ,

should not be considered as an est imate of the p robab i l i t y of such a

Z ° — e*e"Y decay because it does not t a k e into considerat ion all conf igura t ions

which a r e less l ike ly than t h e observed o n e .

T h e r e a re severa l possible ways to d e f i n e t h e re la t ive l ikel ihood of

Z ° — e*e"v conf igura t ions . For cases of non-col l inear ev p a i r s , t h e e v e n t

d i s t r i b u t i o n in t h e Z ° res t f rame is g iven b y t h e d i f f e ren t i a l cross-sect ion

d 2 o CÍ x5 + x | .

- a0 — (10 )

dxjdxs 2TT (I - X 1 K I - X 2 )

- 1 6 0 -

w h e r e cr0 is the total cross-sect ion f o r Z ° — e*e" w i t h o u t r a d i a t i v e correct ions

and x. - 2 E . / M Z , E. be ing t h e e lect ron e n e r g i e s . We say t h a t a conf igura t ion

is less l ikely than t h e observed one if its d i f fe ren t ia l c ross-sect ion is smaller

than t h a t calculated at t h e point co r respond ing to t h e observed Z ° - e*e"y

e v e n t . I n t e g r a t i n g E q . ( 1 0 ) o v e r all conf igura t ions which a r e less l ike ly t h a n

the observed one we f i n d a p robab i l i t y of 1,4% p e r e v e n t o r 11% to o b s e r v e a t

least one such e v e n t in a sample of e i g h t . I t should be noted t h a t de tectab le

Z ° — e*e"v decays can be d iv ided in to two classes of c o n f i g u r a t i o n s , t h e f' s t

consist ing of t h r e e c lear ly resolved e n e r g y c lusters and t h e second conta in ing

unreso lved ev pairs which resul t in e n e r g y c lusters inconsistent w i t h an

isolated e l e c t r o n . T h e cor responding probabi l i t ies a re 1.0% and =¡ 0 . 1 % per

e v e n t , r e s p e c t i v e l y . T h e remaining Z° -* e +e"*v decays cor respond to

conf igura t ions which a re not detectable in t h e UA2 a p p a r a t u s .

F u r t h e r possibi l i t ies to calculate a p robab i l i t y for o b s e r v i n g such an e v e n t

a re g iven in R e f . 3 .

12 . S E A R C H FOR T H E D E C A Y W - evy

Given the in te res t in unexpec ted decay modes of t h e Z D we have also

looked f o r events o m p a t i b l e w i th t h e decay W — evy in t h e fu l l data sample:

in t h e cen t ra l d e t e c t o r , we search f o r events conta in ing an e lect ron

candidate wi th p^ . e > 8 G e V / c , which passes t h e e lect ron c u t s , and an

addit ional photon wi th a momentum k in excess of 8 G e V / c . A photon is

de f ined as an e n e r g y c lus te r , wh ich sat isf ies the same c r i t e r i a on size and

hadronic leakage as an e lec t ron , b u t has no c h a r g e d p a r t i c l e t r a c k po in t ing to

i t . If also the photon c luster is seen in the cen t ra l d e t e c t o r , we r e q u i r e an

angu la r separat ion w > 30° between t h e c l u s t e r centro ids in o r d e r to resolve

the ey p a i r . Six evencs sat is fy these condi t ions . H o w e v e r , none of them

s u r v i v e s t h e addi t ional requ i rement of a t r a n s v e r s e momentum imbalance

compatible w i th t h e presence of a n e u t r i n o hav ing p T

v > 10 G e V / c . A Monte

Car lo est imate of the number of W — evy d e c a y s , which a re expec ted to

sat is fy all of these requirements as a resul t of r a d i a t i v e c o r r e c t i o n s , g ives

0 . 1 e v e n t .

- 161 -

In t h e f o r w a r d detectors we can i d e n t i f y ey pairs w i t h v e r y small open ing

angles b y re leasing t h e cond i t ion , t h a t t h e e lect ron momentum p and t h e

e n e r g y E agree wi th in t h e measur ing errors, in th is case, h o w e v e r , we limit

our search to e lect ron t r a n s v e r s e momenta in excess of 20 G e V / c (measured in

the c a l o r i m e t e r ) , f o r which we expect a b a c k g r o u n d cont r ibut ion of 0 . 2

e v e n t s . We f i n d one e v e n t which contains a c l u s t e r of t r a n s v e r s e e n e r g y

E T = 41 GeV (E = 8 6 . 2 G e V ) and a t r a c k of 3 . 6 G e V / c momentum po in t ing to

the c lus te r and sa t is fy ing all o t h e r e lectron ident i f ica t ion c r i t e r i a . L a r g e

missing p ^ is detected in this e v e n t as expected in t h e case of an associated

n e u t r i n o . T h e est imated b a c k g r o u n d f o r p^. e > 35 G e V / c is 0 .01 e v e n t s .

Since t h e open ing angle of th is ev pa i r is compatible w i th z e r o , we aiso

consider the e f fec t of e x t e r n a l b r e m s s t r a h l u n g and we obtain a p r o b a b i l i t y of

0.5% p e r W - ev decay or 4.5% to observe one such event in t h e sample of 9

W - ev and evy candidates wi th p^. e > 20 G e V / c de tec ted in the f o r w a r d

d e t e c t o r s .

13. C O M P A R I S O N W I T H THE. S U ( 2 ) © U ( 1 ) MODEL

T h e I V B mass values p r e d i c t e d in the f ramework of t h e s t a n d a r d model

t a k i n g into account r a d i a t i v e correct ions a r e [ 23 ] M w = 8 3 . 0 * ? " ^ G e V / c 2 and +2 4

= 9 3 . 8 _ 2 * 2 G e V / c 3 . These values a re in exce l lent agreement w i th o u r

exper imenta l r e s u l t s .

We can e x t r a c t r. va lue f s ; n 2 6 ^ f r o m the de f in i t ion s i n 2 6 ^ = l - M ^ V M ^ 2 ,

w h e r e the systematic e r r o r s on the mass scale resu l t ing f rom the u n c e r t a i n t y '

in t h e ca lor imeter ca l ibrat ion cancel o u t . We f i n d

sin 2 e.„ = 0 .196 ± 0 .047 (11 ) w

in good agreement wi th t h e wor ld a v e r a g e resul t of deep- ine las t ic n e u t r i n o

exper iments ( inc lud ing rad ia t ive cor rec t ions ) s i n 2 9 ^ = 0 .217 i 0 .014 [ 2 4 ] .

We can also e x t r a c t a more prec ise va lue of s i n 2 6 ^ f rom t h e relat ion

M w = A / s i n 9 w , w h e r e the numerical va lue A = 3 8 . 6 5 ± 0 . 0 4 G e V / c a is obta ined

t a k i n g into account rad ia t ive correct ions [ 2 3 ] , In th is case we f i n d

s i n z 9 w = 0 .216 ± 0 . 0 1 0 ( s t a t . ) ± 0 . 0 0 7 ( s y s t . ) . (12)

- 162 -

A tes t of t h e s t a n d a r d model is p r o v i d e d b y t h e re lat ionship

p = M w

2 / [ M 7

2 ( 1 - A a / M w

a ) ] , which should be equal to 1 f o r t h e minimal Higgs

s t r u c t u r e . We f i n d

p = 1.02 t 0 . 0 6 . (13)

14. C O N C L U S I O N S

We have s tud ied t h e product ion of e lect rons wi th v e r y high t r a n s v e r s e

momentum at t h e C E R N pp col l ider . From a sample of even ts conta in ing an

e lectron cand idate w i t h p.j- > 15 G e V / c , we have e x t r a c t e d a c lear signal

r e s u l t i n g f rom t h e product ion of the c h a r g e d in termediate vec to r boson W~,

which s u b s e q u e n t l y decays into an e lect ron and a n e u t r i n o .

We have also g iven new and more re f ined resul ts on the product ion and

decay of t h e n e u t r a l vec tor boson Z ° .

O u r exper imenta l resul ts show good agreement w i th t h e pred ic t ions of the

s t a n d a r d model of the un i f ied e lect roweak t h e o r y . F u r t h e r m o r e , the

product ion cross section and t h e d i s t r i b u t i o n s of t h e t r a n s v e r s e momentum of

the in termediate vec to r bosons a r e w i th in t h e pred ic t ions of Q C D calculat ions.

- 163 -

REFERENCES

1) For a review see J . Ellis et a l . , A n n . Rev . N u c l . P a r t . Science 32 ( 1 9 8 2 ) ,

4 4 3 .

2) T h e UA2 Col laborat ion , p resen ted b y G. Sauvage and J . Schacher , Latest

results from the UA2 exper iment at the CERN pp C o l l i d e r , Proc. of t h e

I n t . Europhysics Conf . on High E n e r g y Phys ics , B r i g h t o n , J u l y 1983,

p . 472 .

A . G . C l a r k , Results f rom the UA2 exper iment at t h e C E R N pp Co l l ide r ,

Proc . of the 1983 I n t . S y m p . on Lepton and Photon In teract ions a t H i g h

Energ ies , C o r n e l l , A u g u s t 1983, p. 5 3 .

3 ) P .Bagnaia et a l . , A s t u d y of high t r a n s v e r s e momentum electrons

produced in pp collisions a t 540 G e V , C E R N - E P / 8 4 / 3 9 , submit ted to

2 e i t s c h r i f t f ü r Phys ik C .

4) B . Mansoul ie, T h e UA2 appara tus a t the C E R N pp Co l l ider , Proc. of t h e

3 r d Moriond Workshop on pp phys ics ( 1 9 8 3 ) , p . 609 (edi t ions F r o n t i è r e s ) .

5) M. Dialinas et a l . , T h e v e r t e x detec tor of the U A 2 e x p e r i m e n t ,

L A L - R T / 8 3 - 1 4 ( 1 9 8 3 ) .

6) A . Beer rît a l . , T h e centra l calor imeter of t h e UA2 exper iment at the

C E R N pp Co l l ider , C E R N - E P / 8 3 - 1 7 5 ( 1 9 8 3 ) , to be publ ished in N u c l .

I n s t r . M e t h .

7) M. Banner e t a l . , Phys . Le t t . 115B ( 1 9 8 2 ) , 59 .

M. Banner et a l . , P h y s . Let t . 122B ( 1 9 8 3 ) , 322 .

8) C . Conta et a l . . T h e system of f o r w a r d - b a c k w a r d d r i f t ch?mbers in the

UAX d e t e c t o r , C E R N - E P / 8 3 - 1 7 6 ( 1 9 8 3 ) , to be pub l ished in N u c l . I n s t r .

M e t h .

9 ) K. Borer e t a l . , Mut t i tube propor t iona l chambers f o r t h e localization of

e lectromagnet ic showers in the UA2 de tec tor , C E R N - E P / 8 3 - 1 7 7 ( 1 9 8 3 ) , to

be publ ished in r-iucl. t n s t r . M e t h .

10) R. Batt iston e t a ! . , P h y s . L e t t . 117B ( 1 9 8 2 ) , 126.

11) P. Bagnaia et a l . , Z . P h y s . C20 ( 1 9 8 3 ) , 117.

P. Bagnaia et a l . , Phys . Le t t . 138B ( 1 9 8 4 ) , 430 .

12) P. Bagnaia et a l . , Phys . Le t t . 129B ( 1 9 8 3 ) , 130.

- 164 -

13) G . A l t a r e l l i , R . K . El l is , M . Greco a n d G. M a r t i n e i i i , V e c t o r boson

product ion at Col l iders : a theore t ica l r eappra isa l , Ref . T H . 3 8 5 1 - C E R N

( 1 9 8 4 ) .

F . Halzen a n d W. Scot t , Phys . L e t t . 78B ( 1 9 7 8 ) , 3 1 8 .

14) P. Bagnaia e t a l . , P h y s . L e t t . 139 ( 1 9 8 4 ) , 105.

A . Roussar ie , these Proceedings.

15) M. Glück et a l . , Z . Phys . C13 ( 1 9 8 2 ) , ' 1 9 .

16) Review of Par t ic le P r o p e r t i e s , P h y s . L e t t . 111B ( 1 9 8 2 ) .

17) G . Arn ison et a l . , Phys . L e t t . 129B ( 1 9 8 3 ) , 273.

18) P. M i n k o w s k i , Remarks on W produc t ion in pp coll isions at V s = 540 G e V ,

U n i v e r s i t y of Bern p r e p r i n t B U T P - 8 3 / 2 2 ( 1 9 8 4 ) , to be pub l ished in P h y s .

L e t t . B.

19) G . Arn ison et a l . , Phys . L e t t . 126.5 ( 1 9 8 3 ) , 398.

20) C . J a r l s k o g a n d F.J. Yndurain, Phys. Lett. Í02B (1983), 367 .

F. Halzen and K. M u r s u l a , Limits to t h e number of n e u t r i n o s , a comment

on Z ° d i s c o v e r y . U n i v e r s i t y of He ls ink i p r e p r i n t H U - T F T 83 -36 ( 1 9 8 3 ) .

K. H i k a s a , Count ing n e u t r i n o species at h i g h - e n e r g y p r o t o n - a n t i p r o t o n

col l is ions. U n i v e r s i t y of Wisconsin p r e p r i n t M A D / P H / 1 4 4 ( N o v . 1983 ) .

21) B. Humper t and W . L . van N e e r v e n , P h y s . Let t . 93B ( 1 9 8 0 ) , 4 5 6 .

22) D. A l b e r t , W . J . Marc iano , D. Wy le r and Z . Parsa , N u c l .

P h y s . B166 ( 1 9 8 0 ) , 460.

F . A . Berends and R. K le iss , H a r d Photon Effects in W" and Z ° d e c a y .

U n i v e r s i t y of L e i d e n , T h e N e t h e r l a n d s , N o v . 1983.

23) For a rev iew see W . J . M i r c i a n o , E lectroweak i n t e r a c t i o n s , Proc . of t h e

1983 I n t . S y m p . on Lepton and Photon In teract ion at High E n e r g i e s ,

C o r n e l l , A u g u s t 1983, p . 8 0 .

24) A . S i r l in a n d W . J . Marc iano , N u c l . P h y s . P.Î89 ( 1 9 8 1 ) , 442 .

C . L l e w e l l y n Smith and J . Wheater , P h y s . Le t t . 105B ( 1 9 8 1 ) , 486 .

- 165 -

ELECTKOWEAK INTERACTION PARAMETERS

William J . Marciano

Brookhaven National Laboratory ft. u41nn26171 Upton, New York 11973

O B T U S E

1. Standard Model Parameters 2. sln 2fl H ^ 3. W*, Z Masses and Widths 4. Radiative Z and W Decays 5. Kiggs-Top Quark Masa Connection 6. Grand Unification and New Physics 7. Comments and Speculations (A 93 GeV Pseudoscalar?)

1. STANDARD HÖDEL PARAMETERS

Let me begin by listing the presenc "best" values of some standard SU(3) C

x SU(2) L x U U ) modo! parameters').

A ^ > - l O o ! 1 ™ Mev (1.1) MS 5

o f 1 ^ ) = 127.70 ± 0.30 + ^ (» ' s ^ e V 1 C 1 - 2 >

(MS definition) (1.3)

By - 82.2 t 1.8 GeV (1.4)

- 93.2 i 1.5 GeV (1.5)

p - 1.01 i 0.02 (1.6)

m - O.Sllxío" 3

e GeV m d = 9xlD" 3 GeV a u

= 5xl0" 3 GeV (1.7a)

m = 0.106 GeV V

m g = 0.175 GeV m c = 1.25 GeV (1.7b)

m = 1 . 7 8 GeV T

m b - 4.5 GeV m t > 22 GeV (1.7c)

In addition to the above, there are 4 KM quark mixing parameters (see C, Jarlskog'a talk for a detailed discussion^) and the masa of the Hlggs scalar, mg, which Is bounded by theoretical arguments to lie In the range (see D. Wyler's talk 1J),

- 166 -

(1.8)

Subsequent sections will discuss sin 6y, ny, a% and p in detail. Here, let me make a few remarks concerning some of Che other par^úietera«

The determination of the QCD mass scale, A ^ , in Eq. (1.1) comes from MS —

radiative upsilon decay ¿' T + Ygg. That parameter is defined by MS (modified minimal subtraction) through the relationship^)

b 0 ° " "2T C U " 2 V 3 ) ( l M

*»i - - — r <51 - 1 9 N _ / 3 ) (1.9c) 1 4T T 2 F

with a s ( u ) the running MS QCD coupling and Np che number of quark flav with mass _< u. Continuity of a

8 ( v ) for all u then leads to the approximate relationship'4' (for = 36 GeV)

(6) (5) (4) (3) A : A : A : A = 27 : 63 : 100 : 130 (l.!0) MS MS MS MS

<N ) A reduction in the A uncertainties (now about a factor of 2) is in. .irtai . for

MS testing QCD and grand unified theories (see section 6 ) . Quarkonia spectroscopy and .lattice calculations offer the best possibility of reducing the present errors.

Th U - my, is obtained ¿rom the usual fine structure constant via the perturbatlve relationship^)

a~ l(u) = a" 1 - |_ I Q f 2 i n {]j/m^ + 1__ + ^

where th.a summation is over all charged fermions with mass, nf < U. To incorporate strong Interaction effects, the light quark contribution to Eq. (1.11) is actually obtained from a dispersive analysis of e +e~ + hadrons rather than the percurbative corrections**). Most of the uncertainty in Eq- (1.2) i.e. -0.30, stems from e +e~ data unceri. -ties. The 7.3X increase in a(u) in going from u > 0 to my is very Impartant. That effect Is the dominant radiative correction to the V* and Z mass formulas^) (ae¿ section 3)* It

7 GeV < rüg < 1 TeV

- 167 -

is, therefore, reassuring that QED tests at PEP and PETRA verify the running of a(u) by effectively measuring a(/s). Indeed » I fiad from a cursory examination of PETRA data

a~V>*.5 GeV) = 130 ± 2 (1.12)

which la in agreement with the prediction in Eq. (1.11). The quark masses In Eq. (7) are taken from the cocprehensive review by

Gasser and Leutwyler?) while the bound on m^ comes from täTRA data. An important development is the long b-quark lifetime which was measured at PEP last year to be =* 1 0 " ^ sec. Combining t^, the branching ratio r = r(b+uX)/ r(b+cX) < 0.05 and the CP violating e parameter, tíinsparg, Glashow and Wise**) derived an Interesting bound on m c

( 1 - 1 3 )

Their result suggests a large roc or a much larger value for B than the conventional 0.33. Some implications of large u c (> njj/2) will be discussed In section 5.

There are two popular definitions of the renormalized weak mixing angle. The quantity sln Z9y(my) given in Eq. (1.5) is defined by MS (modified minimal subtraction) and e'aluateù at u « ray. It is very useful for model Independent discussions and analysis of grand unified theories'*). Indeed, In Che latter case It makes sense to define all couplings by the san - renormalization prescription. A second definition")

sln 2 e H = 1 - m,//*./ (2.1)

is appropriate only for the standard model with p « 1. Nevertheless, by the very nature of Its definition, it is well suited for discussions Involving and m z . These two definitions differ by 0(a) corrections which for m^ " m z are numerically^^

sin 2 e w = 1.006 ain 2 3 (n^) (2.2)

(The exact relationship Is given in Ref. 10.) The 0(a) radiative corrections to deep-inelastic v y-N scattering and el

asymmetry experiments were calculated in 1981. They allowed a precise determination of ain^ötf, 9» 1 1)

- 168 -

8in 29 M = 0.217 ± 0.014 (1981 vN world average) (2.3)

sin2fl„ = 0.218 ± 0.020 w

(eD asymmetry) (2.4)

Other more recent measurementa of sin 2Gy from v uN, vê, atomic parity violation, e +e" + u +u~ etc. are all consistent with Eqs. (2.3) and (2.4) but they I- e larger errors.

Combining deep-inelastic neutrino and antineutrino data (Ry and R ^ ) , one

where p = my 2/m z2co8 2 e t j should be exactly 1 in the standard model with

minimal Higgs structure. This determination lends great support to the standard model. However, I should interject a word of caution. The small errors in Eq. (2.5) result from the extremely sensitive dependence of on p. That sensitivity also pertains to QCD effects and sea quark contributions. Hence their theoretical error may add somewhat to the uncertainty in Eq. (2.5).

3. W* AND Z MASSES AND WIDTHS

With the discovery of the W* and Z now completed, it becomes important as a next step to test the standard model by precise measurements of their masses and decay properties. In that regard, radiative corrections to vector boson masses and widths are timely and interesting.

To obtain the 0(a) corrections to the W* and Z mass formulas requires a complete one-loop calculation of the y, W- and Z self-energies aa well as the full 0(a) corrections to rauon decay. Combining those calculations

finds 1 2» 1 3>

p = 1.02 i 0.02 (2.5)

gives-.5,9,13,<4)

(3.1>

m_ = m-j/cosfl. w where Ar denotes the complete 0(a) radiative corrections.

a 1/137.035963 (3.3)

and G u is the muon decay constant which is coaventioaally defined byl^)

(3.4)

- 1 6 9 -

Recent measurement of the muon lifetime now yields a new (slightly higher) value 1 6'

G - 1.16638 ± 0.00002 x 10" s GeV _ J (3.5) V

From Eqs. (3.I)-(3.5) one obtains

_ 37.2804 ± 0.0003 „ „ . slno w(l-Ar)

(3.6)

Setting Ar = 0 would give the uncorrected predictions fDr and mg as functions of sin 2(5 w. Including the calculated Ar significantly shifts those predictions because Ar is quite large due to the vacuum polarization effects in Eq. (1.11) for y - ni[j. The complete analytic expression for or is given in Ref. 9. Numerically, for m t = 36 GeV ax.1 ray = m z, one f l n d s ^ » 1 ^

Ar = 0.0696 ± 0.0020 (3.7)

where the uncertainty comes from hadronic vacuum polarization effects, this value into Eq. (3.6) yields the "corrected" predictions

„ 38.65 t 0.04 GeV °Hj sin8„

Putting

(3.8)

= 77.30 ± 0.08 GeV "z sin 2e„ (3.9)

Given a value for sinÔw one can predict my and mg; or inverting these formulas, a determination of my or mg yields sin 26y.

Recently updated values 1 J 1 ^ for my and m z are given in Table I.

1 and UA2 Values for and

UAl OA2 Average

"^(GeV) 80.911.5±2.4 83.1*1.9*1.3 82.2*1.8

o^GeV) 95,1*1.5*2.9 92.7*1.0*1.4 93.2*1.5

The average masa values in Table I when used in conjunction with Eqs. (3.8) and (3.9) yield (both v%¡ and m z give the same aln26(j)

sin 2 e w - 0.221 ± 0*007 (3.10)

- 1 7 0 -

whicfr) is in excellent agreement with the 19B1 scattering resulta in £qs. (2.3) and (2.4). The value for Bln28w(mH-) given in Eq. (1.3) was obtained by computing the weighted average of these various independent determinations and dividing by 1.006 (see Eq. (2.2)).

One can also determine s i n 2 8 u = 1 - m ^ 2 / m 2 2 directly from mu and mz without using Ar. Prom Table I, one finds

s i n 2 8 H = 1 - rn/Zmj2 - 0.222 * 0.020 (3.1!)

The agreement between Eqs. (3.10) and (3.11) provides strong support for Che standard model.

Alberto Sirlin and I recently examined how one could test the standard model by precise determinations of W*1 and Z masses. Eliminating 9y by combining Eqs. (3.1) anrl (3.2), we obtained the following uceful formulas*^

1 + Jl~ 1/2 ( 3 . 1 2 )

• v /r (3.13)

"z - '

1 + fl ( 3 . K )

Ar . l - (37.28 GeV) Z f . 2 , 2 .

" i l 1 " " » ' " ! »

( 3 . 1 5 )

A 2 / * / ) (3.16)

A . 37.280 GeV . 3 8 . 6 5 G e V < 3 . (l - o r ) 1 ' 2

These formulas are used to compare che UAl and UA2 results with theoretical expectations in Table II. (The P value in Eq. (1.6) was obtained by averaging the values in the table witii Eq. (2.S).)

TABLE II. Comparison of Che UAl and UA2 results with standard model expectations for sin 2«^ = 0.220+0,006. 100% correlation in the my and m z systematic » tcertainties is assumed.

UAl UA2 Standard Model with sinV w

- 0.220 ± 0.006

By (GeV) 80.9 ± 1.5 i 2.4 83.1 ± 1.9 ± 1.3 82.4 ± 1.1

(GeV) 95.1 ± 1.5 ± 2.9 92.7 ± 1.0 + 1.4 93.3 + 0.9

- m,, (GeV) 14.2 ± 2.1 ± 0.4 9.6 ± 2.1 ± 0.2 10.9 i 0.2

4r 0.232 ± 0.079 ± 0.045 -0.025 ± 0.172 ± 0.032 0.0696 t 0.0020

P 0.938 ± 0.038 ± 0.016 1.025 ± 0.040 ± 0.009 1

, •>_ ,38.65 GeV,2 0.228 ± 0.008 ± 0.014 0.216 ± 0.010 ± 0.007 0.220 ± 0.006

aln2e w - 1 - mÂn/ 0.276 ± 0.035 0.196 ± 0.040 0.220 ± 0.006

- 172 -

Eventually, m z will be measured to within +0.1 GeV at LEP while the DO detector1**) at Tevatron (if approved) promisee to measure to within ±0,05 GeV, Such measurements will determine sin 2fl w to within ¿0.00041 Using both masses as Input will determine p to within ±0.002 and the radiative correction Ar to within ±0.003. At that level one is certainly probing radiative corrections. Indeed such measurements would be sensitive to new phyBics present only as loop effects.

Let me complete this section with an update of the predicted W* and Z decay widths. For sin 2flu • 0.22 and m t SÍ 36 GeV, one expects (Including radiative corrections and effects)*^)

r(W * all) = r(Z .* all) = 2.80 GeV (3.20)

Deviations from these predictions could signal new physics euch as Ath generation mixing, larger mc, additional neutrinos etc. For example, the number of neutrino species, N y , Is given by*")

2.8 GeV 0.178 GeV (3.21)

The UA2 groupie has already made a good determination of r(W+all)/r(Z-*all) which when combined with QCD gives N y < 6 (902 CL). The DO detector 1 8) is capable of measuring that ratio to better than 10%.

4 . RADIATIVE Z m d W* DECAYS

Out of the 13 Z + e +e" or u +u~ candidate events In the UAl and UA2 data, 3 have a distinct energetic photon in the decay products. That represents a 23%

branching fraction for radiative events; much too large to be bremastrahlung. Even more -mysterious are new v + missing energy events that could represent

Deviations from the standard model predictions could signal new interesting physics or provide information regarding a very heavy t or H. Indeed, one finds 1 3) Ar - 0.0696+S where

„ cos 2 Qu m 2

5 = Zp. , » » 36 CeV (3.18)

iOTT . U . „ 2 C

6 " ^ s i k - 1 " < ° h 2 / ° z 2 ) • v ° z ( 3 , 1 9 )

w

- 173 -

A conservative view 1B that the flrBt three events are merely bremsetrahlung and that the branching fraction will decrease as the statistics Improve• To address that possibility, I will give a general branching ratio formula for the

bremsstrahlung decays B •*• fif2Y where B is a generic gauge boson with electric charge Qi*KJa• The percentage of events in which the photon carries a fraction of the total energy Ey/m^ > £ and has an opening angle greater than 25 relative to any charged fennion in the final state is given by (for ö,e < l)21*)

r(B*f,f 2T) Q l 2 + < Í 2 2 r Tl 2 7,

r 2[*ii 2e + 5/6] + 0(6) + 0(e)) (4.1)

For 2 + e +e~Y and W * e«Y this formula gives r < Z * e + e r ) . S [(4 tn 2e + 3) In i + I'- - I]

r ( Z * e + 0 + r(z->-e + e-r) (4.2)

W y J i X , ) - ^ ' * 2 E + 3 ) - « + 2»-2- + i - - 4 r ] (4.3)

If we cake c - 0.1 (Ey > 9 GeV) and 2<5 > 10° (0.17 radians), these branching fractions are 0.023 and 0.01. The latter is consistent with the lack of observation of H + eVY while the Z * e +e"Y prediction is about 1/10 of the observation. It will be interesting to see what happens with increased stat Jstics.

5 . HIGGS - TOP QUARK MASS COffiECTIOH

The Higgs scalar and top quark are the only missing particles of the standard model. In time, the top quark should be discovered either by W>tb or tt production (unless it is very heavy). On the other hand, the Higgs scalar may be more elusive. If < 60 GeV, it should be observable through the decays Z •»• HP +u~ or HY. Somewhat higher masses (up to = 100 GeV) may be detectable at LEP II via e +e~ -*• ZH if high luminosity = 1 0 3 2 c m - 2 sec - 1 ia achieved. On the other end of the scale, for m^ very large, the Higga scalar can be best produced by gluon-gluon fusion at a hadron-hadron collider. If m^ > 2my, then the decay H * wHt" should dominate and provide a distinct signal.

What If my < mjj; < 2m« = 166 GeV? W.-Y. Keung and I recently considered that possibility 2*). We compared the rates for H •*• W^X and H •*• qq

where X is anything and q is a generic heavy quark. Our result

1 7 4

líSíOi . _ 2 _ . ^ ! ) - 3 / 2 F ( S ) (5.1a) r(H*q5) 4usln 8 W m

F ( e ) - { 3<l-e«W) a r c c 0 6 ( 3 ¿ - l j . ( 1. e2 ) C|l e2 .

- 3(1 - 6e 2 + 4 E 4 ) Än e} (5.1b)

where £ = nty^H* This ratio can be significant if e is near 1/2 and is not too large. If ra^ « m t - 36 GeV, then this branching ratio exceeds 10% only for mn > 160 Gevi On the other hand, if m t > mq/2 ( then we need only compare with H * bb. In that case T(H + tf~X)/r<H + all) exceeds .10% for my > 125 GeV and 50% for m-j > 150 GeV. Thia point is illustrated in Fig. 1. (For further details aee Ref, 21.)

If the branching ratio for H + W^X is significant, one could try to detect this mode via leptonlc decays W •»- ev or uv with X • 2 hadronic jetB. Of course, one still needs a significant number of Hlggs acalare. They can be beat produced at a high-energy high-luminosity hadron collider.

Is the scenario > 125 GeV and m t > a realistic possibility? A recent analysis by Beg, Panagiotskopoulos and Sirlin 2 2) based on theoretical consistency in the standard model suggests that mg > 125 GeV may actually require that m t (or some more massive fermion) be greater than m^/2.

Could a Higgs scalar with m^ in the range 80 ** 160 GeV have been produced at the CERN pp collider? Unfortunately, the cross-section for pp * H via gluon fusion 1B quite small at a ^s * 540 GeV collider. The cross-section Is given

by23) -Än/r

2 o-(pp-H) * r(tfgg) / dyTF r(/ïe y)F r(/Te" y) (5.2)

T = mjj2/s , F Q - Gluoo distribution function

where r(H->-gg) is the 2 gluon decay rate of the H. For the standard model this cross-section is approximated b y z D

a a 4xl0" 3 6 exp[- mg/21 GeVjcm 2, for 80 GeV < m H < 160 GeV (5.3)

(There may be a factor of 10 uncertainty in this formula due to uncertainties in F Q . ) Given the total integrated luminosity at CERN^ e 1.3*10 3 5 c m - 2 , one

- 1 7 5 -

Fig 4 1 Higgs decay branching ratios m c > mg/2.

- 176 -

expeccs about 0,01 events for îr * q 0 GeV and 0*0004 events for i £ = 150 GeV* If for some reason r(H*gg) Is ouch greater than the standard model prediction, then the production cross-section can be enhanced. However,

3

increasing it by a factor of 10 to make H production at present CERN luminosities viable would elevate H+gg to the dominant decay mode* That would still make its observation difficult, since one would have to find it in the 2 jet cross-section.

6. GRASD UNIFICATION Affi> JBtf FBYSICS

Grand unified theories (GUTS) provide Important motivation for precise measurements of the standard model parameters. To illustrate this point, I give in Table III predictions of the "minimal" SU(5) model 2 4) (assuming no new physics between and the unification mass my).

TABLE III. Minimal SU(5) model predictions using aduy) • 1/127.7 and values for lS^} as input. 2 5)

MS

(4) AMS m Z m X T

P

(MeV) (GeV) (GeV) (GeV) (yr)

25 0.226 81.3 92.3 3*10 1 3 3 * 1 0 2 6 ± 1

50 0.222 82.0 92.8 6.2*10 1 3 3 X 1 0 2 7 Î I

100 0.218 B2.8 93.6 1.3*10 U 5 X 1 0 2 8 ± 1

200 0.214 83.5 94.3 2 . 7 » 1 0 W 5 x l 0 2 9 ± 1

400 0.210 84.3 94.9 5.5x10 1 4 1 1 + 1

For Agg = 100 MeV, the sin 9y, niy and predictions are in good agreement with experiment. However, the predicted proton lifetime r p > is well below the experimental bound2**) Tp > 1 0 3 Z yr. That bound requires a unification mass ntjr 10 GeV. The value of c a n Increased only by appending new physics between mjj and mj(. (Of course one always anticipated new physics in that domain.) The new physics could be additional relatively light Higgs scalars, fermions, technicolor, supersymmetry, new gauge bosonB, etc.

As ne» physics is uncovered above ray, the GUT predictions will be modified. It is, therefore, important to have precise measurements of

177 -

8±n 2 e w etc. available to teat the altered GUT. Of course, it should be obvious that continued searches for proton decay must remain a very high priority.

7 . CONKERS AND SPECULATIONS (A 9 3 GeV Pseudosca lar?)

Discovery of the W± and Z haa provided signl£leant evidence in support of the standard nodel. Precise measurements of their masses and decay widths will next test the model at the level of its quantum radiative corrections, perhaps unveiling new physics along the way. What else is left? The top quark is certainly waiting to be found and the elusive Higgs scalar (or some alternative dynamics) will be the object of an intense search. Rut what other physics is on the horizon? Grand unified theories now require some new physics; but they don't specify what it should be. We will have to be guided by experiment.

At this meeting we have learned about exciting events found by the UAl and UA2 collaborations 1) which do not seem to have a simple explanation in the framework of the standard model. The UAl jet + missing energy and UA2 W* + jet events are suggestive of a new phenomenon opening up at n 150 GeV and manifesting itself with very large cross-sections. They seem to imply that the present generation of pp colliders will provide additional excitement. Hopefully, CERN and Fermilab (starting in 1986) will fully exploit the potential of their colliders.

Another interesting UAl event has y + missing energy at 100±10 GeV, (there are other candidates) 1^). It it related to the anomalous e"*e~Y A N A " U + U ~ Y

events previously uncovered? I would like to conclude this talk with a speculation by suggesting that these radiative events are not Z decays. Perhaps Instead, there is a new pseudoscalar particle (I will call it P) which nas a mass near m^ I.e. at about 93 GeV.^?) The P could be produced by gluon-gluon fusion (the Pgg coupling must be large). It could then decay into ffy via a virtual Z (see Fig. 2 ) . (p+ ff is hellclty suppressed.) For such decays to be competitive with P+gTuon+gluon, the PZy coupling must also be very big. The near degeneracy of the P and Z should enhance this vertex; however, such a scenario would most naturally occur in a composite model where the 2 ia a very tightly bound QQ vector state and the P is a *S 0 onium. (In that CBBe I would rename P the nz-)

For radiative decays P*ffY, dominated by the amplitude in Fig. 2, one expects a photon spectrum of the form (for mp « m ^ ) ^ )

1 _ dr(P>ff r) . cltrxhlTMl2 , 0 < * < 1 (7.1)

i-(p*ffY) 1 1

where x - 2E Y/mp, F(x) is e form factor that depends on the dynamics of the

- 178 -

Flg. 2

- 1 7 9 -

PZv vertex and G la a normalization constant

1

0

C" 1 - / dx (x-x 2)|*(x)| 2 (7.2)

Approximating F(x) by a constant leads to a distribution symmetric about the x - 1/2 (Ey - mp/4) maxinum. That would imply an average photon energy <E V> • ap/4 s 23 GeV (In the P rest system) and an Invariant mass for the ff pair at m p < l - x ) ^ 2 which is peaked at mp//2 * 66 GeV. The characteristics of such decays closely resemble the UA1 and UA2 e"*"e~Y, u +u~y (vvy) events. They are very distinct from the 1/x bremsstrahlung spectrum which tends to be collinear with charged fermions.

The above speculation has several implications which can be used to test it. They are: 1> r(P+ b

+y~Y> " r(P+e +e"» = l / 6 r(P+wy)* 2) ?(P+2 jets+^) « 24 r(P+e +e~Y). 3) P+2 gluon jets should be prevalent In the 2 jet cross-aection. The radiative events vvy and 2 jets+Y should be looked for In the present data sample. The 2 jet decays would at present be difficult to separate from background.

It would be amusing if the P particle does exist. In chat case history

would be repeating itaelf. We would be experiencing a replay of the u-»

discovery as we disentangle the F and Z.

ACKNOWLEDGMENT

Work supported by Department of Energy Contract Ho. DE-ACO2-76CH00016.

1. Talks in these proceedings.

2 . G.P. Lepage, Proc. of the 1983 Lepton-Photon Conf., Cornell University.

3. W.A. Bardeen, A. Buras, D. Duke and T. Muta, Phys. Rev. Dlfl 3998 (197B). 4. W„ Bernreuther and W. Wetzel, Nucl. Phys. B197.» 2 2 6 (1983); W, Bernreuther,

Ann. of Phys. 151, 127 (1983); W. Marciano, Phys. Rev. D29, 580 (1984).

5. W. Marciano, Phys. Rev. D20, 274 (1979).

6. W. Marciano and A. Sirlin in Proc. of the Second Workshop on Grand Unification, Ann Arbor, 1981, Eels. J, Level lie, L. Sulak and D. linger, (Birkhauser, Boston); Fhys. Rev. Lett. 46, 163 (1981).

7. J. Gasser and H. Leutwyler, Phys. Rep. J 7 , 77 (1982).

- 1 8 0 -

8. P. Ginsparg, S. Glaahow and H. W a e , Phys. Rev. Lett. 50, 1415 (1983).

9. A. Slrlln, Phys. Rev. 022, 971 (1980); W. Marciano and A. Slrlln, Phys. Rev. D22, 2695 (1980).

10. S. Sarantaltos, A. Sirlln and W. Marciano, Nucl. Phys. B217. 84 (1983).

11. A. Sirlln and W. Marciano, Nucl. Phys. P.189, 442 (1981); C. Llewellyn Smith and J. Wheater, Phys. Lett. 105B, 486 (1981).

12. J. Kim, P. Langacker, M. Levine, and H. Williams, Rev. Mod. PhyB, 53, 211 (19B0) r

13. W.J. Marciano and A. Sirlin, Phys. Rev. D29, 945 (1984).

14. F. Antonelli, M. Conaoli and G. Corbo, Phys. Lett. 91B, ':0 (1980); M. Veltman, Ibid. 91B, 95 (1980); K. Aoki et al., Prog, lheor. Phys. 65, 1001 (1981); D. Bardin, P. Christova and O. Fedorenko, Nucl. Phys. B197, 1 (1982).

15. A. Sirlin, Phys. Rev. D29, 89 (1984).

16. K.L. Giovanetti et al., Phys. Rev. D29, 343 (1984).

17. Talks by C. Rubbla and J. Schacher in these proceedings.

18. Talk by M. Marx in these proceedings.

19. D. Albert, W. Marciano, D. Wyler and Z. Paraa, Nucl. Phys. B166, 460 (1980); W. Marciano and Z. Parsa, Proc. AIP DPF Summer Study, Snowmsss, 1982, pl55.

20. The formula in Eq. (4.1) is a simple extension of similar expressions In Ref. 19.

21. W.-Y. Keung and W. Marciano, BNL preprint 34578, 1984.

22. M.A.B. Bég, C. Panagiotakopoulos and A. Sirlin, Phys. Rev. Lett. 52, 883 (1984).

23. N. Georgl, S. Glaehow, M. Machacek and D. Nanopoulos, Phys. Rev. Lett. 40, 692 (1978).

24. H. Georgl and S. Glushow, Phys. Rev. Lett. 32^ 438 (1974); H. Georgl, H. Qulnn and S. Weinberg, ibid. 33, 451 (1974).

25. W. Marciano, Proc. of the VPI Miniconference on Low Energy Tests of Conservation Laws, 19B3.

26. IMB collaboration, R. Blonta et al., Phys. Rev. Lett. 5¿, 27 (1983); Published talks by 1MB members.

27. W. Marciano, unpublished.

28. L. Amelios, W. Marciano and 2. Parsa, Nucl. Phys. B196, 365 (1982).

- 1 8 1 -

(W~, 21 Î PRODUCTION FROM pp AND DECAY

D: 8 4 1 Q Q 2 6 1 B 0

Peter Minkowski

institut für Theoretische Physik

Universität Bern

Sidlerstrasse 5, CH-BERN, Switzerland

'"A Abstract: Electroweak parameters at the scale of 1 0 0 GeV are presented and put

to work in the calculation of cross sections for w and Z production from pp col

lisions. {

1 . SETTING FOOT OH THE 1 0 0 GeV PLATEAU

We shall resume coupling constants and characteristic masses at a reference

scale of g ^ m which we fix to the initial value of 1 0 0 GeV;

1 8 2

a,? - ( . l o r * ! ) Q z r / / 3 ) 6 t s * i

/ . o í r

/•oír

// (í?. C2«]= 0.2/ ST " a.u The Fermi constant is obtained from n decay

r

The triad of coupling constants referring to the (standard) SU3 cxSU2 LxUl gauga groups (g , g, g') are rescaled from their values at zero momentum transfer

e 2 3

(a = — ) to the 100 GeV scale as a consequence of radiative corrections through the vacuum polarization referring to W-H, Z-Z and Y-Y currents*.

+ // <

I

<1.3)

We rescale the strong coupling constant from a reference scale of 5 GeV to lOOGeV using the effective four flavour formula to two loops

«x ( 1 - ^ ^ s * -

- 1 8 4 -

A — = 0 . 1 G e V MS

A = 0 . 2 G e V A = 0 . 5 G e V

a s

0 . 0 9 4 0 . 1 0 3 0 . 1 1 9

y - 1 0 0 G e V

*s 1 . 0 9 1 . 1 4 1 . 2 2

a s

0 . 1 5 5 0 . 1 8 4 0 . 2 4 7

V = 5 G e V

9 s 1 . 4 0 1 . 5 2 1 . 7 6

T a b l e 1 : s t r o n g c o u p l i n g c o n s t a n t s a » g g = / 4 n a , f o r A — = 0 . 1 , 0 . 2 , 0 . 5 GeV e v o l v i n g f o r f o u r e f f e c t i v e f l a v o u r s f r o m \i = 5 GeV t o y = 1 0 0 G e V .

2

F o r s i n e w = 0 . 2 1 5 , A r = 0 . 0 7 a n d y = 1 0 0 G e V , A — = 0 . 1 GeV t h e c o u p l i n g

c o n s t a n t s a r e s h o w n i n T a b l e 2.

SU3 SU2 0 1 e . m .

s 1 0 41T 2 7 . 5 0 3 4 * 6 0 . 2 5 3 4 7 . 9 7

g « 1 . 0 9 g = 0 . 6 7 6 g = 0 . 3 5 4 e = 0 . 3 1 3

T a b l e 2 : C o u p l i n g c o n s t a n t s r e l a t i v e t o S " 3 c , S 0 2 L , U l a t t h e 1 0 0 G e V r e f e r e n c e

I n T a b l e 1 w e c o m p a r e = 5 GeV w i t h u = 1 0 0 G s V f o r A — = 0 . 1 , 0 . 2 a n d

0 . 5 GeV r e s p e c t i v e l y . T h e e v o l u t i o n o f ^ - a c c o r d i n g t o e q . ( 1 . 4 ) i s s h o w n i n s

F i g . l -

- 185 -

. -2 5 -,2 _ We n o t e t h a t a , , — * - — a n a — a a r e c o n s t r a i n e d t o b e e q u a l i n t h e s y m -s 4 ir 3 âïï 3

me t r y l i m i t of a u n i f y i n g g a u g e g r o u p f o r w h i c h o n e f e r m i o n f a m i l y i s a c o m p l e t e

r e p r e s e n t a t i o n ( n o t n e c e s s a r i l y i r r e d u c i b l e )

2 . M A S S , W I D T H S , B P A N C 3 I H G F R A C T I O N S OF W , Z

+ a ) W

S e t t i n g t h e e l e c t r o w e a k p a r a m s t e r t o t h e v a l u e s g i v e n i n T a b l e 2 w e h a v e

* i w = ( 8 2 . 2 1 ) M >

F o r t h e h a d r o n i c d e c a y c h a n n e l s W •*• d u , s c , t h e w i d t h t o o r d e r a g i s c a l c u l a t e d

t c b e , n e g l e c c i i x g a l l q u a r k m a s s e s r e l a t i v e t o m w :

f ¿ /C77 \ TT /

(2.2)

I n t h e t b s y s t e m t h e p h a s e s p a c e i s r e d u c e d s i g n i f i c a n t l y b y t h e m a s s o f t h e t o p

T (hU t u ¿ ) fu Jía-jf/- V

Çu *1 Y/- jal y *t°i°*i' l /( *¿ / '- j. £<// **i - *o < w y

- 1 8 6 -

TI¿J À a ¿rol, j- )- 1 -

2 Jv? y f7<¡(/ nt tÔ (2.4)

The total width and branching fractions :.nto (e v^) then are

(2.6)

We choose as representative reduction factor 0.7 and set

- 1 8 7 -

" V " " ~ / To T ö — / /. 02f ' t : * *W / ( 2 . 7 )

F o r t h e h a d r o n i c d e c a y c h a n n e l s we d i s t i n g u i s h

T r u s t i n g £>CD p e r t u r b a t i o n t h e o r y a t t h e g a u g e b o s o n m a s s s c a l e w e o b t a i n

We note that the uncertainty in the mass range of the top quark brings a

2 0 * u n c e r t a i n t y i n t h e b r a n c h i n g f r a c t i o n i n t o t r i e e " v m o d e a n d t h u s a c o r -e

r e s p o n d i n g u n c e r t a i n t y i n t h e e v a l u a t i o n o f t h e p r o d u c t i o n c r o s s s e c t i o n f o r

t h e r e a c t i o n

?p —-> i j ' r

b) Z

The mass of the z ooson for the electroweak parameters chosen is given

- 188

ü t* Cn+0( C C . (2.8>

Similarly we have for the = - V2 flavours d, s, b neglecting in , ms, re

lative to m

/ 1 2 TT öpr ^ w

The reduction of the width for » t ^ 0 relative to the flavours c, u is given by

i + /•*. J

- 1 8 9

• * ».

<2.10) 2 J

The suppression factor in eq. ( 2.10) for m = 30 and 40 GeV respectively amounts

t o

0.2 O Alf. =• Ôfol/ (2.!

We obtaiii for the hadronic width of 3;

/ 3 3 7 . 0 M t i /

Il 62f S ftte.(/ o (2. 1 2 )

^ 3 2.9 Air¡/

1 9 0

= 7? 7.1 Af?¿/

3 é 7 T 6 ° j * J , ,

ZÏSTJ.2 fTcl/ «4t~>

? - j 2 / ¿ j . o Ait!/ Af^Jffiei/ 3 o <P9. / rte" — °

'3.2 Y. h,t •> *<ir/z

3^(ï-)e+e~J - / 3 . 2 y o % ± 2 r t e i /

- 1 9 1 -

+

We c o n s i d e r t h e c r o s s s e c t i o n s f o r W a n d 2 p r o d u c t i o n f r o m p p i n c l u d i n g QCD

; o i 2 2

c o r r e c t i o n s o f order a (Q ^ m ) ^ 0 \0, f i x i n g the A— ( 4 f l a v o u r s ) parameter = Z — MS t o b e 0 . 1 GeV

F o r t h e O ( o ( ° ) w p r o d u c t i o n c r o s s s e c t i o n r e s t r i c t i n g o v x s e l v e s t o t h e s u b -

p r o c e s s d + u w" -> e " v

cr .

? * 1 9

2 / g 2 * ? v

2

F o r A = 0 . 1 a n d 0 . 2 G e V we o b t a i n u s i n g t h e s t r u c t u r e f u n c t i o n s o f r e f . 5

122/> 4

3 . PRODUCTION OF H ~ AND Z - CROSS S E C T I O N S AND D I S T R I B O T I O M S

2

T h e p a r a m e t e r s w h i c h w e d e t e r m i n e d f r o m t h e r e f e r e n c e v a l u e s s i n Q w = 0 . 2 1 5 ,

m^ = 8 3 . 2 2 G e V , ra^ = 9 3 . 9 2 G e V a n d m t * 3 5 GeV i m p l y r^° f c « 2 . 9 G e V , r ^ 0 t ^ 2 . 9 G e V .

- 192 -Comparing with the results obtained in analytic form modulo the leptonic

4) branching fraction of W by Altarellt- Ellis, Greco and Hartinelli we see that the difference in the resulting cross section is due to différent re-scaled structure functions. However in the subsequent evaluation of the °tCtS correction we differ from the above work in that we do not define through that order the differential quark densities by the deep inelastic structure function

Although I äiffer in the choice of structure functions from Altajrelli et al. with respect to their definition, their specific value as rescaled from

2 deep inelastic scattering at small values of Q is a matter of judicious approx-

2 imation in the absence of measurement at the relevant Q values, which are hopefully forthcoming at the HERA facility.

The process of hard gluon bremsstrahlung within specified kinematic limits for the emission of a gluon jet, which is understood as observable in principle refers to the subprocess

The differential reduced cross section in eg. (3.3) contains infrared and col-linear divergent terms and thus necessarily applies within a safe region to be defined only

( 3 . 3 )

*3 f~K i

'J Cor Jt(*fj

/ *) J - azimuthal angle between the transverse momenta * of e and the gluon jet.

The region of safe gluon jet momenta and angle we choose as follows

The corrections due to virtual gluon contributions to 0*^ and the redefinition of quark structure functions can be discussed as dependent on the Kinematic

- 1 9 4 -

boundaries since the remaining contributions cancel within the claimed accuracy of 20% relative to the hard gluon emission cross section. We obtain

for the ratio of 0(a°) Z to W production cross sections we find

* / G"

Thus we estimate

è //r j>&

These cross sections are to be compared with the experimental results ^ ' '

F f l U ^ - / = J r,_ ,

8)

( 7 ) ) / " / * * o * ? o 7 ¿ t/AT. (3.9)

- 1 9 5 -

We calculate the number of events expected In the DA2 detector (forward and central detectors) given the avoce cross sections and the distributions in ref. 2 with the signature

In eq. (3.10) the distributions in transverse momentum and rapidity of the charged leptons as generated by a Monte Carlo program and yield for the kinematic constraints in angle and transverse momentum of the charged lepton above the reduction fraotor 0.65. H denotes the probability that within the given exp kinematic domain an electron (positron) is actually detected by the UA2 apparatus.

We take the average between the cross sections calculated forA= 0.1 and 0.2 GeV respectively and obtain 7*

- 196 •

background estimate or" 1.5 events and of 2.5 events due to misinterpreted S decay. Due to the similar decay distributions we also estimate the n-imber of z events for which one of the charged leptons falls within the kinematic region above.

The probability that the second electron is not detected we denote by p

3>~re°y e, » r / » 3./?J

e, „,;t, s. n J 4 ( o . 2 j [ o . b r J + o . i r ^ o . yj>

estimate. From eq. (3.13) it follows

We show the distribution of Monte Corlo generated events in transverse intim, of the

Figs. 2 and 3. momentum of the gauge boson for W, Z production for \p^f K | ^ GeV in

acknowledgements : i should like to thank the members of the v&2 group of Bern, in particular J. Schacher, H. Hänni and B. Hahn for many illuminating discussions. Thanks are also due to Z. Kunszt, I. Crewther-Rose and R. Stierlin for their critical suggestions and help with the numerical calculations.

- 197 -

R e f e r e n c e s

1 ) A . S i r l i n , P h y s . R s v . D2p_ ( 1 9 8 0 ) 9 7 1 i W . J . M a r c i a n o a n d A . S i r l i n , P h y s . R e v . D 2 2 ( 1 9 8 0 ) 2 6 9 5 ? s e e a l s o W . J . M a r c i a n o , c o n t r i b u t i o n t o t h e s e p r o c e e d i n g s .

2 ) P . M i n k o w s k i , i n " T h e o r y o f F u n d a m e n t a l I n t e r a c t i o n s 1 9 8 2 " , L X X X I C o r s o , S o c . i t a l i a n a d i F í s i c a , B o l o g n a , I t a l y .

3 ) D . A l b e r t , W . J . M a r c i a n o , D . W y l e r a n d Z . P a r s a , N u c l . P h y s . B 1 6 6 ( 1 9 8 0 ) 4 6 0 .

4 ) F . Pa± g e I S A J e t p r o g r a m , BNL 2 9 7 7 - 7 ( 1 9 8 1 ) ? p. c h i a p p e t t a a n d M . P e r r o t t e t , M a r s e i l l e p r e p r i n t C P T - B 3 P - 1 5 2 5 ( 1 9 8 3 ) G. Ä l t a r e l l i , B.K. E l l i s , M . G r e c o a n d G . M a r t i n e i i i , CERN p r e p r i n t T H . 3 8 5 1 ( 1 9 8 4 ) ;

P . M i n k o w s k i , B e r n p r e p r i n t B U T P - 8 3 / 2 2 ( 1 9 8 4 ) t B. H u m p e r t a n d W . L . v a n N e e r v e n , P h y s . l e t f c . 9 3 B (1980) 4 5 f a j B . H u m p e r t , p r i v a t e c o m m u n i c a t i o n .

5 ) P . S a l a t i a n d j . c . W a l l e t , A n n e c y p r e p r i n t L A P P - T H - 6 4 ( 1 9 8 2 ) .

6 ) U A l C o l l a b o r a t i o n , C . R u b b i a , c o n t r i b u t i o n t o t h e s e p r o c e e d i n g s ,

7 ) UA2 C o l l a b o r a t i o n , J . S c h a c h e r , c o n t r i b u t i o n t o t h e s e p r o c e e d i n g s .

8 ) R . K . E l l i s , c o n t r i b u t i o n t o t h e s e p r o c e e d i n g s ,

9 ) D . W . D u k e and J . F . O w e n s , F l o r i d a S t a t e U n i v . p r e p r i n t F S Ü - H E P 6 3 1 1 1 5 ( 1 9 8 4 ) .

- 1 9 8 -

F i g u r e c a p t i o n s

U = 1 0 0 G e V .

d a F i g . 2 : D i f f e r e n t i a l c r o s s s e c t i o n - — — f o r t h e p r o c è s p + p -*• W + j e t + X

Pm

^ — ? e _V ai»d (

2 0 < 6 < 1 6 0

- e - w

T h e d a s h e d c u r v e c o r r e s p o n d s t o t h e p^, d i s t r i b u t i o n a c c o r d i n g t o 9 ) R . K . E l l i s p r e s e n t e d a t t h i s w o r k s h o p i n v o l v i n g t h e s t r u c t u r e

9 ) f u n c t i o n s o f D u k e a n d O w e n s :

e / a - /

T F i g . 3 : D i f f e r e n t i a l c r o s s s e c t i o n f o r j e t p r o d u c t i o n — f o r t h e p r o c e s s

d P T p + p -*• Z + j e t + X

u n d e r t h e same k i n e m a t i c c o n s t r a i n t s a s i n F i g . 2 .

F i g . 1 : E v o l u t i o n o f t h e i n v e r s e s t r o n g c o u p l i n g c o n s t a n t 1 / a = ^ V g f o r f o u r 2

- 1 9 9 -

FI6. 1

- 201 -

10

9 .

O 4 12 20 28 FIG. 3

36 44p*<GeV)

D : 8 4 1 0 0 2 6 1 9 8

Q C D p E F F E C T S I N W / Z A N D J E T P R O D U C T I O N

M . G r e c o I N F N - L a b o r a t o r i N a z i o n a l i d¡ F r a s c a t i , F r a s c a t i , I t a l y

A b s t r a c t

/ T h e o r e t i c a l a s p e c t s of t r a n s v e r s e m o m e n t u m d i s t r i b u t i o n s i n Q C U a r e d i s c u s s e d i n c o n n e c t i o n to w e a k bosons and d i j e t p r o d u c t i o n at SppS c o l l i d e r e -n e r g i e s .

T h e p r o d u c t i o n of W and Z b o s o n s 1 ^ at the C E R N SppS c o l l i d e r a l l o w s a

v e r y i m p o r t a n t tes t of the D r e l l - Y a n m e c h a n i s m ' in p e r t u r b a t i v e Q C D in a

c o m p l e t e l y new k i n e m a t i c a l r e g i m e . T h e 0 ( a s j c o r r e c t i o n s to t h e t o t a l p r o d u c

t ion cross section a r e of r e d u c e d s i z e c o m p a r e d to f i x e d target e n e r g i e s and

t h e r e f o r e the a b s o l u t e p r o d u c t i o n r a t e s can b e q u i t e r e l i a b l y p r e d i c t e d I 'rom

p e r t u r b a t i o n t h e o r y

On the o t h e r hand the t r a n s v e r s e m o m e n t u m d i s t r i b u t i o n i s p r o b e d i n the

sof t r e g i o n of ( ¡ , j , « Q , w h i c h , a t l o w e r e n e r g i e s , i s not c l e a r l y s e p a r a t e d f r o m

the " i n t r i n s i c q T " A) and l a r g e q T ( q T ^ Q ) r e g i o n s , w h e r e non p e r t u r

b a t i v e and 0 ( a g ) e f fec ts r e s p e c t i v e l y d o m i n a t e the s p e c t r u m . T h e r e f o r e one

e n c o u n t e r s h e r e a un ique o p p o r t u n i t y to tes t t h o s e t h e o r e t i c a l i d e a s w h i c h h a v e

b e e n d e v e l o p e d to r e s u m e to a l l o r d e r s the c l a s s of l a r g e l o g a r i t h m s of Q 2 / q ' J -

a r i s i n g f r o m the e m i s s i o n of sof t q u a n t a . C o n v e r s e l y , a p r e c i s e e v a l u a t i o n of

t h e s e Q C D e f f e c t s i s q u i t e i m p o r t a n t f o r o b t a i n i n g the a c c u r a c y d e s i r e d tc t e s t

the e l e c t r o w e a k p a r t of these p r o c e s s , r e f e r r i n g i n p a r t i c u l a r to the W m a s s ,

w h i c h i s d e t e r m i n e d f r o m the t r a n s v e r s e s p e c t r u m of the d e c a y l e p t o n .

M u c h t h e o r e t i c a l w o r k has b e e n r e c e n t l y d e d i c a t e d to th is s u b j e c t ^ . I n

p a r t i c u l a r a v e r y d e t a i l e d a n a l y s i s of the q T s p e c t r u m h a s b e e n r e c e n t l y p e r

f o r m e d 5 ^ , w h i c h a u t o m a t i c a l l y c o m b i n e s the sof t g l u o n r e s u m m a t i o n a t q T «

« Q w i t h the 0 ( a s ) p e r t u r b a t i v e d i s t r i b u t i o n at l a r g e q T , w i thou t the ad hoc

i n t r o d u c t i o n of m a t c h i n g p r o c e d u r e s b e t w e e n h a r d and sof t r a d i a t i o n . T h e m a i n

f o r m u l a e and the c o m p a r i s o n w i t h U A l and U A 2 e x p e r i m e n t a l r e s u l t s h a v e

b e e n a l r e a d y d i s c u s s e d b y K. E l l i s ^ . I n the f o l l o w i n g I w i l l f i r s t c o m p a r e those

202 -

- 203 -

7)

results with recent theoretical analyses ' of the s a m e problem in order to cla

rify the different approximations performed and the corresponding limits of va

lidity. Next 1 will discuss the transverse m o m e n t u m spectrum of the leptons

produced in the decay of the weak bosons, which are closely related to the pa

rent distribution and are of great Importance for an accurate determination of

the W boson's m a s s . Finally s o m e transverse m o m e n t u m effects in the produc

tion of dijets will be briefly discussed, showing possible evidence in favor of

the three gluon coupling at collider energies.

The expression for the cross section for the production of a W + boeon

reads 5*

da A r - A * V b V e S l b 2 ' Q 2 ' A t \ [ b 2 < ^ > +

loin"!!... I» 1 q

2

+ Y (q2,Q2,y) + (gluon terms) ,

! 2

V » V . y > - H ( 4 4 P 2 ) [l + ^ U + f * * - ta2<£) -

,2

g ! J 2jr L / o z q i 2'

J o z q 1 z J

P 2 ) + (2)

and T = M 2 / S , x° = exp (±y), A 2 -- [ ( S + Q 2 ) 2 / 4 S c o s h 2 y - Q 2 ] Is the ki-

nematical bound of the transverse m o m e n t u m squared for gluon emission, and

f (z) = 3 / 2 ( 1 - z ) ^ 1 - (1 +z 2)|jn(3-z)/(J-z>] + + (l+z2)lnz/(l-z) - 2 - 3z. Further

m o r e the product of the parton distribution functions is defined

H ( x r x 2 , P 2 ) = | [ u ( x 1 , P 2 ) d U 2 . P 2 ) + c ( v P 2 ) s ( x 2 . P 2 ) ] c o s 2 e c

> j ^ ( x r P 2 ) ï ( x 2 , P 2 ) + c ( x 1 P Z ) d ( x 2 P 2 ) j E i n 2 O c | + jl ~ 2 J , (3)

9 2 where the scale P*1 at which the parton densities are probed is given by P •**-

-27 i "-4 e E / a at large b.

T h e Sudakov f o r m f a c t o r 3 { b 2 , Q 2 , A ^ ) „ at t h e l e a d i n g doub le and s i n g l e l o

g a r i t h m i c H u c u r a c y , i s g i v e n by

»V,4,„>.s / " ^ " ^ . „ • . M . - i l k M - . l . . . . - ï / ~ ^ . ^ [ * 3 f . - î ] k « - . ] .

2 2

w i t h \ T n i a x

= A f T n e r e s i d u a l t e r m i n e q . ( 1 ) ' n c l u d e s f i n i t e t e r m s f r o m

a n n i h i l a t i o n g r a p h s f o r q T —» 0. F i n a l l y t h e g l u o n t e r m s r e f e r to the C o m p t o n

s c a t t e r i n g g r a p h s , w h i c h g i v e a d d i t i v e c o n t r i b u t i o n s to and Y ^ .

T h e b u l k of the q^, d i s t r i b u t i o n , w h e r e m o s t of the da ta have b e e n c o l l e c

t e d , c o m e s f r o m the sof t p a r t of eq . ( 1 ) . O f c o u r s e t h e r e s i d u a l f i n i t e t e r m s

p l a y a m a j o r r o l e f o r l a r g e q,p> say £ - 3 0 G e V w h e r e eq, (1) tends to t h e

0 ( « s ) p e r t u r b a t i v e r e s u l t . T h e n , f o r c o m p a r i s o n w i t h p r e v i o u s a n a l y s e s o f t h e

sof t c o n t r i b u t i o n , i t i s u s e f u l to d i s c u s s s o m e a p p r o x i m a t e f o r m s of the S u d a

kov f o r m f a c t o r ( 4 ) .

2 2 F i r s t , t a k i n g q _ = Q a s u p p e r l i m i t , the r e p l a c e m e n t can be m a d e s T T m a x > r

A t

e*p[s(b 2,Q 2,A 2)] a exp[s(h 2 ,Q 2 ,Q 2)] ( 1 + f ) . (5) 2 2 2 w i t h obv ious n o t a t i o n s . T h i s is a l l o w e d b e c a u s e a ( q ) i s s m a l l f o r Q < q <

2 < A^_ T h e r e s u l t i n g a d d i t i o n a l c o n t r i b u t i o n to R c a n c e l s i n th is c a s e the t e r m s

l n 2 ( A 2 / Q 2 ) - 3 1 n ( A 2 / Q 2 ) a p p e a r i n g i n eq . (2 ) i n the l a r g e b l i m i t . A s i m i l a r r e 2 2 3 2

suit ho lds a p p r o x i m a t e l y f o r Q - r i n î x = Q / e ~ ( Q / 4 ) . D i f f e r e n t c h o i c e s of

c^Tmax' w i t h no c o m p e n s a t i n g t e r m s , w o u l d not a g r e e w i t h the exac t r e s u l t (1 ) .

F u r t h e r m o r e the next to l e a d i n g constan t t e r m in i n t e g r a n u of eq, ( 4 ) i s g i v e n

by ( - 3 / 2 ) , and i t s p r e s e n c e is q u i t e r e l e v a n t f o r the f a l l o f f of the d i s t r i b u t i o n

( d o / d q T d y ) a f t e r the peak . I n fac t the so c a l l e d " l e a d i n g a p p r o x i m a t i o n " ,

w h e r e one k e e p s on ly the l o g a r i t h m i c t e r m l n ( Q 2 / q 2 ) i n eq . (4 ) g i v e s a v e r y

poor d e s c r i p t i o n of the w e a k boson d i s t r i b u t i o n and c o n s e q u e n t l y of the decay

l e p t o n s p e c t r u m , a s d i s c u s s e d l a t e r . F i n a l l y no d o u b l e c o u n t i n g b e t w e e n t h e

soft and trie h a r d f i n i t e c o n t r i b u t i o n m u s t b e p r e s e n t , as i n eq . ( 1 ) .

T h e above d i s c u s s i o n puts s o m e doubts on the a c c u r a c y of p r e v i o u s analy_

s e s 7 ' of th is p r o b l e m and i n d e e d only i n a f e w c a s e s 8 ) the a n s w e r i s r e a s o n

a b l y good up to q T - i 2 0 G e V , w h e r e h o w e v e r the t r e a t m e n t of h a r d e f f e c t s i s

205 •

u n s a t i s f a c t o r y . I n the o t h e r hand a d e t a i l e d k n o w l e d g e of the f u l l q,p d i s t r i b u

t i o n , w h i c h i s c r u c i a l to d e s c r i b e the Q C D b a c k g r o u n d f o r new p h e n o m e n a a t

9 )

l a r g e , c a n only be o b t a i n e d f r o m r e f . 5 .

W e would l i k e to d i s c u s s now t h e p^, d i s t r i b u t i o n of the decay lep tons f r o m

W / Z d e c a y s , w h i c h i s relevant for an a c c u r a t e d e t e r m i n a t i o n of the c h a r g e d

boson 's m a s s . T h e s t a r t i n g f o r m u l a i s g i v e n b y * 0 ^

p d 3 p J E k k d d. k (6 )

w h e r e do is the i n v a r i a n t c r o s s s e c t i o n f o r p r o d u c i n g a W b o s o n , t i m e s i t s

l e p t o n i c b r a n c h i n g r a t i o , s e e eq . ( 1 ) , and the ô f u n c t i o n r e f l e c t s the two body

d e c a y k i n e m a t i c s . T h e t e c h n i c a l d e t a i l s of i n t e g r a t i n g e q . (6 ) a r e g i v e n i n r e f .

1 1 . W e w i l l g i v e h e r e on ly t h e m a i n r e s u l t s , c o m p a r e d w i t h t h e l e a d i n g a p p r o

x i m a t i o n a n a l y s e s 1 0 ' 1 2 ' . I n F i g . 1 w e s h o w 1 1 * t h e i n v a r i a n t c r o s s s e c t i o n at

k A ( G e V / c ) k x ( G e V / c )

F i g - 1 F i g . 2

a l^pton ang le 9 = 9 0 ° , h a v i n g used the G l ü c k et a l . p a r a m e l r i z a t i o n of the

s t r u c t u r e functions. A different c h o i c e of the p a r t o n d e n s i t i e s , g i v e n f o r e x

a m p l e , by B a i e r et a l . ^ , g i v e s s i m i l a r r e s u l t s . T h e l e a d i n g a p p r o x i m a t i o n

( s o l i d c u r v e ) , d e f i n e d a b o v e , g i v e s r i s e to a m u c h b r o a d e r p T d i s t r i b u t i o n

t h a n the one r e s u l t i n g f r o m the i n c l u s i o n of s u b l e a d i n g t e r m s (dashed c u r v e )

c o r r e s p o n d i n g lo e q . ( 1 ) w h i c h i s r e m i n e s c e n t of w h a t o b s e r v e d f o r the q T

d i s t r i b u t i o n of the W . S i m i l a r r e s u l t s a r e found at / s = 2 G 0 0 G e V ( s e e

F i g . 2 ) , w h e r e h o w e v e r one o b s e r v e s a n e x c e s s of even ts f o r s m a l l p T c o m -

- 2 0 6 -

p a r e d to yfa = 5 4 0 G e V , due to the m u c h m o r e s i z e a b l e e f f ec t of the s e a w h e n

t h e e n e r g y i n c r e a s e s . T h e r e l e v a n t r o l e p l a y e d by the s u b l e a d i n g t e r m s i s con

s i s t e n t w i t h t h e U A l d a t a * 5 ) , wh ich show no events f o r pj_ a b o v e 5 0 G e V .

A s l a s t t o p i c s , I w o u l d l i k e t o d i s c u s s now s o m e t r a n s v e r s e m o m e n t u m ef

f e c t s i n d i j e t p r o d u c t i o n . T h e b a s i c i d e a is the f o l l o w i n g 1 6 , 1 ? ) . A t c o l l i d e r e n e r

g i e s the s u b p r o c e s s of g l u o n - g l u o n s c a t t e r i n g g i v e s t h e d o m i n a n t c o n t r i b u t i o n

to j e t p r o d u c t i o n , i n c o n t r a s t to t h e c a s e of w e a k b o s o n p r o d u c t i o n , w h e r e only

the q u a r k s e s s e n t i a l l y p l a y a r o l e . T h e c o r r e s p o n d i n g Sudakov f o r m f a c t o r s

d e p e n d s upon i n s t e a d of C p , l e a d i n g to a r e l a t i v e k T d i j e t d i s t r i b u t i o n

w h i c h i s r e g u l a t e d b y the p r o c e s s of b r e m s s t r a h l u n g i n i t i a t e d b y g luons i n s t e a d

of q u a r k s . T h i s o b s e r v a t i o n p r o v i d e s a r a t h e r c l e a n t e s t of the t h r e e g l u o n cou

p l i n g w h i c h c a n b e e a s i l y s t u d i e d by l o o k i n g a t the r e l a t i v e k T d i s t r i b u t i o n of

t w o h a r d b a c k - t o - b a c k j e t s . T h e n f o r k-p not very large, s a y k ^ 20 GeV, the

d i s t r i b u t i o n is d o m i n a t e d by sof t g l u o n

e m i s s i o n and i s m u c h b r o a d e r t h a n the

c o r r e s p o n d i n g q u a r k c a s e . T h i s is shown T 7)

i n F i g . 3 " , w h e r e t h e s p e c t r u m o b

t a i n e d by u s i n g a G l ü c k at a l . * ^ p a r a m e

t r i z a t i o n of the g l u o n d e n s i t y ( f u l l l i n e ) ,

i s c o m p a r e d to the h y p o t h e t i c a l c a s e

w h e r e g l u o n s w o u l d r a d i a t e l i k e q u a r k s

( C A = C p j d o t t e d l i n e ) . T h e t h e o r e t i c a l

u n c e r t a i n t y r e l a t e d to o u r poor k n o w l e d

ge of t h e gluon. s t r u c t u r e f u n c t i o n is r«3

p r e s e n t e d , i n the s a m e f i g u r e , by the

dashed l i n e w h i c h g i v e s t h e ana logous

r e s u l t f o r t h e C D H S g l u o n p a r a m e t r i -

z a t i o n 1 8 * .

E x p e r i m e n t a l l y , i t i s b e t t e r to d e

f i n e a p r o j e c t e d k T d i s t r i b u t i o n p y r p e n

d i c u l a r l y to the t r i g g e r j e t ÜCf^)* T h e n the U A Î p r e l i m i n a r y d a t a 1 9 ) a r e shown

i n F i g . 4 and c o m p a r e d to t h e t h e o r e t i c a l p r e d i c t i o n s the t w o s e t s of g luon d e n

s i t i e s . A n e x p e r i m e n t a l r e s o l u t i o n o = 5 G e V i s a l s o i n c l u d e d i n the c u r v e s .

T h e r e i s a q u i t e good a g r e e m e n t b e t w e e n t h e o r y and e x p e r i m e n t s f o r ( k T . ) ^

- 207 -

i i i i i i i i t I 1 i I i i i i i i I

4 6 IE IB 20 24 2B fcT>* 4 6 12 IG 20 24 2B(k,)x

Fig. 4 Fig. 5

In conclusion, w e have discussed the relevance of detailed studies of p ^

effects in w/Z production for precise tests of Q C D as well as for the deter

mination of the electroweak parameters. Similar effects observed in the pro

duction of back-to-back jets at collider energies are in good agreement with

the expectations from the three gluon coupling.

^ 20 GeV. At higher transverse m o m e n t a the theoretical predictions are not

reliable, not including finite terms of order aB coming from hard gluon b r e m s

Strahlung and virtual one loop corrections, which have not been all computed.

Finally, in Fig. 5 the hypothetical case of gluons radiating like quarks is also

shown, clearly in a m u c h poorer agreement with data.

208 -

R e f e r e n c e s

1) U A l C o l l a b . . G . A r n i s o n et a l . , P h y s . L e t t e r s 1 2 2 B , 103 ( 1 9 8 3 ) ; 1 2 6 B , 392 ( 1 9 8 3 ) ; U A 2 C o l l a b . , G . B a n n e r et a l . , P h y s . L e t t e r s 1 2 2 B , 4 7 6 ( 1 9 3 3 ) ; 1 2 9 B , 130 ( 1 9 8 3 ) .

2) S. D . D r e l l and T . M . Y a n , P h y s . R e v . 2 5 , 3 1 6 ( 1 9 7 0 ) . 3) F o r a r e v i e w , s e e G . A l t a r e l l i , P h y s . R e p . Jl, 1 ( 1 9 8 2 ) . 4) S e e , f o r e x a m p l e , P . C h i a p p e t t a and M . G r e c o , N u c l e a r P h y s . B2: ' , 2 6 9

( 1 9 8 3 ) , and r e f e r e n c e s t h e r e i n . 5) G . A l t a r e l l i , R. K. E l l i s , M . Grr -co a n d G . M a r t i n e i i i , C E R N p r e p r i n t

T H - 3 8 5 1 ( 1 9 6 4 ) . 6 ) R . K. E U l s , these P r o c e e d i n g s . 7 ) P . A u r e n c h e a n d R . K i n m m e n , P h y s . L e t t e r s 1 3 S B , 493 ( 1 9 8 4 ) ; P . C h i a p

p e t t a and M . G r e c o , P h y s . L e t t e r s 1 3 5 B , 190 ( 1 9 8 4 ) ; A . N a k a m u r a , G . P a n c h e r i a n d Y . S r i v a s t a v a , y i b m i t t e d to P h y s . R e v . L e t t e r s ; L . Trenta_ d u e , P a r m a p r e p r i n t ( 1 9 8 3 ) ; P . H a l z e n , A . D . M a r t i n and D . M . S c o t t , P h y s . R e v . D 2 5 , 754 ( 1 9 8 2 ) .

8) P. C h i a p p e t t í f a r . d M . G r e c o , r e f . ( 7 ) ; L . T r e n t a d u e , r e f . ( 7 ) . 9) C . R u b b i a , t h e s e P r o c e e d i n g s ; A . R o u s s a r i e , these P r o c e e d i n g s .

1 0 ) F . H a l z e n , A . D . M a r t i n and D, M . Sco t t , r e í . ( 7 ) . 11) P . C h i a p e t t a , M . G r e c o and J . S o f f e r , F r a s c a t i p r e p r i n t L N F - 8 4 / 1 4 ( 1 9 8 4 ) . 12) A n a n a l y s i s b a s e d on the p r o p o s a l to e x p o n e n t i a t e t h e w h o l e f i r s t o r d e r con

t r i b u t i o n h a s b e e n a l s o c a r r i e d out by F I H a l z e n , A . D . M a r t i n and M . Scot t , P h y s . L e t t e r s 1 1 2 B , 1 6 0 ( i g 8 2 ) .

13) M . G l ü c k , E . H o f f m a n n and E . R e y a , Z , P h y s i k C 1 3 , 119 ( 1 9 8 2 ) . 14) R. B a i e r , J . E n g e l s a n d B . P e t e r s s o n , Z . P h y s i k Ç 2 , 265 ( 1 9 7 9 ) . 15) U A l C o l l a b . , G . A r n i s o n et a l . , P h y s . L e t t e r s 1 2 9 B , 273 ( 1 9 8 3 ) . 16) M . G r e c o , P r o c e e d i n g s of the X V I H , R e n c o n t r e de M o r i o n d , L a p. lagne,

1 9 8 3 . 17 ) M . G r e c o , F r a s c a t i p r e p r i n t L N F - 8 4 / 2 1 ( 1 9 8 4 ) . 18) H . A b r a m o w i c z et a l . , Z . P h y s i k C 1 2 , 289 ( 1 9 8 2 ) . T h e e x p l i c i t p a r a m e t r i -

z a t i o n u s e d is g i v e n b y M . A n s e l m i n o , P . K r o l l and E. L e a d e r , C E R N p r e p r i n t T H - 3 4 7 1 ( 1 9 8 3 ) .

19 ) M . D e l i a N e g r a and W . S c o t t , p r i v a t e c o m m u n i c a t i o n . W e a r e g r a t e f u l to M . D e l i a N e g r a , C . R u b b i a and W . S c o t t f o r p r o v i d i n g us the U A l p r e l i m i n a r y i n f o r m a t i o n p r i o r to p u b l i c a t i o n and f o r s e v e r a l d i s c u s s i o n s .

- 2 0 9 -

0: B41Q026201

TESTING THE Wfy COUPLING OF THE GLASHOW-SALAM-WEINBERG MODEL AT pp COLLIDERS

J. Cortea*, K. Hagiwara and F . Herzog

Physics Department, University of Wisconsin, Madison, Wisconsin 53706 USA *CBRN, Theory Division, CH-1211, Geneve 23, Switzerland

Presented by Franz Herzog

ABSTRACT

We propose methods to measure the anomalous magnetic moment

W-boson, a quantity which la o£ foremost importance for testing the non-abelian ,

structure of the electroweak gauge theory.

1. IHTRODUCTION The standard model 1 of the electroweak interaction la a reno ratal Iza ble

non-abelian, spontaneously broken gauge theory; an outstanding feature of auch a theory is the self coupling of the gauge bosons. It la thus of great Importance to teat those vertices, and in the following we shall propose a method to probe the triple coupling of a photon (y) with the charged intermediate vector bosons ( W £ ) . We work la a minimally extended standard model where we attribute an anomalous magnetic moment K to the U boson; 2^ the magnetic moment of the V boson is then given b)

Here e denotes the modulo of the electron charge and the masa of the U. Every

gauge theory, based on an arbitrary non-abelian group, predicts:

* - 1 + 0 ( 4 ) * < 2>

Any experiment that finds a substantial deviation from K - 1 would thus disprove the gauge nature of the electroweak interaction.

2 . THE PROCESS pp •» yÜv tX The process proton(p) + antiproton(p) •+ photon ( I F ) + charged lepton(JL) +

antineutrino(v^) +• X takes place via a quark(d) - antiquark(ü) annihilation; the corresponding tree level Feynman diagrams are

- 2 1 0 -

«her« ve denote four -aonente lo. pa ren theses* By apply ing the ze ro width

approximation t o t h s W p ropaga to r , t h e s e diagrams can be a p i l e taco two s e t s of

d l s g r a o s , which tta c a l l Hp and H n r e s p e c t i v e l y :

The W p r o p a g a t o r i where we app l i ed t h e ze ro -wid th approximat ion a r e cu t by dashed

l i n e a . We s h a l l t r e a t t he "p roduc t ion" and "decay" p rocess s e p a r a t e l y , a s they

c o n t r i b u t e i n d i f f e r e n t r eg ions of phase s p a c e ; t h i s can be seen In t he

d i s t r i b u t i o n of che c l u s t e r t r a n s v e r s e a a s s 3 ^ def ined a s

i^(yltvt) - (/p|<Yl>-ha 2(TA>'+ P r ( v x ) ) 2 " ( P T ( Y W + ÍT( v * > ) 2 - (3a)

The c l u s t e r t r a n s v e r s e o a t s l a bound- by Che I n v a r i a n t U I B ,

«TC ÏA .VJ) <*<y&¿ . <3b)

I n F i g . 1» we show t h e B ^ C Y Ä » ^ ) d l a t r i b u t Ion .

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2 . 1 The p r o d u c t i o n proceas pp -» WY ^ I W ~* iv 1 *^

According t o the theorem on r a d i a t i o n c e r o s ^ the ampl i tude Hp has a zero a t

<*3 P X - P y P 2 ' P Y

( 4 a )

where QJCQJ) 1» thft e l e c t r i c charge o f Che d ( 5 ) quark* I n the par t o n i c

c m . frame c h i s reads

cose* - j » 9* * < P i » í Y )

l o n g i t u d i n a l momentum o f thft W boson ( o r e q u i v a l e n t ! ? t h s l o n g i t u d i n a l momentum

o f the v¿). I s the z e r o w i d t h approx imat ion - there a ra two s o l u t i o n s f o r cos 9* which we c a l l eosB*; I t s e x p l i c i t form can be found i n . Ref* Because o f the

"V-A" s t r u c t u r e o f the W b o s o n - f e r a i o a c o u p l i n g and the tendency o f the photon t o

f o l l o w the 5 quark r a t h e r Chan the d quark d i r e c t i o n , t h e q u a n t i t y 8* i s moat of

t h e Clue Che t r u e s c a t t e r i n g a n f U e . I n F i g . 2 we show che cosa* d i s t r i b u t i o n s a t

f% m, 2000 GeV f o r d i f f e r e n t v a l u e s o f K*

F i g * 1> C l u s t e r t r a n s v e r s a mass d i s t r i b u t i o n

o f a process pp •+ avy + X a t S* - 540 GeV. As

a consequence o f E q , ( 3 b ) v s cau d e f i n e two

k l n e m a t l c a l r e g i o n s : l) ^ » f ( Y A | V ¿ ) > my: o n l y t h s p roduc t ion process pp - VyX; V X\>x

i s k i n e m a t i c a l l y «1 lowed. 2 ) j ^ m ^ Y * » V|) < By. ttas a a l n c o n t r i b u t i o n l a t h i s r e g i o n comes f rom

the decay process pp * W; W • Y ^ j t * Note che

Jacob lan pealt a t aîyt^vj^ -

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-I -0.5 0 0.5 I -I -0.5 0 0.5 | COS0Î C0SÔ*

Fig. 2. coaQ* distribución for the process pp •+ WyX; W Iv at -/a - 2000 GeV fo r different values of the anomalous aagnetic moment K of the W boson. The following cuts are laposed: |pYxl.lï\trt * 1 0 îf^jt} > 9 0 a n d

ly¿l»IyYl * where yY(yj¡) Is the rapidity of the photon (charged lepton) in the pp cm. frame. We used the distribution functions of Bef. 6 with Q 2 <-(pj +pj?2 " * d a s R e d lines denote the estimated background (to be discussed in Section 3) from pp •+ W"y"X where " y " represents a Jet that may fake photons.

2.2 The decay process pp -*• WX; W •* The theorem on radiation zeros5^ states that if we have a neutral and

mass less particle a zero appears In the amplitude when the photon is coilineat to this neutral particle:

P V P y - 0 * "D * 0 • (5a)

In the rest frame of the W boson the condition (5a) reads

cos9*¿ - -1 d*i i (Px»Py) • (5b)

Similar to the case of che production procesa, there are two solutions coa ft*^ for the photon-lepton opening angle cose*^ in terras of the observable final state

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variables; Its explicit expressions can be found in Ref. 7. In Fig. 3 we present the cos6 Y|_ distribution.

Flg. 3. cosôÇ^. distribution for the process pp -*• WX, W -*• ySS^ at /s" - 540 GeV

for different values of the anomalous magnetic moment K of the W boson. The

fallowing cute are imposed: 1p. v I!»|pjj| > 10 GeV, 30 GeV < mjCyl, v¡) < 90 GeV,

ly^1.|y 7 l < 3 a * d [cos8 y¿l < .95 where 9 y ¿ la the photon-lepton opening angle in

the pp c a . fra»iä. We used the distribution functions of Ref. 6 with Q 2 - B .

The dashed lines denote the estimated background (to be discussed below) from

pp -• W"*y" where "y" stands for a Jet thae may fake photons.

3. BACKGROUNDS

To extract the signal from the bulk of data three requirements have to be

met: i) high transverse momentum, isolated charged lepton, Li) large missing

transverse momentum, and ill) high transverse momentum isolated photon. The

successful Identification of U ->• iv events by UAl and UA2 have demonstrated the

effectiveness of the first two trigger conditions 8'; therefore we need to worry

only about backgrounds that fake the third trigger condition. Main backgrounds

will come from the process:

pp + w + Jet + x , (6)

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Table 1. Number of (yJtv^) events expected at colliders by assuming an integrated

luminosity /it dt - 1 0 j 7 cm" 2, K - 1. year

/a"- 540 GeV 2 TeV

Production Decay Production Decay

3 events 24 events 30 events 135 events

whs M a QCD jet fake a a photon. The contribution front the cascade process pp -»• W + Jet -I- X; W -+ tvj T •+ Jlvv turns out to be saall, but we have included it in our analyses. Assuming a rejection rate p " v " / j e t " 1/200, as suggested by la a jet analysis 1 0), we obtain the dashed lines given in Figs. 2 and 3 for the background estimate*

i

4. EFFECTS OF FINITE W-WIDTH AND HIGHER ORDER QCD CORRECTIONS

By dropping the zero width approximation for the W propagator, we have extra

contributions such as an Interference between "production" and **decay** amplitudes

which destroy the separate radiation zeros at Eq. (4) and Eq. (5). We evaluated

these 0(a) effects since the cosO^" distribution in Fig. 2 shows a drop-off of a

factor of 100 due to the radiation zero. We f o u n d c h a t Che effect Is

numerically negligible in both the cos9_ as well as in the coaö * j j_ distributions.

The QCD higher-order corrections of 0(<xa) nay be «ore serious. In the case

wf the "decay" process, however, we expect small radiative corrections in cos6*^_

distributions. This is because gluon emission in che Initial state can only

affect the polarization of the W boson, On one hand, this cannot influence the

distribution near the zero at cos8*¿ • -1 because every polarization amplitude

has a zero at the saue place. On the other hand, it has been shown 7^ that the

cosö* Ä_ distribution for the decay of a longitudinally polarized W boson is

almost Identical to the cos9*^ distribution for the decay of an unpolarized W

boson in the entire cosQ*^ region.

In the case of "production" we find no heuristic argument about the size of

higher-order corrections. It is a challenging task for theorists to study quan

titatively the effects of higher-order corrections to the dip structure shown In

Fig. 2-

5. CONCLUSIONS

Adding up all e~, yr contributions, we show in Table 1 the expected event

rates for K • 1 at CERN and Fennilab colliders. He have not included the QCD

motivated K-factor.

- 21S -

By cons ide r ing r i t e , background, and e f f e c t * of 0 ( a a ) c o r r e c t i o n s , we f ind t h a t

Che beer p l ace t o probe the WWy coupl ing a t p reaent -day pp c o l l i d e r s i s t he

r a d i a t i v e decay procese» W -+ Avy> We urge e x p e r i m e n t a l i s t s t o ? -Jk a t t h i s

t r i p l e coupl ing t h a t I s of ou t s t and ing importance for any gauge theory of the

e lec t roweak i n t e r a c t i o n .

8 . ACKNOWLEDGMENTS

This r e sea r ch uas suppor ted i n p a r t by the Un lve ra l ty of Wiaconein Research

Committee wi th funda g ran ted by the Wisconsin Alumni Research Foundation« and i n

p a r t by t he Department of Energy under c o n t r a c t DE-AC02-76ER00881.

7 . REFERENCES 1 . S. L. Glashow. Nucl. Phys. 22 , 579 (1961) ; S. Weinberg, Phya. Re». L e t t .

19. 1264 (1967) ; A. Salam I n Elementary P a r t i c l e Theory, ed . by H. Svarcholm (Almqulst & Wlkse l l , Stockholm, 1968) , p . 367.

2 . T. D. Lee and C. K. Yang, Phys. Rev. 1)128, 88S (1962) . 3 . V. Barger , A. D. Mar t in and R . J .N . P h i l l i p s , Phya. L e t t . 2SB, 339 (1963) . 4 . J. C o r t é s , X. Hagivara and P. Herzog, Madison p r e p r i n t MAD/PH/102 ( A p r i l ,

1983). 5 . C. J . Goebel, F . Hal2en and J . P . l e v e i l l e , Phyo. Rev, P23 , 2682 (1981) ;

Z. Dongpel, Phys . Rev. D22, 2266 (1980) ; S. J . Brodsky and R. » . Broun, Phys . Rev. L e t t . 49 , 966 (1982) ; R. W. Broun, K. L. Kowalski and

S. J . Brodsky, Phys. Rev. 28 , 264 (19B3).

6 . A. J . Buras and K . J . F . Gaemera, H u d . Phys. B132, 249 (1978) ; J . F . Owens and E. Reya, Phya. Rev. D17, 3003 (1978) .

7 . J . C o r t é s , K. Hagivara and F . Herzog, Madison p r e p r i n t HAS/PR/108 ( A p r i l , 1983).

8 . UAl c o l l a b o r a t i o n , Phys . L e t t . 122B, 103 (1983) ; 0A2 c o l l a b o r a t i o n , - i iye . L e t t . 1228 . 476 (1983) .

10. S . A. Kahn, T. J . K l l l i a n , H. J . Murtagh and F . E . Pa ige , "Monte Car lo a tudy of pp * W^X a t C8A-, BNL informal r e p o r t 3/83 (1993).

11 . J . C o r t é s , K. Haglwsra and P . Herzog, Madison p r e p r i n t HAD/PH/164 ( A p r i l , 1984).

- Z 1 7 -

The New Events

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EXPERIMENTAL OBSERVATION OF EVENTS W I T H L A R G E MISSING TRANSVERSE ENERGY A C C O M P A N I E D BY A J E T OR A PHOTON i S)

IN p p COLLISIONS AT /s = 540 G e V

UAl C o l 1 a b o r a t i o n , CERN, G e n e v a , Switzer1and

Presented by C. R u b b i a , CERN

N o w r i t t e n c o n t r i b u t i o n r e c e i v e d

A b s t r a c t frrm Physics L e t t e r s , 139B, 115 (1984)

We report the observation of five events in w h i c h a missing transverse energy larger than 40 GeV is associated w i t h a n a r r o w hadronic jet and o f two similar events with a neutral electromagnetic cluster (either one or m o r e closely spaced p h o t o n s ) . W e cannot find an explanation for such events in terms of backgrounds o r within the expectations of t h e Standard M o d e l .

