EUGENE GARFIELDINSTITUTE FOR SCIENTIFIC lNFORMATl ON@J3501 MARKET ST PHILADELPHIA PA 19104

The 1988 Nobel Prize in Physics:Melvin S&wartz, Leon Lederman,

Jack Steinberger, and the Storyof Two Neutrinos

Number 32 August 7, 1989

The 1988 Nobel Prize in physics was awarded to Melvin Schwartz, Leon L.ederman, and Jack Stein-berger for their discovery ( 1962) of the muon neutrino, as well as for their developmentof the methodused in the discovery, The eqmirnerrt is described, and biographical data on the laureates are presented.The citation record of the paper reporting their prizewinning work indicates that its greatest impactwas felt within one year of publication.

In ancient Greece philosophers postulatedthat the ultimate, indivisible element of mat-ter was the atom. There was little refinementin that theory for more than 2,000 years. Atthe turn of this century, the electron wasdiscovered (1897); later, atomic nuclei(19 11). A new view of the basic constitu-ents emerged in the 1920s and 1930s withthe discovery of nuclear components: neu-trons and protons. t Since that time, scien-tists have redefined many times over the ul-timate, indivisible particles of matter. Thepost- 1945 period has seen the number ofidentified subatomic particles grow from approximately 12 in 1950 (including electrons,protons, neutrons, neutrinos, and photons)to more than 100 today,z as powerful ma-chines (called particle accelerators) were de-veloped for smashing bits of matter togetherand studying the scattered by-products. Thismodem’ ‘nuclear particle era” began in thelate 1950s. The 1988 Nobel Prize in physicswas awarded for pioneering work performedduring the first years of this era by LeonLederman, who was, untif recently, at theFermi National Accelerator Laboratory(Ferrnilab), Batavia, Illinois, and who isnow a professor at the University ofChicago, Illinois; Melvin Schwartz, nowpresident of Dlgitrd Pathways, inc., Moun-tain View, Crdiforrsia; and Jack Steinberger,now senior physicist at the European Centerfor Nuclear Research (CERN), Geneva,Switzerland. The prizewinning experiment,which discovered a new type of subatomic

particle while using a new research tech-nique, was performed while all three wereat Columbia University, New York.

According to the awards committee, theprizewirmers

opened entirely new opportunities for re-search into the innermost structure and dy-namics of matter, Two great obstacles tofurther progress in research into weakforces-one of nature’s four basic forces—were removed by the prizewinning work.One of the obstacles was that there waspreviously no method for the experimen-tal study of weak forces at high energies,The other was theoretically more funda-mental, and was overcome by the threeresearchers’ discovery that there are atleast two kinds of neutrino,... The view,now accepted, of the paired grouping ofelementary particles has its roots in theprizewimers’ discovery. g

The neutrino, which figures so prominent-ly in the Nobel laureates’ work, is the“ghost” of particle physics. A neutrino hasno identifiable mass, no electrical charge,no measurable size, and travels at the speedof light. Neutrinos are among the most abtm-h-st particles in the universe. One of theirsources is the interiors of stars, where it isbelieved they are generated in the nuclearplasma. Neutrinos were first proposed anddiscussed in the 1930s, while direct evidenceof neutrinos was discovered in 1956.4These particles are difficult to detect and canpass through astronomical thicknesses of

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bon f.ederman (Ieti) and Melvin Schwartz (right). Jack Steinberger’s photograph was notavailable.

matter without colliding with any other par-ticle. Even near misses are quite rare. Youmay be amazed to know that triUions of neu-trinos are passing harmlessly through yourbody every second as you read this sentence.

Background

The idea of a high-energy neutrino exper-iment was first considered in late 1959. TheColumbia University Physics Departmenthad a tradition of a coffee hour at which thelatest problems in the world of physics cameunder intense discussion. At one of thosemeetings there was a discussion of the pos-sibilities for investigating weak interactionsat high energies. A number of experimentswere considered and rejected as infeasible.As the meeting broke up, there was somesense of frustration about what could bedone to disentangle the high-energy weakinteractions from the rest of what takes placewhen energetic particles are allowed to col-lide with targets.s According to Schwartz,“That night, lying in bed, it came to me.It was incredibly simple. All one had to dowas use neutrinos. ” He was just 27 at thetime.b Soon after, plaming for the experi-ment began in earnest.

The expximent to learn more about weakinteractions used new technologies-a spark

chamber (rexentl y invented at the time) anda newly completed alternating gradient syn-chrotrons (AGS), a type of particle acceler-ator, at the Brookhaven National Laboratoryon Long Island, New York.

