S T A N F O R D L I N E A R A C C E L E R A T O R C E N T E RSpring 1998, Vol. 28, No.1

SPRIN G 1998

A PERIODICAL OF PARTICLE PHYSICS

SPRIN G 1998 VOL. 28, N UMBER 1

EditorsRENE DO NALDSO N, BILL KIRK

Contribu ting EditorsMICHAEL RIORDAN , GORDO N FRASER

JUDY JACKSO N, PEDRO WALOSCHEK

Editorial Advisory BoardGEORGE BROWN, LAN CE DIXO N

JOEL PRIMACK, NATALIE ROEROBERT SIEMAN N , GEORGE TRILLIN G

KARL VAN BIBBER

IllustrationsTERRY AN DERSO N

Distribu tionCRYSTAL TILGHMAN

The Bea m Line is published quar terly by theStanford Linear Accelerator CenterPO Box 4349, Stanford, CA 94309.Telephone: (650) 926-2585IN TERNET: bea mline@slac.stanford.eduFAX: (650) 926-4500Issues of the Bea m Line are accessible electronically onthe World Wide Web at h t tp:/ /w ww.slac.stanford.edu /pubs/beam lineSLAC is operated by Stanford Universi ty u nder contractwith the U.S. Depart ment of Energy. The opin ions of theauthors do not necessarily reflect the policy of theStanford Linear Accelerator Center.

Cover:The cover photo was taken in 1917, plus or minusabout one year. The photographer is unknown or unre-membered. The young lad shown in the photo with histelescope in the garden of hishome in Pretoria, South Africa, isAlan Cousins, at the age of aboutfourteen (he was born in 1903).

Dr. Cousins’ first contributionto the astronomical literature waspublished in 1924. Seventy-fouryears have passed since then,but Alan William James Cousinsis still at work at his home base,the South African AstronomicalObservatory (SAAO), havingrecently published his latest paper (“Atmospheric Extinc-tion,” The Observatory, April 1998). He will be 95 inAugust of this year, continuing a long life among the stars.Happy birthday!

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BEA M LINE

FEAT U RES

2 ALL WE WAN T IS THE WORLD’S BIGGESTMACHINE!O ne of our Contribu ting Editors follows upon his article in the last issue on the originsof internat ional collaboration in Europeto describe the creation of CER N.Gordon Fraser

9 SEARCHING FOR NEUTRIN OOSCILLATIO NSThe au thor describes w hy understandingneutrino oscillations m ight be criticalto the question of whether neu trinoshave m ass.Maury Goodman

17 PHYSICS WIT H CHARMA Ferm ilab physicist describes why t he studyof the charm quark m ight open the way

to physics beyond the Stan dard Model.Jeffrey A. Appel

DEPA RTMEN TS

22 THE U NIVERSE AT LARGEThis Was the Year That Was(Astrophysics in 1997)Virginia Trim ble

31 CO NTRIBUTORS

DATES TO REMEMBER

C O N TEN TS

2 SPRIN G 1998

All We Wan t Is t hContributing Editor

Gordon Fraser follows

up on his piece on the

origins of in ternational

collaboration in Europe

(Winter 1997) to describe

the creation of CER N.

This article is adapted

fro m a chapter in his

book The Quark

Machines on the polit i-

cal history of particle

physics and the parallel

evolution of its big

machines.

Isidor Rabi had proposed the idea of aEuropean physics laboratory at a

UNESCO conference in Florencein June 1950. The signatories to the

initial 1952 agreement to establishCERN sent him this letter.

BEA M LINE 3

BETWEEN 1949 AN D 1959, t he dream of an in ternational European laboratoryfor par ticle physics—‘CERN’—became a reality, briefly sporting the world’s highestenergy proton synchrotron. In those ten years, scien tists from coun tries that had been

a t war on ly a few years earlier se t aside t heir differences and collabora t ed in a dra m at icdemonstration of what could be achieved when national characteristics dovetail smoothly inthe achievement of a com mon goal. The ideals and insights of CERN ’s founding fathers providevital lessons in the con tinued quest for wider in ternational collaboration in par ticle physics.

World’s Bigges t Machine!by GORDO N FRASER

Scientific objectivity is a com mon bond betweenna tions. In every cou n t ry, scien t is ts address t hesame problems. If one nation hushes up its researchfindings, the knowledge will ultimately be acquiredelsewhere. Scien tific curiosity cannot be quenched.In the after math of World War II, science was seenas a poten tial olive branch. However the war hadshifted much of the scenery. Major effor ts to har-ness fission and microwaves had demonstrated thevalue of large-scale collaboration. Militan t nation-al pride had given way to new in ternational aware-ness. Embarrassed by having caused so m uch strifeand inflic ting i t on the res t of the planet , Europefelt i t had to presen t a more united fron t.

The United States, as t he leading post war sci-entific power, a t tracted scientific emigrants fromEurope in w hat would even t u ally be called t he“brain drain.” Th is leak first had to be stem m edif the Continent was not to find itself starved of tal-ent. Following the Congress of Europe in The Haguein May 1949, t he European C ult ural Conferencein Lausanne in December 1949, at tended by 170 in-fluential people from 22 countries, helped set thestage.

At Lausanne, the Swiss writer Denis de Rouge-mont, founder of the European Cultural Centre, de-plored an increasing trend towards secrecy in nu-clear physics and advocated a “European centre forato mic research.” T hen Raoul Dau try, Adminis-t rator-General of t he Frenc h A to m ic EnergyCom mission, read a message from Louis de Broglie,

winner of the 1929 Nobel prize for his elucidationof particle waves. De Broglie main tained that sci-entific collaboration between European countriescould open up projects that were beyond the meansof individual nations. Following up with his ownideas, Dautry affir med that as tronomy and astro-physics on one hand, and atomic energy on the oth-er, would be ideal vehicles for such in ternationalcollaborat ion.

Dau t ry could call on powerfu l colleagues inFrance. One was Pierre Auger, who had made im-portant contributions to atomic and nuclear physicsin the 1930s and became Director of Exact and Nat-ural Sciences of the new United Nations Educa-tional, Scien t ific and C ul t ural Organiza t ion(U NESCO). Another prominent French figure wasn uclear fission pioneer Lew Kowarski, who hadworked in Britain during the war and u nderstoodthe special position of the United Kingdom, whichwas trying to “go it alone.”

At t he U NESC O General Conference held inFlorence in June 1950, however, the seed planted atLausanne still lay dormant. In the U.S. delegationwas Isidor Rabi, winner of the 1944 Nobel physicsprize who had supervised research at the MIT Ra-diat ion Laboratory during t he war. After t he warRabi, with Norman Ramsey, had pushed for the es-tablish m en t of a major new U .S. research labora-tory, Brookhaven, on New York’s Long Island. InRabi’s mind this was a role model for what couldbe achieved elsewhere.

4 SPRIN G 1998

Upon arriving a t Florence, Rabiwas su rprised to discover t hat t heagenda included no m en tion of theEuropea n physics collabora t ionmooted at Lausanne. Setting up phys-ics laboratories was something Rabiknew well, bu t in ternational co m-mit tee work was not. The first thingwas to get an item onto t he agenda,overcoming the apparent indifferenceof h is A m erican colleagues. Morehelpful were Auger and t he Italianphysicist Edoardo Amaldi, who hadworked in Enrico Fermi’s Rome lab-oratory before the war. Invited to theUnited States by Fermi, Amaldi pre-ferred to stay in Italy and help restoreItalian physics after t he chaos of thewar. Amaldi went on to become oneof Europe’s great post war scien tificstatesmen, his achievements appear-ing to stem from a deep sense of dutyrather than personal ambition.

Draft ed wit h t he assis tance ofAuger and Amaldi, the proposal fromRabi at Florence requested U NESC O“to assist and encourage the forma-t ion and organ izat ion of regionalresearch cen tres and laboratories inorder to i ncrease an d m ak e morefruitful the international collabora-t ion of scien tis t s in t he search fornew k nowledge in fields where theeffor t of any one coun try in t he re-gion is insufficient for the task.” Rabipointed out that the initiative “ wasprimarily intended to help coun triesw hic h had previo usly m ade grea tco n t r i b u t i o n s t o sc i e n c e, ” a n dt h a t “ t he crea t ion of a cen t r e inEurope . . . migh t give the impet usto the creation of similar centres ino t her par ts of t he world.” T hemotion was unani mously accepted.Where Europeans had failed to reacha consensus, an American resolution

for Europe at a m eeting of a UnitedN at ions agency had opened a newdoor.

The two men who took Rabi’s ba-to n and sprin ted wit h i t were jus tthose who had helped him draft t heFlorence resolu t ion—A m aldi andAuger. Just a few weeks later, Amaldiwas sti m ulated by a visit to Brook-haven, where t he Cos m otron wasalready taking shape. Few Europeanshad ever seen a physics effort of suchpropor t ions. “ Colossale, ” he re-marked.

Under t he auspices of t he Euro-pean Cultural Centre, a meeting wasorgan ized in Geneva in Dece m ber1950 wit h delegates from Belgiu m,France, Italy, the Netherlands, Nor-way, and Switzerland. Auger u n-veiled a plan for a n ew labora torydedicated to the physics of elemen-tary par t icles. He k ne w t ha t in-triguing new discoveries had alreadybeen made in cosmic rays, bu t t hatthis windfall sprouting could becomea major harvest once the big new U.S.accelerators were up and running.

Initial contacts wit h Britain hadestablished t hat while its physicistswere not against the idea of a Euro-pean laboratory, they still wanted togo their own way. Their support wasvi tal to get the idea off t he ground,however, as in Europe only Bri tainhad experience in major projects. Pos-sible si tes m en t ioned for t he n ewEuropean laboratory included Gene-va and Copenhagen.

T he resolu t ion passed at t heGeneva m eet i ng was st ar t ling. Itrecom m ended t he creation of a lab-oratory for t he cons tr uct ion of apar t icle accelera tor w hose energyshould exceed those of machines cur-rently under construction elsewhere

Edoardo Amaldi in 1971 at the age of 63.One of Europe’s leading postwarscientific statesmen, he played a keyadministrative role in the founding ofCERN. (Courtesy CERN)

BEA M LINE 5

(which meant the mighty 3 GeV Cos-m otron and t he even bigger 6 GeVBerkeley Bevatron). In a field where,apart from Britain, Europe had no tra-dit ion and li t t le expertise, the planwas simply to ju mp into the lead bycash and enthusiasm. These bold pro-posals were enthusiastically endorsedin Italy, Belgiu m, France, N orway,Sweden, and Switzerland. In Britain,where physicists were busy buildingseveral new accelerators, there wasastonishment and skepticism. “Whois beh ind the sch e me?” t hu nderedP. M. S. Blackett, “Is it serious?”

A study group to define t he newaccelerator included Cornelis Bakkerfrom the Netherlands, who had builta synchrocyclotron at Amsterdam,Odd Dahl from Norway, a talen tedengineer responsible for the first nu-clear reactor to be built outside theoriginal “ nuclear club,” and FrankGoward, a British physicist who hadgraduated in to wartime radar work.In a flush of modesty after the initialst riden t proclam at ion, t he new ad-ver tised goal was to copy the 6 GeVBerkeley machine instead of the orig-inal idea of bu ilding t he world’slargest machine.

One suggestion was to use NielsBohr’s laboratory in Copenhagen asa home for the new institute, an ideat hat also found favor in Bri tain, andnaturally stim ulated interest in Nor-way and Sweden. Bohr, who had notbee n par t y to t he previous discus-sions around the Auger-Amaldi axis,began to exert h is considerable in-fluence. Others though t that he waspast h is prim e. T he re m oteness ofCopenhagen and the difficulty of theDanish language were also a deterrent.

To sidestep the challenge of goings traigh t for t he world’s largest

mach ine, a newplan envisioneda s m aller in i t ialmachine to launcht he new laborato-ry. Proposals werepu t forward for a500 MeV synchro-cyclotron an d a 5GeV pro to n syn-chrotron, wit h de-sign and construc-tion proceeding inparallel. Europeanphysicist s seem edopt i m is t ic abo u tgovern ment fund-ing. On the question of the site, newcrit eria, designed t o u nder m i neCopenhagen’s case, stipulated the useof a major language.