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OBSERVATION OF ELECTRONS

PRODUCED IN ASSOCIATION WITH HARD JETS

AND LARGE MISSING TRANSVERSE HOHEN TUM

IN pp COLLISIONS AT / s = 540 GeV o : 84-]

The UA2 Collaboration

Bern - CERN - Copenhagen (NBI) -Orsay (LAL)

Pavia - Saclay (CEN) collaboration

Presented by-A.ROUSSARIE, SACUVY

ABSTRACT _ Using a sample of events collected by UA2 and corresponding to an integrated

luminosity of 1 1 6 nb S we have searched for electron-"neutrino" pairs in which the tranverse momenta of the electron and of the "neutrino" exceed 15 GeV/c and 25 GeV/c respectively. A total of 35 events are observed in low background conditions- Host events can be interpreted in terms of w production from QCD processes. Four events In which the observation of hard jets makes this interpretation unlikely are described in detail. Possible sources of background contamination are considered.

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1. TNTRODUCTIOK

In a previous publication1', we nave studied a sample of events recorded by UA2 at the SppS collider, which contain an electron candidate in the final state with a transverse momentum p ¿ (e) in excess of 15 GeV/c and no significant transverse energy detected at opposit azimuth. These events were analysed in terms of the production and decay of the electroweak bosons W~.

The purpose of this presentation is to report on a systematic search for events containing an electron-"neutrino" pair in the final state, whatever the transverse energy at opposite azimuth to the electron may be. The loss of rejection power against background (mainly two-jet events) resulting from having relaxed this constraint, is compensated by the requirement that both the electron and the "neutrino" (observed missing transverse energy) have large transverse momenta.

Our detector does not distinguish between one or several neutrinos and other possible non-interacting particles, such as the photino postulated by supersymmetry theories. In the remainder of this presentation the word "neutrino" must therefore be understood in a broad sense.

2. APPARATUS

2) The UA2 detector has been described in detail elsewhere . He briefly recall its

main features.

Apart from two narrow cones along tlvs beams, tne detector provides full azimutnal coverage in three distinct regions of polar angles : 40° < d < 140", the central region, and 20° < 9 < 40°, 140" < 9 < 160° the forward regions.

in the centre of the detector a sot of coaxial cylindrical drift and proportionnai chambers detect the charged particles produced in the collision and measure the position of the event vertex.

An array of 480 calorimeter cells, each cell covering a similar domain of longitudinal pnase-space (15° of azimuth and a 0.2 units of rapidity), measures electron energies Ele) to a good accuracy. Each cell is segmented longitudinally to provide electron-hadron separation. While hadron showers are usually contained in the 4.5 absorption lengths of the central calorimeter, providing a measurement of jet energies, they only deposit a fraction of their energy in the forward calorimeters which are = 1.0 absorption length thicfc. These forward regions are equipped with

- 2 2 1 -

magnetic spectrometers which provide additional rejection power against hadrons and converted photons when searching for electrons. In addition they measure the momenta of charged jet fragments, the energy of « 0 , s being measured In the calorimeter ceils.

In both the central and forward regions electron identification is significantly improved by preshower counters which accurately measure the match between the observed incident track and the developing shower.

3. EVENT SELECTION

For this analysis we retain only the data collected during the 1983 period for wnich the a2lrauthai coverage of the UA2 detection was complete^ . Tne corresponding integated luminosity is 116 nb ^.

In each event we reduce the final state to a set of transverse energy clusters 1)2 )

according to simple algorithms which have been described elsewhere

3.1 Electron selection The electron identification criteria have been described in detail in table 1 of

Ref .1. A first set of selection cuts is applied on the calorimeter data only (cluster radius, energy leakage in the hadronic compartment). Further refined criteria make use of the charged track trajectories and of the early shower positions, as measured by the vertex detector and tne preshower detector respectively, and look for their compatibility with the calorimeter cluster. Furthermore in tïie forward regions, the magnetic spectrometer allows additional checks on the momentum-energy match and permits to remove eDnr^rons originating from y conversions where the eê pair is observed. Altogether we have measured 1^ that the probability for a jet to simulate an

—5 —5 electron candidate iE 0.4 * 10 in the forward detectors and 2.3 * 10 in the central one, wnile the global detection efficiency of the electron criteria is estimated to be 80% and 76% respectively.

The present analysis deals with a sample of 200 events containing an electron candidate having P^íeí > 15 GeV/c. We discard 10 events in which the electron candidate is observed near the interface between the central region and one of the forward regions and is associated with nearby calorimeter energy in each of the two regions.

The sample of event satisfying the first level of election criteria (calorimeter cuts) but not the complete set of cuts will be used to evaluate the background, as described in reference l. The background contained in the electron sample for a given

- 222

t o p o l o g y i s o b t a i n e d , v e r y s i m p l y , b y n o r m a l i z i n g t n e b a c K g r o u n a s a m p l e o f t n e same

t o p o l o g y b y a g i v e n c o n s t a n t n u m b e r ( I / 1 4 0 f o r t h e n a t a c o n s i d e r e d h e r e a f t e r ) .

3 . 2 " N e u t r i n o " s e l e c t i o n

E a c h o f t h e c a l o r i m e t e r c l u s t e r s n o t i d e n t i f i e d a s e l e c t r o n a r e c a l l e a " j e t ß " i f

t h e i r t r a n s v e r s e e n e r g y e x c e e d s 3 G e V . Por e a c h e v e n t w e c a l c u l a t e t h e momentum p"

( t r a n s v e r s e c o m p o n e n t p ^ a n d l o n g i t u d i n a l c o m p o n e n t ) a n d e n e r g y E o f t h e e l e c t r o n

c a n d i d i t e ( e ) a n d o f e a c h i n d i v i d u a l j e t ( j ) a s s u m e d t o b e mass l e s s , we a l s o e v a l u a t e

tne momentum p , e n e r g y E a n d m a s s tn of v a r i o u s s e t s o f p a r t i c l e s s u c h a s t h e s y s t e m o f

a l l j e t s , ( J ) o r t h e s y s t e m o f e l e c t r o n u n í j e t e , ( J e ) . T h e q u a n t i t y P j _ ( J e ) m e a s u r e s

t h e m i s s i n g t r a n s v e r s e momentum i n t h e s e t o f a l l d e t e c t e d p a r t i c l e s r e s u l t i n g i n

c l u s t e r s h a v i n g E j _ > 3 G e V . I n a t y p i c a l e v e n t , t h e s o f t e r p a r t i c l e s c a r r y t o g e t h e r

o n l y a s m a l l t r a n s v e r s e momentum a n d , i f n o l a r g e t r a n s v e r s e momentum p a r t i c l e h a s

e s c a p e d d e t e c t i o n , t h e o b s e r v a t i o n o f a l a r g e P j ^ t J e ) r e v e a l s t h e p r e s e n c e o f a n e u t r i n o

( t > ; w i t h p ^ í f ) = p j J J e ) .

4 . DATA A N A L Y S I S AKD BACKGROUND EVALUATION

i . a ) T r a n s v e r s e momentum d i s t r i

b u t i o n o f t h e s y s t e m o f e l e c t r o n

a n d j e t s i n t h e i n i t i a l s a m p l e o f

1 9 0 e v e n t s .

b ) T r a n s v e r s e e n e r g y d i s t r i b u t i o n

o f t h e s y s t e m o f j e t s i n t h e

s a m p l e o f 3 5 e v e n t s h a v i n g p j _ ( J e )

> 2 5 G e V / c . T h e l i n e s c o r r e s p o n d

t o t h e c a l c u l a t e d b a c k g r o u n d

c o n t a m i n a t i o n s . T h e f o u r e v e n t s

h a v i n g P j _ ( J e ) > 2 5 G e V / c , E | ( J ) >

3 0 GeV, a r e c r o s s - h a t c h e d .

- 2 2 3 -

Tue distribution of p^í Je) is shown in Fig.la. The background evaluation measures the probability that a mutijet event contains both a raisidentlfied electron and an undetected jet (or jets) escaping the UA2 acceptance. Its distribution is shown as a curve superimposed on the data of Fig.la.

2.a)Distribution of the 190 events of the initial sample in the p^(Je), E¿(J) plane, seven z° events Bre circled ( the eighth one was collected during the 1962 period). The w region is indicated.

bjDistribution of the background sample in the pj^ ( Je), E ¿( J) plane. A reduction factor of 1 4 1

must be applied to infer from this sample the background contamination to the sample of Fig.2a.

- 224 -

From the results of the analysis presented In Hef.i we expect this sample to contain a number of events iii which the observed electron carries most of the detected transverse energy, and is therefore accompanied by no jet or by jets having small transverse energies. The distribution of the sum of the jet transverse energies, Ej_ (J), confirms tnis expectation (Fig.lb). The 31 events having E^ÍJ) < 30 GeV all belong to the samples of Pigs. 4a and 4c in Ref .1, where they were interpreted in terms of w -+ ec decays, we do not comment furtr*"- on these events. Instead we consider the four events having E A ( J ) > 30 GeV. The distribution of the events in the pjjJe), E^(J) plane is shown in Fig. 2 for each of the signal and background samples. The background contamination expected in the region pjJJe) > 25 GeV/c, Ej(J) > 30 GeV is a 0.45 ± 0.04 events. We first note how well the four events (labelled A,B,C and D) are isolated Î

remember that the background sample has to be normalized by - i/140. In each of the four signal events the electron candidate is detected in the cental region of the UA2 detector. Their transverse momentum configurations are illustrated, in Pig.3.

- 22S -

For each event. In which p^tJe) and E_^ÍJ) take values ana Eg respectively, we evaluate the expected background contamination B p and Bj corresponding to the following configurations : B¡, : PJ. <Je> > po ' E ± t J > > 30 GeV : (isolation along the p x (Je) axis) B j : p X ( J e > > 2 5 G e V/' c' Eai Jï > E

0 s (isolation along the Ej_(J) axis)

In each of the four events, either B^ or Bj is always less than 0.02. Event D (B^ = 0.02, B = 0.13) is mainly singular by the jet transverse energies. It is remarkable that there is no background event in the region p±{Je) > 50 GeV/c, Ej_(J) > 30 GeV, wnich contains everts A to c. we infer from this a background contamination of at most 0.02 events (9C4 confidence level) in this region (see table 1 ) .

The electron and neutrino misidentification is directly measured from the data themselves by the background evaluation. Nevertheless it is useful to add the following comments :

On the quality of the electron identification, we have checked that the characteristic parameters of the four events (see a few of them in table 1) agree well with the ones of the w •+ ev candidates. Each of the four events has been examined in detail with the help of a high resolution graphics display facility. The track multiplicity is of course higher here than in most of the W •* QV events studied in Ref .1 and we cannot exclude tnat tue increased complexity of the signal pattern in tiie central vertex detector could result in some deterioration of the electron identification power.

ÄS far as neutrino identification is concerned, we have checked that in each of the four events there is no sign of largs iransverse momentum particle having hit passive parts of the UA2 detector, such as the magnet coils, in the azimuthai region wnere the neutrino is expected. However, in the case of event D which has an azlmuthal configuration similar to that of a two-jet event (see Fig. 3 ) , such an interpretation cannot be completely excluded. Jet J 2 lies close to the central-forward interface and lost energy may have generatedthe "neutrino". In the cases of events ato C, large transverse momentum particles may have escaped detection because they were produced at small angle to the beam line. We considered for each event the possibility that a jet having the same transverse momentum as the neutrino candidate be produced at 9 = 15 ° (or 165

Under such an assumption we can calculate a lower limit for the invariant mass of the system of all large transverse momentum particles produced in the event, including the small angle undetected jet. In the case Df events A to ; they correspond to impossible or very unlikely kinematical configurations.

- 226 -

Hore generally we know that, for high mass two-jet events, the probability for one jet to escape detection in the UA2 detector, is smaller than 10%. If events A to C were such events, appearing at (p Q ,E Q) in the p^tJe), E^ÍJ) plane of Fig.2, we should observe at least ten times more events with the two jets being detected. They would have appeared in Fig.2 with Pj_(Je) small and E^tJ] s. p Q + E Q .

But the only events having pjjje) + E^(J) > 90 GeV are precisely the four events of Fig.3. The absence of other events in this region, even with low values of p±iJe)r

excludes such an interpretation.

A muon can in principle simulate a neutrino in the UA2 detector. Aitnougn we know of no mechanism which could produce a very massive electron-muon pair at a detectable rate, we looked, in each of the four events, fer a track in the vertex detector near the neutrino azimuth and associated with calorimeter energy consistent with the response to a minimum ionizing particle. We found none.

in each of the four events in Fig.3 the sharing of the jet energies between the various calorimeters compartments^' is consistent witn expectation. Moreover, each jet contains several tracks having their origin at the event vertex. These observations exclude interpretations in terms of a cosmic ray or beam-gas background.

5. EVEKT INTERPRETATION

in this section we study possible sources for events A t o D, under the assumption that tney contain a genuine ev pair.

Event D contains a narrow ei» pair (A4 & 17 °). it consists of a large transverse momentum jet ( p^{ j^) = 70 GeV/cJ emitted at opposite azimuth to the electron-neutrino pair ana to a smaller transverse momentum jet (p^( j^) - 25 GeV/c). The invariant mass of the (epj 2) system depends upon the unknown value of p^{v). It takes its minimum value, 25 ± 5 GeV/c^, v;nen tne neutrino has the same rapidity as the (ej_) system. In

2 this case mievj^j^) - 14S ± IS GeV/c . The configuration of this event suggests an interpretation in terms of a quark-antiquark pair, one member of which decays semileptonically. However, because of the restriction we have made before on the "neutrino" identification of event D, because of tile absence of other events with similar topologies and because of the similarity of its configuration with that of a two-jet event, we prefer to defer such an interpretation until other events of the same kind have been observed.

- 227 -

in the three other events (A to C), the et* pair has a large azlinuthal opening (A* > o

120°). The transverse mass of the ev pair (Table 1) ranges between 56 Gev/c aim 62 2

GeV/c t suggesting an interprétât lor. in terms of a W •+ ev decay, the W boson being the only known particle with a large enough mass, it is indeed possible to adjust the unknown value of P^f*0 t o obtain rafee) = ra(W) and to describe the events in terras of associated W-jet(s) production. There are in general two solutions to this problem, associated with different value? of p^(WJ) m K^{V3)Í/SJ2 and of ra(WJ). We retain the solution minimizing jxpiwj)) (see Table 1 ) .

The distribution of m(WJ) is shown in Fig.4 for all events having px( Je) > 25 GsV/c. While the 31 events having Ej.(J) < 30 GeV cluster in the neighbourhood of m(WJ) = m(w),

2

the three events of Table 1 populate the region 160 S m(wj) £ ieo Gev/c , which might suggest an interpretation in terms of a heavy object decaying into a W boson and a system J of other particles. However, the significance of this observation is weakened by the fact that the background events have a similar m(Wj) distribution (Fig.4) implying that the clustering in mass might simply result from kinematics, in addition such an interpretation should account for the fact that in events A and B, J consists essentially of a single jet, while in event C it consists of a large mass pair of jets.

4.Distribution of m(WJ) for the 35 events having Pj_(Je) > 25 GeV/c. Events having in addition E¿(J) > 30 GeV are cross-hatched. The smooth line corresponds to the calculated background. The dotted line is the background distribution (multiplied by 100) for events having Ej_(J) > 3G GeV.

U A 2

P A ( « ) > 1 5 G e V / c

p (Je)>25GeV/c

ios «s m » M CeV / c 1

If these events are tí •* ev decays, we would like to know if the system of large transverse momentum jets associated to then is understandable in terms of a conventional known processes like CCD. what is the probability to produce these jets in association with the W? A reasonable upper limit can be obtained from UA2 multijet events 3* by measuring the probability to find , associated with a pair of jets j ^ 2

(having the same configuration as the ei» pair ascribed to t h ^ w ) , a jet system (J). we state that

- 228

ffípp •+ V + J + . . . } Í T ( P P - * i¿¿ + J + •*-'

ffípp -* W + . . . ) ~ S I T Í P P •+ J A J 2 + . . . )

We e v a l u a t e s u c h u p p e r l i m i t s f o r e v e n t s A t o C f r o m t h e s a m p l e o f j e t e v e n t s d e s c r i b e d

i n R e f . 3 . We t a x e a s J a n y j e t ( j e t p a i r ) h a v i n g a t r a n s v e r s e momentum ( i n v a r i a n t m a s s )

a t l e a s t a s l a r g e a s t h a t o f t h e c o r r e s p o n d i n g j e t ( j e t p a l - ) i n e v e n t s A a n d B ( C ) .

F r o m t h e t o t a l n u m b e r o f o b s e r v e d W -* e c e v e n t s (3.1 ) , w e c o m p u t e N ^ ^ , u p p e r l i m i t t o

t h e n u m b e r o f e v e n t s w + J e x p e c t e d t o b e p r o d u c e d v i a c o n v e n t i o n a l Q C D . T h e r e s u l t s ,

l i s t e d i n T a b l e i , i n c l u d e t n e d i f f e r e n t a c c e p t a n c e s o f t h e LTA2 a p p a r a t u s t o ev p a i r s

a n d t o j e t p a i r s . T h e y i n d i c a t e t h a t e v e n t s B a n d C , i f t h e y i n d e e d c o n t a i n a g e n u i n e VI

-» BP, a r e d i f f i c u l t t o u n d e r s t a n d i n t e r r a s o f a s s o c i a t e d W - j e t ( s ) p r o d u c t i o n v i a k n o w n

p r o c e s s e s . E v e n t A , o n t h e o t h e r h a n d r h a s a n u n l i k e l y h i g h v a l u e o f ( W J ) ,

c o r r e s p o n d i n g t o a V l o n g i t u d i n a l momentum o f n e a r l y 1 5 0 G e v / c . T n e p r o b a b i l i t y t o

f i n d p a r t o n s i n s i d e t h e b e a m s t o p r o d u c t i t , i s o n l y & * .

I n a d d i t i o n t o t h e i n s t r u m e n t a l u n c e r t a i n t i e s q u o t e d i n T a b l e 1 , t h e m e a s u r e d j e t

e n e r g i e s a r e e x p e c t e d t o b e s o m e w h a t s m a l l e r t h a n t h a t o f t n e p a r e n t p a r t o n s ( w e

n e g l e c t t h e j e t mass a n d we d o n o t i n c l u d e j e t f r a g m e n t s w h i c h do n o t c o n t r i b u t e t o

t h e t r a n s v e r s e e n e r g y c l u s t e r ) . T h e s e e f f e c t s a r e n o t c o r r e c t e d f o r i n T a b l e 1 . U s i n g 4)

t h e I S A J E T p r o g r a m m e t o s i m u l a t e W d e c a y s i n t o a p a i r o f l i g h t q u a r k s , we f i n d t h a t

t h e t w o - c l u s t e r mass i s m e a s u r e d a 1 5 G e v / c ^ l o w e r t h a n m ( W ) . T h e r e f o r e t h e v a l u e m( J ) =

6 3 ± 5 G e v / c o b t a i n e d f o r e v e n t C i s n o t i n c o n s i s t e n t w i t h t h e h y p o t h e s i s t h a t j

r e s u l t s f r o m a W d e c a y .

F i n a l l y we n o t e t h a t t h e i n t e r p r e t a t i o n o f t h e ev p a i r I n t e r m s o f a w d e c a y i n

e v e n t s A t o c i ^ b y n o m e a n s m a n d a t o r y b e c a u s e t h e m i s s i n g t r a n s v e r s e momentum d o e s n o t

n e e d t o b e a s c r i b e d t o a s i n g l e n e u t r i n o b u t m i g h t b e s h a r e d a m o n g s e v e r a l u n d e t e c t e d

p a r t i c l e s .

6 . CONCLUSION

A s e a r c h o f e v e n t s c o n t a i n i n g a n e l e c t r o n - n e u t r i n o p a i r h a v i n g Pj^íe) > 1 5 G e V / e a n d

P x ( j > ) > 2 5 G e V / c h a s r e s u l t e d i n a s a m p l e o f 3 5 e v e n t s , t h e m a j o r i t y o f w h i c h h a v e b e e n

p r e v i o u s l y s t u d i e d 1 ^ a n d i n t e - p r e t e d i n t e r m s o f W p r o d u c t i o n , w i t h c h a r a c t e r i s t i c

p r o p e r t i e s i n a g r e e m e n t w i t h QCD p r e d i c t i o n s .

- 229 -

Four events nave been found, in which the ev pair is produced in association with a jet, or a system of jets, having very large transverse energies. We have given a detailed description of these events and we have considered possible sources of Background contaminations.

Three of these events contain a large transverse mass ev pair and have been interpreted in terms of w-jet(s) associated production. However, their configurations are sucn tnat tneir production via known processes is very unlikely for at least two of then. In each of the three events the invariant mass of the w-jet(s) system is measured

2 to be in the vicinity of 170 GeV/c , but the significance of this observation is weakened by the fact that this mass region is kinematically favoured by the selection criteria.

Interpretations in terms of new processes, including the possibility of ascribing

the observe: missing transverse energy to particles other than a single neutrino, have

not been explicitely considered.

While the present study indicates tnat ve have observed events corresponding to a

genuine signal and suggests the existence of a new phenomenon, more data need to be

collected in order to place this result on firmer ground.

REFERENCES

1. P. Bagnaia et al., UA2 Coll., A study of high transverse momentum electrons produced in pp collisions at 540 GeV, CERN-EP/B4-39, Harch 26 1984, submitted to Z. Phys. C.

2. B. Mansoulié, The UA2 apparatus at the CERN pp Collider, Proceedings 3rd MOriond

workshop on pp physics, editions Frontières, 1S33, p. 609.

3. P. Bagnaia et al., UA2 coll., Measurement of-very large transverse momentum jet pro

duction at the CERN pp collider, CERN-EP/64-12, February 2nd 1984, submitted for

publication in Phys.Lett. B.

4. F. Paige and s. Protopopescu, ISAJET, BNL report 31987 (1981}.

- 230 -

Tuble 1 ; E«ent parameters

Events A B C Unies

f 18.3 ± o.a 22.0 ± 0.9 54.4 ± 3.2 Gev/c a) 0.02 -0.23 0.24

Eleccroiï b) 0.97 0.76 0.002 b) 1] 7 14 mm2

b) 10 6 22 mip

f pT<ii> !? î J 67 i 7 38 t 5 CeV/c s) -0.59 -0.26 0.07 e) 50 3 LO 311 degrees

PT<j¡) 6 - 1 21 ± 3 GsV/c Je t.° < 1 íj!) a) 0.50 0,12

) àUh) c) 53 183 degrees

P.f(j.) 5 i 1 7 ± 1 OeV/c n (ji) s) -1.09 -1.38

c) 70 316 degrees E T(J) 3! ! Í 67 t 7 66 î 6 CeV m (J) 63 î 5 GeV/c2

P T(v) 51 i « 86 I 6 57 t 5 GeV/c C4(v) c) 220 141 141 degrees n\j,(ev) 56 i 2 Bl t 3 82 ± 4 CeV/c2

f" (WJ) 179 t 7 176 ± 9 162 ± 8 CeV/c2

{ » r( w J )

0.« i 0.04 -O.OL ± 0.06 -0.04 î 0,03

»V d) <D.016(9(80.) <0.016(90ÏCI.) <0.01i(902Ct.) d) 0,33 t 0.03 0.06 J 0.01 0.06 t 0.01

"qcD e) 0.4 1.2 10" 2 7 10 _ 1

a) The pseudo-rapidity n is positive in Ehe proton dirección. b ) EUccron quality parameters are defined in *ef. 1, c)-¿4> is che azimuth différente pich respect Co che electron (in degrees). d) Background evaluations Rv and Bj are described in the cexC (Sección A). e) Numbcv of H-jets ever.es expected Erora known producción processes (see

cexcî. f) Jet énergies are expected co be smaller chart Che parent par con energies

(aee text). This has not been corrected for and affeces all parameters depending upon jet energies.

http://ever.es

- 2 3 1 -

Heavy Flavours and Related Topics

- 232 -0 Î 8 * 1 0 O 2 ° " 6

D*" PRODUCTION AT THE CERN SPS COLLIDER (UAl Collaboration)

R. Prey University of California

Riverside, California 92521

1. INTRODUCTION * ^ Wè*report evidence for the production of the charged D nesone in pp

collisions at A - 560 GeV. The search w&¿ confined to the charged particle fragments of hadronic Jets. Preliminary results for the fragmentation

The UAl detector is described elsewhere . We mention briefly the detector elementa of importance for this study. The Central Detector, a large drift chamber immersed in a 0.7T dipole magnetic field, was used for momentum and ionization measurement of charged particles. The mean value of Ap/p 2 is

_2 (0.9x10 )/(GeV/c) for the data discussed here. Ionization accuracy is about ±10% for a track- if Ira length. Total jet energy is measured with accuracy AE/E = 20% by electromagnetic and hadronic calorioetry consii-.ing of lead/scintlllator stacks followed by the instrumented iron of the magnet yoke used as a hadron calorimeter.

The work reported here is based upon the data sample recorded in 1983 with integrated luminosity 118 nb . The following two simultaneously recorded triggers are relevant to this study.*

i) An "electron trigger", namely at least 10 GeV of localized transverse energy deposited in the central electromagnetic calorimeters,

il) A global "Ej, trigger", requiring more than 60 GeV of total transverse energy in all calorimeters with | T)| < 1.5.

The results presented here come from the 1.2^10 electron triggers having a localized electromagnetic cluster with transverse energy In excess of 15 GeV. These events were reconstructed for the W/Z search. However they also contain about 302; of all jets having E T > 20 GeV. A subset (272) of the trigger (i) events which also satisfied the global trigger was selected for this study.

2. METHOD Jets containing a minimum of three charged particles were identified by

applying a clustering algorithm to charged particle tracks. The jete were required to satisfy the following conditions: 16 45° with respect to the horizontal plane. Jets closer to the horizontal plane were excluded because of the relatively poor momenturn resolution in this region.

function and production

- 233 -

The search for D in jeta of cltarged particles followed the now standard procedure of looking for evidence of the decay sequence D * * •» D ° T I + •*• K ft*it+

as well as the charge conjugate mode. (Both modes are implied by the mention of one throughout this paper,) Kn and Knn mase combinations v r e formed from the charged tracks associated with the jets, N O particle Identification was used to distinguish between K and it, so both K and it assignments were considered for each track. However the central detector ionization measurement was used to identify e* arising from photon conversions in the beam pipe, delta rays, etc.; these slow electrons can mimic the n from D + D % + which has a mean momentum of only about 0 . 4 GeV/c in the kinematic range under study.

Figures la,b show the mass difference ÛM = HiVT-it*-!^") - M(K~* 1+) for (a)

all events, and (b) 1 . 8 3 < H ( K " T Ij + > < 1 . 9 2 GeV/c. Figures lc»d show the tC-k*

invariant mass distribution £or (c} all evenrs and (d) 146 < AM < 148 MeV/c 2. A Gaussian fit to the peak in AM (fig. lb) gives a mean of 1 4 7 . 0 MeV/c 2 and an rms deviation of 0 . 6 MeV/c 2, con»>atible with the estimated experimental resolution. The peak value is shifted by 1.6 MeV/c 2 from the canonical valae of 1 4 5.4 ± 0 . 2 MeV/c 2 3 \ This effect is most likely associated with the traversal of the slow n + through the beam pipe. The fitted mass and width of the K~it+ peak in fig* Ld are 1 . 8 7 0 CeV/c 2 and 2 2 Hev/c 2, compatible with the known D° mass and the estimated mase resolution.

3. RESULTS

3 . 1 Fragmentation Function

The peak at 1 4 7 MeV/c 2 in fig. lb containa 2 2 events on a background of 7. We have investigated the distribution in z = P D * * £ j e r / ( p j e t ) 2 f o r t n e a e

events, p^* is the D momentum measured in the central drift chamber and P j e t is the total jet momentum determined from the energy deposited in the calorimeter modules. When the total momentum of the charged particles in the jet was within 2 0 ° of the vertical gap in calorimetry the event was excluded from consideration, and a visual scan was used to further eliminate events with acceptance related problems. îhe z distribution for che remaining 7

events is shown in fig. 2 . The histogram shows the actual data; the points have been weighted to correct for itiefficiency in detecting the slow plon in D* + Du decay for D momentum below 6 GeV/c. This inefficiency increases rapidly below z of 0 . 1 and no attempt has been made here to extrapolate to z < 0 . 1 . The values of p ^ e t for these events range from 2 5 to 4 5 GeV/c. The sensitivity of <z> to various alternative definitions of z is less than 1 0 % .

- 2 3 4 -

3.2 Production Race — — x + + 3

We have observed 22 D ~ •*• K decays l a a t o t a l of 3.4x10 j e t s nee t ing the cond i t ions d i scussed I n s e c t i o n 2 . This number Inc ludes only j e t a

with a t l e a s t 3 t r a c k s . The corresponding t o t a l number of j e t s (from 3

ca l a r ime t ry ) i n the same range of asimuth and r a p i d i t y i s 4.Qxio , with mean

of 27 GeV. The t o t a l number of D * i a obtained us ing B { D * + + D ° T I + *

k " J E + T Í + ) » 1.3 ± 0.4 % y an e f f i c i ency for z > 0.1 of 0.42 ± 0 . 1 8 , and a

f r a c t i o n of D events excluded by the masa c u t s of 0.20 1 0 . 1 3 . Then

N(D* ± ) /N( je t ) » 1.2 t 0 .2 ± 0.7 . 4 . DISCUSSION AND CONCLUSION

Although the sys temat ic e r r o r i s l a r g e , the number of D * per j e t given *o

above Beems s u r p r i s i n g l y h igh , and the number of D could presumably be equa l

to D*~. However we note t h a t t h i s measurement a p p l i e s only to j e t s i n even ts

s a t i s f y i n g combined e l e c t r o n and g loba l t r i g g e r s , and may well be d i f f e r e n t

for an unbiased j e t s e l e c t i o n .

h\ 4. -

Severa l s t u d i e s of heavy quark production i n e e a n n i h i l a t i o n i n d i c a t e

t h a t j e t s i n i t i a t e d by the heavy quark fragment i n such a way t h a t the hadron

ca r ry ing the heavy f l avor t akes a l a r g e f r a c t i o n of the t o t a l j e t momentum

(<Z(D*)> - 0 . 5 ) . However in pp i n t e r a c t i o n s a t A. of 540 GeV, gluon r a t h e r

than quark i n i t i a t e d j e t s a r e expected t o dominate for j e t E_ va lues below c c\ r

about 50 GeV * . Indeed the r a t e of charm product ion observed he re i s about 2 5) a f ac to r of. 10 h igher than p red ic ted for c-quark i n i t i a t e d j e t s ; i n a d d i t i o n the D fragmentat ion func t ion ( f i g . 2) i s much so f t e r than those

measured for c-quark i n i t i a t e d j e t s . A l i k e l y conclusion concerning t h e charm

product ion repor ted here i s then t h a t i t r e s u l t s from the fragmentat ion of

gluon i n i t i a t e d j e t s , a l though product ion v ia t h e decay of a copious ly

produced heavy ob jec t can not be ru led out a t t h i s p o i n t . A gluon j e t would

g ive r i s e to production of charmed p a r t i c l e s i n p a i r s , each p a i r r e s i d i n g

wi th in t he j e t . Even ao, t he l a r g e charm conten t of j e t s observed h e r e i s

perhaps a consequence of t he f l avo r independence of the gluon-quark coup l ing . REFERENCES AND FOOTNOTES

1. UAl C o l l a b . , G* Arnison e t a l . , Phys . L e t t . 122B (1983) 103. 2. The lower limlc_ i s Imposed due to low r e c o n s t r u c t i o n e f f i c i e n c y of the T I

from D D°7i_ a_t+low momentum. Because of s t eep ly f a l l i n g s p e c t r a i n P T few D -* K n Tt a r e l o s t by imposing the upper l i a i t , t hus l eav ing a narrow range of for the fragmentat ion funct ion s t udy .

3 . P a r t i c l e Data Group, Phys. L e t t . U1B (1982) . 4 . See for i n s t a n c e , J . Dorfan t P roc . 1963 Symposium on Lepton and Photon

I n t e r a c t i o n s a t High Energy, Corne l l , (Corne l l U n i v e r s i t y , 1983), p . 686. 5 . R. Horgan and M. Jacob , Nucl. Phya. B179_ (1981) 441 . 6. See c o n t r i b u t i o n a t t h i s conference by K-. K. E l l i s .

- 235 -

132 130 HQ M4 H9 152 IS6 100 188

Fig. ïa. AM distribution in the region of M(D A ±)-M(D 0) for all events.

0 l — i 1 ' ' 1 1 ' >-

1.5 1.7 1.0 3.1 Í . 3

¡1M'M„„-M,, i.'icv 'c""i

Fig. lb. AM distribution for L.83 < M(Kit> < 1.92 GeV/c 2.

Fig. lc. M(Kic) distribution in the region of H(D°) for ail events.

Fig. Id. M(Kn) distribution for 146 < AM < 148 MeV/c 2.

236 -

O 0.1 0,2 0.3 0.4 0.0 O.e 0.7 0.B 0.0 1

dN/dz g

Fig. 2 D - fragmentation function fo:? z > 0.1. The histogram at top shows the uncorrected data. The bottom plot has been corrected for the track finding inefficiency of the + *+ o + ir." from D -+D TÏ . The mean value of z for z > 0.1 I B 0.2.

- 237 -

C. JarlBkog

Department of Physics University of Stockholm

Stockholm, Sweden

0 : 8 4 1 0 0 2 6 2 4 4

A B S T R A C T

The present status of the weak mixing angles, in the standard six quark model, is re

viewed. The implications of the recent measurements of the beauty lifetime and branching

ratios are discussed, in the framework of the Kobayashi-Maskawa and the Wolfenstein

parametrizations. Expectations for B ° - B ° mixing and consequences for the collider data

are given. Other topics briefly reviewed are CP-violation, top quark mass and possible

I implications of the existence of a fourth family.

* On sabbatical leave from University of Bergen, Bergen* Norway.

W E A K MIXING A N G L E S A N D H E A V Y F L A V O U R S

- 2 3 8 -

T h e C E R N A n t i p r o t o n - P r o t o n - C o l H d e r h a s , w i t h i n t h e p a s t c o u p l e o f y e a r s , p r o -

i o

d u c e d v e r y b e a u t i f u l d a t a . T h a n k s t o i t t h e I n t e r m e d i a t e b o s o n s W a n d Z a r e n o

l o n g e r a m o n g t h e f i c t i t i o n s p a r t i c l e s " o n l y " r e q u i r e d b y t h e t h e o r y ' b u t b e l o n g t o t h e

r e a l w o r l d .

D u r i n g t h i s M e e t i n g w e h e a r d t h a t t h e m o s t r e c e n t c o l l i d e r d a t a m a y i n f a c t b e

i n d i c a t i n g t h a t w e a r e n o w e n t e r i n g i n t o a n e w E r a , t h e P o s t S t a n d a r d M o d e l E r a . I n d e e d

I w a s t o l d b y a g r e a t p h y s i c i s t ( i t i s l e f t t o t h e r e a d e r t o f i g u r e o u t w h o ) t h i s m o r n i n g

t u a t " t h e s t a n d a r d m o d e l i s f i n i s h e d " . I t m a y w e l l t u r n o u t t o b e s o , n e v e r t h e l e s s , i n

t h i s t a l k I s h a l l a s s u m e t h a t t h e s t a n d a r d m o d e l i s s t i l l O . K . A f t e r a l l , n o o n e e x p e c t s

t h e s t a n d a r d m o d e l t o b e t h e " U l t i m a t e T h e o r y " , a n d i n d e e d a n y d e v i a t i o n f r o m t h e p r e

d i c t i o n s o f t h e s t a n d a r d m o d e l w h i c h c o u l d h e l p u s i n a d e e p e r u n d e r s t a n d i n g o f N a t u r e

\ v i l l b e m o s t w e l c o m e . N o m a t t e r w h a t h a p p e n s , t h e s t a n d a r d m o d e l w i l l a l w a y s b e r e

m e m b e r e d a s o n e o f t h e g r e a t s t e p s i n p r o g r e s s i n p h y s i c s .

I n t h i s t a l k I s h a l l d i s c u s s t h e f o l l o w i n g t o p i c s :

1 . W e a k m i x i n g a n g l e s i n t h e s t a n d a r d m o d e l

2 . W h a t d o w e k n o w a b o u t t h e V . .

2 . 1 T h e C a b i b b o - s e c t o r

2 . 2 T h e G E M - s e c t o r

2 . 3 T h e K M - 3 > s e c t o r

3 . T h e W o l f e n s t e i n p a r a m e t r i z a t l o n

4 . M ° - M ° s y s t e m s , C P - v i o l a t i o n a n d t h e t o p q u a r k m a s s

4 . 1 T h e b o x a p p r o a c h ; Am a n d Ar f o r t h e n e u t r a l k a o n s

4 . 2 C P - v i o l a t i o n , £ a n d fc' f o r t h e K - s y s t e m

"o - o

5 . B - B m i x i n g 5.1 S i g n a t u r e s o f B ° - B ° m i x i n g

s s

6 . B e y o n d t h r e e f a m i l i e s

7 . C o n c l u d i n g r e m a r k s

R e f e r e n c e s

file:///vill

- 2 3 9 -

1 . W E A K M I X I N G A N G L E S I N T H E S T A N D A R D M O D E L

T h e w e a k m i x i n g , w h i c h I w a s a s k e d t o d i s c u s s , i s r e l a t e d t o t h e c o u p l i n g c o n s t a n t s

o f W -» f f " , w h e r e ( f , f ) d e n o t e a p a i r o f q u a r k s o r l e p t o n s ( F i g . 1 ) .

I t i s i m p o r t a n t t o k e e p i n m i n d t h a t t h e v e r t i c e s i n F i g . 1 ( a s w e l l a s t h o s e f o r W )

a c c o u n t f o r a l l t h e o b s e r v e d f l a v o u r - c h a n g i n g p h e n o m e n a i n N a t u r e . M o r e o v e r , t h e r e

s e e m s t o b e a m a j o r d i f f e r e n c e b e t w e e n t h e l e p t i n l c a n d h a d r o n i e t r a n s i t i o n s i n F i g , 1 .

T h e l e p t o n s p r o d u c e d b e l o n g t o t h e s a m e f a m i l y v a e r e a s t h e q u a r k s m a y e i t h e r b e l o n g t o

t h e s a m e f a m i l y ( e . g . , W - * d u ) o r t o t w o d i f f e r e n t f a m i l i e ( e . g . , W - * d o ) . T h u s , in

t h e l e p t o u i c s e c t o r t h e ( f a m i l y } m i x i n g a n g l e s a r e a l l c o n s i s t e n t w i t h z e r o a n d I s h a l l n o t

d i s c u s s t h e m h e r e ( f o r a r e v i e w o f t h e p r e s e n t s i t u a t i o n s e e , f o r e x a m p l e , R e f . 4 . )

T h e L a g r a n g i a n r e s p o n s i b l e f o r t h e b a d r o n i c t r a n s i t i o n s i n F i g . 1 h a s t h e f o r m

w h e r e t h e V ' s a r e c o u p l i n g c o n s t a n t s ; t h e n o t a t i o n s a r e e x p l a i n e d i n d e t a i l i n R e f s . 5 a n d 6 .

W i t h a r b i t r a r y v ' s , t h e a b o v e L a g r a n g i a n i s a s i m p l e g e n e r a l i z a t i o n o f t h e F e y n m a n - G e l l -

- M a n n W - m e d i a t e d V - A L a g r a n g i a n o f t h e y e a r 1 9 5 8 . A s t h e V ' s a r e , i n g e n e r a l ,

c o m p l e x n u m b e r s i t w o u l d s e e m t h a t i n E q . ( 1 ) t h e r e a r e 2 x 9 - 1 = 1 7 ( a n o v e r a l l p h a s e i s

i r r e l e v a n t ) r e a l p a r a m e t e r s t o b e d e t e r m i n e d b y e x p e r i m e n t . H o w e v e r , i n t h e s t a n d a r d

m o d e l t h e 3 b y 3 m a t r i x I n ( 1 ) , h e r e a f t e r d e n o t e d b y V » i s u n i t a r y a n d m o r e o v e r , a s

s h o w a ^ ^ b y K a b a y a s t u a n d M a s k a w a < K M ) , d e p e n d s o n o n l y 4 r e a l p a r a m e t e r s » 3 r o t a t i o n

a n g l e s ®-j 2 3 a n t * a P n a s G a n g l e 6 . T h e K M p a r a m e t r i z a t i o n ^ ^ i s r e p r o d u c e d ^ b y t h e

f o l l o w i n g p r o d u c t o f 3 r o t a t i o n m a t r i c e s a n d a p h a s e m a t r i x

4

F i g . 1

c 4' » ase* , s» •* sm 0 » , ô i t t í «/« , f f S < A J B •

- 240 -

T h e o b s e r v e d C P - v i o l a t i o n i m p l i e s t h a t a l l f o u r a n g l e s a r e n o n z e r o . L i f e m i g h t

s e e m c o m p l i c a t e d e n o u g h , b u t i t o o u l d h a v e b e e n m u c h w o r s e l F o r e x a m p l e , i f t h e r e

w e r e f o u r f a m i l i e s V w o u l d b e a 4 b y 4 m a t r i x , o b t a i n e d f r o m t h e p r o d u c t o f 6 r o t a t i o n

m a t r i c e s a n d 3 p h a s e m a t r i c e s , a n d t h e d e g r e e o f c o m p l i c a t i o n i n c r e a s e s r o u g h l y q u a d -

r a t i c a l l y w i t h t h e i n c r e a s i n g n u m b e r o f f a m i l i e s ( n ( n - 1 ) / 2 r o t a t i o n m a t r i c e s a n d

( n - 1 ) ( n - 2 ) / 2 p h a s e m a t r i c e s ; n = n u m b e r o f f a m i l i e s ) .

T h e s t a n d a r d m o d e l d o e s not e x p l a i n w h y N a t u r e i s l e f t - r i g h t a s y m m e t r i c . T h e

l e f t - r i g h t s y m m e t r i c m o d e l s d o b e t t e r i n t h i s r e s p e c t , a s t h e a s y m m e t r y i s a t t r i b u t e d

t o t h e s p o n t a n e o u s s y m m e t r y b r e a k i n g . O n t h e o t h e r h a n d , t h e s i m p l e s t l e f t - r i g h t

s y m m e t r i c m o d e l h a s t h r e e m o r e g a u g e b o s o n s a n d m u c h m o r e i n v o l v e d H i g g s s e c t o r .

T h e p o i n t I w o u l d l i k e t o e m p h a s i z e h e r e i s t h a t w e dont u n d e r s t a n d t h e q u a r k m i x i n g

p h e n o m e n o n . T h e e l e m e n t s o f t h e m a t r i x c a n n o t b e p r e d i c t e d f r o m " f i r s t p r i n c i p l e s " .

I n d e e d , a s o f t o d a y , " S u s y d o e s n o t a t t a c k t h e f a m i l y p r o b l e m " \ C o m p o s i t e p e o p l e h a v e

n o f a m i l i e s 1 * ^ , a n d s o o n . H o w e v e r , i n s o m e m o d e l s 1 1 \ b y m a k i n g s o m e a s s u m p t i o n s

a b o u t t h e g e n e r a l s t r u c t u r e o f t h e q u a r k m a s e m a t r i c e s , o n e f i n d s i n t e r e s t i n g p r e d i c t i o n s

f o r t h e c o u p l i n g c o n s t a n t s V . . . A n o t h e r i n t e r e s t i n g p o i n t i s t h a t i f t h e r e a r e m o r e f a m i

l i e s , b e c a u s e o f t h e u n i t a r i t y o f t h e m a t r i x V , b y m e a s u r i n g t h e s t r e n g t h o f t h e o b s e r v e d

t r a n s i t i o n s o n e , i n p r i n c i p l e , o b t a i n s a m e a s u r e o f t h e " l e a k a g e " to t h e u n o b s e r v e d f a m i

l i e s , f o r e x a m p l e

w h e r e k d e n o t e s t h e c h a r g e - 1 / 3 q u a r k s o f t h e a s y e t u n o b s e r v e d f a m i l i e s . T h e m e a s u r e d

( l o n g ) b - l i f e t i m e i s h o w e v e r i n d i c a t i n g t h a t t h e " l e a k a g e " i s d e c r e a s i n g r a p i d l y ( a t l e a s t

f o r t h e t h i r d f a m i l y ) a n d i t m i g h t b e i m p o s s i b l e t o l e a r n a n y t h i n g a b o u t t h e a s y e t u n b o r n

f a m i l i e s , e v e n i f w e c o u l d m e a s u r e t h e c o u p l i n g c o n s t a n t s q u i t e a c c u r a t e l y , s i n . p l y b e

c a u s e t h e h i g h e r f a m i l i e s a r e l e s s c o m m u n i c a t i v e ( s e e s e c t i o n 6 ) .

2 . W H A T D O W E K N O W A B O U T T H E V . . ? l i _

T h e V . . a r e ( f u n d a m e n t a l ? ) n a t u r a l c o n s t a n t s . I n p r i n c i p l e , t h e b e s t w a y t o d e t e r

m i n e t h e m i s t o m e a s u r e t h e s t r e n g t h o f a l l h a d r o n i c d e c a y c h a n n e l s o f t h e W . H o w e v e r ,

a s o f t e n h a p p e n s , w h a t c a n b e d o n e " i n p r i n c i p l e " s e e m s t o b e o r t h o g o n a l t o •wha t i s f e a

s i b l e i n p r a c t i c e . A t t h e m o m e n t i t i s n o t c l e a r w h e t h e r w e s h a l l l e a r n a n y t h i n g i n t h e n e a r

f u t u r e a b o u t t h e V s f r o m t h e W s w h o a r e p r o d u c e d a n d d e c a y a t t h e C E R N p p - c o l l i d e r .

2 4 1 •

2 . 1 T h e C a b i b b o <2 > .

1 3 ^ ß V . h a s b e e n k n o w n f o r a l o n g t i m e , h o w e v e r i t u s e d t o b e c a l l e d G _ r .

u d V I t i s

d e t e r m i n e d f r o m t h e ( t - v a l u e s o f O - O ' n u c l e a r b e t a t r a n s i t i o n s a n d f r o m t h e n e u t r o n

l i f e t i m e . I n t h e m o d e r n l a n g u a g e a l l t h e s e p r o c e s s e s i n v o l v e u • * d + e + + » , d - + u - t - e + y ,

i . e . , t h e b e t a d e c a y o f a v i r t u a l u p o r d o w n q u a r k . T h e s t r e n g t h o f t h e s e t r a n s i t i o n s

c o m p a r e d w i t h t h a t o f th < n u o n d e c a y g i v e s V ^ .

T h e c o n s t a n t V i s d e t e j p i n e d f r o m t h e r e a c t i o n s s - * u + e + iF, s -*u + fi + * u s

( a n d a n t i r e a c t i o n s ) w h i c h t a k e p i ' j e i n a m e s o n o r a b a r y o n . R e c e n t l y t h e C E R N W A 2 -

1 4 Ï C o l l a b o r a t i o n ' h a s p r e s e n t e d u s w i t h t h e m o s t a c c u r a t e v a l u e o f w h i c h i s o b t a i n e d

( F i g . 2 ) .

T h e W A 2 - C o l l a b o r a t i o n h a s a l s o r e a n a l y z e d

t h e p r e s e n t i n f o r m a t i o n o n V ^ . T h e y f i n d ,

a f t e r a p p l y i n g r a d i a t i v e c o r r e c t i o n s ,

| V J I = 0 . 9 7 3 5 ± 0 . 0 0 1 5 u d

JV I = 0 . 2 3 1 ± 0 . 0 0 3

( 4 ) F i g . 2

I t i s g r a t i f y i n g t h a t t h e v a l u e o f V " u g h a s b e e n q u i t e s t a b l e i n t h e p a s t . A c t u a l l y , i t

i s a m u s i n g t o n o t e t h a t t h e v e r y f i r s t e s t i m a t e o f V u s d a t e s b a c k t o 1 9 6 0 w h e n G e l l - M a n n

a n d L e v y 1 5 * , i n t h e f r a m e w o r k c f t h e S a k a t a M o d e l 1 6 ) ( w h i c h h a d n o q u a r k s b u t m a d e

b a d r o n s o u t o f p , n , A a n d t h e i r a n t i p a r t i c l e s ) f o u n d 0 . 2 3 . T r a n s l a t i n g

p , n , A - * u , d , s g i v e s V « * 0 . 2 3 w h i c h h a p p e n s t o b e w h a t o n e f i n d s n o w , E q . ( 4 ) . A f t e r u s

h a v e a p p e a r e d i n

t h e l i t e r a t u r e 1 7 )

w i t h r e s u l t s i n t h e v i c i n i t y o f t h e v a l u e s i n ( 4 ) . T h u s w e d o n t e x p e c t

to c h a n g e m u c h i n t h e f u t u r e .

2 . 2

T h e c o u p l i n g c o n s t a n t s V , a n d V cd c,

a r e m e a s u r e d b y s t u d y i n g d i m u o n p r o d u c t i o n

i n n e u t r i n o a n d a n t i n e u t r i n o i t e r a c t i o n s ( F i g . 3 )

3* / » " Si

x F i g . 3

- 242 -

T h e v ; t l u e oí' V î v r i s , h o w e v e r , b e c a u s e o f t h e u n c e r t a i n t i e s m e n t i o n e d tiuove, very c s

p o o r l y d e t e r m i n e d . A s a n e x a m p l e t h e r e s u l t s f o u n d b y t h r e e i n d e p e n d e n t g r o u p s w e r e

V , V c d c s

P a s c h o s a n d T t i r k e 2 0 * 0 . 2 5 ± 0 . 0 4 > 0 . 8 1 ( t í a )

0 . 2 0 í o . O l i > 0 . ( > 6 ( l i b )

K l e i n k n e c h t a n d R e n k " " ' 0 . 2 4 * 0 . 0 3 > 0 . 5 9 ( B e )

A s f a r a s t h e d e t e r m i n a t i o n o f t h e s e c o u p l i n g c o n s t a n t s d i r e c t l y f r o m d a t a i s c o n

c e r n e d n o t h i n g h a s c h a n g e d s i n c e t h e l a s t s u m m e r , H o w e v e r , i n t h e f r a m e w o r k o f t h e

s t a n d a r d s i x - q u a r k m o d e l , t h e V ' s a r e n o t i n d e p e n d e n t . L s i n g t h e r e c e n t i n f o r m a t i o n

o n b e a u t y d e c a y a n d t h e u n i t a r i t y o í V o n e m a y p i n d o w n t h e c o n s i d e r a b l y , a s I s h a l l

d i s c u s s b e l o w .

2 . 3 """to K M - L e d e r m a n s e c t o r

L a s t s u m m e r , a t t h e B r i g h t o n " " * * a n d C o r n e l l " 4 * C o n f e r e n c e s , a n a m a z i n g l y l o n g

l i f e t i m e f o r t h e b e a u t y w a s r e p o r t e d . I n g e n e r a l o n e e x p e c t e d ' ^ t h e b e a u t y l i f e t i m e to

be s h o r t e r t h a n U t e c h a r m l i f e t i m e . T h e w o r l d - a v e r a g e d D - l i f e t i m e s u r c ^ ' * '

T h e r e a r e s e v e r a l u n c e r t a i n t i e s I n s u c h a d e t e r m i n a t i o n . T h e d o u b l e d i f f e r e n t i a l c r o s s

s e c t i o n s f o r c h a r m p r o d u c t i o n i n n e u t r i n o a n d a n t t n e u t r i n o c h a r g e d c u r r e n t i n t e r a c t i o n s

i n a n i s o s c a l a r t a r g e t a r e o f t h e f o r m

rfirrfj v a l e n c e s e a

+M*3 s e a s e a

1 9 )

w h e r e t h e n o t a t i o n i s t h e s t a n d a r d o n e ; u ( x ) d e n o t e s t h e d i s t r i b u t i o n f u n c t i o n fot* t h e

u p q u a r k i n t h e p r o t o n w h i c h i s a s s u m e d t o be e q u a l to t h a t o f t h e d o w n q u a r k i n t h e

n e u t r o n , e t c . T h u s t h e k n o w l e d g e o f t h e s t r a n g e q u a r k c o n t e n t o f t h e n u c l e ó n i s e s s e n t i a l ,

e s p e c i a l l y f o r t h e a n t i n e u t r i n o c a s e , w h e r e t h e s t r a n g e q u a r k g i v e s t h e d o m i n a n t c o n t r i

b u t i o n . T h e p n r t o n d i s t r i b u t i o n f u n c t i o n s , i n ( 5 ) , a r e d e t e r m i n e d f r o m t h e d e e p i n e l a s t i c

p r o c e s s e s . O n e a l s o n e e d s t o k n o w t h e e f f e c t i v e s e m í l e p t o n i t ; b r a n c h i n g r a t i o o f t h e

m i x t u r e o f c h a r m p a r t i c l e s w h i c h i s p r o d u c e d i n n e u t r i n o i n t e r a c t i o n s . F o r a m o r e d e

t a i l e d d i s c u s s i o n s e e , í o r e x a m p l e R e f s . 20-22. B e f o r e t h e h i s t s u m m e r , t h e r e w e r e s e v e r a l i n d e p e n d e n t d e t e r m i n a t i o n s o f t h e s e

- 243 -

f<tfj = ( 4 . 4 ± 0 . 6 ) 1 0 " s ( 7 )

f * < t f ) = ( 8 . 8 i 1 . 2 ) 1 0 _ 1 3 s .

- 1 4 T h e e x p e c t e d b e a u t y l i f e t i m e w a s o f t h e o r d e r o f 1 0 s . T h e r e a s o n f o r e x p e c t i n g a

s h o r t e r b - l i f e t i m e t h a n t h e c - l i f e t i m e I s d u e t o t h e l a r g e r p h a s e s p a c e a v a i l a b l e I n t h e

5 5

b - d e c a y , s p e c i a l l y i f b " * u w o u l d h a v e b e e n t h e d o m i n a n t m o d e , ( n ^ / n ^ ) « ( 5 / 1 , 5 ) *** 4 0 0 .

O n t h e o t h e r h a n d , t h e c " * s i s a t r a n s i t i o n w i t h i n t h e f a m i l y w h i l e b " * u , c n e c e s s a r i l y i n

v o l v e s a f a m i l y " j u m p " ( s e e F i g . 4 ) .

F i g . 4

T h u s s o m e s u p p r e s s i o n , i n t h e t r a n s i t i o n r a t e , w a s e x p e c t e d . A r e a s o n a b l e g u e s s w a s

0 ~ — 1 / 2 0 . T h u s i f t h e m e a s u r e m c n t g w o u l d h a v e f o u n d T ( b ) / T ( c ) = 1 / 2 0 n o b o d y w o u l d

h a v e b e e n s u r p r i s e d . B u t t h e r e s u l t s r e p o r t e d b y t h e M A C a n d M A R K - I I C o l l a b o r a t i o n s

c a m e a s a r e a l s u r p r i s e . T h e p u b l i s h e d v a l u e s o f t h e b - l i f e t l m e a r e

2 7 \ - 1 2 M A C - C o l l . ' r ( b ) = ( 1 . 8 ± 0 . 6 ± 0 . 4 ) 10 s

( 8 )

M A R K - n - C D l l . 2 8 ) = ( 1 . 2 0 ^ - * g i 0 . 3 0 ) 1 o " 1 2 s

T h i s y e a r t h e M A C - C o l l o b o r a t i o n h a s o b t a i n e d a n e w v a l u e ;

T ( b ) = ( 1 . 6 ï 0 . 4 ± 0 . 3 ) 1 0 _ 1 2 s ( 9 ) 29)

a n d M A R K - U w i l l a l s o s o o n q u o t e a n i m p r o v e d r e s u l t

T h e l o n g b - l l f e t i m e i m p l i e s t h a t b o t h I v ^ l a n d I v ^ l a r e s m a l l ( c C > ( f l ^ ) ,

w h e r e 8 = C a b i b b o a n g l e ) . F u r t h e r m o r e , i t h a s b e e n k n o w n f o r s o m e t i m e t h a t t h e b c '

d e c a y s p r e f e r e n t i a l l y t o c . F r o m c o m p a r i n g t h e s h a p e o f t h e e n e r g y s p e c t r u m o f t h e l e p

t o n s p r o d u c e d i n t h e s e m i l e p t o n i c b - d e c a y w i t h t h e t h e o r e t i c a l e x p e c t a t i o n s f o r b - * u tv

a n d b -* c tv o n e f i n d s

B r ( b - * c e y ) b - » c 1 '

B ^ O . 0 3 9 0 % c . l .

5 0 . 0 4 9 5 % c . l .

o b t a i n e d f r o m c o m b i n i n g t h e C L E O 3 1 ' a n d C t f S P d a t a , f r o m C E S R . T h e a b o v e i n f o r m a t i o n

- 244 -

g i v e s ( f o r d e t a i l s a n d f o r m u l a e s e e , f o r e x a m p l e E e f . 2 6 )

1 ^ 1 * 0 . 1 1 , ( 1 2 ) CD

| V b l = 0 . 0 5 ± 0 . 0 1 ( 1 3 )

T h u s t h e c o u p l i n g c o n s t a n t f o r t h e t r a n s i t i o n f r o m t h e t h i r d t o t h e s e c o n d f a m i l y i s

a p p r o x i m a t e l y e q u a l t o t h e s q u a r e o f t h e c o u p l i n g c o n s t a n t f o r t h e t r a n s i t i o n b e t w e e n t h e

s e c o n d a n d t h e f i r s t f a m i l i e s . F o r t h e r a t e s t h a t m a t t e r s a l o t u s t h e s q u a r e o f t h e

c o u p l i n g c o n s t a n t e n t e r s . T h e a b o v e r e s u l t s i n d i c a t e t h a t w h e r e a s t h e t r a n s i t i o n s b e t w e e n

t h e f i r s t a n d t h e s e c o n d f a m i l i e s a r e o n l y " f i r s t f o r b i d d e n " ( C a b t b b o - s u p p r e s s e d ) t h o s e

a m o n g t h e s e c o n d a n d t h e t h i r d a r e " s e c o n d f o r b i d d e n " ( d o u b l y C a b i b b o - s u p p r e s s e d ) .

T h e r e h a v e b e e n s e v e r a l r e c e n t d e t e r m i n a t i o n s M t h e V ' s i n s p i r e d b y t h e l o n g

b - l i f e t i m e . U n f o r t u n a t e l y f c a n ' t q u o t e a l l o f t h e m h e r e b e c a u s e t h e n I w o u l d v i o l a t e t h e

( p a g e ) u n i t a r i t y l i m i t i m p o s e d b y t h e o r g a n i z e r s . A f e w o f t h e p a p e r s a r e , h o w e v e r ,

q u o t e d i n R e f s . 3 2 a n d 3 3 . T h e s e d e t e r m i n a t i o n s u s e t h e o l d v a l u e o f R , R < 0 . 0 5 . W i t h

t h e n e w l i m i t , R $ 0 . 0 3 , t h e a n a l y s i s n e e d s b e r e d o n e , a s t h e V ' s a r e s o m e w h a t a f f e c t e d .

I n s u m m a r y , t h e V ' s , a s o f t o d a y , a r e

| V , I = 0 . 9 7 3 5 ± 0 . 0 0 1 5 , Iv | = 0 . 2 3 1 ± 0 . 0 0 3 . I v ^ I 0 . 0 0 6 u d u s u b

| V J I = 0 . 2 4 ± 0 . 0 3 [ V |s* 0 . 9 6 |v . I = 0 . 0 5 ± 0 . 0 1 (14) ' c d c s 1 c b

|v_, I S 0 . 0 6 | V , ! S 0 . 0 6 I v.. I 5 0 . 9 9 8 t d t s t b

w h e r e I h a v e t a k e n t h e e x p e r i m e n t a l v a l u e s ( E q s . ( 4 ) , ( 6 c ) ) a n d h a v e u s e d t h e r e s u l t s

( 1 2 ) a n d ( 1 3 ) . T h e r e m a i n i n g e n t r i e s i n ( 1 4 ) f o l l o w f r o m u n i t a r i t y . N o t e t h a t t h e l i m i t

o n | V c s I, f r o m u n i t a r i t y i s n o w b y f a r s u p e r i o r t o t h e m e a s u r e d v a l u e , E q . ( 6 ) . A c t u a l l y ,

o n e g e t s a m u c h b e t t e r f e e l i n g f o r t h e a b o v e c o u p l i n g c o n s t a n t s i n t h e W o l f e n s t e i n a p p r o a c h

w h i c h i s r e v i e w e d i n t h e n e x t s e c t i o n .

3 . T H E W O L F E N S T E I N P A R A M E T R I Z A T I O N '

T h e a b o v e s t r u c t u r e o f t h e e l e m e n t s o f t h e f a m i l y m i x i n g m a t r i x V i s v e r y n i c e l y

s u m m a r i z e d i n a t r a n s p a r e n t a n d e a s y t o r e m e m b e r p a r a m e t r i z a t i o n b y W o l f e n s t e i n , a s I

s h a l l d e s c r i b e n o w .

W e k n o w f r o m e x p e r i m e n t t h a t t h e c o u p l i n g c o n s t a n t |v I i s a r a t h e r s m a l l n u m b e r . us

L e t u s , f o l l o w ! i g W o l f e n s t e i n , d e f i n e V ^ = \ a n d e x p a n d t h e m a t r i x V i n p o w e r s o f \ »

0 . 2 3 . T h i s i s p o s s i b l e t o d o i f w e u s e t h e a v a i l a b l e e x p e r i m e n t a l i n f o r m a t i o n ( E q s . ( 4 ) ,

( 1 2 ) a n d ( 1 3 ) ) t o f i x t h r e e o f t h e n i n e e l e m e n t s o f V . W e p u t

- 2 4 5

w h e r e l ^ ) . 2 3 i o d A i l . 0 f o l l o w f r o m £ q s . ( 4 ) a n d ( 1 3 ) . F u r t h e r m o r e , t h e l i m i t

l v . / V J « 0 . 1 i t e l l s u s t h a t u b c b

T h e r e m a i n i n g e l e m e n t s o f V a r e n o w e a s i l y a c c e s s i b l e , t h r o u g h u n i t a r i t y o f t h e m a t r i x V

w h i c h p r o v i d e s e x t r e m e l y p o w e r f u l c o n s t r a i n t s , r o w U> .row<}>aS»j , w l * * > t c j .

F o r e x a m p i e , t h e c o n s t r a i n t | c o ¡ ( 3 ) | 2 = 1 y i e l d s i m m e d i a t e l y t h a t

— > + h i g h e r o r d e r s

T h u s t h e c o u p l i n g c o n s t a n t f o r X.<-> b i s e v e n c l o s e r t o \ t h a n t h a t o f u * + d , w h i c h f r o m

| r o w ( 1 ) | = I , i s |v d l = 1 - y + h i g h e r o r d e r s . R e p e a t e d u s e o f t h e u n i t a r i t y c o n

s t r a i n t s y i e l d s , t o o r d e r A 3 ,

V = ( x-t A > * I • • i / ) ( 1 7 )

2 2 w h e r e p a n d TJ u r e t w o r e a l c o n s t a n t s r e s t r i c t e d b y o + T) 0 . 2 3 » a r e l a t i o n w h i c h

f o l l o w s f r o m t h e u p p e r l i m i t |v , / V , | < 0 . 1 1 . N o t e t h a t 7) p l a y s t h e r o l e o f 6 , o f t h e u b c b

K M - p a r a m e t r i z a t i o n , a s t h e o r i g i n o f t h e C P - v i o l a t i o n . T h e K M a n d W o l f e n s t e i o p a r a -

r A 3 ,

Í | S * Va

*s« A >*£/•«• i » / *

2 - 3 A s tf Ç 0 . 2 3 o n e i m m e d i a t e l y f i n d s s s _ s i n ô £ 1 0 ; t h i s c o m b i n a t i o n a p p e a r s i n C P -

2 2

- v i o l a t i o n c a l c u l a t i o n s ( s e e s e c t i o n 4 . 2 ) . I t i s n o w e a s y t o u s e ( 1 8 ) a n d p +r¡ £ 0 . 2 3

t o g i v e t h e r a n g e o f t h e K M - p a r a m e t e r s

m e t e r s a r e r e l a t e d , t o o r d e r A 3 , v i a

- 2 4 6 -

I f t h e u p p e r l i m i t o n r a t i o R , E q a . ( 1 0 ) a n d ( 1 1 ) , s h o u l d d e c r e a s e f u r t h e r t h e u p p e r l i m i t

o n n w i l l a l s o g o d o w n a n d t h e s i x q u a r k m o d e l , a s t h e o r l g t n o f t h e C P - v i o l a t i o n , w i l l

b e r u l e d o u t . W h a t a n i r o n y o f f a t e ! T h e s i x q u a r k m o d e l w a s i n v e n t e d * * ' , p r i o r t o t h e d i s -

c o v e r y 3 4 ' o f t h e b - q u a r k , i n o r d e r t o e x p l a i n t h e o b s e r v e d C P - v i o l a t i o n a n d i t m a y w e l l

t u r n o u t t h a t j u s t t h e o b s e r v e d C P - v i o l a t i o n w i l l c a i s s e t h e f a l l o f t h e s i x q u a r k m o d e l .

4 . M ° - M ° S Y S T E M S , C P - V I O L A T I O N A N D T H E T O P Q U A R K M A S S

I n t h e f o l l o w i n g M ° d e n o t e s a n e u t r a l s p i n l e s s b o s o n s u c h a s K ° , D ° , B ° , B ° , . . .

I n t h e p r e v i o u s s e c t i o n s t h e v a l u e s o f t h e c o u p l i n g c o n s t a n t s q u o t e d ( i . e . , E q s . ( 1 4 )

a n d ( 1 9 ) ) w e r e r a t h e r m o d e l i n d e p e n d e n t . O f c o u r s e t h e t r e a t m e n t o f t h e p h a s e s p a c e ,

q u a r l c m a s s e s , etc. do mutter in determining the coupling constants out these dont i n v o l v e

a n y " d e e p t h e o r e t i c a l p r e j u d i c e s . I f o n e w i s h e s t o go f u r t h e r ( a n d a s t h e o r i s t s w e u s u a l l y

l i k e t o g o a s f a r a s w e c a n , p e r h a p s s o m e t i m e s a b i t t o o f a r ) o n e m u s t m a k e a s s u m p t i o n s .

T h e s h o r t d i s t a n c e ( b o x d i a g r a m ) a p p r o a c h In d e s c r i b i n g t h e K ° - K ° s y s t e m ( a n d l a t e r o n

a l s o D ° - D ° a n d B ° - B ° ) h a s b e e n v e r y p o p u l a r , w i t h i n t h e p a s t 1 0 y e a r s . T h e r e a s o n i s

t h a t , in a p i o n e e r i n g w o r k , G a i l l a r d a n d L e e " ^ ' u s e d t h e b o x d i a g r a m a n d p r e d i c t e d t h a t

t h e c h a r m q u a r k c o u l d n o t b e t o o h e a v y . A c t u a l l y t h e i r l i m i t s w e r e v e r y g e n e r o u s ,

m m « m . T h e s u b s e q u e n t d i s c o v e r - / ^ ' o f t h e c h a r m q u a r k t u r n e d t h e b o x - a p -u c w

p r o a c h i n t o a " r e l i g i o n " , w h i c h w a s e m p l o y e d n o t j u s t a s a f r a m e w o r k f o r a n o r d e r o f m a g

n i t u d e e s t i m a t e b u t f o r a p r e c i s i o n c a l c u l a t i o n . F o r t h e l a t t e r p u r p o s e t h e b o x - a p p r o a c h i s

s i m p l y u n r e l i a b l e . F o r s y s t e m s c o n s i s t i n g o f h e a v i e r q u a r k s , h o w e v e r , t h e s b t , i t d i s t a n c e

a p p r o x i m a t i o n a n d t h e r e b y t h e b o x - a p p r o a c h i s e x p e c t e d t o d o a b e t t e r j o b . N e v e r t h e l e s s

I s h a l l r e v i e w t h e b o x - a p p r o a c h , e v e n f o r t h e k a o n s , j u s t b e c a u s e i t i s s o w i d e l y u s e d .

F u r t h e r m o r e , o n e m a y e a s i l y g e n e r a l i z e t h e r e s u l t s t o d e s c r i b e t h e n e u t r a l D a n d fi

n i e s o n s .

4 . 1 T h e b o x - a p p r o a c h ; Um a n d f o r t h e n e u t r a l k a o n s

T h e K ° - K ° m i x i n g , i n t h e s h o r t d i s t a n c e ( b o x ) a p p r o a c h , i s g i v e n b y t h e d i a g r a m s

o f F i g . 5

F i g , 5

- 247 -

ch: n l a - i. r,2

A q u a n t i t y o f g r e a t i n t e r e s t i s t h e d e g r e e o f m i x i n g , d e n o t e d b y Û ,

j + y - v

( 2 3 )

( 2 4 )

w h e r e f r o m 0 £ y < 1 f o l l o w s t h a t 0 $ A Í 1 .

I n t h e c a s e o f K ° - K ° s y s t e m T ( K g ) » T ( K L ) w h e r e b y 7 » 1 a n d m i x i n g i s c o m p l e t e ,

i . e . , t h e p h y s i c a l s t a t e s a r e e s s e n t i a l l y " h a l f K ° a n d h a l f K° ". T h i s i s a f o r t u n a t e c o

i n c i d e n c e w h i c h h a p p e n s d u e t o t h e s m a l l p h a s e s p a c e a v a i l a b l e t o - * 3 ï ï d e c a y s . F o r

a l l o t h e r k n o w n M - M s y s t e m s s u c h a f o r t u n a t e c i r c u m s t a n c e i s n o t e x p e c t e d , b e c a u s e

t h e a v a i l a b l e p h a s e s p a c e i n b o t h H a n d L d e c a y s i s l a r g e . I n g e n e r a l t h e w i d t h s o f t h e H

F o r t h e B° - B ° s y s t e m t h e c o r r e s p o n d i n g d i a g r a m s a r e o b t a i n e d b y j u s t l e t t i n g e i t h e r

d " b , d -» b o r s "> b , s "• 5, i n F i g . 5 . H o w e v e r i n t h e D ° - 5^ s y s t e m , t h e e x t e r n a l

q u a r k s a r e ( u , c ) a n d t h o s e i n t h e l o o p d , s a n d b .

T h e s e d i a g r a m s m a y b e u s e d to c a l c u l a t e t h e M ° - M ° m a s s m a t r i x 3 7 *

•V)-r*' ""'Ti- -T h e p h y s i c a l s t a t e s , w i t h w e l l d e f i n e d m a s s e s w i l l b e d e n o t e d b y K ( h e a v y ) a n d L ( l i g h t ) ,

a l t h o u g h in g e n e r a l t h e m a s s d i f f e r e n c e b e t w e e n t h e m i s m i n u t e . T h e roeasurables o r i g i

n a t i n g f r o m t h e m a s s m a t r i x a r e

A n i s m C W - W ( L )

AP* riH)-r(l) ( 2 1 )

( m = m a s s , T = w i d t h ) a s w e l l a s t h e p a r a m e t e r c w h i c h g i v e s t h e C P - i m p u r i t y o f t h e

m a s s e i g e a s t a t e s - D i a g o n a l i z a t i o n o f t h e m a s s m a t r i x g i v e s i m m e d i a t e l y t h a t

- 2 4 8 -

( 2 5 )

H e r e t h e rç's a r e 3 3 ^ Q C D c o r r e c t i o n f a c t o r s o f o r d e r 1 a n d B ^ i s t h e " i n f a m o u s " b a g p a r a

m e t e r w h i c h m e a s u r e s t h e r e n o r m a l l s a t i o n o f t h e r e l e v a n t | As\= 2 o p e r a t o r w h e n o n e

g o e s f r o m q u a r k s t o h a d r o n s

< K ' | ( D ^ C . - Ï S Î S ) ' | K B > - -X F K ' R N K 8 , , y (26)

f i s t h e k a o n d e c a y c o n s t a n t a n d m „ r e f e r s to t h e m a s s . T h e v a l u e c f t h e c o n s t a n t

K K

B i s n o t k n o w n f r o m f i r s t p r i n c i p l e s a n d t h e l a r g e s t u n c e r t a i n t y i n t h e b o x a p p r o a c h i s d u e

t o t h i s u n k n o w n B . F o r o t h e r s y s t e m s , t h e r e i s a n a d d i t i o n a l u n c e r t a i n t y d u e t o t h e f a c t

t h a t t h e d e c a y c o n s t a n t s f ^ , M = D ° , , . . . > h a v e n o t b e e n m e a s u r e d . I n ( 2 5 ) t h e

f i r s t t e r r a i s d u e t o t w o c h a r m q u a r k s i n t h e l o o p ( s e e F i g . 5 ) ; t h e s e c o n d t e r m c o m e s f r o m

t w o t - q u a r f e s a n d t h e l a s t o n e i s t h e c o n t r i b u t i o n o f t h e p a i r c , t . T h e n u m e r i c a l v a l u e o f

A m f o r i : a n o n i c a l v a l u e s o f B , 0 < B < 1 » c o m e s o u t t o b e t o o s m a l l a n d i n c r e a s i n g t h e t o p 2

q u a r k m a s a d o e s n t h e l p m u c h b e c a u s e m , s „ / m £ 1 a l r e a d y r e q u i r e s 2 2 C

m ^ m / s 9 £ 1 . 5 / ( 0 . 0 7 ) G e V 3 0 0 G e V w h i c h i s a h u g e v a l u e a n d v i o l a t e s t h e a s s u m p -3 9 )

t i o n m « m . E v e n u s i n g t h e e x a c t f o r m u l a e d o e a n 1 h e l p a n d Am i s n o t r e p r o d u c e d . 3 2

T h e r e a s o n i s s i m p l y t h a t t h e c o u p l i n g c o n s t a n t s V ^ a n d V ^ a r e s m a l l , o r d e r X a n d X

r e s p e c t i v e l y . T h u s o n e b e l i e v e s t h a t t l issre i s a s u b s t a n t i a l l o n g d i s t a n c e c o n t r i b u t i o n t o

urn f i x m i d i a g r a m s i n F i g . 6

F i g . «

71

a n d t h e L w i l l b e c o m p a r a b l e a n d y « 1 . A s e c o n d c a s e w h e r e ¿ c a n b e l a r g e i s i f

ß » 1 . I n t h e b o x a p p r o a c h , t h e p r e s e n t v a l u e s o f t h e c o u p l i n g c o n s t a n t s i n d i c a t e t h a t

t h i s i s e x p e c t e d t o h a p p e n i n t h e B ° - B ° s y s t e m , w h e r e fi i s e x p e c t e d t o b e a p p r e c i a b l e

h o w e v e r n o t m u c h l a r g e r t h a n u n i t y .

T h e b o x d i a g r a m s p r o v i d e u s w i t h a » d 1 ^ a n d t h u s w e c a n c a l c u l a t e a l l t h e

q u a n t i t i e s i n E q s . ( 2 2 ) - ( 2 4 ) . F o r e x a m p l e , f o r t h e m a s s d i f f e r e n c e âtri 2 2 2

Am~ m ( K , ) - m ( K „ ) , i n t h e l i m i t m « m , m , a n d m , m « M , i s g i v e n b y L S u c t e t w

- 2 4 9 -

(27}

A s w e s a w b e f o r e , E q . ( 1 9 ) , t h e " K M - c o e f f i c i e n t " i n ( 2 7 ) i s s m a l l . A g a i n t h e q u a n t i t y

i n I . . . I n e e d ? t o b e l a r g e i n o r d e r t o e x p l a i n t h e e x p e r i m e n t a l v a l u e o f | c | . H e r e a

2 l a r g e t o p q u a r k m a s s c a n h e l p t o g i v e a g r e e m e n t , b e c a u s e t h e c o e f f i c i e n t o f ( m t / m c )

c o u l d b e a s m u c h a s 5 0 t i m e s l a r g e r t h a n i t w a s i n t h e c a s e o f A m , E q . ( 2 5 ) , v i z . ,

2 2 4 2 )

( s 2 ) Í ( 0 . 0 7 ) . T h e f o r m u l a (Ü7) w a s u s e d l a s t y e a r b y G i n s p a r g e t a l . } w h o o b

t a i n e d a l o w e r l i m i t o n t h e t o p q u a r k m a s s . T h e n e w v a l u e o f R w i l l i n c r e a s e t h e i r l o w e r

b o u n d . A g a i n t h e l a r g e s t u n c e r t a i n t y c o m e s f r o m t h e u n k n o w n b a g p a r a m e t e r B . So o n e

u s u a l l y q u o t e s t h e l i m i t o n m t o g e t h e r w i t h t h e a s s u m e d v a l u e o f B . T a k i n g a l a r g e r

3 2 )

v a l u e o f B a l l o w s a s m a l l e r l o w e r l i m i t o n . M a n y a u t h o r s h a v e r e c e n t l y p r o v i d e d

g r a p h s o f t h e l o w e r l i m i t o n m f c a s a f u n c t i o n o f 6, B , e t c . T h e g e n e r a l c o n c l u s i o n o f

s u c h s t u d i e s i s t h a t t h e v a l u e o f ] c| i s r e p r o d u c e d p r o v i d e d m t i s l a r g e r t h a n 3 0 ( 9 0 ) G e V

f o r B e q u a l t o 1 ( 1 / 3 ) .

A n o t h e r i n t e r e s t i n g r e s u l t i n t h e K - s e c t o r i s a l o w e r b o u n d o n |c'/«|, w h i c h h a s

4 3 )

b e e n o b t a i n e d b y G i l m a n a n d H a g e l i n . H e r e e ' i s t h e ( o o n - s u p e r w e a k ) C P - i m p u r i t y i n

t h e t r a n s i t i o n . O n e d e f i n e s

ACKs-tn+x') Lq<¡ • _ _ ** C + f •

H e r e A S a m p l i t u d e . G i l m a n a n d H a g e l i n w e r e a b l e t o r e l a t e

S u c h o n e - p a r t i c l e , t w o - p a r t t c l e a n d m o r e - p a r t l c l e i n t e r m e d i a t e s t a t e s h a v e b e e n c o n -

4 0 )

s i d e r e d s i n c e a l o n g t i m e a g o . T h e r e a r e h u g e c a n c e l l a t i o n s b e t w e e n s u c h c o n t r i -

4 0 )

b u t i o n s a n d t h e u n k n o w n h a d r o n i c f o r m f a c t o r s m a k e t h e c a l c u l a t i o n s t o u g h a n d u n

r e l i a b l e . I n c o n c l u s i o n , t h e m a s s d i f f e r e n c e b e t w e e n K L a n d K a i s n o t n a t u r a l l y r e

p r o d u c e d i n t h e s i x q u a r k m o d e l i f o n l y t h e s h o r t d i s t a n c e ( b o x ) c o n t r i b u t i o n i s t a k e n

i n t o a c c o u n t . 4 . 2 C P - v i o l a t i o n , e a n d e' f o r t h e K - s y s t e m

T h e F i t c h - C r o n i n ' p a r a m e t e r c , i n t h e b o x a p p r o x i m a t i o n , i s g i v e n b y

- 250 -

_b ^.t A

J,>>*

| ¿ / * í I * s * S 3 » i » S ' ( k n o w n q u a n t i t y )

w h e r e t h e q u a n t i t y i n t h e p a r e n t h e s i s c a n b e e x t r a c t e d f r o m e x p e r i m e n t . M o r e o v e r ,

s i n c e w e k n o w t h e e m p i r i c a l v a l u e o f c, w e m a y u s e E q . ( 2 7 ) t o c a l c u l a t e $ ^ s ^ s i n 5 ,

f o r a n y g i v e n v a l u e o f B a n d m . A c t u a l l y t h i s c a l c u l a t i o n g i v e s a l o w e r b o u n d o n

t 4 3 )

s 2 s 3 s i " ^' & s W B h a V C n e S * e c t e t * a s m a * l c o n t r i b u t i o n ( w i t h a n e g a t i v o s i g n ) i u t h e R H S o f

E q . ( 2 7 ) . T h e l o w e r l i m i t o n s ^ ^ s l n ö ' c a n t h e n b e t r a n s l a t e d i n t o a l o w e r l i m i t o n

| < y « | w h i c h h a s a p p r o x i m a t e l y t h e f u n c t i o n a l f o r m

lé'/él > ^ (28) " » „ [ ( » W — - J

f o r m . F o r l a r g e r m t h e e x p r e s s i o n , w h i c h r e p l a c e s t h e s q u a r e b r a c k e t i n t h e W 3 9 i 4 3 )

d e n o m i n a t o r i s k n o w n ' a n d h a s b e e n u s e d i n t h e b o u n d . T h e g e n e r a l c o n c l u s i o n o f

R e f . 4 3 i s t h a t } e ' | c a n n o t b e t o o s m a l l , f o r " r e a s o n a b l e " v a i u e s o f m f a n d B . T y p i c a l l y

| C ' / C | £ 0 . 0 1 f o r m £ 3 0 G e V a n d B < 2 / 3 . O f c o u r s e f o r i t r g e r m t a n d / o r B t h e

l o w e r b o u n d b e c o m e s s m a l l e r a n d l e s s i n t e r e s t i n g . T h e p r e s e n t e x p e r i m e n t a l l i m i t

4 4 ) I 4 5 ) r e a d s f € ' / ç f <r 1 / 2 0 b u t t h e o n g o i n g g e n e r a t i o n o f C P - e x p e r i m e n t s a i m t o e x p l o r e '

t h e r e g i o n | C'/e| £ 0 . 0 0 1 . T h u s o n e s h o u l d o b s e r v e Jc'l'o s o o n , I f t h e b o x a p p r o a c h

m a k e s s e n s e a n d B a s w e l l a s m^_ h a v e " r e a s o n a b l e " v a l u e s . I t i s g o i n g t o b e v e r y i n

t e r e s t i n g t o s e e w h a t t h e v e r d i c t ^ f r o m t h e o n g o i n g l o w e n e r g y C P - e x p e r i m e n t s a n d t h e

h i g h e n e r g y p p - c o l l i d e r i s g o i n g t o b e . T h e l o w e r b o u n d o n I eVcl i s a l r e a d y a b i t u n -

4 3 ) c o m f o r t a b l e ' a n d c o u l d e a s i l y b e v i o l a t e d .

5 . B ° - B ° M I X I N G

T h e s h o r t d i s t a n c e ( b o x ) a p p r o a c h , d e s c r i b e d i n t h e p r e v i o u s s e c t i o n , i s e x p e c t e d

t o b e m u c h m o r e r e l i a b l e i n d e s c r i b i n g t h e n e u t r a l D - D a n d B - B s y s t e m s , a s t h e s e

c o n t a i n h e a v y q u a r k s . T h e r e l e v a n t d i a g r a m s a r e s h o w n i n F i g . 7 .

- 2 5 1 -

S S A * 5 «.e^t F i g . 7

N o t e t h a t t h e c r o s s e d d i a g r a m s ( s e e F i g . 5 ) h a v e n o t b e e n d e p i c t e d b e c a u s e t h e y h a v e

t h e s a m e g e n e r a l s t r u c t u r e a s t h e d i a g r a m s w h i c h a r e s h o w n a n d t h u s d o n ' t m o d i f y t h e

c o n c l u s i o n d r a w n b e l o w . I n E q . ( 2 9 ) t h e F ' s a r e f u n c t i o n s o f q u a r k m a s s e s , d e c a y c o n

s t a n t s , e t c . T h e i r g e n e r a l f o r m i s s i m i l a r t o t h e q u a n t i t i e s w e h a d i n E q s . ( 2 5 ) a n d ( 2 6 ) .

F r o m t h e g e n e r a l s t r u c t u r e o f t h e d i a g r a m s i n F i g . 7 w e m a y i m m e d i a t e l y c o n c l u d e t h a t

t h e m i x i n g i n t h e D system is much s u p p r e s s e d , a s c o m p a r e d to t h e B , b e c a u s e t h e

h e a v i e s t i n t e r n a l q u a r k i s t h e b . H o w e v e r t h e c o e f f i c i e n t o f m , i s v e r y s m a l l , v i z . o

1 vUfc vcbI i eco')*) , Xxe.i3, F o r t h e B ' s t h e s i t u a t i o n i s m u c h m o r e p r o m i s i n g , b e c a u s e t h e h e a v y t q u a r k c o n t r i b u t e s .

F u r t h e r m o r e t h e s t r a n g e - b e a u t y l o o k s m o r e p r o m i s i n g t h a n t h e d o w n - b e a u t y . B o t h h a v e a — * 2 2 2

t e r m ( i n F a n d F ) w h i c h g o e s a s na , f o r n v « M . H o w e v e r , t h e c o e f f i c i e n t o f t h i s to t t w

c o n t r i b u t i o n i s m u c h l a r g e r f o r t h e B s y s t e m t h a n f o r t h e B ^ , v i z .

|fW V t ki « i fu l ~ 3«#>'> (30)

T h u s a m o n g t h e h e a v y s y s t e m s t h e m i x i n g i s e x p e c t e d t o b e l a r g e s t f o r

t h e B ° - B ° s y s t e m , o n w h i c h I s h a l l c o n c e n t r a t e f r o m n o w o n .

T h e r e a r e , a s f o r t h e K - s y s t e m , s e v e r a l u n c e r t a i n t i e s i n t h e c a l c u l a t i o n o f t h e

m i x i n g i n q u e s t i o n . A g a i n t h e p a r a m e t e r B i s n o t k n o w n . M o r e o v e r t h e B - m e s o n d e c a y

c o n s t a n t f h a s n o t b e e n m e a s u r e d , a n d t h e t - q u a r k m a a s i s a l s o u n k n o w n . M a n y

4 6 f a u t h o r s h a v e c o m p u t e d t h e r e l e v a n t q u a n t i t i e s n e e d e d t o p r e d i c t t h e B - B m i x i n g . A s

2 2 2 a n o r d e r o f m a g n i t u d e e s t i m a t e , i t I s p e r f e c t l y O . K . t o t a k e t h e l i m i t m L « m « m .

b t w

T h e n

- 2 5 2 -

T h e s i g n a t u r e s o f m i x i n g a n d C P - v i o l a t i o n i n M ° - M ° s y s t e m s w e r e d i s c u s s e d 4 7 *

i n d e t a i l a f t e r t h e d i s c o v e r y o f c h a r m e d p a r t i c l e s . E x p e r i m e n t a l l y , t h e D ° - D ° m i x i n g

i s k n o w n Lo b e s m a l l a n d t h a t i s n o s u r p r i s e , a c c o r d i n g t o o u r e s t i m a t e s a b o v e . S i r . c ? * h e n 4 8 )

t h e t h e o r e t i c a l f o r m a l i s m d e v e l o p e d I n m i d s e v e n t i e s h a s b e e n r e p e a t e d l y a p p l i e d t o t h e

B - B s y s t e m . T h e m o s t s p e c t a c u l a r s i g n a t u r e o f s u c h m i x i n g i s p e r h a p s t h e s o - c a l l e d

s a m e s i g n d i l e p t o n p h e n o m e e o n T h e s e m i l e p t o n i c d e c a y b ( b ) p r o d u c e s a c h a r g e d

l e p t o n ( a n t i l e p t o n ) a s s h o w n i n F i g . 8 .

•jr.*'

F i g . 8

I f m i x i n g t a k e s p l a c e , h o w e v e r , t h e b i o s i d e a n e u t r a l m e s o n m a y t u r n i n t o a b a n d

t h e r e b y p r o d u c e p o s i t i v e l y c h a r g e d l e p t o n s a s w e l l . T h u s a t t h e C E E N p p - c o l l i d e r t h e

f o l l o w i n g s e q u e n c e o f e v e n t s m a y h a p p e n

ff — ? Cbs J + cSs)-» •••

u r ; . . . u

P P — » (Ws> -» c£s>+•

w h e r e t h e q u a n t i t i e s f , B a n d m d e n o t e r e s p e c t i v e l y t h e B - m e s o n d e c a y c o n s t a n t ,

" b a g p a r a m e t e r " a n d m a s s . T h e s e a r e , o f c o u r s e , t h e a n a l o g s o f t h e i r n a m e s a k e s ,

i n t r o d u c e d a f t e r E q . ( 2 5 ) , f o r t h e K - s y s t e m , I n o r d e r t o p r o c e e d f u r t h e r a n d c a l c u l a t e

t h e d e g r e e o f m i x i n g A , E q . ( 2 4 ) , o n e m u s t m a k e s o m e " r e a s o n a b l e " a s s u m p t i o n s a b o u t

t h e a b o v e u n k n o w n q u a n t i t i e s . F u r t h e r m o r e t h e w i d t h , I \ i s c a l c u l a t e d f r o m t h e m e a s u r e d

b - l i f e t i m e . S e v e r a l s u c h e s t i m a t e s o f t h e m i x i n g e x i s t i n t h t . l i t e r a t u r e a n d t h e c o n c l u s i o n

i s t h a t t h e m i x i n g c o u l d b e s u b s t a n t i a l , p e r h a p s e v e n a l m o s t c o m p l e t e . T y p i c a l l y , £ i s

f o u n d t o l i e i n t h e r a n g e 0 . 2 - 0 . 9 . A l t h o u g h w e d o n t k n o w h o w g o o d t h e a s s u m p t i o n s

m a d e a r e t l . s r e i s n e v e r t h e l e s s a g o o d c h a n c e t h a t Ù m a y w e l l b e l a r g e . F o r t h e s a k e o f

s i m p l i c i t y I s h a l l a s s u m e t h a t t h e m i x i n g i s c o m p l e t e i n t h e B ° - B ° s y s t e m a n d d i s c u s s

i t s c o n s e q u e n c e s f o r t h e p p - c o H i d e r e x p e r i m e n t s .

- 253 -

and similarly for the b

W)r ( Avar* J

T h e r a t i o o f t h e o p p o s i t e s i g n a n d t h e s a m e s i g n d i m u o n s i s g i v e n b y

°s ~ '** ' '

w h i c h i s q u i t e a s u b s t a n t i a l n u m b e r . F u r t h e r m o r e t h e m i x i n g b e i n g i n t h e B ^ ~ B ° s e c t o r ,

w h e n t h e b - p i c k s u p a s t r a n g e q u a r k f r o m t h e {ss) i n t h e s e a t h e s i s l e f t b e h i n d a n d m a y

p r o d u c e s t r a n g e p a r t i c l e s , v i z .