By September 1961 Lederman, Schwartz,and Steinberger had set up their equipmentnext to the synchrotrons, using an internalberyllium target for the accelerated protonsto smash into. The collisions gave rise topions, most of which left the accelerator.About 10 percent of these pions decayed,giving rise to neutrinos. 7 To detect neutri-nos, and not other unwanted particles fromthe accelerator, a ftiter was set up outsidethe accelerator and forward of the berylli-um. Armor plating from a scrapped warshipwas used, a wall of steel 13.5 meters thick.Neutrinos would zip right through, althoughvirtually all other particles would be stoppeddead. Behind the steel wall, the detec-tor—the spark chamber-was set up. Thisdetector had to contain enough material tomake a few of the neutrinos react. The sparkchamber consisted of 90 aluminum plates(which in total weighed 10 tons), the targetfor the neutrinos. Sandwiched between thealuminum plates were layers of neon gas.If any of the neutrinos interacted in the alu-minum plates to produce charged particles,the particles would ionize the gas, knock-

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Table 1: Papers authored by J. .%eirrherger, L. Lederman, and M. Schwartz and cited ia the SCI” from1945 to 1988. The papers are arranged in descending order, according to number of citations. A =total numberof citations. B =bibliographic citation, Research frnnts to which the paper is core are listed in parentheses afterthe bibliographic citation.

A

506

362

262

25 I

236

I97

124

119

119

B

Herb S W, Hom D C, Ledermaa L M, Sena J C, Snyder H D, Yoh J K, Appd J A, Brown B C,Brown C N, hum W R, Ueno K, Ymnanoucfd T, Ito A S, Jiistlebr H, Kaplan D M & KephartR D, Observation of a dimuon resonance at 9.5 GeV in 400-GeV proton-nucleus collisions. Phys.Rev. Mr. 39:252-5, 1977. (78-1253, 790261, 80-0019, 81-0183, 82-0661, 830922)

Garwin R L, Lederman L M & Weinrich M, Observations of the failure of conacrvation of parityand charge conjugation in meson decays: the magnetic moment of the free muon, Phys. Rev.105:1415-7, 1957.

hum W R, Appel J A, Brown B C, Brown C N, Ueno K, Yammrouehi T, Herb S W, Hom D C,Ledermrrn L M, Smrs J C, Snyder H D, Ynh J K, F~k R J, Ito A S, Ji%tlein H, Kapkur D M &Kephart R D. Observation of soucture in the (upsilon) region. Phys. Rev, I.@, 39:1240-2, 1977,(78-1253, 79-0261, 80-0019, 81-0183, 82-0661)

Steinberger J. On the use of subtracting fields and the lifetimes of some types of mesnn decay. Phys.Rev. 76:1 I80-6, 1949.

Dmrby G, Gaitlard J M, Goutkuros K, Lederman L M, Miatry N, .%hwartz M & Steinberger J.Observation of high-energy neutrino reactions and the existence nf two kinds of neutrinos. Phys. Rev.Lat. 9:36-44, 1962.

De Groot J G H, Hmrsl T, Holder M, Kaoblocb J, May J, Paar H P, Pabmzi P, Para A, RanjardF, Schiatter D, Steinberger J, Srrter H, von Riiderr W, Wahl H, Wtdtaker S, Wtilimns E G H,E~ele F, Kteinknecht K, Lied H, Spatm G, WiUutzki H J, Dortb W, DYdnk F, Geweniger C,Hepp V, Tittel K, Wotachack J, Bloch P, Devaux B, Lorrratoa S, MaiUard J, Merlo J P, PeyaudB, Rander J, Savoy-Navarro A, Turlay R & Navarria F L. Inclusive interactions of h~gh-energyneutrinos and antineurrinos in irnn. Z. Phys. C—Par. Field. 1:143-62, 1979.

Chriatemon J H, Hicks G S, Lederman L M, Limon P J, Pope B G & Zavattbd E. Observation ofmassive muon pairs in hadron collisions. Phys. Rev. La. 25:1523-6, 1970.

Harral T, Holder M, KnobInch J, May J, Paar H P, Patar.zi P, Ranjard F, ScMatter D,Steinberger J, Suter H, von Riiden W, Watd H, Wfdtaker S, WIllktrns E G H, Eisele F,Kleinknecht K, Lierl H, Spahn G, Willutzki H J, Dm-th W, Dydak F, Geweniger C, Hepp V,T1ttel K, Wotachack J, Bloch P, Devaux B, Loucatoa S, MaiUard J, Peyaud B, Rander J,Savoy-Navarro A, Turlay R & Navarria F L. Results of a brain dump experiment at the CERNSPS neutrino facility. Phys. Mr. B 74:139-42, 1978.