A N ove m ber 1951 m eet ing i nParis suggested that t he energy goalof t he new synchrotron could be ashigh as 10 GeV, bu t t o defuse t het hor ny si t ing issue, the respect ivegroup leaders would remain at theirhome bases—Dahl in Norway work-i ng on t he synchrot ron, Bak ker inThe Netherlands on the synchrocy-clotron, Kowarski in France on in-frastructure, and Bohr in Copenhagenon t heory, wit h Am aldi’s adm inis-trative hub in Ro me.

A meeting at Paris that Decemberbrought represen ta t ives toge t herfrom thir teen European nations, in-cluding West Germany. The Nether-lands delegation put forward a five-fold plan, wit h two poin ts designedto appeal to the Northern faction, ex-pressing interest in using the exist-ing Copenhagen center and Britain’saccelera tors, a nd t he re m ain ingpoin ts designed to appeal to Franco-It alia n sen t i m en t , cover i ng t he

In 1951, before a site for the new labora-tory had been chosen, Odd Dahl ofNorway (standing) was appointed headof CERN’s proton synchrotron group andCornelis Bakker of the Netherlands(seated) head of the synchrocyclotrongroup. After a trip to the U.S. in 1952where he learned of the invention ofstrong focusing, Dahl wisely pushed forthe CERN synchrotron to adopt the new,as yet untested technique. But with thedecision to build the machine inGeneva, Dahl retired from the project in1954. In 1955, following the resignation ofCERN’s first Director General, FelixBloch, Bakker succeeded him.(Courtesy CERN)

6 SPRIN G 1998

longer appropriate. However nobodycould t hink of a bet ter acronym, es-pecially when it had to have multi-lingual appeal, and CERN has stuckever since. With t he four groups dis-persed and Amaldi still in Rome, theorganization advanced only slowly.

A m ajor in ternat ional physicsmeeting at Copenhagen in June 1952heard that the first beams had beenproduced by the new Cosmotron. ACERN Council meeting im mediatelyadvocated that Dahl’s group ai m fora scaled-up Cosmotron to operate inthe energy range 10–20 GeV.

To m ake their scaled-up versionof the Cosm otron, t he group need-ed to go to Brookhaven and inspectthe new machine. That August, Dahland Goward made the trip. Also pass-ing through was accelerator pioneerRolf Wideröe, t he n working onbetatrons. To receive their Europeanvisitors, M. Stanley Livingston hadorgan ized a t hi nk t a nk. T he Cos-motron’s C-shaped magnets all faced

construct ion of t wo new machinesand t he es tablish m e nt of a “Euro-pean Council for N uclear Research ”—in French “Conseil Européen pourla Rec herche N ucléaire.” T heacronym CERN was born.

T he m eet ing was con t in ued i nFebruary 1952 in Geneva, where theprovisional CERN Council was askedto prepare plans for a laboratory. Theproposal was im mediately acceptedby Ger m an y, t he Net herlands an dYugoslavia, and accepted subject tora t ifica tion by Belgiu m, Den m ark,France, Greece, Italy, Norway, Swe-den, and Switzerland. Den mark of-fered the new Council the use of thepre m ises a t t he Ins t i t u te of T heo-ret ical Physics of the U niversity ofCopenhagen. While this meeting wasa major step forward, the enigmaticBritish were not even present.

Emphasis switched from negoti-ation to organizat ion and planning.Wit h the new organization open forbusiness, the word “Council” was no

An early CERN Council meeting in 1953.Left to right, Jean Bannier representingThe Netherlands, and Pierre Auger andJean Mussard of UNESCO. (CourtesyCERN)

BEA M LINE 7

ou t wards, m aking i t easy for nega-t ively c harged par t icles to be ex-tracted, bu t not positive ones. “Whynot have the magnets alternately fac-ing inward and out ward?” suggestedLivingston. Ernest Courant, HartlandSnyder, and John Blewet t seized ont he suggestion and quickly realizedt ha t t h is increased t he focusingpower of t he m agnets. The new sug-gestion, variously called “strong fo-cusing” or “al ter nat ing gradien t,”m ight allow t he proton beam to besqueezed in to a pipe a few centime-ters across, instead of the 20×60 cen-t i m e ters of t he Cos m otron bea mpipe. T he rela t ive cost of t he sur-rounding m agnet, t he m ost expen-sive single item in synchrotron con-struction, would be greatly reduced.

T he European visitors arrived atBrookhaven prepared to learn how tomake a replica of the Cosmotron anddiscovered inst ead t hat t he designhad suddenly become outdated. This1952 visi t se t t he tone for t herela t ionship bet wee n t he n ewEuropean generation of physicists andt heir American cou nterparts. Basedon m utual respect and colored by ahealthy spirit of competition, this re-lationship was to work to their m u-t ual advan tage. Un te m pered, com-pet i t ion can lead to jealousy andsecrecy, bu t in particle physics thishas rarely occurred. Alt hough eachside has striven to push its own petprojects, collaboration and assistancehave always been available, and thecom munity as a whole welcomes andadmires breakthroughs and develop-ments, wherever they may be made.

Dahl was adam ant that t he newstrong-focusing technique had to beused for t he CER N m ac hine t heywere planning. It would open up the

prospect of at least 20, and possibly30 GeV, and save money. T he onlyproble m was t hat nobody had builtone yet. Although a gamble, takingthis unexplored strong-focusing routeturned ou t to be one of the most im-portant decisions in CERN’s history.In Britain, t he s trong-focusing pro-posal gave a new appeal to the Euro-pean project. The traditional nationalapproach and the more ambitious in-ter nat ional ve n t ure beca m e co m-plementary. However before Britaincould be persuaded to join CERN , keyfigures had to be convinced, includ-ing t he for m idable Lord Cher well,Winston C hurchill’s stau nch friendand scientific advisor.

In Dece m ber 1952 EdoardoAmaldi was given a frosty receptionby Cherwell in London. Within min-utes, Cherwell told Amaldi in no un-certain terms t hat he was skepticalof the CER N idea. U ndeterred,Amaldi wanted to m eet some of theyoung Bri tons who m igh t be in ter-ested in joining Dahl’s group. Dele-gated to drive Amaldi from Londonto Harwell was John Adams, a youngengi neer w ho had m oved to syn-chrotron development after wartimeradar work. At Harwell, Amaldi metothers who were working on both theCER N m achine design and a m ajornew British machine.

With the national m achine com-mit ted to the old weak-focusing de-sign, Adams and colleagues had beentaking a close look at s trong focus-ing, and discovered t hat t he ini tialidea was optimistic. Small errors int he m agnets—tiny m isalign m en tsand field variations—would be nat-urally amplified and might cause thebeam to blow up. To allow for thispossibility, the aperture of the strong

Fate led British engineer John Adams tobecome head of CERN’s protonsynchrotron project in 1954 at the age of34. Under his inspired leadership, CERNwas to fulfill the dreams of its foundingfathers. (Courtesy CERN)

8 SPRIN G 1998

Dubna Synchrophasotron a t taining10 GeV, and even by Britain’s 1 GeVsync hrot ron at Bir m ingha m. Eyeswere focused on the race between thet wo pro ton synchrot ron t ea m s atBrookhaven and CERN .

O n N ove m ber 4, 1959 , CER N ’snew proton synchrotron unexpect-edly accelerated protons all the wayto 25 GeV, beco m i ng t he world’shighest energy machine, easily out-stripping Dubna’s 10 GeV. The CERNtea m was jubilan t, a nd e m ot ionaland dramatic scenes offered a sharpcon tras t in nat ional s tereot ypes.Gilberto Bernardini from Italy jubi-lantly kissed a disconcerted Adams

focusing m achines would have to belarger t han t he Brook haven p hysi-cis t s had in i t ially sugges t ed. Toaccom modate a larger tube, t he en-veloping m agne t had to be m uchlarger too, and the design energy oft he CER N m achine was co m pro-mised to 25 GeV.

In parallel wi t h t hese techn icaladvances, t he Bri t ish suddenlyswitc hed from aloofness a nd for-mally joined CERN , which finally de-cided on Geneva as t he si te for t henew laboratory. On the map, the can-ton of Geneva appears as a curiousappendage at t he ext re m e west ofSwitzerland. Al m ost to tally sur-rounded by France, it is joined to therest of Switzerland by an u mbilicalcord a few kilometers across. Begin-ning with the Red Cross in 1863, thecity of Geneva has become the homeof many international organizations.

An advance par ty of the pro tonsynchrotron group arriving in Genevawas joined by Joh n and HildredBlewet t from Brookhaven. After be-stowing crucial insigh ts, Dahl pre-ferred to remain in Bergen, first ap-point ing Goward as h is on-si tesupervisor, and finally resigning fromt he new project. Just a few mon t hslater, in March 1954 and only 33 yearsold, Goward died of a brain tumor. Atthe tender age of 34, Adams becameleader of CERN’s proton synchrotronproject . Fate had provided t he newproject with its leader. John Adamswas to be the Moses who would takeCERN into the Promised Land.

CER N ’s firs t mach ine, t he 600MeV synchrocyclo tron, was com -m issioned in 1957 a nd soon beganproducing useful physics. Howeveri t was far ou tgu n ned by t he Cos-motron and Bevatron, by the big new

on both cheeks. The laconic Adamsphoned Alec Merrison, who later re-called, “He did not tell me in highlyexcited tones. He said ‘Re m e m berthose scintillation coun ters you andFidecaro pu t in t he ring? Will t heydetect 20 GeV protons?’ I paused longenough to grab a bot tle of whisky andProfessor Fidecaro, in that order, andcame along to celebrate.”

T he followi ng day, at a specialnews meeting for CERN staff, Adamsshowed a vodka bot t le he had beengiven several months earlier on a tripto Russia with strict instructions thatit should be drunk when t he CER Nsynchrotron surpassed Dubna’s en-ergy. The bot tle was now empty.

But Dubna’s vodka bot tle was notthe only unfilled thing at CERN . Alsovery em pty were t he experi m en talhalls around the new synchrotron. Inthe rush to build the new machine,few people had paid at ten tion to theinstrumentation needed to carry outexperi m en ts. At Brook haven, t henew Alternating Gradien t Synchro-tron (AGS), the twin of the new CERNmachine, did not accelerate a beamuntil six months later. Bu t this delaywas more than compensated by theenthusiasm and ingenuity that wentin to plan ni ng experi m en ts. U .S.physicists had cu t their high energyaccelerator teeth on the Cosmotronand the Bevatron. Within a few yearsof its com missioning, the AGS reapedan impressive harvest of i mportan tnew physics results.

CERN had risen to the challengeof building t he world’s most power-ful m ach ine fro m scratch in jus t afew years, bu t developing researchinfrast ruct ure and fostering experi-m en tal prowess was to take som e-what longer.

On November 24, 1959, CERN’s protonsynchrotron accelerated protons to25 GeV and briefly became the world’shighest energy accelerator. Here ajubilant Gilberto Bernardini from Italyembraces John Adams.

Search ing for N eu t rinoOscilla t ions

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HYSICISTS FROM AROU N D theworld are engaged in a wide variety of ex-perim ents to deter mine whether neu trinoshave m ass. T his possibility has intrigued

physicists and cosmologists for two decades, ever since neu trinos emerged asa leading candidate for the dark mat ter though t to inhabit the Universe. Acomprehensive new experimen t is being buil t in Illinois and Minnesota tostudy neutrinos from an in tense new Fer milab beam impinging on a detector500 miles away. It is one of the most ambitious of a new round of experi-ments being planned and proposed to search for neu trino oscillations, aprocess in which neutrinos can transfor m from one kind into another—ifthey have mass. A positive result could have implications for the density ofthe Universe, as well as for the generation of energy by the Sun.

Often, given a well-defined physics problem, one or two well-designed ex-periments can answer the question one way or the other. Bu t this is not t hecase for neutrino mass, because there are three differen t kinds of neutrinosand a wide range of possible mass scales. This situation has led physicists to at-tempt a large number of experiments that are quite different from each other.