F i g . 9

A r o u g h e s t i m a t e o f t h e e x p e c t e d r a t i o o f t h e n u m b e r o f s a m e s i g n ( S S ) a n d o p p o s i t e

( O S ) d i l e p t o n s , s a y d i m u o n s , m a y b e o b t a i n e d a s f o l l o w s . A s s u m e t h a t t h e p r o d u c e d

b - q u a r k h a s e q u a l p r o b a b i l i t y o f p i c k i n g u p a u., d o r s f r o m t h e s e a . T h e n n e g l e c t i n g t h e

b e a u t i f u l b a r y o n s , a p r o d u c e d b q u a r k w i l l e n d u p a s t h e m e s o n s E ^ , B ° o r B ° w i t h e q u a l

p r o b a b i l i t i e s ( 1 / 3 e a c h ) . F u r t h e r m o r e t h e p r o b a b i l i t i e s o f f i n d i n g t h e p r o d u c e d B ° a s B °

o r a s B ° a r e e q u a l ( 1 / 2 e a c h ) , b y o u r a s s u m p t i o n o f c o m p l e t e m i x i n g . T h u s t h e " p r o b a -s

bility c h a r t " l o o k s a s f o l l o w s

- 254 -

T h u s t h e s i g n o f t h e I e p t o n a n d t h e s t r a n g e n e s s q u a n t u m n u m b e r o f t h e p r o d u c e d h a d r o n s

a r e c o r r e l a t e d . O n e e x p e c t s

pp -*r~r~cÄ*,

O f c o u r s e t h e a b o v e d i s c u s s i o n h a s b e e n o n p u r p o s e m u c h s i m p l i f i e d i n o r d e r t o e x p l a i n

49) t h e u n d e r l y i n g i d e a s . H o w e v e r w e h a v e d o n e a m o r e d e t a i l e d r e a l i s t i c c a l c u l a t i o n ,

t a k i n g i n t o a c c o u n t b a c k g r o u n d s , e t c . a n d h a v e c o m p a r e d o u r r e s u l t s w i t h t h e U A 1 d i m u o n

5 0 ) o — o d a t a . T h e c o n c l u s i o n i s t h a t t h e s a m e s i g n d i m u o n s c o u l d b e d u e t o B - B m i x i n g

s s

p h e n o m e n o n , % I f s o , t h i s w o u l d b e q u i t e r e m a r k a b l e i n v i e w o f t h e f a c t t h a t t h e s t r a n g e

b e a u t i f u l m e s o n h a s n o t b e e n s e e n y e t l S h e c e r t a i n l y d e s e r v e s h e r n a m e " t h e s t r a n g e

b e a u t y " .

I h a v e n o t d i s c u s s e d C P - v i o l a t i o n i n t h e B - B s y s t e m w h i c h w o u l d h a v e a s a s i g n a

t u r e , f o r e x a m p l e , t h a t t h e n u m b e r oí }S p a n d fi u , p r o d u c e d d u e t o m i x i n g , a r e n o t

e q u a l . U n f o r t u n a t e l y , t h e v e r y s a m e t h e o r y w h i c h p r e d i c t s l a r g e m i x i n g ( a t l e a s t f o r

B ° - B ° ) a l s o t e l l s u s t h a t e s s e n t i a l l y a l l C P - v i o l a t i n g e f f e c t s ( s u c h a s f o r t h e s a m e s s

s i g n d i m u o n s ) w i l l b e v e r y s m a l l . T h u s i t i s e x t r e m e l y i n t e r e s t i n g t o t e s t t h i s s t r o n g

p r e d i c t i o n o f t h e s t a n d a r d m o d e l .

I n c o n c l u s i o n t h e B - p h y s i c s w h i c h s o Ear h a s s u p p l i e d u s w i t h s u r p r i s e s a n d t a u g h t

u s l e s s o n s m a y w e l l c o n t i n u e t o d o s o a l s o i n t h e f u t u r e .

6 . B E Y O N D T H R E E F A M I L I E S ?

I w a s a s k e d b y t h e o r g a n i z e r s o f t h i s w o r k s h o p t o t a l k a l s o a b o u t h e a v y f l a v o u r s .

I h a v e a l r e a d y d i s c u s s e d s o m e a s p e c t s o f t h e b - p h y s i e s a n d p o s s i b l e s i g n a t u r e s a t t h e

C o l l i d e r . T h e t h e o r e t i c a l a s p e c t s o f t h e b a n d t - p h y s i c s a t t h e C o l l i d e r a r e a l s o r e v i e w e d

b y F r a n c i s H a l z e n 5 1 * a n d A l l a n M a r t i n 5 2 * . T h e r e f o r e , i n t h e r e m a i n i n g f e w m i n u t e s 1

5 3 \ s h a l l s p e c u l a t e a l i t t l e a b o u t a h y p o t h e t i c a l f o u r t h f a m i l y ' .

W e h a v e s e e n a l r e a d y t h a t t h e d e g r e e o f f a m i l y m i x i n g s e e m s t o d e c r e a s e w i t h t h e

i n c r e a s i n g f a m i l y n u m b e r . T h u s t h e t h i r d a n d s e c o n d f a m i l i e s m i x m u c h l e s s t h a n t h e

s e c o n d a n d t h e f i r s t d o . T h i s p a t t e r n m a y c o n t i n u e o n , i f t h e r e a r e m o r e f a m i U e s y s o t h a t

t h e n e w f a m i l i e s b e c o m e l e s s a n d l e s s " c o m m u n i c a t i v e " . So f a r , t h e r e i s n e i t h e r a n

u r g e n t n e e d n o r a n y s e r i o u s o b j e c t i o n a g a i n s t t h e e x i s t e n c e o f a f o u r t h f a m i l y . T h e m a g n i

t u d e o f t h e C P - v i o l a t i n g p a r a m e t e r e , i n t h e K s y s t e m , i s s o m e w h a t p r o b l e m a t i c i n t h e

s h o r t d i s t a n c e a p p r o a c h . O f c o u r s e o n e h a s t h e f r e e d o m o f blaming the disagreement o n

t h e u n k n o w n b a g p a r a m e t e r B a n d t h e t - q u a r k m a s s . A n o t h e r p o s s i b i l i t y i s , h o w e v e r , t o

- 2 5 5

h a v e m o r e f a m i l l e s . A l t h o u g h t h e r e a r e r e s t r i c t i o n s o n t h e n u m b e r o f n e u t r i n o s

( a n d t h u s o n t h e n u m b e r o f f a m i l i e s ) f r o m t h e B I G - B A N G n u c l e o s y n t h e s i s , I b e l i e v e t h a t

i f a n e w f a m i l y i s d i s c o v e r e d i t w i l l b e a c c o m o d a t e d . M u c h m o r e p o w e r f u l r e s t r i c t i o n s a r e

e x p e c t e d t o c o m e f r o m t h e m e a s u r e m e n t o f t h e r a t i o o f w i d t h s o f t h e Z a n d W a t t h e

C E R N p p - c o U i d e r .

S u p p o s e t h a t t h e r e i s a f o u r t h f a m i l y w i t h t h e q u a r k s ( a , r ) h a v i n g c h a r g e s 2 / 3 a n d

541 - 1 / 3 r e s p e c t i v e l y . T h e n i t f o l l o w s f r o m V e l t m a n ' s c a l c u l a t i o n , o f t h e c o r r e c t i o n s t o

t h e W a n d Z p r o p a g a t o r s , t h a t t h e m a s s d i f f e r e n c e | m - m | c a n n o t b e t o o l a r g e .

3 r 55)

¡ m ~ m

r [ jÇ3ÔO G e V . F u r t h e r m o r e t h e m o s t r e c e n t d a t a f r o m D E S Y s h o w t h a t t h e r e

a r e n o s u c h q u a r k s w i t h m a s s e s b e l o w 2 0 G e V .

W e d o n t k n o w h o w t h e f o u r t h f a m i l y w i l l c o m m u n i c a t e w i t h t h e o t h e r t h r e e . O n e

s u g g e s t i v e p a t t e r n i s a s s h o w n i n F i g . 1 0 -

T h e m o s t a m u s i n g s i t u a t i o n o c c u r s i f y, ^ ^ _ ^ m < n v a n d m . T h e n t h e r w i l l

r t w

p r e s u m a b l y d e c a y p r e d o m i n a n t l y t o t h e

c - q u a r k ( F i g . 1 0 ) .

W e d o n t k n o w t h e c o u p l i n g constant for

t h e r « r * c t r a n s i t i o n s - A " g o o d " g u e s s

^ 4 , 3 , 6 i s V X - À = A , I f s o t h e r - q u a r k c r

c o u l d b e r e m a r k a b l y l o n g l i v e d . F i g . 1 0

w h e r e t h e f a o t o r 1 / 9 , f r o m t h e n u m b e r o f

d e c a y c h a n n e l s , c o u l d b e 1 / 1 0 i f t h e r e i s

a n e w h e a v y l e p t o n w i t h m a s s s m a l l e r t h a n *" c - 1 2

m . P u t t i n g m ^ 4 0 G e V g i v e s T « 1 0 r r r

s e c . w h i c h i s a r e m a r k a b l y l o n g l i f e t i m e

f o r s u c h a h e a v y o b j e c t . T h e p o i n t h e r e i s t h a t w i t h t h e p r e s e n t p a t t e r n o f f a m i l y m i x i n g

u n e x p e c t e d t h i n g s m a y h a p p e n a i d t h e r e c o u l d i n d e e d b e o n e o r m o r e v e r y l o n g l i v e d h e a v y

f l a v o u r s .

7 . C O N C L U D I N G R E M A R K S

I n t h i s t a l k I h a v e r e v i e w e d t h e p r e s e n t s t a t u s o f t h e f l a v o u r m i x i n g i n t h e s t a n d a r d

m o d e l . T h e s t a n d a r d s i x q u a r k m o d e l h a s n o s e r i o u s d i f f i c u l t i e s i n a c c o m o d a t i n g t h e o b

s e r v e d p a t t e r n o f f a m i l y m i x i n g . H o w e v e r t h e s i m p l e s h o r t d i s t a n c e a p p r o a c h d o e s n o t

- 256 -

R E F E R E N C E S

1 . O . K l e i Q i n " L e s N o u v e l l e s T h é o r i e s d e l a P h y s i q u e " , E d i t i o n s F r o n t i è r e s ( P a r i s

f 9 3 6 ) p . 8 1 .

S . L . G l a s h o w , N u c l . P ^ Ï . 2 2 ( 1 9 6 1 ) 5 7 9

S . W e i n b e r g , p h y s . R e v . L e t t . J 9 ( 1 9 6 7 ) 1 2 8 4

A . S a l a m i n E l e m e n t a r y p a r t i c l e T h e o r y , E d . N . S v a r t h o l m , A l m q v i s t a n d W i k s e i l ,

S t o c k h o l m 1 9 6 8

A . S a l a m a n d J . C . W a r d , P h y s . Lett.IS ( i 9 6 4 ) 1 6 8 .

2 . G . A r n i s o n e t a l . , P h y s . L e t t . 1 2 2 B ( 1 9 8 3 ) 1 0 3 , 1 2 9 B ( 1 9 S 5 j 2 7 3 j 1 2 6 B ( 1 9 8 3 ) 3 9 8 ,

_ 1 3 4 B ( 1 9 B 4 ) 4 6 9

G. Banner et al., Phys. L e t t . J 2 2 B ( 1 9 8 3 ) 4 7 6

P . B a g n a i a e t a l - , p h y s . L e t t . J 2 9 B ( 1 9 8 3 ) 1 3 0 .

3 . J . R . H a n s e n ( U A 2 - C o l l a b o r a t i o n ) , t h e s e p r o c e e d i n g s

C . R u b b i a ( U A î - C o l l a b o r a t i o n ) , t h e s e P r o c e e d i n g s .

4 . F o r a r e c e n t r e v i e w s e e , f o r e x a m p l e ,

K . W i n t e r , p r o c e e d i n g s o f t h e 1 9 8 3 I n t e r n a t i o n a l S y m p o s i u m o n L e p t o n a n d p h o t o n

I n t e r a c t i o n s a t H i g h E n e r g i e s , C o r n e l l 1 9 8 3 , E d . D . G . C a s s e l a n d D . L . K r e i n i c k ,

p . 1 7 7 ;

M . H . S h a e v i t z , i b i d . , p . 1 3 2 .

5 . C . J a r l s k o g , P r o c e e d i n g s o f t h e 1 9 8 1 C E R N - J I N R S c h o o l o f P h y s i c s ( H a n k o , F i n l a n d ) ,

C E R N Y e l l o w R e p o r t 8 2 - 0 4 » p . 63 .

w o r k a s w e l l a s i t d i d b e f o r e . F u r t h e r m o r e , t h e C o l l i d e r m a y t u r n o u t t o b e a n i d e a l

i n s t r u m e n t f o r s t u d y i n g B ° - B ° m i x i n g . T h i s y e a r m a r k s t h e 2 0 t h a n n i v e r s a r y o f t h e

4 1 )

d i s c o v e r y ' o f t h e C P - v i o l a t i o n , a n d y e t t h e r e i s n o s i g n o f C P - v i o l a t i o n a n y w h e r e e x c e p t

i n t h e m a s s m a t r i x o f t h e K ° - K ° s y s t e m . T h e o n g o i n g e x p e r i m e n t s l o o k i n g f o r i t ' / c i

m a y s u p p l y u s w i t h t h e f i r s t i n d i c a t i o n o f C P - v i o l a t i o n i n a t r a n s i t i o n . F o r h e a v y q u a r k

systems, the s t a n d a r d m o d e l g i v e s l i t t l e h o p e o f s e e i n g a n y e f f e c t - A f e w y e a r s a g o t h e

s i t u a t i o n l o o k e d v e r y p r o m i s i n g * * * * * f o r t h e c h a r g e d B d e c a y s . S i n c e t h e n w e h a v e l e a r n e d ,

f r o m e x p e r i m e n t , t h a t i t i s u n l i k e l y t h a t t h e r e w i l l b e , i n s u c h d e c a y s , t w o o p p o s i t e C P

a m p l i t u d e s w i t h c o m p a r a b l e s t r e n g t h s . W i t h i n t h e s t a n d a r d m o d e l s u c h C P - e f f e c t s a r e

h o p e l e s s l y s m a l l .

P e r h a p s t h e s t a n d a r d m o d e l h a s a l r e a d y d o n e i t s j o b , a s t h e l i n k t o t h e n e x t E r a i n

f r o n t o f u s ? S o m e o b s e r v e d p h e n o m e n a m a y b e j u s t t h e f i r s t i n d i c a t i o n s i n t h i s r e s p e c t .

P u t t i n g a s i d e s u c h d e e p q u e s t i o n s a s w h y f a m i l i e s , m a s s e s , e t c . , l e t u s r e m e m b e r t h a t

w e d o n t u n d e r s t a n d 5 7 )

- t h e s a m e s i g n d i m u o n s o b s e r v e d i n neutrino interactions

- Z ~* e + e y, u + / i y o b s e r v e d 5 8 * a t t h e C o l l i d e r

- s o m e o f t h e p h e n o m e n a o b s e r v e d b y U A 1 a n d U A 2 a s r e p o r t e d 3 * a s t h i s W o r k s h o p .

I r a t h e r n o t q u o t e t h e s e e f f e c t s h e r e , a s t h e r e s u l t s w e r e s t a m p e d " p r e l i m i n a r y " .

- 257 -

6. C. Jarlskog, tn Proceedings of the 1978 Nato Advanced Stud." Institute on New phenomena in Lepton-Hadron Physics, Ed. D.E.C. Fries and J. Wess.

7. R.p. Feynman and M . Gell-Mana, Phys. Rev. 109 (1958) 193 (especially page 197, discussions concerning a heavy charged W-boson).

B. M . Kobayasb' and T. Maskawa, Prog. Theor. Phys. 49 (1973) 652

9. This master remark is due to Guido Altarelli.

10. For a review of composite model see R. Peccei, these Proceedings.

11. For a review see, for example, B. Stech, Heidelberg Preprint HD-THEP-83-31, to be published in the Proceedings of the 1983 Advanced S u m m e r Institute, Munich.

12. N. Cabibbo, Phys. Rev. Lett, H> (1963) 531.

13. For a review see for example, D.H. Wilkinson, Prog, in Particle and Nuclear Phys. 6 (1980) 325.

14. W A 2 Collaboration, M . Bourquin et al., Z. Phys.Ç12 (1982) 307¡ Ç21 (1983) 1, 17, 27.

15. M . Gell-Mann and M . Levy, Nuovo Cimento 25 C 9 6 0) 7 0 5-16. S. Sakata. Prog. Theor. Phys. .16 (1956) 686.

17. See, for example, L.M. Chounet, J.M. Gaillard and M . K . Gaillard, Phys. Rep. 4C (1972) 199.

18. S.L. Glashow, J. Iliopoulos and L. Maiani, Phys. Rev. D2 (1970) 1285.

19. See for example C H . Llewellyn Smith, Phys. Reports 3Ç (1974) 264 F.E. Close, An Introduction to Quarks and Partons (Academic Press 1979), Chap. 11.

20. E.A. Paschos and Ü. Türke, Phys. Lett. 116B(1982 ) 360.

21. L. Chau, W . Keung and M . D . Tran, Phys. Rev. D27 (1983) 2145.

22. K. Kleinknecht and B. Renk, Z. f. Physik£16 (1982) 7.

23. G. Hanson, proceedings of the Internationel Europhysics Conference on High Energy Physios, (Brighton 1983), Eds. J . Guy and C. Costain, p. 330,-G. Chadwick, ibid. 333.

24. N . W . Reay, Proceedings of the 1983 International Symposium on Lepton and Photon Interactions at High Energies (Cornell 1983), Eds. D.G. Cassel and D.L. Kreim'ck, p. 244.

25. For a review see, for example, L. Chau, Phys. Reports 95 (1983) 1-94, see especially p. 59.

26. see, fcr example, C. Jarlskog, Proceedings of the International Europhysics Conference on High Energy Physics (Brighton 1983), Eds. J. Guy and C. Costain, p. 768.

27. E. Fernandez et al., Phys. Rev. Lett. 51.(1983) 1022.

28. N.S. Lockyer et al., Phys. Rev. Lett. (1983) 1316.

29. Talk presented by Y. Yeltou at the 19th Rencontre de Moriond, La Plagne, Feb. 26 -March 4, 1984; to appear in the Proceedings.

- 258 -

3 0 . T a l k p r e s e n t e d b y J . L e e - F r a n z i n i a t t h e 1 9 t h R e n c o n t r e d e M o r i o n d , L a P l a g n e , F e b . 2 6 - M a r c h 4 , 1 9 8 4 ¡ t o a p p e a r I n t h e p r o c e e d i n g s .

3 1 . A . C h e n e t a l . , P r e p r i n t C L N S - 8 4 / 5 9 7 = C L E O - 8 4 - 1 .

3 2 . K . K l e i n k n e c h t a n f 1 B . R e n k , p h y s . L e t t . 1 3 0 B { 1 9 8 3 ) 4 5 9 . X . P h a m a n d X . V u , p r e p r i n t P A R L P T H E 8 3 / 2 8

E . A . P a s o h o s a n d U . T ü r k e , P r e p r i n t N S F - I T P - 8 3 - 1 6 8 .

L . C h a u a n d W . K e u n g , P h y s . R e v . D 2 9 ( 1 9 8 4 ) 5 9 2 . A . J . B u r a s , W . S t o m i n s k i a n d H . S t e g e r , p r e p r i n t M P I - P A E / P T h 7 7 / 8 3 . S e e a l s o R e f . 2 6 .

33. L. Wolfensteia, Phys. Rev. Lett. 5 1 ( 1 9 8 3 ) 1 9 4 5 .

3 4 . S . W . H e r b e t a l . , p h y s . R e v . Lett.3S ( 1 3 7 7 ) 2 5 2 .

3 5 . M . K . G a i l l a r d a n d B . W . L e e , P h y s . R e v . D I O ( 1 9 7 4 ) 8 9 7 .

3 6 . J . J . A u b e r t e t a l . , P h y s . K e v . L e t t . 3 3 ( 1 9 7 4 ) 1 4 0 4 .

J . E . A u g u s t i n e t a l . , i b i d . 1 4 0 6 .

3 7 . S e e , f o r e x a m p l e

J . S . B e l l a n d J . S t e i n b e r g e r , p r o c e e d i n g s o f t h e I n t e r n a t i o n a l C o n f e r e n c e o n

E l e m e n t a r y P a r t i c l e s , O x f o r d 1 9 6 5 , p. 1 9 5 ( 1 9 6 6 ) .

3 8 . F . J . O i l m a n a n d M . B . W i s e , P h y s . H e v . D 2 0 ( 1 9 7 9 ) 2 3 9 2 ; D 2 7 ( 1 9 8 3 ) 1 1 2 8 .

3 9 . T . l h a m i a n d C S . L i m , P r o g . T h e o r . p h y s . 6 5 ( 1 9 8 1 ) 2 9 7 .

4 0 . C . I t z y k s o n , M . J a c o b a n d G . M a h o u x , N u o v o C i m e n t o Supp. 5 ( 1 9 6 7 ) 9 7 8 .

F o r a r e c e n t r e v i e w s e e R e f , 2 5 .

4 1 . J . H . C h r i s ' e n s o n , J . W . C r o n i n , V . L . F i t c h a n d R . T u r l a y , P h y s . R e v . L e t t . _Ki ( 1 9 6 4 ) 1 3 3 .

4 2 . P . H . G i n s p a r g , S . L . G l a s h o w a n d M . B . W i s e , P h y s . R e v . L e t t . 5 0 < 1 9 8 3 ) 1 4 1 5 .

4 3 . F . J . G i l m a n a n d J . S . H a g e l i n , P h y s . L e t t . _ 1 2 6 B ( 1 9 8 3 ) 1 1 1 ; P r e p r i n t S L A C - P U B - 3 2 2 6 .

4 4 . F o r a r e v i e w s e e K . K l e i n k n e c h t , p r o c e e d i n g s o f t h e X V I I t h I n t e r n a t i o n a l C o n f e r e n c e o n H i g h E n e r g y P h y s i c s , L o n d o n 1 9 7 4 , E d s . J . R . S m i t h , p. I I I - 2 3 .

4 5 . K . K l e i n k n e c h t , t a l k p r e s e n t e d a t t h e 1 9 t h R e n c o n t r e d e M o r i o n d , L a P l a g n e , F e b . 2 6 - M a r c h 4 , 1 Ö 8 4 , to a p p e a r i n t h e P r o c e e d i n g s .

4 6 . J . E l l i s e t a l . , N u c l . P h y s . B 1 3 1 ( 1 9 7 7 ) 2 8 5

A . A i i a n d Z . Z . A y d i n , NucT. P h y s . B 1 4 8 ( 1 9 7 8 ) 1 6 5 , S e e a l s o R e f . 2 5 , a n d R e f e r e n c e s t h e r e i n .

4 7 . A . P a i s a n d S . B . T r e i m a n , P h y s . R e v . D 1 2 ( 1 9 7 5 ) 2 7 4 4

L . B . O k u n , V . l . Z a k h a r o v a n d B . M . P o n t e c o r v o , L e t t . N u o v o C i m e n t o J 3 ( 1 9 7 5 ) 2 1 8 .

4 8 . J . S . H a g e l i n , P h y s . R e v . D 2 0 ( 1 9 7 9 ) 2 B 9 3

A . B . C a r t e r a n d A . I . S a n d a P h y s . R e v . D 2 3 ( 1 9 8 1 ) 1 5 6 7 .

J . S . H a g e l i n , N u c l . p h y s . B 1 9 3 ( 1 9 8 1 ) 1 2 3

S e e a l s o R e f s . 3 2 a n d 4 6 c i t e d a b o v e .

4 9 . A . A l i a n d C . J a r l s k o g , S t o c k h o l m P r e p r i n t , I T P - 8 4 - 1 ( C E R N P r e p r i n t T H - 3 8 9 6 ) .

5 0 . F o r f u r t h e r t h e o r e t i c a l e x p l a n a t i o n s o f t h e U A 1 d i m u o n s s e e , f o r e x a m p l e ,

V . B a r g e r a n d R . P h i l l i p s , M a d i s o n P r e p r . P H / 1 5 5

E . W . N . G l o v e r , F . H a l z e n a n d A . D . M a r t i n , D u r h a m R e p o r t D T P 8 4 / 2

R . K i n n u n e n , C E R N - E P - 8 4 - 1 9 .

- 259 -

5 1 . F . H a l z e n , t h e s e P r o c e e d i n g s .

5 2 . A . D . M a r t i n , i b i d .

5 3 . S e e a l s o V . B a r g e r e t a l . , M a d i s o n P r e p r i n t P H / 1 5 0 .

5 4 . M . V e l t m a n , N u c l . P h y s . B 1 2 3 ( 1 9 7 7 ) 8 9 .

5 5 . M . A l t h o f f e t a l . , D E S Y B e p o r t 8 4 - 0 0 1 .

5 6 . J . B e r n a b e u a n d C . J a r l s k o g , Z . I . P h y s i k Ç 8 ( 1 9 8 1 ) 2 3 3 .

5 7 . F o r a r e v i e w s e e F . H a l z e n , J o u r n a l d e P h y s i q u e 4 3 C o l l o q u e C 3 - 3 8 1 ( P r o c e e d i n g s

o f t h e 1 9 8 2 I n t e r n a t i o n a l C o n f e r e n c e , P a r i s ) .

5 8 . G . A r n i s o n e t a l . , P h y s . L e t t . 1 2 6 B ( 1 9 8 3 ) 3 9 8 .

P . B a g n a i a e t a l . , P h y s . L e t t . 1 2 9 B ( 1 9 8 3 ) 1 3 0 .

D : 8 4 1 Û Û 2 6 2 5 2

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THE SEARCH FOR NEW FLAVOURS

* + F. Halzen and A.D. Ma: in

*Physics Department, University of Wisconsin, Madison, USA

ABSTRACT We discuss the search for new quark flavours with pp colliders. We

emphasize the following subjects: (a) production cross sections: central and "diffractive" production, heavy flavours in jets, Cb) production of same and opposite sign dileptons, (c) signatures of heavy flavour production.

1. EVENT RATES FOR HEAVY FLAVOUR PRODUCTION Event rates for pp-KJQX (with Q = c,b,t,...) are routinely*^calculated

from the qq •* QQ and gg -+• QQ QCD fusion diagrams shown in Fig. 1. One should be aware however of other sources of heavy quarks: (i) "diffractive" production of A Q M Q (A=Qud, Mq - Qu), (ii) heavy quarks in jets and (iii) weak production, e.g. pp -* WX followed by W tb. Sources (i), (ii) could be potentially more copious than heavy quark production via the standard fusion mechanism and, although this is certainly not the case for (iii), W •+• tb could be a preferable experimental trigger because of its clean signature.

That fusion is only part of the story is clearly illustrated by glancing back a t the production of charm at lower energies; see Figs. 2, 3. Absolute cross sections seem to be in excess of those computed from the fusion diagrams (Fig. 2 ) . Finding excuses for this is a useless effort as the fusion mechanism does not yield charmed particles with large longitudinal momentum (say x^>0.2) contrary to observation; see Fig. 3. As m^Ji/a is likely to be the crucial variable in the problem, t-quark production at the pp collider could be qualitatively similar to c-quark production at the ISR as we might guess that, to within a factor of three or so, (m t/540) - (m c/63). One might also expect that the "diffractive" cross section has a logarithmic energy dependence and varies with the quark mass as (m^) . This behaviour however cannot be correct:

it predicts that a./ff =1/8 which disagreees with ISR experiments, the b ? . . . 2) leptonic decays associated with such a large h-cross section are inconsistent

with the experimental fact that (e,u)/ir = 10

- 2 6 1 -

A three-step scenario for producing diffractive '^^q pairs is depicted in Fig. 4 . When che QCD-evalveá proton is in a stace uudQQ (step A ) , one of che heavy quarks (Q in Fig. 4) interacts with the colliding p (step B) and finally the interacting Q recombines with a valence u quark to form M-while the spectator Q recombines with the other u„d valence quarks to form AQ

(step G ) . The Q,Q which originate with low v. from gluon emission, nevertheless emerge in particles with large Feynrnan x. As indicated in Fig. U, the emerges az large x because the heavy quark Q combines with two valence quarks, whereas the Mr containing one valence quark has intermediate x.

Fig. 1 : Order a g diagrams for charm production. The production via flavour excitation is sketched in (d).

- 262

to io£

(6eV)

Reliable predictions cannot be made because cf the severe ambiguities 3)

associated with each of the steps in such a calculation. Barger et al. perturbatively compute the Q(Q)-hadron cross section (step B) from the "flavour excitation" diagrams shown in Pig. 1, They lump the structure functions of steps A, C into one and basically let the charm dats determine it. ' Such a model can then be scaled in ra^. The prediction for the "diftractive" production of heavy quarks is shown in Fig. 5, where it is compared to the standard fusion calculation. In the m n range where the t quark is expected,

3) an increase of the yield bv roughly a factor 10 is predicted. Collins and

it) Spiller on che other hand perturbatively compute step A, explicitly incorporate the recombination in step C, and guess ( in one _>ersion of their

-2 calculation) that o(Qp) ^ (in ) in etep B. This is reasonable: one determines

" -2 o(Qp) by the additive quark model and the (m^) suppression reflects the fact that the QQ scattering state is a short-time fluctuation (or alternatively that the scattering Q is off-shell because of its large mase m ^ ) . Their predictions for m f c = 25, 35, 45 GeV are also shown in Fig. 5.

- 264 -

These calculations are able to describe the diftractive production of strange and charm quarks (see Figs. 2, 3 and Refs. 1, 3, 4, 5) and to the extent that the predictions in Fig. 5 represent an extrapolation in T t i _

of data, they might well be a reliable guide to top production. In a collider experiment when the proton dissociates into A Ï the forward going A t is presumably not detected, but, as emphasized by Horgan and Jacob, the r meson produced at intermediate x (and low p ,) ray be observed by its semileptonic decay T A \>X. The transverse momentum distribution of the I should peak at p£ T- r a

t/4. A lepton charge asymmetry should result, since when alternatively the incoming antiproton dissociates into A T the A goes

+ + undetected and the I from T •*• i v X may be observed. If the X jet can be identified then the "cluster" transverse mass (see section 3.2) may be exploited to estimate the mass of the T meson.

Notice that this hierarchical structure in x (A . at large x, T at intermediate x, tt pairs at low x; compare Fig. 3) does not exist in the intrinsic heavy quark model.^ Here the t,t themselves have large x and an intrinsic tt pair would be hardly separated by the recombination with light u,d quarks. No lepton asymmetry is expected. Finally it is interesting to speculate that a "diffractive" mechanism could De an unexpectedly abundant source of Higgs,^ gluioos, ... and everything else that is routinely calculated from qq, gg fusion.

. . 9) We also draw attention to an intriguing result presented at this

conference: roughly 30% of the (mostly gluon) jets observed in pp collisions contai-i a charmed D particle which is observed through the D D transition. This means that almost every jet could contain some type of charmed particle. The jets are preferentially produced at small angles as they approximately

-4 8 , follow a sin Rutherford angular distribution. This source of charm is therefore also expected to preferentially populate the forward direction. The occurrence of such a "boring" production mechanism of new flavours could force us to completely reconsider the heavy flavour situation at the collider.

2 . DILEPTONS: THE KEY TO HEAVY QUARKS? The intimate connection between QQ and I I production is well illustrated

by some typical processes which lead to dimuons from fab production and decay:

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1* bh bb bb (1) L - I - I i

1—» su v I—* s

unlike sign, unlike sign, like sign, like sign from opposite sides same side opposite sides B°-B° mixing

A calculation of the production cross section of opposite sign dileptone from cc, bb and tt origin is shown in Fig. 6 as a function of the dilepton invariant mass (assuming m ¿ = 35 GeV). Also shown is the production of large mass lepton pairs by the Drell-Yan mechanism qq -> y ( Z ) Ä ' Ä - .

Figure 7 shows the results of the same calculation after imposing cuts on the transverse momentum of the lepton. In the real world such cuts are required to identify the lepton in the detectors. In the mass range M - 10 GeV where the dimuon signal peaks (for p ^ > 5 GeV) the Drell-Yan and bb sources of dileptons closely compete. Dileptons of bb crigin can however be separated by the following distinctive features: (i) presence of charm jets, (ii) presence of strange particles, (iii) the possible production of same sign dileptons.

In Table 1 we give the total event rate for dimuon production from various sources, including those of eq. (1). We see that bb production dominates at low p ^ but is sooti overtaken fay Drell-Yan production. The table also shows the effect of B°-B° -mixing on the relative number of like-and unlike-sign muon pairs. Our understanding of the bb dilepton signal should be a very high priority in two respects: it is the background to the "anomalous" and

13)

puzzling dimuon events presented a t this conference (or is it really the

origin of these events?) and it ie also the background in the t-quark search using the dilepton signal (see Figs. 6, 7 and Section 4 ) .

14) We suggest using i|i Ts as a tag for b mesons through the decay b •*• X.

This decay of b-flavoured mesons has been observed* -^ with the theoretically expected branching ratio of order 1%, For B(B -*• i|>X) = O.Ol the production of via b decay dominates (at least a t large p^, where the 41 •> JJ +U can be experimentally identified) the production of V's via the conventional QCD mechanisms gg gifi and gg -*• Xjg followed by Xj **" <PY ( J - 0, 1, 2 ) .

- 2 6 6 -

Fig. 6: The cross section for dilepton production, (as a function of the invariant mass of the lepton pair) in pp collisions at /s = 540 GeV, taken from ref.10. No K factor is included, that is K=l.

20 40 69 £0 100 120

7 : The same as Fig. 6 tut with minimum p cuts imposed on che leptons.

1 1 ' I ' I 1 1 » 1 1 ; : \ (bl p p - * e * e - X

\ (p,r>15GeV)

\ \ \

_ \ /I -> / i X \ v ; z / \ N A / J \

•

: 1 t \ « ;

i . i . i . i ,

0-1

001

0 ZO 40 60 60 100 M b V ) IGeV)

• la)

20 40 60 80 BO H[eV> (GeV)

W

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rabie i. The number of dimuon events expected*"^ in pp collisions at Ss, = 540 GeV

from various production mechanisms for differentminimum p^, cuts on the muons

(p _ shown in GeV/c). The event rate is shown for an integrated luminosity -1

of 100 nb : that is, the table entries multiplied by 10 give the cross sections in pb. The figures in brackets show the effect of the maximal expected B°-B° mixing, that is a mixing parameter E = 0.15 in the notation of ref, 12. Dimuons from tt, tb and tb cascades may compete at high p^. and are considered further in section 4 (see, in particular, Pig. 13). Ko K factor is included (K al).

mechanism for dimuon production

> 3 P m > 5

bb decays:

u +u~, opposite sides 143 (118) 12 (10) 0.4 (0.3) same side 15 1 0.01

p + u + , u"u~ 42 (67) 3 (5) 0.04 (0.1)

ce -y y +u~ 23 2 0.1 b -> if y +u" 16 3 0.2 Drell-Yan Y <Z) * v * v - 58 19 5

This is shown in Pig. 8. ii * s could provide us with a good measurement of the b-quark cross section- The "background" QCD process, dominated by gg •*• Xjg CXj * C'Y) is also interesting. It is a sensitive measure of the gluon structure function at Ss = 540 GeV. Its determination at Ss = 540 GeV would be invaluable to help us control perturbative calculations in the small x (x = m^/i's) range that is so important for making predictions*^ for TeV energies (SSC, Juratron). For example, cross sections for i|i production via x's are increased by one order of magnitude if we replace the structure functions of Ref. 17, used in calculating the results shown in Fig. 8, 6y a scaling 3(l-x)^ gluon distribution.

268 -

t — i — i — i — i — i — r

I I I I ' I L

Z 6 10 14

PT (GeV)

Fig. 8: The p r distribution of J/p production in pp collisions at </s = 540 GeV, together with some of the basic diagrams.

3. SIGNATURES FOR TOP There are systematic procedures for isolating a t quark from the

observation of its semileptonic decay products, t •> bAv, regardless of the way in which it is produced. We are concerned with events in which there is a charged lepton, jet activity and (provided the detector is hermetic) missing momentum transverse to the beam directions (p^ T)- The major problem is to distinguish such a t decay from the large background of b -»- civ decays arising from the much more numerous bb pairs produced at the collider (see Fig. 5 ) .

- 269 -

3.1 Hv transverse mass If only the charged lepton and the missing transverse momentum are

identified then it is appropriate co form tiie transverse mass, M^,(jiv), of the fi,\) system, defined by

where = m^ + p^. For the seroileptonic decay of a heavy quark (Q •*• qJlv) M , is restricteu to the range

Fig. 9 shows the "idealized"' M , distributions expected from t and b seraileptonic decays, together with that from the W leptonic decays*^. The heavy quark decays may be distinguished from the W decays by their accompanying je' activity. The difference in the kinematic end-points of the distributions can be exploited to separate the t from the b (and c) decays. In practice the sharp cut-offs at ra_-m only occur when í and v result from

" q 20) the same primary decay; cascade semxleptontc decays lead to tails above the end-points (see Fig. 12 (a)). Moreover uncertainties in the observed values of p v T smear the distributions and, in particular, there is a tendency of the M, distribution of the much more numerous b decays to spill

21) over to large M , and to mask the t signal . Therefore other criteria need to be invoked to convincingly isolate a t quark signal. We discuss these

3.2 Cluster transverse mass In t •+ bZv events in which the b decay jet is also identified and

measured we can form a much more selective transverse mass distribution. We treat the bSL system as a cluster '.rith

P T « P b T + P A T

M 2 = (p b + P f c ) 2

18] and form a "cluster transverse mass"

( M Î V ) = CET + E , T ) 2 - ( L + p u T ) 2 ( 4 )

- 270 -

gig* 9 i The transversa ^ 8.V mass distributions ' resulting from t -* b£v and b •+• c£v decays, compared to that from the sum of the W leptonic decays: W + 2v and W •*• T V •*• Ävv, where £ = e or u. It is assumed that m = 35 GeV and that (Ba) w - 2<Bcr)t. With perfect resolution M^CÄV) for b C Ä V is confined to the region Mj. < 3 GeV.

M r d v ) (GeV]

Fig, 10: The predicted rauon p^ distributions from heavy quark production and decay in pp collisions at * s = 5Ó0 GeV: (a) without cuts and (h) with the requirement that each event contains two p^ > 8 GeV jets, together with an isolated rauon such that the summed hadronic |p„| is less than 3 GeV in a 30° cone about its direction. Only events from QCD fusion or W decays are shown; diffractive tt production is not included. For comparison the u _ spectrum from W •» uu decay is also shown. The figure is taken from refs. 22 and 23.

- 2 7 1 -

This leads te sa effective two body (t + hi + v) decay distribution with a sharp Jacobian peak at >L,(bfi.;\0 « m (see Fig. 3 of ref. 18). Realistic

22,23) . . . . . calculations , including missing p^ uncertainties and full cascade decays, smear the sharp peak (see Fig. 12) hut leave a very pronounced t

24) signal at m t. A further discussion of this variable is given by Stirling

3.3. Lepton isolation The heavy quarks produced by QCD fusion (tt,bb) D r by W decays (tb»tb)

will lead to two jets which are approximately back-to-back in the transverse plane. The more massive the heavy quark the broader will be the jet of its decay fragments. Indeed for a massive t quark the t and t decay jets may overlap and even three subjets from a hadronic t decay may be visible. If we sum the moduli of the transverse momenta relative to the jet axis of the eventual light decay fragments of a Q decay jet we find^^ ^ l^í jj ~ ïïmq^* which is about 30 GeV for a t quark of mass 40 GeV, but Dnly about 4 GeV for b decay. Moreover when concentrating on a decay lepton at fixed large p , to the beam axis a relatively light quark like a h is itself inevitably produced at large and so its decay products will appear ccllimated. Such a collimation need not occur for the decay of the massive t quark. We conclude that leptons at high p T which result from b decay will belong to narrow jets containing hadronic decay debris, whilst those from t decay have a good chance of being isolated. However the lepton in b + c£v may appear isolated if the accompanying c jet has low p T« An effective way of removing the large bb (and also cc) background from tt or tb, tb events is therefore to select events with an "isolated" lepton * » , together with two large p T hadronic jets. This is well illustrated by the muon p T

distributions shown in Fig. 10, which assume rat = 35 GeV, Although muons from bb decays dominate the spectrum (figure (a)), they can be eliminated at large by criteria requiring muon isolation and two energetic jets (figure (b))- Indeed if m = 35 GeV, figure (b) predicts

-1 that in the present data sample (integrated luminosity of 136 nb ) there should be about 10 "clean" t quark events with p ^ > 8 GeV/c, about half coming from W -*• tb, tb decays and half from the tt produced by QCD fusion.

There is still a chance of events arising from higher-order QCD

23 26 27) processes ' * , such as gg bbg escaping the acceptance cut, see Fig. 11.

23) An upper limit to these contributions is shown by the bbx curve on Fig.10(b). This residual background may be eliminated by exploiting transverse mass techniques, as can be seen in Fig. 12.

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> r M b ,

Fig. 11: The t signal of an isolated muon and two high p T jets and a higher-order QCD background contribution in which one b decay fakes an isolated muon.

Finally, a nice property*^ of, the W tb events is that the p T

distribution of the b jet has a Jacobian peak at p r(b) =

and so the identification of a few events of this type would give an 29)

estimate of the t quark mass. Indeed one UAl event in the 1982 data sample has all the characteristics of W •*• tb although the decay electron is more energetic than expected: an isolated electron of E , = 30 GeV which recoils against a 29 GeV jet containing a reconstructed charm particle. Taking this event seriously would give rac - 40 GeV.

4. OTHER TOP SIGNALS 4.1 Multileptons

30,10,12) In many ways the multileptcn signatures of t quark production

are superior to the single iepton events. The main disadvantage is that the event rate is an order of magnitude smaller. Possible signals from p-;raary semileptonic decays are

gg,qq tt ->• qq' -»- W •*• tb * * V x

and so the signals are just beyond the present data sample. The bb background (discussed in detail in section 2) can be greatly suppressed because isolation criteria can now be imposed on two leptons. Such data will be of immense interest as the luminosity increases.

- 2 7 3 -

Mjlfív) (GeV) MT(b¡í,v) (GeV)

Pig. 12r The yv and cluster transverse mass distributions calculated from complete cascade decays with possible multiple neutrinos and including resolution smearing. The bbx backgrounds Clashed curves) are due to higher-order QCD processes which partially survive the p T > B GeV/c and nuon isolation cuts imposed in Fig. 10(b). The figure is" taken from ref. 23.

Fig. 13: Dependence of the cross section for dilepton production on the lepton p r cut at /s = 540 GeV, with m c « 35 GeV. The figure i s from ref. 12 and includes leptons from the full t b •+ c •* a cascades.

- 2 7 4 -

4.2 T production? Jus.t as i|< production may act as a trigger 1^' for b quark production

via the decay B 0X, can T •+ u +u be used to indicate t quark production via T TX? Unfortunately the T -> TX branching ratio is much too small and T production is dominated by the subprocess gg Tg. 4.3 Toponium

31) The most frequently produced toponium state is predicted to be

n t C 1 S Q ) . If m n c = 7 0 GeV then the cross section, calculated from gg fusion, is about 5 pb at /s = 540 GeV rising to 0.1 nb at /s = 2 TeV. These estimates use a scale breaking gluon distribution, no K factor (K = 1) and assume |iKD) I ~ m^. On each count they therefore represent a lower limit to n t

production. However the best signature is the decay mode n t *** YY which is expected to have a branching ratio of only about 1£.

ACKNOWLEDGEMENTS We wish to thank B. Hahn and his colleagues at the University of Bern

for arranging an excellent Workshop and tö thank H. Baer, V, Barger, E.W.N. Glover, F. Herzog and R.J.N. Phillips for enjoyable collaborations which led to many of the results presented here.

REFERENCES 1. F. Halzen, Rapporteur's talk at the 21st High Energy Physics Conference,

Journal de Physique, supplement to 12, C3-381 (1982). 2. F. Halzen, A.D. Martin and D.M. Scott, Zeit, für Phy. C13, 291 (1982). 3. V. Barger, F. Halzen and W.Y. Keung, Phys. Rev. D24, 132S (1981) and

D25. 112 (1982). 4. P.D.B. Collins and T. Spiller, Durham preprint DTP/84/4 (1984). 5. R. Odorico, Phvs. Lett. 107B, 231 (1981) and in AIP Conf. Proc. No. 85,

p. 100 (1981). 6. R. Horgan and M. Jacob, Phys. Lett. 107B, 395 (1981). 7. S.J. Brodsky, P. Hoyer, C. Peterson and N. Sakai, Phys. Lett. 93B, 451

(1980). 8. V. Barger, F. Halzen and W.Y. Keung, Phys. Rev. D25, 1838 (19B2). 9. C. Frey, UAl Collaboration, these proceedings.

10. E.W.N. Glover, F. Halzen and A.D. Martin, Durham preprint DTp/84/2, Phys. Lett. B (to be published),

11. We chank E.W.K. Glover for preparing table 1. 12. V. Barger and R.J.N. Phillips, Madison preprint MAD/PH/155 (1984). 13. C. Rubbia, UAl Collaboration, these proceedings. 14. F. Halzen , F. Herzog, E.W.N. Glover and A.D. Martin, Durham preprint

DTP/34/8. 15. S. Stone, CLEO collaboration, Proc. of the Int. Symp. on Lepton and

Photon Interactions at High Energies, Cornell (1983). 16. See, e.g., I. Hinchliffe, these proceedings. 17. M. Glück, E. Hoffman and E. Reya,Z. Phys. C13, 119 (1982).

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18. V. Barger, A.D. Martin and R..J.N. Phillips, Phys. Lett. 125B, 339 (1983).

19. V. Barger, Madison preprint MAD/PH/165, to be published in Proc. of Physics of 21st Century Conference, Tuscon (1983).

20. V. Barger, A.D. Martin and R.J.N. Phillips, Phys.Rev. D28, 145 C1983). 21. F. Halzen and D.M. Scott, Phys. Lett. 129B, 341 (1983);

G. Ballocchi and R. Odorico, Bologna report IFOB 83/11. 22. V. Barger, H. Baer, A.D. Martin and R.J.N. Phillips, Phys. Rev. D29,

887 (1984). 23. V. Barger, H. Baer, K. Hagiwara, A.D. Martin and R.J.N. Phillips,

Phys. Rev. (in press). 24. W.J. Stirling, these proceedings. Z5. R. Odorieo, CERN preprint TH 3678 26. S. Aronscn, p. Paige, S. Protopopescu and D. Weygand, reported at

the Gordon Conference, Aug. 1983. 27. I. Schmitt, L.M. Sehgal, H. Tholl and P.M. Zerwas, Aachen preprint

PIIHA 83/26. 28. V. Barger, A.D. Martin and R.J.N. Phillips, Phys. Lett. 125B.343 (1983). 29. D. DiBitonto, Proc. of Third Moriond Workshop on pp Physics p.473 (1983). 30. M. Abad, R. Gatto and C.A. Savoy, Phys. Lett. 79B. 435 (1978);

S. Pakvasa, M. Dechantsreiter, F. Halzen and D.M. Scott, Phys. Rev. D20, 2869 (1979); N. Cabihbo and L. Maiani, Phys. Lett. 87B, 366 (1979); L.L. Chau, W.Y. Keung and S.C.C. Ting, Phys. Rev. D24, 2862 (1981); F.E. Paige, AIP Conf. Proc. 85, 168 (1981).

31. R. Baier and R. Riickl, Nucl. Phys. B 2 0 8 , 381 U 9 8 2 ) .

D: 8410026260 - 276 -

THE M I N I M U M MASS T E C H N I Q U E FOR D E T E C T I N G NEU HEAVY STATES

I N H I G H ENERGY HADRON C O L L I S I O N S

W . J . S t i r l i n g

C E R N , G e n e v a , S w i t z e r l a n d

M a n y p r e d i c t e d h e a v y s t a t e s a r e e x p e c t e d t o d e c a y f r e q u e n t l y i n t o t h r e e / o r m o r e b o d y f i n a l s t a t e s I n w h i c h a t l e a s t o n e p a r t i c l e , s u c h a s a n e u t r i n o

o r p h o t i n o , i s n o n - i n t e r a c t i n g . A m e t h o d i s d e s c r i b e d f o r o b t a i n i n g e s t i m a t e s oE b o t h t h e m a s s a n d t h e l o n g i t u d i n a l m o m e n t u m o f t h e p a r e n t s t a t e . Two a p p l i c a t i o n s - t h e d e c a y o f t o p q u a r k h a d r o n s a n d g l u i n o s ( i n t h e R s y m m e t r y s c h e m e ) - a r e d i s c u s s e d i n d e t a i l .

I N T R O D U C T I O N

I n r e c e n t y e a r s t h e r e h a s b e e n a p r o l i f e r a t i o n o f t h e o r e t i c a l p r e d i c t i o n s

f o r new h e a v y s t a t e s . E x a m p l e s I n c l u d e t h e t o p q u a r k a n d H i g g s b o s o n o f t h e

s t a n d a r d m o d e l , a n d m o r e e x o t i c ' c o n s t r u c t s ' s u c h a s s u p e r s y m m e t r i c p a r t i c l e s ,

t e c h n l c o l o u r p a r t i c l e s a n d e x c i t e d q u a r k s , l e p t o n s a n d w e a k b o s o n s > A

c h a r a c t e r i s t i c f e a t u r e o f many o f t h e s e s t a t e s i s t h e i r f r e q u e n t d e c a y i n t o

m u l t i p a r t l c l e ( o r m u l t i - j e t ) c h a n n e l s i n w h i c h a t l e a s t o n e p a r t i c l e i s n o n -

i n t e r a c t i n g . F o r e x a m p l e h

T —» jju v B 9 - <l*L f _

w h e r e T , B d e n o t e h a d r o n s c o n t a i n i n g t o p , b o t t o m q u a r k s , g a n d y d e n o t e t h e

s u p e r s y r m n e t r i c g l u i n o a n d p h o t i n o , a n d H i s e i t h e r t h e H i g g s b o s o n o c a (WW)

b o u n d s t a t e * H e r e w e a r e a d o p t i n g t h e u s u a l a s s u m p t i o n t h a t t h e p h o t i n o i s t h e

l i g h t e s t s u p e r s y m m e t r i c p a r t i c l e a n d t h a t t h e t h e o r y i s R i n v a r i a n t , i . e . , t h e

l i g h t e s t ( s t a b l e ) s u p e r s y m m e t r i c p a r t i c l e h a s t o be f o u n d a t t h e e n d o f t h e

d e c a y c h a i n .

W h i l e t h e o b s e r v a t i o n o f m i s s i n g e n e r g y i n t h e f i n a l s t a t e i s a u s e f u l

s i g n a t u r e f o r s u c h p r o c e s s e s , t h e mass a n d m o m e n t u m o f t h e p a r e n t c a n n o t b e

d e t e r m i n e d d i r e c t l y f r o m t h e d a t a s i n c e o n e o f t h e f o u r - m o m e n t a i n t h e f i n a l

- 277 -

stace is not measured. It Is important therefore to search far techniques which provide goad estimates of these quantities. This talk will summarize the "minimum invariant mesa" approach emphasized recently in Ref. 1). This method uses the four-momenta of the observed final state particles to construct invariant mass and longitudinal momentum distributions for the parent which are sharply peaked at their true values. Section 2 contains a general discussion of the method and two applications are considered in Section 3.

2. THE MINIMIZATION PROCEDURE Consider a heavy state Q (=top meson, gluino,...) of mass M produced

predominantly at small transverse momentum in a high energy process. Suppose that Q decays into n+ 1 (effectively massless) particles or jets, n of which are observed and their four-momenta measured. The missing transverse momentum is ascribed to the non-interacting particle, and so the four-momenta of the decay products can be written

P™ = ( ^ P ? , P r . Z ) Pr - -gPn

where z labels the unknown longitudinal momentum of the missing particle. As a function of z the invariant mass of the system M(z) hos a unique positive minimum, i.e.,

The minimum mass M * is defined to be the minimum invariant mass which can be constructed for the system, i.e.. M * = M ( Z Q ) « A corredponding longitudinal momentum P * ^ = s " = ^ P T, + z 0 can also he defined. Explicitly*^,

- 278 -

where F is the hypergeometric function. The distributions for n = 2 and n = U

are shown in Fig. 1 - the sharp peak at Ç = 1 Is evident. Taking the £ •* 1 limit of Eq. (5) gives

( 6 )

which shows that the singularity gets stronger as n increases. [The quantity In { } in Eq. (6) is a monotonically increasing function of n for n ^ 0 . ] This result is intuitively obvious, since as n increases a smaller fraction of the information about the true invariant masa ia "Lost" with the non-interacting particle. Similar remarks apply to the longitudinal momentum distribution l/r dT/dP*. There is, however, no simple analytic analogue of Eq. (6) - the distribution corresponding to the particular case n - 2 is calculated numerically in the next Section.

Finally, it can be shown that the above distributions are quite insensitive to the inclusion of transverse momentum smearing for the heavy state Q and also final state particle tuasses, provided that ^ P ^ Q , m^ « M .

(Note that both these quantities are functions oí the measured parameters only.) The assertion is that the decay distributions dr/dM* and dlVdP* are sharply peaked at the true values M and P^. Thus tie method allows an accurate determination of the mass and longitudinal momentum (more generally, the longitudinal momentum distribution) of the heavy state Q.

To see this explicitly, consider a simple phase space model for the decay Q •> P^* For this, the M* distribution can be calculated analytically. Defining a diraensionlesa variable E, = M*/M, the result is

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3 . TWO A P P L I C A T I O N S

3.1 A process which appears Ideally suited to the above analysis is the associated production and senti-leptonic decay of a top quark meson. Experience with the ISR shows that single large mass diffractive excitation is likely to

2) give a particularly favourable signal to background ratio in such a case :

«hère T = (tq), = (tqq). It is difficult to predict the cross-section from first principles, but the observation of a l¿rge diffractive charm signal at

the baryon is expected to keep some leading role, the meson should be produced predominantly at smaller (the ïeynman scaling variable) and with a rather small transverse momentum. The T meson should therefore be more easily detected, and more often, since fragments of the A^ baryon are likely to be lost at very forward angles-

As pointed out in Ref, 6), there is a special charge correlation effect in the semi-leptonic decay which can. provide aiv additional signature. When the antiproton "flares" the t quark stays with the antlbaryoa whereas the t quark forms a meson with eventual u production. The opposite is true when the proton flares. It will be assumed that in an experiment it is possible to isolate events in which only the top meson decay products - in. the farm of a single jet, a leptjn of the appropriate charge and missing transverse energy -are observed. This separation of the two top quark hadrona is necessary since the missing transverse momentum has to be attributed to a single non-interacting particle.

The situation is summarised as follows: the top meson is produced with an a priori unknown (hut assumed soft) x , distribution, and with small p^, and subsequently decays into a lepton, a neutrino and a hadronic jet* The four-momenta of the tauoa and jet are measured and the missing transverse momentum is ascribed to the neutrino. As described above, the minimum invariant mass method uses these parameters to determine (a) the mass and (b) the longitudinal momentum distribution of the cop meson.

(7)

the ISR suggests that the top quark rate may be sizeable* 3)-6) Insofar as

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Top quark signatures have also been analyzed extensively by Barger, Martin and Philips^. Their "cluster transversemass" defined in Kef. 7) is in fact identical to the minimum mass. The cluster transverse mass distribution for top quark decay has been presented in Ref. 7 ) . Here the analysis is generalized to include the longitudinal momentum distribution, and to explore the sensitivity to experimental cuts^.

Figure 2 (solid line) shows the Ç = M*/M distribution for top meson decay. The light quark spectator in the decay T + u-vB has been ignored and the exact weak interaction matrix element for t + uvb has been used. Comparison with Fig. 1 (n = 2) shows that the inclusion of the matrix element has a negligible effect on the distribution. Note that by definition [Eq. ( 4 ) ] , the minimum mass distribution is invariant under longitudinal boosts and so the same curve obtains for any top meson x^ distribution.

Now consider the distribution in the "longitudinal momentum," P*. It Is again convenient to define a dimensionless variable R* = P*/M» Figure 3 shows the distributions 1/T dlYdR* for various values of the top meson longitudinal momentum = RM. The distributions are different for different R (unlike M*, P* L is not boost invariant) but in each case the peak is close to the "true" value of R. Thus the distribution can be unfolded from the experimental P* spectrum.

The distributions shown in Fig. 3 are integrated over all values of M*. Not surprisingly, th.: peaks can be made sharper by restricting the events to those which have M* values close to M. This is illustrated in Fig. 3 by the batched distribution (for R = 2) which has the additional constraint M*>0.95M.

The above calculations are, of course, rather naive in that the effects oc detector geometry, experimental cuts, backgrounds, etc., have not been included. Ultimately, the utility of the method depends on its ability to survive these effects and still yield useful information. It turns out that the M* and P* distrilution;1 are in fact quite insensitive to restrictions on

i \ the decay phase space . Examples of this are illustrated In Fig. 2. The dashed line shows the M* distribution with the additional requirement that the jet, muon and neutrino each have a transverse momentum greater than some threshold value, p^* n, chosen here to V ¿ 1/8M. This presumably removes the contamination of leprous, neutrinos and jets from other (background) sources. Although some of the top meson signal Is also lost, there Is evidently little change in shape. A second type of cut relates more to the geometry of the detector. If the muons are required to be central in the laboratory, then the M* distribution Is no longer invariant under longitudinal boosts. In fact for top mesons with 0» such an experimental restriction introduces a bias In

281

favour of events In which the muon Is moving backwards In the meson centre-of-raaas frame. Figure 2 (dotted line) shows the M* distribución for a meson of longitudinal momentum = 2M, with the requirement th t the (laboratory) pseudorapidity of the muon he between -1 and +1. Although the normalization is reduced by a factor of about 4, the characteristic shape is the same and the Jacobian peak at M* 3 tt persists. The conclusion is therefore that the minimum mass is iudeed a reliable indicator of the true invariant mass, even in the presence of quite severe cuts. 3.2 Tn the previous application, the fragments of the lieavy state Q were assumed to be isolated in phase space from all other final state particles, thus allowing a precise determination of the mass and longitudinal momentum. IT, however, the heavy states are produced in pairs which are not well separated In phasa space, then there is clearly a difficulty in disentangling the appropriate &?cay fragments for each Q. An interesting example is provided by the pair production of supersymmetric gluinos. According to the usual Ideas, these are expec'.ed to decay Into a light qq pair '.ith an unobserved "light" photino"'. Consider, therefore, the process

with the gluinos produced predominantly at small P t but with arbitrary p ? . The signature is four large hadron jets with missiig transverse momentum.

A minimum mass M*j can be constructed for each of the six possible pairings of the jets [Eq. (4), n = 2 J . Two of these pairings correctly identify the same gluino fragments and for these the M* distribution shows the usual peak at M* = M. The other four permutations correspond to wrong pairings and for these the M* distribution has of course no Jacobian peak - the wrong-pair distribution is broad over the range 0 < M* < M with a maximum at M* = M. However, when sll the different pairings are considered in total, the sharp peak at M* = M does dominate over the combinatorlc background. A Monte Carlo calculation is shown in Fig. 4, for a phase-space-only model. Evidently che gluino zaass can be readily determined from this minimum mass distribution. The method is particularly useful when, because oí p^ threshold and rapidity cuts, rot all the jets are observed. By simply extending the definition to include all observed jet pairs, the signal can again be shown to dominate over the background. By subsequently selecting those events which are in the vicinity of the peak, informática can be obtained on the gluino distribution, as described in the previous application.

( 8 )

- 2 8 2 -

ACKNOWLEDGEMENTS The work presented here was done in collaboration with Edmond Berger,

Daryl DiBltonto and Maurice Jacob. I am very grateful to them for many stimulating discussions. I would also like to thank Professor Hahn and his colleagues for organizing such an excellent workshop.

REFERENCES 1) E.L. Berger, D. DiBitonto, M. Jacob and H.J. Stirling - CERN Preprint

TH. 3821 (1984), to be published in Phys.Lett. 2 ) D. DiBitonto - Proton-Antiproton Collider Physics, 1981 (Madison, g T ) f

Eds. V. Barger, D. Cline and F. Halaen (AIP, N.Y., 1982), p. 26. 3) F. Halzen and A.D. Martin - These Proceedings. 4) S.J. Brodsky, C. Peterson and N. Sakai - Phys.Rev. D23 (1981) 2745. 5) P.D.B. Collins and T.P. Spiller, University of Durham Preprint DTP/84/4

(1984). ó) R. Horgan and M. Jacob - Phys.Lett. 107B (1981) 395. 7) V. Barger, A.D. Martin and R.J.N. Philips - Phys.Lett. 125B (1983) 339,

343; Phys.Rev. D28 (1983) 145. 8) D.V. «anopoulos - These Proceedings.

FIGURE CAPTIONS Figure 1 Minimum mass distributions (? s M*/M) in a phase space model with

two and four observed particles in the final state. Both curves have unit area.

Figure 2 Minimum mass distribution for the decay t * buv: (a) with no cuts (solid line), (b) with all final state transverse momenta>M/8 (dashed line), and (c) with J?L » 2M and a cut on the muoa pseudo-rapidity, jn^j < 1 (dash-dotted line).

Figure 3 P* (= MR*) distributions for three different cop meson longitudinal momenta, P^ 9 0,2M,4M. The hatched distribution is obtained when the additional constraint M* >0.95M is imposed.

Figure 4 Minimum mass distribution for double gluino decay* summed over all six possible pairings of the four jets. The dashed line is the background contribution from the four wrong pairings, and the normalization is such that / | J dÇ dN/dÇ - 6.

- 283 -

5P/JP J A

F l g . 3 F i g . 4

- 285 -

UA5 Results

- 286 - D*. 8 4 1 0 0 2 6 2 7 9

N E W R E S U L T S F R O M UA5: S T R A N G E P A R T I C L E ( K ° , A , S ~ )

P R O D U C T I O N A N D L A R G E F L U C T U A T I O N S I N M U L T I P L I C I T I E S

U A 5 C o l l a b o r a t i o n

B o n n - B r u s s e l s - C a m b r i d g e - C E K N - S t o c k h o l m

j / r e s e n t e d b y i J . C a r l s o n

/ Preliminary results are presented from about Ci500 non single diffrnctive m'-ù- \

mum bias events taken with the UA5 streamer chambers ut the collider with a j

o '

beryllium beam pipe. Significantly increased statistics on V production has permitted f

the first observation of X as well as a more accurate estimate of the average rrans- |

verse momentum of K° and A . The nun single difLractive multiplicity distribution has I

been studied in detail and revealed non scaling behaviour. In very narrow rapidity /

intervals large fluctuations, "spikes", in multiplicity occur. /

287 -

1 . I N T R O D U C T I O N

T h e U A 5 d e t e c t o r , c o n s i s t i n g o f t w o l a r g e s t r e a m e r c h a m b e r s , w a s o p e r a t e d a t

t h e C E R N p p c o l l i d e r d u r i n g i t s f i r s t r u n io O c t o b e r 1 9 8 1 a n d a l s o d u r i n g a r u n i n S e p

t e m b e r 1 9 8 2 , S o m e o f t h e p r o p e r t i e s o f t h e d e t e c t o r a r e g i v e n in T a b l e 1 . F o r f u r t h e r

d e t a i l s , t h e r e a d e r i s r e f e r r e d t o p u b l i s h e d a r t i c l e s [ l ] . T h e n e w d a t a t h a t i s p r e s e n t e d

h e r e c o m e s f r o m t h e 1 9 8 2 r u n , w h e r e a b e r y l l i u m b e a m p i p e w a s i n t r o d u c e d in o r d e r t o

r e d u c e t h e b a c k g r o u n d f r o m c o n v e r s i o n s . T h i s d a t a i s h e n c e f o r t h c a l l e d 1 9 8 2 d a t a a s

o p p o s e d to t h e 1 9 8 1 d a t a . T h e t o t a l n u m b e r o í n o n s i n g l e - c U f f r a e t i v e e v e n t s u s e d i n t h e

a n a l y s i s p r e s e n t e d h e r e i s a b o u t 6 5 0 0 . *

T a b l e 1 . p r o p e r t i e s o f t h e U A 5 d e t e c t o r

S t r e a m e r c h a m b e r v i s i b l e v o l u m e ( e a c h ) 3

6 x 1 . 2 5 x 0 . 5 m

S t r e a m e r c h a m b e r s e p a r a t i o n 1 0 c m

P s e u d o r a p i d i t y a c c e p t a n c e 9 5 % l o r \t)\<3 f a l l i n g

t o 0 % a t 1771 = 5

R a n g e c o v e r e d b y t r i g g e r 2 < I i , | < c 6 . 6

T r i g g e r a c c e p t a n c e ( M o n t e C a r l o e s t i m a t e )

f o r n o o s i n g l e - d i f f r a c t i v e e v e n t s 9 5 %

C o l l i d e r l u m i n o s i t y 1 0 2 5 c m ~ V 1 ( 1 9 8 1 )

1 0 2 6 c m " 2 s " ' ( 1 9 8 2 )

B e a m p i p e 0.4 m m F e ( 1 9 8 1 )

2 m m 130 ( 1 9 8 2 )

R e s u l t s on t h e p r o d u c t i o n o f K ° a n d A f r o m t h e T9S1 d a t a h a v e b e e n p u b l i s h e d

[ 2 j . T h e n e w 1 9 3 2 d a t a h a s g i v e n a f i v e f o l d i n c r e a s e i n s t a t i s t i c s o f V ° p r o d u c t i o n

a n d t h e p r e l i m i n a r y r e s u l t s g i v e n b e l o w i n c l u d e t h e f i r s t e v i d e n c e f o r t h e p r o d u c t i o n

a t t h e c o l l i d e r o f S , f o r w h i c h a f u l l k i n e m a t i c f i t c a n h e m a d e .

T h e 1 9 8 2 d a t a h a s p e r m i t t e d a m o r e d e t a i l e d s t u d y o f t h e m u l t i p l i c i t y d i s t r i b u t i o n .

R e s u l t s s h o w i n g t h e v i o l a t i o n o f K N O s c a l i n g ( i n t h e f u l l r a p i d i t y r a n g e ) f a v o u r i n g h i g h

m u l t i p l i c i t y e v e n t s ct t h e c o l l i d e r h a v e b e e n p u b l i s h e d [3]. R e s u l t s a r e g i v e n b e l o w

f r o m a s y s t e m a t i c s t u d y o f t h e m u l t i p l i c i t y d i s t r i b u t i o n i n d i f f e r e n t r a p i d i t y r e g i o n s .

V e r y l a r g e f l u c t u a t i o n s a r e o b s e r v e d i n n a r r o w r a p i d i t y i n t e r v a l s .

- 2 8 8 -

2 . E V I D E N C E F O R T H E P R O D U C T I O N O F S ~

F i g . 1 s h o w s a s t r e a m e r c h a m b e r p h o t o g r a p h o f a n e v e n t w i t h a S d e c a y i n g i n t o

ATT~. *} 1 5 e v e n t s o f t h i s t y p e h a v e b e e n f o u n d . T h e a n a l y s i s p r o c e d u r e f a r V ' s a s s o

c i a t e d w i t h t h e p r i m a r y v e r t e x a r e d e s c r i b e d i n o u r p u b l i s h e d r e s u l t s f r o m t h e 1 9 81 d a t a

o n s t r a n g e p a r t i c l e p r o d u c t i o n [ 2 ] , F r o m t h e k i n e m a t i c s o f t h e d e c a y s K ° ** ! M r o r

A - * p ir t h e m o m e n t u m o f t h e n e u t r a l p a r t i c l e c a n b e c a l c u l a t e d . F o r t h e d e c a y

™ ~ •* TT~ + A w h e r e t h e A p o i n t s t o t h e d e c a y v e r t e x a n d n o t t o t h e p r i m a r y v e r t e x a 2

c o n s t r a i n t f i t c a n b e m a d e . A l l e v e n t s w i t h a A p o i n t i n g t o a n d c o p l a n a r w i t h t h e d e c a y

v e r t e x ( " k i n k " ) g i v e a g o o d f i t t o t h e £ h y p o t h e s i s . A f e w o f t h e e v e n t s a r e a l s o c o n

s i s t e n t w i t h t h e d e c a y Û •* K ~ + A , H o w e v e r , f o r t h i s d e c a y t h e a c c e p t a n c e i s m u c h

s m a l l e r a n d f u r t h e r m o r e t h e p r o d u c t i o n o f t h r e e s t r a n g e q u a r k s i s v e r y l i k e l y f u r t h e r

s u p p r e s s e d . W e t h e r e f o r e t a k e t h e 1 5 e v e n t s a s H , n o t f î ,

J l a c k g r o u r i d _

A n u m b e r o f p o s s i b l e b a c k g r o u n d r e a c t i o n s w e r e s t u d i e d b y s i m u l a t i o n , e . g . :

r a n d o m a s s o c i a t i o n o f a V t o a s e c o n d a r y v e r t e x ( k i n k )

r e a c t i o n s in t h e s t r e a m e r c h a m b e r g a s o f t h e t y p e

+ o K n -» K p

c o n v e r s i o n o f o n e p h o t o n f r o m a v d e c a y :

L y y e e

F r o m 1 0 O 0 0 s i m u l a t e d e v e n t s w e c o n c l u d e t h a t l e s s t h a n o n e i s e x p e c t e d a s a

b a c k g r o u n d , a n d t h a t t h e 5 s i g n a l t h e r e f o r e i s r e a l .

P r e d u c t i o n _ra te_

T h e a c c e p t a n c e o f t h e s t r e a m e r c h a m b e r s t o o b s e r v e a H d e c a y i s s m a l l a n d

d e p e n d s s t r o n g l y o n t h e S t r a n s v e r s e m o m e n t u m p ^ , . T h e o b s e r v e d 1 5 e v e n t s h a v e

f i t t e d t r a n s v e r s e m o m e n t a i n t h e r a n g e 0 . 7 - 3 . 5 G e V / e a i *d t h e p r o d u c t i o n r a t e f o r

p ^ > 1 G e V / c i n t h e p s e u d o r a p i d i t y i n t e r v a l |TJ| < 3 . 5 i s 0 . 0 4 * 0 . 0 1 S p e r e v e n t . A

d e t a i l e d a c c o u n t o f t h e H p r o d u c t i o n , i n c l u d i n g a n e v a l u a t i o n o f t h e H / A p r o d u c t i o n

r a t i o R , i s u n d e r p r e p a r a t i o n i . 4 ]

" ) S i n c e t h e r e i s n o m a g u e t i c f i e l d w e c a n n o t d i s t i n g u i s h S f r o m H n o r A f r o m A .

W e d e n o t e e i t h e r o f t h e m w i t h S a n d A .

- 289 -

T a b l e 2 . R a t e s o f K ° a n d A - E r r o r s a r e s t a t i s t i c a l o n l y .

U A 5 1 9 8 2 d a t a

| ) j l < 3 . 5 \v\<3

U A 5 1 9 8 1 d a t a [ 2 ]

l * l l < 3

A c c e p t e d e v e n t s K ° 3 4 4 3 1 8 9 2

A 2 4 7 2 3 7 4 6

C o r r e c t n u m b e r K°s 1 . 1 Ï 0 . 1 1 . 0 Î 0 . 1 1 . 0 * 0 . 2

p e r e v e n t

A 0 . 4 3 1 0 . 0 5 0 . 4 4 1 0 . 0 5 0 . 3 5 * 0 . 1 0

K > 2 . 1 5 Í 0 . 3 2 . 9 ± 1 . 0

0 . 1 2 Í 0 . 0 1 0 . 1 1 ± 0 . 0 2

T h e r e i s g o o d a g r e e m e n t b e t . ' e e n t h e 1 9 8 2 d a t a a n d t h e p u b l i s h e d 1 9 8 1 d a t a . T h e

a d d i t i v e q u a r k m o d e l o f A n i s o v i c h a n d K o b r i n s k y [ 7 ] g i v e s K ° / A = 2 . 1 6 , i n e x c e l l e n t

a g r e e m e n t w i t h o u r m e a s u r e d v a l u e 2 . 1 5 . T h e e n e r g y d e p e n d e n c e o f t h e K / f r r a t i o i s

s h o w n i n F i g . 2 w h i c h i l l u s t r a t e s t h e c o n U n o u s u l e r e a s e i a t h i s r a t i o .

A m e a s u r e m e n t i n e ^ e c o l l i s i o n s a t E = 3 4 G e V g a v e a s r e s u l t c m .

R = 0 . 0 9 ± 0 . 0 3 ± 0 . 0 3 [ 5 ] ( t h e l a s t e r r o r i s s y s t e m a t i c ) , a n d i n p p c o l l i s i o n s a m e a s

u r e m e n t a t E c m = 6 3 G e V g a v e R - 0 . 0 6 - 0 . 0 2 f o r a p ^ r a n g e o f 1 . 2 - 2 . 4 G e V / c a n d

f o r a r a p i d i t y r a n g e | y [ < 0 . 2 [ 6 ] .

3 . I N C L U S I V E K g A N D A P R O D U C T I O N

T h e p r e l i m i n a r y r e s u l t s b a s e d o n 6 5 0 0 m i n i m u m b i a s e v e n t s a r e s u m m a r i z e d i n

T a b l e 2 .

- 2 9 0 -

T h e p d i s t r i b u t i o n f o r K i s s h o w n , i n F i g . 3 w h e r e i t i s c o m p a r e d to o u r p u b -T S H.

l i s h e d 1 9 8 1 d a t a a n d a l s o t o t h e p u b l i s h e d m e a s u r e m e n t s o f K p r o d u c t i o n b y t h e U A 2

c o l l a b o r a t i o n f o r |t)|< 0 . 8 [ 8 ] . T h e i n c r e a s e d s t a t i s t i c s r e v e a l s t h e d e v i a t i o n f r o m a n

e x p o n e n t i a l b e h a v i o u r , s i m i l a r t o t h e o b s e r v a t i o n b y t h e U A 1 c o l l a b o r a t i o n [ 9 ] f o r

c h a r g e d p a r t i c l e s . T h e c u r v e i s a f i t t o t h e f o r m [ 9 ] :

d N

d p ! ^ = A [ P T 0 / ( P T 0 + P T > ]

[1)

I n c a l c u l a t i n g t h e a v e r a g e t r a n s v e r s e m o m e n t u m , ^ p ^ , ) , t h e f o r m (-1) i s u s e d f o r

p > 0 . 2 G e V / c . H o w e v e r , t h e u s e o f ( 1 ) f o r t h e r e g i o n p ^ < 0 . 2 G e V / c w o u l d u n d e r

e s t i m a t e ( p „ ) s i n c e t h e b e h a v i o u r f o r s m a l l p i s p r o b a b l y l i k e e x p ( B • m ) w h e r e

2 2 2 i ra,j,= m + P . J , a n d m i s t h e p a r t i c l e m a s s [ 1 0 J . T h e r e s u l t s o f t h e f i t a r e g i v e n i n

T a b l e 3 .

T a b l e 3 P r e l i m i n a r y r e s u l t s o f t h e f i t t o t h e i n c l u s i v e K ° p ^ d i s t r i b u t i o n .

P a r a m e t e r U A 5 K ° U A l c h a r g e d [ 9 ]

n

 a ) ( Q e V / c )

5 . 7

0 . 7 3

0 . 5 6 ± . 0 6

9 . 1

1 . 3

0 . 4 7 ± 0 . 0 1

r e g i o n t h a t i s u n m e a s u r e d . T h e v a l u e o f t h e p a r a m e t e r B

w a s i n t h i s c a l c u l a t i o n t a k e n t o b e B = 4 ( G e V / c ) 1 f o r t h e

U A 5 d a t a a n d B » 5 . 7 ( G e V / c ) - 1 f o r t h e U A 1 d a t a .

T h e i n c l u s i v e p T d i s t r i b u t i o n f o r A i s s h o w n i n F i g . 4 a n d i s i n g o o d a g r e e m e n t

w i t h t h e p u b l i s h e d 1 9 8 1 d a t a [ 2 ] , T h e d i s t r i b u t i o n i s w e l l d e s c r i b e d b y a n e x p o n e n t i a l .

( T h e d e v i a t i o n f r o m a n e x p o n e n t i a l - a s f o r t h e K ° d i s t r i b u t i o n - p r o b a b l y s e t s i n a t a

h i g h e r p^, f o r t h e h e a v i e r A ) . T h e a v e r a g e t r a n s v e r s e m o m e n t u m i s ( p ^ , ) =

0 . 6 4 ± 0 . 0 7 G e V / c . A l s o s h o w n i n F i g . 4 a x e t h e i n c l u s i v e p , p d a t a f r o m UA2 ¡8]

w h i c h s e e m s to o b e y t h e s a m e p ^ d e p e n d e n c e w i t h a r a t i o A / p = 2 . 7 .

- 291 -

T h e e n e r g y v a r i a t i o n o f t h e a v e r a g e t r a a s v e n e m o m e n t u m i s s h o w n i n F i g . 5 .

T h e r e i s a s i g n i f i c a n t i n c r e a s e i n f o r a l l p a r t i c l e t y p e s a t t h e c o l l i d e r .

R a p i d i t y d i s t r i b u t i o t i _

T h e K g p s e u d o r a p i d i t y a n d r a p i d i t y d i s t r i b u t i o n s a r e s h o w n i n F i g . 6 a a n d b .

T h e r a p i d i t y d i s t r i b u t i o n i s c o n s i s t e n t w i t h b e i n g f l a t o u t t o y fe 2 , s i m i l a r i n s h a p e t o

t h e 4 0 0 G e V / c d a t a o f K i c h i m i e t a l [ 1 2 ] ,

M ^ l t j p U c ^ t y _ d ^ e n d e n t ^ f f _ e c t s _

A p o s s i b l e s i g n a l o f a q u a r k g l u o n p l a s m a i s a n i n c r e a s e d p r o d u c t i o n o f s t r a n g e

q u a r k s . A t t h e s a m e t i m e t h e o v e r a l l m u l t i p l i c i t y i s e x p e c t e d t o i n c r e a s e . W e h a v e

e x a m i n e d o u r s a m p l e o f s t r a n g e p a r t i c l e s f o r m u l t i p l i c i t y d e p e n d e n t e f f e c t s . F i g . 7

s h o w s t h e i n c l u s i v e p T d i s t r i b u t i o n f o r K ° i n t w o m u l t i p l i c i t y b i n s , n

c h > 3 0 .

T h e r e i s DO s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e d i s t r i b u t i o n s . F i g . 8 s h o w s t h e

n u m b e r o f c o p l a n a r V ' s ( K ° o r A ) a n d t h e n u m b e r o f c l e a n K ° p e r c h a r g e d t r a c k a s a

f u n c t i o n o f t h e o b s e r v e d ( u n c o r r e c t e d ) m u l t i p l i c i t y . T h e r e a p p e a r s t o b e a n i n c r e a s e

w i t h i n c r e a s i n g t h o u g h t h e d i s t r i b u t i o n s a r e c o n s i s t e n t w i t h b e i n g f l a t .

4 . C H A R G E D P A R T I C L E M U L T I P L I C I T Y D I S T R I B U T I O N

T h e L o w e r b a c k g r o u n d f r o m c o n v e r s i o n s w i t h t h e B e b e a m p i p e h a s p e r m i t t e d a

m o r e d e t a i l e d s t u d y o f t h e m u l t i p l i c i t y d i s t r i b u t i o n . T h i s i s o f t e n d o n e i n t e r m s o f t h e

K N O s c a l i n g c o n c e p t [ î 3 ] , o r i g i n a l l y d e r i v e d u s i n g F e y n m a n s c a l i n g w h i c h i s n o w k n o w n

n o t t o b e v a l i d . T h e f r a m e w o r k o f K N O s c a l i n g h a s s t i l l b e e n f o u n d u s e f u l . I f K N O

s c a l i n g i s v a l i d , t h e m u l t i p l i c i t y d i s t r i b u t i o n s c a l e s i n t h e v a r i a b l e z = n / ( n ) :

o

n

w h e r e n i s t h e ( c h a r g e d ) m u l t i p l i c i t y . 0 ( z ) i s a u n i v e r s a l f u n c t i o n , i n d e p e n d e n t o f

e n e r g y .

I n t h i s p a p e r w e p r e s e n t r e s u l t s o n t h r e e d i f f e r e n t a s p e c t s o f t h e n o n s i n g l e

d i f f r a c t ¡ v e m u l t i p l i c i t y d i s t r i b u t i o n :

• t h e s h a p e o f t h e m u l t i p l i c i t y d i s t r i b u t i o n a s a f u n c t i o n o f e n e r g y ,

• t h e s h a p e o f t h e m u l t i p l i c i t y d i s t r i b u t i o n f o r d i f f e r e n t r a p i d i t y i n t e r v a l s a t

E = 5 4 0 G e V , a n d c m .

• t h e o b s e r v a t i o n o f i n d i v i d u a l e v e n t s w i t h l o c a l l y v e r y h i g h d e n s i t y o f t r a c k s

ia r a p i d i t y .

- 292 -

T h e m u l t i p H o i t y _ d i s t r i b u t i o n a s _ a _ f u o . e t i o n o f _ e n e r g y _

R e s u l t s i n t h e E r a n g e f r o m 1 0 t o 5 0 G e V h a v e s u g g e s t e d t h a t t h e m u l t i -c m .

p l i c i t y d i s t r i b u t i o n ( f u l l p h a s e s p a c e ) o f n o n s i n g l e d i f f r a c t i v e e v e n t s o b e y K N O s c a l i n g .

R e c e n t r e s u l t s f r o m t h e U A 5 e x p e r i m e n t , h o w e v e r , s h o w t h a t t h e r e i s a s i g n i f i c a n t

c h a n g e o f t h e s h a p e o f t h e m u l t i p l i c i t y d i s t r i b u t i o n f a v o u r i n g h i g h m u l t i p l i c i t i e s ¡ _ 3 j .

T h i s i s s h o w n i n F i g . 9 w h e r e t h e n o r m a l i z e d m u l t i p l i c i t y d i s t r i b u t i o n ( n > o ^ / E a r ^ ,

f u l l p h a s e s p a c e , i s p l o t t e d a s a f u n c t i o n o f t h e K N O v a r i a b l e z a n d c o m p a r e d to l o w e r

e n e r g y d a t a [ 1 4 , 1 5 j . T h i s c h a n g e o f s h a p e i s q u a n t i f i e d i n F i g . 10 w h e r e t h e C m o

le k

m e n t s , d e f i n e d a s = ( n > / < n > , a r e s h o w n a s a f u n c t i o n o f e n e r g y . T h e d a t a s u g

g e s t s a s i g n i f i c a n t c h a n g e i n a l l m o m e n t s a t t h e c o l l i d e r .

T h e m u l t i p l i c i t y d i s t r i b u t i o n i n a f i x e d l i m i t e d r a n g e o f r a p i d i t y |TJ ! < 1 . 3 o b e y s

K N O s c a l i n g i f o n l y e v e n t s w i t h a t l e a s t o n e c h a r g e d t r a c k i n t h e r e g i o n a r e i n c l u d e d .

T h i s i s s h o w n i n F i g . 1 1 w h e r e U A 5 d a t a [ 3 j a r e c o m p a r e d w i t h r e c e n t d a t a f r o m t h e

I S R [ 1 6 ] . T h e e x c l u s i o n o f z e r o p r o n g e v e n t s ( o n l y r e f l e c t i n g t r i g g e r i n g c o n d i t i o n s ) ,

h o w e v e r , h a s n o o b v i o u s p h y s i c a l j u s t i f i c a t i o n a n d f u r t h e r m o r e w i l l - b e c a u s e o f t h e

v a r i a t i o n o f ( n ) w i t h e n e r g y - c h a n g e z i n a n e n e r g y d e p e n d e n t w a y .

T h e m u l t i p l i c i t y d i s t r i b u t i o n a t E c ^ = 5 4 0 G e V i n d i f f e r e n t r a p i d i t y i n t e r v a l s

M o d e l s f o r p a r t i c l e p r o d u c t i o n h a v e b e e n p r o p o s e d t h a t t r e s t d i f f e r e n t l y t h e

" c e n t r a l r e g i o n " f r o m t h e t w o f r a g m e n t a t i o n r e g i o n s [ l 7 j . I n t h e s e m o d e l s s c a l i n g i s

s u p p o s e d t o h û l d f o r t h e d i f f e r e n t r e g i o n s s e p a r a t e l y . I t i s t h e r e f o r e o f i n t e r e s t t o s t u d y

t h e c o r r e c t e d m u l t i p l i c i t y d i s t r i b u t i o n i n a r e g i o n ¡TJ I^TJ w h e r e IJ^ i s a l l o w e d t o v a r y

i n s m a l l s t e p s a n d Look f o r s c a l i n g p r o p e r t i e s i n t h e s e d i s t r i b u t i o n s .

F i g . 12 s h o w s a s a m p l e o f c o r r e c t e d m u l t i p l i c i t y d i s t r i b u t i o n s w i t h = 0 . 5 , 1 , 5 ,

3 a n d 5 . T h e d i s t r i b u t i o n s a r e s m o o t h a n d r e m e m b e r i n g t h a t dn/d7j i s a p p r o x i m a t e l y

f l a t o u t t o |TJ| = 3 o n e s e e s a l r e a d y t h a t t h e r e l a t i v e f l u c t u a t i o n s g r o w l a r g e r a s t h e

j ) - i n t e r v a l b e c o m e s m o r e n a r r o w . T h e s a m e d i s t r i b u t i o n s n o w p l o t t e d a s a f u n c t i o n o f

t h e K N O v a r i a b l e z a r e s h o w n i n F i g . 1 3 . H e r e t h e e f f e c t i s v e r y c l e a r : f o r i n c r e a s i n g

7j r e g i o n t h e d i s t r i b u t i o n b e c o m e s m o r e n a r r o w a n d t h e p e a k s h i f t s o u t w a r d s . T h e t a i l

f o r z > 1 f o l l o w s a n e x p o n e n t i a l i n z o u t t o a l a r g e r v a l u e o f z f o r a m o r e n a r r o w i n t e r

v a l . T h e r e l a t i v e f l u c t u a t i o n s o b s e r v e d a r e a s h i g h a s z = 7 f o r | | 0 . 5 b u t r e d u c e s

t o z < 4 f o r *£ 5 . T o i l l u s t r a t e t h i s i n o r e q u a n t i t a t i v e l y w e s h o w i n F i g . 1 4 t h e C

- 293 -

U A 5 U A 5

1 9 8 2 d a t a M o n t e C a r l o

P a s s i n g c u t 0 . 7 % 0 . 5 %

< n u > c h

4 7 4 1

< N ) i n 1 m a x S. 1 2 . 9 1 2 . 2

2 - D s p e r i c i t y 0 . 7 3 0 . 7 3

( D i s c 1 . j e t 0 )

m o m e n t a s a f u n c t i o n o f t i . F o r p e r f e c t s c a l i n g o n e w o u l d e x p e c t a c o n s t a n t C , b u t t h e

m e a s u r e m e n t s s h o w a c o n t i n o u s d e c r e a s e o f a s TJ^, i s i n c r e a s e d f r o m 0 . 5 t o 5 . W e

t h u s c o n c l u d e t h a t t h e r e i s n o e v i d e n c e f o r a c e n t r a l r e g i o n T J C ^ 1 t h a t o b e y s s c a l i n g .

H o w e v e r , f o r d i f f e r e n t e x p e r i m e n t a l r e a s o n s [ 1 6 , 1 8 ] t h e z e r o p r o n g e v e n t s h a v e

o f t e n b e e n e x c l u d e d . S u c h a s u p p r e s s i o n w o u l d a f f e c t s m a l l e r r e g i o n s m o r e t h a n l a r g e r

o n e s s i n c e ( n > c h a n g e s m o r e . C a l c u l a t i o n s s h o w t h a t s u c h a n e f f e c t i s n o t i m p o r t a n t

f o r T jç > 2 b u t r e d u c e s t h e v a l u e o f C ^ f o r T/^ ^ 2 . T h e p h y s i c s s i g n i f i c a n c e o f t h i s

o b s e r v a t i o n i s n o t e n t i r e l y c e r t a i n , s i n c e t h e s u p p r e s s i o n o f z e r o p r o n g s a f f e c t t h e d i f

f é r e n t r e g i o n s i n d i f f e r e n t w a y s .

V e r y _ l a r g _ e j l u c b u a t i o n s i n n a r j r ç j . v j r a p y i t 3 F J n t _ e r v a _ l s _

W e h a v e s e a r c h e d i n o u r d a t a f o r s i g n s o f v e r y h i g h e n e r g y d e n s i t y w h i c h c o u l d

p o s s i b l y s i g n a l s o m e n e w p h y s i c s [ 1 9 ] . F i g . 1 5 s h o w s t h r e e i n d i v i d u a l e v e n t s f r o m

o u r d a t a s a m p l e t o g e t h e r w i t h o n e M o n t e C a r l o e v e n t . T h e e v e n t s w e r e s e l e c t e d t o g i v e

a v e r y h i g h n u m b e r o f o b s e r v e d t r a c k s i n a n i n t e r v a l A * ) = 0 . 5 a n y w h e r e a l o n g t h e r a

p i d i t y a x i s . T h e r e a r e a s m a n y a s 1 5 t r a c k s i n ATJ = 0 . 5 i n t h e t o p e v e n t , c o r r e s p o n d i n g

t o d n / d 7 j = 3 0 ( c f < d n / d T i ) *** 3 ) . T h e s e e v e n t s d o n o t s h o w a n y j e t s t r u c t u r e , a s s h o w n i n

F i g . 1 f i . T h e s o a t t e r p l o t i n F i g . 1 7 s h o w s a s a f u n c t i o n o f t h e n u m b e r o f o b s e r v e d

t r a c k s t h e m a x i m u m n u m b e r o f t r a c k s i n ÙT) = 0 . 5 f o r e a c h e v e n t . T h e s t r a i g h t l i n e

r e p r e s e n t s t h e a r b i t r a r y c u t u s e d t o d e f i n e t h e " s p i k e " s a m p l e . T h e d i s t r i b u t i o n l o o k s

r a t h e r s m o o t h a n d t h e " s p i k e " s a m p l e r e p r e s e n t s t h e t a i l o f i t . T h e p r o p e r t i e s o f t h e s e

s e l e c t e d " s p i k e " e v e n t s a r e s u m m a r i z e d i n T a b l e 4 w h e r e a l s o a c o m p a r s o n w i t h M o n t e

C a r l o i s m a d e .

T a b l e 4 . P r o p e r t i e s o f " s p i k e " e v e n t s

- 2 9 4 -

T h e a r b i t r a r y c u t c o r r e s p o n d s t o z *** 5 , w h e r e a s w e d o o b s e r v e f l u c t u a t i o n s a s

l a r g e a s z = 1 0 . T h e f l u c t u a t i o n s o c c u r w i t h a p p r o x i m a t e l y t h e s a m e f r e q u e n c y i n o u r

d a t a s a m p l e a s i n o u r M o n t e C a ' l o s i m u l a t e d e v e n t s . I n f a c t t h e U A 5 ' c l u s t e i ' M o n t e

C a r l o [ 2 0 , 2 1 ] s u g g e s t s t h a t t h e f l u c t u a t i o n s m i g h t o c c u r f r o m r a n d o m s u p e r p o s i t i o n o f

c l u s t e r s .