Kaplan D M, Fisk R J, ItoA S, J6stlein H, Appd J A, Brown B C, Brown C N, Imea W R,Kepbart R D, Ueno K, Yammroucbi T, Herb S W, Horn D C, Ledermao L M, Sara J C,Snyder H D & Yoh J K. Study of the high-mass dirnuon continuum in 400-GeV proton-nucleuscollisions. Phys. Rev, I.@t. 40:435-8, 1978, (79-0121, 80-0164)

ing electrons from atoms. Then, under theinfluence of an electric field, the gas wouldbreak down and spark where ionized, re-vealing the passage of the newly created par-ticles (hence the term “spark chamber’ ‘).

A further tiftering factor (besides concreteand lead bricks) was the amount of time (twomicroseconds, or 2 x 1o-6 seconds) duringwhich the beam was hitting the target sparkchamber. This $‘time gate” was instafled tominimize the number of events due to cos-mic-ray background radiation (neutrinosfrom solar activity). The very short time“window” meant that any detected eventsthat occurred outside of the window couldthen be excluded as not due to accelera-tor-induced, high-energy radiation.~ Theneutrino-beam technique, first used by theselaureates, is now a mainstay at particle ac-celerators around the world.

In eight months of episodic ruining,the estimated 1014 neutrinos that passedthrough the 10-ton spark chamber yieldedonly 56 recorded events that looked like neu-trino collisions. But almost all of the 56events showed the collision producing amuon (similar in characteristics to an elec-tron, but 200 times heavier) rather than anelectron. Far fewer electrons had been pro-duced than one would expect if all neutrinoswere dike-of otdy one kind. Thu8, thi8 dis-covery was the first demonstration of tJtedoublet pairing of leptons (electrons andneutrinos). The electron had its own privatenetrtrino, and with Ledermart, Schwartz, andSteinberger’s discovery, so dld the muon.The experiment was succasfully completedin June 1962. A year later the Brookhavenaccelerator result was confirmed atCERN.8

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F@e 1: Year-by-year cites to papers authored by 19S8 Nobel Prize winners in physics. Dotted line=Herb S Wet sI. Phys. Rev. Lerr. 39:252-5, 1977. Solid line= Garwin R Let sI, F’hys. Rev. 105:1415-7, 1957,Dashed line =Danby G et al. Phys. Rev. Letf. 9:36-44, 1962.

2oo-

175.

Year

“Observation of high-energy neutnno re-actions and the existence of two kinds ofneutrinos, ” the paper that reported the No-belists’ discovery of the muon neutrino, ap-peared in the September 1962 issue of Phys-ical Review Letters. g According to datafrom the Science Citaliort Irra’exm,the papergathered five citations in its first year. In1963, the year the group’s findings wereverified at CERN, the full impact of the dis-covery was felt: nearly 60 explicit citations.As we have observed in dozens of citationstudies, significant findings in particle phys-ics produce nearly instantaneous citation rec-ognition. Table 1 is a list of the laureates’most-cited works. Figure 1 depicts the ci-tation record of the 1962 Physical ReviewLztters paper from time of publication untilLederman, Schwartz, and Steinberger wonthe Nobel Prize in physics. Also charted inFigure 1 are the citation records of the twomost-cited papers in Table 1.

Today, the two neutrinos form part of the“Standard Model” of the fundamental na-ture of matter. Although still incomplete, themodel posits that there are two basic kindsof building block particles: the quarks and

the Ieptons. All leptons have a correspond-ing member among the quarks (the so-called“doublet” nature of particles). The quarksfeel the strong nuclear force and form thebasis of particles such as the protons andneutrons of atomic nuclei. The leptons in-clude three charged particles: the electron,the heavier muon, and the still heavier tauparticle. There are also three neutrrd lep-tons—three neutrinos, one associated witheach of the charged leptons. 10Table 2 out-lines the specific particles and forces pres-ently known to make up all matter.11,12

Biographical Data on the Laureates

Lederman, Schwartz, and Steinbergerwere all physics professors at Columbia. Atthe time of the initiation of the prizewinningexperiment, Schwartz was in his late twen-ties; Lederman and Steinberger were in theirlate thirties. As can be seen from Table 1,the paper describing their Nobel Prize-win-ning efforts has over 230 references to it todate. The apparently small number of cita-tions— usually uncharacteristic of an impor-tant physics paper-is essentially an exam-