In this article, I relate why so many physicists are excited by neutrino-oscillation experiments. First, I describe the properties of neu trinos them-selves. Then I cover some of t he experimental hints supporting neu trinooscillations. Finally, I close with a description of the Fer milab-to-Soudan,Min nesota, long-baseline neutrino project, an ambitious program to searchfor changes in the properties of a neu trino beam as it speeds silen tly beneaththe far ms and prairies of the American Midwest.

by MAURY GOODMAN

Experiments of the past forty years have revealedthree families of the ghostly particles called

neutrinos. Continuing studies hint that a neutrinoof one family might sometimes change into a

neutrino of a different family, by a mechanismknown as neutrino oscillation. The author describeswhy understanding this phenomenon might be criti-cal to the question of whether neutrinos have mass.

P

10 SPRIN G 1998

source of copious neutrinos, but I amnot aware of any experiment that hasdetected them.) Neu trinos are eitherm assless or far ligh ter t han t hequarks and ot her leptons. T his dif-ference might be related to the factt hat ne u t rinos have no elec triccharge, while the quarks and ot herleptons do have charge. The questionof mass remains one of the big mys-teries remaining in particle physics.T here is no clear predic t ion rela t-ing t he masses of t he nine chargedfermions, and none for whether theneutrino masses are zero or just verysmall.

However, most physicists expectthat if neutrinos do have mass, evena t iny amount, the phenom enon ofneu t rino osci lla t ions shou ld exis t(see t he box on t he opposite page).These transformations are closely re-la t ed to t he quan t u m -m echa nicalphenomenon of mixing. If neutrinososcillate, they can be produced in oneflavor, such as νµ, a nd be detec tedas anot her flavor, such as ντ , so m edistance away.

When Pau li predic ted t he exis-tence of the neutrino in 1930, he didnot suppose there wou ld be m orethan one kind. He was only trying toexplain the wide distribution of elec-t ron e nergies observed in n uclearbeta decay. The idea that neutrinoscome in different flavors became ac-cepted in 1962, when an experimentat Brookhaven National Laboratorydirected neu trinos from pion decayat a target and found t hat al most allof the events had a muon, and not anelectron, emerging from the point ofthe neu trino in teraction. This resultled to t he idea that each lepton fla-vor (e, µ, τ) has a conserved quantity—something that doesn’t change in an

T HERE ARE T HREE“flavors” of neu t ri nos, t heelec tron ne u t rin o νe, t he

m uon neu trino νµ , and t he tau neu-trino ντ . Each is closely related to thecorresponding lepton: t he electron,m uon, and tau lepton. These six lep-tons toget her wit h six quarks con-s t i t u te t he fu nda m e n t al “ m at ter ”par t icles of t he Standard Model ofhigh energy physics.

The three neutrinos in teract veryweakly wit h ordinary mat ter. Physi-cists originally thought that the greatweak ness of t he in teract ion wouldmake them impossible to detect, butneu tr inos have been see n co m i ngfrom accelerators, from nuclear re-actors, from cosmic-ray in teractionsin the at mosphere, from the sun, andfro m Supernova 1987A . ( N uclearweapon explosions are also t he

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Melvin Schwartz in front of the Brookhaven detector thatshowed experimenters in 1962 that the muon had its own

neutrino, different from the electron neutrino.Schwartz, Leon Lederman, and Jack Steinberger

won the Nobel Prize in 1987 for this discovery.(Courtesy Brookhaven National Laboratory)

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in teract ion—associa t ed wit h i t.When the pion decays, it almost al-ways becomes a m uon and a neutri-no and hardly ever an elect ron anda neutrino. The Brookhaven NationalLaboratory result could be explainedif t he π+ decays in to a µ+ and a νµ ;w hen they in teract wit h the targetnuclei, the νµ’s generate m uons, notelectrons.

When t he t hird lep ton, t he tau,was discovered a t t he Stanford Lin-ear Accelerator Center in 1975, it wasnatural to conjure up a third neutri-no, the ντ , to account for missing en-ergy in tau decays. In the 1980s physi-cists discovered and began producingcopious nu mbers of Z bosons; t hisparticle served as a neu trino counterbecause its decay rate is proportion-al to the number of fundamental par-t icles wi t h less t han half i t s m ass.Measure men ts of this rate a t CERNand SLAC confir m ed t hat t here areonly three neutrino-like particles inthe elementary particle zoo—a resultt hat had been predicted by cosmolo-gists. So far, t here has not been anyconvincing evidence that the ντ in-teracts wit h nuclei to make taus ina manner equivalent to the other twoneutrinos. But a current Fermilab ex-peri ment is expected to find these ντin teractions.

The two factors affecting neutrinooscilla tions (see adjacen t box) t hatare under the con trol of the experi-m en ter are t he neu t rino energy Eνand t he dis ta nce L betw een t heirsource and t he detector. T hese ap-pear in t he ra t io L/Eν, so an experi-ment designer needs a large distanceand low energies in order to measures mall values of the mass differencebetween two neutrino types. This re-quirement m ust be balanced againstthe fact that large distance and lowenergy bot h m ake i t more difficul tto detect a large nu mber of neutrinoeven ts.

Let’s go back to the Brookhavenexperi m en t t hat di scovered t hem uon neu tri no. If t he m ixi ngs t rengt h and m ass difference hadboth been large enough, that exper-i m en t would not have been able todiscover the νµ. It would have seenbot h elect rons and m uons co m ingfro m t he poin t of t he neu trino i n-teractions! We can use the success oft hat experim en t to place li m its onthe combination of the two parame-ters. We usually do this by making agraph in t he parameter space calledthe “∆m 2 − sin2 (2θ) plane,” these be-ing two parameters t hat specify themixing strength and mass difference(see t he box on t he nex t page). An

Probability of NeutrinoOscillations

IN ORDER TO MEASURE neutrinooscillations, the experimenter wantsthe probability that one neutrinotransforms into another to be as largeas possible. This probability is givenby

Pν1→ ν2= sin2(2θ12)sin2(1.27∆m2

12L/Eν),

where sin2(2θ12) is the mixing angle,∆m2

12 = m21 − m2

2 is the difference inmass squares of the two neutrinos, Lis the distance (in km) from theneutrino production point to the ex-periment, and Eν is the neutrino ener-gy in GeV. If either sin2(2θ) = 0 or∆m2 = 0, the phenomenon of neutrinooscillations does not exist. If all threeneutrinos are massless, ∆m2 = 0.

As a result of the above equation,the neutrino “oscillates” with astrength sin2(2θ) and an “oscillationlength”

Losc = _______

The oscillation probability varies assin2(πL/Losc). It is the sinusoidal na-ture which gives the name to“neutrino oscillations.”

1.27∆m2πEν

12 SPRIN G 1998

Si m ply pu t , five solar-neu tri noexperi m en ts have m easured asignificantly smaller nu mber of neu-t r ino i n t erac t ions t ha n expected,based on t he measured heat ou tpu tof t he Sun and nuclear physics mod-els of both the Sun and the detectors.Each experiment observed fewer neu-trinos than expected, but the act ualdeficit each measures depends on thedetecting medium and energy thresh-old. While it is not possible to explainthe data with alternate models of theSun, one can accoun t for all the datawit hin t he fra m ework of neu tri nooscillations.

As disc ussed in t he box onpage 11 , t he lengt h scale of a n ex-perim en t provides a possible oscil-lation length. There are two possiblescales for solar neu t rinos: t he dis-tance from the Sun to the Earth andthe radius of the Su n. Each lengt hscale leads to a separate neu tr ino-oscillation solution for the solar neu-trino deficit. One (labeled “vacuum ”in the illustrat ion on the left) arisesfrom a s t raigh tforward solu t ion oft he relat ionship bet ween neu trinomass and oscillations (see the box onthe left). The other solutions (labeled“ MSW ” after St an islav Mi kheyev,Alexei Smirnov, and Lincoln Wolfen-stein, who for m ulated t he relevanttheory) obey more complicated equa-tions that take into account the hugedensity and density gradients of mat-ter in the Sun, and how they can af-fect neutrinos emerging from its core.Both of t hese solu tions involve os-cillations of electron neutrinos intoother kinds.

The at mospheric neu trino deficittakes us underground to experimentsthat were originally built for anotherpurpose—to search for proton decay.

experi men t that is consistent wi t hsmall or no neutrino oscillations cor-responds to a curve in that plane thatexclu des t he values of m ixingstrengt h and mass difference aboveand to the right of the curve.

Since the early 1960s, neutrino ex-periments at Brookhaven, Fermilab,CERN , and the Institute for High En-ergy Physics a t Serpukhov, Russia,have grown from tens to thousandsto millions of neutrino events. Noneof these experi ments has witnessedevidence for νµ → νe or νµ → ντ os-cillations. And at the same time, ex-peri m en ts a t nuclear reactors havefound no evidence for νe oscillationsi n detectors si t uated up to a k i lo-me ter from the reactor. T he pub-lished lim its have steadily crept tolower val ues of t he neu tri no m ix-ing strengt h and mass difference.

BU T T HE STORY by nom eans ends t here. While ex-periments at reactors and high

energy accelerators have found noevidence for the m, four hin ts haveem erged suggest ing the real possi-bili ty of neutrino oscilla t ions andhence mass. These are the solar neu-trino deficit, the at mospheric neutri-no deficit, the Liquid Scintillator Neu-trino Detector (LSN D) experiment atLos Alamos National Laboratory, andthe missing mat ter problem. T hesehints suggest the existence of neutri-no oscillat ions in regions of t heparameter space that have not beencompletely ruled out by acceleratorexperiments.

T he solar-neu tri no defici t hasbeen arou nd for t h ir ty years. (See“What Have We Learned About SolarN eu trinos” by John Bahcall in t heFall 1994 issue of t he Bea m Line.)

103

100

10–3

10–6

10–9

10–410–5 10–3 10–2

Mixing Strength, sin2(2θ)

Mas

sD

iffer

ence

,∆m

2(e

V2 )

10–1 1

Vacuu m

Missing Matter?

LSN D

At mosphericRatio

Up/Dow n

MSW

Relevant NeutrinoParameter Space

This graph shows the regions of neutrino mass(∆m2) and mixing strength [sin2(2θ)] which aresuggested and ruled out by present data. Theshaded regions are ruled out above and to theright of the curves labeled νµ → νe and νµ → ντ.The hatched areas are suggested regions of pa-rameter space from the LSND, atmospheric, andsolar neutrino experiments. The band labeled“Missing Matter” is where one might expect tofind neutrino oscillations if neutrinos contributesignificantly to the Dark Matter problem. Newlong-baseline experiments will explore the re-gion of parameter space suggested by the at-mospheric ratio and up/down results.

BEA M LINE 13

T hese m assive detect ors, w h ichweigh from one to fifty t housandt ons, haven’t discovered prot ondecay, bu t t hey do observe abou t ahundred in teractions of at mosphericneutrinos per year for every thousandt ons of det ector m ass. T hese neu-trinos are created near the top of theat m osphere w hen cos m ic-ray pro-tons initiate a particle cascade, mak-ing one or more charged pions, eachof which decays in to a m uon and aνµ. T he muon subsequen tly decaysin to an electron, a νµ, and a νe. Thus,t he ratio of νµ flux to the νe flux ob-served in an underground detec torshould be abou t t wo. T his is quitea s trong predict ion, regardless ofcosm ic-ray rates and t he subt let iesof calcula ting the nu mber of par ti-cles produced in the cosmic-ray cas-cades. Underground detectors seemto be measuring the expected nu m-ber of electron neu trinos, bu t onlysixty percen t of t he expected m uonneutrinos. This νµ deficit could be ex-plained by νµ → ντ oscillat ions, witht he ντ too low in energy to producea tau lepton by interacting with a nu-cleus. This deficit seems to indicatea value of ∆m 2 betyween 10−3 and1 eV2 (see region labeled “At m os-pheric Ratio” in t he illustration onpage 12).