T h e c o r r e c t e d m u l t i p l i c i t y d i s t r i b u t i o n i n -ûrj = 1 ( c e n t e r e d a t Î J = 0 ) s h o w n i n

F i g . 1 3 o b e y e d f l u c t u a t i o n s u p t o z — 7 - T o i l l u s t r a t e t h e e f f e c t o f e v e n f u r t h e r r e d u c i n g

t h e i n t e r v a l w e s h o w i n F i g . 18 s u p e r i m p o s e d u n c o r r e c t e d m u l t i p l i c i t y d i s t r i b u t i o n s i n

a n i n t e r v a l A?j = 0 . 5 . F l u c t u a t i o n s o f z > 3 , 6 anc! 8 o c c u r w i t h f r e q u e n c i e s o f 6 % ,

- 3 - 4

2 x 1 0 a n d 2 x 1 0 . T h e d i s t r i b u t i o n i s s m o o t h a n d t h e r e i s n o s t r u c t u r e f o r h i g h z .

A l s o s h o w n f o r c o m p a r i s o n a r e a s i m p l e a n d a c o m p o u n d P o i s s o n . A l t h o u g h t h e l a t t e r

i s m u c h w i d e r , t h e l a t a s h o w s s i g n i f i c a n t l y l a r g e r t a i l .

5 . C O N C L U S I O N S

F : o m a d e t a i l e d s t u d y o f t h e U A 5 1 9 8 2 d a t a a t E = 5 4 0 G e V w e m a a e t h e c m .

f o l l o w i n g p r e l i m i n a r y c o n c l u s i o n s

f i r s t e v i d e n c e f o r t h e p r o d u c t i o n o f E h a s b e e n f o u n d ,

t h e a v e r a g e t r a n s v e r s e m o m e n t u m f o r i n c l u s i v e K ° a n d A p r o d u c t i o n h a s i n c r e a s e d

t o 0 . 5 6 = 0 . 0 6 G e V / c a n d 0 . 6 4 ï 0 , 0 7 G e V / c r e s p e c t i v e l y a n d t h e K / f f r a t i o h a s i n

c r e a s e d to 12 — 19o,

t h e n o n s i n g l e d i f f r a c t i v e m u l t i p l i c i t y d i s t r i b u t i o n i n f u l l p h a s e s p a c e i s m u c h

w i d e r t h a n a t E = 5 3 G e V a n d c m .

t h e n o n s i n g l e d i f f r a c t i v e m u l t i p l i c i t y d i s t r i b u t i o n , w h e n s h o w n a s a f u n c t i o n o f t h e

K N O s c a l i n g v a r i a b l e z = n / ( n > , w i d e n s c o n t i n o u s l y w h e n t h e r a p i d i t y i n t e r v a l g e t s

m o r e n a r r o w , a n d ¡ u a n a r r o w i n t e r v a l A17 - 0 . 5 f l u c t u a t i o n s a s l a r g e a s z = 10

o c c u r ; t h e s e e v e n t s a p p e a r l i k e s p i k e s w h e r e i n t h i s n a r r o w i n t e r v a l a s m u c h a s

1 5 t r a c k s a r e o b s e r v e d w i t h o u t j e t s t r u c t u r e .

R E F E R E N C E S

[ 1 j K . A l p g a r d e t a l . , p h y s . L e t t . I 0 7 B ( 1 9 8 J ) 3 1 0 , 3 1 5 , P h y s . S c r . 2 3 ( i 9 8 1 ) 6 4 2 .

T 2 j K . A l p g a r d e t a l . , P h y s . L e t t . J M 5 B ( 1 9 8 2 ) 6 5 .

3 ] J . A l n e r e t a l - , P h y s . L e t t . 1 3 R B ( 1 9 8 4 ) 3 0 4 .

T 4 ] U A 5 C o l l a b o r a t i o n , J . G . A l n e r e t a l . : " O b s e r v a t i o n o f S p r o d u c t i o n i n p p i n t e r

a c t i o n s a t *Ja = 5 4 0 G e V " , t o a p p e a r .

- 2 9 5 -

5 ] M . A l t h o f f e t a l . , P h y s . L e t t . 1 3 0 B ( 1 9 8 3 ) 3 4 0 .

r o ] T . A k e s s o n e t a l . , C I ' R N - E P . ' 8 4 - 2 6 ( t o b e p u b l i s h e d ) .

! 7 ] V . V . A n i s o v i c h a n d M . N . K o b r i n s k y , P h y s . L e t t . 5 2 B ( 1 9 7 4 ) 2 1 7 g i v e t h e r a t i o

K ° / A = 2 ¿ + 0.6\ w h e r e X i s t h e s t r a n g e q u a r k s u p p r e s s i o n . W e u s e d t h e v a .e

X = 0 . 3 8 i 0 . 0 7 a s d e t e r m i n e d b y K . B e c k m a n n : " p a r t i c l e p r o d u c t i o n i n p p i n f r

a c t i o n s a t 5 4 0 G e V a n d s t r a n g e ^ u a r k s u p p r e s s i o n " , p r o c e e d i n g s o f t h e V I W a r s a w

S y m p o s i u m o n E l e m e n t a r y P a r t i c l e P h y s i c s , K a 2 i m i e r z , M a y 1 9 8 3 ( t o a p p e a r )

a n d T'i. M ü l l e r : " S t r a n g e n e s s s u p p r e s s i o n a t c o l l i d e r e n e r g y " . P r o c e e d i n g s o f t l i e

X V I n t e r n a t i o n a l S y m p o s i u m o n M u l t i p a r t i c l e D y n a m i c s , L a k e T a h o e , 2 2 - 2 7 J u n e ,

1 9 8 3 ( t o a p p e a r ) .

[ 8 ] M . B a n n e r e t a l . , P h y s . L e t t . 1 2 2 B ( 1 9 8 3 ) 3 2 2 .

[ 9 ] G . A r o t s o n e t a l . , P h y s . L e t t . 1 1 8 B ( 1 9 8 2 ) 1 6 7 .

[ 1 0 ] K - G u e t t l e r e t a l . , N u c í . P h y s . B T 1 6 ( 1 9 7 6 ) 7 7 .

[ 1 1 ] A . M . R o s s i e t a l . , N u c l . P h y s . B S 4 ( 1 9 7 5 ) 2 6 9 .

[ 1 2 ] H . K l c h i m i »» a l . , P h y s . B e y . D 2 0 ( 1 9 7 9 ) 3 7 .

[ 1 3 J Z . K o b a e t a l . , N t j l . P h y s . B 4 0 ( 1 9 7 2 ) 5 1 7 .

[ 1 4 ] V . V . A m m o s o v e t a l . , P h y s . L e t t . 4 2 B ( 1 9 7 2 ) 5 1 9 ;

H . B . B i a l k o w s k a e t a l . , N u c l . P n y s . B 1 1 0 ( 1 9 7 6 ) 3 0 0 ;

W . M . M o r s e e t a l . , p h y s . B e v . E H 5 ( 1 9 7 7 ) 6 6 ;

S . B a r i s h e t a l . , P h y s . B e v . D 9 ( 1 9 7 4 ) 2 6 8 9 ;

A . F i r e s t o n e e t a l . , P h y s . B e y . D I O ( 1 9 7 4 ) 2 0 8 0 ;

C . B r o m b e r g e t a l . , P h y s . R e v . L e t t . 3 1 ( 1 9 7 4 ) 1 5 6 3 ;

J . W h i t m o r e e t a l . , P h y s . B e p . J 0 C ( 1 9 7 4 ) 2 7 3 .

[ 1 6 ] A . B r e a k s t o n e e t o l . , C E B N - E P / 8 3 - 1 6 5 .

r i6] A . B r e a k s t o n e e t a l . , P h y s . L e t t . 1 3 2 B ( 1 9 B 3 ) 4 5 8 .

f 1 7 ] S e e e . g . L i u L i a n - S o u a n d M e n g T a - C t m n g , P a y s . B e v . D 2 7 ( 1 9 8 3 ) 2 S 4 0 .

Í I S ] W . T h o m é e t a l . , N u c l . P h y s . B 1 2 9 ( 1 9 7 7 ) 3 6 5 .

[ 1 9 ] S e e J . G . R u s h b r o o k e : " I n e l a s t i c h a d r o n - h a d r o n - h a d r o n p r o c e s s e s a t c . m .

e n e r g i e s u p t o 4 0 T e V " a n d r e f e r e n c e s t h e r e i n , C E R N E P / 8 4 - 3 4 t o a p p e a r i n

P r o c e e d i n g s o f t h e w o r k s h o p o n p p o p t i o n s f o r t h e s u p e r c o l l i d e r , 1 3 - 1 7 F e b r u a r y ,

1 9 8 4 , U n i v e r s i t y o f C h i c a g o .

[ 2 0 ] U A 5 C o l l a b o r a t i o n , P h y s i c s R e p o r t s t o b e p u b l i s h e d .

[ 2 1 ] K . A ' p g a r d e t a i . , P h y s . L e t t . J 2 3 B ( 1 9 8 3 ) 3 6 1 .

- 296 -

F i g . 1 A p h o t o g r a p h o f a n e v e n t w i t h a S •* A i r d e c a y . T h e d e c a y p o i n t i s a t A

a n d t h e A - ^ p n - d e c a y a t B . T h e k i n k a t A i s m o s t e a s i l y v i s i b l e i f o n e

l o o k s a l o n g t h e ir t r a c k i n t h e p l a n e o f t h e p h o t o g r a p h .

- 297 -

o UA5 1962 PRELIMINARY

» UA5 1961

F i g . 2 T h e e n e r g y v a r i a t i o n o f t h e K / f f

r a t i o R , D a t a a t l o w e r e n e r g i e s

a r e t a k e n f r o m [ 2 ] .

[Gevi

p T (GeV/c)

F i g . 9 T h e p d i s t r i b u t i o n f o r K g f r o m

f r o m t h e U A 5 1 9 8 2 d a t a c o m p a r e d

t o t h e p u b l i s h e d 1 9 8 1 d a t a [ 2 ] a n d

t o t h e U A 2 K * d a t a [ 8 ] . T h e f u l l

l i n e i s a f i t d i s c u s s e d i n t h e t e x t .

298

• UAS A 1982 PRELIMINARY

P, (GfV/c)

F i g . 4 T h e p T d i s t r i b u t i o n E o r A f r o m t h e U A 5 1 9 8 2 d a t a c o m p a r e d

t o t h e p u b l i s h e d 1 3 8 1 d a t a [ 2 ] . A l s o s h o w n a r e t h e p r o t o n

d a t a f r o m t h e U A 2 e x p e r i m e n t [ ô ] . T h e s t r a i g h t l i n e i s a f i t

d i s c u s s e d i n t h e t e x t .

08

a?

OS

Ï as

A ( X 0.4 V

03

O UA5 7982 PRELIMINARY

S 10 20 SO 100 500 SOCO

F i g . 5 T h e a v e r a g e t r a n s v e r s e m o m e n t u m a s a f u n c t i o n o f E

L o w e n e r g y d a t a i s t a k e n f r o m R e f , [ i i ] . T h e UA1

v a l u e i s t h e p u b l i s h e d v a l u e 0 . 4 3 G e V / c [ s ] , n o t t h e

v a l u e 0 . 4 7 G e V / c g i v e r , i n T a b l e 3 .

- 299 -

t 1 I 1 1 r an "1

dN

0.1 • UA5 1982 m • UA5 1392 0.1 o UA5 19 Bl - 400 Gev/c

03 - 03 -

02

0.1

M

01 : i . .

0 1 2 3 1 1 2 3 *

111 1*1

F i g . 6 T h e K ° p s e u d o r a p i d i t y d i s t r i b u t i o n c o m p a r e d t o t h e p u b l i s h e d

1 9 8 1 d a t a L 2 J a n d t h e r a p i d i t y d i s t r i b u t i o n c o m p a r e d t o r e s u l t s

a t 4 0 5 G e V / c ( E = 2 8 G e V ) [ l 2 j .

7 T h e p d i s t r i b u t i o n f o r K ° f o r F i g . 8 T h e n u m b e r o f c o p l a n a r v ' s q

t w o b a n d s i n o b s e r v e d e v e n t ( K ^ a n d A ) a n d t h e n u m b e r o f K g

m u l t i p l i c i t y . p e r c h a r g e d t r a c k a s a f u n c t i o n

o f o v e r a l l o b s e r v e d e v e n t m u l t i

p l i c i t y .

- 3 0 0 -

I DV I I I I I I I I I I I I I I I I — i — i — i ¡ i r:

\ UA5

t E nl<n>

F i g . 9 T h e n o r m a l i z e d n o n s i n g l e d i f f r a c t i v e m u l t i p l i c i t y d i s t r i b u t i o n a s

a f u n c t i o n o f t h e K N O s c a l i n g v a r i a b l e z . T h e U A 5 d a t a i s t h e

p u b l i s h e d j o i n t 1 9 8 1 a n d 1 9 8 2 d a t a [ 3 ] . L o w e r e n e r g y d a t a i s f r o m

R e f s . [ 1 4 , 1 5 ] . F r o m [ s ] .

- 301 -

F i g . 10 T h e C m o m e n t s o f t h e n o n

s i n g l e d i f f r a c É i v e m u l t i p l i c i t y

d i s t r i b u t i o n s a s a f u n c t i o n o f

e n e r g y . F r o m [3-1,.

F i g . 11 T h e m u l t i p l i c i t y d i s t r i b u t i o n f o r

n o n s i n g l e d i f f r a c t i v e e v e n t s i n

t h e r a p i d i t y r e g i o n \n\ < 1 . 3 .

O n l y e v e n t s w i t h a t l e a s t o n e

t r a c k i n t h i s r e g i o n a r e i n c l u d e d .

F r o m [ 3 ] ,

- 302 -

12 Corrected non single difíractive multiplicity distributions for four different 7) regions: |íj¡<0.5, 1. 5, 3,5. 1982 data.

- 303 -

Fig. 13 Corrected non single diffraciive multiplicity distributions plotted as a function of z = n / ( n c b ) for the same TÏ regions as in Fig. 12: | n | < 0 . 5 , 1.5, 3, 5. 19P2data.

Fig. 14 The C^ moment of the corrected non single dtffracUve multiplicity distribution^ in a region |TJI < as a function of TT . C^ is defined as C 3 = (n > /<n>*.

- 3 0 4 -

F i g . 1 5 T r a c k d e n s i t y f o r t h r e e e v e n t s

f r o m t h e d a t a s a m p l e a n d o n e

e v e n t ( b o t t o m ) f r o m t h e M o n t e

C a r l o s i m u l a t i o n . T h e e v e n t s

w e r e f o u n d i n a s c a n w h e r e t h e

m a x i m u m n u m b e r o f t r a c k s i n

a n i n t e r v a l ùy = 0 . 5 w a s

s e a r c h e d f o r .

360'-

0 ISO"

O* - •

- 5 0 5

1

F i g . 1 6 f}t 0 d i s t r i b u t i o n f o r t h e t o p

e v e n t i n F i g . 1 5 . 0 I s t h e

a z i m u t h a i a n g l e a r o u n d t h e

b e a m p i p e .

- 3 0 5 -

J 1 I I I L 0 20 40 60 80 100

n c h (obs)

Fig. 17 The m a x i m u m number of tracks in Ä7\= 0.5 in each event as a function of the observed event multiplicity. The area of each small circle is proportional to the number of events with that combination. The straight line is N m a x = 0.1 x n c t l (obs) + 7 and represents an arbitrary cut used to get the "spike" sample.

-i 1 1 1 r

0 2 4 6 8 10 Z

. 18 The uncorrected (for acceptance) multiplicity distribution in an interval &t) =0.5. A U possible windows of interval An = 0.5 in the range -£<*)< 2 were superimposed. The straight and dashed lines represent a Poisson and a compound Poisson distributions having the observed meaa (Poisson) and mean and dispersion (compound Poisson).

n 1 1 r

- 307 -

pp and pp Elastic Scattering

- 308 -

ELASTIC SCATTERING

A . Martin 0 : 8410026287

Theoretical Physics Division, CERN CH-1211 Geneva 23

What! I wont t o present here ahoulj perhapo b a t t e r ba.aali.a4 ""theoretlcaJ comments on experiments .-Let-ao c omina1 yoa t ha t l^ a o ï t t h a - a g o , iw Howe 't~'<—

• l - T t d i e a t e d - aanawhafc acbitrarily - cheeq p A S t t i M l Ittas for t h e high-anergy behaviour of proton-antlproton scattering at collider energies^ Çjn '^JH

L) The Froissart hound is not saturated, i.e., c^/Clogs) 2 •*• Ü. The simplest situation would be that o tends to a constant sufficiently large to avoid contradiction with existing data . Another interesting special case is that of the "critical Pomeron" for which o behaves like

0.3 t o t

(logs) asymptotically and a&^°tot ^creases.

2) The Froiasart bound is saturated and we are already in the asymptotic regime at present energies, which means:

where b = d/dt (log{do/dQ)) is the slope of the diffraction peak, ard da/at = F(to ), where F(z) i s an entire function of order %. Supporters

3) of this point of view are, for instance, P. Kroll and J. bias de Deus

3) The Froissart bound is saturated, but we are still far away in energy front the asymptotic regime and, in particular, the opacity of Che nucleón is still increasing. This is realized in some eikonal models like the Chou-Yang model 1 (in which what is given is the Imaginary part of the amplitude, the real part being obtained from dispersion relations) and

incorporates a priori real part effects and Kegge pole effects. In these two models, the nucleón becomes "black" at infinite energy and therefore CTei/°toC * The supercritical string model, of Kaidalov and Ter Martyroslan^\ has similar features.

In Rose I favoured possibility N° 2, which was a priori appealing sin. Kroll and Dias de D e u s ^ had succeeded In explaining nicely the ISR data ai in particular the motion of the dip in pp scattering, given by t

á í ^ x aT =

56 mb*(GeV) 2, and the depth of the dip by real part effects. However, the

http://ba.aali.a4

- 309 -

situation has changed, as you have heard. Let me summarize the situation in the following Table. The first column contains ISR data at the arbitrarily chosen energy of 52 GeV cm; however, the ratio of elastic to total cross-sections shows no definite energy dependence in the whole I5E range, from 30 to 60 GeV. The second column contains a summary of the "old" data from UA4 at the nominal energy of 540 GeV/cm. The last column contains the main new results of UA4.

ISR

52 GeV

SPPS 1982

"540" GeV

SPPS 1933

546 GeV

4 0 e l / o T

b(t=0)

K |t| =0.4)

43 mb

0.175 ±0.00,5

13 GeV - 2

10.5

65-70 mb

O.2±0.02

17.2±1

13.6±r.2

62-63 mb

0.213 ±0.006±0.002

15.7±0.2*>

13.3±0.2

In the Appe obtained b;

ndix I explain why I prefer this value UA4 from a quadratic fit.

This Table shows very clearly that it is no longer more possible to say that the asymptotic regime of the saturation of the Froissart bound has been reached (possibility N° 2), or more exactly that it was certainly not reached at the ISR, for the ratio a

e j / ° t o t i s definitely increasing from the ISR to

the collider, and the ratio of the slope to the total croBS-section is definitely decreasing. Still the cross-section is rising and in fact compatible with the extrapolation of Amcldi et a l . ^ , ba3ed on measurements of real parts and total cross-sections at the ISR, so that case N ° 1 does not seem very likely. In particular, it seems extremely difficult to believe that the Pomeron Is "critical" because this would lead to a decreasing ratio of elastic to total cross-sections.

At present, models of type N° 3 are clearly favoured, i.e., models in which opacity increases. Not only opacity but also sharpness, because the shoulder observed at t = -0.8 GeV 2 (which is understood to be a shoulder and not a dip because of real part effects) is too high compared to the predictions of geometrical scaling. In fact, Bourrely 8^ has refitted the parameters of the Bourrely-Soffer-Wu model 5^ and found that he can fit aJl pp

and pp data, from ISR to collider, with the six parameters contained in their

- 3 1 0 -

model. The only problem they have Is that b Is a very rapidly varying function of t in the interval -0.2 t 0. Though there is no indication for such a fact, it is not clear that it really contradicts experiment. This model

How I would like to eay a few words about the problem of the dip. The dip has been seen in pp scattering at the ISR and its depth explained by real part effects. Now, recent experiments on pp scattering at the ISR give results with relatively large errors which might indicate that a shoulder, in the case of - 9) pp, Is preferred to a dip . The trouble is that we shall never know the truth

for the ISR will be closed and this is very sad (not that they are closed one day but that they are closed so earlyt). There is a model, by Donnachie and Landahoff*^ in which the three-gluon exchange term acts as an effective odderon, i.e., a real contribution to the pp and pp amplitude which changes sign when one goes from pp to pp. In pp it cancels the real part of the even signature amplitude while it does the contrary for pp, thus eliminating the dip. This is possible, but let me stress that It is a non-asymptotic situation. As the energy goes to infinity either both the pp and pp dips will survive or they will disappear. This is the content of the theorem that Cornille and T. obtained some years ago 1 1"^. The only weak point of this theorem is connected with spin effects. So one could violate the theorem by having non-diagonal helicity amplitudes with a phase which increases to infinity. However, none of the existing models, including that of Donnacliie and Landshoff, possess this property.

Finally, I would like to stress the importance of forward teal part measurements (such a measurement is being planned in March 1985 by the UA4 group). We have already seen that the real part measurement was very effective in the past since it allowed the successful prediction of the cross-section at 540 GeV cm energy. Now that we know that we are far from the asymptotic regime, we have doubts on the (logs) 2 behaviour of the cross-section and, furthermore, we want to know this cross-section at 10, 20 and 40 TeV era. energies at which machines might be built.

With Bourra/, we have made a little exercise, which is similar to the 2)

one made by Block and Cahn ' some time ago. We take an explicitly analytic and crossing symmetric form of the even signature amplitude:

predicts c ./a r el t « 0.27 at 10 TeV cm., and 0.29 at 20 TeV c m .

>

311 -

and make a fit (not a best fit in the mathematical sense) to the ISR data (p and o+) with the constraint

In the first fit we take C = 0, and we saturate the Froissart bound. In the second fit we try to take C as large as possible without spoiling the agreement with experiment. The parameters are the following.

I Froiasart saturated II Oj. •*• const.

A 41.695 41.824 B 0.43 0.815 C 0 0.006 s 243.6 277.7 0

and we get

[ I 4 p+ - 4 P +

30 41.4 0.043 41.2 0.051

52 43.1 U.075 « . 5 0.0S9

62 43.9 0.085 44.5 0.099

550 62.4 0.154 63.1 0.119

2 000 81.1 0.161 75.4 0.094

10 000 112.5 0.155 98.7 0.065

20 000 128.8 0.152 92.9 0.058

40 000 146.6 0.145 97.a 0.047

This Table shows that there is a big variation of p at the collider energy from 0.154 to 0.119. If the experimentalists can really measure p with an accuracy of 0.1 they will be able to separate these two possibilities and obtain precious indications on the trend of o_.

- 312 -

This inequality would be constraining if the accuracy was very great, because it shows that by taking t^-t 2 small enough, one gets a contradiction if d 2A/dt 2 vanishes at t. and not at t 2. In fact a complete set of unitarity

12) constraints has been obtained by S.M. Roy , but some work is necessary in order to confront them with experiment.

APPENDIX I want to explain why I prefer the value b(t=0) = 15.7Í0.2, obtained from

the quadratic fit

\> - 15 .7 ± o.Z ¿-- ~Z£± OA* CW

for O.03<-t¿*0.5 GeV 2 to the value

obtained from a linear fit to the data for 0.03^-t^0.15 GeV 2. First of all, the differential cross-section is analytic inside an

ellipse in the t plane. The right extremity of this ellipse is at t = +0.Û8 GeV 2. If log(da/dtJ has a second derivative non-zero for t^-0.13 GeV 2, this shoald contiaue for t^ -0.15 GeV 2. One can invent a more quantitative argument using the positivity of the absorptive part, more specifically the fact that the absorptive part is a sum of Legendre polynomials with positive coefficients. In the limit of |Ci~C 2J |ti| or |t 2| one can provs

'4-

- 3 1 3 -

REFERENCES

1) A. Martin - Third Topical Workshop on Proton-Antiproton Collider Physics, Rome (January 1983), CERN Yellow Report 83-04 (1983) 351, Eds. C. Bacci and G. Salvinl.

2) H.H. Block and A. Calm - Phys.Lett. 120B (1983) 224. 3) J. Dias De Deus and P. Kroll - Acta Phys.Polco. B9 (1978) 159. 4) T.T. Chou and C.N. Yang - Phys.Rev. D19 (1979) 3268; Phye.Rev.Lett. 46

(1981) 764; Phys.Lett. 128B (1983) 457. 5) C. Bourrely, J. Softer and T.T. Hu - Phys.Lett. 76B (1978) 481, Phys.Rev,

D19 (1979) 3249. 6) A.B. Kaidalov and K.A. Ter Martyrosian - Moscow Preprint ITEP-51 (1982). 7) U. Amaldi et al. - Phys.Lett. 66B (1977) 390. 8) C. Bourrely - Private communication, to be published. 9) Experiment R420, preliminary result (1983).

10) A. Donnachie and P. Landshoff - Preprint DAMTP 84/6, M/C-TB 84-8; See also; M. Fukujita and J. Kwiecinsky - Phys.Lett. 83B (1979) 119.

11) H. Cornille and A. Martin - Phys.Lett. 40B (1972) 671. 12) S.M. Roy - Phys.Lett. 135B (1984) 191.

- 314 -

NEW SHAPE-EFFECTS IN PRQTON-ANTIPROTON ELASTIC SCATTERING

Roland Henzl D: 8Í10Q26295 McGill University

Following a series of startling CERN discoveries in the measurement of the proton-proton and the proton-antiproton elastic scatterings and total cross sections, among them the one-dip diffraction pattern and the total-cross-section rise, both not yet fully understood, new surprising features in the evolution of the diffraction pattern with increasing e. ¡rgy have been observed in the recent CERN experiments done by the UA4 group at the pp collider^. Especially a rise of

a and an evolution of the dip-bump structure into a relatively high shoul-el tot 2 )

der. This energy evolution of the diffraction pattern can be traced back to a behaviour of the proton which is more dynamical than previously thought, it becomes £iacker, Edgier, and Larger - BEL. In a sense, we are approaching even closer the step-function profile of the famous Froissart-Martin bound^ . Here, (ï~~a« .going -to- summarize the arguments leading to the discovery of thjfefl| BEL effect, and pre- M £ sent some diffraction-theoretical predictions for future measurements, especially at supercolliders^lThe work reported here was done in collaboration with P. Valin.

Betöre going into details, I canuot resist saying that the story of elastic scattering and total cross sections reminds me of my last visit to the Bear Pit in Berne. I grew up near Berne, have a special relationship to the Bear Pit from my childhood on, and the hear keeper is a good friend of mine. Well, he took me to the Bear Pit. A huge crowd was there - all excited. I looked down. T didn't trust my eyes - a bear and a sheep sitting together. "Fantastic, how did you do it?", I turned to the bear keeper. Said he, "No problem. We change the sheep every day!"

1. TOOLS OF DIFFRACTION THEORY The scattering amplitude normalized by do/dt = Tr|f | is given by a Fourier-

Bessel integral over the impact parameter b,

where Jo is the famous Bessel function. The impact-parameter amplitude h(b,s) is related to the partial-wave amplitude f^Cs) by h(b,s) = f^Ca) where I = b/s/2 - 1/2; hence, if we introduce the blackness G(b,s), where O _< G(b,s) < 1, h satisfies the s-channel unitarity condition

f(s,t) = J h(b,s) Jo(b/^t) b db (1)

{Re h(b,s)} 2 + {Ira h(b,s)-l} 2 * 1 - C(b,s) < 1 ( 2 )

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The blacks-?s G equals the inelasticity of the colliding particles, more precisely, the differential inelastic reaction rate, as a function of the impact parameter, and is ¿lao sometimes called the inelastic overlap function. We use these formulae for the elastic scattering at ISE. and Collider energies by making two assumptions: dominance af the crossing-even amplitude, and neglect of spin. Both are compatible with the presently available information (but keep in mind the Bear Pit saga.).

Crossing-even dominance entails that at the same energy the pp and pp diffraction patterns are identical so that one single blackness G controls both scatterings. Hence, an ISR measurement (say at v ^ = 53 GeV) of the pp blackness and the SppS measurement (at /s = 540 GeV) of the pp blackness translate into a measurement of the evolution of the pp (or pp) blackness with increasing energy. The outcome is the BEL proton, Its shape and the new effects resulting from the latter's dynamical behaviour being described in terms of the blackness G(b,s). Crossing-even dominance also determines Re h in terms of In h through

Re h(h,s) = Im h(b.s) (3)

which is a generalisation of Martin's 1973 method for dealing, at high energy, In a good approximation with the dispersion relation for the crossing-even amplitude. Upon substituting Re h given by the Eq.(3) into the Eq.(2), we get an inhomogenous differential equation for Im h whose source term is the blackness G. This equation determines In? h, and with it Re h through the Eq.(3), in terms of G. We have therefore established that, as was already mentioned above, the blackness G indeed controls the scattering amplitude and vice versa.

In. practice we solve (in a good approximation) this differential equation, and with it our scattering problem, by the following four-step procedure: (1) we solve the Eq.(2) for h o with Re h^ = 0 and get h Q - iCl-i/l-G(b,s)] , which does however not satisfy the Eq,(3) if G is energy dependent; (2) we taka

h = i{l-#Î-G(b,se"lïï/2)} = (i + TT I s — ) {1-/1-G(b,s)] (4) ¿ à in s

which is obtained from h Q by replacing^ s by se l l í ^ 2J satisfies the Eq.(3) in a

good approximation (in fact, crossing symmetry exactly), and yields

Hs.t) = £o(se-i,r/2,t) . « + ïlj-) ta £o(S)t) (S;

where £ q is given by the Eq.(l) with h o(b,s) as J.nput; (3) we generate a modified blackness G^b^s) by putting h into the Eq.(2); (4) If G 1 - G we have found in h a good approximation to the solution of the differential equation and, there-

- 3 1 6 -

fore, in f given by Eq.(5) a good approximation to our scattering amplitude. This procedure works well for (An s)-physlcs, that is, when the blackness G considered as a function of Jin s varies slowly with the energy. Then, the

2 Eq.(3) of course implies that Reh is small, while G^ - G - (Re h) .

The SPS and ISR curves in the Argand diagram of Fig. 1 summarize the results of our analysis based on the above method, which will be further detailed in Section 2. The Tevatron and SSC curves are predictions (see below), (in s)-physics Is apparent, esp. Reh « In h. The BEL effect In the blackness G is illustrated by the various sequences of equal-fermi-points on the curves: with increasing energy, each sequence converges toward the center (h = i) of the unitarity circle, that is, toward increasing blackness G.

2 . THE ACTUAL BLACKNESS-PROFILE l THE BEL EFFECT For a detailed analysis, one needs an explicit expression for the black-

2) ness G, which wa take as

G(b,s) = G(0,sj e ™ U + S2E + fi4ç2J (6)

-, h2 - Y ~2TS « = ey2 | j e (?)

BEL ansatz. the largeness parameter B, and the parameter y may depend only on s. The impact parameter b and the largeness parameter B occur in the combination h}f&

which, through Fourier-Bessel transformation, leads to the combination /-Vb for the squint of momentum transfer t and the largeness B, Hence, built into the BEL ansatz, if B depends on s, is a scaling variable tB(s) whose presence

of t

nected to geometrical scaling^ , of the Froissart-Martin bound : a scaling property da/it = TIB 2 {[imf (tB) ] 2 + p 2(3,0)[d/dt(Iiiif(tB)O] 2}, where p(s,0) = Re f(s,0) / lmf(s,0) , exists if and only if for sufficiently large energy G(û,s), 6 ^ , o^, and Y do not depend on s.

The following energy dependences very precisely describe the pp diffraction at the Collider, assumed to equal the pp diffraction, and the pp diffraction at the ISR:

.92 + .0264 An 2(s/s 0) (g\

G(O.s) = 5 — w

1 + .0264 Zn (s/s 0) 6 2 - .12 + .00086 £n 2(s/s 0) ,- <5^ = í í 2 (9)

1

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B = 6.6 + .051 JLn2(s/s0) G e V - 2 ; y2 - .78 C10)

2 5) where a Q = 100 GeV and the relation between <5 and & 2 follows from jet physics. We call this parametrization BEL II; it improves our original BEL I para-

2) metrization . These parametrizatIons entail « G; hence, our fundamental criterion of the step (4) of Che process described in the previous section is satisfied, and G describes the actual blackness. The central blackness G(0,s), the edginess' 6^ and o^, and the largeness B all increase with increasing energy: the BEL effect! No scaling *n the above sense occurs (it may however approximately hold in some limited t--intervals), 5^ asymptotically also have to be of a form similar to G(0,s), to avoid a violation of the unitarity limit G <. 1.

Fig. 1 shows the impact parameter amplitude h at various energies calculated on Che basis of the Eq.(4) with the Eqs.(6-10) as input: ISR and SPS aire data-reproducing, Tevatron and SSC are predictions. The dotted line is a calculation of the SPS curve based on scaling in the above aense the ISR data up to the SPS. The deviation of this line from the actual SPS curve, on the one hand, illustrates again the absence of scaling (ae the deviation, becomes more pronounced \& b decreases, scaling "violation" should become more pronounced as |t| increases) and, on the other hand, once more the BEL effect; relatively to scaling, Reh is larger, hence, according to Eq.(3) the variation of Imh with energy, and with it of G, stronger. Fig. 2 illustrates t.ie "blacker-and-edgier" component of the BEL effect in a plot of the difference ¿G of two scaling functions G^ and G^»

ag<!> • v!> - vl> where H and L refer to two selected higher and lower energies /s^ and t/s~ , and

) H L the scaling parameter R is a function of s, R<s) = v/B(s)/B(sH> . With the definition G(b,s) = r(b/P,s), the two scaling functions and are given by G y = r<b/R,s H) and G^ = r(b/R,s L). If G scales, that is, depends on b/R only, then G^ equals G^, and we get a zero AG-signal for .;ty energy SB. For s = s H , we have ¿G = G(b,s H) - G^(b), that is, ÛG equals the difference between the actual blackness G at s = s^ and a fictitious blackness scaled up to s » s H

from s = B l ; the "larger" component of the BEL effect has been subtracted out. ItB "blacker-and-edgier" component is now isolated in terms of AG evaluated at e = Sy, and displayed in the Fig. 2. The upper curve details the effect in going from the ISR to the SPS. It peaks near .7 fm and is distinctly present at 0 fm. The lower curve comes from our 1979 pp analysis 7^ which unveiled

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a similar albeit much smaller effect in the ISR range. Although our 1979 curve is

outside the error bars of the Amaldi-Schubert analy3Í3 * , which favoured scaling,

it is according to the standard-deviation criterion not inconsistent with their

results! the BEL effect already signalled itself In the era of pre-Collider phy

sics, though not conclusively!

Figure 3 illustrates the uncertainties of our analysis (BEL II) of the áEL effect. Here, R = /a* _(s)/o\ .(s„), which assures that contrary to the previous tOt tot n. choice the scaling functionsC^ and reproduce the total cross section exactly. The curve goes negative since a

t o t increases slightly more rapidly with s than B. The very generous errors originate from many sources: rescaling of do/dt, of b, and so on. This figure illustrates also the insignificant uncertainties due to the difference between G 1 and G . Note that according to Fig. 1 Re n ( n » s i S R ) >

Re h ( 0 , s g p s ) and, therefore, that A G ^ O ) = A{G(0) - [Re h(0)] 2} > AG(0), as born out in the figure. We have further investigated the BEL effect by a method entire-ly independent from the one described here , which gave results in excellent agreement with the present results. In sum, the BEL effect is well established on the basis of our present knowledge.

3. OH dg/dt: TOWARD SUPER-t AND SUPERCOLLIDERS

The BEL parametrization accurately describes the diffraction pattern, for instance BEL II, completed before the new data presented by Cervelli at this workshop were known, has excellent p(s,0) and ö t o t down to FNAL energies. ° e l / a

t ; o t

increases from -18 at the ISR to .21 at the Collider, a 17 % increase to be compared to the new value of = 20 % reported by Cervelli*^ at this workshop. This increase is due to the "blacker-and-edgier" component of the BEL effect. Near t = 0,

? -2 -4

BEL gives dO/dt Œ exp(at+ct ) with a = 16.6 GeV and c = 4.43 GeV , to be compared with a = 15.7±.2 G e V - 2 and c = j.6±.5 G e V - 4 reported by Cervelli 1^. Fig. 4 illustrates the linearly decreasing logarithmic slope A = a*2ct of do/dt near t = 0. This slope decrease is a diffraction-theoretical rescattering effect 5^ due to the ¿econd term in the Eq. (4) rewritten as

This rescattering tem, near t s 0, gives rise in f to a term whose slope is flat-2

ter (because of the G ) than that of the f-term due to G; hence, the slope of their sum decreases because they interfere construetivoly. Fig. S Illustrates how accurately BEL I (BEL II is similar) describes the diffraction patterns measured at the ISR and the Collider, and Fig. 6 compares BEL I's performance with some other models - only BEL seems to be able to describe the Collider pattern correctly.

Fig. 5 also shows the BEL I prediction for super-t at the Collider, that is,

( 1 + , -} (12)

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REFERENCES

1. G. Matthiae, Plenary Talk in the Proceedings of the International Europhysics Conference on High Energy Physics, Brighton, July 1983, published 19B3 by Rutherford Appleton Laboratory, pages 714-742; and F. Cervelli, Invited Talk in the Proceedings of this Fourth Proton-Antiproton Collider Physics Workshop.

2. B. Henzi and P. Valin, Phys. Lett. 132B(1983)443. 3. A. Martin, Invited Talk in the Proceedings of the Third Topical Workshop on Pro

ton-Antiproton Collider Physics, Rome, January 1983, pages 351-371; and A. Martin, Invited Talk in the Proceedings of this Fourth Proton-Antiproton Collider Physics Workshop.

4. A. Martin, Nuovo Cimento Letters 7(1973)811. 5. R. Henzi and P. Valin, "What Is Elastic Scattering Past the Diffraction Dip

Telling Us?", to he published In Zeltschrift für Physik C (1984).

6. For example, see P. Kroll, J. Phys. G 9 ( 1 9 8 3)L81.

7. R. Henzi and P. Valin, Nucl. Phys. B148(1979)513.

the experimentally quite challenging range of momentum transfers beyond |t] = 1,5 2

GeV , The uncertainty hand for the prediction represents the propagation of the BEL uncertainty due to the errors of diffraction pattern measurement. Fig. 6 shows that BEL's prediction differs markedly from other models. BEL's predicted slope decrease for increasing super-t is again due to rescatterlng"^ (second term of Eq.(12)) which in this t-region gives rise to an exponential-in-/^t~ law; plotted versus |t], this entails the slope decrease just mentioned. Fig. 7, finally, takes us to the Tevatron and the SSC supercolliders: BEL XI's predictions, under the assumption that the Eqs. (fe)-(10) continue to hold, are shown together with the SPS curve, the uncertainty bands having the same meaning as that of Fig. 5 explained above. The forward peak continues to rise and to shrink, the dip comes back and continues to move inwards, super-t* s continue to rise: relatively to the forward peak, the secondary-maxiraum/shoulder-to-forward-maximura ratio increases from fixio"0 at the Collider to 2,xl(T5at the Tevatron to 4.6xlO - i*at the SSC. At the SSC, the proton has become sufficiently edgy to produce a second dip near |t| = 3.4 GeV 2. Quite striking predictions! 4. THE BEL EFFECT: ITS UNDERLYING DYNAMICS

Although jet physics is able to provide a certain dynamical basis for the BEL effect^, the proton's blackness and its evolution with energy remain fundamentally unexplained. But the BEL effect is phenomenalogically well established. Its predictions for super—t and supercolliders are Intriguing and, hopefully, will be confronted with experiment in a not too distant future. I hope by that time the question of the dynamics underlying the proton-proton blackness, a central question of the strong Interaction, would have been answered.

I thank the organizors for a splendidly run workshop.

- 3 2 0 -

8 . U. Amaldi and K.R. Schubert, Nucl. Phys. B166(1980)301. 9. H. de Kerret et al., CERN-tt.u'-jrg-Heldelberg-Annecy-Vlenna Collaboration,

Phys. Lett. 683(1977)374.

10. T . T . Chou and C.N. Yang, Phys. Lett. 128B(1983)457. 11. A. Donnachle and P.V. Landshoff, Phys. Lett, 123PU983)345, and contribution

203 to the International Europhysics Conference on High Energy Physics, Brighton, July 1983.

1. Argand diagram for the pp (or pp) impact parameter amplitude h at the indicated facilities (BEL II). Each point on a curve corresponds to a given impact parameter b. The blackness G is related to the distance of h from h=i by /Ï-G, The unitarity circle corresponding to Eq.(2) for G - 0 is indicated. (Dashed line, see text.) ISR - Intersecting Storage Rings: pp(v^=53GeV); SPS - Super Proton Synchrotron Collider: pp(v's=540); Tevatron: pp(v's=20Q0) ; SSC - Superconducting Super Collider: pp(^=40000) .

2. The "blacker-and-edgier" component of the BEL effect shown in terras of AG = G(b , S y ) - G (b), the difference between the actual blackness G at the higher energy /s^ and a fictitious blackness G L scaled up with R(s) = /B(s)/B{s H) from the lower energy S&^> The lower curve shows a result of our 1979 analysis?) done in the days of pre-Collider physics. Upper Curve: BEL I.

3. Same as Fig. 2 upper curve, but for BEL II with errors (see text) and a scaling parameter R(s) = i/CT t o C(s)/a t Q t(s H) . Solid and dashed lines: calculated with and G, respectively. 2

4. Decrease of the logarithmic slope A = a+2ct of da7dt ~ ea t + c t

Q e a r t = 0.

5. BEL description of the measured Collider(»^s=540) J and ISR(v^=53) diffraction patterns, and BEL prediction with uncertainty band for super-t at the

6. Comparison of the BEL description of the measured Collider diffraction pattern and of the BEL prediction for Collider super-t with some models. Long-dash linei De Dias-Kroll^, short-dash line: Chou-TanglO), dash - d D t line: Donnachie-Landshoff 1 1?, solid line: BEL I.

7. BEL II predictions with uncertainty bands for the indicated facilities, at the energies detailed in the caption of Fig. 1 . At the SSC, the proton has become sufficiently edgy to produce a second dip.

FIGURE CAPTIONS

Collider.

(Kr /a t^mb/Gav*

àtr/ût m b / G e V *

5 DA/DT MB/GOV* G

-V S w "ni |\ i m -1 J o ' Q

<

ûg«gh-gl

I 1 j

r I \ •

*\ ) f i X

/ I f !

/ H

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N E W M E A S U R E M E N T O F E L A S T I C S C A T T E R I N G A N D T O T A L

C R O S S S E C T I O N A T T H E C E R N p p C O L L I D E R

U A 4 C o l l a b o r a t i o n , C E R N , G e n e v a * S w i t z e r l a n d

P r e s e n t e d b y F . C e r v e l l i , C E R N a n d P i s a

N o w r i t t e n c o n t r i b u t i o n r e c e i v e d

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LEAR Physics

Dï 8A1D026309 - 324 -

PHYSICS WITH ANTIPROTONS AT LEAR

Kurt KILIAN

CERN - EP Division CH-1211 Geneva 23

ABSTRACT

The low energy antiproton ring LEAR started to work, at CERN in 1983. It provides clean p beams of much higher intensity and much better quality than available so far in the range from 0.1 to Z GeV/c momentum. 16 of the 17 accepted experiments are installed and 14 of them took first data in 1983. After = 240 hours of LEAR operation very first results are available. One can expect that exciting physics results be produced in many different domains provided LEAR gets enough p in the future.

1. IMTRODUCTIOH

LEAK 1^ is the low. energy end of the GERN antiproton (p) complex whose center is a p factory*-' consisting of the 26 GeV proton synchrotron (PS) and the antiproton accumulator (AA), During 1983 LEAR provided for =240 hours p beams at 300 and! 600 MeV/c for physics experiments. Of course 16 newly installed experiments cannot all produce physics results in such a short running time. Therefore this report is mainly a previewt Nevertheless there are first results and indications how things may go in some experiments.

The present experimental program is well balanced and covers a wide range of physics. In order not to be lost in details it is worthwhile to ask: What is the most interesting aspect at the beginning of p LEAR physics ? It could be the chance to gain understanding of quark gluon dynamics in the low energy non-perturhatlve region and to develop on this basis a more microscopic description of low energy hadron interactions and hadron structure.

Hadrons are believed to be made from colored quarks (c-triplet) which interact by exchange of colored gluons (c-octet). Nature seems to restrict observable hadrens to overall e-singleta, which means that free colored quarks and gluons do not reach our detectors. This "explains" confinement and justifies the concept of bag models. The simplest c-singlets are three quark (qqq) fermions, the baryons and quark antiquark (qq) bosons, the mesons. In the one boson exchange (03E) models the color singlet baryons (B) and mesons (M) are taken as basic entities. In HB (and MB) interactions where the (3q) c-singlet baryon bags always come out again it has been shown that the simplifying assumption of c-singlet one boson exchange allows for a very successful parametrization of experimental data.

In the case of BB interaction where the unique process of hadronic annihilation comes Into the game 0BE models have problems. (A medium range absorptive potential has to be put in "by hand"). Here the original B (3<j) and B (3q) c—Binglets can he dissolved. Valence quark pairs can be annihilated and created at minimal baryon energy in infrared slavery. The quarks and antiquarks can finally appear reshuffled, but now in (qq) c-singlet mesons alone. All this occurs inside overlap regions of bags involving colored quarks and gluons rather than asymptotic c-slnglet mesons or baryons*

- 3 2 5 -

Fig. 1 indicates how, foc example, annihilation Into two and three mesons could proceed. Only the extrema cases of re-arrangement and qq annihilation-recreation are shown. Theoretically BB interaction appears as a very complex many body problem. Experimentally BB interactions at low energy are characterized by a correspondingly rich system of many different annihilation and reaction channels. It is a challenge for experimentalists at LEAR to do so many and so specific experiments that one finally can piece together sufficient information for a better understanding of the basic quark gluon dynamics.

An open question is to what extent one may Isolate experimentally the effects of individual quark lines in diagrams like in Fig. 1. One alternative is for example to study the creation of a single qq pair (such as on the right side of Fig. lb) under clean conditions by selecting a strange antistrange quark pair.

2. THE LEAR FACILITY

LEAR 1^ is a small storage and stretcher synchrotron installed in the old PS South Hall (Fig. 2 ) . It is a strongly focusing synchrotron with four laminated dipoles and a separate focusing structure with quadrupole doublets on either side of the dipoles. Some parameters ate shown in Table 1. LEAR gets antiprotons from the CERN "antiproton factory" 1'. High density p batches, free of any contamination, are peeled off from the AA stack. They are injected into the PS, decelerated in the PS down to fixed momentum of 0.6 GeV/c, and then injected into LEAR- The batches can contain up to = 4.10 9 p and they are transferred once every ^ 75 minutes. This is compatible with the accumulation in the AA and corresponds t D an average p flux with = 100% duty cycle of « 1 0 6 p/s. A new scheme of ultras low "stochastic" extraction ' (normal resonance extraction with feeding via diffusion) has been developed for that purpoße in LEAK. It provides the necessary spill out time of 1 hour. The p momentum can be tuned in LEAR (Finally from 100 MeV/c to 2000 MeV/c). Stochastic cooling 'is used and provides very good beam quality.

Table 1: Some LEAR parameters

Momentum range: 0.1-2 GeV/c Circumference: 78.54 m Free length of long straight sections between quadrupoles: 8 m Approximate working point: Q H»2.3; Q v=2.7; v g —(14.5) 2

Maximum acceptances (in itmm.mrad) : E ü=240; E v=48; Ap/p="±l. I X

The stochastic extraction system feeds an external beam which is split into three simultaneously working branches The beam performance is : Emlttance £JJ and Ey (better than) ~ 3 to 5 ranm mrad and Ap/p (better than) = 1.3«10~ 3. (It Is worthwhile to recall that in the "pre-LEAR time" normal secondary beams e.g. at 400 MeV/c had only = 10~ of the Intensity of LEAR, had a duty cycle of only = 0.1, had = 100 times more pions than p* s, a momentum spread of Ap/p = ±1% and emit tance s of about 100 TÏULIIL mrad). The extracted p intensity can be distributed freely on the 3 split branches. Each branch can be switched by a dipole into two experimental areas (Fig. 3)*

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3. A SHORT LOOK AT THE FIRST GENERATION OF EXPERIMENTS

The 17 approved experiments'^ are listed in Table 2. The majority of them (10) are addressed to studies in the pu system. Six others are related to p nucleus interactions. In one experiment (PS18 U) which is not yctginstalled the masses of p and p will be compared to an accuracy of 10" (CFT test) using a magnetic spectrometer with RF modulation.

At low LEAR energies short degrades with negligible hadronic losses can be used to slow down p and to stop them effectively with small energy straggling in thin targets. This is an obvious advantage for the p stop experiments (9 in total).

Eight experiments will do studies with transmission targets. Here the high beam quality ensures good angular resolution, the small moment uni spread gives good energy resolution and the hi¿h p flux allows foi statistical precision even with the thin targets which one needs if one wants to avoid energy smearing.

Table 2: LEAR - List of experiments

Exp. Title CERN Do.-.

pel 70 Precision ociieurunonts of the proton electromagnetic lota facto like region and vector neson spectroscopy

re in the ti=e- FSrc/BO-W aiil|.iaz ::-a„li)

PS171 A study of pp Interactions at rest Ln a H2 gas target at LEAR P5CC/8Û-1LH Rluaat PSL72 PP total c oss-EQctions and spin effects in pp'K'+*~>"+"~>pp 8bo t>i 200 HeV/C PSCC/eü-76

PS 17 3 MeaSure=en of pp cross-sections at low p oonenta PSCC/B0-Ö5

ps:7- Precis Lor. uc eji of X-rays fro3 pp (pd) atons using the Initial LErtR Lean PSCC/8U-Ö1

PS17 5 -it very loi.

of the antiprotonlc Lycan and Balcer X-rays of pli a target pressures

d pJ atois PbCc/B'j-ya IKÙchJ

PS176 Study i>r X-ray und Y-ray spectra froa ant1protonic ateas at the pKirdcccd antiproton beao of LEAR

s'.-Iy PSCC/S0-IU3 Put il tTauKlier)

ynu *

PS 178

A search f

Study ai an

r boavj, hypcmuelci at LEAR

tlneutron production at LEAH

PSCC/BÜ-TS

pscc/ao-91 CJollPllSSDtO Voei

PS 179 Study of tl oui: let lib In

L- interaction of lou-cricrey p and Í with H, 2H, he, Nie,Ho and ''"Ar B a streamer chamber In a uagnetie field

PSCC/80-7B Ursino

PS 182 IiWesUijiiU hluTi résolu ons on biicyoniura and other rare pp annihilation mude usina PSCC/80-U2

FS183

PS 184 Searcii for

Study of p-

bound SN states using a precision y & charged pton s

nucleus Interaction with a high resolution magnetic H pectrometer

F33C/ao-93

P5CC/«0-HiO

5 <ul ill (Arrastrony) Garruta

PS1H5 PS186

Study ot tl

Nuclear exc

rea lio Id producción of ïï pairs ln pp interactions at

ltatlons by antiprotons and antiprotonlc atoms

LEAH PSCC/Cl-bS

PSCC/B0-S3

Milan (Johansson) von E B U y

PS 187 A good stat istlcs study of antiproton Interactions vich nuclei PSCC/B1-51 DlGiacoBO

PS 189 lliiih precis Application

ion mass ne a su remanes «Ith a radio frequency masa spectrometer _ to the measurement of the pp man s difference

PSSC/81-B4 Thibault

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3.I p atop experiments with hydrogen targets

The negatively charged p are captured in atomic orbits of "protonium" where they cascade down emitting an X-ray spectrum with a hydrogen like pattern but with =10 3 times higher photon energy. From distortions in the X-ray spectrum (especially in the Lyman and Balmer Beries where annihilation effects become important) parameters of low energy pp interaction will be extracted.

proton!um has no atomic electrons and it is so small that it can reach the high electric field of neighbouring target protons. With increasing target density the Stark effect will therefore mix more and more S-wave strength into the atomic states which provokes fast annihilation from high n states owing to the increased hadronic overlap. Lyman transitions are therefore not observable with dense LH2 targets. But variable target density is a tool to "select" experimt;ui.ally S or P wave annihilation.

Three experiments (PS171, 174, L75, see Table 2) are s tudying protonium. In PS174 the stop target density is variable from normal pressure gas to liqcid hydrogeu and high resolution Si(Li) detectors are used. In PS175 p are degraded and stopped in low density hydrogen (400 mbar done, 15 tnbar planned). The novel trick is to spiral p into the center of a focusing cyclotron field where they come to rest. High resolution semiconductor detectors are used here s well. There are first indications that Lyman transitions (K-X rays) in pp atoms have been seen in PS175 . In experiment PS171 (Asterix; the X-ray detector is a cylindrical drift chamber immediately surrounding a gaseous itop target. The resolution is moderate but =90î£ of the solid angle Is covered. PS171 has two primary goals. The first is to disentangle the dependence ot annihilation reactions on the quantum numbers of the pp system (S or V states etc.), These quantum numbers will be determined from the coincident X-ray transitions. The second is to identify multibody annihilation events with a large acceptance magnetic solenoid spectrometer (DM1 from Orsay). A search for resonances, glueballs or narrow baryonium states below threshold can be done this way.

There are two experiments (PS182, 183) which hunt for narrow bound states X, emphasising high resolution. PS182 looks at pp •*• T I * - TX° and also pp •* yX." • The TC° spectrum will be determined by reconstructing the n° •*• yy kinematics with a pair of BOO spectrometers and also by looking at coincidence between one BGO detector and a lead glas array. PS183 searches for monoenergetic y and Tt±. The y spectroscopy is done after a y -*• e + e ~ conversion target. A large dipole magnet, filled with wire chambers La used as spectrometer (Fig. 4). Inclusive lit spectra measured in experiment PS183 show monochromatic pion lines (Fig. 5). While two lines In the t& spertra at 236 and 205 MeV/c can be explained ty decays of stopped KT1* (K + + p^v and •+ i&n") a line at 200 MeV/c which appears in both the TU*" and it~ spectrum la an indication for the existence of a narrow bound state baptized C~ below threshold at a mass of 1620 MeV .

Baryonium^ yes or no. That was one of the first controversies which stimulated the demand for a machine like LEAR. The results of PS 183 supports evidence for bound narrow states. Are these elusive objects BL systems of nuclear physics type bound by OBE forces and stabilized by high angular momentum ? Or are they a manifestation of quark chemistry: color singlets with new substructures like for instance color triplet or color sextet diquark-antiiiiquark?

- 3 2 8 -

In experiment PS170 the rare annihilation channel pp •*• eê" will be measured. This reaction has Its highest branching ratio at rest of only =3.L0~ . The necessary very good background rejection against hadroa pairs is obtained with a magnetic dipole spectrometer combined with gas Cerenkov and shower counters. The electromagnetic form factor of the proton in the timelike region can be determined from pp + e +e~.

3.2 p experiments in flight with hydrogen targets

In PS170, e + e ~ production will also be studied in p interactions in flight. For the first time angular distributions can be obtained and one will ge*: separately the electric and magnetic form factor Gg and in the timelike region. The spectrum of vector mesons also and especially in the unphysical region (fig. 6) is strongly related to these conn factors.

There are two experiments (PS172, 173) which look for resonances by measuring pp excitation functions down into the unknown region below 300 MeV/c momentum. So far p energy variation was done with dégradera of variable thickness. This of course reduced the beam intensity drastically and limited the statistical precision. PS173 measures differential elastic and charge exchange (CEX) cross-sectione with wire chambers and an n calorimeter array. A large spherical leadglass scintillator array also measures neutral and charged annihilation. PS172 first made a precision scan of O'totaj and a

p p - » . n e u t r a i i n a n absorption measurement and no indication of a narrow resonance was found between 600 MeV/c and 3Ô0 MeV/c ^. Next da/d£2 and P(9) will be scanned in the charged two body channels PP*PP» pp+rc**" and pp+K +K~ with a polarized target. Narrow and also broad resonances may be disentangled with these data. The polarization of scattered protons (and possibly also p) is determined by a Polarimeter with carbon scatterer.

LEAR covers some interés ting thresholds (Table 3 ). The CEX threshold is at =100 MeV/c (=5 MeV). Experiment PS178 studies the 0° production of ñ through pp * Hn and the possibility of using 5 from this reaction for experiments. Above 1.43 GeV/c are the thresholds for strangeness 1 byperon-antlhyperon paire pp •* ïï. Experiment FS1Ö5 which investigates these reactions will be discussed in more detail in Section 4.

3.3 p stop experiments with nuclear targets

In experiments PS176 and ÏS186 antiprotonic atoms are studied. Measured X-ray yields, line shifts and widths tell something about pA hadronic interaction and also about p mass and magnetic moment. Nuclear y ray measurements permit one to identify nuclear fragments after annihilation. The atomic quantum numbers before annihilation can be deduced from v - y coincidences. The clean p beam allows for very low background* Fig. 7 shows as an example the high quality of antiprotonic X-ray spectra reached at LEAR.

PS177 is the smallest experiment at LEAR with the aim ta measure the lifetime of a A particle in a heavy hyper-nucleus • This may give the "six quark in a hag" probability in a nucleus or could show whether the weak interaction is influenced by the extremely high electromagnetic field Inside a heavy nucleus, p will be stopped on a very thin (3Qug/cm 2) U or

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Fu target. Annihilation on the nuclear surface produces KK+X in -11 of ail cases. The R mo men tuco distribution la optimally suited tec recoillees N(K,ic)A strangeness exchange an nucleoas i a the same nucleus. Produced A can be bound and reach the hypernuclear ground state* During its lifetime the hypernucl'ius «til leave the target foil (compare t A = 2.6*10~ 1 0sj and go into the vacuum with the Fermi recoil of the originally annihilated nucleón* The target will be choosen such that the weak decay of A leads to fission- Fission products can be measured free from any background in low pressure gas counters* The distance of the fission point from the target plane gives a measure for (he hypernuclear lifetime. For that the well known "recoil distance method"*^ will be applied.

Table 3: Combinations of < 4 Stable Particles which cen be formed with Antiproton (S Proton) Beams from LEAR on a Proton Target.

Particle combinations uich Threshold mass Beam momentum with p bean p beam /i f i x e d p t a r g e t

(MeV/c*) (HeV/c) PP PP 1876.559 0

- 1879.146 98.706 _ 1974.676 646.353 - 1982.678 676.110

- 1990.680 704.729

P>° 2011.522 776.492 Hnn° - 2014.109 785.16B

- du* 2315.20 788.814 pnir*. pñir p m i + 2017.420 796.207

ppfr°Tr* pptrV 2146.454 2191.968 - 2149.071 • 1199.495

- dn+Tic 2150.162 1202.664 pnn + Tr 0

1 pñTi~nB p m r + i 0 Z152.382 1209.1U ppIT+TT" ppTî+ir~ 2155.693 1218.722 ñntr+ir nnir*it* 2158.280 1226.219

ÄA - 2231,20 143S.070 ÄE\ Al" - 2306.06 1652.736 ÂAn° _ 2366.163 1B17.301

- 2378.720 1852.962 - 2381.-9 20 1870.586

XTÏT 2394.68 1S98.356

3.4 p experiments in flight with nuclear targets

There are three experiments In this field (PS179, 184 and ltt7) which took data at 300 and 600 MeV/c. Here p annihilation deposits a small momentum but -2 GeV &£ energy in a nucleus. la central col lie ions this energy deposit could give localized "hot spots * with characteristic decay properties. One expects that many nucléons and nuclear fragments are emitted, while for peripheral pA annihilation preferentially lower multiplicity mesonic reactions are expected.

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In PS187 these differences have been seen^^. This experiment uses a dipole magnet spectrometer with large acceptance which permits high statiseical precision and capability to measure events wi th large multiplicity- High energy deposit in an active target was used as another good signature for central collisions. It was speculated that p might occupy narrow single particle-hole stetes in nuclei which could be rhe best seen in a recoilless forward knock on (p-*p) reaction. No such effects are detected in the forward proton spectrum in PS187^J.

In PS 179 a self shunted streamer chamber in a magnetic field is used with large acceptance and moderate momentum resolution. Fillings with H 2> D 2 , 3He, ^He, ^°Ne, 1 + 0Ar are foreseen. The experiment with ^He filling could tell whether D and hie have been produced at the very beginning of the universe from p 4 H e inte rae tions. Several thousand high quality photos with ''He and Neon filling have been taken.

PS1ÍJ4 uses a high resolution magnetic spectrometer (SPSS II from Saclay). Emphasis lies on measurements of elastic and inelastic angular distributions and also on (pp) knock-on reactions. This group has already published data on elastic and inelastic p scattering at 300 HeV/c on i 2 C . Fig. 8 which is taken from the first LEAK, publication 1 3' shows that p 1 2 C scattering has a pronounced dip in the angular distribution characteristic for a very strong imaginary potential.

4. STUDi OF pp ->- ÄA

The more detailed discussion of PSL85 wh^.ch so far has only had parasitic test runs should he taken as an arbitrarily chosen example indicating the richness of physics in the LEAR experiments. The experimental set-up is sketched in Fig. 9. The p beam passes through a timing-counter SI and a 2.5 mm polyethylene target T. The target length and the beam diameter (=lmm) define the production vertex. Veto scintillators around the target identify beam p, and prompt charged p interactions in the target* As signature for Ä"A, the appearance of delayed charged decays is used. Four hadronic decay combinations occur within typically 3 to 12 cm after the target.

!PpTt+it~ four charged (4L.2X)

pnn + i i 0,npn° n~ two charged (23% each) nnit0-";0 no charged (12.8&)

The threshold klnematicB permits small but fully efficient detectors since even the combined kinematics of the production pp •*• 3ÎA and of the decay A + pit confine the decay (anti)baryons into a rather small forward cone (£42° half aperture for a 2 CeV/C p beam). The trigger for the delayed charged decays is obtained by requiring a hit in a forward scintillator hodoscope H =30 cm downstream of the target.

The klneinatlcal details (decay vertices, decay planes) of an accepted event will be reconstructed from hits recorded ln a stack of 23 planes of MWPCs and drift chambers. Which vertex belongs to A or A will be determined by the "baryon number identifier"(Fig. 9 ) . Three drift chamber planes are used here in a solenoid type magnet* Left or right bending tells about the charge and therefore the particle type of the decay products • The decay products of ? and ï come from the field-free chamber stack and pass trough the aluminium coil of -1 cm thickness. This "low mass" solution keeps Che main background from n annihilations low.

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From the measured it and A production and decay vertices one can extract total and differential cross-sections. Since in the weak decay A -*• pi: the proton goes preferentially in the direction of the A polarization vector, one can extract from the recorded decay tracks the A (similarly Ä") polarizations and (for the 41% of decay combinations with four charged particles) even the lA spin correlations. The sensitivity for fully reconstructable "4 track" events will be with 1 0 6 p/s = 45U events per day and ubatn.

4.1 Quantum numbers of strange quark pair creation

The spin S and Isospin 1 of a light diquark in the baryon 56-plet are related by a symmetry condition: a diquark (qq) has S = 0 (1) if I B 0 (1) For the isospin zero A with its single strange quark, s of iaospin zero (Fig. 10) this implies that the light (ud) diquark has isospin zero and therefore spin zero (similarly for 7L. Note that for 2 the diquark has S=I=1). As a consequence the measurable Ä and A polarization vectors and spin correlations (singlet or triplet) are related to the ss loop. We get detailed information on the polarization behaviour of ss quark pair creation!

So far in pp S A all e x p e r i m e n t s indicate large negative polarization for | f | > 0.25 ( G e W c ) 2 for Ä and A 1 4 ) . If it is the ss quark loop which defines the polarization (Fig. 10) then we would predict strong negative A polarisation in all reactions where an ss pair is created. Experiments support this assumption even in high-energy proton-induced inclusive A production where the same quark loop occurs. A model for ss pair creation via string dissociation in a ^P 0 state explains this effect 1 5'.

There are experimental indication that 5ÎA yairs are only produced in triplet states ' which means (if ud and ud diquarks are perfect spin zero spectators) that the sg quark pairs are only made in triplet states.

Approaching threshold, the JÏA system is in an S-wave or P-wave at most. This can be determined from the shape of the differential cross-section and also froo the energy dependence of o*^ (Fig. 11). The three valence quarks In Ä and A are in a pure state of orbital angular momentum 3 e r o with the light diquark in a spin zero state. A relative S-wave or P-wave between Ä and A therefore implies a relative S~wave or P-wave, respectively) for the ss quark pairl What can we learn about the quantuu numbers of ss pair creation ? If the quark pair is created with giuon quantum number 1", we have to find S-wave 7lA production and 7LJV triplet spin correlation. On the other hand,, quark pair creation in vacuum quantum numbers 0 + implies that the ÍA system appears in the P-wave (in order to get positive parity) and again in a triplet state.

4.2 Final state interaction

Close to thresholds the newly produced particles appear with vanishing relative energy. Ln che laboratory syceem they go into a forward cone with very small aperture* For a long time they stay close *o each other, so that there will be strong final-state interaction (f.s.l). If this f-s.i. can be sorted out then we can get information about low-energy interactions of interesting particle combinations which are not available so f a e * ^ (Table 3 ) . The detector shown in Fig. 9 is perfectly suited for such studies of forward confined multlpartide events.

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The f.s,i. in the case of pp •*• 3ÍA will be predominantly annihilation. This should be a pronounced effect if the annihilation is of longer raoge than the production process. For XA production, in an OBE picture, strange mesons with at least kaon mass have to be exchanged, while annihilation might start at longer distance with pion exchange. The ratio of volumes that are characteristic for production and annihilation may then be aB small as ( m ^ / m ^ ) 3 = 1/50. (Note that in the case of pp + En this ratio may be of the order of one owing to pion exchange in ïïn production).

In JA the expected strong annihilation effects in f.s.i. are likely to give a measured cross-section a e x , > which is reduced by a fraction d with respect to the p h a s e - s p a c e b e h a v i o u r a$s close co threshold :

0e X P = o p s ( l - d ) . In Fig. 11 the hatched area indicates where this deviation

may be measured. In the simplest picture the depression d should be proportional (or at most equal) to the inelastic AA interaction probability

d £ < f finel)/<°Inel + 0 el)

Thus the energy dependence of f.s.i. effects gives information on the inelastic SA cross-section. Also the Imaginary part of the ÎA. scattering length could be extracted. Strong ÎA f.s.i. will create particularly strong cusp effects in channels with KK meson pairs if quark rearrangement is important in annihilation.

4.3 Resonances

With tunable p beams from LEAR one can easily look for narrow effects In the direct channel in ÏA production. If there are narrow baryoaium states in pp, then by analogy narrow baryonia could also appear in ÂA. They could show up as spikes In the pp •*• Ä7L cross section if th*y are above 2 m A

mass and as spikes in typical ÄA annihilation channels e.g. Fx. If they are below 2m^.

Recently a narrow resonance £ with a mass of 2220115 MeV has been discovered With Mark III at SPEAR in radiative charmonium decays J/Y -* 7 + £ '. A peculiarity of E. is its large decay branching ratio into K*"K~ and KgXg. The abundance of strange mesons in £ decays has been taken as indication that £ might be a glue ball or a Higgs boson. It supports as well two other speculations : It could be a AA baryonium or a cusp effect as described above. The ÄA. threshold is at 2231.2 MeV just within the mass range reported for the E,. It is interesting to note that the detector of experiment PS185 is very well suited to measure pp + £ + K s K s * û a e c a n fiet

angular distributions for K f i and determine width ana mass of S with 0.5 MeV precision.

4.4 Scattering of polarized A" and A

At high p momenta at LEAR (2 GeV/c) A* and A are produced with momenta between 376 and 1624 MeV/c. The cross-section for ÄA production is about 100 ub. Already with a thin target this gives 6.101* ÄA paira per day (with

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10 6 p/s) which decay into A charged decay particles* These events are full analysable even if A or 2 undergo a secondary scattering.

A secondary scatterer can he Installed close to the "production" target and one can use I and A mutually as tag for A and A" scattering experiments. Energies, directions and polarizations before and after scattering can be determined both if A or TL are scattered. We can then study e.g. with a secondary polyethylene target the elastic scattering of polarized A and A" on protons and carbon. For 10" 3 Interaction length of the scatterer +one gets ~ 50(Atp+A+p) scattering events per day. similarly it works for S~ and

Both the elementary and nuclear spin-orbit interaction can be determined by including the detection of the left-right asymmetry. In view of currently discussed models with different predictions of the spin-orbit interaction of hyperons in hyperauclei, particularly for the Z case an Improvement of the experimental value would be Important.

For the understanding of the dynamics it is also of great value to be able to study the three channels related by crossing:

pp + AA, Ap -* Ap, Ap + Ap pp + EE, Xp + ïp t 2p + Lp

4.5 CP violation

CP violation effects In the partial hadronic decay ratio of Y and Y may occur. They are probably very small '. But an observation of CP violation in this field would be of extreme interese since it could allow to distinguish between different models for quark mixing In weak interaction. The experiment PS185 seems to be a necessary first step and already a good approach to check if such effects exist. A difference in the rates for {patten0 j and {np«*ii**} would be the signal for CP violation. The normalized difference

{pnit+it0} - {HpTt Tt"} A = —

ípnit+n*} + {ñpTt°7í } can be determined to = 10" 3 statistical precision within 5 to 10 days with 10* p/s. The problem will be to get control of systematic errors. They occur mainly (besides "wrong" triggers) awing to asymmetries in the behaviour of A" and A and their decay products. One can control the knowledge of systematic errors by performing the experiment at different p beam momenta. With some modifications a similar check of CP violation can be done for pp + £*T+.

Another good test for CP violation effects should be a comparison of the decay asymmetries 3 and a for A* and A. Here a + a = 0 has to be checked and one can reach a statistical precision of_ -5.10 - 3 within 5 to 10 days with 1 0 6 p/s in experiment PS185. (If a + a * 0 this would simulate an apparent difference in X and A polarization).

- 3 3 4 -

5. CONCLUSION

It is not possible in a short paper to present all physics ideas around LEAR. Many other exciting subjects have been presented already at the Erice Workshop two years ago and earlier, for example ideas around the strong and weak CP violation effects in RK channels 1 9^* Despite the fact that LEAR will improve the experimental situation in the low energy range very substantially one has to face the fact that it is difficult to supply enough p beam time and p flux for these many interesting experiments* Therefore It is worthwhile to proceed with technical developments like A C O L 2 0 ^ which increase the p flux, and with developments which allow to économise antiprotons.

Electron cooling for LEAR is under construction. It will further improve the efficiency af low energy scattering and stop experiments. Perfect cooling is needed for all projects which aim at further deceleration. Postdeceleration might be done with a radiofrequency quadrupole (RFQ) or with another small storage synchrotron (ELENA projec t ) . The "p eco no my " in high resolution transmission target experiments at LEAR can be improved to 1Q0ÎS efficient use once Internal targets are operational. pp mini-c-)llider operation and p~H~ corotating beams may increase the efficiency -n high resolution pp Interaction studies at high energy and threshold espectively.

FOOTNOTES AMD REFERENCES

1) The most complete collection of contributions to machine and physics aspects of LEAS, can be found in the proceedings of the workshop on: Physics at LEAR with Low Energy Cooled Antiprotons, Erice, May 1982, Plenum Press, E. Majorana Int. Science series Nr. 17 Physical Sciences (U. Gastaldi & R. Klapisch Editors). We refer to these proceedings here as "Erice 82". LEAR is described in: - P. Lefèvre "Erice 82", p.15 - W. Hardt, L. Hoffmann, P. Lefèvre, U. Mb'hl, G. Plass and D. Simon: Conceptual study of a facility for low-energy antiproton experiments, CERN/PS/DL/Note 79-1 (1979).

The idea to make something like LEAR, at CERH was (to my knowledge) brought up and studied by Ü. Mb'hl in 1 9 7 a .

2) R. Billinge: The CERN Antiproton source. These proceedings.

3) S. Van der Meer: CERN/PS/AA /78-6 ( 1 9 7 t t ) . R. Cappl and W. Hardt: Proc. of the XI International Conference on High Energy Accelerators, Geneva 1 9 8 0 . U. Hardt and R. Glannini "Erice 82",p. 4 9 .

4) S. Van der Meer: Stochastic damping of betatron oscillations, CERN/1SR-PO/72-31 (1972). D. Höhl, G. Petrucci, L» Thorndahl and S. Van der Meer: Phys. Rep.,5B,73(1980). D. Mühl, "Erice 82",p. 27.

- 3 3 S -

5) D. Simon "Erice 82", p.55. 6) More information about the 17 LEAR experiments in:

- CERN Grey Book: "Experiments at CERN in 1983" - Proposals (document numbers are given in Table 2) - "Erice 82".

7) L. Simons, private communication and invited talk at Frühja^hrstagung Kernphysik der DPG/6'pG/SPG Innsbruck 1984

8 ) A. Angelopoulos et al. CEKN-EP/84-47(1984> Submitted to Phys. lett.

9) L. Montanet, C.C. Rossi and G. Veneziano, Phys. Rep. 68 (1980) 149. See also contributions from the collaborations of PS173.182,183 ln "Erice 82".

10) A. Clough ec al., Evidence against the S-meson, Submitted to Phys. lett. and 0. Bugg, private communication

11) V. Metag et al., Nucl. Instr. Meth. 114 (1974) 445.

12) N. DiGlacomo, private communication

13) D. Garreta et al., Phyr.. lett. 135 B (1984) 266

14) H.W. Atherton et al.,_Nucl. Phys. B 69 (1974)1. B. Jayet, Proc. 3rd Europ. Symposium on N - N Interactions, Stockholm 1976 (Pergamon Oxford 1977), p. 393. ftf. Kwak et al., Nuovo Cimento 23A (1974) 610. S.M. Jacobs at al., Phys. Rev. D17 (1978) 1187.

15) B. Andersson et al., Phys. lett. B 85 (1979) 417.

16> P.D. Barnes et al. "Erice 82" ¡>. 843

17) K.P. Einsweiler et al. SLAC-P4B(1983)3202

18) L.L. Chau, Quark mixing in weak interactions. Fhys. Rep. 95 Nr.1(1983)

19) E. Gabathuler and P. Pavlopoulos, "Erice 82", p. 747 and CERN/EP/82-118. J . Six "Erice 82", p. 739

20) Design study of an antiproton collector for the antiproton accumulator (ACOL). Yellow Report CERN/83-10 (1983). Editor E.J.N. Wilson.

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Fip. 3 : General layout of the LEAR with magnet lattioe and i n s t a l l a t i o n s . The signal linea for the stoohaatio sooting ays tema are aleo ehem.

- 3 3 8 -

, , i Momentum spectra of positiva (top) and negativa (.bottom) + 1 j{H pians rteaourcd in Ecpt. PS193. iFhe aut-Jca aheu the reaulte

% J ^ l M t l bf fitc t o c smooth baekgrmtnà pino Cauasian line ohapas. • jijlf The momentum aoalen ara uncorrected for energy lose, Tiie fÚr |U line at *J9J MûV/c (^200 MeV/c corrected) in the positive j/ Ijt. and negative cocaine* eûircapOHdc to a miacing rasa

í bJpV V | n„~-!C20 AMV in pp - * **• S*« toe addition ¿¡J' Vi t n t V A pQB'-tàve speatner. correspond to dcaaun of stopped

\ \{ ' X , ** (it - n +v and ¡C *

X

i x \

A/' us.

f « \ ISO W S . JOG ï î S ! S 0 275 JOO

uaucuiuu {»CV/C]

e Z e c i r a - m a g n e t i c / a r m factor of the proton. The

time-like region will be

scanned in Expt. PSJ70 at

LEAR.

Energy [k e V J

Pig-

X ray speatxim from antipro-tonic oxygen measured in Expt. PS17S (top) and comparison of a detail for Z oxygen isotopes (bottom). The energy shifts for the isotopes result from a shift in reduced masses. The reduction of the strength of bK? transition with increasing atomic weight corresponds to increasing hadronio absorption.

Fia. S

differentia} or03S aaetiótt far p y¿C elastic (a) aid fcirlastia scattering to the 4, if lieV Stat* Ib) nsasurcâ in expt. PSW*. Crooc portions far p are »haut for c^parieai. Curven are renulto of nodcl aaicklations. For details oee t-cf. 13.

S2 S3 54 Target Region

Fig. 9: Detecto» aystam for Etpt. PS185

- 341 -

" i í ^ - ^ X . J ^ - ^ s . v * K - ; ^ - ^ : * r

Fia. 10: Quark lina diagram for tke reaction pp * and sama cther reactions which also have a sa quark pair areaHan.

I 1U0 «60 H8Ö fSOÔ ^HcV/cl

ßp.'p.lb4

J l

Excitation function for the réaction pp ->- AA /OÍ* p a r e S-vave (o •* c ) and P-uave (a « € u h e r e M e e x c e s s

energy e. - /g-2m„. The hatched area indicates the region alase ta threshold uhere a final otate interaction man be expected.

343 -

Upgrading of CERN pp Collider and Experiments

- 3 4 4 -

THE SPS P -PBAR COLLIDES.

PRESENT PERFORMANCE AMD FUTURS PROSPECTS . „

- D: 841U02631 7 B. de Raad

CERN, Geneva, Swi tzer land.

1. INTRODUCTION

The SPS p-pbar c o l l i d e r has now operated for a t o t a l of S months and has de l i ve r ed an i n t e g r a t e d luminos i ty of ISO nb 1 t o each of the two experiments UAl and UÀ2. The ope ra t ion of the a c c e l e r a t o r complex i s we l l mastered and the performances a re s t e a d i l y improving.

The peak luminos i t y reached in 1983 was 1.6 X 1 0 a s c m ~ 2 s " 1 , a luminosi ty l i f e time of about 16 h , which i s compatible with one r e f i l l

per day, a t y p i c a l product ion r a t e being 4 nb 1 per day.

The presen t peak, luminos i ty i s a f a c t o r 6 below the o r i g i n a l design £ iguce of 1 0 B O o m ~ a s ~ l for the CERN p-pbar proj e c t , e s s e n t i a l l y s i nce the an t ip ro ton c o l l e c t i o n r a t e i s lower by about the same f a c t o r . The CERN p-pbar improvement program, which i s cen te red around the cons t ruc t ion of the an t ip ro ton c o l l e c t o r ACOL, i s aimed a t inc reas ing the product ion r a t e of the SPS c o l l i d e r up t o 50 nb~* per day.

This paper de sc r ibe s the p resen t performance of the SPS and the developments which are I D p r epa ra t ion t o dea l wi th Mgher an t ip ro ton

Z. OPERATIONAL RESULTS 2 .1 Review of p a i t c o l l i d e r rung

The f i r s t p ro ton -an t ip ro ton c o l l i s i o n s a t a c e n t e r - o f - M s s energy of 540 GeV were observed in the SPS on the 10th J u l y , 1981. The f i r s t physics run took place a t the end of 1981 and produced a t o t a l i n t e g r a t e d luminos i ty of

- 345 -

0.2 ab~l. Duri ng the second r u a , from Oc bober t o December 1982, the machine operated wi th 3 bunches of protons c o l l i d i n g aga ins t 3 bunches of a n t i p r o t o n s with be ta va lues a t both experimenta of fi*H= 2m, ß * v = Im. The proton bunch i n t e n s i t y reached i t s des ign va lue of 1 0 a l p t whereas the an t ip ro ton bunch i n t e n s i t y was l imi t ed to around 1.3 X 1 0 1 0

a n t i p r o t o n s . The peak luminos i ty reached S.3 X 10 a > cm *s 1 and the t o t a l i n t e g r a t e d luminos i ty was 28 nb 1 .

From Apr i 1 t o June 1983, the SPS opera ted in e s sen t i a l l y the same conf igura t ion but the longer du ra t ion of t h i s t h i r d run , an increased proton i n t e n s i t y , f u r the r reduced B*'s, and b e t t e r o p e r a t i o n a l s k i l l for a l l machines of the p ro ton -an t ip ro ton complex r e s u l t e d i n a peak luminosi ty of 1.6 x 1 0 a * c m - 3 s - 1 and an i n t e g r a t e d luminosi ty de l i ve r ed t o each of tbe two experiments of 153 ab \

2.2 Operation

s t a r t i n g up a cold machine may t ake 24 hours , but a ca re fu l readjustment dur ing r o u t i n e opera t ion i s u sua l ly c a r r i e d out in 4 t o 6 hour s . This happens two to t h r e e times a week, i f pos s ib l e during working hours when s p e c i a l i s t s a r e more e a s i l y a v a i l a b l e . During week-ends, one t r i e s t o p r o f i t from the b e t t e r o v e r a l l s t a b i l i t y to have longer runs and f a s t e r r e f i l l s . F i l l i n g times of down t o one h m r have been achieved.

Opera t iona l techniques have been developed t o cope with the machine "mode" changes and with t he requirement of r e l i a b l e d a t a - t a k i n g a t i n j ec t i on and during the s t o r e . Tbe f i r B t of t h e s e problems - for ins tance b r ing ing the machine out of s t o r e and prepar ing for proton r e - i n j e c t i o n from the SPS back i n t o the CPS t o check tbe t r a n s f e r l i n e - was t ack led using a mul t ip rocessor job con t ro l s t r u c t u r e 1 * c a l l e d the "sequencer" . Using t h i s , t he execution of a l i s t of up t o 60 programs can be def ined o f f - l i n e , each such l i s t i s c a l l e d a sequence. Tbe most complex of these sequences c o n t r o l s the countdown t o p-pbar i n j e c t i o n . This switches some a c t i v e equipment but mainly ensures t h a t da t a - r ead ing equipment i s armed and t h a t a l l beam measurements a re saved for r e f e r ence . Software s t r u c t u r e s have a l s o been developed t o ga the r and archive da t a dur ing s t o r a g e .

Tbe success of the run owed much t o the e x c e l l e n t r e l i a b i l i t y of t he AA

which on one occasion kept i t n beam for a record 30 days . The AA-SPS t r a n s f e r

- 3 4 6 -

e f f i c i ency r eac t ed 80%. with 10% l o s t a t e x t r a c t i o n from the CPS and 10% a t low energy in the SPS.

2.3 Performances for phys ics

Figure 1 shows the i n t eg ra t ed luminosi ty for the 1983 c o l l i d e r run. After a l abor ious s t a r t - u p c h a r a c t e r i z e d by low t r a n s f e r e f f i c i ency and h e c t i c o v e r a l l c o n d i t i o n s , a r egu la r opera t ion could be e s t a b l i s h e d producing an average of 2 nb 1 per day under cond i t ions s i m i l a r to those a t the end of 1982. Through a number of improvements the performance increased s t e a d i l y u n t i l a f t e r a s h o r t t e c h n i c a l s top t he product ion reached a record of 6 nb~ l per day. Towards the end, t e c h n i c a l f a i l u r e s in the AA, CPS and SPS, and heavy d a i l y storms reduced the product ion r a t e .

A shor t run was made in a high be ta conf igura t ion ( ß * H = ß * v = 100 m) t o a l low d a t a - t a k i n g on e l a s t i c s c a t t e r i n g a t very small angles (> 0.4 mrad) .

nb-1

i. i l l i l l

Werts 1983

Fig 1 . I n t e g r a t e d SPS luminosi ty in the 1983 c o l l i d e r run .

- 3 4 7 -

Table 1 g ives a comparison of the b e s t r e s u l t s ob ta ined in the c o l l i d e r runs of 1982 and 1983. The d i s cus s ion of the performance l i m i t a t i o n s given below w i l l be based on the 1983 column of t h i s Table .

Table I. Best Co l l i de r Performance in 1982 and 1983

1 10R? 1 1983

AA s tack ing r a t e (10*pbar h " 1 ) ! 5.5 1 1 1 6.6 1

Transfer e f f i c i ency 1 70* I 75S 1 p i n t e n s i t y per bunch ( 1 0 1 1 ) 1 1 1 1.4 1 pbar i n t e n s i t y per bunch d o 1 1 ) j .13 1 -15 1 number of p and pbar bunches 1 3 1 3 1 Normalized emi t tances 1 1 1 <».10~* rad.m) p 1 20 1 18 1

pbar 1 15 1 14 1 Beam-beam parameter Ç 1 0.0025 1 0.004 1 B*H (m), B* v (m) 1 2 i 1 1 1.3 1 . 0 6 5 1 Luminosity a t s t a r t of coas t / j /

1 0.53 1 1.6 1 Luminosity l i f e t i m e (h) 1 18 1 16 1 I n t e g r a t e d luminosi ty ( n b - 1 ) 1 1 1

per day 1 2.2 1 6.2 1

3 . BEAM PARAMETERS AMD PERFORMANCE LIMITATIONS

3.1 Antiproton i n t e n s i t y

The maximum product ion r a t e of the AA is a t p r e sen t 6.6 x 10* pbar/hour and t h e r e f o r e a d a i l y f i l l of the c o l l i d e r could i d e a l l y consume up t o 1.6 X lo" pbac. Unfor tunate ly the AA i s not always funct ioning a t i t s optimum while breakdowns in the CPS. s e t t i n g - u p of the SPS with protons and the need t o se rve o the r use r s af the CPS decrease the number of protons a v a i l a b l e for pbar p roduc t ion . Furthermore, about 50% of the s t o r e s end prematurely by a t e c h n i c a l f a u l t in t he SPS o r too l a r g e a v a r i a t i o n cf t he mains vo l t age , which reduces t he a v a i l a b l e AA B t ack ing t ime . As a consequence, t he maximum i n t e n s i t y e x t r a c t e d from the AA in one f i l l has bees 0 .8 x lO 1 1 pbar , with r o u t i n e va lues around 0.6 X 1 0 1 1 l ead ing to 3 bunches o í 1.5 x 1 0 1 0 each s t o r e d in t he SPS.

3.2 Proton i n t e n s i t y and emit tancos

The proton i n t e n s i t y i s l i m i t e d 3 ' t o i . û x l o 1 1 p/bunch by l o n g i t u d i n a l i n s t a b i l i t i e s during a c c e l e r a t i o n and by the L a a l e t t space charge detuning a t the i n j e c t i o n energy of 26 GeV. The normalized t r a n s v e r s e emi t -

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tance c* = cßy of these intense proton bunches is usually about 18ir X 10~* cad.ra. (Eraittances are defined at 2a, i.e. c = 4o a/beta).

3.3 Antiproton lifetime at 270 GeV

the antiprotons are strongly perturbed by the crossings with the intense proton bunches while the protons are practically not affected by the weak antiproton beam.

The tune diagram at 270 GeV is shown in Fig. 2. All protons have approximately the same working point Q^. The average tune shift experienced by a small amplitude antiproton at each crossing with a proton bunch is equal to the be am-beam parameter \, resulting in a total incoherent tune shift per turn of ÛQ = 6 x 0.004 = 0.024 in the present operation wi th 3 proton against 3 antiproton bunches. The small amplitude antiprotons therefore have the working point Qpbar.

Large amplitude antiprotons experience a smaller Q-shift because of the reduced particle density in the transverse tails of the proton bunches. The antiproton beam therefore occupies the cigar-shaped region shown in Fig. 2 extending from Q p to Q p D > r » Btraddling the resonances of order 13 and 16 for the large amplitude antiprotons and some resonance lines of order 10 for the snail amplitude antiprotons.

The SPS collider is operating in the weak-strong régime' 3> in which

. 6 7 .70 Û H

M S - 2 7t>. time HtgtêM tt 270 CeV.

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The rate of amplitude blowup of an antiproton caused by the repeated ticke in the strongly nonlinear field of the proton bunches is s rapidly increasing function of the antiproton amplitude. In the situation of Fig. 2 where only the small amplitude antiprotons touch the 10th order resonance, the beam-beam limited lifetime of the antiprotons is about 50 hrs. whereas an increase of 0.01 of the Q-value of the SPS decreases this lifetime to about 15h.

For this reason a large effort has been made to improve the stability of the machine parameters, which used to be a limiting factor for the antiproton lifetime. In particular the stability of the tunes which is essential for e good lifetime has been improved by a new current regulation system for the main magnet power supplies. Short-term variations, measured from the width of Schottky lines 4*, are smaller than ÄQ = 3 X 10~*. Long term drifts, possibly due to thermal effects, of a few times 10 3 , are corrected by programming the magnet currents.

The antiproton loss caused by the noise of the RF system corresponds to a lifetime of about 200b, so that the actual lifetime of the antiprotons in the SPS is 40 h (average value over a 20h. coast).

3.4 Antiproton omittances

The need for a good antiproton lifetime places a high premium on a small antiproton emittance. The design values of the cooled AA beam emittances are e* v = 3.7* x 10"*, e* a = 5.2* x 10"* rad.m and the best performances achieved so far closely approach these values.

Great care must be taken in setting up the transfers between the machines to avoid emittance dilution due to injection errors. The CPS/SPS transfer is particularly critical because it must accept a beam of 0.6 % momentum spread. Early in the 1983 run the dispersion vector between the two machines was carefully matched. As a result the beam can now be transmitted in good conditions with a blow-up factor of the order of two, which gives in storage «n eoittance of 12 w x l0~*r*d.». Unfortunately, deficiencies of the AA cooling system or badly adjusted transfers can result in a stored emittance a i high a s 18 « X 10 * rad .m leading to a reduced lifetime of the antiproton bunches. This i» illustrated in Fig. 3 where the loss rate of

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t h r e e an t ip ro ton bunches of the same i n t e n s i t y but with d i f f e r e n t i n i t i a l emit tances a re compared. Ant iprotons whose amplitudes exceed the average dimension of the s t rong proton beam a re r ap id ly peeled off, a f t e r which the decay r a t e approaches the same va lue fo r a l l t h r e e bunches.

Time (hours)

Fig . 3

Decay r a t e of pbar bunches wi th d i f f e r e n t emi t t ances . Emittance of the an t ip ro ton bunches c*^ => 17», c* = 15* . c* = 12w.

y z Emittance of pro tons 17*. Beam-beam parameter I = 0 .004.

3.5 Proton l i f e t i m e a t 270 GeV

The n i t rogen equ iva len t gas p ressu re for m u l t i p l e Coulomb s c a t t e r i n g of 1.2 x 1 0 ~ 1 0 ntbar in the SPS can only account for an omit tance growth of t he protons which i s an o rde r of magnitude lower than the measured v a l u e . In a d d i t i o n , t he l o n g i t u d i n a l omit tance of t he denBe proton bunches grows cons iderab ly f a s t e r than t h a t of the weak an t ip ro ton hunches.

