Mike AlbrowRencontre de Blois May 2005QCD and Hard Diffraction at the LHC 1 Introduction: QCD at the...

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1Mike Albrow Rencontre de Blois May 2005QCD and Hard Diffraction at the LHC

QCD and Hard Diffraction at the LHC

Introduction: QCD at the Tevatron (overview)

The High Q^2 Frontier: Jets, tops, W/Z, Q or X?

LHC: A new arena for QCD. Detectors

Very High Mass Diffraction

High Mass “Central Production” (a.k.a. DPE)

The FP420 Project

Recent QCD studies at the Tevatron (CDF & D0)

Every interaction is QCD!+ - + -{Exception: pp p e e p, p W W p}!

In May 2003 – May 2005 CDF (D0) published 43 (10) “QCD” papers:

pp and pp

other topics to follow...

... even that!

JETS: Production cross section (E ,η, s) and α ( )

Jet Algorithms: cone, k

Jet shapes/structure: n , fragmentation, q/g differences, c/b content

3-jet events and α ( )

0 (')S

Particle production cross sections (tot, p , η, s)

Strongly interacting: K , Λ, c(D), J/ψ , B, BB, , t t

Not S.I. : γ, e e , W, Z, (& F-B assymetries), VV (all 6 combs)

0 0 * + -S

Hadron decays (B-hadrons, lifetimes τ and BR's) :

B , J/ψ ; B had, γX, J/ψX, J/ψK π π

( / )J

Hadron spectroscopy :

(3872) J/ψ

(D -D )

B J/ψ π (CDF discovery)

Pentaquark searches (negative)

Underlying event:

n ,p etc in soft vs hard collisions

... in jet events

[in WW, (in general in V and VV events)]

Diffraction / rapidity gaps:

Diffractive production of dijets, J/ψ

DPE inclusive [GXG], double gaps:[xGxGp]

QCD Topics in TeVPublicationsMay 03 – May 05

JETS: Production cross section (E ,η, s) and α ( )

Jet Algorithms: cone, k

Jet shapes/structure: n , fragmentation, q/g differences, c/b content

3-jet events and α ( )

Angular (or y) distributionswell fit (log scale!) ... buty = 2.4 still “central”

Below 50 GeV mostly gg (at y=0)Above 400 GeV mostly q-qbar

Can study g and q fragmentationAt LHC pp p JJ p ~ pure gluons

1~ Run 2 expectation

Cone algorithm

Run 152507 Evt 1222348

All hits/tracks tracks pT > 2 GeV/c

At the top of the spectrum:

618 GeV

552 GeV

CDF kT algorithm

Here is a beautiful 3-jet event!

155 GeV

402 GeV

444 GeV

Tp (tracks) > 2 GeV/c

ET > 0.5 GeV

Run/Event 162498/4411694

Projected Jet Cross Sections at LHC

Spectra drawn to few/100GeV bin in 100 fb^-1

Let us hope these are quite wrong:Peak(s), excesses, cut-off (black hole production?) --- the end of high pT physics!

Coverage in (x,Q2) extended by more than an Order of Magnitude

Smallest x requires veryforward detectors:

2 8 2 1810 GeV d 2.10 cmQ

EVENTSHOWN

Production Cross Sections Rise Strongly with Energy

(Except at fixed x)

~ 1 top/secat 10^33

BFKL and Mueller-Navelet Jets

Color singlet (IP) exchange between quarksEnhancement over 1g exchange – multiRegge gluon ladderJets with large y separationn minijets in between (inelastic case)large gap in between (elastic case)

TMeasure fn(η, p , s, Δη)Fundamental empirical probe of new regime:non-perturbative QCD at short distances.

Cross section enhanced

4 ln 2α 0.5 for α 0.19

~ ln ~ 3 4

Very forward calorimeters OS

Berger, Qiu, Wang, hep-ph/0404158

D0 Run II Y-production

Cacciari, Frixione, Mangano, Nason, Ridolfi, hep-ph/0312132

CDF B-hadrons Run IICDF, hep-ex/0412071

TeV 03-05T

0 (')S

Particle production cross sections (tot, p , η, s)

Strongly interacting: K , Λ, c(D), J/ψ , B, BB, , t t

Not S.I. : γ, e e , W, Z, (& F-B assymetries), VV (all 6 combs)

0 0 * + -S

Hadron decays (B-hadrons, lifetimes τ and BR's) :

B , J/ψ ; B had, γX, J/ψX, J/ψK π π

( / )J

SFirst Observation B

5SBR(B ) [1.4 0.6(stat) 0.2(syst) ± 0.5(BRs)] 10

u,c, t

Penguin diagram

TeV 03-05

CDF-7142

0 + - 6dBR (B π π ) = 5 ×10

Rare Charmless B decays

0 0* -5dBR (B K ) =1.1×10

At LHC: LHC-B +ATLAS/CMS?

Hadron spectroscopy :

(3872) J/ψ

(D -D )

B J/ψ π (CDF discovery)

Pentaquark searches (negative)

*Future : ,c c cB B B

pQCD !

cIP(gg)IP(gg) B BDX ?