T he dis ta nce t hat a t m osphericneutrinos travel before hit ting a de-tector varies from 25 kilometers fort hose com ing fro m overhead to12,000 kilom eters for t hose co mingfrom the other side of the Earth. Thisprovides an opportunity to deter minewhether there is any difference in thesignal between the up-going and thedown-going neu trinos. If so, t he os-cilla t ion lengt h for typical at m os-pheric neu trino energies (500 MeV)

would be betw een 25 k m and12,000 km. There is strong evidencefrom the SuperKamiokande experi-ment this is the case. This “up/downasym metry” observed seems to favora value of ∆m2 between 10−4 and 10−2

eV2 (region labeled “ Up/ Dow n” inthe illustration).

The LSN D experi m en t a t LosAlamos, unlike the solar and at mos-pheric neutrino experiments, was ex-plicitly built to look for neu trino os-cillations. Operating near the targetof t he LAMPF accelerator, it uses avery intense π+ beam. The pions stopin the target, decay in to a µ+ and a νµ,and the µ+ decays in to an e+, a νµ, anda νe. Except for a small and calcula-ble background from negative piondecays, there are no ν–e’s in the beam.So if excess n um bers of these par ti-cles are detected, they probably arosefrom ν–µ → ν–e’s oscillat ions. The ex-periment has a 170 ton tank of min-eral oil that can detect the reactionν–ep → ne+ by measuring a 15–30 MeVpositron in coincidence with a signal

The LSND detector is designed to searchfor the presence of electron anti-neutrinos with great sensitivity. Over1200 photomultiplier tubes line the innersurface of the oil tank, shown above withLSND physicist Richard Bolton of LosAlamos. (Courtesy Los Alamos NationalLaboratory)

14 SPRIN G 1998

density should just equal the criticalvalue, t hough t here are recen t ob-servational data which suggest onlyt wen ty percen t of t hat value. Ordi-nary baryons, t he s tuff t hat m akesup s tars a nd s t uffed pizza, is on lyabou t five percen t of t he critical val-ue, based on bot h observational dataand t he rates of ligh t ele m en t pro-duction during t he Big Bang. So m eof this missing m at ter m ay well beneu t ri nos; t here are h u ndreds oft he m in every cubic cen t i m eter oft he Universe. If t hey had a mass ofjust 5 eV, neu trinos would outweighall t he s t ars a nd pizza in t heUniverse.

Experim en ters wan t to confron tthese hin ts of neut rino oscillat ionswith more definitive measurements.New solar neu trino experimen ts aredeter m in ing t he size, t i m e depen-dence, and energy dependence of thesolar neu trino defici t . Ne w sh or t-baseline oscillation experiments arest udying m ass differences in the re-gion of the missing mat ter problem.T he repor t ed LSN D effect will besough t by anot her collaboration a tthe Rutherford Laboratory in Britain,and t here is a proposal for a fu t urefollow-up detector a t Fer milab (seetable on the left for a small selectionof these experimen ts).

WHILE UNDERGROUNDexperiments will continueto study t he at m ospheric

neutrino deficit, there is another planto s t udy possible neu trino oscilla-tions in the same region of parame-ter space. These are the long-baselineexperim en ts. While short-baselineexperim en ts are typically one kilo-meter from the point where the neu-t rinos are produced, long-baseline

from neutron capture, which yieldsa 2.2 MeV ga m m a ray. The experi-ment has reported a signal that couldbe explained by neutrino oscillationswith a strength P(νµ→νe) = 0.003.

Unlike the at mospheric and solarneutrino deficits, the LSN D signal hasbeen observed in only one experi-ment. In fact, other experiments thatare sensi t ive to t hese oscil la t ionsover si m ilar regions of para m et erspace have obtained negative results.The region favored by LSN D bu t notruled ou t by ot her experi m en ts(labeled “LSN D ” in t he figure onpage 12) sugges ts a value of ∆m 2

around 1 eV2.The final hin t, t he missing m at-

ter proble m, is really sugges tive ofneu tr ino m ass rat her t han oscilla-tions. There is a cri t ical density ofmat ter in the Universe (see article byAlan Gut h in the Fall 1997 issue ofthe Beam Line, Vol. 27, No. 3), aboutone hydrogen ato m per cubic m e-

t er, abovew hich theUniverse isclosed andwill so m e-day collapseback in to asingle point.If the densi-t y is a t orbelow t hiscritical den-sity, the Uni-verse is openand will ex-pand forev-er. Thereare st rongt heoret icalargu m e n tst h at t he

Select Present/Future Neutrino Experimentsa

NeutrinoExperiments Energy Location Status

SolarSuperKamiokande 7 MeV Kamioka, Japan CurrentSudbury (SNO) 4 MeV Ontario, Canada Beginning

AtmosphericSoudan 2 600 MeV Minnesota CurrentMACRO 5 GeV Gran Sasso, Italy Current

ReactorChooz 5 MeV France CurrentPalo Verde 5 MeV Arizona Future

Short-baselineNOMAD 50 GeV Geneva, Switzerland CurrentLSND 40 MeV Los Alamos Current

Long-baselineMINOS 20 GeV Fermilab to Minnesota FutureICARUS 30 GeV Switzerland to Italy FutureK2K 1 GeV Tsukuba to Kamioka, Japan Future

aA more complete list of neutrino experiments can be found athttp://www.hep.anl.gov/ndk/hypertext/nu_industry.html

BEA M LINE 15

experiments in the United States andEurope will be located 730 km awayfrom the source. And another exper-imen t in Japan will have 250 km be-t ween neu trino product ion and de-tector. All three of these choices arem at t ers of convenience—t he dis-tances between existing acceleratorsand existing underground facilities.As luck would have it, however, allt hree projects will substantively ad-dress t he possibili t y that t heat mospheric neutrino deficit is dueto neutrino oscillat ions.

As an example of one of the mostambitious new neutrino oscillationprojec ts, I will now focu s on t heFer m ilab-to-Soudan long-baselin eproject (see map on the right). Thereare three elements to the project: theneutrino beam, a near detector at Fer-m ilab, and a far det ector a t t heSoudan underground physics labora-tory in nort hern Minnesota.

A high-in tensity neu trino bea mfrom Fermilab will be made possibleby a new high-intensity 120 GeV pro-ton source called the Main Injector.Sc hedu led for co m plet ion i n 1999,t his facility is being built to replacet he presen t Main Ring as one stageof accelerat ion. The Main Injec torwill also allow a very h igh-intensityneu trino progra m, known as N uMIfor “ Neutrinos at the Main Injector,”to be run sim ultaneously with otherexperi m e n t s . T he i n t ense prot onbeam makes a neutrino beam by hit-ting a target to m ake the maxim u mnu mber of pions and kaons, whichare focused forward to give a bea mwith as lit tle divergence as possible.Then they travel through a one kilo-meter pipe where many of them de-cay in to neu trinos, which cont inuem oving forward. The kinem atics of

the pion decay results in an averageangle bet ween a neu trino and t heoriginal bea m of abou t 1 /20 t h of adegree.

One obvious concern in ai m inga beam at a target so far away is theprecision required to hit it, bu t thist urns ou t to be only a m inor prob-lem. Hit ting the target is a similar toai m i ng a flashl igh t a t t he m oon.Most people could hold the flashlightand poin t accu ra tely en ough. T heproble m com es in seeing the flash-ligh t w hile s tanding on t he m oon.T h is could on ly be accom plishedwit h a powerful enough ligh t. T helong-baseline neu tri no proble m issimilar. The neutrino beam spreadsout as it recedes from Fermilab, los-ing its intensity. And, neutrinos arevery weakly interacting, so one needsa very m assive target in order to de-tect just a few of t he m. In order tostudy such long oscillation lengt hs,the detectors m ust be far away fromthe source and can only in tercept as mall fraction of t he bea m. Thus i tis necessary to make the beam veryintense at its origin.

The far detector will be located inan old iron mine beneath the SoudanState Park in Minnesota. A half milebeneath the surface—at t he deepestlevel of a historic iron mine—is theexis t ing Soudan 2 fine-grained de-tector. The mine, which operated foralmost one hundred years, is currentlybeing maintained for tourists by theState of Minnesota Depar t m en t ofNatural Resources. Scientists plan tobri ng ten t housand to ns of iron t obuild the MINOS detector, which willjoin t he one t housand tons already inSoudan 2 , to s t udy neu trinos fromFer milab. It’s a bit like taking coal toNewcastle.

12 km

SoudanLake

Superior

LakeMichigan

Fermilab

Fermilab Soudan

Madison

Duluth

MN

IA

MO

IL IN

MI

WI

730 km10 km

Map showing long-baseline neutrinoexperiment planned from Fermilab inIllinois to Soudan in Minnesota.

The home of the MINOS detector—acavern in Soudan, Minnesota—beinginstalled in the 1980s.(Courtesy Fermilab)

16 SPRIN G 1998

new MINOS detector in 2002. Givenall t he ot her neu trino experi men tsaround the world, I can promise thatthere will be substantial progress inunderstanding neutrinos and the pos-sibility of neutrino oscillations dur-i ng t he n ext decade. Bu t I suspectthat progress will come slowly andgrad ually. T he large and growi ngeffort being devoted to neutrino ex-peri m en ts is indicat ive not only ofthe interest in these ghostly particlesbu t also the difficulty of doing pre-cision work in this field. Even if wedefini tively show t hat neutrino os-cillations exist, t here will be a largeset of neu tr ino m ass and m ixi ngparameters to determine. And if neu-trino oscillations do not turn up, wewill need alternative explanations fort he presen t observat ional hin ts. Inone form or another, the experimen-tal study of neutrino oscillations willprobably con tin ue for t he nexttwen ty years!

T he new MI N OS (for “ Main In-jector Neutrino Oscillation Search”)detector will m easure abou t twelvet housand neut rino in teract ions peryear out of t he five trillion that passthrough. It will consist of six hundredlayers each of scintillation countersand m agnetized iron. If t he at m os-pheric neutrino deficit is due to νµ →ντ oscillations, MIN OS will observedifferen t rates of even ts, differen tfractions of even ts with m uons, anddifferen t energy distribu t ions fromt hose seen in the near detector.

A small version of the MIN OS de-tector at Fermilab is a necessary partof the experiment. This detector willbe used to understand the beam andcalibra te i ts in tensi ty, by m easur-ing t he i n t erac t ions of neu tr inosbefore t hey have had any chance tooscillate into ot her species.

Physicis ts hope to begin takingdata wi t h t he exis t ing Soudan de-tector and t he firs t sect ions of t he

The headframe atop a former ironmine at Soudan in northernMinnesota. (Courtesy Fermilab)

Physicists recognize that

the Standard Model

conceals as m uch as it

reveals abou t the ulti-

m ate work ings of

m at ter. Migh t the study

of the char m quark help

open the way to the

physics beyond the

Standard Model?

BEA M LINE 17

AYBE WE SHOULD CALL IT somethingdifferen t. “The Standard Model” sou nds so def-inite, so final. Perhaps another name wouldbet ter describe the part-monu ment, par t-

punching-bag nature of t he world’s best t heory of how mat-ter is pu t together at t he smallest scale. The Standard Modelis a monu ment—a m onu ment to the power of t heory and ex-perimen t to explore and explain t he seemingly trackless in-ner reaches of t he mat ter around us. But it is a punching bag,too, the so-far in tact target of experimen tal jabs and thrustsat tempting to expose its weaknesses. The punches haveincluded searches for forbidden processes, neu trino mass,and other sym metry violation. Now, in a dizzying mix ofmetaphor, t he Standard Model has become something else aswell—a curtain that physicists know is about to go up, re-vealing the true drama on the stage behind it: The PhysicsBeyond the Standard Model. For we know that t he StandardModel conceals as m uch as it reveals abou t t he ultimateworkings of mat ter. We know t hat marvelous scenes will un-fold before us, if only we can find which rope to pull to makethe cur tain rise.

Most of the theoretical and experimental energy of t hefield of particle physics at t he end of the twentieth cen tury isconcen trated on raising the Standard Model curtain on thedrama that will be twen ty-first cen tury physics. And most ofthese efforts are devoted to pulling on two ropes: high-energysearches for the origin of mass and the quest to find m at ter-an timat ter asym metry in the behavior of mesons containingthe bot tom quark. Bu t besides these mainstream efforts,might there be another way to raise t he cur tain? Migh t we atleast lift its corner by using—char m?