Al l these f e a t u r e s were po in t ing towards . in t ra-beam s c a t t e r i n g , i . e . m u l t i p l e Coulomb s c a t t e r i n g between protons in t he same bunch. Careful measurements of l o n g i t u d i n a l and traoBverse growth r a t e s under d i f f e r e n t cond i t ions of i n t e n s i t y and emi t tances were found in good agreement wi th the t h e o r y * > .

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Longi tudina l ly the high i n t e n s i t y bunches blow up u n t i l the t a i l of t h e i r d i s t r i b u t i o n reaches t he bucket s e p a r a t r i x . Thereaf te r protonG s ta-*- t o l e a k out and an equ i l ib r ium d i s t r i b u t i o n is e s t a b l i s h e d . Because of the d i s p e r s i o n in the machine and the coupl ing of h o r i z o n t a l and v e r t i c a l b e t a t r o n o s c i l l a t i o n s , iutrabeam s c a t t e r i n g a l so causee a growth of the t r a n s v e r s e emi t t ances . Por the parameters of Table 1 , the r e s u l t i n g proton l i f e t i m e i s 60 h , whi le the e fo ld ing time of the emit tance growth i s 50h. (average values over a 20h c o a s t ) .

Combined with an an t ip ro ton l i f e t i m e of 40h. t h i s leads to a luminosi ty l i f e t i m e of 16h.

3.6 Space charge e f f e c t s a t i n j e c t i o n .

The tune spread of the an t ip ro tons caused by the beam-beam e f f e c t a t the i n j ec t i on energy of 26 GeV i s t he same as a t 270 GeV, s ince the e f f e c t s of the lower p a r t i c l e energy and the l a r g e r emit tance a t low energy c a n c e l . However, the incoherent L a s l e t t space charge detuning of the in tense proton bunches, which i s n e g l i g i b l e a t 270 GeV, i s p r o p o r t i o n a l t o 1/y 2 and a t 26 GeV amounts to 4Q « -0 .003 for email amplitude p ro tons . Similar t o t he case of the beam-beam e f f e c t , the l a r g e amplitude protons bave a smaller aQ. By choosing Q„ = 26.70 and Q„ = 26.71 i t i s j u s t p o s s i b l e t o keep the pro tons above the t h i r d o rder resonance Q v = 26 and the an t ip ro tons below the four th o rder resonance = 27 . The i n j e c t i o n of 3p + 3pbar bunches

r e q u i r e s a "coas*" a t 26 GeV of 14.4 s and t h i s du ra t i on i s shor t enough for l o s s e s by resonances above the four th order to be unimportant .

3.7 The low beta i n s e r t i o n s

The design conf igurat ion** with ß*^ = 2m, ß * v = Im in both experiments which bad been commissioned in 1982 was used up to the middle of the 1983 run . Af te r the t e c h n i c a l s top i t was pushed t o JB*^ = 1.3m. ß * y = .65 m wi th the expected gain in luminosi ty of a f a c t o r l . S , which is apparent in F i g . i .

In on experiment a t t he end of the per iod the be ta* were f u r t h e r reduced t o B* H 9 1» , B * v = 0 .5b . Even in t h i s s i t u a t i o n the ch rona t i c a b e r r a t i o n s could B t i l l ba cor rec ted and i t i s planned t o use t h i s low beta conf igura t ion during the 1984 run .

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4. FUTURE DEVELOPMENTS

4.1 Collider operation at 310 GeV

During the winter shutdown at the beginning of 1984 the main power supplies have been upgraded and pumps have been added to the water coaling system of the magnets to permit collider operation at 310 GeV in the autumn of 1984. The gain in luminosity, because of the smaller beam cross-section at the higher energy, is about 15% but since the cross-sectionB increase rapidly with increasing energyi the production rates for W E and 1 will he enhanced

o by a factor 1.5 and those for high p , jets by a factor 2.

4.2 The low beta insertions

The existing low beta insertions were designed for ß * H X ß * v = 2m X lm at 270 GeV and they will now be operated with ß * H X B* v = 1m X 0.5 m at 310 GeV. This corresponds to the maximum strength of the existing low beta quadrupoles. Furthermore, tbe resulting large chromatic aberration, which is inversely proportional to ß* for a given quadrupole layout, is at the limit of what can be compensated with the 4 existing families of chromâticity sextupoles of the SPS.

To decrease the B*-valuea further it is necessary to use stronger, smaller aperture low beta quadrupoles which are placed closer to the crossing point. Possible layouts are being studied and an increase in luminosity of about 20% seems possible.

4.3 Increased antiproton intensity

The order of magnitude increase of the available number of antiprotons resulting from the construction of ACOL will, of course, mainly be used bo increase the antiproton intensity and therefore the peak luminosity, in the S?S. In addition, it will also give the possibility of more frequent refills of the SPS. This will increase the ratio of average to peak luminosity during a coast and will also improve the overall efficiency of the collider operation by allowing a more rapid refill after a technical fault.

At present the collider is optimized for a weak-strong regime and it is not clear whetiic. the machine would work with the same beam-beam parameter ç

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in a strong-strong régime. Nevertheless, the present conditions, with the well-proven 3 bunch mode should remain valid up to about 6 x 1 0 1 0 pbar/ bunch, a factor 4 about the present pbar intensity.

4.4 Beam separation

To increase the luminosity further will require operation with 6 bunches in each beam. With the same proton intensity per bunch and therefore the same beam-beam parameter Ç = 0.004, the incoherent Q-shift per turn of the antiprotons then becomes ÛQ - 12 X 0.004 = 0.048 and inspection of Fig. 2 shows that this would place the antiproton beam right across the 10th order resonances. In an experiment where one pbar bunch was stored together with 6 dense p bunches, the pbar lifetime was reduced by a factor 4.

Therefore a scheme has been proposed 7^ to separate beams of up to 6 bunches everywhere except: in the detectors UAl and UA2 and at one point in between. This reduces the total number of bunch crossings per turn to 3, i.e. even a factor 2 lower than in the present 3 bunch mode of operation. An accurate compensation of the deflections will be needed to make the beams collide head-on in the useful intersections. An experiment has shown that a difference in orbit of 0.2 rms beam size already halves the antiproton lifetime because of the appearance of all the nonlinear terms of order (2a + 1) in the beam-beam force.

During tbe last winter shutdown, 4 existing separator tanks have been installed in the SPS to enable tests on beam separation to be made during the autumn 1984 run.

4.5 A 100 MHz RF system

The existing RF system of the SPS operates at a frequency of 200 MHz.. A

100 MHz RF syptem** with a moderate voltage of 2MV would be adequate to hold the bunches at 310 GeV but since the bunch length would be twice as large, the intrabeara scattering of the protons would be reduced or alternatively a somewhat larger proton intensity would be tolerated. (Tbe beam-be am effect remains unchanged since it is independent of the bunch length).

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Also at injection the 100 MHz system has advantages. The longer proton bunches have a smaller incoherent Laslett space charge detuning, thus leaving more space in the tune diagram for the beam-beam induced Q-spread of the antiprotons. Alternatively, this could be used to increase the intensity of the injected proton bunches.

As the antiproton Intensity in the AA increases, the longitudinal emittance of the extracted antiproton bunches may also increase. Also in this situation a 100 MHz system in the SPS has strong advantages since it permits to capture antiproton bunches which are twice as long, whereas the CPS extraction channel does not allow to increase the momentum spread above the present value ûp/p = i 3 X 10 a .

The 2MV of the proposed 100 MHz RP system are not sufficient for acceleration. The solution is, to adiabatically convert each single 100 MHz bunch into two bunches at 200 MHz, to accelerate with the 200 MHz system up to 310 GeV and then to recombine the two bunches again into a single one.

The small values of beta at the crossing point are associated with a strong beam divergence. Therefore the longer bunches of the 100 HHa system would reduce the luminosity for the UAl detector by 7% while for the UA2 detector, which has a limited acceptanc«, this reduction becomes 18%.

In the case of stochastic cooling of the stored beams, which is being studied for the SPS**, the cooling times are reduced by a factor two by doubling the bunch length and in the case of a 100 MHz RF system, the cooling times could just be made equal bo the presently observed luminosity lifetime of 161).

In general, a 100 HHz, Rf system provides a great flexibility to adapt the proton and antiproton bunches to the best operating conditions for maximum luminosity.

5. CONCLUSION

The SPS collider has now become an operational machine and its present luminosity has already led to very important physics results.

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I t s planned improvements should permit to t ransform the increased an t ip ro ton i n t e n s i t y r e s u l t i n g from the cons t ruc t ion of ACOL i n t o a t en fo ld inc rease in luminos i ty .

References

1 . C. Sal tmarsh, A mul t ip rocesso r , m u l t i - t a s k c o n t r o l s s t r u c t u r e for the CERN SPS -

Conference on Computing in Acce le ra to r Design and Operat ion, B e r l i n ,

20-23 Sept . 19B3.

2 . J . Gareyte , The SPS p-pbar C o l l i d e r , CERN SPS/B4-3 (DI-MSD, Lecture given a t the CERN Acce le ra to r School Course on Ant iprotons for Co l l id ing Beam F a c i l i t i e s , CERN, 11 - 21 October, 1983.

3 . L.R. Evans, The Beam-Beam I n t e r a c t i o n , CERN SPS/83-38 (DI-MST), Lectures given a t tbe CEJttl Acce le ra to r School Course on Ant iprotons for Co l l id ing Beam F a c i l i t i e s , CERN, 11 - 21 October, 1983.

4 . T. Linnecar and U. Scandale , Continuous tune measurements using the Schotbky d e t e c t o r , US P a r t i c l e Acce le ra to r Conference, Santa Fe, 21 - 23 March, 1983, IEEE Trans . Nucl. S e i . Vol . KS-30. No. 4 p . 2185-2187.

5. L.R. Evans, Intrabeam S c a t t e r i n g in the SPS Antiproton C o l l i d e r , 12th I n t . Conf. on High-Energy P ro ton -Acce l e r a to r s , Fermi lab . Ba tav ia , 111 . U.S.A. , 11 - 16 August, 1983.

6 . P .E. Faugeraa, A. Faugie r , A. H i l i a r e and A. Warman, The Low Beta I n s e r t i o n s of the SPS Proton-Ant iproton C o l l i d e r , 12th I n t . Conf. on High-Energy A c c e l e r a t o r s , Fermi l a b , Ba tav ia , 1 1 1 . , U.S.A., 11 - 16 August, 1983.

7 . L. Evans and A. Faug ie r , Beam-beam sepa ra t ion us lng e l e c t r o s t a tic d e f l e c t o r s , r.SKS SPS/DI-MST/Note 8 3 - 1 .

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8. D. Boue sard, A I0t> MHz K? syBtem in the S P S ,

CBRfJ SPS/ARF/Note/DB/gw/83-83.

9 D. Boussard, S. Chattopadhyay, 6. Done and T. Linnecar, Feasibility Study of Stochastic Cooling of Benches in the S P S . Lecture given at the CERN Accelerator School Course on Antiprotons for Colliding Bean Facilities, CERN, 11 - ZI October. 1983.

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CERN'S pp SOURCE

b ; B410O26325 R. B i l l i ngs

CËRN, Geneva, Switzerland

1 I H T R O D U C T I O H

The in t ense bunches of protons and r . i t iprotons needed for the SPS Col l ider are provided by the PS Complex as one of i t s many modes of opera t ion . The PS Complex which began opera t ion twenty-f ive years ago (November, 1959 1 cons is ted of a 200 m diameter proton synchrotron, fed by a 50 tieV Alvarez Linac ( f i g . 1 ) . The same synchrotron i s now the hub of a complex of ten in t e rconnected machines ( f i g . 2 ) , s ix of which are in operat ion and a fur ther four under cons t ruc t ion . To da te in addi t ion t o beams of protons at a whole range of ene rg ie s , i n t e n s i t i e s and s p i l l t imes, a n t i p r o t o n s , H ions , deuteroos and alpha p a r t i c l e s have been provided and the l i s t i s shor t ly to be extended to include Oxygen ions , e l ec t rons and p o s i t r o n s . In what follows [we **vaLL descr ibe how an t ip ro tons are produced, accumulated, compacted by s t o c h a s t i c cooling then acce le ra ted and shaped for t r a n s f e r t o the SPS. j ¡Q/i^t, j n ^ T ~\

2.4 secondai of protons a t 26 GeV/c, which i s focused onto a 3 mm diameter copper t a r g e t . In order to match the circumferenca of the Antiproton Accumul a t o r (AA) the production beam must occupy only a qua r t e r of the PS machine circumference. To achieve t h i s the four r ings of the Booster Synchrotron are f i r s t f i l l e d by a 150 mA proton beam from Linac I I . Following acce l e ra t ion to SOD MeV the beams i r e ex t rac ted from two r ings a t a time and combined vert i c a l l y for i n f ec t i on i n t o tne PS, This g ives two s e t s of f ive double r . f . bunches of protons to be acce le ra ted an harmonic number h=ZQ. Once acce le ra ted to 26 GeV. the r . f . system i s divided in two opera t ing on harmonic numbers 19 and 21 such t ha t the two s e t s of f ive bunches approach each o ther az imuthal ly . When they ovelap. thus occupying i M t h of the PS circjroference, they are ejectod and t ranspor ted to the production t a r g e t where pulsed quadrupaJ.es focus the beam to a spot s i ze of about 2 mm diameter .

2 OVERALL SCHEUE

2.1 Antiproton Production

The an t ip ro tons a re produced by an in tense beam (up to 1.5 x 10 every

http://quadrupaJ.es

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7.7. t n t i n m t o n Col lac t ion

Antiprotons a re c o l l e c t e d around a momentum of 3.5 GeV/c, corresponding t o the peak of the production spectrum. A pulsed magnetic focusing horn j u s t a f t e r the t a r g e t is used to capture a momentum b i t e of I.5Z at angles up t o 50 mrad. This is then t r anspor t ed and matched i n t o the AA machine ( f i g . 3 ) . This machine is designed to accommodate widely separa ted o r b i t s for a t o t a l momentum range of 62.

The newly in j ec t ed an t ip ro tons occupy a momentum spread of 1.51 and t r ansve r se emit tances of mo ¥ mm.mrads. In some of tne l o c a t i o n s where they are widely separa ted from previous ly stacked: a n t i p r o t o n s , they are separated from the stack by moveable f e r r i t e s h u t t e r s , which form the inner s ide of s i n g l e turn t r a n s former- l ike s t r u c t u r e s . These c o n s t i t u t e the s t o c h a s t i c Pre -Cooling System which d e t e c t s and reduces the v a r i a t i o n s in r evo lu t ion frequency such tha t the momentum spread i s reduced from 1.5Z to D.2I in about 2 seconds. After t h i s , the s h u t t e r s are opened, and a convent ional r ad io frequency system i s used to capture the p a r t i c l e s and move them inwards ( d e c e l e r a t i o n ) where they ara deposi ted in the low d e n s i t y " t a i l " of the an t ip ro ton s t ack . From t h e r e , they are p rogress ive ly cooled in t r a n s v e r s e phase space and compacted in momentum towards the dense s tack core . Each 2.4 seconds, a new pulse of a few mi l l ion an t ip ro tons i s i n j ec t ed , pre-cooled and stacKed, so t ha t a f t e r about two days the dense s tack reaches a few

A dense bunch of an t ip ro tons i s then captured from the s t i c k by the r . f . system, acce le ra t ed out t o the i n j e c t i o n / e j e c t i o n o r b i t and ex t r ac t ed from the machine. I t is t r anspo r t ed to the PS and in jec ted counter -c lockwise , then acce l e r a t ed from the accumulation momentum of 3,5 GeV/c to 26 GeV/c. At t h i s s t age , the bunch of a n t i p ro tons nas a lengtn of a few hundred nanoseconds - much too long to f i t i n t o a s i n g l e 2Q0 hHz bunch in the SPS. To achieve the l a t t e r , the PS r . f . system makes a phase jump to the uns tab le f ixed point so t h a t the hunch s t r e t c h e s out I f i g . 41, Then the phase i s re tu rned t o t he s t a b l e point and with maximum ava i l ab l e vo l t age , the long, t h i n bunch r o t a t e s u n t i l i t occupies a momentum spread of +. 0.<Z and a bunch length of 3 ns .

I t i s then t r a n s f e r r e d t o the SPS and captured i n t o a s ing le ûnch of the 200 HHz a c c e l e r a t i n g system. This process i s repeated t h r e e times with a n t i -p ro tons , having been preceded by th ree bunches of p ro tons , s i m i l a r l y sho r t ene -d. and the c o u n t e r - r o t a t i n g bunches of protons and an t ip ro tons a re then acce l e r a t ed toge the r up t o t he SPS c o l l i s i o n eneigy of about 300 GeV.

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3 PERFORMANCE AHO FOTPRE UPGRADING

The o r i g i n a l design aims of the Antiproton Accumulator 1 ' corresponded to c o l l e c t i n g 2.5 x 10 7 p'S in a momentum range of l .Sjt and t r a n s v e r s e omit tances of tOO i mm mrads, each 10 protons on t a r g e t and each 2.4 seconds. This , a f t e r 20 hours of s tacking and coa l ing , was to give 6 x 1Q1 p ' s in 0.3Z momentum and t r a n s v e r s e omit tances of 1.4 r x 1 f ram mrads. This corresponds to an inc rease in phase-space dens i ty g¿.ven by

? * x l ^ i „ " 0 ir « 100 ir s B B k 1 0 8 2.5 X 10 0.3X 1.4 IT X 1 ir

subsequent ly , i t was found t ha t the assumed y ie ld was o p t i m i s t i c by more than a fac tor 2 and the achieved cooling r e s u l t s in a d e n s i t y inc rease

1 H 1D 0 . 3 1 2 v M 1 . 5 T

a f t e r about to hours of accumulat ion.

2) I t i s now proposed t o inc rease tne c o l l e c t i o n r a t e by about t f a c t o r 10.

This improvement p ro jec t has thre>. main components: t a r g e t t i n g , a c o l l e c t o r r ing 1AC0LJ and upgrading of the AA s t o c h a s t i c cooling systems to cope with the higher f lux .

In the f i r s t component, i t i s intended t o use powerful Lithium Lens focusing devices around a t a r g e t through which a high cu r ren t i s pu lsed . In t h i s way i t i s hoped to cap ture a 6Z momentum range and t r a n s v e r s e omit tances of 200 i mm mrads.

This beam w i l l then be captured i n the new r i n g being b u i l t around the AA ( f i g . 5) by a spec ia l r.f. system which w i l l first r o t a t e the shor t bunches in phase space, thus exchanging bunch length for momentum spread, and then a d i a b a t i c a l l y debunch t h i beam. In t h i s way the momentum spread i s reduced to 1.5Î. Next, t r a n s v e r s e cool ing w i l l be used to reduce the omit tances from 200 « to about Id T I M mrads and then the momentum i s cooled from t . 5 ï t o 0 . 2 1 .

This p r e - c o d e d beam of about 10 8 p ' s i s then t r a n s f e r r e d to the Accumulator, where cooling syst tms working up t o 4 GHz w i l l parmit t he accumul a t i o n of ov t r 10 an t ip ro tons per day. with t he s tack d e n s i t i e s a l ready achieved, t h i s would c o n s t i t u t e an adequate p source t o reach * luminosi ty of 1 0 3 ' a t 10 TeV.

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REFERENCES

1 . Design Study of a Proton-Antiproton Colliding Beam Facility. CEPN/PS/AA 78-3.

2. Design Study of an Antiproton Collector for the Antiproton Accumulator (ACOL). CERN 83-10.

Fig. 1 : The CERN PS in 1959

Fig. 5 : The ACOL Ring around the AA

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UAl IMPROVEMENT PROGRAMME

Presented by H. H o f f m a n n , CERN

No w r i t t e n contribution received

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UÄ2 FUTURE

Presented by P. J e n n i , C E R N

{Due to internal agreement of the UA2 C o l l a b o r a t i o n , no w r i t t e n contribution w a s submitted to the editors.)

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Fermilab pp Collider and Experiments

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T H E F E R M I L A B PP C O L L I D E R

D : 8 4 1 0 0 2 6 3 3 3 M i k e H a r r i s o n

F e r m i N a t i o n a l A c c e l e r a t o r L a b o r a t o r y * P . O . B o x 5 0 0 B a t a v i a , I L 6 0 5 1 0 USA

I n t r o d u c t i o n

1 9 8 3 s a w t h e s t a r t o f c o n s t r u c t i o n o n t h e F e n n l l a b p p c o l l i d e r , t h e

T e v a t r o n I p r o j e c t , a s w e l l a s t h e c o m m i s s i o n i n g o f t h e n e w s u p e r c o n d u c t i n g

a c c e l e r a t o r , t h e T e v a t r c n , f o r h i g h e n e r g y f i x e d t a r g e t p h y s i c s . [ " T h e g o a l o f

t h e T e v a t r o n I p r o j e c t i s t o a c h i e v e p p c o l l i s i o n s i n t h e c e n t r e - o f - m a s s e n e r g y

r a n g e u p t o 2 T e V w i t h a l u m i n o s i t y o f a t l e a s t 1 0 3 ° c m ~ 2 s e c ~ 1 . T h e p r o 1 " . . c i n

v o l v e s a d a p t i n g t h e T e v a t r o n t o f u n c t i o n a s a s t o r a g e r i n g a n d m o d i f y i n g t h e

l a t t i c e t o p r o v i d e l o w - b e t a I n t e r a c t i o n p o i n t s ; c h a n g e s t o t h e M a i n R i n g t o

a l l o w p t r a n s f e r s a n d t h e i n s t a l l a t i o n o f e x p e r i m e n t a l e q u i p m e n t ; a n d t h e c o n

s t r u c t i o n o f a p s o u r c e . M a j o r e x p e r i m e n t a l a r e a s w i l l b e l o c a t e d i n t h e s o -

c a l l e d BO a n d DO s t r a i g h t s e c t i o n s - ( d c - f e o i l o d d a o o r - i p f e i o n o - o f -thaaa a reas — { H S o a o n t o d - o l g o w h o r c - l a - t J i c o c p r o e c e d i a g p ) t o g e t h e r w i t h s m a l l e r , m o r e s p e c i a l i z e d

e x p e r i m e n t s i n s e v e r a l o f t h e o t h e r i n t e r a c t i n g r e g i o n s , Ô'fY^^j^f^

T h e a n t i p r o t o n s o u r c e c o n s i s t s o f a t a r g e t t i n g s t a t i o n a n d t w o s e p a r a t e

r i n g s ( t h e D e b u n c h e r a n d t h e A c c u m u l a t o r ) c o n n e c t e d t o t h e M a i n R i n g , t h e

B o o s t e r , a n d e a c h o t h e r b y v a r i o u s t r a n s f e r l i n e s ( s e e F i g u r e 1 ) . T h e D e b u n c h e r

r i n g p r o v i d e s a l a r g e a c c e p t a n c e f o r t h e p ' s p r o d u c e d o n t h e t a r g e t a n d p r e -

c o o l s t h e p ' s p r i o r t o i n j e c t i o n i n t o t h e A c c u m u l a t o r w h i c h s t o r e s a n d f u r t h e r

c o o l s t h e p ' e i n a s i m i l a r f a s h i o n t o t h e A A r i n g a t C E R N . T h e u s e o f t w o i n

d e p e n d e n t s y s t e m s f o r c a p t u r e a n d s t o r a g e a l l o w s t h e d e s i g n o f e a c h o n e t o b e

o p t i m i z e d o n t h e s o m e w h a t c o n f l i c t i n g r e q u i r e m e n t s w h i c h i n t u r n p r o d u c e s a

c o r r e s p o n d i n g l y h i g h o v e r a l l s y s t e m p e r f o r m a n c e .

I n o r d e r t o a c h i e v e a l u m i n o s i t y i n t h e r a n g e o f 1 0 3 " c m ~ 2 s e c ~ 1 t h e a n t i -

p r o t o n s o u r c e m u s t h e a b l e t o a c c u m u l a t e ~ 2 x l 0 1 1 p ' s w i t h i n a t i m e c o m p a r a b l e

t o t h e l u m i n o s i t y l i f e i ' i m e . H e a d o n c o l l i s i o n s a r e o b t a i n e d i n a l l s i x s t r a i g h t

s e c t i o n s b y i n j e c t i n g t h r e e b u n c h e s o f p r o t o n s a n d t h r e e b u n c h e s o f c o u n t e r -

r o t a t i n g a n t i p r o t o n s i n t o t h e T e v a t r o n . We p l a n t o m a x i m i z e t h e l u m i n o s i t y

l i f e t i m e b y u s i n g b u n c h e s o f t h e same t r a n s v e r s e e m i t t a n c e f o r b o t h p r o t o n s

a n d a n t i p r o t o n s ( 2 4 TT m m - m r a d i n v a r i a n t ) a s w e l l a s t h e same i n t e n s i t y t o m i n i

m i z e t h e b e a m - b e a m t u n e s h i f t f o r a f i x e d l u m i n o s i t y . W i t h a 8 * o f 1 m a t t h e

I n t e r a c t i o n p o i n t t h e d e s i g n l u m i n o s i t y i s a c h i e v e d u n d e r t h e s e c o n d i t i o n s

* ) O p e r a t e d b y t h e U n i v e r s i t i e s R e s e a r c h A s s o c i a t i o n , I n c . , u n d e r c o n t r a c t w i t h t h e U . S . D e p a r t m e n t o f E n e r g y .

- 369

with a 6x1o 1 0 particles per bunch which leads to a linear beam-beam tune shift of 0.0017 per crossing.

It is difficult to make an accurate estimate of the luminosity lifetime which arises from residual beam-gas scattering, intrabeam effects, beam-beam interactions and overall machine stability. Based on operational experience in the SPS amongst other things we have chosen a design specification of 5 hours for the luminosity lifetime. The design of the antiproton source has a predicted accumulation rate of -IxlO 1 1 p's per hour which provides UB with a safety margin of approximately 2.5 which hopefully will be sufficient to account for the inevitable operational inefficiencies in such a complex syetetn.

The sequence of events leading to pp collisions involves several distinct operations. We shall describe each step in more detail.

Proton Targetting The production of antiprotons for subsequent storage is accomplished by

the acceleration and targetting of protons from the Main Ring. Data from nuclear targets when taken with the energy dependence of the Main Ring cycle time1-* exhibit a broad maximum in p flux around an incident proton energy of 150 GeV. The desirability of locating the Antiproton Source near the Booster requires the protons to be extracted from the Main Ring at the F17 medium straight section (see Figure 1 ) . This extraction location effectively limits the proton energy to 120 GeV but only reduces the p flux slightly. The Main Ring cycle time at 120 GeV is approximately 2 seconds.

Cooling the initial flux of p*s is made easier if the phase space density at production is optimized. This is accomplished by minimizing the initial proton beam area and time spread. The proton beam area cannot be reduced arbitrarily since the temperature rise in the target is inversely proportional to the beam area for a fixed number of protons. The flux density which heats the target to the melting point defines the practical limit. Calculations show that a pulse of 2 x l 0 l z protons with an rms radius of 0.6 mm can be safely targetted on a 6 cm long tungsten-rehnlum target every 2 seconds.

A single Booster cycle will suffice to produce a batch of B2 53 MHz bunches of protons with an intensity of 2xl0 1 2. The normal time spread (several nsec) of the proton hunches will be reduced to 0.6 nsec by bunch rotation in the Main Ring just prior to extraction. This resulta in a momentum spread of 0.4% for the protons. The circulating beam is extracted in a single turn using a relatively slow rise time kicker magnet (-2 usees) located one sector upstream of the extraction channel in the E17 medium straight section.

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Antiproton Production and Transport The narrow bunches of protons produce equally narrow bunches of antiprotons

We chose to collect these p's at 8.9 GeV/c as this is almost the optimum momentum and it corresponds to the standard Booster energy, which greatly simplifies the re-Injection process and also allows the Booster to be used as a direct source of protons for reverse operation, for tune-up and commissioning purposes.

The yield of p's per incident proton Is proportional to the product of the solid angle and the momentum spread accepted by the collection system, hence these quantities should be optimised in an efficient design. We plan to collect p's produced in a 60 rarad core using a pulsed lithium lens 2 cm in diameter and 15 cms long producing a peak field gradient of 1000 T/m. Under these conditions we expect to produce -7xl0 7 ppp transported to the Debuncher ring with a momentum spread of Z"Á and an invariant emittance of 20 ir ¡tun-rarad in each plane.

The Debuncher Ring The primary purpose of the Debuncher is to reduce the large momentum spread

of the ß-GeV p beam at production to 0.2% prior to injection into the Accumulator. This reduction is accomplished by RF bunch rotation and adiabatic de-bunching after the p beam is injected into stationary 53 MHz buckets. The debunching time is only slightly greater than 10 msec, the remainder of the 2 second cycle is used for betatron cooling in each plane. The design calls for the reduction of transverse enilttance from 20 TT to 7 TI mm-mrad prior to injection into the Accumulator.

The Debuncher lattice consists of 57 P0D0 cells with a ~60° phase advance per cell, the regular quadrupole spacing is preserved throughout the 3 long straight sections where the RF, beam transfer and stochastic cooling systems are located. The maximum value of the beta function in either plane is ~20 m which keeps the beam size small enough to permit the stochastic cooling pickups and kickers to have a 30 mm aperture suitable for operation in the 2-4 GH2 range. The Debuncher ring operates above the transition energy (y^ = 7.66) with a natural chroraaticity of - -10 in each plane. This choice of machine lattice requires an RF voltage of S MV for the bunch rotation and debunching. Table 1

lists the major machine parameters.

Table 1. Debuncher Lattice Parameters

Nominal tune v x = v y

Y T

Transverse acceptance Momentum acceptance Natural Chromatlcity £ x , £y Maximum Amplitude function ßt

9.75 7.66 20 T mn-mrad

-10.A, -10.6 20 m

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Table 1. (Cont.) Debuncher Lattice Parameters

Maximum Dispersion function Timax 2.1 m R.F. Voltage 5 MV Machine Circumference 505 m Superperiodicity 3.

The horizontal and vertical betatron cooling systems consist of 4 modules of pickups and 4 modules of kickers. Each pickup module has 32 pairs of loop couplers with a maximum response at 3 GHz. The signals from each side are added in phase and subtracted from each other to give a final signal proportional to the bead position. Signals from 2 modules aro ¿dded to each other amplified by 40 db and added to a similar signal generated 180' away in betatron phase. The resultant is further amplified by 40 db and then split and used to drive the 4 kicker modules arranged in a similar fashion to the pick-ups.

With the very low beam intensity in the Debuncher the pickup signal is dominated by thermal noise in the termination resistor and the preamplifier. To optimize the signal-to-noise ratio the pickups and the preamplifiers are cooled to liquid nitrogen temperatures. A schematic layout of the Debuncher and Accumulator cooling systems is shown in Figure 2.

After 2 seconds the beam is transferred from the Debuncher to the Accumulator by a fast kicker magnet and magnetic septa located in the #10 straight section. The injected orbit in the accumulator is displaced in momentum by -0.9% from the central momentum of the stack core.

The Accumulator The Accumulator is desi£ned to cool and accumulate a flux of - 1 0 1 1 p's

per hour up to a maximum of 12 hours. To provide operational flexibility the accumulator should also be capable of storing cooled p's for much longer than the accumulation cycle.

The Accumulator possesses six independent cooling systems which provide horizontal and vertical betatron, and momentum cooling for both the newly injected batch of p's (the stack tall) and the circulating beam (the core). The momentum cooling systems require pick-ups in high dispersion regions and kickers in zero dispersion ones. The core betatron cooling takes place in zero dispersion areas, the stack tail betatron cooling in high dispersion ones. The physical layout of the cooling systems is shown In Figure 2. The lattice which accommodates this layout consists of 6 16 m straight sections which alternate between zero and high dispersion. The high dispersion (9 m) was achieved by concentrating the bending around the appropriate straight sections which gives the ring Its' characteristic triangular shape. The beta functions

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throughout the straight sections are leas than 16 m which allows an aperture of 30 mm to be used for both the pickups and the kickers.

The gain of the stack tail momentum system must be large In order to move the incoming p's from the stacking orbit to the tail of the core distribution before the next pulse of p's. This large gain will cause thermal noise In the bandwidth of the core unless the appropriate frequencies are strongly suppressed (Ï40db). This is achieved by a system of notch and correlation filters which in turn provide practical limitations on the maximum bandwidth D Í the stack tail cooling system which was chosen to be 1-2 GHz. The requirement of non-overlapping Schottky bands In this frequency range together with the aforementioned aperture limitations defined the Accumulator acceptance for incoming p's to be Ê 10 IT mm-mrad in both planes. The momentum spread of the Incoming flux (0.2%) is limited primarily by the output power of the stack tail momentum system. The core momentum cooling system is similar but somewhat simpler than the s_ack tail and will operate in the 2-4 GHz region. In a similar fashion to the Debuncher ring thermal noise will be minimized in the pickups and preamplifiers by operating these devices at liquid nitrogen temperatures. To provide acceptable performance with regard to transmission losses and dispersion in the frequency ranges required the notch filters consist of a 1.6 mm, 50 Ü superconducting transmission line immersed in a liquid helium cryostat. Each notch filter is driven by a travelling wave tube amplifer rated at 200 W of saturated output power. The design output power for each element is -40 W which is well beneath the quench level for the notch filter (-200 W ) .

The gain profile of the various cooling systems are adjusted by displacing the appropriate pickups by a different amount relative to the central orbit. There are 3 series of pickups (-25 MeV, -1 MeV, 16 MeV) appropriate combinations of each output can he made to maximize the required signal, for example by subtracting the -1 MeV signal from the 16 MeV one the amplifed Schottky signal from the core particles is essentially zero. The particle density with respect to energy is shown in Figure 3.

Antiproton-Proton Collisions After cooling and accumulating -5x10* 1 p's the Accumulator will be ready

to transfer beam for subsequent collisions. The transfer process starts by adiabatically capturing -SxlO 1 0 p's from the core using a single h = 2 bucket and slowly moving the beam to the extraction orbit. This beam is then extracted from the Accumulator in a single turn using a shuttered kicker magnet and transported towards the Main Ring via the same beam line used for proton targetting, bypassing the target and collection system. The p bunch is

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injected into a matched bucket in the Main King at h = 53 (-2.515 MHz). The normal Main Ring R.F. system is then slowly turned on and the beam rebunched into 13 53 MHz bunches and accelerated to 150 GeV. The 13 bunches are then coalesed into a single bunch prior to injection into the Tevatron, at this energy. The whole cycle is then repeated until 3 bunches of p's are circulating in the Tevatron along with three bunches of protons injected in the normal way prior to the p f s .

The counter-rotating bunches are then accelerated up to the experimental energy. The final step in the collision process involvas turning on the low-beta Insertions In the experimental regions. The low-beta insertions are formed by replacing the normal 37" quadrupoles with stronger and separately powered quadrupoles and the addition of eight extra quadrupoles within the long straight section itself. During injection and acceleration these extra quadrupoles are turned off and the stronger elements at each end of the long straight are de-excited to provide the standard lattice configuration. After acceleration these elements are slowly adjusted until the final beta value of 1 m is reached. At this point the machine is in storage mode and the Main Ring can resume the 2 second cycle of p production.

Tevatron Operations A major milestone on the way to colliding beams occurred in 1983 with the

commissioning of the Tevatron as a fixed target rcachine and the subsequent first operational run which ended in February of this year. Machine commissioning started with the cooldowu of the final sections of the machine which was accomplished at the beginning of May although prior beam tests had been made on the injection system and the first two sectors of the ring. Stable circulating beam was achieved seven weeks later after a shutdown to repair two magnets which were unable to carry sufficient current, and make small machine modifications to relieve aperture limitations. Beam was accelerated to an energy of 512 GeV at the beginning of August. A series of machine studies were then initiated which culminated with the resonant extraction of slow spill to the Switchyard dump. Operational high energy physics was started in October 83 with the machine running at 400 GeV with a 39 second time and a 15 second spill. The average beam intensity was slowly raised during the run up to 8 x l 0 1 2 ppp. The operational efficiency of the machine improved during the run with the final week showing beam delivered to the experimental areas for -80% of the scheduled hours. It was encouraging to note that the downtime logged to the cryogenic systems remained a relatively constant 25-30% of the total.

The superconducting nature of the magnets placea a stringent limit on the

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amount of beam loss which can be tolerated before the a .gnets will quench. Special designs were adopted in the areas of unavoidable heam loss (extraction, abort) to protect those superconducting elements immediately downstream of the known loss points. The beam abort is a single turn extraction system which takes the circulating beam out of the machine to an external beam dump within three turns (60 usees) of receiving an alarm. The decision to abort the beam is made primarily by information received hy the loss monitor and position detector system. Individual thresholds can be set on each element in the ring which can be varied as a function of energy within the cycle. This system has proved very effective in reducing the number of beam induced quenches as operational experience revealed the appropriate threshold settings under various operational situations.

In spite of this quite sophisticated abort system, magnet quenches in a superconducting accelerator can be regarded as a fact of life. The problem then becomes to reduce the number of quenches per day to an acceptable level when taking into account the recovery time of the magnets. The amount of energy deposited in a magnet during a quench is the sun of the beam energy and the stored energy in the magnetic field, and consequently the magnet recovery time depends strongly on the machine energy at the time of the quench. We have found that this time varies between ~20 minutes at injection energy (150 GeV) up to ~1 hour at 800 GeV. Throughout the 400 GeV run the number of quenches was reduced from -1 per 3 hours of HEP to -1 per 15 hours of HEP. In the current 800 GeV run this number has been reduced further to approximately 1 per day. We believe Chat while a lot of work still needs to be done to increase the operational efficiency of the Tevatron, we have demonstrated that superconducting technology has come of age in particle accelerators and that large scale cryogenic systems can he made to operate reliably over long periods of time.

Initial Collider Studies While the main thrust of machine development work to date has been con

cerned with fixed target machine operation a small amount of machine time has been made available for colliding beam work. The mechanics of beam storage were established over several study sessions and protons were successfully stored at 400 GeV for periods of up to 4 hours. Crude measurements indicate that the beam lifetime is consistent with that expected from the residual beam-gas scattering. The background rates in the collision region were also small (~30 kHz) measured with a 1 meter square scintillation counter horoscope. The transverse beam stability was good and we were unable to detect any signs of fifth order resonances. The sensitivity of the fixed target beam diagnostics co these effects is not high emphasizing that these results are encouraging

- 375

rather than conclusive In any way. longitudinal phase space dilution was observed during the stares with debunching times of the order of 1 hour. More effort will be needed to reduce the amount of noise present in the Tevatron low level R.F. system.

Modifications to the Tevatron lattice to allow the establishment of the low beta interaction region at B0 were made in February of this year. To date beta values at the interaction point have been reduced from the 'normal' 70 ¡n to 2 m. Attempts to achieve the design value at ß* = 1 m have resulted in fast beam loss. Work is proceeding to understand and rectify thir situation.

Schedule The civil construction for the antiproton source ring enclosures and tar-

getting hall is well underway. Initial installation work of tunnel utilities will start in June 84 with the magnet and power supplies following immediately afterwards. The goal is to have both the Debuncher and Accumulator rings under vacuum by December 84. During the upcoming major summer shutdown (July -November 84) installation of the injection and extraction systems and the tar-getting station will take place in the main tunnel, as well as a test line from the Booster. Commissioning of the p rings with protons and targetting and production studies will start at the beginning of 1985. Initial attempts to obtain collisions in the Tevatron are scheduled for the Summer of 1985-

Conclusions We are currently constructing an Antiproton Source that is capable of

providing sufficient p's to achieve a luminosity Df - I D 3 0 for collisions involving 3 bunches of protons and antiprotons. The Tevatron has been operational now for over six months in the fixed target mode with energies up to 800 GeV and intensities Í 1 0 1 3 ppp. Machine studies associated with the collider mode of the superconducting ring are now underway.

Reference 1) Calculation of Antiproton Yields for the Feroiilab Antiproton Source,

Fermilab PUB 82/43, C. Hojvat and A. Van Glnneken.

The Antiproton Source

Fig. 1

- 377 -

Fig. 2

- 378 -

Fig. 3

- 3 7 9 -

THE COLLIDEH DETECTOR (CDF) AT FERMILAB - AN OVERVIEW

Dennis Theriot

Fermi National Accelerator Laboratory* Batavia, Illinois 60510 8410026341 USA

CDF, the Collider Detector at Fermilab, is a collaboration of almost 150

physicists from ten U. S. universities (University or Chicago, Brandeis

University, Harvard University, University of Illinois, Uni varsity of

Pennsylvania, Purdue University, Rockefeller University, Rutgers University,

Texas A&M University, and University of Wisconsin), three U. S. DOE supported

national laboratories (Fermilab, Argonne National Laboratory, and Lawrence

Berkeley Laboratory), Italy (Frascati Laboratory and University of Pisa), and

Japan (KEK National Laboratory and University of Tsukuba).j The primary phy:ios

goal for CDF la to study the general features of proton-antiproton collisions at

2 TeV center-of-mass e n e r g y O n general grounds, we expect that parton

subenergies in the range 50-500 GeV will provide the most interesting physics at

this energy. Work at the present CERN Collider has already demonstrated the

richness af the 100 GeV scale in parton subenergies.

To set the scale for physios with CDF, lower energy processes can be

extrapolated to these higher energies. One such example shown In Figure 1 is

large -p f c jet production predicted by QCD. Jets tfith p t aa large as 250 - 3 0 0 GeV

are accessible to experimental study. Another example probing the same energy

scale is that of W or Z pair production, shown in Figure 2. Again practical

rates should exist for this process at 2 TeV. The increased energy also will

yield higher cross sections for single W and Z production by approximately an

order of magnitude compared to that now seen at 5^0 GeV.

*0perated by Universities Research Association Tnc. under contract with the United States Department of Energy

- 380 -

How did we design CDF around these considerations? Since CDF will be

observing hadron collisions, the natural coordinates to use are rapidity, y,

azimuthal angle, and the transverse momentum, p f c. As a very crude guide, the

events of interest oan be pictured as being produced uniformly in y up to a

cutoff given by energy conservation, uniformly In and with a steeply falling

P t dependence. To see moat of the events at the 100 GeV scale, such as W and Z

production, the deteotor roust cover a y range from - 3 to + 3 . If we allow for

the deoay products as well, another unit in y must be added. Thus, ths

acceptance for the full calorimetry and tracking of CDF was chosen to be -4 < y

< 4, 0 < $ < 2ir. The y acceptance translates into a polar angle acceptance of 2°

< 6 < 178°. Events at higher masses are well contained by this acceptance.

What partióles do we want to detect? Since the basic processes are

expected to involve quarks, gluons, leptons, and photons , we want to measure as

mush about those particles as possible within practical constraints of available

technology and money. Since quarks and gluons manifest themselves aa clean,

narrow jeta of hadrona, CDF haa chosen ahower counters and hadron calorimeters

in a tower geocetry to detect jets. One of the central calorimeter modules

called a wedge is shown in Figure 3 . The shower counter composed of lead and

scintillator is at the bottom. The hadron calorimeter made of steel and

scintillator is above. The projective tower geometry is obvious. The

granularity of the calorimeter towers Is sufficient to just resolve the jets

without being able to measure reliably every particle within the jet. Since

hadrona in a typical high Jet will form a circular pattern in y - <|> spaoe

with a diameter of roughly one unit, the calorimeter- towers were chosen to be

0.1 unit in y and between 5* and 15* in 4. A plot of this granularity ia shown

in Figure 4. Leptons are characterized by single particles which have different

interactions in the various component detectors in CDF. Charged particle

tracking in a magnetic field, shower counter and hadron calorimeter response.

- 3 8 1 -

and penetration through several interaction lengths of material are the

techniques planned for detecting electrons and muons. Neutrinos are observed by

missing energy and momentum. Photon detection 13 achieved with finely segmented

shower counters and the absence of a charged track.

An isometric drawing of CDF is shown in Figure 5. The detar-tor is divided

into three aiain pieoes, the Central Detector and two Forward/Backward Detecfcora.

All three pieces are centered on the Tevatron bearaline at the B0 collision area

at Fermilab, A vertical section through the Central Detector is shown in Figure

6. The heart of the Central Detector is a 1.5 Tesla, 3.0 ra diameter, 5.0 m long

superconducting solenoid magnet. This magnet and the Central Tracking Chamoer

are used to measure individual particles with p^ less than 40 GeV. It gives

information that l3 complementary to that of the calorimeters and provides a

pictorial representation of the event. The choice was a solenoid to provide

maximum efficiency In the study of large p t events. Surrounding this magnet are

the shower counters and hadron calorimeters. The shower counters in the region

between 90° and 33° are made of a lead scintillator sandwich read out with

wavelength shifter plates and light pipes. A strip proportional chamber has

been inserted at a depth of five radiation lengths to provide fine grained

information on the shower location. Between 33° and 10° the shower counters are

a lead proportional pad chamber sandwich. These chambers are gas filled

proportional counters fabricated out of resistive plastic tubes with cathode pad

readout. A strip proportional chamber is also provided in these detectors at

the shower maximum to provide precision Information about shower location.

Outside the shower counters are located the hadron calorimeters. In the region

between 90° and 30° these calorimeters are made of steel and scintillator read

out by wavelength shifter bars and light pipes. Between 30° and 10° the hadron

calorimeters are steel and proportional pad chambers. Outside the hadron

calorimeters in the region between 90° and 50° are located the central muon

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detectors. These detectors are composed of four layers of drift chambers and a

hard wired trigger which provides precision information on the direction of

penetrating particles. The return legs of the magnet are located above and

below the central calorimeters. These central calorimeters are assembled into

four arches which surround the magnet cryostat. One of these arches is shown in

the photograph labeled Figure 7.

A detailed section of one quadrant of the core of the central detector is

shown in Figure 8. The beam pipe is 5 em in diameter composed of 2 mm Be.

Surrounding this in the vicinity of the interaction region are seven small

atmospheric pressure VTPC's which have a good r - z tracking ability. The

principal roles of the VTPC'a are to record the occurence of multiple events and

to provide three dimensional information about the general event topology for

use in pattern recognition by the calorlmetry and the central tracking chamber.

A drawing of one of the VTPG modules is shown in Figure 9. Surrounding the

VTPC'a is a large cylindrical drift chamber which provides the precision

momentum measuring instrument in CDF, The central tracking chamber ia an axial

wire chamber with 81! layers arranged into 9 superlayers. Five of the

superlayers each contain 12 sense wires. These five axial layers are separated

by four superlayers of "stereo" wires each containing 6 sense wire3. Both axial

and stereo superlayers are divided into cells similar to the JADE detector.

Each cell is tilted 45° with respect to the radial direction so that the drift

direction ia predominately circumferential when the magnetic field is 1.5 Tesla.

Completing the tracking system is a radial wire drift chamber which covers the

angular range of 2° to 10* in the forward direction. This chamber Í3 composed

of twenty layers of sense wires arranged in 72 radial cells each covering 5° in

$ tipped at a 2° angle to provide ambiguity resolution.

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Located outside the central tracking chamber Is the cryostat of the

superconducting solenoid magnet. This raagnefc ia being produced in Japan by

Hitachi as a collaboration between physicists from the University of Tsukuba and

Fermilcb. Tho total thlokness of the coil and its cryostat is less than one

radiation length. This small thickness was achieved by locating the support

bobbin outside the Buperconduoting coil rather than inside as in previous

magnets of this type. A detail of this arrangement is shown in Figure TO, The

coil was originally wound on a large mandrel. The bobbin which is used to

propogate a quench wa3 then slipped over the coil in a shrink fitting operation

in which the bobbin was heated then allowed to oool in order to achieve a tight

fit. The mandrel was then removed from the coil. This operation was

successfully carried out in January of this year.

An elevation view of half of the detector is shown in Figure 1 1 . Particles

produced between 2° and 1 0 ° pass out of the central detector through a hole in

the end plug and enter wie forward and backward detectors. The first layer of

these detectors is a shower calorimeter composed of alternate layers of lead and

proportional pad Chambers. Again a strip chamber giving fine grained

information about shower location is located at shower maximum. The projective

geometry used in the central detector is continued into c h i s angular range as

well. Located behind the shower calorimeter is the forward hadron calorimeter.

This calorimeter is composed of steel plates instrumented with proportional pad

chambers. Small angle muons originating between 2° and 1 7 ° will be detected and

momentum analysed by the magnetized iron toroids and muon tracking chambers of

the forward rauon detector located immediately beilind the hadron calorimeter.

Overall there are more than 6 0 , 0 0 0 channels of detector information in C D F .

The job of acquiring and recording all of this Information is not trivial. He

have chosen to mount the front end amplifiers and the sample and hold circuits

- 3 8 4 -

as close as possible to the detector components. In the case of the central

wedges on the actual wedges themselves a redundant multiplexed ADC system will

read out the analog signals locally and transmit the digital results to the data

acquisition electronics located in the Bfl counting roora3. FASTBUS will be used

in the data acquisition system.

A multilevel trigger is planned for CDF. The basic interaction rate is

expected to be 50,000 Hz. Three trigger levels are planned. Level 1 must

decide within one beam crossing or 7 raicroseoonds whether to keep the event for

digitization. This trigger 13 derived from analog signals provided by the front

end electronics about energy deposited in the shower counters and hadron

calorimeters. Level 2 look3 for patterns of energy deposition, high p f c tracks

associated with muon hits, large missing p ., and other similar inputs. Level 2

may take several beam crossings to make its decision. The final stage Level 3

is made when fully digitized event information is available to the data

acquisition system and dedicated processors will make software cuts to reduce

the trigger rate to the data logging level. The three levels are expected to

reduce the original rate to approximately 1 Hz. The control, monitoring,

calibration, and data logging for CDF will be handled by a system of VAX

computers.

A plan view of the B0 experimental area is shown in Figure 12. The

collision hall is an underground enclosure 30 m long and 15 m wide located

around the Vevatron beam line approximately 15 m below the surface. This is

shown in the lower part of Figure 12. The collision hall is accessed by means

of a 10.5 m x 10,5 m tunnel which connects it to the assembly hall which serves

as the assembly and service area of CDF. The assembly hall is a 7 5 m x 30 m

surface building containing a 23 m x 30 ra pit at Tevatron elevation where CDF is

actually assembled, a 50 ton crane, counting rooms, offices, and shops. An

- 3 8 S -

elevation view of the facility is shown in Figure 13. The central detector is

provided with heavy duty rollers so that it can be moved easily between the beam

line and the assembly area. The control rooms are located over the tunnel

connecting the collision hall and the assembly hall. The detector will be

connected to the control room by a flexible cable tray not shown in the figure.

Currently, Ferratlab has CDF scheduled for a test run in June ï935 with

another run in January 1986. The experimental area at B0 is essentially

complete. The low beta quads for the interaction region have been installed

and are expected to undergo testing this spring. The coil has been wound, is

currently being installed in the cryostat, and is scheduled to be cooled down in

April with shipment to the United Stater expected in June. The assembly of the

magnet yoke will begin In the B0 assembly hall pit in April. Production lines

for the various assemblies that go into the central wedge modules have been

running for almost two years now. Some of these lines have actually finished

their work and are beginning to shut down. Assembled wedges are beginning to go

to the beam line for final calibration. A diagram showing the assembly pit

sequence Is shown in Figure Ti. We expect to have most of the central detector

and parts of the backward detector ready for the June 1985 run. The central

tracking chamber and the end plugs cannot be used in this run because two beam

pipes will still go thru B0 at that time. The entire detector will be in place

for the January 1986 run. The electronics production will be complete by the

end of 1986. At that time, we expect to begin sharing beam time with the fixed

target experimental program at a fraction that will approach 50J.

Given the time limitations of this talk and the space limitations for the

proceedings I have chosen to give an overview of CDF in order to acquaint many

of you who are not familiar with the project with the main goals and general

design. I f you seek more details on various aspects I refer you to the appended

bibliography which has served a3 the source of most of this talk and paper.

- 386 -

CDF Bibliography

1) Design Report for the Fermilab Collider Lstector Facility (CDF), CDF Collaboration, August, 1981, Fermilab Internal Dooument.

2) CDF, Roy Schwitters, Feroilab Reports, September, 1983-

3) Charged Partiole Tracking in CDF, M. Atac, et al., CDF Note #178, August 11, 1983.

4} A Radial Drift Chamber, H. Atac and G. Chiarelli, CDF Note A193-

5) Title I Design Report: Colliding Seam Experimental Area at B 0 Straight Section, August 28, 1981, Ferrailab Internal Dooument.

- 387 -

Figure 3: Side view of one wedge module with side skin removed exposing the Cower structure

forward plug

.wall

plug em

< 7

10° 3tf 43.6?S1.8°

Figure 4: G r a n u l a r i t y of the shower counter and hadron c a l o r i m e t e r system

Figure 5: An isometric drawing of CDF

Figure 6 : V e r t i c a l sect ion through the C e n t r a l Detector oF CDF

Figure 8: One quadrant of the core of the Central Detector of CDF showing the relationship

- 3 9 2 -

VTPC Modul«

Figure 9: VTPC nodule of CDF Tracking System

Figure 1 0 : Detail c-f one end of CDF solenoid magnet

Figure 1 1 : Elevation view of half of the CDF detector

- 3 9 4 -

F i g u r e 12: A. p l a n v i e w o f t h e B0 E x p e r i m e n t a l A r e a a t F e r m i l a b

HOIIZONIAI v i i w or f Aciury

A-> -B F i g u r e 1 3 : A n e l e v a t i o n v i e w o f t h e B0 E x p e r i m e n t a l A r e a

F i g u r e 14: Assembly Sequence and T imetab le f o r mechanical assembly of CDF compoi ¿nts i n the B0 Assembly H a l l

THE DÛ PROJECT AT FERU I LAB D : ^ ^ 2 6 3 5 °

M i c h a e l D. l i a r H S t a t e U n i v e r s i t y o f New Y o r k S t o n y B r o o k

T h e DÛ P r o j e c t m i l e x p i a r e 2 f e V pp c o l l i s i o n s a t r-ermi 1 ab u s i n q a h i g n i y c g t i n r i z e d c a l o r i a e t r i c d e t e c t o r , t o e i u c i t u u i n « new p h y s j c t coniinij o u t o f u a >

, S p p S , and t o e x p l o r e the new higher u n e r q y recjioc.

1 , H I S T O R I C A L

S o o n a f t e r the beginning oí the T e v a t r o n construction! K e r n i l a b - f a r m e d ¿i g r o u p I C D F 1 t o d e s i g n a n d c o n s t r u c t a m a j o r experimental f a c i l i t y t o s t u d y pp c o l l i s i o n s a t t h e BO r e g i o n . T h r e e y e a r s l a t e r , i n F e b r u a r y 1981, they s o l i c i t e d p r o p o s a l s for a s e c o n d experiment t o b e performed a t DO, T h i s BHperiment was i n t e n d e d t o b e o f a more modest a n d U n i t e d scope. P a c e d w i t h an a r r a y o í s u c h l i m i t e d e x p e r i m e n t s , t h e P r o g r a m C o m o i t t e e ( P A C ) s u g g e s t e d m o r e a m b i t i o u s Efforts. T h r e e 4 i r calorimetric d e t e c t o r s w e r e t h e n proposed .'ii t h e f o l l o w i n g y e a r , A g a i n t h e PAG f o u n d w e a k n e s s e s i n a l l p r o p o s a l s , and u r g e d construct: i an o f a detector a t DO h a v i n g t h e following features (partially e m b o d i e d i n t h e t h r e e p r o p o s a l s ] :

1) Good e l e c t r o m a g n e t i c e n e r g y r e s o l u t i o n w i t h s u f f i c i e n t b a c k g r o u n d s u p p r e s s i o n .

2 ) Good h a d r o n i c c a l o r i m e t r y w i t h s u f f i c i e n t t h i c k n e s s and a m i n i m u m o f c r a c k s .

3 ) t l u o n i d e n t i f i c a t i o n a n d m e a s u r e m e n t . 4 ) H i g h l y s e g m e n t e d c a l o r i m e t r y .

A c o l l a b o r a t i o n c o n s i s t i n g o f many 0 + t h e o r i g i n a l p r o p o n e n t s , a u g m e n t e d by s e v e r a l o t h e r g r o u p s s u b m i t t e d a DE-SI qn R e p o r t 111, w h i c h h a s b e e n en d or s u 0 ( f i n a l l y ) by t h e p f t t . 'Hie d e t e c t o r , w h i c h 1 w i l l d e s c r i b e , e m b o d i e s these d e s i r e d f e a t u r e s , s u r p a s s i n g t h e G U L D S I I N E S for p e r f o r m a n c e , a n d has b e e n o p t i m i z e d u s i n g t h e e x p e r i e n c e o f t h e g r o u p s at C E R N .

2_¡ E j t P E C T A T I Q N S FDR DO

By t h e t i n s T e v a t r o n I t u r n s on f o r p h y s i c s i n l a t e 1 S B 4 , UAl a n d urt2 w i n p r o b a b l y h a v e a c c u m u l a t e d an i n t e g r a t e d 1 umi ¡jc-si a p p r o a c h i n g 1 G' 1 +eai_--f. T h i s t r a n s l a t e s i n t o a p r o b a b l e s a m p l e o f 2 0 0 0 M * e V a n d 2 0 0 2 " •* e e e v e n t s . T h e g e n e r a l p r o p e r t i e s o f t h e l e p t o n i c d e c a y s of t h e b o s o n s w i l l h a v e b e e n s t u d i e d , but t h e s n a i l s a a p l e o f " n e u p h y s i c s " e v e n t s U s h e a r d h e r e a t B e r n ) Í21 w i l l p r o b a b l y n o t be c o m p l e t e l y u n d e r s t o o d , k c h a v e h e a r d , f o r e x a m p l e , t h a t Hitfv t h i s g e n e r a t i o n o f d e t e c t o r s i t i s u n l i k e l y t h a t e v i d e n c e f o r t h e t o p q u a r k K i l l b e f o u n d 131«

By c o n t r a s t , i n a s i n g l e f o u r - m o n t h r u n a t TGV I , H i t h 5 OX e f f i c i e n c y J *. = 1 0 ^ ° c a ~ a s - 1 , we w o u l d e x p e c t t o a c c u m u l a t e f i v e tines t h e t o t a l CETcN s a m p l e o f W~ a n d I e . T h e m a s s s c a l e f o r p r o d u c t i o n o f new o b j e c t s w o u l d be e x t e n d e d by a f a c t o r o f three.

T h i s A L L O H I t h e p o s s i b i l i t y o f p r e c i s i o n s t u d i e s o f t h e w e a k p a r a m e t e r s

- 397 -

(sin aÔ and J>í and detailed studies D f rare decays (like Z° * ee/l. In addition, the hints that we have heard of new physics at higher masses will translate into an even greater advantage at feV I, where the cross suction for production of I5û GeV abjects toll be an order o f magnitude h igher.thanjCfcRN.

¿Jt « Thus we -feel that the canbination of the higher energy and luminosity will

yield rich and exciting physics opportunités.

3. PESIAN CRITERIA FOR DO

The design of the DO detector has been able to USQ its u t e start in the LIAI » UA2, and CDF field to advantage, by optimizing the parameters based on our perception of the strengths and weaknesses of the present generation of detectors. In view of the spectacularly successful runs at ths SppS we now feel that the list of particles which will be relevant at 2 TeV are the leptons — electrons and muons and "neutrinos" — jets, and photons. Far each of these we have attempted to design a detector which would establish their identities and accurately measure energy and angle over the largest possible solid angle.

3.1 improved Measurement of Electrons snd Muons

For electrons we intend to stress excellent energy resolution, which should not be dominated by systematica or cal ibration problems. This w¿.ll enable us to precisely study the+para,meters of the electronic decays of the W~ and I a and to search for narroH e e states. In addition, we hope to improve on electron identification, oath at lower transverse moinentuœ and for electrons in the vicinity of other particles. This feature, we hope, Hill per«it us to search for and tag heavy flavor decays. Me do not Intend to measure the sign of the electrons, and feel that this will not limit most of the physics we Hill address.

For muons, the e/npiiasis will be on identification, even in the core of jets. He intend to measure the sign and also to obtain ffioderate oomentuo resolution over oust of the s-,lid angle. Thus we expect to use the muons as a check an lepton universality in any new effects, ana as a means of aonitorinç backgrounds to lepton and dilapton signals. This will be useful for flavor tags and for understanding the difiuon signals reported by UAl at this conference.

This sensitivity to both electrons and muons will be crucial in such things as supersymnetry searches, where the presence of leptans must be excluded, and N i l l greatly increase the sample of events for studies of multilepton events from heavy flavor decays.

3.2 Improved Hadronic Energy Resolution

Me intend to greatly improve hadronic calorimetry over existing experiments. This resolution will permit studies af multi jet masses for studies of hadrtfnic decays of the ooians as well as better sensitivity to such effects as the ISO BaV dl-jet enhancement reported by UA2 here. Me m i l also oe able ta improve tissing measurements, which as we have heard hers-, are needed for studies of events with neutrinos or supersymnetric particles.

Both of these resolutions are determined by the inherent calorimeter resolutions, by the relative response to electronagnetic or hadronic particles, by the cracks and dead spaces in the calorimeter and by the angular resolution at small angles to the beam.

- 398 -

3 . 3 I i p r a v f d S a g n e n t i t i a n

T h e DO d H s i g n l i l i i m p l e m e n t a much U g h e r d e g r e e o i s e g m e n t a t i o n í o r thL>

c a l o r i ß i t r y , b o t h i n t r a n s v e r s e t o w e r s i z e a n d i n l o n g i t u d i n a l s e g m e n t a t i o n . T h e t r a n s v e r s e s e g m e n t a t i o n M i l l p e r m i t b e t t e r e l e c t r o n d i s c r i m i n a t i o n D y i a p r o v e d r e j e c t i o n o f c h a r g e d h a d r o n - p r c t o n o v e r l a p s , i m p r o v e d d e t e c t i o n ' o f e l e c t r o n s n e a r j e t s , b e t t e r s e n s i t i v i t y t o a m i t i j e t e v e n t s and i m p r o v e d a n g u l a r r e s o l u t i o n f o r m i s s i n g p T r e s o l u t i o n . T h e l o n g i t u d i n a l s e g m e n t a t i o n p e r s i t s n e a s u r a n e n t o f s h o w e r p r o f i l e s f o r e l e c t r o n h a d r o n d i s c r i m i n a t i o n a n d w i l l p e r m i t a s t a t i s t i c a l d i s c r i m i n a t i o n b a t n o o n s i n g l e a n d m u l t i p h o t o n i n d u c e d e l e c t r o m a g n e t i c s h o w e r s . T h i s M i l i p e r n i t m e a s u r e m e n t s o f / / Ï Ï ° r a t i o s a n d d i s c r i m i n a t i o n a-F g l u o n j e t s .

3 . 4 A b s e n c e o f C e n t r a l F i e l d

Me h a v e made a d e s i g n c h o i c e o f e l i m i n a t i n g a c e n t r a l i i a g n e t i c F i e l d . W h i l e t h i s d o e s n o t a l l o w u s t a d e t e r m i n e t h e s i g n s o f p a r t i c l e s ( e x c e p t m u o n s , e x t e r n a l l y ) , we g a i n t h e a d v a n t a g e s o f s i m p l i c i t y i n s t r a i g h t l i n e t r a c k i n g ; c o m p a c t n e s s , w h i c h p e r m i t s t h e f u l l c o v e r a g e -Far c a l o r i m s t r y a n d m u o n s ; a n d v e r y l i t t l e m a t e r i a l i n - f r o n t o f t h e c a l o r i m e t r y r e d u c i n g t h e c o n v e r s i o n b a c k g r o u n d a n d i n t r o d u c i n g no d e g r a d a t i o n i n e l e c t r o m a g n e t i c r e s o l u t i o n .

F i n a l l y , w i t h o u t t h e c o m p l e x i t i e s i n t r o d u c e d e v e r y w h e r e b y a m a g n e t , t h e s c o p e o f t h e p r o j e c t i s s u c h t h a t i t c a n be d e s i g n e d a n d b u i l t on a l u c h s h o r t e r t i n e s c a l e .

3 . 5 H o m o g e n e i t y

F i n a l l y , HB h a v e o p t e d f o r a d e s i g n w i t h o n l y t h r e e b a s i c s y s t è m e , e a c h o f w h i c h w i l l h a v e u n i f o r m p e r f o r m a n c e a n d r e s p o n s e o v e r t h e f u l l s o l i d a n g l e . E a c h s y s t e m H i l l b e o f p r o v e n t e c h n o l o g y w i t h o n l y e x t e n s i o n s o f s c a l e f o r DO.

4 . P H Y S I C S P O T E N T I A L

T h e p h y s i c s g o a l f o r DO w i l l c a v e r t h e same g r o u n d a s t h s o t h e r c o l l i d e r e x p e r i m e n t s , a l b e i t w i t h a s l i g h t l y d i f f e r e n t e m p t w s i s . T h i s p r o g r a m d i v i d e s n a t u r a l l y i n t o t h r e e c l a s s e s — f i r s t . , p r e c i s i o n s t u d i e s o f t h e e l e c t r o w e a k m o d e l s i n c l u d i n g p r o p e r t i e s o f t h e i n t e r m e d i a t e b o s o n s ] s e c o n d , QCD s t u d i e s by m e a n s o f H ~ , Z ° p r o d u c t i o n , h i g h j e t s and s i n g l e p a r t i c l e s s p e c t r a ; a n d f i n a l l y , s e a r c h e s f o r new p h e n o m e n a s u c h a s t o p , a d d i t i o n a l b a s o n s , h e a v y q u a r k s a n d l e p t o n s , B u p e r s y m m e t r i c p a r t i c l e s , and we h o p e , new t h i n g s we h a v e n ' t t h o u g h t o f . As an i n d i c a t i o n o f t h s p o w e r Df o u r d e s i g n , we d i s c u s s t h e e x p e c t e d p e r f o r m a n c e on a f e w o f t h e s e t o p i c s .

4 . 1 P r o p e r t i e s o f W * a n d Z »

C r u c i a l t e s t s o f t h e s t a n d a r d e o d e l c a n b e p e r f o r m e d b y c o m p a r i s o n o f t h e W a n d Z ( n a s s e s a n d w i d t h s , By d i s c a r d i n g o n e e l e c t r o n f r o m t h e 2 d e c a y , o n e c a n m e a s u r e t h e s e p a r a o e t e r s -For b o t h U a n d Z w i t h a s i a i l a r t e c h n i q u e . T h u s o n e c a n c o n s t r u c t t h e t r a n s v e r s e o a s s i

M T

2 • 2 E _ * E . " 1 " (1 - c o s 0 I ( l )

T T T Oñ W h e r e E - B i s t h e t r a n s v e r s e e n e r g y o f t h e e l e c t r o n , e 8 1 6 5 i s t h e m i s s i n g t r a n s v e r s e e n e r g y , a n d & i s t h e a n g l e b e t w e e n t b * e l e c t r o n a n d m i s s i n g

599

momentum d i r e c t i o n . Smith et a l . [43 have shown t h a t t h i s quan t i ty i s s e n s i t i v e t o the mass and width of che object hut not i t s production dynamics. This Is siïown in Figures I and 2 which show the s e n s i t i v i t y oí the !îj d i s t r i b u t i o n for the H far d i f f e r e n t production p_ and for d i f f e r ? n t na tu ra l widths . The r e s o l u t i o n in M, depends c r i t i c a l l y on the r e s o l u t i o n in missing p . . Figure 3 shows the n i s s ing E . r é s o l u t i o n for DO and CDF for a sample of ISAjET-generated 50 SeV p T j e t s . For DO, 1.27. of t he se events a re l easured to have over 10 BiV missing while f D r CDF the f r a c t i o n , by t h e i r e s t imâ t» , would be ISA.

Using t h i s method, He a n t i c i p a t e , in a s tandard four-iionth run , achieving an er ror on the masses of

ffMw 5(3 tleV Stiz " 150 MeV , (2)

about six times b e t t e r than Uñí. For the r a t i o of the widths , we expect

£ (r*w / q ) < iOY, . (3)

This wi l l y i e ld e r r o r s on the electroweak parameters of

S s i n 2 * . ? .002 w (4)

S P * .003 .

This p rec i s ion wil l be c r i t i c a l for t e s t s of GUT models, determining the Hlggs s t r u c t u r e , c o n s t r a i n t s on the tap mass, and t e s t s of QCD c o r r e c t i o n s to the aasses and widths .

We can a lso make a d i r e c t aeasuran tn t of t-.ht width of the I o , u t i l i z i n g our super io r e lec t romagnet ic r e s o l u t i o n . This measurement d i r e c t l y counts the_ nunber of neu t r ino spec ies and can give a c o n s t r a i n t on the ex i s tence of t t s t a t e s below the I ^ a s s .

The measurement depends on both the e l ec t ron r e s o l u t i o n and s t a t i s t i c s , such t ha t the e r ro r on the width i s given by

•Mlf (i • i " f where N i s the number of decays and 0* i s the mass r e s o l u t i o n . This i s shown in Figure A where one sees t ha t with l e s s than 1000 events we wil l be b i l an the c o n t r i b u t i o n of an add i t i ona l n e u t r i n o .

1 . _ ? e ajrç h _ _fo r_the__X°-P_^-Ë.ri\.

The present genera t ion of d e t e c t o r s have been unsuccessful in the search for top . One oF the best p laces to look i s in the decay

H. * tb

U b e + v .

To car ry out t h i s search one needs r a t e , exce l l en t e l ec t ron i d e n t i f i c a t i o n a t lower p T and in the neighborhood of other p a r t i c l e s (in a j e t ) , a high degree of segmentat ion, and good Kissing p . r e s o l u t i o n . Figure 3 shows the s igna l we

- 400 -

would expect above background for a tap mass of 30 or 60 fieV. This is after minimal isolation cuts on the electron, and cuts such that

E r(elactroni>10 Gev/c E T<mlssing>>10 BeV/c.

In a four-month run, we would have 75 events for a top mass of 3u eev and ISO events at ¿0 GeV, Far similar cuts, the tàppS experiments expect l - 2 events and see a background of order 10 events L33,

5, THE DETECTOR

The detector we have designed is shown in cut-awöy perspective in Figure 6, and a quadrant is shown in section in Figure 7. Starting from the collision region one encounters the threo main detection systems: a central tracking system including transition radiation detectors; a liquid argon uranium calorimeter system having a central section* two end caps, and two plug calorimeters close to the beam lines; ana finally a muon system consisting of proportional drift tubes (PDT's) and over 3000 tons of magnetized iron toroids.

5.1 Central Tracking System

The central tracking wystem consists of a drift chambers system with delay line readout for the second coordinate and a transition radiation system (TRD). A primary purpose for both of these systems is the suppression of backgrounds to many of our interesting signals. Tftus, for electrons, the drift chambers must supply a direction for the track that can be accurately correlated with a shower in the calorimeter, to suppress the background of a soft, charged hadron overlapping a stiff photon or TT°. The system must have sufficiently good two-track resolution to permit identification of electrons in or near jets. The drift chambers will also M e a s u r e the dE/dx lass to be able to distinguish converted photon pairs from electrons. The tracks i h the drift chambers will provide a collision vertex for use in triggering on nuons. The TRD system will be used to provide additional electron identification, especially for those electrons burisd in jets. Finally, a constraint on the design of this system is that it be conpact, and yet provide little extra material for conversion of photons, and permit space for eventual inclusion of a micro-vertex detector.

The drift chamber system is shown in Figuro Q. The chamber is shown in Figure 9. The chaober is comprised of inner and outer sections consisting of two and four sections respectively. Each section is divided into 32 supercells as shown in Figure 10, with adjacent layers of supercells rotated to resolve left-right ambiguities, Each supercall contains four sansa wires a n d two delay lines, so that one obtains two space points and two additional azimuthal coordinates, and four samples of dE/dx per supercell [53.

The TRD syst?« will be located betneen the two drift chanbsr sections, and will consist of four layers of radiator (probably lithium foils) each followed by a Xe-?r PWC which acts as the X-ray detector. This detector will be equipped with cluster counting electronics, and thus will be effectively blind to che sea of ionizing partidas below the X-ray cluster threshold t¿l.

5.2 Liqi'id Argon. Calorimetry

At the heart of the DO detector is a system of five liquid argon calorimeters. These calorimeters will use alternated plates of copper and

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unntua as the absorber. The system is designed to be completely "hermetic," and homogenous «Ith coverage down to l g fro* each bean line. Uranius has been chossn not only for its density, but for its property of fission compensation, which will enable us

to achieve hadronic resolutions of ~ ^ and equally important,

almost equal response to electromagnetic and hadronic showers. The design will ensure that no detector cracks or dead spaces point to the interaction region. Because of the unit gain and stable response of such a system, we expect,to be able to control systematic effects at the l/2%level.

These properties will enable us to measure the energy flaw of jets, electrons, and photons with unprecedented precision) and to measure missing Energy and momentum with about half the error of current detectors.

Although design studies havB not been completed, one of the designs for the central calorimeter is shown in Figure 11. It consists of 16 azimuthal wedges, U S cm thick, with three longitudinal sections along the bean. Figure 12 shows the internal structure of one section, The front electromagnetic compartment has 1/2 radiation length assortir plates and is read out 4our tiftss longitudinally to enable us to reject non-electromagnetic backgrounds. The size of the transverse towers is apprcximately 6 H 6 en 2 with 1 ci strips located at the peak of the shower. The hadrcnic section has three longitudinal readouts with 4 mm thick uranium plates and one leakage section with very coarse saapling. The typical hadrcnic tower is 15 x 15 cm".

The two end cap calorimeters which cover the region down to 5°, and end plugs which go to I o , wili be similar devices. They have the simplification of having all absorber plates standing vertically, and the complication of having readout towers which vary greatly in si:e, with very high readout density close ta the beat. He hope, however, to share as nuch as possible in mechanical, cryogenic, and electrical techniques between all five calorimeters.

Dur original scheme -for readout of the signals utilized three-layer printed circuit boards, with the readout pattern etjfched onto the two nutside layers, and the signals lines in the inside layer, connected to-the outsides by plated-through holes, This method is conceptually simple, but extraordinarily expensive. He are exploring other schemes, such as subdividing the copper absorber plates and reading the signals directly from the copper. WB are also investigating laminating these copper tiles between fiberglass sheets, effectively making thick PC boards.

The »lactronics for readout of the small signals has been optimized for the time structure of TeV I. A circuit has been designed which samples the signal before and after » bunch crossing, as shown in Figure 13, and performs a subtraction. This signal is then available as a DC level and can be multiplexed, allowing a drastic reduction in cables 4raa the SQ,QQ-> channels ts be analyzed.

5.3 Huon Systea

Thi euon system has been disignid to aeaiure the spectrum of muons froa very low p <* 2 GiWc) out to the highest observable «ementa, with moderate resolution. The coverage extends down to Q° of either beam, Dur design

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surrounds tha mínimum of i e v t n absorption lengths of the alaritaetry, with an additional raster of magnetized iron. Uith this much absorber it would take a 600 GeV incident hadron at ?0° (5000 GeV at 10°) to produce Dn average one punchthrougrt particle. The aomentum measurement is accomplished with P U f ' s , distributed at two places between the calorifaeter and iron, and at thret! stations outside the iron. Each station measures each coordinate twice to resolve ambiguities.

Uith this system we H i l l achieve a momentum resolution <ap/p 2vr. up to p x

of 200 GeV/c. To this momentum we H i l l be dominated by n u l t i p I e" Coul onib scattering in the iron and uranium. For those isolated muons where we ire able to match with a track in the central drift chambers, «e can improve the resolution to Ap/p * is?..

In order to have accflss to the detector, the iron is designed in five pieces as can be seen in Figure 6. Ths central iron consists of two retractable clamshells and a baseplate which supports the central and end cap calorimeters. The end iron toroids, which support the und plug calorimeters, can be separated from the central iron, The system is designed ta allow personnel access into tha detector in the collision hall.

The detector parameters are summarized in Table I.

h. STftTUG

TeV I is on schedule with first collisions expected by raid-19Ö5 and a first physics run in late 1986. The expected luminosity is L03° cm-2 sec - 1 with low ß insertions at B0 and 00.

Me feel that given an aggressive funding schedule DO could be ready by mid-1987. There Is, however, a funding crisis in the US, and competition for funds between DO, SLD (the second detector at SLC) and present commitments that will slow this down. We are at present negotiating a funding pro-lile with Fermilab and thm DUE which we hope will assure completion of the detector by the end of 1988, Me, of course, would expect to take beam earlier than this with a partial datoctor.

Prototypes of all systems will be tested in beams this spring, and engineering of the systems has begun. The collision and assembly halls are presently being detailed, and is shown in plan in Figuro 14.

Me are all very excited by the hints of new physics presented at this conference, and feel confident that tha DO detector will have an opportunity to contribute to this exciting field.

REFERENCES

1. Design Report -- An Experiment at DO to Study Antiproton-Proton Collisions at 2 Tcv. The DO Coollaboration, 12/63 (unpublished). The Collaboration presently consists of * 7S physicists iraai University of Ariiona, Brookhaven National Laboratory, Brown University, Columbia University, Fernilab, Florida State University, University of Maryland, Michigan State

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University, Norueste™ University, University of Pennsylvania, CERN, Saclay, Stita University of Nan fork (Stony Brook), and Virginia Polytechnic Institute.

2. Ssi talks by UAl ( C . Rubbial and UA2 (J. Hansen and fi. Roussaria) tnesa Proceedings.

S. Sae talks by F. Halien and A. Martin, these Proceedings.

4. J, Snith et al,, Phys. REV. Utters M UVU3I

5. T. Behnke, et al., Progress in the Design of tha Central Drift Cnamcer for DO, CO Internal note * 59, 2/84 (unpublished).

i. C . Fabjan et al., CERN-EPfBZ-il.

Table I DETECTOR SUMMARY

1 . Resolutions e, n Ê 107. + 0.5X

Hadrons: Ê

407. •TE

huons:

2. Coverage e, |/, Hadran: muons:

S 2 l'a ï 8*

3. Segmentation

Central Electromagnetic: Central Hadron: Ena Eltetroiagnetici End Hadron: Plug Electrooagnet:c Hadran:

12B0 towers/end (x 4 depth) 576 towers/end In 3 depth)

Î60 towers/end C» 7 depth)

3360 towers ( K 4 depth) 600 tonara U 4 depth)

4. Total« 2SO0 total hadronic towers 6500 total EM towers 1400 drift «ires 700 delay Unas

29000 proportional drift tubes

F I G U R E C A P T I O N S

F i g . l i D i s t r i b u t i o n o f e v e n t s w i t h t r a n s v e r s e m a s s , m , f o r 14 * eV^ f r o m R e í , 4 . T h e s o l i d l i n e a s s u m e s p T = Oj t h e d a s h e d l i n e i s f o r p., = 5 0 G e v V c , 1 1

F i g . 2 i D i s t r i b u t i o n o f e v e n t s w i t h t r a n s v e r s e mass f o r W -> e V w i t h P . - I 6 e V ( d a s h e d ) , 2 . 5 G e " ( s o l i d ) , a n d 5 GeV ( d o t - d a s h e d ) .

F i g . 3 : C r o s s s e c t i o n v s . m i s s i n g p_ f o r v a r i o u s c o n t r i b u t i o n s . T h e s o l i d l i n e i s f a r l o s s e s i n a 1 ° b e a n h o l e o n l y , - o - i s f o r I a beam h o l e and e n e r g y r e s o l u t i o n i n c a l o r i m e t r y . T h e d a s h e d l i n e i n c l u d e s t h e e f f e c t o f beam h o l e , o n e r g y r e s o l u t i o n , a n d a n g u l a r s s e a r i n g e f f e c t s ( a i l

h a d r o n i m p a c t p o i n t s a r e s m e a r e d w i t h <s , C =2 e c u . T h e e f f e c t o f 8 a z i m u t h a l c r a c k s o f w i d t h 2 , 5 cm o v e r t u e c e n t r a l c a l or^ i met a r ( n o t s h o w n ) i s t o b r o a d e n t h e M i s s i n g p _ - d i s t r i b u t i o n f o r p-j > 1 0 G e V / c w i t h o u t a p p r e c i a b l e e f f e c t b e l o w 1 0 G e V / c . T h e c o n t r i b u t i o n s f r o m s i g n a l s d u e t o v ( h e a v y q u a r k ) p r o d u c t i o n a n d 1 0 0 GeV g l u i n o s a r e a l s o s h o w n .

F i g . 4 i E r r o r on Z ° w i d t h v e r s u s n u m b e r o f e v e n t s u s i n g t h e mass r e s o l u t i o n o f t h i s d e t e c t o r ( o v = l . i * ? S e V ) .

n

F i g . S i D i s t r i b u t i o n o f e v e n t s f a r t •> be*V a n d b a c k g r o u n d ( s h a d e d b a n d s ) a f t e r c u t s a n an i s o l a t e d e l e c t r o n , E - ( e l e c t r o n ) > 10 Q e V , a n d E T ( m i s s i n g ) > 1 0 G e V . T

• : n T B 3 0 S e V , A i « T = 6 0 S e V .

F i g . 6 t C u t a w a y p e r s p e c t i v e o f t h e DO d e t e c t o r s h o w i n g m a j o r s u b - s y s t e m s ,

F i g . 7l S e c t i o n o f o n e q u a d r a n t o f t h e d e t e c t o r .

F i g . 8 : P r o f i l e o f t h e c e n t r a l c h a m b e r p r o p o s e d f o r DO i n t h e r i - p l a n e ,

s h o w i n g p o s s i b l e l o c a t i o n s f o r t h e end c h a m b e r s . ( O n l y o n e q u a d r a n t s h o w n . )

F i g . 9 t C r o s s - s e c t i o n t h r o u g h t h e p r o p o s e d c e n t r a l c h a m b e r i n t h e r < * - p l a n e , ( O n l y o n e q u a d r a n t s h o w n . )

F i g . 1 0 : S c h e m a t i c v i e w i r t f - p l a n e ) o f t h e w i r e g e o m e t r y i n s u p e r c e l l s .

F i g . 1 1 : End v i e w o f c e n t r a l U r a n i u m L i q u i d A r g o n c a l o r i m e t e r .

F i g . 1 2 : R e a d o u t s e g m e n t a t i o n for c e n t r a l c a l o r i m e t e r i n r - $ a n d r - z v i e w s o f a t y p i c a l m o d u l e .

F i g . 1 3 t J t o p l — C h a r g e p r e a m p l i f i e r s i g n a l . I b o t t o m ) B l o c k d i a g r a m o f t h e e l e c t r o n i c s .

F i g . 1 4 : P l a n V Í B H o f t h e Dû c o l l i s i o n a n d a s s e m b l y h a l l .

Fig. 4

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>

•S o

"o :

M T ( G e V )

Fig. 5

Fig. 6

I 1 I 1 1 1 I I I 1 I — 0 1 2 3 4 5 6 7 8 9 10

Z(m) Fig. 7

410

R t (cm)

OUTER MODULE M SUPERLAYERSï

INNER MODULE 17.9 (2 SUPERLAYERS) 9 0

OEAD-SPACE (HV.Mt.) —I I— 7cm

T R D ( û r * 3 0 c m !

I •—TRD iú2»30cm)

CENTRAL CHAMBER

Fig. 8

END CHAMBER

INNER 'MODULE

OUTER - MODULE

Fig. 9

- 411 -

A PARTICLE ? TRACK

SENSE WIRE

SUPERCELLS

F i g . 10

- 412 -

VIEW SHOWiJ WITHOUT ENDPLATES

F1g. 11

NOT TO S-ALE (TYP)

Mem TTP. HADRDN TOWER

J_..

- . . 0 ( 0 0 P.C.) { l I S m m (ARCON L10U1D)

<-2Cmm tu2SMi

LIQUID)

t4Qmm . I.Snifi (ARGON UQUIO) REÍ I

r1.9mm (ARGON LIQU10)

V

_ i

F i g . 12

- 414 -

Vol

ts

(arb

itrar

y un

its)

/ signal / I

Vol

ts

(arb

itrar

y un

its)

e ariy f 1

late S W 2

- 1 0 1 2 Time (yu.see)

sensitive Baseline MPXR preamp subtracter

F i g . 13

F l g . 14

- 416 -

TRANSVERSE ENERGY PHYSICS WITH THE CDF CALORIMETER J. Freeman, R. Perchonóle, J. Yob. Fermi National Accelerator Laboratory* o: 8610026368 P.O. Box 500, Batavia, Illinois 60439 USA

ABSTRACT C We have studied CDF's ability to measure missing transverse energy and >nstruct the ma3s of the W 2 Jet system by use of a QCD Monte Carlo and a

detailed simulation of the CDF detector. For monojet events and events with multiple jets and large missing E T , we

have studied backgrounds from "old physics sources" (Z •*• 2v and heavy quark jets) and from deteotor mismeasurement. These backgrounds are found to be comparable.

For W + 2 jets, we find that the mass resolution is dominated by the ability to discern between particles from W decay and the underlying event. CDF detector mismeasurement causes only a small deterioration in mass resolution.

INTRODUCTION The present era of high energy hadron colliders has opened up an entirely

new mass region for the exploration of physics phenomena. New massive objects or phenomena are expected to manifest themselves in their decays into "partons" - electrons, muons, jets (quarks or gluons) and missing E T (neutrinos, photinos, etc.). In 1986, the Fermilab Tevatron Collider will bring a four-fold increase in energy and accessible mass range above that presently available.

In this paper, we address the ability of the CDF detector at Fermilab to measure jets and isolate missing E T . Our study employs a realistic Monte Carla simulation including QCD effects and detector imperfections such as cracks, dead areas, shower leakages, and nonuniformities.

CDF's ability to detect missing E T physics is studied for two extreme cases of event topology - (i) the loose signature of multijet events with large missing E T , and (ii) the tight signature of monojet events, where no energetic cluster is allowed opposite an observed high p T jet. For the multijet/large raissing &J, events, we determine that the background from detector miaraeaaureinent of jets is comparable to that due to neutrinos and/or muons from heavy quark jet decays (This rate is comparable bo the signal expected from gluinoa). Both the "detector" and the heavy quark backgrounds can oe reduced by a factor of 3-5

*0perated by Universities Research Association under Contract with the United St.'tes Department of Energy

- 417

using additional vetos such as muon and electron tagging or by determining that a high charged particle has entered a "crack" in the calorimetry. The dominant "old11 physics backgrounds for monojet events are the events with a Jet reooiling against a Z° which decays into two neutrinos or events with heavy quark cascades into neutrinos. The level of this background is about two orders of magnitude below the multljet/large miss. We find that the "detector" background arising from completely missing a leading Jet to be comparable to the jet + Z° background.

The accuracy of jet energy determination was studied by determining the mass resolution of events with If + ud, He find that the dominant factor in mass resolution is due to clustering - i.e. the difficulty in determining which particles come from the jets from W decay and which come from the underlying event ("beam-Jets"). This factor dominates the detector energy resolution or mismeasurement,suggesting that improvements in resolution (such a3 using uranium) or uniformity (such as reducing cracks) will not lead to significant improvements in W mass resolution.

CDF CALORIMETRV The CDF detector is a 4TT calorimotor which covers 2° to 17ß° in polar angle

(relative to the beam axis) and full 360° coverage in azmuthal angle. It has a projective tower geometry with electromagnetic shower counters surrounded hadron calorimetry. The detector has a thickness of 108 centimeters of iron equivalent at theta - 90°, increasing to 160 cm of iron equivalent in the forward direction. The central region (theta between H0° and 140°) contains scintillator plastic sampling calorimetry with 12%/ "f~E (65$/ "V~E) resolution for the electromagnetio (hadronic) component. The remaining solid angle Is covered by proportional tube sampling calorimetry with a resolution of 25%/ V~É (100*/ Tf~E) electoromagnetic (hadronic).

CDF SIMULATION An extensive simulation of the CDF detector has been utilitized for the

analysis reported in this paper. The physics events of interest are first ( i

generated via the ISAJET Monte Carlo. 1 After smearing the production vertex (o z

= 30 cm), the events are processed by a geometrically detailed detector simulation (eg. cracks and dead areas in the calorimetry are included). Physical processes such as in flight decays, gamma conversions, dE/dx, and

- 4 1 8 -

multiple scattering are included. Hadronic and electromagnetic 3howers are simulated including effects such as transverse and longitudinal shower profile fluctuations, energy leakage, and noninteracting punchthrough.

LACK OF CALORIMETRY AT VERY SMALL FORWARD ANGLES To find the effect of limited coverage of calorimetry for small polar anjle

(the half angle of the conical hole in the calorimetry is 2°), we studied hard scattering events with minimum parton p T > 15 GeV and > 50 GeV. We looked at the final state particles and calculated the magnitude of the missing E T vector for various assumptions about the limit of forward calorimetry coverage. Results are shown in Fig. 1A and B. In each of the figures, we see three curves: "No smearing" which shows the effect of the hole considering only geometry; "o E = .55 lf*E"^ where the no smearing curve is smeared by intrinsic calorimetry resolution; and finally, "CDF uncorrected" which contains all cracks and nonunifonnities in CDF, as well as the effect of neutrinos and noninteracting punchtrough, but where no correction for these effects are attempted. From Fig. 1A, we see a "knee" in the distributions for a hole of 2°* As the size of the hole is increased above that, it becomes probable for one of the 15 GeV p T jets to flow into the hole region. Consequently, the missing E T

resolution worsens. The probability of a jet flowing into the forward direction decreases with increasing jet transverse energy. Hence, in Fig. 1B, for 50 GeV

jets, we see that the knee for worsening Ej resolution has moved upward to about 5°. We conclude that for hard scatterings of more than 15 GeV E T per parton, the 2° hole in the CDF calorimetry does not contribute to missing E T

resolution.

BACKGROUND FOR M I S S I H G E ? * J E T S

It is possible for conventional hard scattering events to be observed possessing missing Ej. Causes for missing E T In these events include semi-leptonic decays of heavy quark jets and detector imperfections. To study the relative importance of the different contributing factors, we looked s'éventa of the process pp + 2 jets, with p T (parton) > 50 GeV p T .

The results obtained from a sample of 1700 events are plotted in Fig. 2. In this figure, we see four distributions: 1/N d N / d E T | n i s a l n g versus E T missing for those events with only the effect of the 2° hole ("no smearing"); adding the effects of missing y and v, as well as finite calorimetry resolution

- 4 1 9 -

('".55/ "fi"); and two additional curves that include all the imperfections of the CDF detector. The curve "CDF-uncorrected" shows the rate of missing E T

events if no attempt is made to veto events that have particles hitting oraeks, identifiable leptons, etc. The curve "CDF after veto" will be described below.

We see that "CDF uncorrected" has a significant high missing E T tail. To understand this tail, we looked at all events with E T m i S 3 i n g > 15 GeV to find out the cause of missing E T . There were three causes for the missing E T : Cracks in the calorimetry, intrinsic oalorimetry resolution, and neutrinos. Table 1 shows the number of events for each cause.

