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

SPRING 1998

A PERIODICAL OF PARTICLE PHYSICS

SPRING 1998 VOL. 28, NUMBER 1

EditorsRENE DONALDSON, BILL KIRK

Contributing EditorsMICHAEL RIORDAN, GORDON FRASER

JUDY JACKSON, PEDRO WALOSCHEK

Editorial Advisory BoardGEORGE BROWN, LANCE DIXON

JOEL PRIMACK, NATALIE ROE

ROBERT SIEMANN, GEORGE TRILLING

KARL VAN BIBBER

IllustrationsTERRY ANDERSON

DistributionCRYSTAL TILGHMAN

The Beam Line is published quarterly by theStanford Linear Accelerator Center PO Box 4349, Stanford, CA 94309. Telephone: (650) 926-2585 INTERNET: beamline@slac.stanford.eduFAX: (650) 926-4500 Issues of the Beam Line are accessible electronically onthe World Wide Web at http://www.slac.stanford.edu/pubs/beamlineSLAC is operated by Stanford University under contractwith the U.S. Department of Energy. The opinions 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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BEAM LINE

FEATURES

2 ALL WE WANT IS THE WORLD’S BIGGEST

MACHINE!

One of our Contributing Editors follows up

on his article in the last issue on the origins

of international collaboration in Europe

to describe the creation of CERN.

Gordon Fraser

9 SEARCHING FOR NEUTRINO

OSCILLATIONS

The author describes why understanding

neutrino oscillations might be critical

to the question of whether neutrinos

have mass.

Maury Goodman

17 PHYSICS WITH CHARM

A Fermilab physicist describes why the study

of the charm quark might open the way

to physics beyond the Standard Model.Jeffrey A. Appel

DEPARTMENTS

22 THE UNIVERSE AT LARGEThis Was the Year That Was(Astrophysics in 1997)Virginia Trimble

31 CONTRIBUTORS

DATES TO REMEMBER

CONTENTS

2 SPRING 1998

All We Want Is thContributing Editor

Gordon Fraser follows

up on his piece on the

origins of international

collaboration in Europe

(Winter 1997) to describe

the creation of CERN.

This article is adapted

from a chapter in his

book The Quark

Machines on the politi-

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.

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BETWEEN 1949 AND 1959, the dream of an international European laboratoryfor particle physics—‘CERN’—became a reality, briefly sporting the world’s highestenergy proton synchrotron. In those ten years, scientists from countries that had been

at war only a few years earlier set aside their differences and collaborated in a dramaticdemonstration of what could be achieved when national characteristics dovetail smoothly inthe achievement of a common goal. The ideals and insights of CERN’s founding fathers providevital lessons in the continued quest for wider international collaboration in particle physics.

World’s Biggest Machine!by GORDON FRASER

Scientific objectivity is a common bond betweennations. In every country, scientists address thesame problems. If one nation hushes up its researchfindings, the knowledge will ultimately be acquiredelsewhere. Scientific curiosity cannot be quenched.In the aftermath of World War II, science was seenas a potential olive branch. However the war hadshifted much of the scenery. Major efforts to har-ness fission and microwaves had demonstrated thevalue of large-scale collaboration. Militant nation-al pride had given way to new international aware-ness. Embarrassed by having caused so much strifeand inflicting it on the rest of the planet, Europefelt it had to present a more united front.

The United States, as the leading postwar sci-entific power, attracted scientific emigrants fromEurope in what would eventually be called the“brain drain.” This leak first had to be stemmedif the Continent was not to find itself starved of tal-ent. Following the Congress of Europe in The Haguein May 1949, the European Cultural Conferencein Lausanne in December 1949, attended 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 foratomic research.” Then Raoul Dautry, Adminis-trator-General of the French Atomic EnergyCommission, read a message from Louis de Broglie,

winner of the 1929 Nobel prize for his elucidationof particle waves. De Broglie maintained that sci-entific collaboration between European countriescould open up projects that were beyond the meansof individual nations. Following up with his ownideas, Dautry affirmed that astronomy and astro-physics on one hand, and atomic energy on the oth-er, would be ideal vehicles for such internationalcollaboration.