P h y s i c s w i t h C h a r mby JEFFREY A. APPEL

M

18 SPRIN G 1998

at fixed-target experim en ts (wherebea m s of m oving par t icles hi t s ta-tionary mat ter, instead of collidingwit h bea ms of par ticles co ming theo t her way) h as elucidated t he dis-tribution of the gluons inside garden-variety hadrons con taining up anddown quarks, and even wit hin lessordinary hadrons con taining strangequarks. (A hadron is a particle madeof quarks held toget her by gluons.)

T he fusion of a pho to n wi t h agluo n fro m a target hadron is t hedo m inan t process for produci ngcharm-an tichar m pairs wit h a pho-ton beam. The fusion of two gluonsin hadron-hadron in teractions is thedominant process for creating charmquarks in t hat environ me nt . Bot hof these processes depend on the dis-tribu tions of gluons in hadrons. Bycarefully studying the characteristicsof char m production, we work back-ward to t he way gluons are dist rib-uted in target neutrons and protons,as well as in beam hadrons, such aspions, kaons and protons. Gluon dis-tribu tions in pions and kaons (eachcomprising a quark and an antiquarkheld together by gluons) appear to besimilar. In protons, which are madeof th ree quarks, t he gluons are

Since its famous discovery almosta quar t er ce n t ury ago, t he char mquark has in t rigued par ticle physi-cist s as a unique part icle, t he firstof t he heavy quarks—an d m ore. I tis t he only quark wit h ch arge +2 /3t hat is both unstable (unlike the upquark) and yet survives long enough(unlike the top quark) to bind wit ho t her quarks and for m observableparticles. Thus the char m quark of-fers a u nique way to discover effectst ha t m ay occur only in t h is “ up-quark” neighborhood of t he par t i-cle world. Such effects migh t nevershow u p in t he dow n, s tra nge andbot to m quarks, wit h t heir −1 / 3ch arges. C har m m igh t give us alonged-for peek beyond the StandardModel curtain.

FASCINATIO N OF CHARM

Until 1974, three kinds of quarks hadappeared in experi men ts: up, downand strange. But theorists, reasoningt ha t quarks shou ld co m e in evenn u m bers, predic ted a four t h k ind,dubbed charm. If it existed, besidesevening up the quark score, char mwould explain a puzzle: why do neu-tral kaons decay only very rarely in toa pair of m uons? Char m did indeedm aterialize, sim ultaneously on t heeas t and wes t coas ts of t he Uni tedStates, and it proved to have the prop-erties the theorists had said it would.Since i ts appearance, the char mquark has taugh t physicis ts m uchabou t t he s trong and weak n uclearforces and how they in teract.

Charm also teaches us about or-di nary m at ter. Most of t he m at t ert hat we see is made of quarks, heldtoget her by gluons, in neutrons andprotons. Producing char m part icles

“softer,” that is they keep closer tothe quarks. Charm particles interestthe experimenter because they allowthe identification of well-defined glu-on interactions and give us a windowin to w hat is going on in the main-st ream mat ter of t he Universe.

In t he s tory of char m , as i n t hes tory of all par t icle physics, t ech-nology is the deus ex m achina t hatmoves the plot forward. Advances inaccelerator, detector, and computingtechnology have let us make the ac-quain tance of charm, and advancesin tech nology will take us still fur-t her in t he s t udy of i t s charac ter.Learning more abou t charm will notonly help us understand the gluons,bu t illu m inate t he differences be-tween the quarks and—and!—get tothat physics beyond the You-Know-What. For charm part icles may holdclues to why, for example, char m isone of only six quarks, and why thosesix come t wo by two, like creaturesfrom Noah’s Ark.

THE DISCRETE CHARMOF FERMILAB FIXED-TARGETEXPERIMEN TS

T he fixed-target run t hat ended inSepte m ber 1997 m ay have seen t helast dedicated charm experim ent atFermilab. This moment—t he end ofan era of char m—is a good t i m e tolook at where we have come so far inchar m research and at w here wemight be going.

Today, precision results on charmphysics come from electron-positroncollision experi m en t s a t Cor nell’sCESR a nd fro m Fer m ilab’s fixed-target experiments. Where Fermilab’sprecision measurements come to thefore, we can credit the large numbers

The charm quark has

intrigued particle

physicists as a

unique particle, the

firs t of the heavy

quarks—and more.

BEA M LINE 19

of fu lly reconst ruc ted decays ob-served and the cleanliness (wit h re-spect to background) of t he experi-m en tal signals. The Fer m ilabexperiment with the most prodigioussample of clean, reconstructed charmdecays now has 200,000; bu t i t willsoon relinquish i ts ti tle to a char mexperiment from the last fixed-targetrun that projects a million or more,all told. When we consider t ha tcharm appears only once in every 200relevan t photon in t erac t ions andonce in every t housand hadron in-teract ions, and add in the fact t hatexperi m en ts typically recons tructonly about half a percent of these, werealize that experimen ters are look-ing for on e clean decay in abou t100,000 in teractions.

The nat ure of fixed-target experi-m en ts can lead to clean char m sig-nals. Most of the charm particles pro-duced move rapidly in the direct ionof the incident beam. They live longenough (about a picosecond) to movea few millimeters beyond their pro-duc t io n poi n t before t hey decay.Experimen ters can observe this dis-tance, but i t requires precision mea-sure m ent of t he trajec tories of t hedecay products, unclut tered by a lotof d is t ract ing “ju nk ” in t he way.Depending on how the char m par-ticle decays, knowing the identity ofthe decay products leads to the clean-est signals. In t he electron-positronmachines used so far to study charm,t he char m par t icles are at res t ormoving slowly at production, so theydecay on top of t he product ionpoint—a m uch messier sit uation. Infixed-target experimen ts, physicistscan use the decay topology to selecton ly t hose in teract ions t hat couldcon tain char m part icles. For t hose,

t hey t hen exa m ine only t hose par-ticles com ing from single vertices.

T he co mbinat ion of these s tepshelps to select t he precious char meven ts from t he m ore copious, un-in teres t ing false candidate even ts.Applying selection criteria using ver-tex separation and particle iden tifi-cat ion reduces backgrou nd m uc hfaster than signal. The more certainwe are that a charm decay vertex can-didate is separated cleanly from theeven t’s in teraction vertex, the morecertain we can be t hat we have ob-served a real char m decay.

The methods developed for thesefixed-t arget experi m en ts have notonly bagged many a char m particle,bu t have influen ced t he design forhadron colliders doing bot tom andtop quark research a nd for asy m-metric B factories where we need tomeasure the separation bet ween thedecay sites of t he particles contain-ing bot tom quarks.

TECHN OLOGY OF CHARM

Advances in t h ree areas of tec h-nology have produced today’s large,clean sa m ples of char m in fixed-target experi men ts. Silicon micro-s t rip detec tors (SM D s), videot apes t orage, and co m put er far m s—alllinked together—have taken char mphysics to new levels.

The figure above right shows howthe history of production and decayof char m particles in one event canbe reconstructed from the trajectoriesof t he resu l t ing charged par t icles.Tracks (t he records of par t icle t ra-jectories) emerging from the primaryinteraction vertex and the two charmdecay vertices (one for the charm andone for the sim ultaneously produced

–22

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–18

–10.4 –10.2Y-Coordinate (m m)

–10.0

Z-C

oord

inat

e(m

m)

σZ1

∆Z12

σZ2π–

π–

π+D– 0

D0

K+ K–

A charm production event from Fermilabexperiment E691. The two white areasrepresent regions from which tracks emergeand are separated from the initial collisionpoint. This indicates that charm particles D0

and D–0 were produced and decayed in theseregions.

Silicon Microstrip Detectors

MODERN MICROELECTRONIC TECHNIQUES make possiblethe silicon microstrip detectors that have brought charm physics such along way. How do SMDs work? When a charged particle traverses a thincrystal of pure silicon, it deposits energy that frees electric charges tomigrate.

If an appropriate voltage is applied across the crystal, the migratingcharges will produce signals on metal electrodes. The signals, suitablyamplified by sensitive electronics off the silicon plate, are digitized andrecorded for later analysis. On SMDs, the electrodes are closely spaced

strips, typically 25 to 50 microns from center to center, with amplifiersattached to each strip. The large number of strips allows experimenters torecord the passage of many charged particles through each detector,reduces the capacitative load on the fronts of the amplifiers, and improvesthe achievable spatial resolution. The SMD signal collection takes just afew billionths of a second, making SMDs useful in the intense, high-rate en-vironments that characterize more and more particle physics experiments.

20 SPRIN G 1998

an t ichar m) appear to e m erge fromdistinct vertices. This is only possibleif t he char m par t icles live longen ough, if t hey are m oving fas tenough, and if t he tracking resolu-tion is sufficiently fine. A charm me-son that decays after one typical life-time has traveled several millimetersin the direction parallel to the inci-den t bea m and 150 m icrons in t hetransverse direction. SM Ds provideresolu t io ns abou t t en t i m es m oreprecise t han t hese dist ances. Thisprovides powerfu l separat ion be-t ween com bina tions of t racks t hate m erge from char m decay vert icesand background.

Over t he pas t fiftee n years, t hera w dat a fro m fixed-target experi-ments has gone from a few gigabytesto 50,000 gigabyt es. It wou ld havecost a fortune to handle so much datausing the old open-reel magnetic tapesystem. Fortunately, new technologyin the for m of 8 m m videotape cameto the rescue with greater capacity ata far lower price. However, becauseof the less-than-lightning speed of anindividual 8-m m tape-writing device,one fixed-target charm experimen tused 42 of the tape drives writ ing outevents in parallel. The data-acquisitionarchitect ure supported this paralleltape writing, along with parallel-pathdata accu m ulat ion from t he fron t-end electronics.

Massive new data se ts also re-quired greater economy in analysiscomputing. Char m experiment E691first used massive parallel-processingcomputer far ms at Fer milab for thispurpose. At that time, experimentersused laboratory-designed, si ngle-board computers (over a hundred inone syste m) wit h com mercial CPUchips and home-built control software.

5 cm

5cm

~ 1000Collecting Strips

50 µm Pitch

300 µm

Par ticlesA silicon microstripdetector.

BEA M LINE 21

Later, com mercial workstations tiedtoget her wit h custo m soft ware be-ca me m ore cost effect ive. T his ap-proach of using large data sets com-bined wi t h si m ple early even tselec tion offers cer tain advan tages,including the ability to do analysisafter detector calibrations are tunedup and sophisticated computer codesare debugged. The analysis can thenapply final track- and vertex-finding.This approach works bet ter than theuse of only t he cruder infor m ationavailable at data-taking ti me, whichnecessarily throws away some of thein teres t i ng char m even t s. I t alsohelped that the price of computingpower dropped rapidly in the in ter-val between the purchase of systemsfor on-line and those for off-line use.

CHARM OF THE FUTURE

Massive data storage, massively par-allel com puting and silicon micro-strip detectors have all become par tof the standard tool box for modernh igh-energy physics experi m en ts.The experiments that discovered thetop quark at Fermilab’s Tevatron col-lider, the experiments that study bot-t om quark p hysics i n Z decay atSLAC and CER N , and experi m en ts

THE FIRST 8 MM videotapes held theequivalent of thirteen of the old open-reeltapes in use before 1990, and current ver-sions hold two times that amount. To putit in perspective, a typical weekend ofdata-taking in experiment E769 resulted ina forklift of open-reel tapes (see photoabove). In the next series of fixed-targetruns, E791 recorded a comparableamount of data in three hours and storedit in a tray of 8 mm tapes (see photobelow).

that will study CP violation in asym-metric B factories all used, use or willuse these techniques. Charm showedthe way.