Table 1

Number of Events/Cause for Events with Missing E T > 15 GeV Veto and Crack

Cause CDF-Uncorrected After Veto Instrumentation Y hitting cracks 25 6 l Intrinsic resolution 14 8 8 Neutrinos 17 ^

We found that some of the events in the high rai3slng E T tail could be vetoed. These events possessed charged high p T particles hitting cracks, or Identifiable leptons associated with neutrinos. Vetoing these events brought about a factor of 3-5 reduction in the high tail ("CDF after veto" in Fig. 2). The fractional causes of missing events in the high tail changed after the veto. The -lew balance of causes is shown in Table 1. We see that intrinsic resolution becomes more important as a contribution.

A proposed upgrade to CDF would instrument the the inactive regions between calorimetry modules in the central region with 7 X Q tungsten and a single sampling chamber. 1 This instrumentation would allow flagging of photons that hit these cracks. If we apply thi3 final rejection, we are left with the third set of numbers in Table 1. We see that the Intrinsic calorimetry resolution has become the predominant cause of the high tail.

For this type of signature (50 GeV Jets with missing E T ) , CDF's calorimetry resolution seems to lead to backgrounds twice as severe as une neavy quark background. A thicker calorimeter with better resolution (for example, uranium-liquid Argon) could conceivably get 1/3 the hackground CDF can expect. Since the Intrinsic resolution is a gaussian distribution, it can be expected

- 4Z0 -

that, for higher missing E T events, neutrinos will become more important as a source of the high missing &¡. tail. BACKGROUND FOR MONOJET EVEMTS

One possible signal for the presence of aupersyrametric particles is the observation of "raonojet" events. These are events containing a single observable jet and missing transverse energy. Sources of background to mcnojet event* include g + 1Q •* g + uu, cascade decays of heavy quarks, and detector dependent effects such as finite energy resolution, cracks, and nonuniformitles. The existence of a 3 0 GeV mass scalar quark could produce events with a 20 GeV E T jet, and no second jet to balance transverse energy. One source of conventional background would come from hard scattering of about 30 GeV p-j. per parton, where one jet was nob observable. We decided to study events with the monojet signature: A cluster with transverse energy equal to or greater than 20 Gev E T with less than 5 GeV E T balancing the jet in the opposite hemisphere.

Our clustering procedure was.-1) Require a 1 GeV E T deposition in a 15°(phi) X 0,1 (pseudorapidity)

tower. 2) Look at all neighbor towers, and add their energy tothe cluster if there

is at least 0.1 GeV but lesa than 1.5X the parent tower's energy in the tower. The last requirement prevents merging cf cloae but distinct clusters.

3) Merge all clusters whose centrólos are less than l unit apart in (pseudorapidity-phi) space, where phi distances are measured in radians. We picked the distance of î unit for cluster merging after a hand scan of energy

flows for a sample of the events. We studied 6o r000 events of the process pp •»• Jets with p T of each parton >

30 GeV. After very loose precuts to eliminate events that could not possibly satisfy our monojet criterion, we simulated the remaining 1500 events using the detailed CDF detector simulation and applied cur mono-Jet selection. 11 events satisfied the signature. We then identified the source of missing Er for these 11 events. There are three sources of missing E^.: 5 events with a high energy v from heavy quark decay; 3 events with photons hitting the phi cracks between elements of calorimetry in the central regions and 3 events caused by other calorimetry imperfections including finite thickness and limited theta coverage.

One of the five events caused by neutrinos was recognizable as a weak decay event. (It had a 5 GeV Pj u that was detectable.) The remaining four events had very low energy leptons associated with the neutrinos. All of the events

- 421 -

due to missed photons could be tagged if CDF adopted the proposal to instrument the oracks in the central calorimetry. None of the events due to other properties of the caloriraetry were recognizable as being caused by the detector. Hei-JG, we are left with 4 v events and 3 events due to detector limitations. The ZQ + Jet source of background would contribute about 2 events.

We conclude that CDF calorimetry imperfections generate a background to monojet events which is comparable to the physics background of ZQ + jets or heavy quark decay. In other words, a perfect calorimeter would not have a significantly lower background for monojet events caused by supersymmetry.

MASS RESOLUTION OF W * ud •» 2 Jets We studied CDF's ability to reconstruct the invariant mass of a 2 jet

system by considering the procesa W •+• ud + 2 jets. Our method of analysis war to first identify the factors contributing to finite mass resolution. We then added each factor to our sample of simulated events and observed the effect on the measurement. The effects we identified as Interesting to study were: 2° hole in calorimetry; energy lost by neutrinos and muons; intrinsic calorimetry resolution; calorimetry imperfections, such as finite thickness, cracks, and nonuniformity; and the effects of clustering algorithms used to reconstruct the fragmented jets.

A summary of our conclusion is shown in Table 2. Several invariant mass distributions for sets of conditions A through H are shown in Figs. 3 and 4, we note that the clustering algorithm used is the same aa descrloed in the section on monojet identification.

In Fig. 3, we see results for: C, a .25/ ~f~E resolution ideal calorimeter, D, a .55/" V~Ë" ideal calorimeter; and F, the .25/ Yi~calorlmeter after the effect of clustering. We observe that the .25/ "fit calorimeter, after clustering, has poorer resolution than the .55/ Y~É" calorimeter before clustering. In Fig. 4, we see results for cases; F, again the .25/ V~Ë"

calorimeter after clustering; G, the .55/ YeTcalorimeter after clustering; and H, CDF including all cracks, nonuniformities etc., after clustering. From Fig. 4, we conclude that there are no dramatic differences between distributions F, G, and H.

T a b l e 2

F a c t o r s c o n t r i b u t i n g t o d e g r a d e d m a s s r e s o l u t i o n i n W + 2 j e t s .

F a c t o r q R e s o l u t i o n (56)

A . 2° b e a m h o l e 0.6%

B . A + m i s s i n g v, u 1 . 3 Í

C . B + . 2 5 / Y~È r e s o l u t i o n 3.0%

D . B ••• . 5 5 / ~ \ T É r e s o l u t i o n 5 - 3 Í

E . B + c l u s t e r i n g 7 Í

F. C + c l u s t e r i n g 8%

G . D + c l u s t e r i n g 9 Í

H . CDF 1 0 Ï

0 I s d e f i n e d u s i n g o n l y t h e 5 O Ï - 8 0 ? i n t e r v a l o f t h e r é v é l a n t d i s t r i b u t i o n .

E v e n t s w e r e e n t e r e d I n t o d i s t r i b u t i o n ? E t h r o u g h H o n l y i f t h e y p o s e s s e d a t

l e a s t 2 c l u s t e r s , e a c h w i t h E T > 1 5 G e V .

O u r c o n c l u s i o n i n t h i s s t u d y i s t h a t , w i t h t h e c l u s t e r i n g a l g o r i t h m

e m p l o y e d , i m p r o v e d c a l o r i m e t r y r e s o l u t i o n d o e s n o t c a u s e a n i m p r o v e m e n t i n m a s s

r e s o l u t i o n . I t r e m a i n s t o b e d e m o n s t r a t e d i f t h e r e a r e s i g n i f i c a n t l y b e t t e r

c l u s t e r i n g s c h e m e s t h a n t h e o n e t h a t we u s e d .

C O N C L U S I O N S

CDF w a s d e s i g n e d t o s e r v e a s a f u l l UTÍ c a l o r i m e t e r w i t h h o m o g e n o u s

r e s p o n s e . Some c o m p r o m i s e s w e r e n e c e s s a r y i n o r d e r t o r e a l i z e t h e d e s i g n . T h e

c r a c k s a n d n o n u n i f o r m i t i e s I n t h e c a l o r i m e t r y a r e a t t r i b u t a b l e t o t h e

r e q u i r e m e n t o f m o d u l a r i t y , c o u p l e d w i t h t h e n e c e s s i t y o f r e a d i n g o u t t h e

s i g n a l s . F i n i t e c a l o r i m e t r y t h i c k n e s s , a n d l i m i t e d s o l i d a n g l e c o v e r a g e a r e

f o r c e d u p o n o n e b y g e o m e t r i c a l c o n s t r a i n t s . We f o u n d t h a t t h e s e i m p e r f e c t i o n s

w i l l n o t s e r i o u s l y d e t r a c t f r o m o u r a b i l i t y t o s t u d y j e t s a n d m i s s i n g E^.. F o r

m a n y o f t h e p r o c e s s e s s t u d i e d , C D F'3 i m p e r f e c t i o n s c a u s e o n l y i n s i g n i f i c a n t

d e g r a d a t i o n s t o t h e b e s t a c h i e v a b l e r e s o l u t i o n , a n d i n t h e w o r s t c a u s e , t h - ^ a e

i m p e r f e c t i o n s c r e a t e a b a c k g r o u n d t h a t i s c o m p a r a b l e t o t h e i n t r i n s i c b a c k g r o u n d

f r o m p h y s i c s p r o c e s s e s .

- 423

REFERENCES 1. F. E. Paige and S. D. Protopopesou, 19S2 £>PF Summer Study,

Snowmasa, Co., June 2 8 , 1962, page 171. We used ISAJET version H.O for these studies. The ISAJET evwnt ¿unoraior does not contain the effects of initial state gluon bremsatrahlung. For the studies presented in this paper, initial state bremsstrahlung i s expected to be several orders of magnitude less important than the other effects studied, and is consequently ignored.

2. Throughout this paper, we consider 2 "ideal" detectors: a "conventional" calorimeter, and a "liquid-Argon Uranium" calorimeter. These calorimeters have finite energy resolution ( o/E = 0.55/ "/"IT for the conventional one¡ 0.25/ ifÈ" for 1A-U), and Infinite thickness. They also have perfect spatial resolution. The energy resolutions wore determined by averaging electromagnetic and hadronic calorimeter responces over a sample of hard scattering events.

3. CDF internal note number 225

Edge of Calorimeter Ccireraqe idegiees) Fig. 2. Missing Ej distributions

for CDF and ideal detector. Fig. 1 . Effect of limited theta

coverage on missing E , resolution.

- 424 -

Fig. 3. Reconstructed mass fractions for V -*• 2 jets.

Mp = M reconstructed ( M overoqe

Fig. 4. Reconstructed mass fractions for W -*• 2 jets after clustering.

- 425 -

1 . MISSING-p T PHYSICS + 1)

The discovery and study of the H~ boson at CERN has clearly established the missing-p T technique, In association with lepton identification, as a powerful tool in the study of physics involving resonance production with a neutrino (v) in the final state. It is anticipated that it will also be very useful for analysis of more complicated processes with more than one

2) "non-interacting" particles in the final state, i*e. v, photlnos (y), etc. However, their conclusive study, especially in view of United statistics may require, in addition, tagging of eemileptonic heavy quark (q)-decays, for

3 4)

example by detecting secondary vertices * ' . - - N .

r He mention several "missing-p T" physics topics*^" with estimated rates J

mostly based on QCD and the standard model at 2 TeV and an integrated luminosity /

of 5 piT J ( Q ^ l ü í t ) ^ J i) Precise determination of masses and widths of W and Z and their ratios, for

testing the standard model. W •+ ev (15000 events), Z •+ e +e~ (1500 events)

li) Diquark H and 2 decays* For example discovering of the top quark (t) in _ 2

tf -* tb ; t -4-Klepto.n) v b. 150 events (m t = 60 GeV/c ) iii) Associated production of W or 2 in

pp •* W(lv) + y (P T > 10 GeV/c) + X (20 events) or W(lv) + W (2 jets) + X (A few events)

iv) Heavy lepton (L) and quark (q) production. For example w •*• I A > L ; L -»• (1650 events) PP * Q (Wq) + Q (Wq) + X 100 eventB (m Q - 120 CeV/c 2).

v) production of Higgs particles decaying into 2 quarks:

W f cf, öS, ce for 2m^< < 2m z

vi) Technicolor octet, r^, production*^ Op + tt

vil) Superayómetry. production of gluinos (g) In

PP * ggX -* (qq^) + (qqy) + X

DO ! MISSIHG-p PHYSICS AND DETECTOR DESIGN CONSIDERATIONS

George E. Tbeodosiou

University of Pennsylvania ^ 8 4 1 0 O 2 6 3 7 6

- 4 2 6 -

Fig. 1 shows the signal for several glulno masses up to 125 GeV/c 2, as a function of the maximum "jet"-p T and the background after cuts on missing-p and absence of energetic leptons associated with background production

T +0

of heavy quarks decaying semileptonically.

2. CONTRIBUTIONS TO KSSIHG-p

Fig. 2 shows a Monte-Carlo raiss-p_ distribution for high-p_ 2-jet 7)

production using ISAJET for two different energy resolutions , It also includes angular smearing assuming the present DO design segmentation and 2° beam holes. Even though hard to quantify, one can hardly underemphasize several related virtues of the uranium-liquid argon calorimetry such as the stability of the energy scale and calibration, the uniformity of response and absense of radiation damage as well as the uniformity of response to electromagnetic (e-m) and hadronic showers.

Fig. 3 shows the effect on miss-p due to several widths of radial 7)

cracks in the central calorimeter , These cracks are pointing slightly off the beam axis and shower particles going into them are considered lost. In a more realistic M. Carlo Including shower development due to material Inside cracks the results may be slightly better, but the serious problem of narrow showers of high-p_ photons (Y) and electrons (e) lost in such cracks still

7 8) remains. Finally extensive M. Carlo BtudieB of 2-jet production * , indicate that the choice of a l 4 hole is an optimal one. Fig* 4 shows contributions from several sources: I a hole, energy (402/^) and angular resolution (o = 2 cm for single hadrons) as well as contributions from neutrinos (v)

X T of heavy quark decays and from 100 GeV/c gluinos (g). This implies that with U-calorimetry one starts to become sensitive to v-production, for miss-p T above 5-10 GeV/c. Miss-p^ and Y and e identification impose rather stringent requirements on the design of the forward/backward calorimeters, which we discuss next*

3. FORWARD/BACKWARD CALORIMETERS 9)

As illustrated elsewhere in this Workshop , 2 "end-cap" calorimeters sandwich the central one, looking directly at particles with angles down to 5°. Fig. 5 shows a side view, containing the beam. Each consists of parallel U (6 a.l.) and Fe-platea (3 a.l,, back section), each of a polygon shape with a round hole in the middle around the beam. The gape between plates contain liquid argon, readout pads and lines carrying pad signals to preamplifiers.

After each "end-cap" on each side there is an "end-plug" calorimeter with a simiLar structure. It is placed right before the low-beta quadrapole,

- 427 -

as is shown in Fig* &, at the maximum possible distance from the center,

to preserve a tolerable angular resolution at small angles. It has a

slightly higher density than the end-cap one to also minimize shower

transverse size.

4. TRANSVERSE AND LONGITUDINAL TOWER SEGMENTATION

The readout transverse segmentation of hadron towers is basically determined by 2 considerations 6^:

a) One must have A 9 / 9 < AE/E for the best possible Ap T/p T resolution. The shower axis for hadrons cannot be determined to better than 1/5 of the tower size. For a U-cal AE/E > .02, so A6 /6(tower) (= An (pseudorapidity)) -.10. In order to have square-like towers one must have A<ji -6°. However for 6

less than 4° the tower size becomes less than the shower size.

]i) The tower size need not be smaller than the shower size, since the large fluctuations in hadron-showers, limit their position resolution. Fig. 7 shows the end-plug segmentation. We have about 1000 hadron towers per end-cap and 360 per end plug calorimeter.

Since large fluctuations are absent from e-m showers, the front e-m

sections have finer segmentation, for example 1.5-2.0 era pads, and 0.5 cm

strips, promising to give resolutions of 1-2 mm, and also to improve

separation of nearby showers of y vs TT° and e Cor y ) vs jet. Fig. 8 shows

the probability of two jet-fragments hitting the same tower or adjacent

o W ° > .

Each tower is also subdivided longitudinally into 7-8 segments for readout as shown in Fig. 5. Subdivision of a shower's longitudinal distribution provides:

a) high resolving pewer for e vs T T " , y vs 7i° and e vs (it* + TT") overlaps, b) information on the depth of the first y conversion, which also helps to

resolve Y vs T T°* Fig. 9 shows this for Y , T T° etc., indicating the usefulness of having 2 thin (1-2 r.l.) segments as the first part of the e-m section.

5. CALORIMETER DENSITY

As indicated above, higher calorimeter density ieniies more compact showers

and better angular resolution* The smaller the angle 6 , the more important

the compactness becomes.

First, it minimizes the A 9 / 6 contribution to ûp^/p^. Fig. 10 shows

this dependence as a function of Ö for Jets, with a discontinuity at the

end-cap, end-plug interface (5°)-

- 428 -

Finally, it improves the spacial resolution for nearby showers of an e (or y ) v s jet, e vs Y and y vs T T ° .

REFERENCES

1. Experiments UA-1 and UA-2 at CERN.

2. DO Design Report, FNAL, December 1983.

3. Workshop on Searches for Heavy Flavors in Como, Italy, August 1983.

4. A proposal to upgrade the UA-1 Detector in order to extend its physics programme, UA-1 Collaboration, CERN, August 1983.

5. C. Baltay and H. Gordon, Snowmass 1982, p. 500.

6. Private communication with W. Selove.

7. S. Protopopescu, BNL, DO Report, 1984.

8. J. Freeman, FNAL, CDF Collaboration, talk presented at this Workshop.

9. The DO Detector by M, Marx, Stonybrook, DO Collaboration, talk presented at this workshop.

10. II. Welsberg, Stonybro-jk, DO Report, 198?.

FIGURE CAPTIONS

Fig. 1 Signal and background for production of 2 gluinos as a function of maximum "jet'-p^,, for various gZuino masses.

Fig. 2 Missing-p T distribution. Energy and angular resolution contributions.

Fig. 3 Missing-p T distribution. Central calorimeter cracks contribution.

Fig. 4 Total missing-p distribution. Contributions from I o hole, energy and angular resolutions.

Fig* 5 Schematic side-view of the readout longitudinal segmentation for the end-cap calorimeter.

Fig. 6 Schematic side-view of the end-plug calorimeter.

Fig. 7 Schematic front-view of the transverse segmentation for the end-plug calorimeter.

Fig. 8 Probability of 2 jet fragments to "hit" the same or adjacent calorimeter segments, as a function of jet-p^.

Fig. 9 Probability for electromagnetic shower initiation by a photon as a function of calorimeter depth, for various particle species.

Fig. 10 The e-depsndence of the p T-resolution for jets due to calorimeter angular resolution alone*

rig. 3 Flg. i

- 4 3 1 -

I i i • i ^ i i 'i i O I Z 3 4 5 6 7 8

D E P T H (IN RADIATION L E N G T H S J F i g . 9

C D

<J

ZQ crx;:0'y = 8mm

.15 -END PLUG

.10 -/ END CAP.

.05 i i i ^ —

i ! i ! c i i i i i

ANGLE TO BEAM AXIS S[deg] Fig. 1 0

- 432 -

CDF ELECTROMAGNETIC SHOWER COUNTERS D ¡ g4lrj0263ß^ Kunitaka Kondo University of Tsukuba, Ibaraki, Japan

1. INTRODUCTION F The collider detector a:: Fermilab (CDF) has 3 types of the electromagnetic

shower counters (hereafter abbreviated as EMSC) covering different angular ranges; i.e. the central (40° í 9 í 140°), the end plug (10° < 6 < 4 0 % 140° Ä 9 s 170°), and the forward/backward (2° S 6 £ 10°, 170° £ 6 £ 178°) electromagnetic calorl-

The central EMSC's have the lead/scintillator sandwich structure, while the end plug and the forward/backward EMSC's consist of the lead/proportional chamber layers. Each component has a conical tower structure pointing to the interaction point, armed with tracking chambers in the magnetic field of 1.5 tesla in front and hadron calorimeters and muon counters behind.

In the present report, the structure of each component is shown, and the characteristics, including the energy resolution, the linearity, the position resolution for the incident particles and the hadron rejection capability, as designed and/or observed by the beam tests will be discussed. Some features of the CDF EMSC's IréHl °

be discussed in the context of their physics capabilities.

2. CENTRAL EM SHOWER COUNTERS The structure of the central EMSC module is shown in Fig. 1. The signals from

scintillators are read out from two sides with wavelength shifters. The main parameters and the characteristics are listed in Table 1. The test results of the

2 )

first prototype have been reported elsewhere . To improve the characteristics, a new type of scintillator with two kinds of secondary fluors and wavelength shifter which matches the scintillator in wavelength have been developed^'. The main improvements are In a relatively long attenuation length ( ï 90 cm) and a large light output.

A second prototype similar in structure to the tower near 90° was built with 4)

the new materials and tested in the pion and electron beams . In Fig. 2(a), the output oí the counter as a geometrical mean of the pulse heights of two phototubes viewing the wavelength shifters is shown as a function of the beam energy. The res.-onse Is linear within 1 % up to 125 GeV. Since the photomultiplier gain saturation is less than 1 % in the observed charge range, the non-linearity above 125

- 433 -

GeV Is due to the longitudinal shower leakage. The energy resolution observed in the same test was 11.4 X/T/Ë (riß. 2(b)), which is consistent with our estimation of the sampling fluctuation of 10.4 and the photon statistics of 5.0 The response of the test tower cell was observed to be uniform within ± 5 % over more than 90 % of the area, which was well reporoduced by an optics simulation.

In the production process of the central EMSC's, careful quality controls were made on thickness and chemical uniformities of sclntillator-and wavelength shifter plates, smoothness of their surfaces, geometrical precision in the assembly. Special efforts'*^ were made to make the effective response of the wavelength shifter plate uniform over its whole area. This was practically done by putting an aluminum reflector printed with black pattern on the back of each wavelength shifter,

Uniformity among 48 equivalent tower cells is a crucial factor to achieve the accurate measurements without recouping to unrealistic precise mapping of all cells. Eased upon the quality controls and various measurements in the production line, we estimate the uniformity among 48 equivalent cells to be controlled better than 1 % in terms of the final output.

Calibration and mapping of the central EMSC are being made with beams at Fermilab. The calibration monitoring will be done with a movable &®Co source scanning the scintillator, with Xe flasher lamps at the edges of the wavelength shifter plates and LED flashers on the transition blocks in front of the photo-multipliers.

3. END PLUG AND FORWARD/BACKWARD EM SHOWER COUNTERS In the end-plug and forward/backward regions, tha gas ealorimetry is adopted.

The choice was made because of (a) relatively high energies of particles which are favorable to the energy resolution and (b) high, radiation background in these regions. The main parameters and expected or observed characteristics of the gas EMSC's covering these regions are listed in Table 2 .

The structure of an end plug EM and hadron shower counter set is shown in Fig. 3. The active detector here are proportional chambers with arrays of extruded resistive plastic tubes interleaved with G-10 cathode boards. Two prototypes of EMSC's were built and tested with the electron and pion beams in the energy range of 25 * 150 G e V 6 \

The linearity of the total collected charge to the energy of electrons is shown in Fig. 4(a). The observed saturation effect is well represented over a wide range of collected charge by a formula y = •— In ( 1 + ax) with a = 0,027pc where

- 4 3 4 -

x is the expected charge with no saturation and y is the observed charge. The observed energy resolution is 24 %/ VE~ (Fig. 4(b)), consistent with 3 0 % /t/E , where t is the sampling thickness.

The lateral profile of the shower is observed as the distributed signals on the cathode pads. Finite conductivity of the resistive plastic tubes causes lateral signal spread of the order of 3 cm in a , which helps determining the shower axis or the impact point of the incident particles. We obtained the spatial resolution of the order of 1.5 mm for E > 50 GeV.

Informations useful to identify electrons and photons against hadrons are the total energy deposit, the lateral shower profile, the longitudinal shower development as observed by the 3 segments of EM-and 2 segments of hadron shower counters* Contamination of the pion beam with electrons gave a lower limit of the pion rejection factor of 10 3 for the 80 % efficiency of electron detection. The calibration is being made by the beam at Fermilab, and will also be made by 5 5 F e sources placed at typical spots o£ the shower counters.

The forward/backward EMSC's have similar structures and expected characteristics as the end plug EMSC's. The cathode consists of extruded Al multi-channels with resistive surface on one side. The calibration with Rn mixed in Ar/methane gas is being planned and tested.

4. DISCUSSIONS Physics objectives of the electromagnetic shower counters include the single

y and ir° detections, the measurements of ;-he mass and width of Z° , the precise measurement of the mass ratio of 2° and W~, and use of the electron signal in search for new heavy particles.

The capability of the CDF EMSC's to separate two showers down to 10 mrad allows identifying 70 % of t r 0 ls from single y's up to about 20 GeV^. The expected Z° raass width (o) to be directly measured at CDF is 1.5 GeV1"^, The mass ratio between Z° and W~ will be measured to a few tenths of a per cent with the integrated luminosity of 1036 cm Z.

one of the unique features of CDF is the possibility of identifying electrons in a j e t 7 \ The detection or identification of leptons in a jet gives a signature for a heavy quark jet. Such"identification serves to find (a) new heavy quark(s) as well as to reject heavy quark backgrounds in search for new (e.g. g) particles^. Because of the fine granularity of CDF EMSC's only a single electron is contained in a tower to large fractions of the heavy quark jet events. A simulation study

- 435 -

REFERENCES 1) Dlsign Report for the Fennilab Collider Detector, August 1981, unpublished.

The groups involved in the EMSC's are AML, Brandeis, Fermilab, Harvard, KEK, Pennsylvania, Saga, and Tsukuba.

2) L. Nodulman et al. Nucl. Instr. and Meth. 204 (1983) 351. 3) T. Kanon et al. Nucl, Instr. Meth. 213 (1983) 261. 4) T. Kamon et ai. Submitted to Nucl. Instr. and Merh. 5) This was done at ANL. 6) Y. Hayashide et al. Nucl. Instr. and Meth. 204 (1983) 361,

Y. Hayashide et al. TEEE Trans. Nucl. Sei. NS-30 (1983) 112. 7) The author thanks S. Miyashita and S.F. Kin for discussions on the subject. 8) I. Hincliffe et al. Proceedings of the 1982 DPF Summer Study on Elementary

rar t i d e Physics and Future Facilities, Snowmass (1982) 242. 9) F.E. Pa'ge et al. Proceedings of the 1982 DPF Summer Study ou Elementary

Particle Physics and Future Facilities, Snowmass (1982) 471.

on this point was made by using ISAJET^. Table 3 (a) shows the probability a b-jet has no particles Inside the -jone with the axis along the electron momentum and the opening angle 6 C . At 6 = 20°, for example, a pad of the end plug EMSC has a dimension, of 6 cm * 6.5 cm which corresponds to 2° from edge to edge. The table

shows that, with the aid of tracking informations, we can identify about 80 % of che electrons in the b-jet with pion rejection factor better than 10 3 aa disfcussed before.

Photons accompanied with charged particles give signals similar to those of electrons. Since our shower couriers give the position resolution of the order of 2 ^ 3 mm, which corresponds to 1VL.5 mrad in the central and end plug regions, we can reduce this background down to less than a per cent only by the position information (see Table 3(b)). If one asks the consistency between the energy and the momentum measurements, the background will be reduced by another factor of 10,

The cracks in the boundaries of modules and 2° holes in the very forward and backward angles may sometimes mimic the missing neutral particles. The detailed simulation study on this problem and planning for possible detector improvement are under way.

- 436 -

Table 1. Parameters and Characteristics of the Central Electromagnetic Calorimeters

Size Chambers Number of Modules: 48 Location (Diipth) : 6 X 0

Tower Size: = 1 5 % 4n = 0.1 Wire Local Width: 1.4 cm Number of Layer: 30 Strip Width: 1.7 cm. 2.0 cm Thickness of Lead: 3 mm Tower Thickness: 20 X 0

Light Collection Characteristics Primary: polystrene Linearity: £ 99 % uo to 100 GeV Secondary Fluors: b-PBD, BDB Resolution: 12 %}JÊ*

WLS Fluors: Y-7 Position Resolution: < 2 mm*

PMT: Hamamatsu R580 Hadron Rejection**: £ l 0 3 * Sensitivity: 400 p.e./ GeV*

A) **) See next page.

- 4 3 7 -

Table 2 . Parameters and Characteristics of the Endplug and Forward/Backward Gas Calorimeters

End P I u k EMSC Forward/Backward EMSC

AnRular coverage 1.1 s n s 2 . 3 , 0 s $ s 360° 2.3 s n s 4 .0

Lead-chamber Sandwich Lead Thickness 2.7 mm 3.18 mm Number of Layers 34 40 Total Thickness 20 X 0 23 X„

Pad Readout Tower (Pad) Sise in •-• 0.1 for 1.6 s |r| s 2 .3 an = 0 .1

*= 0.05 for 1 . 1 5 s |n| S i . 6

no = 5° Number of Longitudinal Segments 3 2

n, $ Strip Chamber Location (Depth) 4.5 X 0 í d s 9.5 X 0 4 X„ n - Strip Size A n = 0 .02 , A4, = 30" A n = 0 . 02 , A4, = 30-Í - Strip S i 2 e A4, = 1 ° , 1.1 s |n| < 2.3 A 4 = 1° , 2.3 s |n| s 3 .1

Expected Characteristics Energy Resolution 24 U / / Ë * 25 1- 30 %//Ë Position Resolution o n ^ 04, £ ¿ mm o n ^ ^ 3 mm Hadron Rejection** > 1 0 3 * > 1 0 3

*) These values have been confirmed by the beam tests. **) The informations from hadron shower counters are assumed to be available.

- 438 -

Table 3(a) Probability that a b-quark jet has no particle (with energy E > 0.1 E e ) inside the 9 C cone.

Bç jets with "isolated" electrons

2" 60.4 % 1" 90.8 % 0.5° 95.2 %

Table 3(b) Probability that a light-quark or a gluon jet has a charged particle (with energy E > 0,1 E-y) within the 9 C cone.

e jets witH y accompanied with c a charged particle

2° 27.1 % 1° 11.7 % 0.5° 4.4 %

- 4 3 9 -

O 25 50 75 lOO 125 150 175 200 « M > °- M " 2 OJE ft2 OJU Fig. 2 (a) Linearity of Central EMSC Fig. 2 (b ) Energy Resolution of Croîtrai EMSC

- 4 4 1 -

Supercolliders

- 442 -D: 8 4 1 0 0 2 6 3 9 2

SUPERCOLLIDER PHYSICS

l a n H i n c h l i f f e Lawrence B e r k e l e y L a b o r a t o r y

Un ivers i ty o f C a l i f o r n i a B e r k e l e y , C a l i f o r n i a 9 4 7 2 0

' T h i s t a l k is c o n c e r n e d w i t h t h e phys ics o p p o r t u n i t i e s o f u n e x t r e m e l y h i g h e n e r g y p r o t o n - p r o t o n or

p ro ton a n t i - p r o t o n machir i^j (SSC) I t is based o n w o r k d o n e in c o l l a b o r a t i o n w i t h E. E i c h t e n , K. L a n e a n d

C . Q u i g g . 1 W e set o u t to d e t e r m i n e h o w t h e phys ics r e a c h o f a h i g h e n e r g y co l l i de r is a f f e c t e d b y i t s e n e r g y ,

l u m i n o s i t y a n d t y p e o f b e a m . I s h a l l se lect a f e w topics a n d discuss t h e m i n t h i s t a l k , t h e r e a d e r m a y r e f e r t o

RcF. 1 f o r a r a o r e c o m p l e t e d iscuss ion .

T h e t r i u m p h o f t h e G l a s h o w - W e i n b e r g - S a l a m m o d e l 3 i n c o r r e c t l y p r e d i c t i n g t h e W a n d Z masses* 1 h a s

m a d e e v e n more a c u t e t h e p r o b l e m o f h o w t h e e l e c t r o - w e a k s y m m e t r y is b r o k e n . W e h a v e a l m o s t no

e x p e r i m e n t a l g u i d e n c e i n t o t h e d y n a m i c s o f t h i s b r e a k i n g . T h e s i m p l e s t o p t i o n fqr t h i s d y n a m i c s is t h a t t h e

b r e a k i n g is caused b y a s c a l a r f ie ld a c q u i r i n g a v a c u u m e x p e c t a t i o n v a l u e . T h e s i m p l e s t m o d e l o f th is t y p e

h a s o n l y one p h y s i c a l p a r t i c l e , t h e H i g g s . U n f o r t u n a t e l y t h e c o n s t r a i n t s o n t h e H i g g s m a s s a r e r a t h e r w e a k

7 G e V < m H < 1 T e V . T h e l o w e r b o u n d cornea f r o m c o s m o l o g y . 4 T h e u p p e r bound is looser , i t is d e r i v e d

f r o m t h e o b s e r v a t i o n 5 t h a t a H i g g s w i t h m o r e m a s s hecomes s t r o n g l y i n t e r a c t i n g , i m p l y i n g t h a t p h e n o m e n a

not p resen t i n p e r t u r b a t i o n t h e o r y m u s t occur . M a n y t h e o r i s t s r e g a r d th is s i n g l e H i g g s p o s s i b i l i t y as

u n a p p e a l i n g . * T h e q u a d r a t i c d i v e r g e n c e s p r e s e n t i n p e r t u r b a t i o n t h e o r y l e a d to i n s t a b i l i t i e s i n t h e m a s s o f

t h e H i g g s . ' T h i s is s o m e t i m e s p h r a s e d i n t e r m s o f a h i e r a r c h y p r o b l e m w h i c h , p u t a t its s i m p l e s t , is the

i n a b i l i t y to u n d e r s t a n d w h y t h e sca le o f t h e F e r m i c o n s t a n t ( . l / V G p ~ 3 0 0 G e V ) is m u c h less t h a n the

P l a n c k mass ( ~ 1 0 1 9 G e V ) or t h e scale o f g r a n d u n i f i c a t i o n í - 1 0 1 * - 1 0 " G e V ) i f t h e l a t t e r e x i s t s .

M a n y t h e o r e t i c a l a l t e r n a t i v e s t o t h i s s i m p l o H i g g s m e c h a n i s m ex is t . S u p e r s y m m e t r i c 8 m o d e l s ,

w h e r e t h e H i g g s is s a v e d f r o m t h e s e q u a d r a t i c d i v e r g e n c e s b y h a v i n g a p a r t n e r s p i n 1/2 p a r t i c l e , p r e d i c t a

host or n e w p a r t i c l e s w i t h t h e s a m e q u a n t u m n u m b e r s as those i n t h e s t a n d a r d m o d e l b u t w i t h s p i n d i f f e r e n t

b y 1/2 u n i t . I n t e c h n i c o l o r m o d e l s 9 t h e H i g g s is n o t u n e l e m e n t a r y p a r t i c l e b u t is a b o u n d s t a t e o f a n e w

f e r m i o n a n t i - f e r m i o n p a i r . T h e p r o l i f e r a t i o n o f q u a r k s a n d lep tons h a s a lso led to t h e s u g g e s t i o n t h a t

q u a r k s u n d lep tons a r e n o t e l e m e n t a r y p a r t i c l e s b u t a r e b u i l t f r o m s o m e m o r e f u n d a m e n t a l p a r t i c l e s

(composi te m o d e l s ) . 1 0 A l l these a l t e r n a t i v e s (except p e r h a p s t h e las t ) h a v e o n e f e a t u r e i n c o m m o n ; t h e y a l l

p r e d i c t n e w phys ics o n t h e scale o f t h e F e r m i - c o n s t a n t . I t is t h i s scale t h a t a h i g h e n e r g y h u d r o n - h u d r o n

co l l i de r w i l l p r o b e . S i n c e n o p a r t i c u l a r m o d e l is c o m p e l l i n g , t h e m a c h i n o r e q u i r e m e n t s c a n bes t he d e f i n e d

by p e r f o r m i n g some k i n d o f e n s e m b l e a v e r a g e o v e r a l l these m o d e l s . T h i s done i n Kef. I.; t h e r e s t o f t h i s t a l k

f T h e scato logica l s i g n i f i c a n c e was r e c e n t l y d iscussed by S . G lushow. 1 *

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is arranged as follows. 1 first discuss the parton model and the structure functions; needed to estimate the production rates. ï then discuss hadronic gets, production rates of gauge bosons, searching for the Higgs, signals for compositness, and for a sequential heavy lepton. Supersymmetric predictions and those dealing with technicolor and non-minima] Higgs are discussed by some other speakers.11

A) The Parton Model Production rates in a hadron collider with center of mass energy Vs are given by

O h = a/dx lebt if i(x | 1Q2)rjJ[ic8.QBïo 5(£tÎu» ID

ÍJ"

where o-j(s, t, ul is the cross section for producing a particle of interest in a collision of two constituents of the beams labeled ij; they could be quarks or gluons. (ptv Q 2) is the probability of finding a constituent of type i inside the beam particle with momentum fraction x of the beam. Q 2 is some scale characteristic of the hard scattering process (o¡.) e.g. s* = XjXjS. The f¡(x, Q 2) fall rapidly with x, so if we are interested in producing some new particle with mass M, XjXg > M2/s and most of the integral (l)is dominated by x — M/\/s. Typically Oy a c/s, withe — a s

2 fora strong interaction orocess such as the production of a jet pair ora heavy quark, and c — o E M

2 for the production of a pair of gauge bosons. At a collider with V's = 40TeV, we could be interested in masses as low as 100 GeV (inaccessable at

LEP) or as high as tO TeV implying !

(10012GcV'2< Q 2 < (10*)2GeV2,x > 10"5 (2] with dominant region around x 5: 10"" 1 / 2 It is straightforward in principle to obtain these distributions. One takes data at all x for some small value of Q~ (Vim deep inelastic scattering experimenta and uses the Attarellî-Parïsî equations12 to evolve up in Q 2. The problems we encounter arc as follows.

1. Data do not exist below x = 0.01, and di/Tcrentset5ofdata are not consistent with each other. 2. tand b quark distributions may be needed, and the t quark mass is unknown. 3. The gluon distribution g(x, Q 2) is not directly measured, rather it is inferred from the Q2

evolution of the anti-quarks. 4. The Q C D parameter A is not well known and is correlated with g(x, Q-i). 5. Q C D perturbation theory may not he applicable at large and small values of x. The large x

region is irrelevant since fix, Q 2) is very small there. The small x region is more problematic but again is not relevant for tie tt i tig the upper reach of a machine (the largest M which can be produced) since for most processes this limit is set hy x -* O. I or greater.

In order to estimatP the effects of these uncertuinties (we can do nothing ubout the last one) the following technique was adopted1. Two puramctizations hased on those of the C D H 5 collaboration10 were evolved and compared. These pa ra motorizations di.Tcr in that a different value of It = n[;o-p was assumed in the analysis. A t Q 2 = 5 GeV 2 the values of xg(x, CJ-'lund x arc

set I: XHlx.ii2) = 12.62 + 9 17xK 1 - xl 5 9, A = .2 GeV (:0 set2: xglx.Q") = (1.7 + IS.f>7E)xHI-x>,!0:,,A = .29GeV (hî (31

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A s u s u a l t h e g l u o n d i s t r i b u t i o n w i t h m o r e suppor t a t l a r g e x (set 2 ) is c o r r e l a t e d w i t h a l a r g e r v a l u e o f

A . F i g u r e I shows t h e b e h a v i o r o f x g ( x , Q 2 ) a s a f u n c t i o n o f Q 2 f o r v a r i o u s x (se t 1 s h o w n ) . T h e d i f f e r e n c e

b e t w e e n t h e t w o sets is less t h a n 2 0 % o v e r t h e e n t i r e x a n d Q 2 r a n g e ( Q 2 < 1 0 6 G e V 2 ) .

I n o r d e r to e s t i m a t e t h e poss ib le u n c e r t a i n t i e s assoc ia ted w i t h t h e absence o f d a t a i n t h e s m a l l r e g i o n ,

t h e i n p u t d i s t r i b u t i o n s w e r e c h a n g e d for x < 0 . 0 1 as fo l lows .

Í 2 5 . 5 0 x m ( a )

( 4 )

.44 x " m - 1 . 8 8 6 (b)

T h e s e m a t c h a t x = O.Ol o n t o 3 ( a ) . A t Q 2 = 5 a n d x = 1 0 ' 4 4 ( a ) a n d 4 ( b ) d i f f e r b y a fac tor o f 1 6 0 , b u t a t Q 2 =

1 0 0 0 G e V 2 t h e d i f f e r e n c e is o r d e r 2 . T h e s e c o n c l u s i o n s a r e e n c o u r a g i n g because t h e y s u g g e s t t h a t t h e

u n c e r t a i n t i e s decrease as Q 2 i n c r e a s e s , a n d t h e d i f f e r e n c e s i n t h e s t a r t i n g d i s t r i b u t i o n s w a s h out . (See a lso

Ref. 14.) C o m p a r i s o n s w i t h o t h e r d e e p i n e l a s t i c s c a t t e r i n g d a t a e.g. those o f t h e C H A R M c o l l a b o r a t i o n 1 5

i n d i c a t e t h a t our a n t i - q u a r k d i s t r i b u t i o n s m a y be too s m a l l ( F i g . 2 ) . T h e s e p r o b l e m s c a n n o t be r e s o l v e d

u n t i l the d a t a i n t h e s a m e Q 2 r e g i o n a g r e e . T h e e f fec t o f a c h a n g e i n A f r o m ,2 G e V to .1 G e V for 3 ( a ) is less

t h a n 3 0 % o v e r t h e e n t i r e r a n g e o f x a n d Q 2 .

A usefu l q u a n t i t y to e s t i m a t e t h e r e a c h o f a c o l l i d e r is

r / sdE /d t = r/( 1 + 8^) / (fj(x, Q 2 ) t\ (tlx, Q 2 ) + i ± . j ) d x / x s ( 5 )

T h i s q u a n t i t y has t h e d i m e n s i o n o f a cross-sect ion a n d c a n h e used to e s t i m a t e t h e p r o d u c t i o n r a t e o f

s t r o n g l y i n t e r a c t i n g objects b y m u l t i p l y i n g by <zs". F i g u r e 3 s h o w s th is q u a n t i t y as a f u n c t i o n o f s a t f i x e d s

fo r g l u o n g l u o n co l l i s ions i n p p co l l i s ions . ( T h e pp r a l e is t h e s a m e . ) i t c a n be seen f r o m t h i s f i g u r e t h a t u t

v ' s — 4 0 T e V t h e r e w i l l be a r e a s o n a b l e n u m b e r o f e v e n t s a t v ' s — 10 T e V for a s t r o n g i n t e r a c t i o n process a t

a l u m i n o s i t y o f 1 0 3 3 « n " 2 s e c T h e f i g u r e shown t h e p r i c e p a i d i n t h e r e a c h o f a m a c h i n e a t f i x e d e n e r g y a s

the l u m i n o s i t y is l o w e r e d . T h e s a m e n u m b e r o f e v e n t s u t E = 1 0 3 ' cm ' 2 sec" ' is r e a c h e d a t V s = 3 T e V .

F i g u r e 4 shows £/sd£/dr for u u co l l i s ions i n pp c o l l i d e r s . T h e r a t i o pp /pp is s h o w n i n F i g u r e 5 . T h e s e

t w o f i g u r e s s h o w t h a t a c e r t a i n m i n i m u m l u m i n o s i t y is r e q u i r e d to e x p l o i t t h e a d v a n t a g e o f pp. F o r a w e a k

process (e .g . the cross s e c t i o n d o / d p t d y f o r t h e p t t h e p r o d u c t i o n o f a h e a v y g a u g e boson) t h e r a t e is r o u g h l y

a g M id£/dr/s. I f w e t a k e a y e a r o f 1 0 7 seconds a n d r e q u i r e IODO e v e n t s F i g . 4 shows t h a t a Vs = 4 0 T c V

m a c h i n e roaches v ' s — 7 , 4 , 2 T e V a t l u m i n o s i t i e s or 1 0 3 2 , 1 0 3 2 . 1 0 3 1 e n r see" 1 . F i g u r e * n o w s h o w s t h a t a t

t h e s m a l l e s t o f t h e s e l u m i n o s i t i e s t h e r e is e s s e n t i a l l y no a d v a n t a g e i n a pp m a c h i n e . A s d e c r e a s e s t h e

a d v a n t a g e e f p p a t t h e s u m e l u m i n o s i t y b e c o m e s w c u k c r .

11) I t u d r o n i C ' l e t s

I f u d r o n i c j e t s a t (u rge t r a n s v e r s e m o m e n t a ipj w i l l p r e s e n t a b a c k g r o u n d to n e w phys ics a t a h i g h

tmcrt fy co l l i de r so i t is i m p o r t a n t t h a t t h e y be w e l l u n d e r s t o o d . G i v e n p u r t o n d i s t r i b u t i o n s t h e r e a r e s t i l l

u n c e r t a i n t i e s i n t h e p r o d u c t i o n r a t e . T h e s c a l e w h i c h a p p e a r s a s

2 < Q 2 t c o n t r o l l i n g t h e 2 - * 2 s c a t t e r i n g

process a n d a p p e a r s i n f i x , Q 2 ) is u n d e t e r m i n w l . W e use p y V * Isee Ref . 14 a n d 16 ) , th is u n c e r t a i n t y is m o r e

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T A larger rate may he possible in non-minimal models with more than one physical Higgs particle.

important at the SpflS collider than at higher energies. Figure 6 shows the cross section do/dptdy at y = O for the SppS collider. A comparison with the data 1 7 reveals no gross differences. The contributions of the different final states, gluon-gluon, gluon quark and quark quark are shown separately. Notice that configurations with gluons in the final state dominate over the region of most of the data. The cross section at V's = 40 TeV is shown in Fig. 7 and at Vs = 10 TeV in Fig. 8. Even a high luminosity machine will have great difficultly in obtaining a clear sample of quark jets. The production rate of these jets is enormous; Fig. 9 shows the cross section for the production of two jets with rapidity y corurained, |y| < 2.5 and transverse energy E T greater than E T 0 for Vs = 10,40,100 TeV as a function of E T 0 . At a luminosity of 10 3 3 cm"2 sec'1

the rate of jet production for Ef 0 = t TeV at Vs = 40 TeV is 400 Hz. The production rate in pp and pp

colliders at the same Vs is equal to within 20%. The number of three jet events is also impressively large.1

C) Production of Gauge Bosons. The total cross sections for the production of W + in pp and pp collisions is shown in Fig. 10. Since

s = M w2 and hence c is rather small at Vs = 40 TeV the production rate is dominated by sea quarks and the

advantage in rate provided by the vaience anti-quarks in pp collisions is extremely slight. At Vs = 40 TeV the production rate is very large (— 120 nb) but most of the W's are produced at small angle. Figure 11 shows the rapidity distribution; approximately 75% of the W's are emitted within 5° of the beam.

There rruy exist new W's with a larger muss than 100 GeV. If we assume a coupling to quarks equal to that of the standard W the production rate of Fig. 12 is obtained. The cross-section has been integrated requiring that the new W has |yj < 1.5 and the figure shows pp collisinns. The rate for pp is lightly larger (Fig. 13) but ag-ii a minimum luminosity is needed to exploit the advantage. If we require 000 produced new W's, which should be enough to discover one, given a reasonable branching ratio into vi, <-e obtain a maximum mass which can be explored at fixed values of Vs and integrated luminosity. Figure 14 shows this massas a function of Vs for different values of f£dt in a pp machine. It can bo seen that a 10 3 3cm "sec"1

machine at Vs of 40 TeV can reach masses of 7 TeV.

D) Searching for the minimal IHggs

The Higgs is not a typical member of the zoo of particles predicted by nodcls to have masses in the 1 TeV region. H has a rather small production cross-section and is one of the most difficult particles to see. In this respect it places the strongest demands upon energy and luminosity. If the Higgs is lighter than 2 M w , it decays into heavy quarks (tt if m H > 3mt, bb otherwise). In this case the background is from the Q C D production of heavy quarks, assuming that the detector can distinguish between light and heavy quarks. This background is much greater than the signal,1 so it seems difficult to delect a light Higgs unless its production rate is much larger than the estimate given here.* If m (| > 2 M W or 2M Z, it decays almost exclusively into '/.'/, und W W final states with a width

- 4 4 6 -

T(H -» WW) = 2HH -» ZZ) = 320 m, 3 GeV (6)

where m H is measured in TeV. Two mechanisms Tor the production of the Higgs are relevant. Gluon-gluon fusion18 via an intermediate quark loop yields the rate shown in Fig. 15. The rate is sensitive to the .jp quark mass, and also to the presence, if any, of extra generations. M t = 30 GeV has been used and the figure should probably be viewed a lower bound on the production rate for this mechanism. The Higgs can also be produced by WW (or ZZ) Fusion.19 The rate for this process is shown in Fig. 16. At large values of mu this mechanism dominates since it exploits the large width for II —» WW.

The signal for a heavy Higgs will be a peak in the invariant mass of a W or Z pair. 2 0 The background is from the continuum production of W pairs, 2 1 Figure 17 shows the cross-section for pp -> W+W~ 4- X as a function of energy. The W's from the continuum are produced with a flatter rapidity distribution than those from Higgs decay. Fig. 17 also show the rate if the W's are restricted to have rapidity less than 2.5 or 1.5. Figure 18 shows the signal and background in the W pair channel for a Higgs produced at Vs = 40 TeV. The W's are required to have rapidity less than 2.5. The background is obtained from r ( I do/dM where M is the masäof a pair of W's produced in the continuum. The signal and background are comparable. Figure 19 show'i the signal and background at v's = 10 TeV. The signal to noise ratio is worse.

Luminosity is extremely critical, as is the efficiency with which the W's (or Z's) can be detected. It may be possible to detect W pairs from the hadronic modes of the W. There is a lurge background from the QCD production of multi jets and a preliminary study of the problem22 indicates that this will be very difficult. If gauge bosons can only be detected in leptonic modes, only the ZZ final state can probably be dearly reconstructed with an efficiency of (0.06)2. Figrr^ 20 shows the signal and background in this channel. For m H = 500 GeV there are approximately 10 detected events for j£dt = 10 4 0 , which is probably enough given the cleanliness of the signal. One will have to look hard to find a Higgs but it does seem possible. The production rates in pp are the same but the background is somewhat worse.1 One final word; the production rates used could be tno small if the t quark mass is larger than 30 GeV or if there arc more generations of quarks.

The proliferation of quarks and leptons has led to speculation that they may not be pointlike particles but are rather built from some more fundamental objects called prcons. These preons are bound together by a new force with a binding scale A. At energies much loss than A, this composite structure could manifest itselfas u four fcrmion interaction between quarks ofthc- following form.2*

I Icrc u» represents u quark, g is the coupling strength of the new interaction whose spin structure is specified by A and 11. This term is a low energy residue of the now interaction and will interfere with one gluon exchange to produce u cross-section Tor quark quark scattering at wide ungte und center of muss energy v's, which has the following symbolic form

E^The search for compositness of quarks and leptons.

gÂ'tpAtpipBtp (7)

o - B o,.-/* 4- F a^WV2 + G s u 4 / * * (8)

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H e r e E , F , G depend o n t h e s c a t t e r i n g a n g l e a n d F a n d G a lso d e p e n d o r O e d e t a i l e d s t r u c t u r e spec i f i ed b y A

a n d B. T h i s f o r m Is v a l i d o n l y w h e n s < A . 2

I f w e a s s u m e t h a t t h e i n t e r a c t i o n ( 7 ) is d i a g o n a l i n f l a v o r a n d t h a t t h e c o u p l i n g i n v o l v e s o n l y l e f t

h a n d e d q u a r k s ( A , B - y ^ l - y 5 ) ) ) , t h e n w e o b t a i n t h e r e s u l t s h o w n i n F i g . 2 1 w h i c h shows t h e e f fect o n t h e

j e t cross-sect ion d o / d p T d y a t y = 0 a n d V s = 4 0 T e V i n pp co l l i s ions as a f u n c t i o n o f A for £l4n = I . T h e

scale Q 2 i n t h e p a r t o n d i s t r i b u t i o n s w a s t a k e n to be P T

2 , a c o m p a r i s o n w i t h F i g . 7 . r e v e a l s t h e s e n s i t i v i t y to

t h i s choice (see sect ion B ) . F o r t h e v a l u e s o f A s h o w n t h e eiTects o f t h e second a n d t h i r d t e r m s i n e q u a t i o n 8

a r e c o m p a r a b l e .

A s e a r c h Tor s u b s t r u c t u r e invo lves l o o k i n g a t t h e j e t c ross -sec t ion a n d s e e i n g t h a t i t is f l a t t e r i n p T

t h a n expected f r o m Q C D a l o n e . T h e r e is a p o t e n t i a l p r o b l e m i n t h a t t h e Q C D e x p e c t a t i o n d e p e n d s on t h e

s t r u c t u r e funct ions w h i c h n e e d to be k n o w n w i t h r e a s o n a b l e a c c u r a c y . F o r t u n a t e l y , r e g i o n s of x r e l e v a n t

a r e such t h a t one c a n h a v e conf idence t h a t t h e s t r u c t u r e f u n c t i o n u n c e r t a i n t i e s a r e less t h a n a fac tor o f t w o .

T h e f o l l o w i n g c r i t e r i o n s h o u l d be a d e q u a t e for d e t e c t i n g a c o m p o s i t e e f fec t . I f A ( p T ) is g r e a t e r t h a n one or

less t h a n 0 .5 w h e r e

A ( p T ) = d ° / d p T d y L 3 c r v e ( 1 - d o 7 d p T d y | Q C D

E (9) ^PTôbsGrverf

I f w e a s k t h a t t h i s c r i t e r i a be sa t is f i ed a n d t h a t t h e r e b e m o r e t h a n 5 0 e v e n t s per u n i t o f y t h e n the 4 0 T e V

co l l i de r h a s s e n s i t i v i t i t y u p t o A = 15 T e V for a n i n t e g r a t e d l u m i n o s i t y o f l O 4 0 c m - 2 s e c " 1 .

F Ï S e a r c h i n g for a h e a v y l e p l o n

O n e is used to t h i n k i n g t h a t i t is v e r y d i f f i c u l t to find a h e a v y lepoon i n a h a d r o n c o l l i d e r s ince the

p r o d u c t i o n ra tes a r e s m a l l a n d t h e s i g n a l poor. H o w e v e r , a n e w h e a v y l e p t o n L a p p e a r i n g i n a d o u b l e t ( L , N )

w i l l decay L - » W + N i f m L — m N > I w i l l a s s u m e t h a t t h e m a s s o f t h e n e w n e u t r i n o N is v e r y s m a l l .

L + L " c a n be p roduced i n p a i r s in t h e D r e l l - Y a n m e c h a n i s m . T h e final s t a t e w i l l consist of W + W " + m i s s i n g

m o m e n t u m ( c a r r i e d of f b y N ) g i v i n g a s i g n a t u r e w h i c h s h o u l d he r e c o g n i z a b l e e v e n w i t h t h e s m a l l r a t e .

T h e l e p t o n c a n a lso be p roduced s i n g l y b y the w e a k a n a l o g o f t h e D r e l l - Y a n m e c h a n i s m

q q - » W * - » L N ( 1 0 )

th is process leads to a s i n g l e W in t h e final s t a t e a t l a r g e p T w i t h a l a r g e a m o u n t o f m i s s i n g p T F i g u r e 2 2

shows d o / d y a t y = 0 for t h e process pp - > I . * N + X > w h e r e y is t h e r a p i d i t y o f t h e L N p a i r , as a f u n c t i o n o f

m ( . T h e r a t e s a r c s m a l l b u t t h e o n l y b a c k g r o u n d f r o m o l d phys ics is t h e final s t a t e W + Z w h e r e t h e 7.

decays i n t « n e u t r i n o p a i r s . W e c a n e s t i m a t e t h e b a c k g r o u n d as f o l l o w s . C o m p a r e t h e s i g n a l w i t h |y| < 1.5

w i t h t h e b a c k g r o u n d w h o r o b o t h W a n d 7. h a v e jy| < 2 . 5 . T h i s l a r g e r b i n is needed to t a k e a c c o u n t o f t h e

nn ih i t i t y o f the W f r o m h decay . R e q u i r i n g a n excess « f 5 0 e v e n t s o f s i g n a l o v e r b a c k g r o u n d g ives F i g . 2 3

w h i c h s h o w s t h e c e n t e r or mass e n e r g y needed to r e a c h u p a r t i c u l a r l ep ton mass for fixed v a l u e s o f e f fec t i ve

l u m i n o s i t y . T h e t r u e l u m i n o s i t y ia t h e e f fec t i ve v a l u e d i v i d e d by t h e e f f i c iency for d e t e c t i n g a W . 11' t h i s

448

eff ic iency is 0(1/10> t h e n a t v ' s = 4 0 T e V a co l l ider wfth l u m i n o s i t y o f 1 0 s 3 c m " 2 sec" 1 c a n r e a c h masses o f

order 7 0 0 G e V .

G ) C o n c l u s i o n

I w i l l s u m m a r i z e v e r y b r i e f l y t h e c o n c l u s i o n s d r a w n f r o m R e f . I . S e v e r a l u n s o l v e d p r o b l e m s

c o n c e r n i n g b a c k g r o u n d s p r e v e n t one f r o m c l a i m i n g t h a t s o m e p a r t i c u l a r s i g n a l is c l e a r l y o b s e r v a b l e . O n e of

the most c r i t i c a l issues concerns t h e o b s e r v a b i l i t y o f W*s a n d 2 's f r o m t h e i r d e c a y s i n t o h a d r o n i c j e t s . M a n y

s i g n a l s for n e w phys ics i n v o l v e f i n a l s ta tes w i t h W ' s or Z's (e .g . t h e m i n i m a l H i g g s d iscussed i n D ) . I f one is

r e s t r i c t e d to o b s e r v i n g t h e W ' s a n d Z*s v i a t h e i r l ep ton ic m o d e s ( w h i c h m a y n o t be possib le fo r f i n a l s ta tes

i n v o l v i n g m o r e t h a n one W ) o n l y a s m a l l n u m b e r o f e v e n t s w i l l be d e t e c t e d — 5 0 0 0 Z p a i r s d e c a y i n g in to ce

a n d p p resu l ts i n o n l y 18 de tec ted e v e n t s . T h e phys ics b a c k g r o u n d to h a d r o n i c d e c a y s o f W a n d Z is f r o m

Q C D e v e n t s w i t h m u l t i p l e j e t s . I n t h e case of final s t a t e s w i t h 4 j e t s w e h a v e no r e l i a b l e Q C D e s t i m a t e .

M a n y p a r t i c l e s e a r c h e s ( e . g . s u p e r s y m m e t r i c o n e s ) i n v o l v e s i g n a l s w h i c h h a v e m i s s i n g t r a n s v e r s e

m o m e n t u m , so t h e i m p o r t a n c e o f h e r m e t i c de tec to rs w i t h 4 n c o v e r a g e c a n n o t be o v e r s t a t e d .

T h e d i f f e r e n c e b e t w e e n a pp a n d a p"p co l l i de r is l i m i t e d to a f e w specia l cases w h e r e t h e presence of

v a l e n c e a n t i q u a r k s i n t h e a n t i - p r o t o n is i m p o r t a n t ( for e x a m p l e in t h e p r o d u c t i o n of a n e w W ) . I n o r d e r to

e x p l o i t th is a d v a n t a g e a c e r t a i n m i n i m u m l u m i n o s i t y i s r e q u i r e d . (— 5 x 1 0 3 1 c m " 2 s e c - 1 for v ' s = 40 T e V ) .

I n conc lus ion a 4 0 T e V m a c h i n e o p e r a t i n g a t a l u m i n o s i t y o f a t l e a s t 1 Q 3 2 c m - 2 s e c ' 1 , s e e m s c a p a b l e o f

a n s w e r i n g the f u n d a m e n t a l ques t ions s u r r o u n d i n g t h e b r e a k i n g of w e a k i n t e r a c t i o n s . T h e s a m e a s s u r a n c e

c a n n o t be g i v e n f o r a 1 0 T e V M a c h i n e a t t h e s a m e l u m i n o s i t y .

A c k n o w l e d g m e n t s

I w ish to t h a n k m y c o l l a b o r a t o r s E s t i a E i c h t e n , K e n L a n e a n d C h r i s Q u i g g f o r t h e i r u n c e a s i n g e f fo r ts

i n o u r s e e m i n g l y end less c o l l a b o r a t i o n . T h e w o r k w a s s u p p o r t e d b y t h e D i r e c t o r , O f f i c e of E n e r g y R e s e a r c h ,

Of f ice of H i g h E n e r g y a n d N u c l e a r P h y s i c s , D i v i s i o n o f H i g h E n e r g y Phys ics o f t h e U . S . D e p a r t m e n t of

E n e r g y u n d e r C o n t r a c t D E - A C 0 3 - 7 6 0 0 0 9 8 .

- 4 4 9 -

Referances I. E. Eichten, I. Hinchliffe, K. Lane.C. Quigg, FNAL84/17-T, LBL-16875, DOE/ER/01545-345 (1984). 2 S. L. Glashow, Nucl. Phys. 22,579 (1961);

A. Salam in "Elementary Particle Theory" p 367 ed W . Svartholm, Almquist and Wiksell (1968). S. Weinberg, Phys. Reu. Lett. Ig, 1264 (1967).

3. G.Arnison.etal., Phya. Lett. J22B. ¡03 (1983); Pkv. Leu. 126B. 39811983).

M. Banner, et al., Phys. Leu. 122B. 476(1983);

P. Bagnaia, et al, Phy. UU. 129B. 130 (1983).

4 A. P. Linde, Sou. Phys. JBTP Lett. 23 64 (¡978);

S. Weinberg, Phys. Reu. Lett. 38,29411976).

5. B. W . Lee, C. Quigg, H. B. Thacker, Phys. Reu. DIS, !S19 (1977).

6. S. L. Glashow in Science 84 February 1984. 7. K. A. Wilson, Phys. Reo. D3,18¡8 (¡971).

8. H. Haber and G. L. Kaue, Phys. Rep. to appear and Refs. therein. S. Dawson, E. Eichten, C. Quigg, F N A L &3/82-THY0984).

9. E. Farhi and R. Jackiw (editors) Dynamical gauge symmetry breaking. World Scientific Publishing Singapore (1982) and Rcfs. therein.

10. R. Peccei, these proceedings. II. D. V. Nanopoulos, these proceeding:

D. Wyler, these proceedings. 12. G. Altarelli and G. Parisi, Pud. PJrys. B126.298 ( 1977).

13. II. Abramowicz et al., Z. Physik C¡7.199< ¡983):£132. S3IÍ982).

14. R. K. Ellis these proceedings. 15. F. Bergsma et al., Phys. Lett. 123B. 269(1983).

Iß. R. K. Ellis etnl, ATucí Phys. B173,397(¡980);

W. Slominski, Jagellonian University Thesis (1981 í. 17. P. Bagnaia et al., Z. Physik (M, 117(1983); CERN-EP 84/12. 18. H. Georgi, etat., Pftys. Reu. Lett. 40, 692(1978).

19. R. N. Cahn and S. Dawson, Phys. Lett. 136B.196I1984).

20. H. Gordon, et al-, in Proceedings of the 1982 DPF Summer Study on Elementary Particle Physics and Future Facilities ed. R. Donaldson, R. Gustafson and F. Paige Batavia, IL (1982).

21. R. W. Brown and K. O. Mikoelian, Phys. Rev. 019,922 ( ¡979).

22. M.K. Gaillard. UCB-PTIÍMI2 ( ¡984).

M. Shochct in Proc. ofOPFstudy on pp colliders L'. Chicago, Feb. 1974. 23. E. Kichen. K. Lane, M. Pcskin, Phys. Reu. Uli. SU 811 (1910).

- 450 -

Fig. 1 The distribution xg(x, Q 2 ) vs Q 2 in GeV aat x = 10 _ Afeolid line) x « :0 - 3(dotted) x x = .1 (dashed).

20" ¿(dot-dashed) Fig, 3. The function T / S di/dr in nanobarns (eq, 5) as a function of / s for /s = 2, 10, 20, 4D, 7C, 100 TeV for gluon gluon collisions.

Fig. 2. Comparison at Q 2 = 50 GeV 2 of x times the distribution functions, of Che CHARM collaboration 1 5(dashed regions) with these of Ref, I . (dashed line) twice the anLi-quarks (dotted line) and the sum of up and down valence quarks (dot-dashed line).

Fig, 4. The function r/s d£/dt in nanobarn (eq. 5) as a function of /I for /s = 2, 10;^20, 70, 100 TeV for uu collisions in a pp collider.

- 451 -

Fig. 5 The ratio of T / S di/dr for uu collision in pp to that in pp at /s = 2, 10, 20, 40, 70, 100 TeV as a function of Sí.

T 1 1 1

Fig. 7. As Fig. 6 except for pp mollis-g ions at /s = 40 TeV.

4.14 0.19

Fig. 6 . The cross-section do/dp dy in nb/GeV at y = 0 for the production of a - 7

jet in pp collisions at /I « 540 SeV (solid line) the final states, gluon gluon (dot dashed) gluon quark (dotted) and

- . 1 0 r-

quark quark (dashed) are shown separately. F i £ - 8 - As Fig. 6 except for pp colli-ions at /« - 10 TeV.

- 452 -

Et T«V

Fig. Il The rapidity distribution dç_/dy in nanobarns for the production of w in

zo PP collisions at - 40 TeV.

Fig. 9. The cross-section in nanobarns for the production of a pair of jets each vith ]y| < 2.5 and with total transverse energy greater than E _ n . /s = 10, 40 100, TeV shewn. X V

Fig. 10 Tito total cross section in nano- U r T e V

barns for the production of W+(doCtûd , J . I line), M " (dashed li«e) in pp collisions' 1^ "he cross section for pp VP as a function of /s. Also shown are t h e i n nanobarns as a function of the mass of rates ly I <1.5. t n e n e w ^ • The " is contrained to

100 TeV shown. 1.5. rs - 2» lOv 20, 40,

- 453 -

- 454 -

0.2 0.4 0-0 6. B I

*.* 0.4 O.B O.B 1 Tig. 18. Signal and background in nanobarns *, w , for ttie process pp + H •» N »" with |y v| < 2.5 at /s - 40 TaV. p i g . 20. Signal and background in nanobarr.

for the process pp -f H ->• ZZ with < 2-5 at /s = 40 TeV.

- 4 5 5 -

T 1 1 1 r

o.a t6 s.t> s.e «.« PI T«T/c

Fig. 2L. The jet cross section do/dp dy at = 40 TeV and y = Q in nanohams/GeV aso ' 1 • 1 ' 1 • 1 i L_

a function at p showing the effect of the 0 Z Q 4 0 0 0 8 0

term Eq. 8. A « 5, 10, 2u TeV shown. sqri(»> uv -2

Ml T«V

F i g . 22 . The c ross s e c t i o n do/dy i n nano?-ba rns a t y * 0 for the p roduc t ion of an (LN) p a i r by che p rocess r*f Eq. 10. / s -2 , 10, 20, 4 0 , 70, 100 TeV

- 456 -

tAPfig HAOPON COLLIDER TH THE LEP TUNHEL (AN EXAMPLE OF A HADRON COLLIDER) A f e a s i b i l i t y studv of p o s s i b l e n o t i o n s

Jh*—CERN Machine Group presented by 6. Brianti D : 8 ^ 1 0 0 2 6 4 0 6

European Organization for Nuclear Research 1211 Geneve 23 - Switzerland

1 . n:rftooucTiON Hadron colliders (proton-proton or proton-antiproton) with bunched beams

seem to be the only practical way of obtaining center-of-mass energies of several TeV or even tens of TeV. which opens the way to investigate collisions at constituants level in the TeV mass region.

Two examples of such colliders are the SSC (Super-Superconducting Collider) being studied in the U.S.A. and the LHC (Large Hadron Collider in the L£P tunnel) in Europe. [~A*rather comprehensive account of the possibilities offered by the LEP tunnel is given as an illustration of the technical aspects and of the interplay between machin* parameters and experimental requirements4'. J(0</U$jfc

At the time of writing (May i960 the SSC reference design report has become available2. It concerns a proton-proton collider of 20 TeV beam energy presunted in three variants depending upon the chosen magnetic field of 3, 5 and 8.5 T .

The reader should refer to this report for further details.

2. REVIEW OF POSSIBLE OPTIONS A widt rang* of possibilities exists for a Hadron Collider in the LEP

tunnel, as shown in Fig. 1. Th* conceptually simplest option is f. op ring with a single beam channel which can »ither be built with super-conducting magnets of present technology or with high-field magnets after a fair amount of research and development effort. Th* luminosity is relatively low because antiproton sources are not very intense. In ordar to make provision for bunch separation at unwanted b*am crossings, th* aperture must be somewhat enlargsd with respect to a single beam machins.

Using two beam channels gives a more versatile collider. The rings can have either a common magnetic circuit, #hich couples both rings magnetically, or two independent circuits. For spice reasons, the two beam channels will always be in one cryostat. The most interesting option is the one where the two beam channels are side by side allowing for high luminosity pp collisions with many bunches. Depending on the desired field level, the two apertures may be part of a common magnetic circuit or of separate circuits.

- 4 5 7 -

In the first case icoimon magnetic circuit) there is enough space in the LEP tunnel to install high-field magnets. At high field level, the field must be necessarily equal and opposite in the two apertures as required for pp operation. This precludes pp with the beams in two separate channels. At considerably lower field level, the magnets can be excited such that the field is the sane in both apertures and pp operation in two channels becomes possible. Of course it would be possible to put both the proton and the antiproton beam in one of the apertures, and either work with a low number of bunches at low luminosity without separation or instill separators.

In the second case (independent magnetic circuits), pp and pp operations are equally passible at nominal field but, for space reasons, only moderate fields {* 5 T) can be obtained.

Having the two coupled channels on top of each other allows for a pp machine which can have as many bunches as required without being beset with the problem of bunch separation as the one channel pp option. However, since this configuration does not provide a pp option, it is not considered any further.

These arguments favour very clearly the side-by-side, two-channel pp collider with one magnetic circuit; it holds the promise of top pp performance while leaving the door open for pp physics. The machine study focused on this option because it also appears as the more demanding one from the technological point of view.

The other option which has received some attention is the one-channel, high field pp collider. These two options represent in a certain sense two extremes and, therefore, provide a good coverage of the total range of possibilities.

Before turning to the machine performance of these two options we cast first a glance at the detector performance. Fig. 2 shows a graph of luminosity L versus the time elapsing between two bunch collisions in the deetector. Also drawn are lines of constant L.T t along those lines the number of events <n> per bunch collision is constant for a given total proton-proton cross-section I. Since it is very difficult to handle more than one event per

25 -2 bunch collision, the line 1x10 cm therefore becomes an upper limit of the working region for a total cross-section of 109 mb. The maximum possible trigger-rate of the detector puts a lower limit on T^ providing a boundary on the left. One of the results of the March 1984 CERN-€CFA workshop was that values for T^ as low as 25 ns are conceivable without this being a too hard limit. Thus it can be seen that a luminosity of about 4.10^* can be obtained if tha operating point of the machine is put at the top left corner of the region allowed for bj the detector performance. For experiments which can accept a higher <n>, luminosities up to < 1.5xi033 (cm~2s~S could possibly be reached.

- 458 -

From the machine point of view this high luminosity operation is indeed feasible with the pp option. The number of bunches k is between 3000 and 1000. In order to make the bunch-to-bunch distance a multiple of the ftF wave-length in the LHC and in the SPS, only discrete values of k irt permitted. The value of 3564 fulfils this requirement and was chosen as nominal value. The graph also indicates the total number of particles which does not appear to be excessive, since it corresponds to only a few SPS pulses at the present performance level. The stored energy in the beam remains acceptable in the range under consideration: it reaches 10 HJ at H - 5x1Q13. The beam-beam effect, imposing a limit on the number of particles per bunch, is of not much concern because it cannot become very strong as long as the constraint of one event per collision is respected. The bunch intensity also seems low enough such that beam instabilities are avoided or can be dealt with by feed-back systems. Table 1 (see section 21gives a list of the main parameters.

If detectors with a higher trigger rate were developed, the operating point could move upwards along the line L.T = 10 Z S cm - 2 and eventually approach

33 -2 -1 * L = 10 cm s for s 10 ns. Howevt»*-, this implies an increase of the total number of particles H, which in turn means more stored energy in the beam. The increased number of bunches makes the beam also more prone to coupled-bunch instabilities. For this reason it is preferred to keep the nominal numbr- of bunches at 3564, in agreement with the presently estimated detector performance, and to work out a consistent set of parameters on this basis, though it is not unreasonable to expact the eventual operating point somewhere in the shaded area of Fig. 2

In the pp option the luminosity is limited by the p accumulation rate, which determiies the total number of particles N - accumulated in a time

P comparable to the luminosity decay time in the LHC. Ks explained in section 3 we may expect M- = 1Q 1 2 vit h the new antiproton source under construction in

3 1 - 2 - 1

CERN. Thxs imposes an upper limit on the luminosity around 1.5x10 cm s . In order to minimize the number of unwanted bunch crossings in the one-channel machine, this limited number of antiprotons is distributed over the minimum number of bunches compatible with the requirement of one event per bunch collision. This leads to th* working point shown in Fig. 2 for N- = 10 1 2

P and, taking into account th* constraints by the RF system, to lue bunches in the machine, corresponding to T^ = 825 ns.

If a ten times more intense antiproton source became available, the luminosity could be increased in principle to a level of about I.5xt032. However, as can be inferred from Fig. 2, this leads either to an elaborate system for bunch separation at about 2QQ0 unwanted crossing paints, which becomes especially tricky near the interaction points, or to many events per

459 -

bunch c o l l i s i o n in t he d e t e c t o r , which i s hardly accep tab le . Obviously, a wide range of combinations in between these two extremes e x i s t s but a l l of them are bese t with the problems of beam separa t ion and of mu l t i p l e events per bunch c o l l i s i o n . Thus i t seems to be d i f f i c u l t to exp lo i t a more powerful source for peak luminos i ty . I t shoulti be noted, however, t h a t the luminosi ty averaged over a run can be much improved by a b e t t e r source because the machine f i l l i n g can De more f requent . Nore d e t a i l s a re given in s ec t ion 3 .

2 . THE on OPTION 2 . t payout, parameters and performance

Fig . 3 shows schematical ly the r ing layout with the 8 i n t e r a c t i o n p o i n t s . The two beam channels a re separated h o r i z o n t a l l y by < 180 mm, and the i n s e r t i o n s are designed such t h a t the beams cross with a small angle of 96 prad in the i n t e r a c t i o n p o i n t s . Detectors can be put over a t l e a s t s ix i n t e r s e c t i o n p o i n t s . Two long s t r a i g h t s ec t ions a re reserved for the dumping of tne beams though i t might be poss ib le to put eventua l ly both dump systems in to one s t r a i g h t s e c t i o n . Fig. 4 gives a c r o s s - s e c t i o n of the LEP tunnel with the d ipo le of the LHC above the LEP magnets. I t i s apparent t ha t the space ava i l ab l e for the Hadron Col l ide r i s adequate . The assumption of i n s t a l l i n g i t in the LEP tunnel determines the circumference which should be equal to tha t of LEP, £6658 m, within a very small margin; the number and length of the s t r a i g h t i n s e r t i o n s , e igh t i n s e r t i o n s of about 490 m leng th ; and the average rad ius ov tbe a r c s , R = 34 94 m. Because cf t he fixée" r a d i u s , t he maximum energy in each beam becomes a function of the magnetic f i a ld in the d ipo les and of the layout of the LHC p e r i o d s . The study i s based on a d ipo le f i e l d B = 10 T.

The two proton beams are assumed t o be bunched, c o l l i s i o n s between the bunches occur only i n t he i n t e r a c t i o n r e g i o n s . This i s achieved by a small c ross ing angle between the two beams. Bunched beams are prefer red over continuous beams because they held the promise of a higher luminosi ty for a given c i r c u l a t i n g c u r r e n t , and a l s o because the energy lo s s due to synchrotron r a d i a t i o n i s au tomat ica l ly compensated by the RF system.

From the u s e r s ' point of view, the most important parameters a re the luminosi ty L, the bunch spacing T^ and the average number of events per bunch c l a s s ing <n> r e l a t e d by

<n> . L . T x . E where Z i s the t o t a l proton-proton c r o s s - s e c t i o n . At the CERN-ECFA workshop a consensus was reached t h a t , in the most genera l case . <n> should not exceed

u n i t y . For a c r a s s - s e c t i o n of 100 mb, t h i s means t h a t the product ion L.T 25 -2 * should not exceed a value of 10 cm Given t h i s c o n s t r a i n t , the l a r g e s t

460 -

luminosity is obviously achieved with the smiliest possible which can be obtained by the machine and is still acceptable by the detector. The bunch spacing in time T^ cannot be varied continously because it must be a multiple of the RF wave-length in the LHC and in the SPS. However, the step-size is sufficiently small (5 ns] in the range between 5 and 35 ns such that the machine can produce the smallest bunch spacing the trigger of the detector can cope with. Since it seems that the detectors can handle bunch spacings as low as 26 ns, this spacing was adopted provisionally as nominal value in order to have a basis for one consistent set of parameters. However it should be noted that each of the possible bunch spacings needs a special small RF system in the PS. Thus the bunch spacing cannot be changed at a moment's notice.

It can be seen from Fig. 2, which gives a synopsis of all these limits based 32 -2 -1

on the parameters given before, that the maximum luminosity is 4x10 cm s for T x = 25 ns and <n> = 1. Although the machine operation would become more difficult, it is not unconceivable that the luminosity could eventually approach

33 -2 -t or even exceed 10 cm s provided a smaller or a larger <n> i s a c c e p t a b l e

for the detector. This is indicated by the shaded area around the nominal working point in Fig. 2.

Table 1 gives the general parameters and performance.

Tahle 1 : GENERAL PARAMETERS AMD PERFORMANCE

GENERAL PARAMETERS

COLLIDER TYPE IN LEP PROTON-PROTON

SEPARATION BETWEEN ORBITS (mm) 1 35-180 NUMBER OF BUNCHES 356« BUNCH SPACING (ns) 25 NUMBER OF CROSSING POINTS a BETA VALUE AT CROSSING POINT (m) 1 NORMALIZED EMITTANCE into1 Iß (|im) 5 ¥ FUL'. BUNCH LENGTH [ml 0 31 FULL CROSSING ANGLE 1madl 9

LATTICE PERIOD LENGTH (ml 79 156 LATTICE PHASE ADVANCE 1/3 1/2 DIPOI.E HAGNETIC FIELD (T) 10 10 OPERATING BEAM ENERGY (TeVI 6.14 6.99

- 461 -

PERFORMANCE

<n> it [ - 100 (tub) LUHINOSITY lcm"Zs"' 1

10 1.34x10

4 33

1 .5x10 10

2.6x10 NUMBER OF PARTICLES/BUNCH 10

1.34x10

4 33

1 .5x10 10

2.6x10 CIRCULATING CURRENT IroAl 86 167 BEAM-BEAM TUNE SHIFT o . o o n 0.0025 BEAM STORED ENERGY IMJ] 63 121 RMS BEAM RADIUS luml BEAM LIFE-TIME (h)

12 42 21

at interaction point for ß = 1 m t*

particle less due to beam-Learn collisions

The lattice consists of modules similar to the LEP lattice with arcs containing regular lattice cells, low-ß insertions for collisions and dispersion suppressors for matching.

The LEP arcs and their support and supply systems are built in modules of length corresponding to half a cell, i.e. 39.5 m. We have limited the choice of LHC cell lengths to 79 and 158 m, associated respectively with 60* and 90" betatron phase advance. Fig. 5 shows the layout of the magnetic elements in a cell.

Fig. 6 shows a schematic layout and the optical functions. The quadrupole gradients are 250 T/m, the same value as in the standard lattice period. The value ß can be increased by a factor 3 in order to overcome aperture restrictions and chromaticity problems during injection and energy ramping. The free space for the experiment between the Quadrupoles is ± 10 m.

Two different inner diameters of the dipole coils were assumed for the study. The larger one [50 mm) allows for 40 mm inner diameter of the vacuum chamber; the smaller one (35 mm) leaves only 30 mm as inner pipe diameter, which precludes the use of the 90*, higîier energy lattice as the injected beam diameter is 18 mm in this case.

The dominant field error effect is due to the persistent currents; it is a large sextupo.le component in the field af the dipoles. In any given magnet, this component is reproducible from cycle to cycle. However, between dipoles there is a random variation. The resulting chromaticity is compensated by appropriately exciting the sextupoles next to the quadrupoles in the LHC periods.

The widths of non-linear resonance stop-hands due mainly to the position tolerances of t'ie superconducting wires are comparable to those in operating machines.

- 4 6 2 -

Intra-beam scattering imposes a minimum longitudinal emittance of the oroer of 2.5 eVs. This value is also sufficient to stabilize the beam via Landau damping against most of the presently known collective effects.

Host of the intensity dependent effects of importance in the LHC arise from the interaction of the beam with the vacuum chamber surrounding it. Therefore the relevant properties of the vacuum chamber must be carefully considered. Beam induced wall currents will heat the vacuum chamber, and together with the synchrotron radiation, contribute to the heat load of the cryogenic system. Table Z shows the heat losses per unit length from the two counter-rotating beams averaged over the arcs.

Heat-loss Nm 1

Resistive wall .014 -Broad-band .09 Bellows .026 Synchrotron Radiation .24

Total .37

t emitted power per unit length

All intensity dependent effects discussed above are evaluated in the most difficult case of the 79 m long cell and a vacuum chamber radius of '~ mm. tt was found that all collective phenomena could he handled in this lattice, with the help of appropriate feedback systems where required.

With the assumed parameters, a crossing angle of 36 urad is large enough to ensure a sufficient separation at the first near-crossing. The long range b«am-beam tune shift is only a fraction of the beam-beam tune shift at the interaction point and should pose no problems. Because of the short bunch-length involved, the loss of luminosity compared to head-on collisions is only 4Z.

Eventually, a choice will have to be made. The arguments entering the choice are the maximum energy, the good field region of the magnets, field errors due to persistent currents and coil position errors in the dipoles, and collective phenomena. The advantages and disadvantages of the two period lengths, and the two vacuum chamber diameters are shown in Table 3.

- 463 -

Table 3 : COMPARISON OF CHOICES

Period length 79 79 159 isa m Chamber r ad ius 15 20 15 20 mm Energy a.136 8.136 8.993 8.993 TeV

RF vol tage 16 16 28 28 MV Tune spread 0.026 0.0114 0.6T6 0.088 Required good f i e l d r ad ius t . 5 9 .5 12 12 mm Dynamic ape r tu r e due t o - p e r s i s t e n t c u r r e n t s 9 13 4 mm - c o i l pos i t i on 8 1« 7 14 nun

2.2 Mannet system According to p resen t knowledge, the design and cons t ruc t i on of a c c e l e r a t o r

magnets with f i e l d , say up t o 6 or 7 T can be based on e x i s t i n g superconductors and on t echnolog ies a l ready developped in Fermilab for the Tevatron and f u r t h e r t e s t e d in Desy far Hera, in 6NL for CBA, in Serpukhov for UNK, and in KEK For T r i s t a n .

Tne pioneer ing work done in various o ther l a b o r a t o r i e s (LBL-USA, CEA-Saclay, KfK-Karlsruhe, NIKHEF-Amsterdam, Rutherford Appelton Lab., CÉRN, e t c . ) can a l s o serve as a very good base for fu ture work.

Of course , before launching such an important p r o j e c t , s eve ra l a l t e r n a t i v e des igns should be considered with the prime aim of reducing product ion c o s t s , and t h e i r f ea tu re s should be t e s t e d in an adequate number of p ro to types , However, no fundamentally new development would be r equ i r ed . This i s not t r u e for magnets of higher f i e l d l e v e l up to 10 T.

Indeed, the purpose of the s t u d i e s descr ibed in t h i s sec t ion i s to make a f i r s t assessment of the e lec t romagne t i c , cryogenic and mechanical problems which have t o be faced for the design and cons t ruc t i on of LHC magnets with a f i e l d as high as 10 T, would a s u i t a b l e superconductor be a v a i l a b l e in t ime .

The development of such a superconductor , which can be i n d u s t r i a l l y produced, i s an abso lu te ly necessary p r e r e q u i s i t e to the f i n a l design and cons t ruc t i on of such magnets. Small q u a n t i t i e s of superconductors almost s u i t a b l e for t h i s a p p l i c a t i o n have already been made in i n d u s t r y .

Another important i n g r e d i e n t i s tne a v a i l a b i l i t y of i n s u l a t i o n m a t e r i a l s and techniques s u i t a b l e for winding the c o i l s according to the "wind and r eac t " method.

- 464 -

Therefore all what is indicated below should be considered as a first assessment of the situation and as a guide-line for the indispensable development.

Dipoles and quadrupoles of the two rings are combined into "two in one" units, each having a common yoke and cryostat. The two rings are, therefore, magnetically coupled, especially at high field, which imposes the same energy for the two beams. Focusing quadrupoles in one ring are paired to defocusing quadrupoles in the other. Sextupole and dipole corrector pairs need to be magnetically uncoupled and can indeed be made so by means of independent cores. Horizontal dipole correctors in one ring are paired with vertical correctors in the other ring. The complete set of quadrupoles, sextupoles and dipole correctors will be contained in a common cryostat.

The dipole magnets should be made in units as long as passible, both because the bending length loss at each end reduces the attainable energy and in order to minimize the number of ends, which are the most difficult part of the magnet to fabricate. An upper limit to the unit length is, however, given by the access facilities (shafts, service tunnels, etc.) to the LEP tunnel, which are designed to allow installation of single components up to 12 m long. Another limitation to unit length is given by safety at a quench. It is estimated that 12 m long magnet plus cryostat units can be built, handled and operated without excessive difficulties and risks.

Existing evidence, gathered from experiments at the ISR and from the Tevatron, confirms the feasilibity of a cold vacuum chamber. Accordingly, no space for thermal insulation needs to be reserved in the magnet coil bore. For the sake of the present study it is assumed that the final choice for the inner diameter of the coil will fall in the range between 35 mm and 50 mm. Most of the work was therefore dona on a version corresponding to the upper limit of 50 mm, which is more demanding in magnet size, excitation and structure. A possible dipole design is given in Fig. 7 with parameters in Table 4. One has also established that scaling to 35 mm is feasible from the magnetic point of view and probably acceptable for beam dynamics.

- 46S -

f a h l R > : I l T P n i F PARAMETERS

nominal f i e l d 10 T Peak f i e l d in windings < 11 T Average o v e r a l l cu r ren t dens i ty -2

300 A.mm Exc i t a t ion (per d ipo le ) 1300 kA-turns

Maximum cur ren t - (0 kA Stored energy ( f u l l "2 in 1" magnet) 730 kJ/m Coil inner diameter 50 mm Distance between gap c e n t e r l i n e s 180 mm Transverse s i z e of a c t i v e p a r t

width - 60Q m height - 500 mm

Transverse s i z e of the c r y o s t a t width 750 mm height 900 mm

Magnetic l eng th 10.25 m Cold mass per un i t l ength - 1.5 t/m

2.3 .Cryogenics The product ion , t r a n s p o r t and d i s t r i b u t i o n of the cryogenic f l u i d s (He and

ti), a re compatible with the space in the LEP t u n n e l . One r e f r i g e r a t o r per oc tan t should be i n s t a l l e d in the i n t e r a c t i o n r e g i o n s .

2 . t Vacuum Pro f i t i ng from the magnet c r y o s t a t s , cold bore w i l l be used, which

i n t r i n s i c a l l y provides a very low p r e s s u r e .

2.5 R a d i o-frequency

only 30 m of a c t i v e c a v i t y s t r u c t u r e a re in t o t a l needed for both r i n g s . To allow a l a rge number of bunches in the Hadron Co l l i de r , the frequency should be - +00 MHz, namely the double of the SPS frequency.

2.6 In-iection. beam t r a n s f e r s and dumps At l e a s t two a l t e r n a t i v e layouts of t r an s f e r tunnels a re poss ib le between

SPS and LEP (Figs . 8 and 9 ) . Beam dumps are f e a s i b l e with p resen t technology.

- 466

It has been established that there are no problems for the environment. Beam losses must however be controlled very well to avoid quenches of the superconducting magnets.

3. THE DO OPTION Only a one-channel machine is considered as stated in the introduction. The

layout of this single ring is shown schematically in Fig. 10, In order to make the bunches collide only in the eight interaction points, the orbits of protons and antiprotons outside the collision regions are kept apart by electrostatic separators which are positioned downstream and upstream of each interaction point.

The transfer of protons and antiprotons seems easier following Variant 2 (Fig. 9) since both types of particles circulate in the SPS in their normal dir/ection. Using Variant 1 (Fig. 61 would combine the longer transfer lines with the disadvantage of polarity reversal of the SPS (far p) and the construction of a new beam line linking the PS/SPS antiproton transfer lino TT70 with TT10. Also TT10, the injection system in LS S1 and the extraction in LSS4 must be able to operate at reversed polarity.

Since there is only one channel in the ring, the magnets are simpler than for the pp collider, but the aperture possibly larger to accomodate the separation of the orbits. The stored erergy in the beam is lower, and the beam is likely to be more stable because the number of bunches is reduced by more than an order of magnitude compared to the pp option. Unfortunately, these advantages have to be paid for by a lower luminosity and by the necessity of having separators. The separators deflect the beams in opposite directions electrostatically; their length is about 40 m per station. The operation of pp rings ia also more complicated and the limited accumulation rate has adverse effects on the luminosity, especially when averaged over time.

As explained before, the peak luminosity is limited by the total number of antiprotons available at the beginning of a run. With the new CERN antiproton source approximately 1o' 2 particles can be expected, resulting in a peak

31 -2 -1 luminosity around 10 en s (see Fig. 2 ). Respecting <n> < 1 and selecting a bunch spacing compatible with the RF yields 108 bunches as nominal number corresponding to T^ = 825 ns. The separators are installed behing the low-0 quadrupoles but before the first unwanted crossing occuring at 124 m from the interaction point. The most promising scheme of beam separation makes the orbits spiral around each other by means of a set of vertically deflecting plates and a set of horizontally deflecting plates. Hence, the bunches always circulate off-centre in the arc. which might adversely influence their stability.