Dautry could call on powerful 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, Scientific and Cultural Organization(UNESCO). Another prominent French figure wasnuclear fission pioneer Lew Kowarski, who hadworked in Britain during the war and understoodthe special position of the United Kingdom, whichwas trying to “go it alone.”

At the UNESCO 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-diation Laboratory during the war. After the warRabi, with Norman Ramsey, had pushed for the es-tablishment 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 SPRING 1998

Upon arriving at Florence, Rabiwas surprised to discover that theagenda included no mention of theEuropean physics collaborationmooted at Lausanne. Setting up phys-ics laboratories was something Rabiknew well, but international com-mittee work was not. The first thingwas to get an item onto the agenda,overcoming the apparent indifferenceof his American colleagues. Morehelpful were Auger and the 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 the chaos of thewar. Amaldi went on to become oneof Europe’s great postwar scientificstatesmen, his achievements appear-ing to stem from a deep sense of dutyrather than personal ambition.

Drafted with the assistance ofAuger and Amaldi, the proposal fromRabi at Florence requested UNESCO“to assist and encourage the forma-tion and organization of regionalresearch centres and laboratories inorder to increase and make morefruitful the international collabora-tion of scientists in the search fornew knowledge in fields where theeffort of any one country in the re-gion is insufficient for the task.” Rabipointed out that the initiative “wasprimarily intended to help countrieswhich had previously made greatcontributions to science,” andthat “the creation of a centre inEurope . . . might give the impetusto the creation of similar centres inother parts of the world.” Themotion was unanimously accepted.Where Europeans had failed to reacha consensus, an American resolution

for Europe at a meeting of a UnitedNations agency had opened a newdoor.

The two men who took Rabi’s ba-ton and sprinted with it were justthose who had helped him draft theFlorence resolution—Amaldi andAuger. Just a few weeks later, Amaldiwas stimulated by a visit to Brook-haven, where the Cosmotron wasalready taking shape. Few Europeanshad ever seen a physics effort of suchproportions. “Colossale,” he re-marked.

Under the auspices of the Euro-pean Cultural Centre, a meeting wasorganized in Geneva in December1950 with delegates from Belgium,France, Italy, the Netherlands, Nor-way, and Switzerland. Auger un-veiled a plan for a new laboratorydedicated to the physics of elemen-tary particles. He knew that in-triguing new discoveries had alreadybeen made in cosmic rays, but thatthis windfall sprouting could becomea major harvest once the big new U.S.accelerators were up and running.

Initial contacts with Britain hadestablished that while its physicistswere not against the idea of a Euro-pean laboratory, they still wanted togo their own way. Their support wasvital to get the idea off the ground,however, as in Europe only Britainhad experience in major projects. Pos-sible sites mentioned for the newEuropean laboratory included Gene-va and Copenhagen.

The resolution passed at theGeneva meeting was startling. Itrecommended the creation of a lab-oratory for the construction of aparticle accelerator whose 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)

BEAM LINE 5

(which meant the mighty 3 GeV Cos-motron and the even bigger 6 GeVBerkeley Bevatron). In a field where,apart from Britain, Europe had no tra-dition and little expertise, the planwas simply to jump into the lead bycash and enthusiasm. These bold pro-posals were enthusiastically endorsedin Italy, Belgium, France, Norway,Sweden, and Switzerland. In Britain,where physicists were busy buildingseveral new accelerators, there wasastonishment and skepticism. “Whois behind the scheme?” thunderedP. M. S. Blackett, “Is it serious?”

A study group to define the newaccelerator included Cornelis Bakkerfrom the Netherlands, who had builta synchrocyclotron at Amsterdam,Odd Dahl from Norway, a talentedengineer responsible for the first nu-clear reactor to be built outside theoriginal “nuclear club,” and FrankGoward, a British physicist who hadgraduated into wartime radar work.In a flush of modesty after the initialstrident proclamation, the new ad-vertised goal was to copy the 6 GeVBerkeley machine instead of the orig-inal idea of building the world’slargest machine.