Bu t now, whit her char m physicsitself? Have the present technologiesrun their course for charm? A lookat t he likely landscape of fu t u rephysics experim en t s shows few ifany long runs of sufficien t ly ener-get ic bea m s to produce great nu m-bers of char m par t icles. Would-becharm investigators will need somesort of new environ ment to pursuetheir explorations. Two possibilitiessugges t t he m selves: asy m m et ricelec tron-positron colliders and t heforward regions of hadron colliders.Both remain to be explored, althoughbot h offer t he prom ise of openi ngnew realms of charm.

As in the past, we will need newtechnologies to deepen our knowl-edge of char m. Bu t if we are inven-tive enough, and alert to new tech-nical opportunities, it is possible thatwe may look to charm for its uniquepotent ial to raise the curtain on theopening act of t hat rivet ing all-starproduct ion, “Physics Beyond t heStandard Model,” coming soon to atheater near you.

8 Millimeter Tape Technology

Fermilab physicist Catherine James holds atray of 8 mm tapes.

Growth of Data Acquisition Parallelismat Fermilab’s Tagged Photon Laboratory

Number Data Set NumberEvents Size Reconstructed

Year Experiment (M) (GB) Charm Decays1980–81 E516 20 70 1001984–85 E691 100 400 10,0001987–88 E769 400 1500 40001991–92 E791 20,000 50,000 200,000

Ferm

ilab

Visu

alM

edia

Serv

ices

Don

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22 SPRIN G 1998

T his Was t he Year T hat Was(Astrophysics in 1997)

b y V I R G I N I A T R I M B L E

T HE PR O GRESS ofscience is not generallym uch li ke t hat of a

kangaroo. Rather, we tend toadvance a moeba-like, cautiouslyex tending pseudopods in som edirections and retracting themin others. 1997 witnessed atleast its share of advances andretreats, w ith perhaps aleap or t wo. The followingsections are m ean t to belogically independent andreadable (or at least noless readable) in anyorder.

THE U NIVERSE AT LA RGE

MICRO- AN D MACRO-MARS: WATER,WATER, EVERYWHERE

Readers my age may remember w hen “I don’tthink so” was an expression of genuine doubt. Last

year’s announcemen t of possible microfossils in ameteorite that had come to us (or anyhow to Antarctica)from Mars provided an opportunity to try out the X-generation meaning of the phrase. Our cur m udgeonlypessimism has been justified. After several months ofrat-like gnawings on the edges of the evidence by otherexperts, the original proponents have essen tially with-drawn the suggestion. Tactfully, they switched fromScience to Nature for the recantation.

BEA M LINE 23

Meanwhile, a n u m ber of Mart ianshave acquired personal names. Bu t it’sno use calling them, because, like catsand Victor Borge’s children, they don’tco m e anyhow. In fact , t hey all see mto be rocks. And while reports from theSagan Memorial Station indicate thatt he said rocks have carefully washedt hei r hands for din ner, t here doesn’tseem to be anything to eat. Continuedanalysis of Pathfinder data will proba-bly yie ld addi t ional i nfor m at ion o nMartian geology,* bu t more advancedprobes will be needed to dig below thesurface and look for possible relics of early pre-biologicalor biological evolu t ion. If you happe n to h ave som eold slides of the Viking lander site lying around, you cancheck my impression t hat the topography of Mars haschanged less in t he last t wen ty years t han t hat of ourfaces.

Liquid water continues its role as t he probable li m-iting factor for the development of chemically based life.It may, however, not be so very rare. Besides t he Earthand Mars, wet places in the solar system appear to in-clude subsurface regions of two moons of Jupiter, Europaand Ganymede. Lots of i mages are already in from t heGalileo m ission, w hic h, after st aring a t Jupi ter for aw hile, has begun con te m plat ing t he moons, and willcontinue to do so in to 1998.

Gaseous and solid water are all over the place. Wehave always suspected t his from t heir prom inence incom ets and other reservoirs of local volat ile material,bu t the inventorying has not been very easy. The prob-lem is terrest rial water—a very good thing in it s way,bu t given to sm earing its absorption features across anyspectrogram you take from Earth’s surface. ISO , the In-frared Space Observatory, a mostly-European effort withgood resol u t ion i n bot h wavelengt h and posi t ion onthe sky, has finally climbed above even the very highest

terrestrial ice crystals and water vapor molecules. It seesH 2O e m ission and absorption feat ures i n star for m a-tion regions, in shells around evolved stars, in externalgalaxies, in the planets, and just about anyplace whereit is cool enough for molecules to remain bound and per-haps clu m p toget her. The water feat ures are often sostrong and numerous that they in effect constitute thenoise in investigations of other species that emit and ab-sorb pri m arily at infrared wavelengths. Just what youwould have expected in retrospect.

Nevertheless, not all water is created equal, at leastnot in its ratio of deu terium to hydrogen. That ratio hasnow been m easured in t h ree brigh t co m et s, Hal ley,Hyaku take, and Hale Bopp. In all t h ree cases, D / H isabou t t wice the rat io in terres t rial ocean water. T hism eans that water supplies from comet impacts cannotbe t he primary source of terrestrial water, unless thereis a com et reservoir not yet probed by the observations.T he old-fash ioned source of vola t iles was ou tgassingof material trapped when the Ear th form ed.

*Areology would see m to be t he obvious word, bu t it justhasn’t caugh t on.

Mars Pathfinder. The view is not so very different from thatrecorded by the Viking lander a couple of decades ago, butthe device itself, including the rover, is clearly much moreelaborate. Additional data on additional particular rocksmakes clear that Mars, like Earth, has experienced a variety ofprocesses, leading to a variety of minerologies andpetrologies. (Courtesy Jet Propulsion Laboratory, CaliforniaInstitute of Technology, and NASA)

24 SPRIN G 1998

THE FAT LADY BURSTS

I have been told on equal authority (that is, none) thatt he pulchritudinous person in question was eit her KateSmith rendering “God Bless America” to end a baseballgame or a Sut herland-like soprano expressing the desireto leave Paris shortly before the end of La Traviata (notat all a bad thing to do, par ticularly if the performancehappens to be in Paris). I would not presume to choosebetween them. But we were told wi th equal au thorityabout three years ago* that the gam ma-ray bursters werelocated eit her in the halo of our own galaxy or in ot h-er galaxies a t d is tances co m parable wit h t he size oft he observable Universe. This choice is now easy. Theyare at cosmological distances.

GRBs are, tautologically, bursts of gam ma rays (mean-ing anything above 50 keV or so) that come to us at com-pletely unpredictable times from completely random di-rections in t he sky, at a rate of abou t one per day (givent he sensi t iv i ty of t he detectors now orbi t ing on t heCompton Ga m ma Ray Observatory). Most last from atenth of a second to a few hundred seconds, show sub-structure and complex spectra, and du mp from 10−8 to10−4 erg/cm2 at the top of the Ear th’s at mosphere, wit ht he faintest ones being co m monest. Oh yes. And un tilFebruary 1997, none of t hem had ever been caught do-ing anything detectable at any other wavelength.

CGRO data had additionally confounded expectationsby showing that we see the edge of the GRB distribu tionin space, despi te seem ing to be at t he cen ter of it (seebox on the next page). Thus the edge was supposed to beeither the edge of an enor mous halo of our own galaxy(not host to any other known sort of object) or an opti-cal illusion, in troduced by the redshifting of the energyof sources far enough away t hat cosm ic expansion isim portant.

In t he las t year, a sui table sa t elli t e, t he m ost ly-European BeppoSAX, began picking up X-ray tails to the

40

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04,200 4,600

λ (A°)

5,000

F ν(1

0–29

erg

cm–2

s–1H

z–1)

Spectrum of the GRB 970508 in blue light. The featuresmarked are absorption lines due to singly ionized iron andmagnesium in intervening gas clouds. The fact that the linesare doublets makes them fairly easy to recognize, and similarlines are common in the spectra of quasars with redshifts ofone or more. The more redshifted of the two systems in theGRB is at z = 0.83, telling us that the event itself must haveoccurred at still larger distance. The visible source has fadedenormously since May 1997, and the spectrogram could notnow be duplicated. (Reprinted with permission from Nature ©1997 Macmillan Magazines Ltd. and the GRB team, PalomarObservatory.)

This is perhaps as good a place as any to tell youthat the animal pictures come from a Dover volume calledAnimals, whose cover specifically declares the images to befree of copyright restrictions.

*A t a 75t h anniversary restaging of the C urt is-Shapleydebate, w hose proceedings appear in the Decem ber 1995issue of Publications of the Astronomical Society of t hePacific.

BEA M LINE 25

events are and roughly how m uch energy each m ust puti n t o ga m m a rays (1051 ergs or m ore, un less t he pho-tons are strongly beamed) has triggered a new round ofsim ulating . Most of the sim ulees involve at least oneneutron star or black hole, or sometimes two in a binarysystem. Given the sub-second time scales of many bursts,t here aren’t really a lot of other possibili ties.

PEOPLE AND PLACES

T his can only be a “good news/bad news” section. Theastronomical com m unity lost more members than everbefore (not surprising; we are, like most of the sciences,an aging com m unity), but Alan Cousins, a South Africanstellar observer (see cover photo), set what appears to bea new world record for longevi ty in publication, wit hpapers in 1924 and 1998.

The SAGE detector for solar neu trinos managed to re-sist for anot her year having its galliu m resold for com-mercial purposes, bu t the HEGRA detector for extensiveair showers partially burned soon after it had confirmedt he second ext ragalactic source of TeV ga m m a rays, aquasar previously seen from the Whipple Observatory.SAGE also su rvived a calibra t ion ru n wit h a radioac-t ive source, showing that, if neutrinos get to it in theirelectron-flavored gar m en t s, i t sees t he m , w hileSuperKamiokande came on line in Japan and confir medt hat, for the highest energy neutrinos expected from thesun, only about half the predicted flux is arriving in dueorder and technically correct.

Some i mportant satelli te launches failed, includingwhat was to have been the High Energy Transient Ex-plorer (HETE) , left looking up the rear end of its launchpartner after they failed to separate. Others did just whatt hey should, including t he Japanese X-ray mission thatcarries both the acronym HALCA and the name Haruka(a type of bird).*

I HAVEN’T SUBJECTED YOU to a calculation for along time, and this one is just too much fun to miss out.Suppose static space is littered uniformly with candles ofa fixed, standard intrinsic luminosity. Count all the onesyou can see down to apparent brightness S. You will getN(S) ~S−3/2, where the 3 is the dimensionality of space,and the 2 is the inverse square law. Add a second popu-lation with a different intrinsic luminosity. It, too, will con-tribute a power-law N(S), and, no matter how manyclasses you add together, N(S) is always proportional toS−3/2. Counts of GRBs rise toward faint S, but not assteeply as S−3/2. Thus either distant events are rare (weare in the center of a finite distribution, and Copernicus isunhappy), or the bursts are being redshifted so that the Swe see is the Newtonian one cut down by a factor (1+z)2,and distant events are lost from the sample equally in alldirections.

COUNTING SOURCES OF RADIATION

bursts fast enough and wit h good enough angular pre-cision to swing other telescopes toward their locationsbefore all the fireworks were over. Three even ts, in Feb-ruary, May, and Dece m ber, have been recorded—briefly!—in visible ligh t, and t he May one as a radiosource. They are not all t he sam e. T he February loca-t ion has an underlying steady, fuzzy visible object thatis probably a distant faint galaxy. Most i mportan t, theMay event (see figure on page 24) had sharp absorptionlines in i ts spectru m that could be ident ified as beingproduced by Mg II and Fe II in clouds of gas between itand us. The lines had a redshift of 0.83, meaning that thesource had to be further away than that (bu t not beyonda redshif t of abou t 2). And no, I a m not going to tellyou how m uch that is in light years because it dependsVERY m uch on your favorite values of t he Hubble con-stant and ot her cosmological fudge factors.

T heorists had, of course, modeled m ost of t he pos-sibilities long before February. Bu t knowing where the

*Yes, they really are nearly iden t ical in pronunciation. Theunvoiced vowel “u” m ay be fa m iliar fro m “suk iyaki.” Asfor t he see m ingly-double-valued consonan t, abou t all Ican suggest is t hat you try saying “rocket fl igh ts” and“locket frigh ts” quickly, in al ternation, un til t hey startto sound the sa m e.