- 467 -

I f t h e n u m b e r o f a v a i l a b l e a n t i p r o t o n s c o u l d b e i n c r e a s e d , s a y , to I t ) 1 * 3 a

h i g h e r p e a k l u m i n o s i t y c o u l d i n p r i n c i p l e b e r e a c h e d . I f t h e n u m b e r o f b u n c h e s

w e r e n o t c h a n g e d t h e n u m b e r o f e v e n t s p e r b u n c h c o l l i s i o n w o u l d b e c o m e

i n a d m i s s i b l y h i g h a s c a n b e s e e n on F i g . 2 . I n c r e a s i n g t h e n u m b e r o f b u n c h e s k

w o u l d h e l p i n t h i s r e s p e c t b u t q u i c k l y t r o u b l e a r i s e s i f tí a p p r o a c h e s 300,

c o r r e s p o n d i n g t o = 3 0 0 n s . A t t h i s p o i n t t h e u n w a t n e d c r o s s i n g h a s a p p r o a c h

e d t h e l o w - H q u a d r u p o l e s l e a v i n g no s p a c e f o r t h e l o n g s e p a r a t o r s . A n o t h e r

s e r i o u s p r o b l e m a r i s e s d u r i n g i n j e c t i o n . T h e s e p a r a t i o n i s n o t s u f f i c i e n t t o

p r e v e n t d e f l e c t i o n o f t h e a l r e a d y s t o r e d b e a m b y t h e k i c k e r m a g n e t w h e n t h e

s e c o n d b e a m i s i n j e c t e d . T h u s t h e i n j e c t i o n k i c k e r m u s t be p o s i t i o n e d b e t w e e n

t w o u n w a n t e d c r o s s i n g s a n d i t s f i e l d m u s t r i s e a n d f a l l w i t h i n T ^ . T h i s i s

a l r e a d y d i f f i c u l t f o r 1 0 8 b u n c h e s b u t b e c o m e s n e a r l y i m p o s s i b l e o n c e k r e a c h e s

2 0 0 t o 3 0 0 , a t l e a s t w i t h p r e s e n t t e c h n o l o g y , T h e p o s s i b i l i t y r e m a i n s t o

s e p a r a t e t h e o r b i t s b y s u c h a n a m o u n t t h a t t h e b e a m i s n o t d i s t u r b e d b y t h e

k i c k e r f i e l d a c t i n g o n t h e o t h e r b e a m . S u c h a s c h e m e h a s n o t y e t b e e n w o r k e d o u t .

I n o r d e r t o o b t a i n a r e s o n a b l e l u m i n o s i t y a v e r a g e d o v e r t i m e , t h e d u r a t i o n

O f a r u n s h o u l d b e a p p r o x i m a t l e y e q u a l t o t h e i n i t i a l l u m i n o s i t y d e c a y t i m e

T l - T a k i n g t h i s ? s a g u i d e t h e n e c e s s a r y p a c c u l a t i o n r a t e b e c o m e s :

A >- » . p / , L

F o r o u r p a r a m e t e r s T, « 2 0 h y i e l d i n g f o r N - = 1 0 , Z A - 5 x l 0 , D h 1 a n d f o r L p

N - = 1 0 1 3 A - 5 x 1 0 t 1 h - 1 . T h e r a t e 5 x t 0 1 0 h ~ 1 i s t h e d e s i g n a i m o f t h e p

t h e new CERN a n t i p r o t o n s o u r c e a n d t h e FNAL s o u r c e u n d e r c o n s t r u c t i o n , w h i l e

5 J Í 1 0 1 1 h * c o u l d p o s s i b l y b e r e a c h e d w i t h a s o p h i s t i c a t e d m u l t i - r i n g s o u r c e .

I t i s a p p a r e n t t h a t e v e n w i t h a v e r y a d v a n c e d p s o u r c e t h e m a x i m u m

e x p e c t e d p e a k pp l u m i n o s i t y i s i n f e r i o r t o t h e p e a k p p l u m i n o s i t y b y a b o u t o n e

o r d e r o f m a g n i t u d e . T h e m a c h i n e b e c o m e s t e c h n i c a l l y r a t h e r d i f f i c u l t f o r 32 -2 -1

l u m i n o s i t i e s a p p r o a c h i n g 10 cm s . M o r e o v e r , t h e r a t i o o f a v e r a g e t o p e a k

l u m i n o s i t y w i l l c e r t a i n l y s u f f e r f r o m t h e o p e r a t i o n a l c o m p l i c a t i o n s a n d w i l l b e

l o w e r t h a n f o r t h e p p , w h i c h w i l l p r o f i t f r o m t h e p o w e r f u l p r o t o n s o u r c e s a t h a n d .

+. f JUAL.RfüA8£S_AND CONCLUSIONS

I n t h i s r e p o r t we h a v e c o n s i d e r e d m a i n l y a p r o t o n - p r o t o n c o l l i d e r , a s t h e

m o s t p r o m i s i n g t o o l f o r e x t e n d i n g t h e p r e s e n t e n e r g y r a n g e f o r r e s e a r c h a t

c o n s t i t u e n t l e v e l i n t o t h e T e V r e g i o n .

T h e b a s i c m a c h i n e s t r u c t u r e c a n o f c o u r s e b e u s e d f o r o t h e r p o s s i b i l i t i e s , I

f o r i n s t a n c e f o r c o l l i s i o n s o f t h e e l e c t r o n s o f LEP w i t h t h e p r o t o n s o f t h e

h a d r o n c o l l i d e r , u p t o a c e n t r e - o f - m a s s e n e r g y o f a b o u t 2 T e V . C o l l i s i o n s o f

- 468 -

ions would a lso be p o s s i b l e , with beam energy per nucleón of about one half of the proton energy. However, no work has yet been done on these o ther p o s s i b i l i t i e s .

The conclusions which can be drawn from the study are :

i ) A proton-proton c o l l i d e r can be i n s t a l l e d in the tunnel above LEP. A center -of -mass energy of about 18 TeV could be reached with superconducting magnets of 10 T.

i i ) In order to achieve t h i s goa l , i t i s necessary t o launch in Europe a vigourous programme of development of m a t e r i a l s and techniques necessary for the cons t ruc t ion of such magnets. Severa l European Labora tor ies and I n s t i t u t i o n s express a g r e a t i n t e r e s t to p a r t i c i p a t e in such a programme.

i iUAccord ing to present knowledge, magnets with smaller f i e l d , say 5 or H (centre-of-mass energy between 10 and 13 TeV], could be b u i l t a f t e r a s h o r t e r programme of t echno log ica l development,

i v ) All other machine components and systems appear to be f e a s i b l e with the present technology.

REFERENCES 1 De ta i l s of the design of the magnet and o ther major a c c e l e r a t o r systems toge ther with a f u l l l i s t of re fe rences are given in the Proceedings of the CERN-ECFA Harkshop on the f e a s i b i l i t y of a l a r g e hadron c o l l i d e r in the LEP tunnel held at Lausanne and CERN in March 1964.

Superconducting Super Co l l i de r . Reference Designs Study for U.S. Department of Energy. Hay 8, 1984.

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LEP Tunnel «ich LHC magt-.ets abOMe LEP dipoles

- 4 7 1 -

Fig. 9 : Beam Transfer through Injector Chain; Variant 2 Fig. 10

- 4 7 3 -

Beyond the Standard Model

- 4 7 4 -

Higas Sea lars and A l t e r n a t i v e s

D. Wyler

T h e o r e t i c a l Physics

ETH Hönggerberg ^

809" Z ü r i c h , S w i t z e r l a n d ç; 8*1QO* 6

1 . I n t r o d u c t i o n

Although the W- and Z-bosons v e r e d iscovered w i t h masses and v i d t h s p r e -1 ) 2 )

c i s e l y as p r e d i c t e d by t h e standard model ' ( i n f a c t , p e r t u r b a t i o n theory 3 ) h)

seems t o be v a l i d w i t h i n a few percent ' ) , ve f e e l t h a t the bas ic dynamics of

the t h e o r y , i n p a r t i c u l a r the way the W and the Z become massive are not under

stood ( s a y , as w e l l as superconduc t iv i t y i s understood by t h e BCS t h e o r y ) . This

i s w i d e l y regarded as one o f t h e most important quest ions i n high energy p h y s i c s .

I t i s i n t i m a t e l y connected t o the ex is tence o f s c a l a r p a r t i c l e s whose e x p e r i

mental d iscovery i s t h e r e f o r e so d e s i r e d * ^ . On a somewhat d i f f o e n t , presumably

secondary l e v e l t h e r e a re o ther open problems whose s o l u t i o n s a ;e conce ivab ly

connected w i t h s c a l a r s : " F a m i l y " s t r u c t u r e o f quarks a i d l e p t o n s ; C P - v i o l a t i o n ;

( i n p a r t i c u l a r i f for thcoming experiments g ive a ve ry smal l e 1 i n the Kaon

system); ve ry r a r e decays such as u * ey. (And, c l e a r l y , super symmetry^ r e q u i

res s c a l a r s , which a r e , however, o f a d i f f e r e n t t y p e ; t h e i r n e c e s s i t y i s r a t h e r . 7 }

o f k i n e m a t i c a l n a t u r e ; t h i s a p p l i e s e q u a l l y f o r models o f composite l ep tons

and q u a r k s } .

The r e s u l t s o f t h e UAl and UA2 groups c l e a r l y r u l e out models w i t h g e n e r a l

i z e d g l o b a l SU(2) s y m m e t r y ^ ; phenomenological models o f y-Z m i x i n g ^ cannot

e x p l a i n why g = e / s i n ö e t c . and o f f e r no a t t r a c t i v i t y . BUT: a l s o models w i t h

W 7 ) composite W, Z , d e r i v e d from composite models f o r quarks and leptons are d i f f i -

+• o

c u l t t o l i v e w i t h . I n such models, the W and Z a re analogous t o the p- and p

(and p o s s i b l y t o K * , . . . w i t h i n t e r e s t i n g (or d e v a s t a t i n g ) consequences). A n t i c i

pated consequences a re r e l a t i v e l y l a r g e w i d t h , somewhat h igher masses than those observed, non-automatic j j - e -quark u n i v e r s a l i t y , sma l le r 6 ( i f u n i v e r s a l i t y i s n W imposed). Furthermore, recent cons idera t ions o f the dynamics o f such t h e o r i e s

. ^ 1 0 ) i n d i c a t e t h a t the observed mass spectrum might not be a t t a i n a b l e

Fach-Informations-zentrum Energie • P h y a l k - M a t h e m a t l k - Q m b H

INPUT S H E E T F O R SUBJECT ANALYSIS

(Arbeitsblatt für inhaltliche Erschließung)

Document Number (001): (Bearbeitungsnummer)

841002 6414

Sachtitel und Standort: Zeilschrift, Vol/Nr.: Repartn ummer:

Page (Seite) 4?M Sachtitel und Standort:

Zeilschrift, Vol/Nr.: Repartn ummer:

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E D Abstract (Short Comm.] . Come. Prog. Doc.

Treatment Cade TC (008): (Art des Inhalts) 1 Treatment Cade TC (008): (Art des Inhalts) 1

I lnf(, J C |computingj P 1 popular 1 E 1 exp. 1 M 1 method?! D j_d

aia j A j appar. | Title in English (200): (eng!. Titel) •

Title In German (240) (deutscher Titel) • Title in French (240) (franz. Titel) • Title Augmentation in Eng!. (620) (Titelergänzung in engl.) • Title Augmentation In German (623) {Titelsrgänzung in dtsch.) • Title Augmentation In French (Tltelergünzung in franz.)

623) • Page (Seite) Input Sheet (Arbeitsblatt)

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{nnglkRhn.q AS« tract) T J \ 1 1 en I 1 Abstract In German: j (deutsches Abstract) 1 I 1 1 de |~ 1 Abstract In French: 1 franr Arrelrarïtt 1 I 1 !

Abstractor Data:

Translator Date:

Assignment of Numbers Descriptive Cataloguer. , , Date: ?3. A A (M 6

" Notes:

COAL. BIOMASS, ASSET only together with EDB. ENERGIE, COAL, BIOMASS, ASSET must have EDB subject categories. Only non-nuclear energy in EDB AT/CH/DD/XE.

DE = Federal Republic of Germany AT ~ Austria CH =• Switzerland DD = German Democratic Republic XE = Commission of the European Communities (CEC) XC = European Organization for Nuclear Research (CERN)

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Compilad Data D O Evaluated Data D 0 Experimental Data D O Statistical Data 0 0 Theoretical Data 0 0

- 475 -

Therefore I will take the view that the W and the 2 are indeed gauge particles; we will stick to the standard SU(2) x U(l) scheme.(Many aspects are, however, not tested. For instance the cubic and quartic gauge boson couplings, which are g and g 2 in the gauge theory (g = gauge coupling) should be measured 1 1^.

2 lote, that in the composite models these couplings are not necessarily g and g ).

Then, in order that the W and Z are massive we must have a eomplex order pa

rameter, a scalar, as pioneered by the BCS theory. It can be elementary or com

posite. After the "Higgs-Kibble" effect, there remain physical scalars (this 12)

holds always as can be seen by simple group theory), unless we "freeze" them out (as in the non-linear O-model), or make its mass very large. The price we pay is loss of renormalizability, e.g. of the ability to carry out sensible perturbative calculations, basically, because some couplings are strong. We do not know how to treat such systems, except in ideal 1zed circumstances. For example, in the two-dimension.J. o-model, although the extra state has been removed in defining the basic Lagrttngian, it reappears in the spectrum of physical states, due to

13) non-perturbative effects . It might be that this does not happen in four dimensions or in a gauge theory. It is, however, remarkable that unlike in the case of the W, making the scalar very heavy results in almost unmearnrably small radiative Corrections and violations of unitarity. Fof instance corrections to p

- 1 * 0

due to a large scalar mass give

2 .

ss ' s f-^rn) -- - " -uriitSfr. + s. W - « r* JSa.

Considerations of W + W scattering yield a violation of unitarity only if ^

{including width effects 1 6')

E ( w * , h - ) i ref , « H * i.s TeV ( 3 )

This effect is called "screening" (Veltman^ ).

[~We Tirm turn to the description of the relevant interactions of elementary

and composite scalars and then to possible production mechanisms. ^Çsfjff^X^j

17)

( 6 )

2 . Elementary sca la rs

I n the s tandard GSW model , t h e r e i s one p h y s i c a l s c a l a r , a n e u t r a l 0 + s t a t e .

I t s coupl ings t o fermions and gauge f í e l a s a re known, but i t s mass n o t . Requ i

r i n g symmetry b r e a k i n g p e r t u r D a t i v e l y g ives a lower mass hound, ^ ^ m > 8 GeV.

19) " (A s e t o f n u c l e a r physics experiments g ives tri >15 Mev J E x p e r i m e n t a l l y , an

2 0 )

upper hound i s more i n t e r e s t i n g . Recent work by r igorous p h y s i c i s t s i n d i c a t e s

t h a t a pure <J> t h e o r y ( e . g . the reno ratal i z able s c a l a r f i e l d theory w i t h q u a r t i c

i n t e r a c t i o n s used i n t h e GSW model) i s a t r i v i a l t h e o r y . I n view o f t h i s one i s 2i) i)

l e d t o o b t a i n an upper mass as f o l l o w s . I f the t¡> coupl ing constant i s too l a r g e (and thus a lso the mass o f t h e s c a l a r ) then the model i s l i k e a pure (and h 22 ) t h e r e f o r e u n i n t e r e s t i n g ) § t h e o r y . These arguments l e a d t o a mass bound

e s c o l a r ¿ I Ä 5 " ®*V" ih)

( I t i s i n t e r e s t i n g t o note t h a t the " s c a l a r " i n t h e BCS theory has about the same 2U)

m&ss as the gauge boson ) . P r o d u c t i o n and d e t e c t i o n o f t h i s s c a l a r have been 23)

descr ibed i n many a r t i c l e s . Less a t t e n t i o n have r e c e i v e d models w i t h s e v e r a l

s c a l a r s , in t roduced f o r many purposes (some a re l i s t e d i n t h e i n t r o d u c t i o n ) ;

and I would l i k e to s t r e s s these hr:re. Note t h a t some o f these might be l i g h t ,

as the bound a b o v e ^ ' need not h o l d ^ ^ . The coupl ings o f t h e s c a l a r s , c o l l e c

t i v e l y denoted by H t o known p a r t i c l e s are g iven by

2.MW

O I n ( 5 ) U"T > D D 1 e t c . stand f o r l e f t h a n d e d — charged quarks, e t c . : K a re

L K 5

Kobayashi-Maskava a n g l e s , e ^ , . . . a re (de)enhanceraenfc f a c t o r s . I n ( 6 ) , o^, c^,

are mix ing f a c t o r s , o r i g i n a t i n g i n the s c a l a r s e l f - i n t e r a c t i o n s . I n ( 5 ) and ( 6 )

H - , stand c o l l e c t i v e l y f o r charged and n e u t r a l s c a l a r s , the - . - i n d i c

a te f u r t h e r s c a l a r s . ( 5 ) and ( 6 ) determine e s s e n t i a l l y product ion and decay of

H \ ° , H - . Ue note t h a t the enhancement f a c t o r s e^. and E . i n (ü>) may change

the naive expec ta t ions cons iderab ly . For example, the decay o f a H° i n t o a p a i r

2 7 )

( T )

where n - number o f t e c h n i c o l o r g e n e r a t i o n s . T h e i r i n t e r a c t i o n s w i t h fermions

are s i m i l a r t o ( 5 ) ; w i t h gauge bosons G^ C we have

vhere VpV = 6 ' = e c t g 2 6 w » Vf W = f J ^ p»p» = 0 and the S are

given i n t a b l e 1 .

Table l : coupl ings S de f ined hy E q . ( 8 ) . c , s r e f e r t o cose , s in6 .

p \ n i I 2y n p.

isc «•se »Tie - - - - -f »vre - - - -r » - - - At'

lté -K - - - - "is -'Pa -

- - - - - - -

o f gluons may dominate over decay i n t o a quark p a i r o f mass m and the f i n a l

s t a t e a n a l y s i s w i l l change a c c o r d i n g l y .

3- Composite s c a l a r s ( T e c h n i c o l o r )

As mentioned afcove t h e t h e o r y o f e lementary s c a l a r s shows some o d d i t i e s

( a l o n g w i t h the notor ious quadra t i c d i v e r g e n c e s ) . I f compared w i t h t h e t h e o r y

o f s u p e r c o n d u c t i v i t y , i t corresponds on ly t o t h e phenoraenological Ginzburg-Landau

t h e o r y . These reasons have l e d t o cons ider ing the sca la rs as composi te , made

from f e r m i o n - a n t i f e r m i o n p a i r s , h e l d t o g e t h e r "by a new f o r c e , the t e c h n i c o l o r 28 ) 29 )

gauge i n t e r a c t i o n s ' . These s c a l a r s a re g e n e r a l l y pseudoscalars . The l i g h

t e s t are expected t o be

coloriées: P°, Pû\ p t mass * 10- so GeV leptovârks : P3 Mass a 3*0 « n'1/» GeV colorocfets: f f , ff, P¿ "ass * M o . n - * C e V

- 4 7 8 -

U. Decay and production

I will only touch on a few topics here; some aspects, in particular of the 23)

standard Higga, have been previously considered in detail

I n the GWS model, the scalar decays into the heaviest particles available.

This need not hold in models with several scalars and the decay modes may be 27)

quite different . Note, however, that the enhancement factors we encountered

in (5) are not possible in technicolored t h e o r i e s ^ . Also, charged scalars can

behave quite differently from neutrals. Let us go through some points.

a) If the scalar mass is below any of the QQ resonances, its production

via these is the most promising mechanism. I n the standard treatment, one con-r

siders QQ»scalar + Y 3 " ^ . Thus a charged scalar is hard to see in this way.

The process may, however, be very important for P , P* if tt is sufficiently heavy. "Lighter" charged scalars are presumably best seen in decays of heavy

+ flavors such as Q —* H + q.

32)

b) Above toponium "gluon fusion has -een proposed as production mecha

nism for a single scalar. Clearly, this is not possible for charged scalars;

it is strongly suppressed for heavy scalars (Vm^ dependence due to it being an

s-channel process). But it is very favorable for models with enhancement fac

tors and for technicolor. For very large c.o.m. energy also other vector fusions

(WW, WZ, etc.) can be important^ 3 . Here,of course, charged scalars can be pro

duced.

c) Another well known mechanism is associated production^\ where a W

is produced which radiates a scalar. This mechanism yields generally smaller

production rates than fusion. It does not apply for charged scalars and the

technicolor particles due to the absence of WZH couplings for tbe former and

the smallness of the couplings (8) for the latter.

d) In models with charged scalars the couplings (6) give rise to a "quasi-

associated" production where the produced gauge boson radiates away a scalar

and turns into another. Clearly this mechanism will be useful i f the scalars

are not too heavy.

e) "open" fusion, by diagrams such as in Fig. 1 . This mechanism requires

the energy to produce the scalar

along vifch the two quarks Q, Q'. fíe expect Q and Q 1 to be rather heavy (to give a larger QQ'H coupling). H can be charged or neutral (and, of Fifi.1 : Production mechanism for HQQ'

course a technicolored particle). We estimate this rate roughly to he fl(tt) X •| = 0(pt) where o(tt) is the tt production cross section. Of course, for large energies, the gluons can be replaced by W etc.

35)

f) Heavy flavor production . Since scalars couple to large masses and the "sea" of the protons at high energies contains heavy quarks, these can be used to produce scalars by diagrams such as in Fig. 2. (it is somewhat similar to e)

' j j above). Again, it applies to both neutral and charged scalars; in particular it might be important for the

P ^ ^ " ^ latter ones. Fig.2: Heavy flavor production.

g) If > 2m$y y the scalar decays presumably predominantly into two

= P C H - W W ) = G£_w£_ U + corrections) » \ (\ + ccrr. ) (9)

where X is the coupling and the corrections have been calculated^^. We see that for large enough X corresponding to a scalar mass of ~ 800 GeV, r ** 1 and the scalar "bump" can hardly be recognized in the W +W spectrum. (The corrections at this point are about +20%i higher corrections might (7) however be negative). The reason for this growing behaviour is that due to the symmetry breaking mechanism the longitudinal part of the W is nothing but the scalar field, and thus A indeed must enter. In models with charged scalars this effect does not happen (no coupling); equally in technicolor theories where the

relevant couplings (8) are small.

5- Conclusions We have given a variety of reasons why scalars are vital for our further

understanding of the weak interactions and why they are also interesting. We have seen that their mass range is within present and next machines. In the last section a few possibilities to search for then, based on the definitions of sections 2 and 3 are discussed. Uo doubt, further ways are possible. We have stressed mechanisms which are suitable for detecting charged ecalars or scalars with enhanced coupling or technicolor scalars. They could be calculated along

23) the lines studied for the production of the standard Higgs .This is particularly interesting in view of the exciting events, presented here, which one is tempted to interpret as scalars. Por example, pome of the 2 vector-boson modes (51

- 480 -

and (8) of the s c a l a r s correspond to the observed p a r t i c l e s , a l though rough

est imates c l e a r l y g i v e a n o n - s u f f i c i e n t r a t e . A p r e c i s e d e t e r m i n a t i o n of back-+ - 37)

ground events i s d e s i r a b l e (W W product ion e t c . ) .

Acknowledgements

I thank t h e organ izers o f t h i s workshop f o r an i n t e r e s t i n g and very p l e a

sant meet ing , I have b e n e f i t t e d from discussions w i t h R. A n i s h e t t y , A. B o v i e r ,

F. H a l s e n , I . H i n c h l i f f e , F. J e g e r l e h n e r , W. Marc iano , P. Minkowski , J . Schacher

and Ch. Sehmid. I thank J . E l l i s and I . H i n c h l i f f e f o r p r o v i d i n g me w i t h t h e i r

c r o s s - s e c t i o n c a l c u l a t i o n s p r i o r t o p u b l i c a t i o n .

References

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2 ) J . Schacher, these proceedings.

3 ) W. Marc iano, these proceedings .

h) P. Minkowski , these proceedings.

5) For preceeding emphasis and summaries o f the s c a l a r problem see f o r ins tance :

L.B. Okun, Proc . o f the 1981 Symposium o f Lepton-Phonon I n t e r a c t i o n s ; Ed.

W. P f e i l , Bonn.

M. Voltman, Proc. o f the t h i r d pp Workshop, Home 1 9 8 3 ; Eds. C. Eacc i and

0. S a l v i n i , CERN, Geneva 1 9 8 3 .

J . E l l i s , 1 9 7 8 S l a c . Summer I n s t i t u t e Proceedings; Ed. M. Z i p f .

G . B a r b i e l l i n i e t a l . , DESY Report 7 9 / 2 7 ( l 9 T 9 ) i A. A l i , P roc . o f the 1 9 8 1

ISABELLE Workshop.

6) D . V . t ïanopoulos, these proceedings and re fe rences t h e r e i n .

7 ) R.D. P e c c e i , these proceedings and r e f e r e n c e s t h e r e i n .

8) J . D . B j o r k e n , Phys. Rev. D19, 335 ( 1 9 7 9 ) .

9 ) P.Q. fîuiig and J.J. B a k u r a i , N u c l . Phys. B l U 3 , S i ( 1 9 T Ô ) -

10) D. Weingar ten , Phys. Rev. L e t t . 5 1 , 1830 ( 1 9 3 3 ) .

C. Vafa and E. W i t t e n , N u c l . Fhys. B23j i , 1 7 3 ( 1 9 Ô 1 * ) .

S. Nussinov, Phys. Rev. L e t t . 5 2 , 963 , 9 6 6 ( 1 9 8 * 0 .

1 1 ) One method was descr ibed by F. Hersog, these proceedings.

1 2 )

I have been informed by J. F r ö h l i c h t h a t t h i s was o r i g i n a l l y considered by

C.C.G. S tücke lberg . I have not found the r e f e r e n c e .

13) 2 . B r e z i n , J. Z i n n - J u s t i n and J.*-. t .2 G u i l l o u , Phys. Rev. D14, 2615 ( 1 9 7 6 ) .

14) J. Van der B i j and M. Ve l tman, N u c l . Phys. B231, 205 ( 1 9 8 4 ) .

15) B.W. Lee, C. Quigg and H.B. Thacker , Phys. Rev. D16, l b l 9 ( 1 9 7 7 ) .

4 8 1 -

16) G. Kane, t a l k a t the conference on Physics o f t h e XXI c e n t u r y , Tucson AZ,

Dec. 1983 and re fe rences t h e r e i n .

Since WW s c a t t e r i n g i s hard t o do , one might look f o r o ther processes

where WW occurs as a subprocess. An example i s product ion c f t h r e e gauge

bosons i n e + e : A. V a i n s t e i n and I . K h r i p l o v i t c h , Sov. J . flucl. Phys. 13»

1 1 1 ( 1 9 7 1 ) , D. Boulware, Ann. Phys. ¿ 6 , lUo ( l 9 7 0 ) ; L. Fadeev, Theor . and

Math. Phys. 1_, 1 (1970). See a lso J . D . B j o r k e n , i n Proc . o f the 1976 Summer

I n s t i t u t e on P a r t i c l e Phys ics , SLAC Report No. 198, Ed . M. Z i p f .

I T ) S t r i c t l y speak ing , t h e " H i g g s " - f i e l a i s on ly t h a t s c a l a r which i s l e f t

over a f t e r gauge symmetry b r e a k i n g . I v i l l t h e r e f o r e r a t h e r use t h e te rm

s c a l a r s ince we consider g e n e r a l l y models w i t h s e v e r a l s c a l a r f i e l d s .

18) A.D. L inde , JETP L e t t . 2 3 , 6U, (1976); Phys. L e t t . JOB, 306 ( 1 9 7 7 ) ; S. Wein

b e r g , Phys. Rev. L e t t . 3 6 , 291* (19T6).

19) For a summary o f these r e s u l t s , see G. B a r b i e l l i n i e t a l . , Re f . 5 ) .

20) M. Aizenmann, Phys. Rev. L e t t . Vr_, 1 (198I)

J . F r ö h l i c h , N u c l . Phys. B2Q0 [FsU] , 28l (19B2).

21) Cabibbo, L. M a i a n i , G. P a r i s ! and R. F e t r o n a i o , H u c l . Phys. 3158, 295

( I 9 7 9 ) i R. Dasken and H. Heuberger , Phys. Rev. L e t t . ¿ 0 , 1Ô97 ( I 9 ß 3 ) i

D . J . E . Ca l laway , U n c i . Phys. B233. I ß 9 ( 1 9 8 ' 0 i M.A.B. Bég, C. Panagio tako-

poulos and A. S i r l i n , Phys. Rev, L e t t , ¿ 2 , 883 (1984).

21)

22) I n w r i t i n g t h i s bound I have used t h e va lue o f Beg e t a l . . They solve 21)

the set o f coupled d i f f e r e n t i a l equat ions f o r m^ and (J^; Cal laway takes

0^ f i x e d . I b e l i e v e t h e former procedure i s more p h y s i c a l .

23) See I . H i n c h l i f f e , these proceedings^ a lso G. B a r b i e l l i n i e t a l . , ftef, 5 ) ,

A. A l i , T i e f . 5 h J . E l l i s , Ref . 5 ) .

24 ) See, e , g . "Type II s u p e r c o n d u c t i v i t y " j D, Sa in t -James , G. Sanaa and E . J .

Thomas, Pargamon P r e s s , Ox fo rd , 1969.

25 ) R.M. B a r n e t t , G. Senjanovic and D. W y l e r , Santa Barbara p r e p r i n t KSF- ITP-

26) Note the absence o f t h e W ± - Z - H c o u p l i n g .

27 ) R.M. B a r n e t t , G. Sen janov ic , L. Wo l fens te in and D, Wy ler , Phys. L e t t .

B13fi, 191 (1984).

2 8 ) S. Weinberg, Phys. Rev. D13 , 974 ( 1 9 7 6 ) i D19_ 1277 (1979)

L. Susskind, Phys. Rev. D20 , 2619 ( 1 9 7 9 ) .

2g) For a rev iew and d iscuss ion o f the phenomenology as w e l l as f u r t h e r r e f e r

ences, see K. Lane, Proc . o f the 1982 summer study on Elementary P a r t i c l e

- 4 8 2 -

Physics and f u t u r e A c c e l e r a t o r s , 1 9 8 2 , E d s . : R. Donaldson e t a l . A l s o :

K. Lane and M.E. P e s k i n , Proc . XV 1 1 1 6 Rencontre de Mor iond, Ed. J . Tran

Thanh Van; E- F a r h i and L . Susskind, Phys. Rep. jhCt 2 7 7 Cl98l); J . E l l i s ,

M.K. G a i l l a x d , D.V. Nanopaulos and P. S i k i v i e , K u c l . Phys. B l B 2 . 5 2 9 ( l 9 8 l ) . The enhancement f a c t o r s a re due t o <fl^? =r= < H 2 > ' l D ^ c ^ n i c 0 1 0 1 " models, we

have , e q u i v a l e n t l y , <WJ>, <DD>, and by the charge independence o f the

t e c h n i c o l o r fo rce we do net expect <UU> r" <DD>.

F . W i l c z e k , Fbys. dev. L e t t . 39_, 1 3 0 U ( 1 9 7 7 ) . H.M. G e o r g i , S .L . Glashow, M.E. Machacek and D.V. Hanopoulos, Phys. Rev.

L e t t . 1(0, 6 9 2 ( 1 9 7 Ö ) . R.Jî. Cahn and S . Davson, Phys. L e t t . £ 1 3 6 , 1 9 6 ( 1 9 8 4 ) . S . L . Glashow, D.V. Kanopoulos and A. Y i l d i z , Phys. Rev. D l 8 , 1724 ( 1 9 7 8 ) . See P. H a l z e n , these proceedings.

J . F l e i s c h e r aad F. J e g e r l e h n e r , Phys. Rev. P23, 2001 ( I 9 8 I Ï . For a d i s

cussion o f t h i s process , see a l s o : T . F i z n o , Phys. Rev. D 2 2 , 7 2 2 ( I 9 8 0 ) ;

H.A. Gordon e t a l . , i n Proc . o f t h e 1 9 8 2 summer study on Elementary P a r t i c l e

Physics and f u t u r e A c c e l e r a t o r s , Eds: K. Donaldson e t a l . , G. Kane, r é f . 2 9 ) . S e e , e . g . B. Humpert, these proceed ings; J . E l l i s et a l . , work i n p r o g r e s s ;

1. Kunszt and K. M u r S u l a » work i n p rogress .

ù : «410026422

COMPOSITFNESS AND THE FERMI SCALE

E.D. Peccei

Max-Planck-ÏDstîtut für Physik und Astrophysik, Werner-Heisenberg-Institut für Physik, Munich, Fed. Rep. Germany

I. INTRODUCTION The KOtivation for considering that the presently known quarks and leptons

are not elementary is varied. Perhaps the most reasonable argument for their compositeness, in my mind, is that the mass spectrum of "elementary" quarks and leptons in the standard model is not calculable. Although complicated dynamical schemes can be constructed beyond tfcj standard model to give a calculable mass spectrum for quarks and leptons, even if they are elementary, one should perhaps heed the lesson of history. Atomic physics, nuclear physics and hadronic physics teach ua that the most economical and reasonable way to obtain a mass spectrum is to assume that the objects in question are hound states of even more fundamental entities. This said, however, one must admit that the whole idea of composite quarks and leptons is beset with problems. Three of the most crucial toes are indicated below and will serve *:o channel my discussion on these matters.

The greatest hurdle that needs to be overcome before s.ime serious interest can be generated for the idea of composite quarks and leptons is that some experimental evidence in its favor must be foundf Until recently ths experimental situation was bleak and discussions of composite models were üore or less restricted to a small coterie of theoretical aficionados. The situation has changed drastically recently with the observation of radiative Z° d e c a y s a n d promises to remain fluid if indeed all, or even part, of the strange events reported by the UAI and UA2 collaborations at this meeting are real. pThe positive attitude adopted up to now, due to the non-observation j

o p effects of substructure, is that the compositeness scale /\ must be large: A t 1 TeV.

Such a large value of f\ gives rise to two theoretical problems which I aholr examine here, namely: J ) What dynamics yields light composite quarks and leptons ( m ^ « A ) and 2 ) What relation does the compositeness scale A have with the Fermi scale ftF = { H G F ) " 1 / 2 S 2 5 0 G e V î J (&sxy-

Although the first problem above is well known, the second problem is equally important and has been largely ignored in the past. I shall try to partially reme^, his situation in this report by focusing mostly on this latter problem.

- 484 -

Before entering the body of the discussion, I should remark that the present bounds on the compositeness scale A are quite model dependent. Two examples will illustrate this contention. It has been normal to parametrize possible deviations from the standard model for the process e +e —» £ 4 K .

by the incorporation of possible form factor effects via the replacement of the photon propagator:

( I . I )

Experiments at PETRA and PEP then yield typical bounds for A oí order ¡50-200 GeV^. Eichten, Lane and Feskin \ however, have recently argued that such a procedure probably grossly underestimates ^ . If there is an underlying theory of which the observed leptons are bound states, one would normally expect to induce effective contact interactions among these

2 2 bound states at low energy <q << A ) of the form;

A * ab

where the particular spinorial structure, present in the coefficients ^¿j^j' is model dependent. Because the underlying theory is presumably a strong coupling theory it is reasonable Co suppose that the effective coupling constant in (1.2) is strong: g /4K 0(1) and not weak: g /4tt^ 0 ( 0 . A reanalysis of the PETRA and PEP data under these assumptions then yields a bound for the compositeness scale A of order A £ 750-1000 GeV.

The ELP analysis, although more reasonable, has at least two caveats. It could be chat the residual interactions due to compositeness reproduce the usual weak interactions. In this case clearly no bound on A can he obtained by parametrizing possible deviations from the standard modelî Of course,in this instance,there must exist a well defined relationship between A and ti. arising from the preon theory. I shall return to this point. The

5) second caveat on the ELP analysis is due to Visjnic . He argues that the

2 presumption that one has g /4if * v 0(1) as a result of a strong coupling underlying theory may not follow, for the case of preon theories. Such theories, as will be discussed below, must preserve some chiral invariance to allow for light bound state fermions. However one knows, from the pioneering work of Nambu and Jona-Lasinio^, that a chirally preserving four-fermion interaction which is sufficiently strong fg^/4ff ï 1/2 in the model of Ref. 6>]

- 485 -

eventually leads to a spontaneous breakdown of chirality. In the context of the present discussion this would be inconsistent and therefore it may-well be that the effective coupling in Í1.2) is rather weak. This of course would allow for a weakening of the bound on A-

A second bound on substructure is provided by the electron and rauon (g - 2) measurements, which are in very precise agreement with QED predictions. Naively, one would argue that if leptons were not point-like one would expect an extra anomalous magnetic moment contribution given by the effective interaction

the present level of agreement between theory and experiment would provide a very strong bound on A indeed: ^ £ 10^ GeV. Howe\ar, if the underlying theory is approximately chiral invariant, the effective magnetic interaction must vanish in the limit of zero lepton mass. Hence, in these more sophisticated models one would expect an effective interaction^

which yield fa-** (m 4 ) . For the u anomaly the above yields a bound A ? 900 GeV, comparable to that of the ELP analysis. The electron anomaly does not yield a useful bound.

I want to remark that if the additional anomaly in (1.4) is due to a heavy lepton of mass m* then in fact the bound on m* is even below that given for A . This can be easily understood since the presence of the heavy lepton is only felt at one loop order and the extra anomaly contribution is then given by Í a *C d ( / m * ) ^ . A detailed calculation of these effects has been

8) performed by Renard and one sees from his paper that heavy muons of mass m* £ 50 GeV would run into no conflict with (g - 2 ) . The bound on heavy electrons from (g - 2) is very weak, certainly well below the direct limits set already by PEP and PETRA searches. Except for the indirect ELP bound on A i 1 TeV, it is apparent that no experimental fact stands directly in the way to lepton recurrences in the 1,0-100 GeV range. This remark will be of interest later.

The ELP analysis and the (g - 2} bounds are the least model dependent bounds on A • Flavor changing processes like u e y , K —f> u e or K°- K°

( 1 . 3 )

The above gives an extra correction to (g - 2) of order Sa -v (ni ) and

(1.4)

- 4 8 6 -

mixing can in principle provide very much more stringent bounds on A , unless the underlying theory somehow suppresses these processes automatically. Because we understand so little about the nature of families, it would appear to me that, at this stage in the game,one should ignore altogether the bounds arising from family mixing (or proton decay, which would imply h% 1 0 C e V ! ) and be open to the possibility that the compositeness scale may be as low as I TeV.

2. THEORETICAL DISQUISITIONS Already if A —0(1 TeV) the dynamic of the underlying theory (preon

model) is rather special to be able to produce bound states, the quarks and leptons, with masses in the MeV-GeV range. These bound states would have a typical size ¿r > 1 /A which in fact would be much smaller than their Compton's wavelength X c 1/m^ - certainly a new phenomena in physics. The usual presumption that is made is that these "light" bound states, with m f<3iA , are a result of some approximate symmetry. This must strictly be the case if the underlying preon theory is a non-abelian gauge theory. These theories have only one dynamical scale A related to where the coupling constant becomes strong and all bound state masses are of 0(fs. ), However, even for other possible preon theories it is difficult to imagine dynamical accidents which would force some states to be of a size iruch less than that given by their Compton's wavelength, unless some symmetry forced this condition.

The usual strategy adopted theoretically is to first invoke some symmetry reasons to keep certain bound states at zero mass. Then by appropriately relaxing these symmetries one hopes to gain some small masses for the mass-less bound states. If one wants to construct models where che only massless excitations are the observed quarks and leptons, the first step in this procedure is already rather hard. The second step, of actually generating an even semi-realistic mass spectrum, however, has proven totally elusive. This is not surprising, since it is clear that the detailed mass spectrum of quarks and leptons is tightly connected with the issue of families. Since the origin of the family replication still eludes us, it is not difficult to understand why no successful spectrum has yet been theoretically generated. There is, however, also a more technical reason for the present theoretical failures and that is that the symmetries one imposes to generate some massless states are, i<i general, very hard to break "slightly" in a non-arbitrary manner. This point, in my opinion, will continue to plague model builders until some radical new idea is found.

- 487 -

There are, at the moment, two main suggestions for keeping the quarks and leptons light: 1) One can assume that the underlying theory has some global chiral symmetry

9 )

which remains unbroken in the binding . In this case the fermionic spectrum would most probably contain some massless states, along with massive chiral partner states. The inassless states must have global transformation properties under the chiral symmetries, so that the Adler anomalies of the chiral currents

9) match at the preon and composite level 2) Alternatively, one can consider supersymmetric preon theories with some global symmetry G ' ^ . If this global symmetry is spontaneously broken to a subgroup H, then one expects certain Goldstone bosons to appear in the spectrum. Because of the supersymmetry, these bosonic states are accompanied by fermionic partners - the so-called quasi Goldstone fermions*'' - and it is these States that one can try to identify with the quarks and leptons. It should be mentioned that if H itself is a chiral group, it can happen dhac some (or all) of the quasi Goldstone fermions may be required by the *t Hooft

1 2 )

anomaly matching conditions . Thus chirality can act as a further reason for the appearance of certain quasi Goldstone fermions and raeréis with this double protection have been constructed ' ' ' ' ' .

It is worthwhile to remark again that, once one follows one of the above scenarios to obtain massless quarks and leptons, it ia then very difficult to break the remaining chiral Symmetries, or the supersymmetry and global symmetry G , in a weak way so as to then get a realistic mass spectrum. In fact, to my knowledge, this problem is totally unsolved and there is no realistic model on the market now which generates a reasonable mass spectrum.

A second very important problem for preon models, besides that of generating light quarks and leptons, is the problem of the origin of the Fermi scale. To my mind, this problem is of equal importance to that of fermion masses and, furthermore, it has some direct practical implications. I begin examining this second problem under the assumption that the electroweak interactions originate from a spontaneously broken SU(2) x U(l) theory, as in the standard model 1 5', except that these interactions act at the preon level. Because Che quarks and leptons are composite, it follows necessarily that there exist some residual interactions among them, due to their compositeness, whose dominant low energy (q ¿(f\) form ia that given in Eq. 0 . 2 ) . Because the standard model works so well, the terms in Eq. (1.2) must be a small perturbación. This obviously requires that

£ p A 1 V» 1 (2.1)

- 488 -

Therefore, une sees that the natural question to ask in these circumstances is why is the Fermi scale so small with respect to the compositeness scale. This, in fact, can be a problem. Let me explain.

The Fermi scale, implicit in G^, in the Stan with the strength of the SU(2) x U(l) symmetry breaking. One has

< * ~ ^ ( 2 .2 )

where ii 1*^ represents here an effective SU(2) x 0( I ) symmetry breaking condensate. Now, if the quarks and leptons are composite it is quite clear that there should be no elementary Higgs with which to associate . In fact, it is very natural to suppose that the condensate is formed precisely by the same mechanism which binds quarks and leptons. That is,

C is a condensate of the underlying preon theory. Unfortunately, if chis is the case, one would conclude that *^<£^ is of 0 ( A ) and thus

2 2 Gj, A, 0(1) and not G p A }71, as required experimentally.

This line of argumentation has three possible conclusions, which reflect the options which are realistically open! 1) The compositeness scale A is nearby, say A * ] TeV. Then some minor dynamical miracle still guarantees that Eq. (2.1) holds with, say

Gt i° >> í (23>

2) The Fermi scale has no direct connection to the preon theory. For example, one can suppose that there is some technicolor theory'^ which causes the spontaneous breakdown of SÜÍ2) x U(l) and thus 4>*> -vA T (,. In this case Eq. (2.1) can be easily satisfied provided

' / * T C > » 1 (2.4)

One should remark, however, that these kind of theories are much more complicated. Not only is there some gauged SU(3) x SU(2) x U(!) theory, but one further needs two more confining gauge theories - one to bind quarks and leptons out of underlying preons and the other to provide SU(2) x U(1) breaking condensates. 3) SU(2) x U(l) is not a fundamental theory. In this case the weak interactions are precisely those given by the residual interactions (1.2). The Fermi scale has nothing to do with the spontaneous breakdown of a local symmetry.

- m -

Rather it reflects the mass of the exchanged bound state massive vector excitations, which arise from the underlying preon theory.

Clearly 3) is an iconoclastic possibility, but one which is interesting and should be taken seriously. It presupposes that the W and Z are not elementary and that the standard Glashow-Salam-Weinberg theory 1 5 is only an effective theory and not a fundamental one. This possibility, however, re-

2 quires also dynamical miracles, akin to Gp f>> Í, but which perhaps are even more difficult to achieve. To explain this point it is worthwhile making a small aside to spell oui: the requirements needed for the weak interactions to be residual. Basically one needs:

f f ft a i l I. ' (2.5)

and

b ) M w ~ HV^ ^ i ö y (2.6)

The first equation above guarantees that all low energy neutral current results are as in the standard model, while the second equation is necessary to reproduce the SppS results.

How to guarantee (2.5) has been known for a long time, from the pioneering work of Bjorken'" and Hung and Sakurai'*". What is needed is an effective

X« ~ ( ^ ' . T ) ; Ç? , i (2.7)

2 and V - W, mixing. Then Eq. (2.5) obtains readily with sin 0„ related to

w g, e and the,as yet free, - mixing parameter > :

^K, - P (2.8) 1 18)

In fact X parametrizes the relation between My and and one hr.s

(2.9)

Thus to reproduce the collider data, the underlying theory must yield

- 4 9 0 -

where the last equality follows from (2.8).

Eq. (2.10) is a dynamical condition which is not easy co obtain, since sin2*? H 1/4 is certainly much bigger than , which would be the naive estimation for the mixing parameter A^ . However, one can argue that X must obey Eq. (2.10), if for some reason the W and Z° are much ligher than other

19) vector meson m the spectrum of the preonic theory . In effect if

\ > - > M w

< 2 - ' °

then one can assume that there is good vector meson dominance of the electromagnetic form factor just by the Z°. This immediately gives Eq. (2.10). Physically, if Eq. (2.11) holds there is a large gap between the "light" y and Z°, and the rest of the J = 1 states and it is therefore not surprising that the mixing, A ^, is large.

I would like to conclude chis sección by emphasising again what are the theoretical conclusions one arrives at if the quarks and Isptons are composite and there is not some technicolor theory. Then one expects: 1) that the underlying preon theory has some protective symmetry so as to guarantee that some light fermions (m^<r< A ) emerge from the binding 2) the compositeness scale is of 0(1 TeV) so that not too big a dynamical miracle is required to guarantee that either

G _ A 2 , » 1 (SU(2) x U ( l ) is fundamental)

A Vf My (weak interactions are residual)

From this point of view one sees that if quarks and leptons ace composite, the probability that the weak interactions are fundamental or residual is probably 50-50. Furthermore, if AV> [ TeV it appears essentially impossible to have ? natural explanation the Fermi scale unless life is much more complicated. New interactions (technicolor) must be introduced to separate the Fermi scale from the scale of preon binding, which leads to the formation of quarks and leptons.

- 4 9 1 -

3. MODEL ILLUSTRATION I would like to illustrate some of the general points indicated above

by means of a model which was developed in collaboration with Wilfried Buch-20)

müller and Tsutoinu Yanagida . We considered a super symmetric preon model based on an S U ( 2 ) ^ x S U ( 2 ) ^ hypercolor confining group. To obtain one generation of quarks and leptons (the model can he extended to more generations) we made use of 13 preon superfields. Six of these <[>? ( q = 1 6) are doublets of S U ( 2 ) H C ; another six (p = 1 6) are doublets of SU(2)¿ C; finally, the thirteenth preon \ ^ is a doublet under both hypercolor groups. The model clearly has a global G ~ U(6) x U(6) r x 0(1)^ symmetry which can be broken down if certain condensates form. Specifically, we assumed that the following condensates appeared in the theory:

v - ? f $ ; > r ( 3 - l a )

V ' í < « ¡ j (3.1b)

(3.1c)

The existence of (3.Jc) in the directions shown is a matter of vacuum alignment, which we assumed proceeded in the way shown. Clearly the condensates in (3.1) break down G-> H = U(4) x U(4)' x SU(2),. . As a result of the breakdown

dia3

Goldstone bosons with m = 0 will arise. Furthermore, supersymmetry will also force certain quasi Goldstone fermions (QGFÏ with zero mass to appear. Since H is a chiral group for the preons, one must require also that certain ra = 0 fermions appear in the bound state spectrum to match anomalies. Remarkably the QGF are precisely the set of fermions needed for anomaly matching. Hence our model gives an example in which the massless fermions are present both because of chirality and because of the Goldstone phenomena for supersymmetric

12) theories

The massless superfields that appear in the theory contain the 16 quarks and leptons of one generation, plus some additional states. These include three neutral superfields (which we have dubbed novinos) and a triplet of fields

which, in a version of the model to be described below, play the role of a technipion superfield (technispions). Because these zero mass fields are

- 492 -

connected to the spontaneous breakdown of G*)H, it is possible to construct 2

an effective Lagrangian which describes their interactions at q —> 0. The analogue in QCD is the chiral Lagrangian for Goldatone piona. In the QCD

case this Lagrangian is written in terms of the pion fields, scaled by f^. -

the parameter which is related to the breakdown of SU(2) L x SU(2) R — » S U ( 2 ) L + ]

The pion decay constant is proportional to A q C D, f ^ Q £ D » and it is intimately connected with the quark condensates <üu>*v A Q C D which cause the dynamical breakdown of the symmetry. In our case, the effective Lagrangian which describes the leading interactions between quarks and leptons due to compositeness will also contain a number of scales, which are related to the dynamical condensates v, v'and V p of Eq. (3.1).

20 A rather lengthy, but straightforward, calculation ' yields for the

dominant residual interaction between quarks and leptons the following expression: ^

Here J . _ are isovector currents for the quarks and leptons with appropriate helicity projections, while Jj.^ are isoscalar currents. The scales v ¡ " v 2 are related to the condensates v; vj, v^ are related to v'; and v^, is related to v p.

Although (3.3) is a general result, there can be specific dynamical circumstances in the underlying theory that may lead to some simplifications. In particular, in the model at hand, the scales V j and V 2 (vj and v£) are scales related to Che left-handed quarks and leptons and novino, respectively (right-handed quarks and leptons and novino). Because these states are built in an analogous fashion in the model, it is to be expected that these scales

- 493 -

are approximately the same: v j ï v j»

scalar currents are probably highly suppressed in Eq. Í3.3). Furthermore, if the Slíí2^¿c dynamical scale, f^'t were to be much bigger than the S U ( 2 ) ^ dynamical scale,A, then one would be led to the hierarchy

In this case Eq. (3.3) reduces to

/ " _i u » _ r ; ) f o . f v ) , £ ( ^ . * ) C 3 5 )

which is precisely of the form (2.7). Thus, under the dynamical circumstances described above, it is conceivable for our model that the weak interactions be residual. Of course, a further necessary condition in this case is that My be much below the scale of the binding of the left-handed quarks A . In fact, even this can be argued in the model, since it possesses a complementary picture. In the complementary picture the only light J - J states present are precisely the W + and the Z°, and one can thus presume that this circumstano still obtains in the confining phase of the theory.

Residual weak interactions, however, are not the only possibility in the model. One can introduce at the preon level a gauged SU(2) x Ufl), where the SU(2) only acts on the 5,6 preons ? (a = 5,6). It is easy to see then that the condensate v^ of Eq. (3.1c) breaks this gauged SU(2) x U(I) down to u C ' ) e m - T n e W and Z superfields get a mass by precisely absorbing the technipion massless bound statesTf . In this case the preon theory acts as technicolor!

For the model to be realistic, however, in this case the condendates v_ must be much smaller than v and v'. Only when this is so will the resi-

2 2 dual interactions, which from (3.3) are of order 0(l/v.) or O O/v,.), be much

2 smaller than the standard weak interactions which are of 0(1/v.^ ). Effect

ively, taking the scales A v A ' , what is needed is that the condensates 2

-< A , but the three body condensate that it is much harder for three diffe

fields to condense together so that this hierarchy happens. These "dynamical miracles" are precisely those alluded to in the last section, which are needed so that the residual interactions due to compositeness do not spoil the agreement with experiment of the gauged weak interactions.

- 494 -

RADIATIVE Z DECAYS: ARE THESE THE FIRST EXPERIMENTAL HINTS OF COMPOSITNESS? The three events reported by the UAl and UA2 collaborations of z —> £ P y 1)2) . . . decays , if taken at face value, seem to indicate a radiative width for

the Z° much greater than what is expected by bremsstrahlung:

(4.1)

Of course the present sample is very small and one could well be dealing with a statistical fluctuation. If the Fall run at the SppS confirms the above rate this will be a clear siga that some physics beyond the standard model is present, and that physics is likely to be connected with compositeness ideas.

Perhaps rather rashly a number of people, including myself, have already tried to interpret these events in terms of various compositeness scenarios. Here, I would like to briefly discuss two of the more popular ideas, which appeal to sequential decays to obtain a radiative rate much greater than e¿ . As will be seen, these suggestions are not without problems. T'iere are other

2 1 ) alternatives, notably the suggestion of Gounaris, Kögeler and Schildknecht , who obtain large radiative rates by having the W and 2. have strong interactions with sequences of other vector mesons. Some of these other possibilities, along with that of sequential decays, have been clearly discussed recently

22) by Renard

If the radiative rate for the Z° is enhanced by a sequential decay, there are clearly two possibilities. Either the Z° de-excites to a scalar state, which subsequently decays to lepton pairsj or the 2° decays into an excited lepton and a lepton, with a subsequent radiative de-excitation of the excited lepton. The scalar scenario (Z°-» Xy', X -» *f t ) vas first suggested, to my knowledge, by Baur, Fritzsch and Faissner^^ and by myself*^- However,

22) it was also analyzed by RenaTd , essentially contemporaneously. The excited lepton scenario was discussed by Cabibbo, Maiani and

25) 26) 22) Srivastava and by Enquist and Maalampi . Again Renard also discusses 27)

some of the points brought forward by these authors. Since G. Pancheri will cover this topic in her contribution to this meeting, my remarks on the excited lepton scenario will be reasonably brief.

It is quite clear that if the radiative 2° decays are due to a sequential decay, then there should appear a clear invariant mass bump in the data. No such bumps are manifest in the data, but one should remember that there

- 49S -

are only 3 events and that the experimental errors are not small. Furthermore, there well may be more than one scalar state and/or heavy excited lepton (e.g., e*, M*)» so that the situation is by no means critical. However, by the next collider run - if the radiative decays remain at the present rate -there will need to be an invariant mass bump for the sequential hypothesis to make any sense at all.

4.1 The Scalar Scenario This scenario is based on a very simple - one may perhaps even call it

naive - premise. If the W and Z are composite and somehow they are dynamically pushed to a mass M ^ « A , it may be that there are also some J = 0 partner states which are light. If one pursues an analogy with QCD, one would expect both isovector and isoscalar states of spin 1 and 0. However, one knows experimentally that both the J =: J, isoscalar state, W and the J = 0 iso-

—» b

vector states, X, cannot be that light. The former states are certainly much -*

heavier than the W triplet, since no isoscalar neutral current appear in the theory - apart from those induced by V - W_ mixing. The isovector states X also must be much more massive than the W, because if not they would spoil the chiral properties of IT -decay : t* ( 17- ur)/f* ( fT -> e V) (^/n^)^.

No such constraints exist for a possible light J = 0 isoscalar state, X. The X could be relatively light and still not affect our phenomenological understanding of the weak interactions. Nevertheless, to ascribe to the X's presence the large probability of a radiative Z° decay is not altogether straightforward. What is needed is that the X itself have a sizable coupling to lepton pairs. Normally such a coupling, unless it were proportional to the fermion masses, will violate very badly chirality. Obviously, it is fatal if the coupling is proportional to the fermion masses, since we would never get a sizable decay rate of X into e +e - On the other hand, if chirality is badly violated it clearly removes the raison d'etre for quarks and leptons to be light. The only way out, as I suggested in Ref. 24), is to suppose that the X is really a chiral doublet, Then one can have a universal coupling of the X = I N,S*J to fermions without violating chirality in the fermion sector. Chiral fermionic rotations are compensated by rotations between the chiral doublet states, as can be checked from the effective interaction:

Such a Lagrangian suggests, by its universality, that for the case of three generations of quarks and leptons, roughly

(4.2)

- 496

(4.3)

Assuming that the rate for Z°-s £ + £ is still given by the standard model rate of roughly 90 MeV, then from Eq. (4.1) it follows that T (Z° -» i V " y ) -S 20 MeV. From the equation

r í í ^ f - y y - r t ? % x Y > ge*

and Eq. (4.3), it is clear that to obtain an explanation of the present radiative data one needs T* (Z°~y X f ) -5:400-500 MeV. Amusingly enough**^ such a rate is not unexpected, if one tries to estimate it in direct analogy with

24) QCD. In my own work I considered an effec-.ive coupling of the W triplet to X of the form (suppressing all indices)

« f f . - -Vs 2

Then by using the y ~ mixing as in Eq. (2.10) and taking k An-*- 0(1), A= 1 TeV and ^ = 50 GeV it follows that P (ZD-i> Xy)0f 450 MeV. This model allows also to estimate a rate for X into 2 ^ and I find, for the same parameters

-1>

Ic should be remarked that (4.5) violates chirality since the W's are inert under chiral rotations, so that the careful chiral protection built in : i Eq. (4.2) is in fact broken in the heavy sector. Unless some special circumstances obtain, this will be seen to be the downfall of the model.

Before discussing this point, a number of phenomenological remarks are in order. Using Eq. (4.2) it is easy to compute the rate of X into lepton

o *• j 24) pairs. One finds

We note that if ¿ lO - 4 then, for VL^ in the 50 GeV range, P (X-»C+-¿~) is only 3 MeV and thus a sizable portion of the X decays are into 2"/. In this case it may be that the branching ratio B(X-* ) is less than b%.

Direct bounds on J , exist from a careful analysis of the PETRA data ^ n at the highest energies available. Some of the necessary theoretical analysis is contained in Ref. 24), but much more detailed considerations are contained

2 8 ) 29) in Lhe reports of Bopp et al. and Hollik, Schrempp and Schrempp . No

- 497 -

significant effects were seen i n e e _ ^ e e , e e - $ 2y , e e u u and in R up to the possible highest energies at PETRA (45.2 GeV). This allows 3 0' to exclude masses for X below Chis range. Furthermore, if £ 50 GeV there would be significant tails in this data unless tt La small enough, J ^ £ 10 . Finally, if one uses the particularly simple model of Ref. 24), where also X-* 2~i is absolutely predicted, then essentially already present PETRA data

30) excludes this hypothesis

A further bound on J exists from the fact that no direct X production 24)

is seen at the collider. One expects

For / h - 10 ^ this would imply about one event of x into . However, for this value of j( the Y*V r a t e of X is proportionally bigger and one should perhaps expect 5-10 events, along with perhaps the same number of 3 Y ' e v e n t s from the sequential decay Z°-» Xf ; X -3 2*f to have been seen. No evidence for these kind of events has yet appeared and this throws some further doubts on the scalar hypothesis.

There is, finally, also 3 disturbing theoretical constraint on the X's existence, which comes from the (g - 2) experiments. If a Z°K •>{ coupling exists, then this coupling can give rise to a nontrLvial contribution to the muon (g - 2). An analysis of this effect, by a number of different g_-oups 3'\ reaches the following conclusions: 1) If there is only one X state, then the value of the coupling W^ and k needed to give a sizable radiative Z° decay imply a muon anomaly roughly 100 times greater than the present (QED-experiment) discrepancy allows. 2) If there are two X states - so chat chirality is preserved at the fermion X sector (cf. Eq. (4.2)) - then in fact a cancellation can occur in the (g - 2) contribution provided that the coupling of che chiral doublets X = I N,S^ to the W's in Eq. (4.5) have opposite signs.

These results ?re discouraging for the X hypothesis. Although one can appeal to chirality to argue for the form of Eq. (4.2), as was done in Ref. 24), no real theoretical reason exists for fixing the relative weight of the chiral breaking couplings of N and S to the W's so that the (g - 2) cancellation occurs. This is a salutary lesson, which was already hinted at in Section I. unless there is appropriate chiral protection, the (g - 2) agreement between (JED and experiment does r.ot allow to have "light" composite objects. Of course, given the infancy of this subject one should perhaps wait until further

- 498 -

experimentation at the collider before eliminating altogether the scalar hypothesis as an explanation for the radiative Z° decays. Indeed, since a priori also other explanations do not look substantially better, this may be a very prudent attitude to take.

4.2 The Excited Lepton Scenario The Z° radiative decays could be due to the existence of excited leptons,

which then de-excite radiatively. If one assumes that the de-excitation via y emission is essentially 100% then to explain a rate P ( Z 0 ^ 20 MeV

one needs a rate P ( Z ° - 9 ¿ * ¿ " ) - 10 MeV, roughly 10% of the normal leptonic 25)

rate. Cabibbo, Maiani and Srivastava (see also Ref. 26)) shows chat such a rate is not inconceivable, via magnetic transitions. Indeed assuming that the excited leptons form an SU(2). doublet , the effective interaction

(4 .9 )

between excited leptons, ordinary leptons and the SU(2) x U( 1 ) gauge fields

leads to a satisfactory rate if the free parameters f and V obey

a perfectly sensible constraint.

As I said earlier, I shall not further discuss the phenomenology of this 27)

hypothesis, since that is done in Pancheri s report . Nevertheless, I shall make some critical remarks which should serve as a warning that also here not everything is as easy as it may seen at first sight: 1) Since there are both u +u V and e e y events one needs both u* and e*'s at roughly the same masses. Indeed, with large errors it appears that the

1)2) u* would be lower than the e* . Why is this so, since after all m ^ / m

e

200? 2) In the same vein, it is somewhat peculiar to hegin to see recurrences of the light e and u families in the energy range where one "ground state" of the other family, the top quark, is presumed to lie. 3) Although if one has a good chiral symmetry - as guaranteed by Eq. ( 4 .9 )

for example - there is no problem with having excited leptons in the 50 to 100 GeV range from (g - 2 ) , it is still peculiar that these excited states should be so much lighter than A >, 1 TeV, as determined by the ELP analysis. 4) Theoretically, having excited recurrences of the known leptons can give too fast a rate for u ^ e ^ , unless intragenerational mixings are severely suppressed, or there is a very good GIH mechanism. One can estimate the

- 499 -

8 )

5. CONCLUDIHG REMARKS By not too perverse a logic I have tried to indicate how the notion of cal-culability of the quark and lepton mass spectrum probably requires that these objects are composite. Furthermore, to try to understand the Fermi scale, and not complicate the theory overmuch, it is sensible that the scale of compositeness is nearby, say A*¡ 1 TeV. Under these circumstances it appears almost equally sensible to suppose that the weak interactions are just residual products of compositeness, as that they are due to fundamental gauge interactions. The recent SppS data on radiative 2° decays furthers this notion that compositeness is nearby. In fact, these events may be too much of a good thing, since with A ** I TeV it is difficult to conceive of scalar states^

or excited leptons in the 50-IOC GeV range! Nevertheless, it is my opinion that if these events are confirmed by further experimentation, and/or if even a fraction of the new exotic events discussed in this meeting are established, then corapositeness is here to stay.

ACKNOWLEDGEMENTS My own understanding in these matters owes much to the insights of my

collaborators Wilfried Buehmüller and Tsutomu Yanagida.

u e y rate due to the presence of exeited leptons by the formula

which requires a suppression mechanism in the curly Lracket above of roughly H f 8 . 5) If excited leptons exist, if is very probable that excited quarks also exist. The phenomenology of these q* (starks) has been analyzed recently

32) by De Rujula, Maiani and Petronzio (see also Ref. 27)). These states could be the source of some, perhaps all, the new UAl and UA2 events presented at this meeting. In this sense, the excited lepton explanation for the Z° radiative decays is perhaps more relevant than that involving a new scalar excitation. Although, in this latter case, since the explanation presumes that the W and Z are composite, one can well expect extra additional states -like colored W's - which could also he the cause of the new events.

- 5 0 0 -

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22) F.M. Renard, Univ. of Montpellier preprint PM/83/11. 23) U. Baur, H. Fritzsch and H. Faissner, Phys. Lett. I35B (1984) 313. 24) R.D. Peccei, Phys. Lett. 136B (1984) 121.

- 501 -

25) N. Cabibbo, L. Maiani and Y. Srivastava, Univ. of Rome preprint No. 381. 26) K. Enquist and J. Maalampi, Phys. Lett. I35B (1984) 329. 27) G. Pancheri, these proceedings. 28) F.H. Bopp, S, Brandt, H.D. Dahmen, D.H. Schiller and D. Wähner, Univ.

of Siegen preprint SI-83-24. 29) W. Hollik, F. Schrempp and B. Schrempp, DES* 84-011. 30) B. Adeva et al., MIT technical report No. 134;

K.J. Behrends et al., DESY 84-020, Phys. Lett, to be published. 31) F. del Asuila, A. Méndez and R. Pascual, UAB-FT-105;

M. Suzuki, Berkeley preprint LSL-17630; L- Maiani, private communication; B. and F. Schrempp, private communication.

32) A. De Rujula, L. Maiani and R. Petronzio, CERN-TIÍ-3779.

- 5 0 Z -

E X C I T E D F E R M I O N S ft< 0

G . Paoeïteri

r N F N , L & W r a t o r i Nazitmali d i Frascatô (Frasca*i,r'OB l a - 0QQ44 Frascati ( I t a ly )

T lsore i ica l ana esper faeata l ímplicatiDas of the existence of excited states of ordinary leptons

and quarks are esamiaed. T h e çoBtributioa of excited electrons and of their neutra! partners t o the

decays S Q - * e**"e—7 and 2¡¡ - * í/f"r are discussed, Signatures of excited quark states are compatea

Tvith reported experimental observations. Through -weak isospin lnvariam:e,ït is also fowad that there

may exist excited quarks w i t h weak isospäa Ia> 1 which nave exotic charge a s s i g n o r - a d decay

only electro-weakly into ordinary quarks aad teptons. These exotic qttarks will give rise to caarge j

4-3 baryoDE and cbarg* ± 2 mesons.

1 . E X P E R I M E N T A L M O T I V A T I O N

I n 19Ä3 U A l and U A 2 Collabor&tá&D. reported th& observation, of the process

Z Q ~* < s + a ~ i ( I event cacft)

and

- S03 -

285*5

6"9.<?±U + S.S>

50.6

11.5t0.ï

m.oth.0 129-9

u.t±u> M.8 ??.o

4.2.7±2.t 5Ö.U1?

T?.?±5.0 30.6*1-3

5.0 * 04 46±[.o f.uo.3 - 5 . 3

aj ¿a is the angular difference in space .

conventional explanation in terms of haid bremsstrahluDg '4'. Furthermore at this conference, there

has been reported the observation of other unusual events :

pp -» missing energy-^- 'photon" + X (UAl)

a n d

pp -i- missing energy single jet-j-X (UAl)

with large value of transverse missing energy and large pt values for the photon and the jet i5I and

pp—* electron -+• missing energy + hard jaí(*) + JC" (UA2)

as well as Zi> C+e - and Zq -*• ii+p~ for a total of 13 dilepton eventsi1'2'. The energy and

«mission angle of the observed photons, which we reproduce in Table I from ref.[3], do not favour a

T A T 3 L E I - P r o p e r t i e s o f t h e e v e n t s .

- 504 -

•with a large total invariant mass Tables H, HI and W reproduce the characteristics of these

events as reported by the experimental groups.

Many suggestions have been advanced to esplain the anomalous Zq events I 7 - 1 2 l In this talk

I shall discuss in detail a model of excited quarks and leptons which hears the signatures of the

reported events, although tie event topology shows other anomalies'^ and the production rates are

not fully consistent between the different processes.

2. T H E EXCITED F E R M I O N M O D E L

The excited fermion model is based on the idea that if quarks and leptons are composite

objects!13!, there may exist excited states which are coupled to ordinary fermions through the usual

electroweak fields as well as through the gluon field and in a such a way so as to conserve weak

isospin. The excited fermion hypothesis can be phenomenologically understood as an extension of

the known three families of light leptons and quarks through the use of weak isospin. In the standard

SU{2) x U(l) model, the known particles can be classified as belonging- to we ,k isospin. multiplets:

right (left) handed fermions belong to isospin singlets (doublets) and the gauge bosons belong to

triplets, Vi7*, or singlets, B**. To the electroweak fields, one can add the color field G*"1 which

behaves like a singlet under weak isospin transformations. One may then consider the existence of

fermionic states which can be excited using light fermions (J i I )=0 J^), Intermediate Vector Bosons

( 0,1) and gluons (IW=Q). To lowest order in a only Iw—^>kt 1 Med be considered. The

resulting spectroscopy is very similar in spirit to the one which was done in the early days of particle

physics when the nucléon isodoublet and the pion isotriplet had been used to obtain the spectrum

of many of the non-strange baryonic resonances. Since all the gauge fields carry no hypercharge Y,

only couplings between excited and light multiplets with the same value of Y are allowed. As it

is well known, the effective coupling has to be of the magnetic moment type transition for current

conservation. This leads to the following effective lagranglan :

The hypercharge current receives contributions only from Iw = 0,£ states as follows :

CD

yJ(/w = o) = \(E-^VQ^R -f- A.c.) + ÍU^.\âpvQ"UR + /i.e.)

(S«)

- 5 0 5 -

T A B L E n - Properlies oí the isolated "photon" events (UAl).

ffuiv, |B TI (freV)

uiltff SI 40 ±4 54 9 3 1 5

w* 390 104 4 0 ± 6 +4 ? t ± 6

T A B L E 111 - Properties of single )et events (UAl).

Run, tirent

3ib («(.«fes Run, tirent is."

:<<.v> frt.y) Liai <¡«VÍC* 1 * 1 9 lí¡Jtl6 a 4 Iii -1.13 Sílice t<a£R

6 »« W

1% So I06tll 45 -lut -0.5Î • « > j

C IZ'2 48? ai 4éiS Si lié -oe j •0

s ra* IM

W « t í « t i l 4-5 4-l.i -54 -0-0* -no ; »

a \ i o 58

e ta W8 9Z titv* 46 0.« ••«355 unrífcníVjitíI

ttaeia

- son 1155 405 «tl» -C3I +' -02f 0.5IÏ iC«S

a) Electromagnetic part of the jet transverse energy. b) Azymulhal angle f). c) Rapidity v=*0 In direction of outgoing p. d) Charged tracks associated to the jet with pt > 0.5 GeV/c. Errors are statistical only, e) This event couid have other unreconstructed tracks in the horizontal plane, rtl Including the muon momentum in the calculation.

- 5 0 6 -

TABLE IV - Properties of the electron -i-miesing energy+jet(s) events. ( U A 2 )

ts A C UrtitS

Eltttwi IÍ.5 ±0-f 0 01

.22,0 ±D.S -0.2S

± 3.2 OM

"PtCjO - Ö.63

50

61 ±? .0.26

it * 5

1/ / átyrtes

Tetz». W3>) "1(3») «D

6i 1 CÍO Ii I Í 3

1 FrCjs5 "7< j}> *>

Sil -1.03

fo ?*/

-US •516

tjcV/e

<m(7) 37* u. 67±7 66t-&

63t- 6 <f<cV

ZZO SS±e 5 ? ± 5

IÁI <f*V/c

sit s m ±i

OkStO-Oí -0.01 ±0.06 162 ig

-0.0*10-05

-0.55 i 66

-0.3' ;<?.4 <j*v/c2

a) The pseudo-rapidity i) is positive in the proton direction. b) As mentlonad in réf. (6), jet energies are expected to be smaller than the

parent parton energies. This has not been corrected for and affects all parameters depending upon jet energies.

c) Ap is the azyrouth difference wilh respect to the electron.

where the notation follows that of Table V and VU, where the multiplet structure of the excited

fermions Is described in detail and fi represents the mass of the excited femiou.

The isovector current receives contributions from I w = £,1 and § :

- 507 -

/„{/„ = I) = ( C ^ J C w Q » l lL + A.c.) + [~ j(*a>„<?"\iL + A.c.) (3a)

UU- = 1) = (^-)(?^<3"=B + A.c.) + (^(ÖCT^Q-tifl + A.c.) +

U ' » = j) = C(j, Ai I 1, m; j, m')^)(F Mcr„ 1 /Q''t m. + A.c.) + ^yûn^Q"^ 4- A.t.)l (3c)

The color current is composed of / w = 0,¿ contributions :

/;(/„ = 0) = ( í ^ c F c v Q - ^ u , ; + A.c.) + ^ ^ D ^ Q ' ^ - d R + A.c.) (4a)

In the above equations, QP denotes the momentum oí the gauge field and p the mass oí the excited fermion. In Eq.(3c), C's are Clebseh-Gordon coefficients. T and X o are the Pauli $U{2) and Gell-Mann SU{2) matrices respectively. W% and are defined in the usual tvay :

fl" = cosi>Wl''-sinfi„2'' (5n)

H'J = sin tÂ* + eos B„2" (5t)

in terms of the physical fields A* Tor the photon and for the Za, 6w is the weaK angle, with the gauge coupling constants g, g' and gB given by :

— = " • — = ° (6n) 4 i r sin20 ' 4 7 r co5 ae w

and = os(e

2) sa —— — ( / o r /iuc flavours) ( 66 ) 23Io ga|

The constants appearing in tbe above equations, f, V and j s will have to be determined by ibe

experimental observations because oí our lack of understanding of the underlying dynamics. As for

the mass of such excited states, while there are no estimates from first principles, earlier guesses

had placed it in the TeV range, i.e. in the range of a passible composite scale a ' 1 4 ' . Indeed there

are indications, from Bhabha scattering for instance, that the composite scale cannot be less than

750GeVl l 5l. Present interest in the interpretation of the collider events, would instead favour a mass

ia the CO -5- lSQGeV range, i.e. of the same order of magnitude of the Intermediate Vector Boson

(rVB) mass.

- 508 -

It is important to notice that the experimental limits on the mass of an excited lepton are

consistent- with

¡1 > GOGeV

and a coupling of order unity. In ref. ¡7], it has been pointed out that coupling of excited leptons to

the light ones may generate flavour changing neutral current processes which are of order [^f with

respect to ordinary weak interactions. Thus the effect is very small if the mass m of the ordinary

leptons does not exceed that of the T and that of the excited ones is not less than, say, ^ 5QGeV.

Limits on both the mass and the coupling are placed by the measurement (at both Petra aud

PeP) or the cross-section for the process

e+e" - -» "77

Present data l i e l are consistent with, the constraint

2 W > (60GeVf\f + /'I

Finally, more stringent limits on these same quantities can be derived from the measured value of

(g — 2) for the muon ' 1 T1. In this case while a pure vector or a pure axial vector type coupling would

give a contribution linear in hence large for any reasonable fi mass, the requirement that the

coupling be of the V — A type leads to a correction like 1 7 , 1 S '

For ¡i > GOGeV this implies

|/ + /1<1.5

All of the above tells us that, while plausibility arguments would place the excited lepton mass in

the TeV range, there are no experimental counterindications for a 'low' mass, like 60-i- 150GeV and

that the coupling may be of the same order of magnitude than that of the usual weak interactions.

Thus both experimental and theoretical constraints seem to allow for excited fermions. Naturally,

one may then also consider the idea of new massive sequential states to not just quarks and leptons

but also to IVB's. This has been the object of many investigations l 1 9 - 2 1 ] . In particular, and to ex

plain the anomalous Z-decays, there has been advanced the hypothesis of a direct coupling between

Z(¡, 7 and a scalar (or pseudoscafar) resonance which decays into From the experimental data,

shown in Table I, one would expect such a state to be in the 40-f-SOGeV range. Recent investigations

- 5 0 9 -

3. EXCITED L E P T O N S

The multiplet structure resulting from the excited fermion model was studied for the leptons

in ref.[7] and is shown in Table V. This table indicates that if the excited leptons are lighter than

the rVB's, the following decay modes can he observed :

- I £ " 2'2 . I 3

''S'S

- 1 3

: 2

where {Jth) represent a fermion-antifermion pair belonging to the same isosptn multiplet. For the

case lu, = ^, the calculation of the expected IVB decay rates into the above radiative channels

produces the rrtes shown in Table VI, where

r = \1 cS= K - I' slnH^fi + Ä f Y i - [JL-fY _ -V P A M, / i _ 4sm 29„- r-Ssta JS„

and

-* e+t 7

2Q —

W — ef T

w - ~ « +e _(/i/a) /«,

IV - i/5(/i/a)

With ths values I 1 : 2

¿í = 7 5 GeV

at Petra Í22' or the possible decay channels of such a state seem to exclude the presence of a resonance

i n the processes

e+e~~ — hadrons, n + u — , e + e — , T Y

at least- u p to energies of 4S.22GeV. At the same time it has b e e n s h o w n f 2 3 , 2 4 ' t h a t t h e c o n t r i b u t i o n

of such a s t a t e to the {g — 2) of the muon would b e quite large and could b e cancelled only b y t h e

c o n t r i b u t i o n from an almost mass -degeneTate p s e u d o s c a l a r (or scalar) partner . This would imply

an hitherto unknown symmetry of the lagrangian.

- 510 -

T A B L E V - Q u a n t u m n u m b e r s ( c h a r g e Q , h y p e r c h a r g e Y ) of

e x c i t e d l e p t o n s ( b e l o n g i n g t o t h e f i r s t f a m i l y } w i t h I w * 3/2

a n d t h e i r c o u p l i n g t o l i g h t l e p t o n s w i t h s a m e Y .

M*£b,>tefc a Y Cou. £e<¿ ko

0 er -i -Z <JÄ ihrou-ah. 0

VI -a Û -1 -1 and "P* %

--(¡') 0

-l -i

•I 0

•i) *i

0 •i -I

-1 X

T A B L E V I - I V B ' s r a d i a t i v e d e c a y r a t e s , I w B l / 2 .

reí??*)

r r

511 -

one obtains good agreement with the experimental observations, i.e. a ratio

r = 0.2

for Z 0 -* e+ e"-*r relative to Z 0 e + e ~ and no TV -* in excess of the expected QED

background'26'. These values or the parameter bear a very definite prediction : tbe existence of

the decay mode

The number of expected events depends upon :

(a) the weak isospin assignment, Iw = £ and/or Iw = §,

(b) for each Iw, the number or excited families contributing to the decay,

(c) the relative sign, and magnitude, of / and f'.

Nothing can be said about the ispospin, although it is plausible thaï it be / = ¿. On the other

hand, the observation of the .u+.u - 7 mode Implies the existence of at least two excited families.

For two families and Iw = à,one has

r" T{Zí> - e+1-) 1 / C 0 S 2 ew - J' sin2 *•

Lacking insight into the dynamics of the model, one cannot predict this ratio and must wait for more

experimental or theoretical information. During the last year, the UAl Collaboration has searched

for this type of events and has reported,at this conference, the observation of two events, with, the

characteristics indicated in Table II. Both events are compatible with 2o-deeay, although one cannot

exclude the possibility that the photon of event G is an electron, which has passed through the

region »vhere the centrai detector is not sensitive.

Another interesting prediction, of the excitad lepton hypothesis is the existence of / w > i

multiplets with exotic charge states, like a positively charged electron and a doubly charged

E . These leptons can only have /3-decays and are coupled to light leptons only through W+ and

W~~. If the mass is in the 70-f- SO GeV range, the denay rate is however very smalL \\".h present

statistics on W-dccay modes, one expects

with ~ 1 event in the e + e — jet jet channel and

- 512 -

4. THE QUARK SECTOR

The excited lepton hypothesis can easily be extended to the quark sector. One finds that excited

quarks can he divided into two groups, those which predominantly decay stronglyl28) and for which

the decay width is

Tsea,it lw = 0,\

and the others which have only electroweak decay modesl27', i.e.

Table VTf shows the quantum n'tmbers of excited quarks belonging ' o the first family and their

coupling to light quarks with same hypercharge.

4.1 The c a s e / , ^ 0 , ^

The case IK = £ has been considered in detail in ref. [26], where quark-gluon fusion was found

to be an important production mechanism for / m = J excited quarks. Once produced these quarks

(starks) can then decay as shown in Figs, la, b and c, the latter mode being allowed only if the

stark is heavier than the IVB. De Rujula et al. have calculated the production cross-section for

these processes relative to the QCD background'25! . For process (a) and before integrating over the

parton densities, the cross-section can be written as

da £ Û £ a fiT jcriM-a -i

ISS ~ ~ U ( A / 5 l . - ^ f + P = r = m " - s )

•with

In this model the constant i,f ' and / s are all of the same order of magnitude. Imposing some

Mnematical cuts and for a stark mass ¡i = 140rJsV De Rujula at al. expect an escess of ~ 20

events in the jet-jet cross-section with a, = 0.1. These estimates are strongly dependent on the

values of the coupling constants (f=f ' = / e — ¿ in this case) and have un uncertainty of at least a

factor 2 -r* 3. This signal is consistent with the observation of an excess of ~ SO ± 16 events in the

jet-jet cross-section around 140 GeV, reported at this conference by the UA2 Collaboration I a 0 ' . If

•with 1—2 events in the missing energy -j- 2j'eis channel and 0.2 -î- 0.3 events m the electron +

missing energy ehannel.The signature of the latter events differ from the usual W -* et/ decay

because the electron should be substantially less energetic than the 'neutrino'.

- 513 -

T A B L E V i l - Quantum numbers ( c h a r g e Q , h y p e r c h a r g e Y ) o f e x c i t e d q u a r k s ^ b e l o n g i n g t o t h e f i r s t l a m i l y l f i l t h I w Í 3 / 2 and t h e i r c o u p l i n g t o l i g h t q u a r k s w i t h s a m e Y.

fI7u£fc/=iefc & Y 0 __U_ - 2 / 3 0

% %

-h P", r k

i

%

-'lb % if"

0 J- zf3 -'6 -»/$

-%

0

% fc

% ù) " 3»

%

(a) (b)

(c )

F I O . 1

- 514 -

th is excess i n i n d e e d d u e t o p r o d u c t i o n o f a s t a r k of mass s¿ 1 4 0 GeV", one m u s t t h e n l o o k for t h e

var ious final states w h i c h a re o p e n e d b y t h e presence o f t h e d e c a y channe l

a n d i n p a r t i c u l a r :

(a ) a n e n h a n c e m e n t i n t h e 3 j e t c ross -sec t ion

| b ) events o f t h e t y p e l e p t o n - i - miss ing energy + h a r d j e t ,

(c ) events o f t h e t y p e miss ing energy or e + e " " -f- h a r d j e t .

N o t i c e t h a t fo r Iw = 0, some o f t h e above channels are p r e c l u d e d , i n p a r t i c u l a r t h e r e is no s t a r k

decay i n t o \ V a n d l i g h t q u a r k s . T h e e s p e c t e d n u m b e r o f events for / « , — ¿ c a n be c a l c u l a t e d m a k i n g

use o í t h e b r a n c h i n g ra t ios

2 ^ S ,

cos ij w T 3 1 sin0w

_ s i n i „ 7 6cosS„

a n d

v's sin»,

r(Z 0 - vi-)

r(Z„ - all) = 0.18 (7)

tu) T(W-all)

E q . ( 7 ) impl ies t h a t i f t h e six ' m o n o j e t ' events r e p o t t e d b y t h e U A l C o l l a b o r a t i o n ! 5 ! are i n t e r p r e t e d

as d u e t o t h e process

PP- t'+X

L+9

o n e s h o u l d e x p e c t o n e

p'f - e+e~ +(hard) jet + X

event . T a b l e Vm g ives some e s t i m a t e o f t h e e x p e c t e d n u m b e r o f events f o r b o t h Ivl = 0 a n d / . = ^

case, w i t h 11 = 140 GeV.

- 515 -

I«, ' ' v v j % 0 zo 0 5.IÓ3 0.56 0

50 a s 5« 10*

% zo 0 1 2 5x10"* 0-36 ö.fl* % 50 0.3 0.-Í3 0.9 ¿•34

a -ai, M w «83GeV, M z -95GeV.

4.2 Excited Quarks with / w = 1, g.

Excited quarks with higher í.sospin. assignments have, as already mentioned, quite different

signature;,. Their main characteristics is that, to lowest order in ce, they do not decay strongly,

although they can he produced in pairs through strong interaction i. The allowed decay modes are :

- q + 1

and

It is also found that the case / w = 1 implies the existence of two weak tsotriplets, which couple to

right handed light quarks with the same hypercharge. Thus there is a triplet O coupled only to ««

and a triplet D coupled only to úr. A S for the case oí excited leptons, the high isospin assignments

imply exotic charge values : one finds excited quart's of charge and — £ both for A-, = 1 as well

as for /„ = §.

The question arises as how to produce these quarks at pp colliders and what are their characteristic production signals. Fig,2 shows the typical diagrams which contribute to the production cross-section to lowest order io or. For the case in which they are lighter ih.in the IVB, one can calculate the decay widths or Zo and W through these At, = 1, $ excited states. Table IX shows these rates. Ia Figs.3a and 3b wc have plotted the ratios

= I W + - jeh -f ¿gf-2 + 1+ + 'A

" rw+ - Ï + + v)

T A B L E V f H

s-* b

IVB

516 -

F I G . 2 - D i a g r a m s c o n t r i b u t i n g t o t h e p r o d u c t i o n of e x c i t e d

q u a r k s t h r o u g h I V B ' s a t h a d r o n c o l l i d e r s .

T A B L E rx - D e c a y w i d t h or Z 0 a n d W + t h r o u g h I w - 1, 3/2 e x c i t e d q u a r k s .

i 0

\

a ) j i r e f e r s t o u o r d j e t s

b ) T h e p h a s e s p a c e f a c t o r i s g i v e n b y

M : IVB c ) T h e b r a n c h i n g r a t i o ^ c o u n t s t h e n u m b e r o f o p e n f e r m i o n i c c h a n n e l s .

- 517 -

and

r(ZJ>-» jet + jet + 7 ) = 3 .

r(Z 0 - E + E - ) SITT<

with / (£ ,=! , Bit-y = £ for different values of coupling constant / a = -f-/j¿ and as a function

of the mass fi. So far, however, there is no evidence that excited quarks with masses less than the

IVB exist. Notice however that the process

is extremely hard to evaluate because of a difficult experimental background .

5. E X O T I C H A D R O N S

If excited quarks exist, one must also consider the possibility that baryons and mesons built

with these quarks and with masses in the same range exist - and can be formed at the collider.

For the case /„, > 1 , the possibility of exotic hadrons with so far forbidden charge assignments,

arises. One would observe exotic mesons of charge ± 2 and baryons with charge -|-3. How would

they decay? In Figs.4a and 4b we show the possible decay of tjryons made of an excited quark

belonging to a hj-pothetical second family and two light quarks into an equal sign dimuon pair, a

strange baryon and a T H " .

pp -> jet+ j e r + T + X

u J

( a )

(C„uu)—* M * U * A * 1t*j*M (b) ( C + d d ) — u - u - A °

FfG. 4

- 5 1 8 -

C. C O N C L U S I Ó N

T h e observa t ion of a n o m a l o u s Z -dccays has s p u r r e d a n u m b e r o f t h e o r e t i c a l specula t ions , of

w h i c h w e have descr ibed t h a t r e l a t e d t o t h e existence of e x c i t e d q u a r k s a n d l ep tons .

R E F E R E N C E S 1 . G . A r n i s o n et a l - , Phys ics L e t t e r s 1 2 6 B . 3 9 8 ( 1 0 8 3 ) . U A l C o l l a b o r a t i o n .

C . R u b b i a . p resented a t t h e 4 t h T o p i c a l W o r k s h o p o n P r o t o n - A n t i p r o t o n C o l l i d e r Physics , B e r n 1984 . 2 . P . B a g n a i a e t a l . -Physics L e t t e r s 120B.130f 10S31. U A 2 C o l l a b o r a t i o n . 3. E . R a d e r m a c h e r , ' T h e E x p e r i m e n t a l D iscovery o f t h e I n t e r m e d i a t e V e c t o r Bosons W+

: W~ a n d Z° at the C E R N pp C o l l i d e r ' , C E R N - E P / 8 4 - 4 L . M a r c h Î 9 S 4 . T o be p u b l i s h e d i n 'Progress i n P a r t i c l e and N u c l e a r Physics ' . 4. F . A . Behrends , R . K l e i s s a n d S .Jadach ,Nuc lea r Physics B202.G3 ( 1 9 8 2 ) . 5. G . A r n i s o n o i a l . . ' E x p e r i m e n t a l O b s e r v a t i o n o f E v e n t s w i t h L a r g e M i s s i n g T ransverse E n e r g y A c c o m p a n i e d b y a J e t or a P h o t o n (s) i n pp Col l is ions a t = 5 4 0 GeV\ C E R N - E P / 8 4 - 4 2 . U A l C o l l a b o r a t i o n . 6 . P . B a g n a i a e t a l . r "Observa t ion or E lec t rons P r o d u c e d I D Assoc ia t ion w i t h H a r d Jets a n d L a r g e M i s s i n g Transverse M o m e n t u m in pp Col l is ions a t i / 5 l O G e V ' , C E R N - E P / 8 4 - 4 0 . U A 2 C o l l a b o r a t i o n . 7. N . C a b i b b o , L . M a i a n i a n d Y . S r ivas tava , ' A n o m a l o u s Z D e c a y s : E x c i t e d L e p t o n s R o m e P r e p r i n t 381 , N o v . 1 9 8 3 . T o be p u b l i s h e d in Ph.vs .Let t . 8. M -J . D u n c a n a n d M . V e l t m a n . ' V a l i d i t y of t h e S t a n d a r d M o d e l a t 90 G e V ' , U n i v e r s i t y of M i c h i g a n P r e p r i n t U M T h 8 4 - 1 . 9 . V . B a u r , H . F r i t z s c h a n d H .Fa issner , Physics L e t t e r s 1 3 5 B . 3 1 3 ( 1 9 8 3 ) . 10 . F . M . R e n a r d , M o n t p e l l i e r Prepr in t . . P M / 8 3 / 1 1 D e c e m b e r 1 9 8 3 . 1 1 . R . D . P e c c e i . M u n i c h P r e p r i n t , M P I - P A E / F T h 8 0 / 8 3 , N o v e m b e r 1983 . 1 2 . R . B a r b i e r i , H . H a r a r i a n d M . L e u r e r . ' A n F x p e r i m e n t a l Tes t of Zq composi teness i n P r o t o n -A n t i p r o t o n Co l l ide rs ' , W c i z m a n n I n s t i t u t e P r e p r i n t , W 1 S - 8 4 / 7 / M a r c h P h . 13 . H . H a r a r i a n d K . S e i b e r g , P h y s . L e t t e r s 2 8 T Í 2 6 9 ( 1 9 8 1 ) . H . F r i t zsch a n d G . M a n d e l b a u m , Physics L e t t e r s 1 0 2 B . 3 1 9 ( 1 9 8 1 ) . W . B u c h m u l l e r , S . T . L o v e , R . D . P e c c e i a n d T . Y a m a g i d a , Physics L e t t e r s 1 1 5 B . 2 3 3 ( 1 9 8 2 ) . 14. F o r a rev iew o n compositeness scale, s c e R . B a r b i c r i in Proceed ings o f t h e I n t e r n a t i o n a l Confe rence o n L e p t o n a n d P h o t o n I n t e r a c t i o n s a t H i g h E n e r g y , C o r n e l l ( U S A J 1983 , 15. E . J . E f c h t e n , K . D . L a n e a n d M . E . P e s k i n , P h y s . R e v . L e t t e r s 50 .811 ( 1 9 8 3 ) . 16 . B . A d e v a et a l . , P h y s . R e v . L e t t e r s 4 8 , 9G7 ( 1 9 8 2 ) ; M a r k J C o l l a b o r a t i o n . 17 . J .Bai ley e t a l . , N u c l . P h y s . B 150 ,1 Í 1 9 7 9 ) . 18 . F . M . R e n a r d , Physics L e t t e r s U G B . 2 G 4 ( 1 9 S 2 ) . 19 . M . K u r o d a a n d D . S c h i l d k n c c h t , Physics L e t t e r s I 2 1 B , 1 7 3 ( 1 9 8 3 ) . 2 0 . 11. F r i t z s c h a n d G . M a n d e l b a u m , Physics L e t t e r s 1 0 9 B . 2 2 4 ( 1 9 8 2 ) . 2 1 . F . M . R e n a r d , Phys ics L e t t e r s 1 2 6 B . 5 9 ( 1 9 8 3 ) : Phys ics L e t t e r s 1 3 2 B . 4 4 9 ( 1 9 8 3 ) . . 2 2 . B . A d e v a e t a l . , "Search for n e w par t i c les i n e + e — a n n i h i l a t i o n f r o m 3 9 . 7 9 t o 4 3 . 2 2 G e V , M I T T e c h . R c p . 1 3 4 , F e b r u a r y 19SJ. 2 3 . F . D e l A g u i l a , A - M e u d e z a n d R . P a s c u a l , B a r c e l l o n a P r e p r i n t U A B - F T - 1 0 5 , M a r c h 1984 . 2 1 . L . M a i a n i a n d Y . S r i v a s t a v a , E r i c e W o r k s h o p on Q u a r k a n d L e p t o u S t r u c t u r e , A p r i l 1984 . u n p u b l i s h e d .