One suggestion was to use NielsBohr’s laboratory in Copenhagen asa home for the new institute, an ideathat also found favor in Britain, andnaturally stimulated interest in Nor-way and Sweden. Bohr, who had notbeen party to the previous discus-sions around the Auger-Amaldi axis,began to exert his considerable in-fluence. Others thought that he waspast his prime. The remoteness ofCopenhagen and the difficulty of theDanish language were also a deterrent.

To sidestep the challenge of goingstraight for the world’s largest

machine, a newplan envisioneda smaller initialmachine to launchthe new laborato-ry. Proposals wereput forward for a500 MeV synchro-cyclotron and a 5GeV proton syn-chrotron, with de-sign and construc-tion proceeding inparallel. Europeanphysicists seemedoptimistic aboutgovernment fund-ing. On the question of the site, newcriteria, designed to undermineCopenhagen’s case, stipulated the useof a major language.

A November 1951 meeting inParis suggested that the energy goalof the new synchrotron could be ashigh as 10 GeV, but to defuse thethorny siting issue, the respectivegroup leaders would remain at theirhome bases—Dahl in Norway work-ing on the synchrotron, Bakker inThe Netherlands on the synchrocy-clotron, Kowarski in France on in-frastructure, and Bohr in Copenhagenon theory, with Amaldi’s adminis-trative hub in Rome.

A meeting at Paris that Decemberbrought representatives togetherfrom thirteen European nations, in-cluding West Germany. The Nether-lands delegation put forward a five-fold plan, with two points designedto appeal to the Northern faction, ex-pressing interest in using the exist-ing Copenhagen center and Britain’saccelerators, and the remainingpoints designed to appeal to Franco-Italian sentiment, covering the

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 SPRING 1998

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

A major international physicsmeeting at Copenhagen in June 1952heard that the first beams had beenproduced by the new Cosmotron. ACERN Council meeting immediatelyadvocated that Dahl’s group aim fora scaled-up Cosmotron to operate inthe energy range 10–20 GeV.

To make their scaled-up versionof the Cosmotron, the 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, then working onbetatrons. To receive their Europeanvisitors, M. Stanley Livingston hadorganized a think tank. The Cos-motron’s C-shaped magnets all faced

construction of two new machinesand the establishment of a “Euro-pean Council for Nuclear Research”—in French “Conseil Européen pourla Recherche Nucléaire.” Theacronym CERN was born.

The meeting was continued inFebruary 1952 in Geneva, where theprovisional CERN Council was askedto prepare plans for a laboratory. Theproposal was immediately acceptedby Germany, the Netherlands andYugoslavia, and accepted subject toratification by Belgium, Denmark,France, Greece, Italy, Norway, Swe-den, and Switzerland. Denmark of-fered the new Council the use of thepremises at the Institute of Theo-retical Physics of the University ofCopenhagen. While this meeting wasa major step forward, the enigmaticBritish were not even present.

Emphasis switched from negoti-ation to organization and planning.With 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)

BEAM LINE 7

outwards, making it easy for nega-tively charged particles to be ex-tracted, but not positive ones. “Whynot have the magnets alternately fac-ing inward and outward?” suggestedLivingston. Ernest Courant, HartlandSnyder, and John Blewett seized onthe suggestion and quickly realizedthat this increased the focusingpower of the magnets. The new sug-gestion, variously called “strong fo-cusing” or “alternating gradient,”might allow the proton beam to besqueezed into a pipe a few centime-ters across, instead of the 20×60 cen-timeters of the Cosmotron beampipe. The relative cost of the sur-rounding magnet, the most expen-sive single item in synchrotron con-struction, would be greatly reduced.

The European visitors arrived atBrookhaven prepared to learn how tomake a replica of the Cosmotron anddiscovered instead that the designhad suddenly become outdated. This1952 visit set the tone for therelationship between the newEuropean generation of physicists andtheir American counterparts. Basedon mutual respect and colored by ahealthy spirit of competition, this re-lationship was to work to their mu-tual advantage. Untempered, com-petition can lead to jealousy andsecrecy, but in particle physics thishas rarely occurred. Although eachside has striven to push its own petprojects, collaboration and assistancehave always been available, and thecommunity as a whole welcomes andadmires breakthroughs and develop-ments, wherever they may be made.