26 SPRIN G 1998

T he literature contemplated itself, with conclusionsthat Einstein (a) really did write down “his” equationsbefore David Hilbert and (b) had tackled calculat ionsof gravitational lensing as early as 1912, but though t theresults hardly worth publishing. A couple of colleaguesin troduced in to t he literature the words “isopedic” and“enstrophy.” Yes, of course you could look them up, butisn’t it more fun to guess “having the same feet” and “anourishing thermodynam ic quan tity?” And the grem-lins of typography and copy edi ting brough t us m anytreats, of which my favorite is the acknowledgment “ tothe TIRG O tune allocation com mit tee for the award oftelescope time. At most observatories, TAC is an acronymfor “ time allocation com mittee,” but having once sharednigh ts at Mt. Palomar with a colleague who kept awakeby singing m usic of t he old Polish church, I can see t hatthe ot her migh t sometimes also be needed. If only theyhad allocated me “99 bot tles of beer on the wall” (thosewere long win ter nights), or even La Traviata.

DO N’T GIVE UP YOUR DAY JOB

Non-Hollywoodi tes m ay need re m inding t hat, alongwith “don’t call us, we’ll call you,” these are words spo-ken to an aspiring actor or m usician who may not bequite ready for the big time. Here I have in m ind caseswhere somebody went out on a limb (often a very sturdy-looking, oak one) only to have some portion of it sawedoff fro m under hi m. Addit ional exa m ples include t heMartian micro-fossils and Type I supernovae as distanceindicators men tioned in other sections.

Our own Local Group of galaxies consists of two bigones (us and the Andromeda Nebula) and a whole bunchof lit tle ones, whose nu mber has see med to increase atabou t one per year of late. Bu t t he 1992 and 1996 “dis-coveries,” sm all, fain t galaxies a million or two ligh tyears away in the directions of the constella tions Tu-cana and Antlia were actually catalogued back in 1977.New at least as confir m ed LG me m bers? Perhaps noteven t hat. An t lia is probably fur t her a way t han t hemillion-parsec limit of gravitational binding to the LocalGroup.

Accretion disks around proto-stars, white dwarfs, neu-tron stars, black holes, and prominen t theorists appearin every year’s highlights of astrophysics because theyare part of the standard models of quasars,X-ray sources, novaexplosions, bipolar molecular outflows, and all sorts of other(real, observed) phenomena. The first, persuasive data-basedproposal came in 1956 from John Crawford and Robert Kraft,

who concluded thatAE Aqr (a nova-likevariable) m ust be abinary syste m withan accretion disk ofm aterial fro m i t snormal star swirlingarou nd the w hi tedwarf. The la tes tword is that AE Aqris actually a net ex-cretor. Accretion ofco urse persis ts formost of the other ad-vertised objects, pre-feren t ially this pastyear in t he for m of“advect ion do m i-nated accre t ion,”meaning that it car-ries a good deal ofheat and kinetic en-

ergy with it down the tubes. The concept, then unnamed,can be traced in the literature at least back to 1977.

Planetary companions to nearby stars, mostly wit hmasses like Jupiter but shorter orbit periods, glim meredout of press releases from the October 1995 announce-ment of 51 Peg onward. Perversely, m uch of t he com-m unity em braced with ent husiasm a late 1996 sugges-t ion t hat no such planets were orbi t ing. Instead, saidDavid Gray of Western Ontario, we were merely seeingwinds and waves in the atmospheres of (unaccompanied)stars. These would perturb profiles of stellar absorptionlines and mimic the effects of small, orbiting compan-ions. A pair of January 1998 papers, from him and from an

One of the dwarf spheroidal galaxiesthat just barely belongs gravitationallyto our Local Group (or just misses).Perhaps the most remarkable point isthat anybody can succeed in findingand recognizing little smears likeAntlia as galaxies in the first place.(Courtesy Mike Irwin, RoyalGreenwich Observatory, UK)

BEA M LINE 27

shift (t hat is, i ts distance) and its angular motion acrosst he plane of t he sky (that is, t wo-dim ensional velocity,if you k now the distance). The com m unity had beencounting on Hipparcos for quite some time to improveour knowledge of t he brightnesses and kinematics of anu mber of kinds of stars t hat are ei ther interesting fort heir own sake ori mpor tan t i ncl i m bing up t he“distance ladder”to far away galax-ies and t he Uni-verse.

T he splash ies tpress release be-lo nged to a prob-lem that has beenarou nd for half acen t ury, “ t he ageof t he Universe.”T he t i me scale oft he U niverse i m-plied by i ts m ea-su red expansio nrate (t he H ubbleconstan t) has spo-radically see m edt o be ra t her lesst han t he ages ofthe oldest stars wesee. And this par-ticular example of“old wine in lessold bot t les” hasnever been one wewere happy with.Fifty years ago, i tled t o t he inve n-t ion of t he SteadyState m odel of the Universe. More recen tly, t he fain tat heart had been driven to invoking Einstein’s notori-ous cos m ological con s tan t or even to doub t i ng t he

independen t group a t U niversi ty of Texas, will havegiven us back our planets by t he t ime you read t his.

Yes, we live in a screwy Universe, bu t is it also chi-ral? Theorists have predicted and observers not seen fordecades any indicat ion t hat space-t i m e is rota t ing orskewed on cosmic scales. This spring, a Physical ReviewLetter, from theorists in Kansas, announced net rotation,based on details of polarization of radio emission fromsources at redshifts exceeding 0.3. The announcers had,however, relied on data that they had not collected them-selves (always risky) and that were mostly well over adecade old, non-uniformly collected around the sky, andof sufficien tly poor angular resolu tion that bi ts of t heso urces wi t h differen t in t r insic polariza t ion weresmeared together. Owners and operators of more recent,more sui table data sets rapidly fired back upper limitsto the twisting of space considerably below the positivevalue claimed in t he Let ter.

In fact (pause for the modest cough of a minor poet)the previous year had seen a published upper limit slight-ly below the PRL number, which, nat urally, wen t uncit-ed. Probably only two people in the world noticed this,Maurice Goldhaber and yours truly, the aut hors of thelimit paper!

Some things really do have net chirality, including, un-expectedly, som e of t he amino acids in t he Murchisonmeteorite. Conta mination by t he sticky fingers of me-teoriticists, you will say? Apparently not, for the 5–10 per-cent excess of L-enantiomers occurs both in some aminoacids that terrestrial creatures don’t use and in associa-tion with non-terrestrial values of nitrogen isotope ratios.

HIP, HIP, HIPPARCOS SAVES T HE U NIVERSE,OR, TWO AND A HALF CHEERS FOR OUR SIDE

Hipparcos is an acronym (origins lost in t he m ist s oft ime), a sligh t m isspelling of the name of a Greek com-piler of s tar ca t alogues, Hipparc hus, and a (m ost lyEuropean) sa telli te t hat scanned t he skies for severalyears, establishing a coordinate system made up of pre-cise positions for more than 100,000 stars. In the process,i t also deter m ined for each star i t s annual parallactic

The Hipparcos satellite. Its launch wasalmost a failure (owing to maloperationof nearly the only part on it of U.S. manu-facture), leading to an elliptical ratherthan circular orbit; but close to100 per-cent of the expected data were obtainedover several years. Hipparcos estab-lished its own coordinate system on thesky by swinging back and forth from starto star to (more than 105 stars), and thisneeds to be tied to other systems ofearth-centered coordinates. (CourtesyEuropean Space Agency)

28 SPRIN G 1998

correct ness of t he basic pic t ure of a universe expand-ing out of a hot dense state (a.k.a. Big Bang).

Two solu tions are possible—make the Universe older(t hat is the H ubble constan t sm aller, by deciding t hatt he galaxies you used to calibrate i t are fur t her awayt han you had thought) or make the stars younger (alsoachieved by shoving them away from you, so that t heyare brighter and use up their fuel faster). One way of look-ing at stars measured by Hipparcos seemed to do exactlyt hese t wo t h ings. Parallaxes of a se t of s t ars calledCepheid variables (a traditional distance calibrator) werea bi t s m aller t han expected, nom inally bot h increas-ing t he t i me l /H and decreasing stellar ages. U nfor t u-nately, equally valid ways of looking at the data, usingyoung clusters of stars to calibrate the Cepheids and sta-t ist ics of stellar m otions to get bright nesses of the oldones, have precisely the opposite effect. 1/H gets small-er, and the stars get older. Some assembly is apparentlystill required.

Any astronomer who had planned ahead by asking in1982 was entitled to some slice of Hipparcos data. My pro-posal (with George Herbig, then of Lick Observatory) wasinspiringly ti tled “parallaxes and proper motions of pro-totypes of astrophysically interesting classes of stars,” butyou m ust read t he archival literat ure to find out whatwe learned (ot her than that fifteen years is a long timeeven to the middle aged). The hundreds of astronomerswho were also 1982 proposers have thus far probably pro-duced an average of one paper each, and many more areexpected, clarifying the evolutionary status of Barium IIstars and other problems you never even knew you had.

WE KNEW YOU HAD IT IN YOU

Some discoveries were bound to be made eventually andfall largely by luck to the first person who happens tot urn t he right sort of telescope or equation in the rightdirection, much like the case in Moby Dick , where Cap-t ain Ahab nails a gold doubloon to t he m as t for t hefirst person to spot the whale, or, said Richard Arm our,the first person up on deck after dark with a claw-headedham mer. Finding the optical counterpart of the May 8th

ga m ma-ray burster was one of these. Some ot her 1997examples follow:

• Radio pulsations from Geminga. This ga m ma-raysource in Gemini was long a mystery because it seemed(like the bursters) to have no coun terpart at any ot herwavelength. Sensitive X-ray and optical detectors reme-died this several years ago and also showed that it wasa rotation-powered neutron star (“ true” pulsar), with aperiod of 0.237 seconds. Bu t all proper pulsars shouldbeep radio signals at us (that is, after all, how t hey werediscovered in 1967), and Geminga seemed to be a failure.Three groups, all cen tered in Russia, have finally foundt he radio pulses, m ore or less sim ultaneously (and eachhas published the discovery at least t wice, once in theRussian literature and once elsewhere). The problem wasthat the source is simply very faint and steep-spectrumed,so that the best bet for catching it was at lower radio fre-quencies than are usually used for the purpose.

• A spiral wave in the accretion disk of a cataclysmicvariable. Theorists have been predicting these for someti me, because a spiral or m = 2 pert urbation is the nat-u ral consequence of having a large poin t m ass off tothe side of a disk (hence the particularly spectacular armsin spiral galaxies wi t h close companions like M51). IPPeg is the first cataclysmic where the wave has been spot-ted, via a clever mapping technique that uses changes inshapes of spectral lines through the orbit period of thesystem to locate bits of gas with different densities andvelocities.

• Central black holes in galaxies. These have becomeso com mon t hey no longer make the Ne w York Ti mes.Whoever happens to get t he first HST i mages and spec-t ra of t he cen ter of a nearby galaxy is just abou t guar-an teed to fi nd a black hole so m ew here in t he range

Reconstructed distribution of densityin the disk surrounding the white dwarfin IP Peg. The central star is blackedout and contrast somewhat enhanced.(Courtesy D. Steeghs, E. Harlaftis, K.Horne, Astronomy Group, Univ. St.Andrews, UK)

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106–109 solar masses. In a few cases, where more t hanone technique has been brough t to bear on a par ticulargalaxy, the results for BH mass are in clear disagreement.You can argue abou t whether this constitu tes progress,but it does at least guarantee employment for future gen-erations of astronomers. Our Milky Way is part of t hegreat m ajori ty wit h a central black hole of 2–3×106 so-lar masses as the only possible explanation of the detailsof the motions of stars and gas near its cen ter.