219

Table 2: Tbe Standard Model of elementary particle physics, which consists of two sets of fundamentalparticles(fermions) and four forces (bosons) that govern interactions between psrticles. 11II

FERMIONS BOSONS

QUARKS LEPTONS PHOTONS (carry electromagnetic force)

UP ELECTRON I GRAVITONS (carry gravitational force)DOWN ELECTRON NEUTRINOCHARM MUON GLUONS (carry strong nuclear force)STRANGE MUON NEUTRINOTOP TAU PARTICLE INTERMEDIATE VECTORS (carrv weak nuclear force)BOTTOM TAUNEUTRINO

I

ple of obliteration by incorporation. The lau-reates’ discovery and method were rapidlyabsorbed into the literature and supersededby other works.

Jack Steinberger

Steinberger, whowasbom May25, 1921,in Bad Kissingen, Germany, has been de-scribed as one of the most gified ex@tnen-talists in high-energy physics.c He emigrat-edto the US in 1934, ending up in Chica-go. He majored in chemical engineering atthe Illinois Institute of Technology, Chicago.Following his enlistment in the Army in1942, Steinberger worked at the Massa-chusetts Institute of Technology radiationlaboratory, Cambridge, where his seriousinterest in physics began. In 1948 he re-ceived his PhD in physics at the Universityof Chicago. Hewasprofessor ofphysicsatColumbia from 1950 to 1971. Steinberger,during his tenure at Columbia, had been co-Nobelist Schwartz’s thesis adviser. They hadbeen doing bubble-chamber experiments to-gether for years at the Brookhaven Cosmo-tron, a predecessor of the AGS that was usedin the Nobel Prize-winning work. Since1968 Steinberger has been at CERN .3,6.8Through 1988 Steinberger has had over1,400 cumulative citations to papers eitherauthored or coauthored by him.

Melvin Schwartz

Schwartz was born November 2, 1932,in the Bronx, New York. He attended theBronx High School of Science. Schwartz didall of his university work at Columbia, earn-ing a doctorate in physics in 1958. Afterserving on the Columbia physics facultyfrom 1958 until 1966, he moved on to Stan-ford University, California, where he re-

mained until 1979. Since then he has beenpresident of Digital Pathways, Inc., whichproduces data communications systems thatsecure computers from tampering by out-siders. s.G Of the three laureates, Schwartzhas the least number of cumulative citationsto his papers (through 1988, almost 500).This is no doubt due in part to the fact thatSchwartz is pursuing entrepreneurial inter-ests and is no longer in academe, where pub-lishing papers is an integral part of cotnmu-nicating science,

Schwartz may have been deprived of anearlier opportunity of winning the NobelPrize, 13In the early 1970s, while workingat the Stanford Linear Accelerator Center(SLAC), Schwartz may have been on hisway to tinding indirect evidence of the ex-istence of the Z particles (which theoristssay may unify the electromagnetic and weakforces of nature). Using a similar equipmentsetup as in the discovery of the muon neu-trino, he detected, besides muon neutrinos,five unusual events with no muons. How-ever, apparently due to the reluctance ofSLAC management to authorize continueduse of the accelerator and the rejection threetimes by the NationaI Science Foundationof Schwartz’s request for funding, the ex-periment went no further. It is believed thatSchwartz had found evidence for the so-called “neutral currents, ” a weak interac-tion involving the Z particle. The Z parti-cle was first detected at CERN in 1983.Carlo Rubbia and Sirnon van der Meer, wholed the effort to discover the Z, shared theNobel Prize in physics in 1984, as we dis-cussed in a previous essay. 14

Leon Lederman

Ledermarr was kern into a Russian itnrni-grant family on July 15, 1922, in New York

220

Table 3 Selected Uatof 1988 SCP research fronts on elementary particles and forces. A =number of core papers.B =mmrher of citing papers.

Nurnher

88-044088-044588-122188-123088-172388-249688-269588-285288-324488-4C0488-407788-471588-472088-559588-695088-726388-7481

Name

Weak and hypoweak interactionsEnergy and symmetry of states in light nucleiCERN collider and the Standard MndelThe quark structure of matterLow-energy nuclear eleztron captore and determining neutrirro massFlavor and the structure of hadrons and nucleiLow-multiplicity collisions at riw CERN ISRCosmology and particle physicsProton-proton scaneringAspects of the third quark mndelQuark plasma oscillationsReview of particle propertiesSum?rswnmeIw and the unification nf fundamental interactionsCc&i; ray n~utrinos in the atmosphereStrangeness in dense matterTheory of heavy fermion systemsNeutrino mass and Iefi-right symmetry