Dahl was adamant that the newstrong-focusing technique had to beused for the CERN machine theywere planning. It would open up the

prospect of at least 20, and possibly30 GeV, and save money. The onlyproblem was that nobody had builtone yet. Although a gamble, takingthis unexplored strong-focusing routeturned out to be one of the most im-portant decisions in CERN’s history.In Britain, the strong-focusing pro-posal gave a new appeal to the Euro-pean project. The traditional nationalapproach and the more ambitious in-ternational venture became com-plementary. However before Britaincould be persuaded to join CERN, keyfigures had to be convinced, includ-ing the formidable Lord Cherwell,Winston Churchill’s staunch friendand scientific advisor.

In December 1952 EdoardoAmaldi was given a frosty receptionby Cherwell in London. Within min-utes, Cherwell told Amaldi in no un-certain terms that he was skepticalof the CERN idea. Undeterred,Amaldi wanted to meet some of theyoung Britons who might be inter-ested in joining Dahl’s group. Dele-gated to drive Amaldi from Londonto Harwell was John Adams, a youngengineer who had moved to syn-chrotron development after wartimeradar work. At Harwell, Amaldi metothers who were working on both theCERN machine design and a majornew British machine.

With the national machine com-mitted to the old weak-focusing de-sign, Adams and colleagues had beentaking a close look at strong focus-ing, and discovered that the initialidea was optimistic. Small errors inthe magnets—tiny misalignmentsand 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 SPRING 1998

Dubna Synchrophasotron attaining10 GeV, and even by Britain’s 1 GeVsynchrotron at Birmingham. Eyeswere focused on the race between thetwo proton synchrotron teams atBrookhaven and CERN.

On November 4, 1959, CERN’snew proton synchrotron unexpect-edly accelerated protons all the wayto 25 GeV, becoming the world’shighest energy machine, easily out-stripping Dubna’s 10 GeV. The CERNteam was jubilant, and emotionaland dramatic scenes offered a sharpcontrast in national stereotypes.Gilberto Bernardini from Italy jubi-lantly kissed a disconcerted Adams

focusing machines would have to belarger than the Brookhaven physi-cists had initially suggested. Toaccommodate a larger tube, the en-veloping magnet had to be muchlarger too, and the design energy ofthe CERN machine was compro-mised to 25 GeV.

In parallel with these technicaladvances, the British suddenlyswitched from aloofness and for-mally joined CERN, which finally de-cided on Geneva as the site for thenew laboratory. On the map, the can-ton of Geneva appears as a curiousappendage at the extreme west ofSwitzerland. Almost totally sur-rounded by France, it is joined to therest of Switzerland by an umbilicalcord a few kilometers across. Begin-ning with the Red Cross in 1863, thecity of Geneva has become the homeof many international organizations.

An advance party of the protonsynchrotron group arriving in Genevawas joined by John and HildredBlewett from Brookhaven. After be-stowing crucial insights, Dahl pre-ferred to remain in Bergen, first ap-pointing Goward as his on-sitesupervisor, and finally resigning fromthe new project. Just a few monthslater, 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 the newproject with its leader. John Adamswas to be the Moses who would takeCERN into the Promised Land.

CERN’s first machine, the 600MeV synchrocyclotron, was com-missioned in 1957 and soon beganproducing useful physics. Howeverit was far outgunned by the 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 ‘Rememberthose scintillation counters you andFidecaro put in the ring? Will theydetect 20 GeV protons?’ I paused longenough to grab a bottle of whisky andProfessor Fidecaro, in that order, andcame along to celebrate.”

The following day, at a specialnews meeting for CERN staff, Adamsshowed a vodka bottle he had beengiven several months earlier on a tripto Russia with strict instructions thatit should be drunk when the CERNsynchrotron surpassed Dubna’s en-ergy. The bottle was now empty.