• Broad absorp t ion lines in a radio quasar. Properquasars are strong sources of radio e mission (the ot h-ers are QSOs or quasi-stellar-objects, u nless you are feel-ing lazy). BALs or broad absorption lines are sat uratedones with redshifts just a smidge less than the redshiftof the em ission lines. They are at t ributed to gas beingblown out of or around the QSO nucleus. Until 1997, t heradio-loud and BAL sets were disjoin t. And it took a sur-vey of something like 105 radio sources to find the first,fain t overlap (t his is a pu n; t he survey is called FIRST).The source’s telephone number is 1551+3517 (actually itslocation in the sky) in case you want to call.

• The most distant galaxy. There is a new one of thesepractically every year, and quite often i t is really a QSO .T he 1997 queen for a day, at a redshift of 4.92, is an or-dinary galaxy. It is visible at that distance partly becauseit is for ming stars like mad (and new, massive stars aret he brightest kind) and partly because it is gravitation-ally lensed and a m plified by a foregrou nd cl us ter a tz = 0.23.

• The most distant supernova. Here too records arefalling constantly, and the current one at z = 0.9 or there-abou ts is not very i mportan t for i ts own sake. Distantgalaxies contain heavy elements, so we know they m ustalready have had supernova explosions. Bu t t he mem-bers of one class of supernova (called Type Ia) all see mto have the same intrinsic lu minosity and so can be usedto measure very large distances and get global values fort he cosmic expansion rate (H) and its change with time,t he decelerat ion param eter, q0. T hese, in t urn, are al-gebraically related to the mean density of the Universe.Through most of 1997, the supernova method seemed tobe the one hold-ou t in finding a q0 or density value large

enough to stop the expansion of the Universe in the (veryremote) fut ure, while a nu mber of other met hods t hatlooked a t m asses of clusters of galaxies or t heir dist ri-bu tion in space were finding perhaps 30 percen t of thatcritical density. Bu t t he result ca me from a very sm allnumber of distan t Ia’s. With a larger sample of abou t fif-teen events, the best fi t is a sm aller deceleration para-m eter, or a density of 30–40 percen t of the cri tical value,agreeing with t he other methods.

• A new class of pulsating variable star. This is a beau-tiful case of theory and observation rising to meet eachot her. Even as a group of French Canadian modelers ofstars were predicting that a particular kind should be un-stable to pulsations wit h periods near one hour, a groupof South African observers of stars were serendipitouslydiscovering a handful of stars whose brigh tnesses varywit h several modes near one hour, in jus t t he part ofluminosity-temperature space where they were predicted.So far, they are merely called pulsating sdB stars (where“sd” says t hey are fain t, compact, and evolved, and “B”says they have surface temperatures of 15–20,000 K), andmy efforts to coin t he term SubDued Bu mpers has metwith resounding failure.

EVERY DOG ISENTITLED TOONE BITE

This is my at titude, asone of the adjectival editorsof a fairly prestigious jour-nal, toward au thors bear-ing papers abou t w hichone is te m pt ed to quot ePauli, “It isn’t even wrong.” Because t here are lots ofjournals, m any of t hese ideas tu rn up as “new ” yearafter year. Still, isn’t it a sor t of relief from the serious-ness of transverse opt ical phonons to contemplate.

a. A model of star for mation t hat produces cylindri-cal stars.

b. A universe whose m etric oscillates with a periodof 160 minutes, and so accounts both for that period

The fact that the parts of a pic-ture can be made to fit togetherdoes not guarantee this is theway Nature actually does things.

30 SPRIN G 1998

in the sun and for the peak mode of the variable starDelta Scu ti (actually 162 minu tes).

c. A scenario for making ga m ma-ray bursters in t heheliosphere.

d. Dark m at ter candidates in t he for m of a vector-based t heory of gravity or solid hydrogen.

e. Redshifts quan tized by “giving up the arbitrary hy-pothesis of the differentiability of space-time.”

ACKN OWLEDGMEN TS

I asked t he editor to perch the amoeba atop t he kanga-roo in the first pict ure so as to have an excuse for men-tioning Robert K. Merton, aut hor of O n t he Shouldersof Gian ts (no, Newton was not the first to say i t), whohas been an occasional, generous reader of these mau n-derings for some tim e. Reviewers, even more than oth-er scientists, are indeed supported by their colleagues.

T he series, A strophysics in 199x, arose from a sug-gestion by Howard E. Bond, the im m ediate past editorof Pu blicat ions of t he A s trono m ical Socie t y of t hePacific, who m ust often have felt like the parent of Rose-mary’s baby, and who also just happens to have been thechap who first spot ted the optical counterpart of the May8th, 1997, gam m a-ray burst—that was the one that hada measurable redshift, but he couldn’t measure it, becausehe was using a 0.9 m eter te lescope (i t t oo k t h e Keck10-meter). I am grateful both to him and to my some-timeco-aut hors, Peter Leonard and Lucy-Ann McFadden, fort heir con tribu tions to the series (and also to the IRS forthe schedule C deduction that has enabled me to pay thepage charges for its publication most years).

READ ON

The complete text of “Astrophysics in 1997” by V. Trimbleand L. A. McFadden appears in the March 1998 is-sue of Publications of the Astronomical Society ofthe Pacific.

The proceedings of the 75th anniversary restaging of theCurtis-Shapley debate, with contributions from R. J.Nemiroff (organizer), V. Trimble (on the original C-Sevent), G. J. Fishman (on observations of gamma-ray bursters), D. Q. Lamb (arguing for events in thehalo of our own galaxy), and B. Paczynski (arguingfor events in very distant galaxies) appear in PASP107, 1131-1176, with a summary by M. J. Rees, themoderator.

The announcement of cosmic chirality is found in B. Nod-land and J. P. Ralston, Phys. Rev. Lett. 78, 3143(1997). One of the refutations is J. F. C. Wardle et al.Phys. Rev. Lett. 79, 1801 (1997); and the prematureupper limit appears in M. Goldhaber and V. Trimble,J. Astrophys. Astron. 17, 17 (1996) . . . and next timewe’re going to publish in a prestigious journal too!

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C O N TRIBU T O RS

G ORD O N FRASER s t udied a tLondon’s Im perial C ollege i n t hem id-1960s, w hen t heoret ical physi-cis t s were a t tack ing spon taneoussym m etry breaking under Tom Kib-ble and relativistic SU(6) theory un-der Abdus Salam and Paul Mat thews.Fraser also wrote short-story fictionand beca me side-t racked in to jour-nalism. He returned to physics as ascience wri ter, even t ually transfer-r ing to CER N . He is edi tor of t hem onthly CER N Courier; co-au thor,with Egil Lillestol and Inge Sellevag,of The Search for Infinity (New York,Facts on File, 1995) which has beenpublished in ten other languages; andauthor of The Q uark Machines (Bris-tol, Institu te of Physics Publishing,1997). He is also edit or of Part icleC en t ury , a collec t ion of con tribu-tions to be published by Institute ofPhysics Publishing later this year.

MAURY G O O D MA N is aphysicist in the High Enery PhysicsDivision of Argonne Nat ional Lab-oratory. He received his BS from theMassachuset ts Institu te of Technol-ogy. His 1979 PhD from t he Univer-sity of Illinois at Urbana came on aphotoproduct ion experi m en t wit hAl Wat t enberg. Aft er a pos t doc a tMIT working on a Fermilab neutrinoexperi m en t, he joined the Soudangroup at A NL, w here he st udies at-mospheric neu trinos and is search-ing for evidence of nucleon decay. Hewas an early advocate of a long-base-line n eu trino progra m at Fer m ilaband is now a member of t he MIN OScollaboration.

JEFFREY A. APPEL has been aphysicis t a t Fer m ilab since 1975.Most recently he has been spokesper-son for Fermilab experiment E769 andcospokesperson for E791. For eigh tyears ending in March of t his year,he headed t he Physics Sect ion andfollow-on Experimental Physics Pro-jec ts. Appel received his PhD fromHarvard University. He is a Fellowof the American Physical Society andhas coaut hored over 120 ar ticles inprofessional journals.

Appel 's in terests extend beyondt he purely scien t ific and technical.For many years he chaired t he Fer-milab Auditoriu m Com m it tee thatorganized the arts, lectures, and ex-hibi tion series t here. He also ini t i-ated a special Illinois Research Cor-ridor su m m er jobs progra m foroutstanding science and math teach-ers. His present in terests are radia-tion-hard vertex detectors and the BTeVresearch and development program.

32 SPRIN G 1998

VIRGINIA TRIMBLE is not sure that she was a turtle in a pre-vious lifetime or deserves to be one in the next, bu t members ofthe genera testudo and pseudymis (order Chelonia) are her favoritecompanion animals. Her graduate days at Caltech (1964–68) werebrigh tened by the silen t sympathy of Triton (a snapper who morethan earned his name), Beauregard (a but ton turtle), Aragorn (a red-eared slider), Golum (a Lousiana soft-shell), and others. Each enteredour home about the size of the silver dollar that was the hourlysalary of a graduate student in those days, and each somewhat out-weighed the prin ted thesis by the time we came to a par ting of theways. Oscillating yearly between the University of California andt he U niversi ty of Maryland is t oo hard a lifes tyle for a t u r t le(and sometimes marginal for a human being), bu t someday I hopeto have anot her opportunity to listen for the voice of t he t urt lein the bat htub.

D ATES T O REMEMBER

Jul 22–30 29th In ternational Conference on High-Energy Physics, Vancouver, Canada (ICHEP 98)(astbury@triumf.ca)

July 31 Sid Drell Symposium, Stanford, California (mpeskin@slac.stanford.edu)

Aug 3–14 26th SLAC Su m mer Institute on Particle Physics: Gravity—From the Hubble Length to t hePlanck Lengt h (SSI 98), Stanford, California (Lilian DePorcel: Conference Coordinator, SLAC ,MS 62, PO Box 4349, Stanford, CA 94309, or ssi@slac.stanford.edu)

Aug 4–8 6th In ternational Conference on Biophysics and Synchrotron Radiat ion, Argonne, Illinois(Susan Strasser, Conference Coordinator, APS, bsr98@aps.anl.gov)

Aug 10–14 10th In ternational Conference on X-ray Absorption Fine Structure, Chicago, Illinois(Tim Morrison, Conference Chair man, phys_morriso@minna.acc.iit.edu)

Aug 23–28 19th In ternational Linear Accelerator Conference (LIN AC 98), Chicago, Illinois(linac98@aps.anl.gov)

Aug 23–Sep 5 1998 European School of High-Energy Physics, St. Andrews, Scotland (Miss Susannah Tracy,School of Physics, CER N / DSU , 1211 Geneva 23, Switzerland, or Susannah.Tracy@cern.ch)

Aug 31–Sep 4 In ternational Conference on Co mputing in High-Energy Physics (CHEP 98), Chicago, Illinois(sak@hep.anl.gov or lprice@anl.gov)

Sep 6–19 1998 CERN School of Co mputing (CSC 98), Funchal, Madeira, Port ugal (Miss Jacqueline Turner,CERN School of Co mputing, 1211 Geneva 23, Switzerland, or Com puting.School@cern.ch)

Sep 7–12 17th In ternational Conference on High-Energy Accelerators (HEACC 98), Dubna, Russia(Natalia Dokalenko, Intern. Depart ment JINR, Dubna, Moscow Region, RU-141980, Russia, orheacc98@sunse.jinr.ru)

Sep 14–18 In ternational Computational Accelerator Physics Conference (ICAP 98), Monterey, California(icap98@slac.stanford.edu)

Oct 13–14 9th Users Meeting for the Advanced Photon Source, Argonne, Illinois (Susan Strasser, Confer-ence Coordinator, APS, carlson@aps.anl.gov)

Oct 14–15 Advanced Photon Source Users Organizat ion Workshops, Argonne, Illinois (Susan Strasser,Conference Coordinator, APS, carlson@aps.anl.gov)

Oct 19–20 25th Annual SSRL Users Conference, Stanford, California (Suzan ne Barret t, SSRL, PO Box 4349,Stanford, CA 94309, or barret t@slac.stanford.edu)

Oct 22–23 ALS Users Association Annual Meeting, Berkeley, California (Ruth Pepe, Lawrence BerkeleyNational Laboratory, Advanced Light Source, MS 80-101, Berkeley, CA 94720, or alsuser@lbl.gov)