City. He grew up in the Bronx, just 10blocks from where co-Nobelist Schwartzlived. Following his secondary schooling atJames Monroe High School in New York,Lederman graduated with a degree in chem-istry from the City College of New York in1943. Although he majored in chemistry, hegot more enjoyment out of physics courses.He went on to study physics on a scholar-ship at Columbia, receiving his doctorate in1951. Lederman was director of Columbia’sNevis Laboratory from 1962 to 1979, whenhe became director of Fermilab. Just recent-ly retired from his directorship, Ledermannow teaches as the Frank L. Sulzberger Pro-fessor of Physics at the University of Chi-cago. Lederman was instrumental in con-vincing Schwartz that the AGS at Brook-haven National Laboratory was powerfulenough to conduct the neutrino experiment,despite Schwartz’s initial misgivings. Hap-pily, Lederman’s hunch was correct. He isan outspoken proponent of the Super-con-ducting Super Collider (ssc).3,6,8

Of the laureates Lederrnan has the mostcumulative citations to his papers—over2,800. Indeed, the most-cited work in Table1, entitled “observation of a dimuon reso-nance at 9.5 GeV in 400-GeV proton-nu-cleus collisions, ” was coauthored by Leder-man. Nearly all of the most-cited papers inTable 1 relate to the use of accelerators inthe discovery and observation of nuclearparticles.

AB

37 43021 299

4 3711 1333 21

10 512 14

13 1538 596 1102 397 1063 452 102 243 302 49

Neutrino Physics Today

High-energy physicists have a continuinginterest in neutrinos, as these particles arebelieved to hold the key to solving funda-mental questions in physics and early uni-verse cosmology. This interest is contirmedby ISI” research-front data. Three 1988fronts are explicitly tied in with neutrinos:#88- 1723, “Low-energy nuclear electronsapture and determining neutrino mass”;f#88-5595, “Cosmic ray neutrinos in the at-mosphere”; and #88-7481, ‘‘Neutrino massand left-right symmetry. ” Table 3 is a se-lected list of 1988 research fronts that dealwith particle physics activity.

Neutrinos figure prominently in the at-tempt to complete the Standard Model ofelementary particles. Although the tats par-ticle has been discovered, there has been nodirect evidence yet in hand for a tau neutrino(which there should be, according to the“doublet” nature of these particles-indeed,a corresponding hypothetical ‘‘top” quarkis still being sought at both the CERN andFermilab accelerators). 15

The search for other types of neutrinos be-sides electron neutrinos and muon neutrinoshas implications for astrophysicists and theirbig bang theory of how the universe wascreated. The theory works extremely wellat present with just the known particles ac-counted for and with the notion that the neu-trino has no mass; however, if further types

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(termed generations) of neutrinos are found,then the big bang theory, as now formulated,would be in serious trouble. If neutrinoshave a nonzero mass, they would constitutea significant fraction of the total mass of theuniverse. This would have a major impacton the issue of whether the universe willcontinue to expand forever or whether it willin fact eventually recompress. If neutrinoshave mass, they would add to the gravita-tional attraction, and they would tend to slowup the universe’s expansion and eventuallyturn it around. ‘b

A related issue, perhaps of more practicalimmediacy to laypersons, is the ongoingpuzzlement by physicists over the discrep-ancy between the number of neutrinos ob-served coming from our sun, which is muchlower than the number predicted to be gen-erated according to the most up-to-datetheories. Neutrinos are created in nuclearreactions that are directly sensitive to thesun’s temperature, and the numbers record-ed that reach the earth are less than one-third of the number predicted by theory. 17If a practical way can be found to show thatneutrinos do have mass, the discrepancymay be explained. The understanding of

how the sun shines, with a correspondinglack of neutrinos being emitted from the pro-cess, will help scientists determine accurate-ly the energy-generating processes in thecore of our star, as well as its health.

In the past decade, seven other physicistshave been awarded Nobel Prizes (in 1979,1980, and 1984) for their discoveries aboutthe fundamental particles of matter. This re-flects the importance that world scienceplaces on this field. As efforts to learn moreabout the constituents of the atomic nucleushave increased, larger and more powerfulparticle accelerators have been built. Theproposed Texas-based SSC would be, ifbuilt, the largest and the most expensive ac-celerator ever. 18 The promise of makingthe Standard Model of elementary particlesmore complete indeed has allure, but can weafford the cost of increasing our knowledgeof fundamental particles?

*****

My thanks to C.J. Fiscus and PeterPesavento for [heir help in the preparationof this essay.

*,W,s,

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