TeV 03-05

Probing Very Small x Gluons

High parton densitiesNew phenomena (gluon saturation)HERA measures q(x) to ~ few 10^-5 g(x) by evolution, charmLHC : measure g(x) to < ~ 10^-5more directly

Instrument few degree region with tracking, calorimetry (em+had), muons, , jets, photons ... CASTOR, TOTEM

1 2 1 21 2

0T 1 2

e.g. s=14 TeV, p = 5 GeV, y = y =4 (2.1 )

x 0.08, 1.4 10

y y y yT Tp pe e e e

Underlying event:

n ,p etc in soft vs hard collisions

... in jet events

[in WW, (in general in V and VV events)]

CDF study: charged particles transverse to high pT jets

TeV 03-05

Beyond Single Parton Distributions

Double and multiple parton scattering

Hint at ISR (4 “jets”), Seen in UA2 and CDF γ + JJJ

(qg) + (qg) cc/bb

& Double Drell-Yan : diquarks – anti-diquarksCorrelations in b (impact parameter) and x

Diffraction / rapidity gaps:

Diffractive production of dijets, J/ψ

DPE inclusive [GXG], double gaps:[xGxGp]

But before May 2003:

dσ dσσ , , (SDE)

dt dM dtSDE JetJet,J/ ,b,W,Z

DPE JetJet

Jet-Gap-Jet [JGJ]

TeV 03-05

Categories of Diffraction at LHC

s2ln 19.2 (cf 15.2 at Tevatron)

Can have a 4-unit gap with 2 TeV SD

Can have (VF)J – G6 – (VF)J

Can have 2 x 3-unit gaps with 700 GeV DP

Can have p-G3-X-G3-X-G3-p with M(X) ~ 12 GeV

Google tev4lhc

Fermilab Sept 2004BNL Feb 2005CERN Apr 2005Fermilab Fall 2005

Very small person (?)

A “QCD machine”, especially if add forward detectors!

CMS at LHC

Bigger people!

(MWPC TRACKING) CASTOR

Detecting Protons with xF > 0.9

K.Eggert’s talk

u-loop : γγ c-loop : χ

b-loop : χ t-loop: H

Central Exclusive Productiongg fusion: main channel for H production.

Another g-exchange can cancel color, even leave p intact. p p p + H + pTheoretical uncertainties in cross section, involving skewedgluon distributions, gluon k_T, gluon radiation, Sudakov ff etc.Probably ~ 0.2 fb at Tevatron, not detectable, but should be possible at LHC (higher L and ~ 3 fb?)

( )SMH

0 0c b

Theory can be tested, low x gluonic

features of proton measured with

exclusive γγ, χ and χ production.

at Tevatron

100 x Acc events in 30 pb^-1

Central Exclusive Higgs Production

Can be inclusive (soft central hadrons) but exclusive (nothing else)is most interesting. Precision measurement of both p M(central) by MM

Possible resolutions (~ 250 MeV at Tevatron) ~ 2 GeV at LHC.

Can go for dominant H(110-130) b-bbar decay mode

Exclusive DPE q-qbar dijets strongly suppressed (Jz = 0 rule)

Selection Rule on central Q.Nos:Scalar ... p correlations confirm (need statistics!)

Non-SM H interesting!

G PC + ++

I J = 0 0 dominant esp. as t 0

I J = 0 2 next

2 2central 1 2 3 4M ( - - ) ; 4 - vectorsip p p p p

Acceptances vs Mx for p + p p + Mx + p

In addition to 215m (TOTEM)420m detectors are

essential for Mx < 400 GeV... region of H, WW, ZZ

Both ATLAS & CMS want this.Join forces: FP420 project

LOI for R&D LHCC June 05

FP420 = Forward Protons at 420 m

Groups in ATLAS and CMS/TOTEM want to addvery forward proton detectors, mainly to study “DPE”, central production.Central states especially : WW, ZZ, H, bb, t t, jet-jet, X ...

Valentina Avati

Inelastic protons bent few mm out of beam6mm x 24 mm detector (e.g. Si pixel)

Albert De Roeck

Diagrams for Prompt VV Pair Production in pp/ppbar

Note different color flows in thesediagrams can give differenthadronic activity.(a) and (b) have color 3 annihilation(d) has color 8 annihilation(c) and (e) have color singlet exchange. (c) high pT q – forward jets; (e) low pT p’s – no jets, can be exclusive

(Prompt i.e. not from top and not from Higgs)

a) Any 0,1 pair. 90% of WW at TeV, less at LHC

b) Only γW, WW, WZ

c) Any pair (even W W ).

Negligible at Tevatron, larger at LHC

d) Negligible

e) Eventually dominant if White is right!

Also γγ ~ 100 fb

Discriminant : t , t

Cross section for WW Production: Energy Dependence

Tevatron cross section agrees with CTEQ NLO

Tev2 sig(ZZ) = 1.39 pbsig (ZW) = 3.65 pbsig WW = 12.4 pb

LHC ~ 10 x higher

If Tevatron RoT apply,At LHC :SD, ~1% ~ 100 fbDP, ~ 10^-3 ~ 10 fb

i.e. Guesstimate for DPE WW (ZZ) + anything ~ 10 (1) fb

Central Exclusive WW Production at LHC

+ - + -

2 2 21 2 3 4 H

H(160) W W p e μ p

MM ( ) M

p p p p

Nothing else on 2-lepton vertex!μ

+ White Pomeron search

2 2invisible 1 2 3 4 visible

See invisible Z νν e.g. in H ZZ

M ( - - )

Distinguish ZZ

from WW

p p p p p

Also W W

Double Pomeron W+W- via Q6 Loop

Photon-Pomeron-Z vertexvia Q6 loop

Photoproduction at LHC?pp {p Z p}γ IP

~ 0 in SM

Summary

Tevatron is, and LHC will be, a cornucopia of QCD physics

At LHC, 2 2Q ~ 0.001 ~ 50,000,000 GeV

Jets, W, Z, b, c, production, spectroscopy, decaysand especially:

rapidity gaps, exclusive production of jets, H, WW, ZZ, BSM

Very Forward Proton Detection – New window on strong and electroweak interactions

Mike AlbrowRencontre de Blois May 2005QCD and Hard Diffraction at the LHC 1 Introduction: QCD at the...

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