But Dubna’s vodka bottle was notthe only unfilled thing at CERN. Alsovery empty were the experimentalhalls around the new synchrotron. Inthe rush to build the new machine,few people had paid attention to theinstrumentation needed to carry outexperiments. At Brookhaven, thenew Alternating Gradient Synchro-tron (AGS), the twin of the new CERNmachine, did not accelerate a beamuntil six months later. But this delaywas more than compensated by theenthusiasm and ingenuity that wentinto planning experiments. U.S.physicists had cut their high energyaccelerator teeth on the Cosmotronand the Bevatron. Within a few yearsof its commissioning, the AGS reapedan impressive harvest of importantnew physics results.

CERN had risen to the challengeof building the world’s most power-ful machine from scratch in just afew years, but developing researchinfrastructure and fostering experi-mental prowess was to take some-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.

Searching for NeutrinoOscillations

BEAM LINE 9

HYSICISTS FROM AROUND theworld are engaged in a wide variety of ex-periments to determine whether neutrinoshave mass. This possibility has intrigued

physicists and cosmologists for two decades, ever since neutrinos emerged asa leading candidate for the dark matter thought to inhabit the Universe. Acomprehensive new experiment is being built in Illinois and Minnesota tostudy neutrinos from an intense new Fermilab 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 neutrino oscillations, aprocess in which neutrinos can transform 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. But this is not thecase for neutrino mass, because there are three different 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 neutrinos them-selves. Then I cover some of the experimental hints supporting neutrinooscillations. Finally, I close with a description of the Fermilab-to-Soudan,Minnesota, long-baseline neutrino project, an ambitious program to searchfor changes in the properties of a neutrino beam as it speeds silently beneaththe farms 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 SPRING 1998

source of copious neutrinos, but I amnot aware of any experiment that hasdetected them.) Neutrinos are eithermassless or far lighter than thequarks and other leptons. This dif-ference might be related to the factthat neutrinos have no electriccharge, while the quarks and otherleptons do have charge. The questionof mass remains one of the big mys-teries remaining in particle physics.There is no clear prediction relat-ing the masses of the nine chargedfermions, and none for whether theneutrino masses are zero or just verysmall.

However, most physicists expectthat if neutrinos do have mass, evena tiny amount, the phenomenon ofneutrino oscillations should exist(see the box on the opposite page).These transformations are closely re-lated to the quantum-mechanicalphenomenon of mixing. If neutrinososcillate, they can be produced in oneflavor, such as νµ, and be detectedas another flavor, such as ντ , somedistance away.

When Pauli predicted the exis-tence of the neutrino in 1930, he didnot suppose there would be morethan one kind. He was only trying toexplain the wide distribution of elec-tron energies observed in nuclearbeta decay. The idea that neutrinoscome in different flavors became ac-cepted in 1962, when an experimentat Brookhaven National Laboratorydirected neutrinos from pion decayat a target and found that almost allof the events had a muon, and not anelectron, emerging from the point ofthe neutrino interaction. This resultled to the idea that each lepton fla-vor (e, µ, τ) has a conserved quantity—something that doesn’t change in an

THERE ARE THREE“flavors” of neutrinos, theelectron neutrino νe, the

muon neutrino νµ, and the tau neu-trino ντ . Each is closely related to thecorresponding lepton: the electron,muon, and tau lepton. These six lep-tons together with six quarks con-stitute the fundamental “matter”particles of the Standard Model ofhigh energy physics.

The three neutrinos interact veryweakly with ordinary matter. Physi-cists originally thought that the greatweakness of the interaction wouldmake them impossible to detect, butneutrinos have been seen comingfrom accelerators, from nuclear re-actors, from cosmic-ray interactionsin the atmosphere, from the sun, andfrom Supernova 1987A. (Nuclearweapon explosions are also the

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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)

BEAM LINE 11

interaction—associated with it.When the pion decays, it almost al-ways becomes a muon and a neutri-no and hardly ever an electron anda neutrino. The Brookhaven NationalLaboratory result could be explainedif the π+ decays into a µ+ and a νµ ;when they interact with the targetnuclei, the νµ’s generate muons, notelectrons.