25. G .A rn ison et a l . , Phys ics L e t t e r s 1 3 5 B . 2 5 0 ( 1 9 8 4 ) . 2G. A . D e R u j u l a , L . M a i a n i a a d R . P e t r o n i l o , ' S e a r c h for e x c i t e d Q u a r k s ' , C e r n - T h 3 7 7 9 , D e c e m b e r 1983 . 2 7 . G . P a n c h e r i a n d Y . S r i v a s t a r a . ' W e a k Isospin Spectroscopy of E x c i t e d Q u a r k s a n d L e p t o n s ' , F rasca t i P r e p r i n t L N F - 8 4 / 1 0 ( P ) , F e b r u a r y 1 9 8 4 . 2 8 . A . P . C o n t o g o u r i s , S . P a p a d o p o u l o s a n d C . Papavass iUou , N u c l e a r Phys ics B v r e . 4 6 1 ( 1 9 8 1 ) . 2 9 . J.D. H a n s e n , P r e s e n t e d a t t h e 4 t h T o p i c a l W o r k s h o p o n P r o t o n - A n t i p r o t o n C o l l i d e r Physics, B e r n 1984.

http://Ph.vs.Lett

- 519 -0 S 8 4 1 0 0 ^ ^ '

GLUIHO MASS AND CP VIOLATION IN SUTER3YMHETRIC MODELS

A. Masiero

CERN» Geneva, Switzerland

la the promising class of supersymmetry (SUSY) theories where global supersymmetry la softly broken at low energy^ as a result of the spontaneous

2) breaking of local supersymmetry by vacuum expectation values of the order of the Planck mass, a rich spectrum of new SUSY particles (susyons) is predicted at testable énergies» However, given the possible difficulty of

3 ) finding a direct evidence of susycns , It is of interest to look for phenomena which cannot be fully explained in the context of the standard model and necessitate extra particles (aueycns?) for a possible Interpretation. JWe consider the "old" phenomenon of CP violation in the K*-K" system which has recently received a considerable amount of interest in view of the unexpectedly long B lifetime. Being the SUSY contribution dominated by gluino (g) and squark (q) insertions in the box diagram, we find it appropriate to start by summarizing our knowledge on the gluino mass which plays a discrimina tory role among different SUSY models . j ^^^^ff^J^^j

Photino Çy) and g masses are so interesting since they vanish at tree level in all the SUSY theories with canonical kinetic term for the Yang-Mills

2) superítelas . On the other hand, in the absence of a relevant chiral symmetry (R-itwariance), small Majorana-type masses may be generated radlatlvely. Ac the one-loop level, the gluino receives a mass fim~ from a

4) ° virtual heavy top-quark contribution (Fig. 1):

e

(1)

(2)

and m - Im 3, ± m I denote the masses of the two top scalar partners. Ihe t l f 2 1 / 2 tl j

phenomenologlcal lower bound on the w-ino mass puta an -'pper limit oa 1113. 1 , ' 2

m 3 , 350 GeV, whilst m < 200 GeV from the measurements of the y-para-2 51 C

meter Within these hounds a gluino mass of 1 * 1.5 GeV Is obtained for m 3 . and m both greater than 150 GeV . The photino mass gets an analogous

- 5 2 0 -

contribution wich a ß replaced by in. Eq. (1). The corresponding limiting value for m ; is ~3Q0 MeV. At the one-ioop level, the Y receives an additional COQtribution from virtual w-iao exchange. For m 3^ one gets the

i.e., for m 3 , = 300 GeV. sr- = 400 HeV. U If n

The lou energy Lagraogians with softly broken N » 1 global SUSY ' have to be considered as effective Lagrangians: indeed, they neglect interactions

+ o> and the locally SUSY Lagrangians from which 2Ï

they derive are noc reaormalizable, * For instance, there exist logarithmically divergent contributions at the two-loop level to the g and y masses and also potentially quadratic divergent gravitational radiative corrections are present- However, putting a natural cut-off at ¡Í . they turn out to be small J •

Although no firm lover bounds on the y and g mass exist, there are possible indications that the above radiative contributions are somewhat coo

small: (i) if che ptiotlno is the lightest sueyon, then cosmology requires it (ii) for q masses below 1QQ GeV, the beam dump

experiment at CERN puts a lower bound of a few GeV's on a~ 7î ( m ) hounds on three and four jet events in the UAl experiment give a preliminary lower limit of 40 GeV on If much greater contributions to g and Y masses turned out to be required, that would be an Indication for SUSY models with

and/or models where grand unification Implies the existence of many more heavy particles which can circulate in the loop of the diagram of Flg. 1

The gluino mass can have a phase which introduces a new source of CP violation. However, this new CP violating contribution cannot yield the required amount of CP violation when the Kobayashi-Maskawa (K-M) phase Ó is turned o f f 1 ^ . Thus, in SUSY modelo» CP violation arises from the usual K-M phase ö which now appears in new gauge interaction between fermions and their SUSY partners and from entirely new sources which are connected to the SUSY soft breaking terms 1^«

What renders this study more attractive are the unexpected results about 11)

Che B-meaon decay - They lower the upper bound on "2 and 0* in the K-M 12)

matrix so thai a heavy top quark is necessary in the non-SUSY case to get

- 5 2 1 -

E ~ 10" 3 For instance, for t = 5*10~ 1 2 sec and B • 0.33 (where B denotes the usual correction factor to the vacuum insertion approximation of the < K° | L

e £ £ | K < > > ^ t r i x element), one needs m t > 60 GeV Avoiding the introduction of a fourth generation, we have shown that in

SUSY models the contributions which come from the g and q exchanges in the box diagram allow for a viable value of £ even with a light top quark

14) (m c = 30 GeV) . Using the following experimental inputs:

we get, in the (m^/M^) 2 « 1 approximation (neglecting Penguin diagrams and gluino mass insertions):

The TV's are QCD correction factors and the parameter c appearing in front of th-î SUSY contribution measures the flavour violation carried by the down squarks. It Is generated through radiative corrections and is expected to be

of order 1. The expression of ï ( x 2 ) and K(x 2) can be found in ref. 10). Notice that the SUSY piece of e S goes like (mt/n )**: this strongly

suggests that the SUSY contribution can allow for a relatively light top quark. The result is illustrated in Fig. 2, where B - 0.33, c - 1, a - 0.1 and we use R = r(b-»u)/r(b+e) • 0.05 as a constraint on the K-M matrix elements. There is a dramatic change with respect to the non-SUSY case which

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is represented by the dotted line. Fixing T„ and m~ or ior, it is possible to d g a

find the corresponding bounds on nrj or nr , respectively. The results are reported in Fig. 3 and Fig. 4. Notice that for = 40 GeV and m t in the 30-40 GeV range, m~ 's required not to exceed 40-50 GeV to get enough CP violation.

REFERENCES

1) R. Bar bier i, s. Ferrara and C. Savoy - Phys.Lett. 119B (1982.1 343; A. Chamseddine, R. Arnoultt and P. Nath - Phys.Rev.Lett. 49 (1982) 970; H.P. Mlles, M. Srednicki and D. Wyler - Phys.Lett. 120B (1983) 346; E. Cremmer, P. Fayet and L. Girardello - Phys.Lett. 122B (1983) 346; L. Ibaïïez - Phys.Lett. 118B (1982) 73; J. Ellis, D.V. Nanopoulos and K. Tamvakis - Phys.Lett. 121B (1983) 123; L. Hall, J. Lykken and S. Helnberg - Pnys.Rev. 1)27 (1983) 2359; M.K. Gaillard, L.J. Hall, B. Zumino, I. Del Águila, J. Polchlnski and G.G. Ross - Phys.Lett. 122B (1983) 35 c.

2) E. Crenmer, S. Ferrara, L. Glrardellt and A. Van Proeyen - Phys.Lett. 116B (1982) 231, and Nucl.Phys. B212 (1983) 413.

3) See, for instance, A. Savoy-Navarro - Preprint CERN-EP/83-13Z (1983), to be part of a Physics Reports on "Supersymmetry Confronting Experiment".

4) R. Barbieri, L. Girardello and A. Masiero - Phys.Lett 127B (1983) 429.

5) R. Barbieri and L. Maiani - Nucl.Phys. B224 (L9fl3) 32.

6) H. Goldberg - Phya.Rev.Le.tt. 50 (1983) 1419. J. Ellis, J.S. Hagelin, D.V. Nanopoulos, K. Olive and H. Srednicki -Preprint SLAC-PUB-3171 (1983).

7) CHARM Collaboration - Phys.Lett. 121B (1983) 429; R.C. Ball et al. - Contribution to the XXIst Int. Coof. on High Energy Physics, Paris (1982).

8) Talk given by C. Rubbia at this Workshop.

9) J.-P. Derendinger and C.A. Savoy - Nucl.Phys. B, in press.

10) J.-M. Gérard, W. Grlmus, A. Raychaudhuri and G. Zoupanos - CERN Preprint TU. 3809 (1984), to appear in Phys.Lett. B.

11) E. Fernandez et al. - Ehya.Rev.LeCt. 51 (1983) 1022; N.S. Lockyer et al. - Phya.Rev.Lett. 51 (1983) 1316.

12) K. Kleinknecht and B. Renk - Phys.Lett. L30B (1983) 459; E.A. Paschos, B. Stech and U. Türke - Phys.Lett. 12BB (1983) 240; L.L. Chau and W.Y. Keung - Phys.Rev. D29 (1984) 592.

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13) P.H. Ginsparg, S.L. Glaahow and M.B. Wise - Phys.Rev.Lett. 50 (1983) 1415.

14) J.-M. Gerard, W. Grinuie, A. Masiero, O.V. Nanopoulos and A. Raychaudhuri CERN Preprint TH. 3837 (1984), to appear in Phys.Lett. B.

FIGURE CAPTIOUS

Figure 1 One-loop contributions to the gluino ( g ) and photino (y) masses from t exchange.

Figure 2 The lower bound on the top quark, mass as a function of the B lifetime for different choices of the equark (q) and g masses. The ordinary (i.e., non-SUSV) bound is shown dotted. B is equal to 0.33.

Figure 3 The allowed range of squark masaes as a function of the top quark mass. The region between the solid (broken) curves is allowed for ß = 1.5 (2.0), with tg 3 ß'10~ 1 2 sec. These bounds correspond to a gluino maas m~ =* 40 GeV.

Figure 4 The upper bounds on gluino masses as a function of the top quark mass, for ß = 1.5 (2.0), with t R = 0 1 0 - 1 2 sec. These bounds

40 GeV.

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I I

IW r gl?)

Fig. 1

Fig. 3 H g . 1

- 526 -: 8410026457

LOW ENERGY PARTICLE SPECTRUM FROM SUPERGRAVITY

Costas KOUNNAS Laboratoire de Physique Théorique de l'Ecole Normale Supérieure, Paris, France.

ABSTRACT -—v fwé discuss the supergravity induced low energy supersymmetric particle spec- '

trum. Tne radiative breaking of the SU(2)xU(l) gauge group is explained as well as the dynamical determination of the weak scale. In the framework of the "no scale" supergravity models the vast hierarchy between the weak scale My = 81 GeV and the

/ fundamental supergravity scale M = 2.4*lo'^ GeV (My/M = 10 ' ) is shown to be dynamically generated in the quantum level. ,

The existence of a symmetry between bosons and fermions is a very attractive 1 2)

idea in particle physics. This kind of symmetry, called supersymmetry , classifies particles with different statistics in supermultiplets. The spin one-half supersymmetry generator transforms fermions into bosons of the same supermultiplet and conversely without changing the other quantum numbers.

BOSON < ^ = " £ f FERMION When supersymmetry is unbroken, the boson and the fermion of the same super

multiplet have identical masses (W\A=MF>. In a realistic model supersymmetry must be broken in such a way that all successful phenomenological implications of QCD and eloctroweak gauge interactions be reproduced. In fact, the boson-fermion mass splitting cannot be zero because we know experimentally that no supersymmetric partner of the known particles have been observed. For instance, no scalar boson with the same quantum numbers as the electron (the so-called scalar electron or selectron) has been discovered yet. The present experimental limit of such a particle is «w20 GeV which implies the following lower limit for

2 the boson-ferraion (mass) splitting

(Jl06evf 4 1 M i - M * I s / * (D However, the main motivation for supersymmetry is its ability to ensure the

stability of the electroweak scale < H ^ S 2 5 0 GeV under radiative corrections. To maintain this property in a broken supersymmetry without any unnatural fine-tuning on the renormalized parameters of the theory, it is necessary and sufficient to impose an upper bound on the boson-fermion mass splitting jLf .

This bound follows from the fact that the radiative corrections o n ^ H > ' are pro-2

portional to the boson-fermion (mass) splitting ^

S R < H > * = Z + - ( » B - W f M c * . O )

where the dots mean some proportionality constants of order one. Note that

the quadratic divergent part, ( Ylg" Y/p) / \ CUT-OFF * ^* * s a ^ s e n t hecause of super symmetry (the bosonic and fermionic degrees of freedom are equal P|g-tfp-O) • Also, if the boson-fermion (mass)^ splitting is small enough, then the stability of ^ H " ^ is ensured even if superheavy particles exist in the theory, as is the case in Grand Unified Theories where particles with masses of order 1 0 I 5 - 1 0 1 6 GeV appear naturally. What follows from the stability condition eq.(2) ie of main phenomenological interest. It implies in fact the existence of many new states with masses around the electroweak scale and therefore accessible experimentally.

3) These new states are just the supersymraetrie partners of the known states like lepCons, quarks, gauge bosons,...

SPIN 4 S = ± 1/2 SPIN LEPTONS ] /2 < •> 0 SLEPTONS QUARKS 1 ¡2 < * 0 SQUARKS HIGGS 0 < ;y 1/2 HIGGSINOS PHOTON 1 « > 1/2 PHOTINO W 1 4 >. 1 /2 W-INOS Z 1 « if. 1 /2 Z-INOS GLUONS 1 4 > 1/2 GLUINOS

The mass spectrum of the superpartners depending on the assumed supersymmetry breakdown is not uniquely defined. In the framework of a simple supergravity^ (N=] local supersymmetry), the suitable breakdown of supersymmetry is generated

massless spin 3/2 gravitino (the superpartnçr of the spin 2 graviton) becomes a massive spin 3/2 state by "eating" the 2-helicity spin 1/2 goldstino.

It is interesting to note that the spontaneously broken supergravity behaves like a softly broken global supersymmetry fer energy scales smaller than the Planck scale M Ä = ].2*1D 1 9 GeV. Therefore a suitable non-zero boson-fermion split-

2) ting appears in the supermultiplets Induced by the soft breaking terms . For instance, after the superHiggs mechanism, the scalar bosons (mass) 2 receives at

2 the tree level a positive contribution proportional to the gravitino (mass) , Z y^lsfa • r h e proportionality constants depend on the superHiggs mechanism we

consider. After radiative corrections an extra positive contribution is generated which turns out to be proportional to the other supersymmetry breaking parameters,

2 _2 2 2 the gauginos (mass) (gluinos M^, W-inos H 2 k B-ino M j ) . Also, for the scalar bosons which interact through the large top^quark Yukawa coupling, the radiative

2 correctionsgenerate non negligible negative contribution to their (mass) . This negative contribution is proportional to the top-Yukawa coupling and to a certain

- 528 -

combination of the supersymmetry breaking parameters Wl$/2» Mgauginos* a s we -'-as the dimensionless parameters A and B. The parameter A is used to define the non negligible trilinear coupling between the two superpartnevs of the top quark i.L , t¿ and that of the Higgs H i -

AwAÍA&rU + É.C.) <*> ( |/^ is the top-Yukawa coupling)

In the presence of a non zero supersyncnetrie mass, for the Higgses H. and H„ 2 2 the breaking parameter E defines the off-diagonal (mass) of the Higgs (mass)

matrix

E w y ^ i H . H î f ce) œ Keeping only the large top-Yukawa coupling and performing the quantum correc

tions one finds the following renormalized mass parameters for the scalar bosons**^ :

( a > Y / ? f - a L w & + Ci K (6> for all sleptons and the squarks which do not couple through the top-Yukawa coupling l?¿ • ÖL'i a r e constants depending on the superHiggs mechanism. They are equal to one in the minimal case**' crd are equal to zero in the maximally symmetric case o- ref. 6 ) . In the last case ¿J^= 0, the gravitino scale does not appear at all in the low energy spectrum, and therefore the gravitino mass may have any value without sensible effect on the low energy spectrum^ . £*- are calculable constants

51 given as integrals of functions of the gauge coupling constants . For the sleptons they are of order Ü.2 to 0.5 and for the squarks 2 to 5 depending on the superheavy contents of the theory. /vl is a typical tree level gaugino mass (for instance the value of the gauginos at the Grand Unification scale),

(b) The two stops , (mass) matrix

(c) The two Higijses ( C „ * 0 . S }

1% = v*»* .

Í 7 )

(8) »Ii * W = B w y t t

In eqa.(7,8) the non negligible negative contribution (— & , 3 —S¿\ ' "

a consequence of the large Yukawa coupling . In fact is proportional to ^ and to a certain combination of the breaking parameters V f l j^ - A f e 3 1 1 ^ A " ^ -

After the important work of Cremmer et a l . ^ qualitative tree-level models were constructed neglecting the quantum corrections = /\ = 0 and assuming a

minimal superHiggs mechanism Q:= 1> . In these models the mass parameters of

- 529 -

5) . 2 scale My S 81 GeV . The reason is that the renonnalized (mass) Higgs matrix (eq.(8)) contains negative (mass)'* eigenvalue for energy scales Q smaller than a

sleptons and squarks are more or less equal to the gravitino mass except for the two eigenvalues of the top superpartners

In these models a light gauge singlet couple to the Higgses must be introduced in order to generate suitable non aero vacuum expectation values for the Higgses and to obtain the correct SU(2)xU(l) breaking. The tree level models neglecting large radiative corrections have only a qualitative interest and therefore it is dangerous to consider them as realistic models.

At the contrary, the more realistic models are those where the radiative correc-5 7 2)

tions are equally taken into account -It follows that the radiative corrections on the supersymmetry breaking parameters are very important and drastically change the naive tree level situation. In fact the radiative corrections are able to generate the correct SU(2)xU(l) breakdown^ 1^ without the introduction of an extra light gauge singlet superfield. Moreover, the radiative breaking mechanism is of main interest because it enables one to generate dynamically a vast hierarchy between the fundamental scale of the theory M = Mf>/ffi¡=

scale My s 81 GeV (eq.(8)) contains critical scale . _ /

< < - n r j a ¿ ° > ¿¿a- c.o) Therefore, SU(2)xU(l) breaking minima are generated dynamically wich the Higgs fields vacuum expectation values of order Q a , « H ¿ > « Q D )» provided the typical boson-fermion mass splitting i s of the same order as or smaller than the dimensional transmutation scale Q 0 ( Í4 £ 0 ( Q O ) ) . However, Q 0 differs by many orders

18 of magnitude from the fundamental scale M = 10 GeV as a consequence of the very smooth variation (logarithmic) of the renormalized parameter VW, , Y0¿ and fÛj .

The vast hierarchy between the weak scale My Q and M is then dynamically generated and easily turns out to be of the correct order of magnitude.

I t s f l . ä M exp-£® a ID'i6M <"> where 0 ^ is the typical SU(2) gauge coupling. Furthermore, the existence of the critical scale Q # requires a large negative contribution to the yff mass parameter (see eq.(B)), or, equivalently, a large value tor the in eq.(8). The fact that A is proportional to the top-Yukawa coupling shows that the ratio

" ^ i / A l w is cons trained''* . A detailed analysis shows that the radiative breaking holds if

Í < * > t M * < 2 (.2) so the top quark mass must be within the range

20 GeV < Wí¿ < 160 GeV (13)

- 5 3 0 -

A typical experimentally accessible low energy physical mass spectrum is given in Table I for low values of the top quark 25 GeVÎÍ^Ô GeV and ¿J¿= 1 .

Note that this spectrum is just the most accessible one. In the general case one may obtain more massive superpartners by changing the masses- of the gravitino and gauginos. However some general figures are valid for almost all realistic supei-gravity induced low energy spectra. For instance the sleptons are always lighter than the squarks except that of the physical stop scalars which may be the lightest charged superpartner. The charged Higgses have always masses above the mass of the W"-bosons. The mass of the three neutral physical Higgses is light (3-20) G E V

which is characteristic of the radiative breaking"^ . The second neutral Higgs has a mass above the M^£92 GeV, and the last one has a mass proportional to the tffy parameter. It is probable that its mass is of the same order as the typical slepton masses. The only pure gaugino states are the gluinos, the Majorana gauge fermions associated with the unbroken SU(3) gauge group. After the SU(2)xU(l) breaking, all the other gauginos are mixed with the higgsinos and form the physical higgsino-gaugino states. Namely* the two charged gauginos W +,W are mixed with the chargedhiggainos H*,H forming two Dirae spinors that we call UH-ino and HW-ino. In all interesting cases, one of them (HW-ino) is lighter and che other one is heavier than My

"HW-ino <C "w <^ "wH-ino (14) Similarly, the two neutral gauginos W^,B mix with the two neutral Higgsinos Hj,H 2

and form 4-physical neutral states (Majorana spinors). We call photino the eigen-state which is dominated by the photon-superpartner component. In most of the models the photino is the lightest supersymmetric state. The two other neutral fermions are mainly mixed states of Z-ino and higgsino. He call them ZH-ino and HZ-ino. Similarly, here, the HZ-ino is lighter than and the ZH-ino heavier than tt, in all interesting cases.

MHZ-ino ¿ M Z ^ "zH-ino (15) The remaining neutral eigenstate is mainly dominated by a higgsino component. This physical state is usually called 'higgsino" and its mass is close to the W¿ mass parameter. Cosmological considerations force us to consider the Higgsino mass as larger than the photino one.

In almost all supergravity models the supersymmetry breaking scales are taken as free parameters. Furthermore) the typical boson-fermion mass splitting j-4 ,

(which is defined by these breaking scales), must be chosen small enough in order to stabilize the weak scale at its low value (see eq.(2))_ Within the radiative breaking mechanism and if we assume the hierarchical ratio f/M ^ l O " 1 6 , the hierarchy between the weak scale and the fundamental supergravity scale M is dynamically generated^. Therefore to "solve" the hierarchy problem in the frame-

- 531 -

work of supergravity theories one must explain w'.iy J4 is so much smaller than M, /*/M - 10 ? Recently a class of supergravity models has been proposed which

8 6) are able to generate dynamically the JVM hierarchy ' ' under certain assumptions. This class of models that we call "no scale supergravity models" are based on a particularly symmetric superHiggs mechanism^'^ in which the breaking scale fi is undetermined at the classical level^**^ (tree level approximation). However the scale ji depends on the value of a scalar field ¿?> the scalar component of Che

goldstino ( l£) supermultiplet ( 2 * $ ) * ^he unde terminât ion of the scale jLt(i) follows from the existence of degenerated minima in the z-direetion of the scalar potential (\/{55)SO). It has been shown that the radiative corrections destroy this degeneracy of the potential generating a preferred value Ho***^- Therefore the scale j4>~ j4(20) is dynamically generated at the quantum level. It is remarkable that ^ ( ? o ) and the weak scale are simultaneously fixed at a scale close to the dimensional transmutation one, Q 0 > and consequently the f /M and M^/M hierarchies are naturally explained*** . At the same tine the stability of the weak scale is ensured by the fact that the breaking scale JA is of the same order as M^. The typical low energy spectrum which follows from the "no scale" models has the same structure as before. The only difference here is that the typical breaking scale ji is not just a free parameter but is rather determined within the radiative breaking mechanism. It follows that the sleptons have typical masses o£ order or 2-3 times larger depending on the assumed superHiggs mechanism and the gaugino to gravitino mass ratios. Simple typical examples of the no-scale supergravity models may be found in refs. 8) and 6 ) . REFERENCES 1) Y.A. Gol'fand and E.P. Likhtman, Pis'ma Zh.Eksp.Teor.Fiz. 13 (1971) 323;

D. Volkov and V.P. Akulov, Phys.Lett. 46B (1973) 109; J. Wess and B. Zumino, Nucl.Phys. B70 (1974) 39.

2) An essentially complete list of references on Supersymmetry and Supergravity see the recent review of H.P. Nilles, Geneva University preprint UGVA-DPT 1983/12-412, submitted to Phys.Rep.C.

3) P. Fayet, Phys.Lett. 69B (1977) 489. 4) E. Cremmer et al., ïhys.Lett. 79B (1978) 23; Nucl.Phys. B147 (1979) 105;

E. Cremmer et al., Phys.Lett. II6B (1982) 231; Nucl.Phys. B212 (1983) 413. 5) C. Kounnas, A.B. Lahanas, D.V. Nanopoulos and M. Quiros, Phys.Lett. 132B (1983)

95; Nucl.Phys. B236 (1984) 438. 6) J. Ellis, C. Kounnas and D.V. Nanopoulos, CEPJJ preprint TH/3824 and TH/3848

(1984). 7) L.E. IbaSez and C. Lopez, Phys.Lett. 126B (1983) 94 and CERN preprint TH-3650

(1983); J, Ellis, J.S. Hagelin, D.V, Nanopoulos and K.A- Tamvakis, Phys.Lett. J25B (1983) 275; L. Alvarez-Gaumé, J. Polchinski and M.B. Wise, Nucl.Phys. B22I (1983) 499.

- 532 -

8) J. Ellis, A.B. Lahanas, D.V. Nanopoulos and K.A. Tanvakis, Phys.Lett. 134B (1984) 61; J. Ellis, C. Kounnas, D.V. Nanopoulos, CERN preprint IH-3768 (1983) to be published in Nucl.Phys. B.

9) E . Cremmer, S. Ferrara, C. Kbunnas and D.V. Nanopoulos, Phys.Lett. 133B (1983) 61 .

TABLE I TYPICAL SPECTRUM 25 G e V ^ Y * ? i < 50 GeV

GeV GeV 20 < SLEPT0NS - R < 30

25 < SLEPTONS - 1 < 40

50 < SQUAKKS < 100

20 < STOP - R < 80

80 < STOP - L 130

83 < HIGGS H < 98

3 < NEUTRAL- < 10

20 < HIGGSES 50

95 < .>, 2, 3 , < 105

40 < GLUINOS < 100

3 < FHOriNO < 12

10 < HIGGSINO < 25

80 < HZ - INO 91

98 < ZH - INO < 118

75 < HW - INO < 81

84 < WH - INO < 90

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SUPERSYMMETRY

Presented by D . N a n o p o u l o s , CERN

No written contribution received

- 535 -

Summary and Conclusions

- 536 -

NEW COLLIDER PHYSICS

John Ellis CERN, Geneva, Switzerland

0. APOLOGIA

My assignment is to offer some conclusions for this meeting. As the highlights have been the presentations of many new and exciting pieces of data, perhaps an experimentalist would have been better able to make sense of what has been going on. As a mere theorist, all I can say is that the new results presented here seem to raise more questions than they provide answers. This is good for everyone except for the person who ia supposed to conclude, but can only find inconclusive things to say! nevertheless, here goes.

As a theorist, I necessarily look for interpretations of the new data in terms of various existing theoretical ideas. Collider data presented here and previously confirm very beautifully that the fundamental interactions are described by gauge theories* Theorists now ask other questions: how is gauge symmetry broken? Do Higgs bosons exist? Are elementary Higgses protected by supersymmetry (SUSO? Or are Higgses composite ("Technicolour")? Are leptons and quarks composite? Are the U~ and Z u composite? Maybe none of these theoretical ideas has anything to do with the new phenomena reported at this meeting: monoJet events, electron + jet + missing p T events, the possible bump in multijet invariant masses at about 150 GeV, dimuon events. Although it is tempting to interpret some of the novel data as favouring one theory over another, they seem to point in different directions and no clear trend emerges, what we need ia more datai In the short term this will be provided by the CEKD SppS Collider operating at a slightly higher centre-of-mass energy. In the medium term the SppS Collider will be upgraded by the addition of the ACOL ring, and will he accompanied by fierce transatlantic competition from the FNAL Tevatron Collider. Hopes for the long term include the Superconducting Super Collider (SSC) in the United States, soaetimes known as the Desertron, and the Large Hadron Collider (LHC) in the LEP tunnel, sometimes known as the Juratron. Included in this review are some comments about the physics which may be possible with such a machine having E c n * 10 to 40 TeV. Not included, though, is anything about the presen' physics with those lower energy colliders, LEAK and the ISR. I apologize fir running out of time to do justice to the eloquent reports " o n their physics presented at this meeting.

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1. WHAT WE HAVE LEARNT

We have learnt Chat the fundamental interactions are gauged with SU(3)xsu<2)xn(l). One of the nice results presented 3^ at this meeting was an analysis of QCD jets at the CERN SppS Collider which provided very clear evidence for the three-gluon vertex, an essential feature of the non-Abelian SU(3) structure of QCD. It was found that the angular distributions of QCU jets had an approximate I/sin1* 8 shape, indicative of gluoa exchange in gluon-gluon and gluon-quarfc scattering as well as in quark-(anti)quark scattering. This result confirms the Rutherford formula and hence the inverse square law for short-distance interactions between gluons. There is an approximately universal angular dependence of 2-2 qq, qg and gg scattering and the simple ratios between their cross-sections:

< T W : 0 ^ , ^ » I: i -. ti* CD

(2)

The ratios of 9/4 In Eq. (1) and 4/9 in Eq. (2) simply reflect 4^ the ratio of th. colour charges of quarks and gluons: they confirm that gluons are octets of colour rather than triplets. This result can be checked in more detail using three-jet events^, which have characteristic bremsstrahlung forms with the same

11 M * W ( 3 )

3 ) Also exhibiting characteristic brems Strahlung shapes were the distributions of jets produced in associ *ion with VT's and Z's. In the immortal words of Sherlock Holmes; "It is glue, Watson. Unquestionably it is glue". He will be meeting Che famous detective quite often in what follows, as we try to adopt his investigative techniques.

Also presented at this meeting were the latest updates on the crowning confirmation of the SU(2)xU(l) electroweak gauge theory, the observation of W and Z 0 ^ . UA2 presented**^ updated mass values, which are listed In Table 1

9) along with UAl and theoretical values including radiative corrections

- 5 3 8 -

+ n Table 1; W and z" masses (in CeV)

UÂ2 UA1 Theory (sin 2e w-o.210±O.0l4)

83.U1.9+1.3

92.7±1.7±1.4

80.941.512.4

95.6Í1.5+2.9

83.0 t \-»

« . 8 « ; *

The latest UA2 results^ correspond to

W 6 W - 0-215 ±O-o\0±o-ooT- (4)

in perfect agreement with low energy data. The production cross-sections^^ for the W~ and Z° are also in perfect

agreement with standard model predictions

UAl had already combined 1 1^ their measurements of the ratio OB (B*ee)/<7B(W+ev) and their upper limit on the natural decay width of the Z° to establish a bound on the number of neutrinos:

(6aj

Ac this meeting UA2 presented 8^ a ne» analysis of the natural width of the Z°:

(6b)

They also obtained**^ a more indirect bound or. from the production ratio öB (Z -*e e ) / dB (W+e v ) :

The smallness of this last limit follows from the surprisingly large number of Z° •>• ee events found by UA2. The UAl Collaboration are also able to improve their limit (6a) by using information fron Z° * Hji decay.

8) The UA2 Collaboration reported here a first indication for a V bump in

the invariant mass spectrum of hadronic jet combinations. They presented a fit which wanted 92±52 events in the W peak (less than 2a) with a fitted mass and cross-section:

W ' (7)

in perfect agreement with expectations 1*^. However, they are correctly cautious and do not yet claim discovery of the W in had'ronic jets. The same talk revealed they had found more than they bargained for in hadronic jets, as we will see again later 1

? . WHAT '."E »Axt- TO LEARN

He are still waiting to learn the mass of the t quark, which did not appear at this meeting. I have no words of wisdom on this subject, and prefer to address what seem to be more basic theoretical issues.

a) How is pauge syraaetry broken? Exact SU(2)*U(1) gauge symmetry would require - m^ - 0, in the Bame way

that QED's U(l) and QCD'e SU(3) synmetries enforce « m g » 0. The facts that trL, and nL jí 0 create problems for the perturbâtive unitarity and

12) lenormallzability of the electroweak theory • These would require the ff •* WW cross-section to fall as 1/E 2 , which it almost doe. . thanks to cancellations cm * due to the non-Abelian three-boson vertex, but there Is a residual excess over the 1/E 2 rule which is proportional to m,f . Similarly, the WW -*• WW cross-

- S40 -

: To cancel out these remaining an additional boson wich -juplings

All hope of renormalizability would he lost If this boson had spin >1. The non-universality (8) of Its fermion couplings Deans that it cannot he a spin-1 gauge boson. The only possibility is spin-O, and we arrive at the Higgs boson of the Standard Model, whose vacuum expectation value breaks gauge invariance spontaneously and gives masses to fermions, the W~ and the Z°*

The introduction of the Higgs boson raises more questions than it answers. 13)

Is it composite or elementary? In the former case , called here technicolour, it is made out of technifermion constituents bound together by a new set of interactions strong at an energy scale 0(1) TeV. If the Higgs Is elementary, its mass has quadratic divergences and other diseases which can be cured by the

14) cancellations of supersymmetry (SUSY) . In both the elementary and composite Higgs cases, we would expect to discover some new particles with masses < 0(1) TeV, and their study is one of the mala motivations for the large hadron colliders to be discussed later. b) Are our present "elementary" particles composite?

Many physicists are appalled by the present proliferation of apparently "elementary" quarks and leptons s and believe that they are composed of more elementary constituents called preons* Some physicists believe that the masses of the W~ and ZD are hints that they are composite, rather than elementary like the massless photon and gluons. In contrast to models of spontaneous gauge symmetry breaking, where either the elementary Higgs, or some technipions, or (In order to get the required cancellations in SUSY theories) some new supersymmetric particles have masses < 0(1) TeV, there is no clear and convincing reason to expect a new composite structure to emerge in an accessible energy range. Furthermore, in contrast to Higgs, technicolour and SUSY, there are no composite theories which are completely respectable theoretically^""^. There are only phenomenological models which may appear seductive but only embody some subset of the theoretical desiderata for a true composite theory. My own prejudices about composite models were presciently summarized by Sherlock Holmes: "Elementary, my dear Hataon".

- 541 -

c) Sigaaturea for new physics SUSY

In moat sup er Symmetrie theorles* -^**^, the supersymmetric particles possess a new multiplicatively conserved quantum number equal to (-1). This means that they can only be produced in pairs, that amoog the decay products of every apartide there must be another sparticle, and hence that the lightest sparticle must be stable. The lightest spartlcle 1B probably neutral and D o t

strongly interacting, and the most likely candidate m a y 1 ^ be the photino y *

Thus a characteristic signature for SUSY could be missing energy-momentum, for example, from gluino g pair-production:

or from supersymmetric W decay:

(9b)

Technicolour All technicolour theories*^ expect technihadrons (p ,, u^, etc.) with

masses 0(1) TeV, and a continuum of technistates starting from a threshold 19)

/s = 0(1) TeV. The "extended" technicolour theories ' which seek to underßtaad 20)

fermion masses as well as m^ and m,, also expect many "light" technlplon bound states, such as colour octets P 8:

« ISOQàJ , <Jä ; fe-fe (10a)

and colour singlet technipions P°*~:

- 542 -

3. WHAT DO WE HAVE?

There is something for everyone in the collider data, with a few candidate events for almost all of the signatures listed above. Unfortunately (7), the interpretations of these intriguing suggestions are not at all clear.

a) Z a Jt+A-T 7) 8) 27) 28)

Some of the parameters of the three observed ' * ' * events are tabulated below.

V y , * « ' DOl&\} (?) , P* 1 * - * ñ , Lv ( 1 0 c ,

Compositeaess Excited quarka and leptons» In addition to their possible detection in Z° •*•

(e***,ev)e decays^ 1^, could also show up in H * (e**eY) v or H + e(v*+vy) or Z° -> (V * -» -VY)V. The decays q* •* q+y would give peaks in (Y+jet) invariant maBs

22) distributions, and <¡* + q+g in dijet invariant masses . Composite quarks and leptons could be expected to bave non-trivial electroweak and strong form factors F(s). There might be new effective four-fermion contact interactions (1/A^)(£fff) which could interfere with conventional gluon exchange^^. Present collider data already tell u s 8 ^ that

|\ ^ 29 -S Qt\J ( U )

24) ± n and competitive limits come from PETRA If the W and Zv are composite there 25)

may be sîn-sero composite bosons X accessible in H * X+y decay , or decaying into W's. There might also be anomalously large multiboson vertices^\ or a truly anomalous magnetic moment for a composite W*.

- 543 -

Table 2: Radiative Z° decays

e+ 2"Y

UA1 UA2 l'Ai

98.7±5 90.6M.9

m(Jl+jr) 42.7±2.4 50.4*1.7

4.6±1.0 9.1*0.3 5.0 ± 0.4

88.5Í2.5 74.7±1.8 3 -9.3

14.4±4.0° 25 ± 1° 7.9°

E Y

38.8±1.5 24.4*1.0 28.3 i 3

First among the (im)poasible explanations (?) is conventional OED bremastrahlung. The rate for this can be calculated reliably :

(12)

which gives R » 0.02 for 6 - 5 ° and c = 0.1. Clearly, the observed configurations are extremely unlikely, and the combined probability that 3 out of 13 Z° events have both 6 and e as large as in Table 2 has been estimated29"* to be OCIO""1* to 1 0 ~ 5 ) . However, if one integrates*^ over all regions of 1+S~y

phase space where the probability density given by the square of the <4CD matrix element is no larger than the density in phase space around the observed events,

- 544 -

then the observation of radiative decays seems much less unlikely. How about excited leptons 2 1 J : Z° + X*JL, A* •* Ay ? It seems that in(Jl*) ^ " ( ^ Y ) ^ since PEP and PETRA have not e +e" •* Jt*+Ä*~ or e +e~ + Ä*~Jt+. Furthermore, the observed m ( * Y ) l o M appear to be different, even for the two eey events. The mCJLY) h lg h also appear different. Moreover, the (Ay) opening angles listed ln Table 2 are surprisingly low: there is no reason in the excited lepton model for the y to emerge anywhere near one of the outgoing lepton lines (Fig. 1)-

29) Indeed, it has been estimated that the probability for three such small angles in the excited lepton model is also 0(10"'* to 1 0 - 5 ) . Another suggestion 1 5^* 2 5^ has been Z -*• X+y, X + X+X~i where X is a spin-zero boson in a composite model. Here again one has the obstacle that the two m C ^ e - ) masses look different, but chiral symmetry arguments anyway favour the existence of two

25) spin-aero particles . One still has the problem that the small values of 8 ^ are a priori very unlikely (Fig. 1). Nevertheless, several theoretical studies

25) of the spin-zero boson hypothesis have been made . An interesting remark is that direct-channel X exchange can interfere with crossed-channel y exchange in Bhabha scattering (Fig. 2), and a useful theoretical lower be j on this

30) interference can be derived - Its non-observation at PETRA means that any spin-zero X boson must weigh more than 47 GeV^ 1^. Since one of the e +e~ pairs in Table 2 has an invariant mass of 42,7±2.4 GeV, this hypothesis looks somewhat ill. As a final proposal, let me mention the i d e a ^ that thr Z° is composite with an anomalously large three-neutral boson verte* which allows Z° •* y +

(virtual Z° -*• X+X~) decays. The virtual Z° does not give . ¡xed m(Ä+£~), but a distribution (Fig. 3) centred around which is consisted wit.L experiment. However, still..no explanation Is supplied for the small values of j ^ .

None of the explanations for radiative Z° decays has great difficulty explaining the o b s e r v a t i o n ^ o f just one radiative W •+ evi decay. The rate is not grossly incompatible with conventional brenustrahlung expectations, few W •* e*v events are expected if m(e*-) = m^, and no W •» evy events are expected if the spin-zero X boson is an isoscalar.

My general criticism of all the unconventional explanations for the radiative z° decays is that the observed kinematlcai configurations (y lose to Â) are at least as unlikely as in conventional QED bremsstrahlung (y *• i- from A) . On the other hand, we know that the physical phenomenon of bremsstrahlung exists with probability one, whereas the observed erotic mechanisms can only have probabilities <1 ( « 1 in some cases I). Therefore, theorists should either invent exotica which naturally yield the observed configur aions, or else

- 545 -

wait patiently to see more data. My own guess is that the events will turn out to hdve been QED bremsstrahlung gone crazy, but I will be happy to be proved wrong!

b) "Zen" events These are events with one jet (or other evidence of activity) on one side of

the Interaction point, and nothing (missing neutrino or ?) on the other side. UAl

reported^*^'^^ at this meeting two events of this type with a "photon" of transverse momentum above 40 GeV with large miss ng transverse energy, some of

whose parameters are listed in Table 3.

Table 3i Some zen event parameters

Event Jet

(GeV)

toisa ing p>

(GeV) (GeV)

Charged

Multiplicity

Invariant mass o£ charged particles (GeV)

A 25 (71 inc. a)

24 ± 4.8 (66±8 inc. [ii

130 ± L6 inc. ¡i 1 0.1

B 48 59 ± 7 106 ± 12 3 0.79 t 0.12 C 52 46 ± B 97 t 17 1 other unre

structed tracks? D 43 42 î 6 85 ± 12 4 3.14 £ 0.38 E 46 41 ± 7 17 i 14 2 utlier unrecon

structed Cracks F 39 34 ± 7 73 + 14 2 0.52 i 0.06 H 54(r) 40 ± 4 93 ± 5 0 0

By "photon" one means either a single y or a highly collimated electromagnetic jet which shows up as an unresolved hit in the electromagnetic calorimeter. Unfortunately, one of the events is at an angle where the central detector could have missed a charged track, and it is possible that the event was W + ev decay whose electron track was not visible. The electromagnetic calorimeter hit is however more energetic than in the majority of W > ev events. There is no such interpretation possible Cor the other "photon" event, and the backgrounds no

- 546 -

this one from multiple gondola hite, cósmica and jet fluctuations are together less than 1 0 - 2 of an e v e n t ^ ^ ' 3 ^ . There is a jet of a few GeV in this second event, which is responsible for the difference between the transverse momentum of the "photon" and the misslag transverse momentum. This event is very beautiful, and we can only hope that its interpretation will become clearer ••-hen more such events are gathered.

In the meantime, let us recall the precept of Sherlock Holmes:"If more than one unusual event occurs, they should be related" and seek a unified explanation which also accounts for other of the UA2 funny events. What about Z° -» vv*. v* -» yy ? The transverse mass of the y and missing transverse momeo tum la the gold-plated "photon" event is 101±8 GeV, compatible with Z ü decay. However, the v and v vould have to emerge collioearly and apposite ia azimuth to the y

(Fig. 4 ) . This is an a priori unlikely configuration, as extreme as the 2 •> e(e* * ey) events though in a different way. What about SUSY ? Certainly massing transverse momeecum wich no detectable charged lepton is a characteristic signature of SUSÏ, but one does not in general expect to get sin¿le photons. Of course, the observed "photon" could be a collimated jet of photons (e.g., Htt or n. •* YY) i D u t only one in 1 0 3 o¿ conventional hadronlc jets fragment purely electromagaetically. In seeking an interpretation for this event, perhaps we should remember the dicta of Sherlock Holmes, and seek a unified explanation with another category of "zeu" events.

There are five events 2 8^* 3 2^ containing a "monojet" of energy above 40 GeV with no jet having > 10 GeV recoiling In the opposite direction in the azimuthal plane (Fig. 5 ) . There are also events with < 40 GeV that are kinematically consistent with W decay. Several of these are probably W •* vv

decay followed by t + hadrons + v, while some may be pp * g + (2° + v v ) 3 3 \ 28) 32)

However, these explanations do not fit * the events above 40 GeV, for which the background frou jet fluctuations is calculated to leas than 0.1 events. Some parameters of these events are listed in Table 3. One of these events is exceedingly spectacular (Fig. 6 ) : the monojet contains just one charged particle, which is identified as a muon, and has a • 0Ç50) GeV. The combined invariant mass of the muon and of the electromagnetic jet is about J GeV. It is a general feature of the monojet events that their jets are quite "small": the charged multiplicities vary between one and three, and the invariant masses of the charged particles with p T > Ö.5 CeV are generally less than about 2 GeV. Thus many of the monojets look like «'s, though not all of them are consistent with this interpretation, and it is difficult to imagine a copious source of high p x's.

The UA1 experiment expects28))32) nine ooaojeta from W * TV decays in its present event sample, bat these should have p^ < AO GeV. They expect 2^*^*^ only one or two events from heavy leptons: W •* L + v , and even fewer could be

34) - ~ expected from analogous supersymmetric decays such as W + W + y. Since the charged multiplicities in the observed monojet events are so small, it is natural to wonder whether the "photon" event might just be another manifestation from the same source, one in which the j»*t charged multiplicity fluctuated down to zero - not so unusual for "small" jets* It is also possible that the "super" event with a high p T muon in the Jet might be related to the e + Jet + missing

35) P T events of UA2 which will be discussed ' shortly.

The most conservative approach to the "zen" events is probably to use them as upper limits on new particles. For example, many eupersymmetric sources would^^ give monojet events when subjected to the experimental cuts used by

28) 32) UAi ** to define their monojet event sample (Fig. 7 ) . The number of monojet events can be used to set upper limits on the cross-sections and hence lower limits on the masses of some supersymmetric particles. For example, assuming that the UAl jet trigger is efficient down to an E_ of 20 GeV, one can argue on the basis of the observed monojet events that tl .• gluino

(13)

and the data can also be used 3 6^ to establish a similar lover bound on squark masses* More excitingly, it should be emphasized that the observed monojet events are compatible with the production and decays of glulnos or squarks with a mass 0(40) GeV. If this is their origin, future collider data on monojet events will be very interesting1

In addition to the monojet events, there are also some multijet e v e n t s ^ ^ 1 ^ ^ with missing p ,, including two- three-Jet candidates, one four-jet candidate and a few two-Jet events in which the missing p^ is coplanar with the two observed jets. These two-jet events seem to be consistent with the jet fluctuation background, but one of Che multijet events (Fig. 5) is very striking and is less likely to be background. The transverse mass of the four-jet, missing p T syatea is about 200 GeV* cleaïJ.y Incompatible with. W~ or Z° decay. SUSY can of course offer interpretations for such an event (pp •* gg, g + qqy or PP + S*J» 1 + <18?)I> although as mentioned earlier many gg events turn out to look like monojets when all the eut» in the experimental selection are made^?

548 -

c) e + jet + missing p, events 35)

UA2 has reported the discovery of four events containing a large p , electron, jets, and missing p^,. Key parameters of these events are listed in Table 4*

Table 4: Some e +- jet + p ^ * ° 8 event parameters

Event P T(e)

(GeV)

E T CJets)

(GeV)

miss P T

(GeV)

m T(ev)

(GeV)

Œ(W jets)

(GeVj

A 18.3 * 0.8 39 t 4 51 i 4 56 ± 2 141

B 22.0 i 0.» 6? ± 7 86 ± 6 W U 166

C 34.4 ± 3.2 66 i 6 57 i 5 82 i 4 164

Views of these events in the plane transverse to the beam axes are shown in Fig. 8. In two of the events the transverse mass of the electron and missing transverse energy vector is around 80 CeV, while in a third It is about 56 GeV. Thus, these three events could be interpreted as W + jet events. In the fourth event, the e and the missing transverse energy vector have similar azirauthai angles and u. transverse mass of only LO CeV. This event looks rather more like

35) heavy flavour production and seolleptonic decay • In a scatter plot (Fig. 9) of E ^ e t s versus p^CJets + e) the three H + jet candidate events appear well isolated from the conventional low p^ W events. They occupy a region which

seems to be devoid of background. One o£ the most dramatic events (B) is shown

- 549 -

in Fig. 10. The UA2 collaboration has estimated the magnitude of the QCQ bremsstrahlung background due to W + gluons by analogy with hadronic jet events. They take dijet events with an invariant mass ^Cm^) and ask how likely they are to be accompanied by a large p^ jet or by a large E , jet pair. They believe that the rate of gluon bremsstrahlung in W production events is likely to be over- rather than under-estimated by such an empirical comparison. This method indicates that indeed the three W + jet candidates are very unlikely to be QCD bremsstrahlung background. Ihe invariant masses of the three events are around 170 GeV> but not too much significance should be read into this,, since the

35) effects of the selection criteria favour events in this mass range .

As far as the interpretation of tbese events is concerned, one's first natural suspicion is that perhaps after all the three W + jet events are QCD bremsstrahlung. After all, if the Z° + XfSTy events teach us that QED breios-strahlung can play on us funny tricks which we do not understand, Burely QCD can be equally mischievous ? So far a detailed comparison of Che VA2 events with a

37) respectable QCD theory calculation has not been made* It would be particularly interesting to have available theoretical calculations of the rates for events with large but snail net p T» since one of the three events is accompanied by a pair of jets whose p^ vectors largely cancel in the vectorial sum. The UA1 collaboration has no comparable e + jet + missing p^ events 3 0'', but It is tempting to emulate Sherlock Holmes and to compare with che muon manojet event of U A l 2 8 ^ * 3 2 * . The transverse masses of the (e"v") and (¿Tv") s y e a a are comparable in the two cases, though the UA1 event has the striking feature that the muon is practically Inside its accompanying jet, whereas the electrons in the UA2 events are well separated.

If you prefer to seek more interesting interpretations of the ÜA2 e + jet events, one suggestion^^ is that we are witnessing excited quark production g + q * q*t followed by q* + q + W decay. If this is the case, we should also expect q* + q + Z° [and UA1 d a e s 2 8 ^ have an excess of jets in its Z° events^, q* •*• q + y (no signal yet in y + jet invariant mass distributions) and q* + q + g (more about this shortly). An alternative explanation for the ÜA2 events

_ « w 39) /w — — ~ evokes pp * W + g production *, followed by W + evv and g * qqy. would produce events tilth e + jet + large amounts of missing p^,. It is difficult to see how the SUSY rate could be leige enough, but this explanation ia consistent with the observation that in the three UA?- "W" + jet candidates, the missing "v" p T

vector is consistently larger than the p T of the observed electron* They should on average be equal in U + ev decay, but could easily be different in SUSY, where the "V 1« actually a combination of one v and two photinos y. However,

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coo much should perhaps not be read i n t o the d e t a i l s of t h r e e even t s : l e t us hope t ha t nore a r e found in the next c o l l i d e r run .

d ) Tbe bump a t 150 GeV 8)

The UA2 Col l abora t ion has a bump (F ig . 11) i n t h e i r m u l t i j e t mass d i s t r i b u t i o n a t 147 ± 5 GeV, u i t h a width of 11 ± 5 GeV (compatible with t h e i r expected mass r e s o l u t i o n ) which conta ins 50 ± 16 e v e n t s . As such, i t i s nominally a 3a peak and hence more s i g n i f i c a n t than the W bump found in the same experiment (<2o) . However, one must be ca r e fu l not t o o v e r i n t e r p r e t 3o bumps, p a r t i c u l a r l y when they occur way down on sharp ly f a l l i n g s p e c t r a . The conse rva t ive r e a c t i o n i s to wait u n t i l the " i n v i t e d g u e s t " , the W bump around 80 GeV, i s confirmed beyond any doubt, before welcoming the "uninvi ted gues t" a t

22) 150 GeV. Neve r the l e s s , some t h e o r i s t s a r e a l r e a d y exc i t ed : perhaps t h i s bump i s the q + g decay of the q* p rev ious ly in t roduced i n an a t tempt to exp la in the e + j e t + missing p^ e v e n t s . The UA2 Co l l abo ra t ion do not exclude the hypo thes i s of a common mass for these two phenomena. e ) Dimuott events

The UAl Col labora t ion has r e p o r t e d 2 8 ^ dimuon e v e n t s , of which seven a r e o p p o s i t e - s i g n (four with j e t a c t i v i t y and t h r e e wi thou t ) and th ree a r e l i k e - s i g n (one with j e t a c t i v i t y and two w i t h o u t ) . The i n v a r i a n t masses of t he uu p a i r s range between 6 and 22 GeV, j u s t above the l i m i t imposed by the p£ > 5 GeV

40) and in the range expected from var ious heavy f lavour sources and from the Orell-Yan continuum (Fig* 12)« The t r a n s v e r s e ene rg i e s l a the events range between 44 and 136 GeV: the h igher ones may seem s u r p r i s i n g l y e n e r g e t i c . However, what i s most i n t r i g u i n g about the dimuon e v e n t s , a p a r t of course from the presence aouang them of t h r e e l i k e - s i g n e v e n t s , i s the abundance of s t r ange p a r t i c l e s t ha t t h e / c o n t a i n . For example, t h e r e i s a u + u~ event with a A®. The i n v a r i a n t masses of the two (litlL1 1) combinations a r e 6 .5 ± 0 .5 and 6.9 ± 0.5 GeV, both of them Incompatible with b decay, which would give U+A° combinations with masses below 5 CeV. There i s a l s o a (uTu,~4°) «vent in, which the ( u - ^ ) i n v a r i a n t masses a r e 4 .1 ± 0 . 1 and 4*6 i 0 .1 GeV; k inemat lca l ly compatible with b decay, but again the wrong s t r a n g e n e s s . Perhaps these s t r ange p a r t i c l e s a re s p e c t a t o r s con ta in ing sea s t r ange quarks ? One of the u,+u~ events con ta ins two K°, and the i n v a r i a n t nasa of the ( t f V 1 ^ ) system i a 10 .5 t 0 . 5 GeV, ba re ly compatible with a bb product ion and decay e x p l a n a t i o n . There i s a l s o a u+u~AuA° event i n which the (u+A°) combination I s k lnemat l ca l ly incompat ible with b

- S 5 1

decay, and a u+[i~A0A°K^ event In which the <u~A°) combination i s incompat ib le with b decay.

He see t h a t , whi le the a s s o c i a t i o n of uuons with s t r ange p a r t i c l e s i s to be expected from heavy f l a v o u r s , in many cases the k inemat ics of simple bb product ion and "deçà;' - or a f o r t i o r i cc product ion and decay - do n i t f i t the d a t a . P o s t u l a t i n g t t product ion he lps by y i e l d i n g n a t u r a l l y ( u + A Q ) o r (u~Ä°) combinations wi th i n v a r i a n t masses above 5 GeV, from t •+ u.+v(b •* A 0 ) and the

corresponding a n t i p a r t l c l e process* I t i s p o s s i b l e t o ge t l i k e - s i g n dimuons from t t or bb p roduc t ion , by combining one primary s e a l l e p t o n i c decay with one secondary: e . g . , (b + u~vc)(b * udc: c *• u ' v s ) . However, the secondary decay muon i s in gene ra l u n l i k e l y to surv ive the cut of 5 GeV on the p„ of the muon.

41) 1

On the o ther hand, the p rocess W •*• t b can ' g ive l i k e - s i g n primary muons: ( t * ( i + vb)(b + u+ve). Another way t o ge t l i k e - s i g n primary muons i s through bb mixing 4 2 ^ . In the s tandard model t h i s i s not expected for the B D = (bd) and B° = (bd) mesons, but could be l a r g e for t he (b s ) and (bs ) mesons* I n t he

± * * ? absence of n i x i n g , one would expect #u uT/rfpTu - 0 ( 1 / 1 0 ) , but the r a t i o could

- A2) be 0 ( 1 / 3 ) with maximal (b s ) «-* (bs ) mixing ' . The f i n a l s t a t e decay products of (b s ) or (bs ) mesons seem u n l i k e l y t o con ta in many s t r ange baryc . 8 , so something e x t r a i s needed t o exp la in the ( ( i + n + A°) and (u~u~Ä°) e v e n t s . As

43) mentioned be fo re , perhaps the s t range baryons con t a in s p e c t a t o r s t r ange

p a r t i c l e s . 40)

C a l c u l a t i o n s ' sugges t t h a t wi th the p resen t luminosi ty 0(2) Drell-Yan u*u~" even ts should have been seen: these might be among the " q u i e t " even ts

40) without j e t a c t i v i t y . Simple g g fus ion p e t t u r b a t i v e qCD c a l c u l a t i o n s sugges t 0 (1) t-*V~ event from bb product ion and decay* In view of p a s t exper ience with cc produc t ion , i t could wel l be t h a t t h i s i s an underes t imate* There a re expected to be an a r d e r of magnitude fewer t t * u+u~" e v e n t s , and a t most 0.4 W * t b •* up. events* This l a t t e r source may be the one wi th the most r e l i a b l y c a l c u l a t e d r a t e .

We should r e j o i c e t h a t the t o t a l nuuber of dimuon events i s somewhat h ighe r than these t h e o r e t i c a l e s t ima tes* The apparent excess i s not a major d i s a s t e r for theory , given the i n e v i t a b l e u n c e r t a i n t i e s . The observed events may come from a combination of d i f f e r e n t s o u r c e s . Presumably, the bulk of them o r i g i n a t e from heavy f l a v o u r s , and the s t r ange p a r t i c l e s observed a r e not t h e r e by a c c i d e n t . However, d e t a i l e d exp lana t ions of each of the even ts a r e not easy to a r r i v e a t . The s i t u a t i o n t e c a l i s the good old days of d i l e p t o n product ion i n

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bubble chamber neutrino experiments. Some exposures found too maay strange particles, some too feu, and there were always some bizarre event with unusual configurations- Eventually the situation settled down, and my hunch is that the same will happen here. It seems quite possible that we may discover some new physics on the way to this resolution: perhaps bb mixing or the t quark? Dimuons are "une affaire à suivre".

4. WHAT PO HE MOT HAVE?

Sherlock Holmes remarked during one of his cases that "the most important clue, my dear Watson, is the dog that did not bark". Here then are a few of the dogs which were silent at this meeting.

a) The t quark No evidence was reported here for W > tb decay, though it is worth

44) recalling that way back in one of the first collider runs there was aa event containing an isolated large p T lepton recoiling against a jet containing a D°, a charged ft which when combined with it made a D*, and even another charged TE

which ciade the invariant mass up to that of a B meson. If m f c < O(bU) GeV, probably It is just a matter of time before W •» f b shows up. The crass-section for gluon fusion to give tt is more sensitive to the t quark mass, and estimates suggest that if ~ 3D to 40 GeV insufficient luminosity has as yet been accumulated for production to be observable. However, it may be that perturhative QCD gluon fusion calculations substantially underestimate the tt production cross-section, and there nay be a substantial rate for the

- 45) diffractive production of tt . A search for this is under way, focusing on the C * b|¿v decay mode, and looking for diffractive events containing a large p

46) u,, a jet, and missing p T- As was discussed * at this meeting, a useful way to estimate the mass of a state decaying into an unobserved neutral is to

47^ „42) compute the "cluster transverse mass ' or minimal transverse mass * This is obtained by minimizing with respect to the choice of p^ the mass of the state decaying into the observed particles with measured p-.'** and p7^ S. and a missing

v neutral for whoa only the is knowni

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The distribution In £ = M*/M (where M is the true mass) peaks sharply at Ç ~ 1:

and Is relatively stable against cuts in the p^ and p , of the observed decay products, smearing due to Che p T distribution at production, etc.

If t quarks can be produced diffractively, why not also supersymmetric particles such as gluinoa ? In the case of pp + (gg) + x followed by g •> qqY decay one has additional problems because there are two states with similar p L

distributions decaying with missing transverse energy. This means that one can 49)

confuse and mix the jet decay products of the two gluinos» Nevertheless , the minimal mass distribution still peaks rlose to the massof the glulno, with "mismatched" combinations providing a smooth and not overwhelming background under the peak (Fig. 13). If there are substantial diffractive cross-sections for the production of heavy quark flavours, Che way may be open for diffractive searches for other species of strongly interacting particle.

One intriguing result on "heavy" flavour production reported here was the observation"**^ of l)*/D production in jets. The signal observed was of comparable cleanliness to the results from e +e~ + cc jets. This was surprising, since the bulk of large p T hadron jets are gluon jetB, not cc. Indeed, the rate of 0*/D production is so high that about 10% of gluon jets are needed to fragment into charm. The longitudinal momentum fractions Z oE the observed D* are much softer than in e +e~ annihilation, supporting the interpretation that they come from secondary gluon. + cc fragmentation rather thau from primary cc fragmentation. Perhaps some of the dimuon events are due to single (=> u +u~) or

- j. + + double g + cc (=> p. p." or u~lO fragmentation? This observation of copious V producción is a potential disaster as it suggests tiie possibility that there may be many heavy flavours produced at future hadron colliders by boring mechanisms, which may obscure the signals from Interesting mechanisms such as Higgs * bb or tt. It may easily be more difficult than expected to get at these interesting events by heavy flavour tagging using a microvertex detector.

b) The quark-gluon plasma We have seen at this meeting that UA5 has observed^^ significant

deviations from previous KNO "scaling" multiplicity distributions. The

(13)

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interpretation of these deviations is not clear, but they can be mimicked by adjusting appropriately the parameters of a cluster production model. This done, one can ask about the significance of the observed"**^ fluctuations in the rapidity density of produced particles. Are they evidence for "hot spots" where the hadronic soup has boiled up into a quark-gluon plasma, or are they merely fluctuations which do not require new physics for their explanation? UA5 has f o u n d 5 ^ that the same cluster model which was adjusted to reproduce the KtfO distribution also give multiplicity density fluctuations comparable with

yet determined whether its cluster Monte Carlo reproduces this effect. However, clearly no evidence yet exists to support the existence of a quark-gluon plasma.

53) Furthermore, recent theoretical arguments cast doubt on the existence and hence observability cf a well-defined phase transition from hadroalc to quark-gluon matter.

5. THE TOTAL CROSS-SECTIQN AMD DIFFRACTIVS SCATTERING The UA4 Collaboration reported ' here a new value of the total cross-

section at the SppS collider:

(16)

äad of the elastic cross-section ratio:

(17)

The elastic cross-section exhibits significant curvature in its t-distrlbution:

It is important for the analyses of these data that the total centre-of-mass energy in the past collider runs has now been re-estimated: • 546 GeV. The

5 4 )

elastic cross-section ratio (17) is significantly higher than at the ISP., which is very helpful 5 5^ in discriminating between different theoretical models

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a) o* t o t/{logsj 2 •*• 0: chis would require ° e ^ at o t

t o decrease at higher energies, which seems now to be excluded by the result (17). b) a t o t / ( l o g s ) 2 • constant between the ISR and the SPS: this would also require ff

ej/*^«. t o *>e constant, which also appears to be excluded by (17). c) a t o t/(logsJ 2 will become constant; c

G ^ a

t o t r i s e s to í aa a > »; this seems to be favoured by experiment.

This third possibility was the one previously favoured by Henzi and V a l i n ^ \ and one can regard the latest UA4 data as confirmation of their "Blacker, Edgier, Larger" proton (the BEL model). According to this model the proton gets slightly blacker at small impact parameters b, but the biggest increase ln opacity Ah is at moderate impact parameters h B 0(1) fm. An interesting measurement which would facilitate predictions nf ofQ^ at future collider energies would be of the real part of the forward scattering amplitude. Predicting the future higher energy behaviour of a

t Q t is not juBt of academic interest: It is important in the design of experiments at future high intensity high energy colliders to known how often one can expect multiple collisions during the same crossing. Also, we should not forget that ultimately theorlata should be able to calculate o from first principles In QCD.

6. FUTURE COLLIDERS Beyond the present-da; CERN SppS collider we have the forthcoming FNAL

Tevatron Collider, as well as the CERN improvement programme based on the new ACOL ring. Beyond these developments, we want to get to effective subprocesa centre-of-mass energies J B A 1 TeV. As discussed in Section Ü, this is the domain in which the physics of gauge symmetry breaking and the gauge hierarchy problem can be expected to reveal itself.

There are basically two ways to reach the magic 1 TeV domain. One is with a hadron-hadron collider having at leaBt 10 TeV centre-of-mass energy"*^ • Such a collider could either be pp or pp: in both cases the technology is already available, since successful pp (ISR) and pp (SppS) colliders have been built. Furthermore, FNAL has demonstrated that a ring of superconducting magnets can be built and operated, while CERN has reduced p cooling to a routine. As we heard fro.ï Brlantl^^ at this meeting, a high-luminosity Bulti-TeV hadron collider is already known to be feasible. The other way to reach 1 TeV is with an e +e~

58) collider . Here one needs the unproven technology slated to be developed by the SLC that ia scheduled to start operation ln 1986. There are formidable

- S56 -

technical hurdles to be overcome with a linear e +e collider, such as guiding to collision two beams of order L urn radius which have densities approaching that of water* Moreover, present: designs for a high energy e~*"e~ collider consume as much power as is produced by a medium-sized nuclear ¿¡awer station"*^. For a linear e +e~ collider to be proposable, one probably needs higher accelerating fields from more efficient cavities, as well as an existence proof of the basic technology from the SLC. At present only high energy pp or pp colliders can be seriously proposed as devices to explore the 1 TeV domain, and thf-y certainly would be great machines for exploring the new physics in this domain, as was

59) discussed by HInchliffe .

Ä general feature of higher energy hadron-hadron colliders is that the new physics always shows up at large angles, while the more traditional physics of lower energies gets squeezed into ever more forward angles* Thus physicists probing smaller angles resemble archelogists probing lower and older sedimentary layers. Today's physics at large angles will tomorrow become yesterday's physics at forward angles, and next week it will become last week's physics at very forward angles (Fig. 14). The W and Z u are no exceptions to this general rule. Produced today at large angles, tomorrow they will be produced at forward angles, and at multi-TeV hadron colliders the bulk of the W and Zv will be produced^^ and decay within 5° of the beam pipes (Fig. 15).

Examples of possible future physics include Higgs bosons. These should be produced centrally (Fig. 16) with measurable rates out to m^ = 0(400) G e V 5 9 ) , 6 ° ^ . The problem is one of extracting a H * W+W", Z°Z° or tt decay signal from the backgrounds of Intermediate boson pair production and of heavy quarks. We must learn to use more than just the kinematlcally

+

unconstrained 15% of W + ev, UAI decays. Can one work with the hulk of W or Z° •> hadronic jet decays, at least in events where another vector boson leptonic decay provides a signature which can be used to suppress hadronic backgrounds? There are large r i t e s " ^ ' ^ ^ for supersymmetrlc squark or gluino pair production for m~, m~ =»(1) TeV. Such events have missing energy signatures: p ^ S S * m~, m^ (Pig. 17), which may stand out above the jet fluctuation background which centrally (Fig. 18) into jets separated by angles of order TI.'I radians, with missing Py, of order several hundred GeV***^. The problem may be to distinguish between the signatures for different SUSY particles. Finally, the technicolour composite Higgs alternative to SUSY has large rates for production of the

Squarks and gluinos are produced and decay

- 5 5 7 -

relatively light technipions, and the signal-co-background ratios appear 60) 0

manageable . For example, the 250 GeV colour octet technipion Pg has a production cross-section of order nanobarns at centre-of-mass energies above 10 TeV, while the ratio

While experiments with high energy hadron-hadron colliders will not he easy, they will enable us to explore the 1 TeV domain.

7. CONCLUSIONS At the close of the last pp Collider Workshop, Leon Lederman^1"^ quoted

T.D. Lee to the effect that "every new energy domain opens up new, unexpected discoveries"* The CERN SppS collider has already made the new discoveries most of us expected it to make* Now we start to smell the unexpected discoveries that Lee and Lederman expected it to make: radiative Z° decays? "Zen" monojet events? Electron + jet +• missing p , events? Bumps in the multijet mass distribution? Anomalous dimuon events? Even if only one of these titillating suggestions turns out to be the harbinger of new physics, the promise of the CERN SppS collider will have been more than amply confirmed. However, theorists should be careful not to over-interpret the details of a few appetizing events• In the cautionary words of Sherlock Holmes: "The temptation-to form premature theories upon insufficient data is the bane of our profession".

We nevertheless expect unexpected discoveries at future hadron colliders such as the Tevatron, the SSC or Desertron, and the LUG or Juratron. Events at this workshop have demonstrated the value of friendly competitive rivalry as a stimulus for extracting the physics. From UAl and UA2 today, to CDF and DO tomorrow, to the Te va tr on and the Sp¿jS collider with ACÛL in the future, and hopefully to the Deeertron and the Juratron in the more distant future, surely there is more than enough physics for everyone. So let us all go back home and find out what it is I

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V . Barger, F. Halzen and W.r. Keung, Phys. Rev, D24 (1981) 14Z8; R. Morgan and M. Jacob, Physi. Lett. 107B (1981) 395.

46) W.J. Stirling, talk at this meeting. 47) V. Barger, A.D. Martin and R.J.N. Phillips, Phys. Lett. 125B (1983) 339 and

Phys. Rev. D28 (1983) 145. 48) E* Berger, D. DiBitonto, M. Jacob and W.J. Stirling. CERN preprint TH.3821

(1984). 49) W.J. Stirling, private communication (1984).

- 560 -

50) R. Frey, talk at this meeting. 51) UA5 Collaboration, G.J. Alner et al. Phys. Lett. 138B (1SM14) 304. 52) UA1 Collaboration, G. Arnison et al., Phyo. Lett. 118B (19B2) 1S7. 53) P. Hasenfrata, P. Karsch and I.O. Stamatescu, CERN preprint TH.3696

(1983); T.A. DeGrand and C. DeTar, Univ. of Colorado preprint COLO HEP b6 (1983); F. Karsch and F. Green, CERN preprint TH.3748 (1983).

54) UA4 Collaboration, F. Gervelli, talk at this meeting. 55) A. Martin, talk at this meeting;

R. Henzi, Calk at this meeting. 56) R. Heoai and P. Valin, Phys. Lett. 132B (1983) 443 and McGill Univ.

preprint (1984). 57) G. Brianti, talk at this meeting. 58) H. Wiedemann, Proc. 1982 SLAC Sumner Institutes, ed. A. Mosher (SLAC,

1982), p. 1; J. Ellis, SLAC preprint PUB-3127 (1983).

59) I . Hinchliffe, talk at this meeting; E. Eichten, I. Hinchliffe, K. Lane and C. nulgg, in preparation (1984).

60) J. Ellis, G. Gelmini and H. Kowalski, talk at the Lausanne workshop on the possibility of a Large (ladrón Collider in the LEP Tunnel, UESY preprint in preparation (1984).

61) L. Lederinan, Proceedings of the third Topical Workshop on Proton-Antiproton, Rome 1983, ed. C. Bacci and G. Salvini, CERN Yellow Report 83-04 (1983), p. 575.

- 5 6 1 -

(a) Fig. I: In the observed Z°

(0 A +A y events (a) the Y tendH to emerge at a small

a n g l e +2.Y F £ 0 I A ° 5 E ° i t h e c harged leptons, whereas the hypotheses ( b ) Z° + l- {JL*+ * A y ) [Ref. 21) J and <c) Z<> + y a 0 * A +A~) [Ref. 25) j would typically lead to larger angles 9 ^ .

Fig. 2; Direct channel spin-0 X boson exchange interferes channel photon exchange in Bhabha scattering.

30) with crossed

\ ' ^ '

1

\ \

ÎC tD 6C m e . T . ( G e V )

Fig. 3: The shape of the mCÂ") spectrum expected^*^ in a composite Z° model.

- 5 6 2 -

Fig. 4: The event

sort of configuration required if the gold-plated UA1 "photon l C28),32> i g t o fce understood as Z° •*• vvy decay.

10 2 0 1 1 '

¿ E „ ( C e V I

5 0

• Single j e t

X " P h o t o n "

O 2 Jets

Û 3 t l more j e t s

7 0

I I S 1° G

/ o ,

IIA 1

2 0 0 0 3000

( A E n ] ! ( G e V ' l

tOOO

Fig. 5: Scatter plot » ^ of inisaiag p^ versus E^, showing all events whose missing p^ are greater than Ua (o « 0.7 **E"J), including monojet events, "photon" events and multijet events.

Event A

Fig. 6: Monojet event A of the HAI Collaboration 2 8^' 3 2^

- 5 6 4

Topological cross-sections for pp •> gg + X production giving l-,2-,3-and 4-jet events 3 6', after imposition of cuts modelled on those applied by the UAl Collaboration.

p x(Je) GeV/c Fig. 9: Scatter plot of UA2 e + jet + missing p T events 3 5^. The horizontal

ax.' is the transverse momentum of the jet + electron system, which is essentially the missing p T > while the vertical axis is the Ej of the jet system. The most interesting events have p>j(j+e) > 25 GeV and E T > 30 GeV.

- 567 -

10: Lego plot of one of the moot dramatic e + Jet + miBaing p T events

- 568 -

Flg. 1 1 : The bump observed by UA2 in their multijet invariant mass distribution.

- 569 -

I I I . I . I . I • I

0 20 40 60 80 100 M(t iV) {GeV}

Fig. 12: Theoretical calculations* 0' of the rates of u +|TX events irom various different sources, retaining only events with pf » 5 GeV.

- 570 -

20

1 5

1 0

Mj = 40 GeV/c 2

/ s = 540 GeV

» 2 jets with |p T |>5 GeV/c

0.5 1.0 M*/M

1.5 2.0

Flg. 13: the minimum transverse mass distribution expected from diffractive production of gluino pairs The misidentiflcation background is indicated by the dashed histogram. There is no such background to the minimum transverse mass distribution for top meson decay K

- 571 -

Angle of archaelogy

Pig. 14: The polar angle variable is an archaelogist's paradise. Today's physics emerges at large angles, yesterday's physics at smaller angles, last week's physics at even smaller angles closer to the beam-pipe, etc.

Rapidify y ».

Fig. 15: The rapidity distribution 5 9^ for W production at »T » 40 TeV.

Fig. 16: Rapidity distribution 6 0^ for production at /s - 20 TeV of a Higgs wich mass 200 GeV in association with a tt pair, for m t - 35 GeV.

- 5 7 3 -

pp / s = 20TeV

p f s s (GeV)

Fig. 1 7 : The d i s t r i b u t i o n 6 0 * i n missing P ~ from pp + gg + X a t /s » 2 0 TeV, for d i f ferent gluino Basses up to 5 0 0 GeV.

574 -

- 5 7 5 -

L i s t o f P a r t i c i p a n t s

B . A u b e r t L A P P , A n n e c y - l e - v i e u x , F r a n c e

C . B a c c i I s t i t u t o d i F i s i c a , U n i v . d i R o m a , I t a l i a

P . B a g n a i a C E R N , G e n è v e , S u i s s e

R . B i l l i n g e C E R N , G e n è v e , s u i s s e

R . B ö c k C E R N , G e n è v e , S u i s s e

K . B e c k m a n n P h y s i k a l i s c h e s I n s t i t u t , U n i v . B o n n , D e u t s c h l a n d

K . B o r e r L a b . f ü r H o c h e n e r g i e p h y s i k , U n i v . B e r n , S c h w e i z

M . B o r g h i n i C E R N , G e n è v e , S u i s s e

P . L . B r a c c i n i L a b . N a z i o n a l i , S a n P i e r o a G r a d o , P i s a , I t a l i a

G . B r i a n t i C E R N , G e n è v e , S u i s s e

J . B ü r g e r C E R N , G e n è v e , S u i s s e

I . B u t t a r w o r t h C E R N , G e n è v e , S u i s s e

L . C a m i l l e r i C E R N , G e n è v e , S u i s s e

P . C a r l s o n P h y s i c s D e p a r t m e n t , U n i v . o f S t o c k h o l m , S w e d e n

G . C z a p e k L a b . f ü r H o c h e n e r g i e p h y s i k , U n i v . B e r n , S c h w e i z

F . C e r a d i n i I s t i t u t o d i F i s i c a , U n i v . d i R o m a , I t a l i a

F . C e r v e l I i L a b . N a z i o n a l i , S a n p i e r o a G r a d o , p i s t . I t a l i a

T . T . C h o u D e p t . o f P h y s i c s , U n i v . o f G e o r g i a , A t h e n s , U S A

A . G . C l a r k C E R N , G e n è v e , S u i s s e

P . D a r r i u l a t C E R N , G e n è v e , S u i s s e

W . D . D a u P h y s i k i n s t i t u t , U n i v e r s i t ä t K i e l , D e u t s c h l a n d

B . D e R a a d C E R N , G e n e v e , S u i s s e

D . D e n e g r i C E N - S a c l a y , G i f - s u r - Y v e t t e , F r a n c e

A . D i C i a c c i o C E R N , G e n è v e , S u i s s e

L . D i L e I I a C E R N , G e n è v e , S u i s s e

M . W . E a t o n D e p t . o f P h y s i c s , H a r v a r d U n i v . C a m b r i d g e , M A , U S A

M . E d e r Z u r i c h , S c h w e i z

K . E g g e r t R h e i n . - W e s t f . T e c h n . H o c h s c h u l e , A a c h e n , D e u t s c h l a n d

J . E l l i s C E R N , G e n è v e , S u i s s e

K . j R . E l l i s I s t i t u t o d i F i s i c a , U n i v . d i R o m a , I t a l i a

R . E n g e l n t a n n C E R N , G e n è v e , S u i s s e

G . E k s p o n g P h y s i c s D e p a r t m e n t , U n i v . o f S t o c k h o l m , S w e d e n

J . F e h l m a n n I n s t , f ü r H o c h e n e r g i e p h y s i k , E T H - Z ü r i c h , S c h w e i z

R . D . F i e l d P h y s i c s D e p t . , U r i v . o f F l o r i d a , G a i n e s v i l l e U S A

- 5 7 6 -

A. Flückiger M. Fraternali J. Freeman D . Frei R. Frey j . Gasser R. Gatto j . Gaudaen S. Geer

Lab. für H o c h e n e r g i e p h y s i k , Univ. Bern, Schweiz Dipartimentc di Fisica, Univ. di ravia, Italia Fermilab, Batavia, IL, USA Lab. für H o c h e n e r g i a p h y s i k , Üniv. Bern, Schweiz CERN, G e n è v e , Suisse Inst, für Theoretische Physik, üniv. Bern, Schweis Dept d e Physique Théorique, Üniv., Genève, Schweiz Dept. N a t u u r k u n d e , Uni . Antwerpen, Wilruk, Belgium CERN, G e n e v e , Suisse

Ch. Geich-Gimbel Physikalisches Institut, Univ. Bonn, Deutschland CERN, G e n è v e , Suisse CERN, G e n è v e , Suisse Dipartimento di Fisica, Univ. di Pavia, Italia Physics Department, Duke Univ. Durham, NC, USA CERN, Genève, Suisse Laboratori N a z i o n a l i , Frascati, Italia Inst, für T h e o r . Physik, Univ. T ü b i n g e n , Deutschland Physics Dept., Univ. of California, R i v e r s i d e , USA Physics Dept., Purdue University, West Lafayette,USA L a b . für H o c h e n e r g i e p h y s i k , Univ. Bern, Schweiz Physics Department, Univ. of Wisconsin, Madison, U S A L a b . für H o c h e n e r g i e p h y s i k , U n i v . Bern, Schweiz CERN, G e n è v e , Suisse

N i e l s Bohr Institut, Kopenhagen, Danmark CERN, G e n e v e , Suisse

Hansl-Kozanecki CERN, G e n e v e , Suisse Harrison Fermilab, Batavia, IL, USA Henzi Rutherford Phys. Bldg., Mc Gill Univ., M o n t r e a l , CAN Eierzog Physics Department, Univ. of W i s c o n s i n , Madison, U S A Hinchliffe Lawrence Berkeley Lab, Berkeley, C A , USA Hofer Institut für H o c h e n e r g i e p h y s i k , ETH-Zürich, Schweiz

II. Hoffmann CERN, G e n e v e , Suisse v.. Hugentobler Lab. für H o c h e n e r g i e p h y s i k , Univ. B e r n , Schweiz (.:. nug Lab. für H o c h e n e r g i e p h y s i k , Univ. Bern, Schweiz LI. Humpert Institut d e P h y s i q u e , Univ., L a u s a n n e , Suisse M. Jacob CERN, G e n è v e , Suisse C. Jarlskog Dept. of P h y s i c s , Univ. Stockholm, Sweden

W . Geist O. Gildemeister

G. Goggi A . T . Goshaw

C . Gossling M. Greco D. Grosser W. Guryn L. Gutay B. Hahn F. Halzen H. Hänni N . Harnew J.D. Hansen j.lï. Hansen

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E . j e a n n e t

F . J e g e r l e h n e r

P . J e n n i

E . J o n e s

C- J o s e p h

K. K i l i a n

V . P . K e n n e y

A . K e r n a n

R. K i n n u n e n

J . K i r k b y

K. K o n d o

C . K o u n n a s

W. K o z a n e c k i

W. K r e b s

2 . K u n s z t

P . K y b e r d

F . L a c a v a

H . L e u t w y l e r

A . L é v ê q u e

P . Le C o u l t r e

M. P . L o c h e r

G . M a n d e l b ä u m

P . M a n i

G . C . M a n t o v a n i

L , M a p e l l i

W . J . M a r c i a n o

A . D . M a r t i n

A . F o r t i n

T . M a r t i n

M . M a r x

A . M a s i e r o

J . - P . M e n d i b u r u

T . Meng

P . M i c h e l

P . M i n k o w s k i

R. M o n i n g

U . MoSQr

I n s t i t u t \ î P h y s i q u e , U n i v . N e u c h â t e l , S u i s s e

F a k u l t ä t f u r P h y s i k , U n i v . B i e l e f e l d , D e u t s c h l a n d

CERN, G e n è v e , S u i s s e


I n s t i t u t d e P h y s i q u e , U n i v . d e L a u s a n n e , S u i s s e

C E R N , G e n è v e , S u i s s e

H i g h E n e r g y P h y s i c s L a b . , U n i v . o f N o t r e D a m e , USA

P h y s i c s D e p t . , U n i v . o f C a l i f o r n i a , R i v e r s i d e , USA



I n s t i t u t e o f P h y s i c s , U n i v . o f T s u k u b a , I b a r a k i J a p .

P h y s . T h é o r . , E c o l e N o r m a l e S u p é r i e u r e , P a r i s , F r a n c e


L a b . f u r H o c h e n e r g i e p h y s i k , U n i v . B e r n , S c h w e i z

I n s « . . f ü r T h e o r e t i s c h e P h y s i k , U n i v . B e r n , S c h w e i z

P h y s i c s D e p t . Q u e e n M a r y C o l l e g e , L o n d o n , GB

I s t i t u t o d i F i s i c a , U n i v . d i R o m a , I t a l i a

I n s t , f ü r T n e o r e t i s c h e P h y s i k , U n i v . B e r n , S c h w e i z


I n s t i t u t f ü r H o c h e n e r g i e p h y s i k , E T H - Z ü r i c h , S c h w e i z

S I N , V i 1 1 i g e n , S c h w e i z

I n s t . f ü r T h e o r . P h y s i k , U n i v . M ü n c h e n , D e u t s c h l a n d

L a b . f ü r H o c h e n e r g i e p h y s i k , U n i v . B e r n , S c h w e i z

D i p a r t i m e n t o d i F i s i c a , U n i v . d i P e r u g i a , I t a l i a


P h y s i c s D e p t . B r o o k h a v e n N a t . L a b , U p t o n , N Y , USA

P h y s i c s D e p a r t m e n t , U n i v . o f D u r h a m , D u r h a m , GE


C o l l è g e d e F r a n c e , P a r i s , F r a n c e

P h y s i c s D e p t . , S t a t e U n i v . o f New Y o r k , Stony B r o o k


C o l l è g e d e F r a n c e , P a r i s , F r a n c e

I n s t , f ü r T h e o r e t i s c h e P h y s i k , F r e i e U n i v . B e r l i n , D

L a b . f ü r H o c h e n e r g i e p h y s i k , u n i v . B e r n , S c h w e i z

I n s t , f ü r T h e o r e t i s c h e P h y s i k , U n i v . B e r n , S c h w e i z



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L . M ü l l e r

T . M ü l l e r

J. M u 1 v e y Y . M u r a k i

K. M u r s u l a

D . V . N a n o p o u l o s

B . N i c o l e s c u

A . N o r t o n

G . P a n r h e r i

F . P a s t o r e

P . p a u s s

R . D . P e c c e i

D . P e r r i n

D . p i t m a n

H . P l o t h o w - B e s c h

M. P o l v e r e l

L - G . P o n d r o m

K. P r e t z l

E . R a d e r m a c h e r

E . R a m s e y e r

J . - P . R e p e l l i n

J . - P . R e v o l

j . R o h l f

A . R o u s s a r i e

R u b b i a

S a c t o n

S a l v i n i

S c o t t

s e l o v e

S e y b o t h

S h e a f f

S m i t h

S w a r t z

S c h a c h e r

R . p . S c h a r e n b e r g

H . S c h e i d i g e r

G . S c h i e r h o l z

L a b . f ü r H o c h e n e r g i e p h y s i k , U n i v . B e r n r S c h w e i z


N u c l e a r P h y s i c s L a b , U n i v . o f O x f o r d , GB

I n s t i t u t e f o r C o s m i c R a y R e s . ü n i v . o f T o k y o , J a p a n

I n s t , f ü r T h e o r e t i s c h e P h y s i k , U n i v . B e r n , S c h w e i z

C E R N , G e n e v e , S u i s s e

I n s t i t u t d e P h y s i q u e N u c l é a i r e , O r s a y r P r a n c e


L a b o r a t o r i N a z i o n a l i , F r a s c a t i , I t a l i a

D i p a r t i m e n t o d i F i s i c a , U n i v . d i P a v í a , I t a l i a


M a x - P l a n c k I n s t i t u t f ü r P h y s i k , M ü n c h e n , D e u t s c h l a n d

I n s t i t u t d e P h y s i q u e , Ü n i v . d e N e u c h â t e l , S u i s s e



C E N , S a c l a y , P r a n c e

P h y s i c s D e p t . , U n i v . o f W i s c o n s i n , M a d i s o n , U S A M a x - P l a n c k I n s t i t u t f ü r P h y s i k , M ü n c h e n , D e u t s c h l a n d


L a b . f ü r H o i h e n e r g i e p h y s i k , ü n i v . B e r n , S c h w e i s

L A L , O r s a y , F r a n c e


H a r v a r d U n i v e r s i t y , C a m b r i d g e , MA, USA

C E N , S a c l a y , G i f - s u r - Y v e t t e , P r a n c e


S e r v i c e d e P h y s . d e s p a r t . E l . , U n i v . B r u x e l l e s , B

I s t i t u t o d i F i s i c a , U n i v . d i R o m a , I t a l i a


P h y s . D e p t . , U n i v . o f P e n n s y l v a n i a , P h i l a d e l p h i a , U S A

M a x - P l a n c k I n s t i t u t f ü r P h y s i k , M ü n c h e n , D e u t s c h l a n d

P h y s i c s D e p t . , U n i v . o f W i s c o n s i n , M a d i s o n , USA

P h y s i c s D e p t . U n i v . o f C a l i f o r n i a , R i v e r s i d e , USA



P h y s i c s D e p t . , P u r d u & U n i v . , W e s t L a f a y e t t e , USA

L a b . f ü r H o c h e n e r g i e p h y s i k , u . - i i v . B e r n , S c h w e i z

DESY, H a m b u r g , D e u t s c h l a n d

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P . S c h l a t t e r T R I U M F , V a n c o u v e r , C a n a d a

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G . Stampfl C E R N , G e n è v e , S u i s s e

J . S t i r l i n g C S 3 R N , G e n è v e , S u i s s e

F . S t o c k e r L a b . f ü r H o c h e n e r g i e p h y s i k , U n i v . B e r n , S c h w e i z

G . S t u c k i L a b . f ü r H o c h e n e r g i e p h y s i k , U n i v . B e r n , S c h w e i z

L . T a u s c h e r P h y s i k a l i s c h e s I n s t i t u t , U n i v . B a s e l , S c h w e i z

G . T h e o d o s i o u P h y s . D e p t . , U n i v . o f P e n n s y l v a n i a , P h i l a d e l p h i a , U S A

D . T h e r i o t F e r m i l a b , B a t a v i a , I L , U S A

G . T h o m p s o n P h y s i c s D e p t . , Q u e e n M a r y C o l l e g e , L o n d o n

J . T i m m e r C E R N , G e n è v e , S u i s s e

A . T o i l e s t r u p F e r m i l a b , B a t a v i a , I L , U S A

S. T o v e y C E R N , G e n è v e , s u i s s e

G . V i e r t e l I n s t i t u t f ü r H o c h e n e r g i e p h y s i k , E T H - Z ü r i c h , S c h w e i z

C P . W a r d C a v e n d i s h L a b . , U n i v . o f C a m b r i d g e , G B

A . W e i d b e r g C E R N , G e n e v e , S u i s s e

R . W i l s o n D e p t . o f P h y s i c s , H a r v a r d U n i v . , C a m b r i d g e , M A , U S A

D . W y l e r E T H - Z ü r i c h , S c h w e i z

H . Z a c c o i i e C E N , S a c l a y , G i f - s u r - Y v e t t e , F r a n c e

L . Z a n e l l o I s t i t u t o d i F i s i c a , U n i v . d i R o m a , I t a l i a

W . Z e l l e r L a b . f ü r H o c h e n e r g i e p h y s i k , U n i v . B e r n , S c h w e i z

Í

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