When the third lepton, the tau,was discovered at the 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 numbers of Z bosons; thisparticle served as a neutrino counterbecause its decay rate is proportion-al to the number of fundamental par-ticles with less than half its mass.Measurements of this rate at CERNand SLAC confirmed that there areonly three neutrino-like particles inthe elementary particle zoo—a resultthat had been predicted by cosmolo-gists. So far, there has not been anyconvincing evidence that the ντ in-teracts with nuclei to make taus ina manner equivalent to the other twoneutrinos. But a current Fermilab ex-periment is expected to find these ντinteractions.

The two factors affecting neutrinooscillations (see adjacent box) thatare under the control of the experi-menter are the neutrino energy Eνand the distance L between theirsource and the detector. These ap-pear in the ratio L/Eν, so an experi-ment designer needs a large distanceand low energies in order to measuresmall values of the mass differencebetween two neutrino types. This re-quirement must be balanced againstthe fact that large distance and lowenergy both make it more difficultto detect a large number of neutrinoevents.

Let’s go back to the Brookhavenexperiment that discovered themuon neutrino. If the mixingstrength and mass difference hadboth been large enough, that exper-iment would not have been able todiscover the νµ. It would have seenboth electrons and muons comingfrom the point of the neutrino in-teractions! We can use the success ofthat experiment to place limits onthe combination of the two parame-ters. We usually do this by making agraph in the parameter space calledthe “∆m2 − sin2 (2θ) plane,” these be-ing two parameters that specify themixing strength and mass difference(see the box on the next 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∆m2

πEν

12 SPRING 1998

Simply put, five solar-neutrinoexperiments have measured asignificantly smaller number of neu-trino interactions than expected,based on the measured heat outputof the Sun and nuclear physics mod-els of both the Sun and the detectors.Each experiment observed fewer neu-trinos than expected, but the actualdeficit 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 account for all the datawithin the framework of neutrinooscillations.

As discussed in the box onpage 11, the length scale of an ex-periment provides a possible oscil-lation length. There are two possiblescales for solar neutrinos: the dis-tance from the Sun to the Earth andthe radius of the Sun. Each lengthscale leads to a separate neutrino-oscillation solution for the solar neu-trino deficit. One (labeled “vacuum”in the illustration on the left) arisesfrom a straightforward solution ofthe relationship between neutrinomass and oscillations (see the box onthe left). The other solutions (labeled“MSW” after Stanislav Mikheyev,Alexei Smirnov, and Lincoln Wolfen-stein, who formulated the 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 these solutions involve os-cillations of electron neutrinos intoother kinds.

The atmospheric neutrino deficittakes us underground to experimentsthat were originally built for anotherpurpose—to search for proton decay.

experiment that is consistent withsmall or no neutrino oscillations cor-responds to a curve in that plane thatexcludes the values of mixingstrength 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 at Serpukhov, Russia,have grown from tens to thousandsto millions of neutrino events. Noneof these experiments has witnessedevidence for νµ → νe or νµ → ντ os-cillations. And at the same time, ex-periments at nuclear reactors havefound no evidence for νe oscillationsin detectors situated up to a kilo-meter from the reactor. The pub-lished limits have steadily crept tolower values of the neutrino mix-ing strength and mass difference.

BUT THE STORY by nomeans ends there. While ex-periments at reactors and high

energy accelerators have found noevidence for them, four hints haveemerged suggesting the real possi-bility of neutrino oscillations andhence mass. These are the solar neu-trino deficit, the atmospheric neutri-no deficit, the Liquid Scintillator Neu-trino Detector (LSND) experiment atLos Alamos National Laboratory, andthe missing matter problem. Thesehints suggest the existence of neutri-no oscillations in regions of theparameter space that have not beencompletely ruled out by acceleratorexperiments.

The solar-neutrino deficit hasbeen around for thirty years. (See“What Have We Learned About SolarNeutrinos” by John Bahcall in theFall 1994 issue of the Beam Line.)

�����������

���

103

100

10–3

10–6

10–9

10–410–5 10–3 10–2

Mixing Strength, sin2(2θ)

Mas

s D

iffe

ren

ce, ∆

m2

(eV

2 )

10–1 1

����

������

Vacuum

Missing Matter?

LSND

Atmospheric Ratio

Up/Down

����

������

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.

BEAM LINE 13

These massive detectors, whichweigh from one to fifty thousandtons, haven’t discovered protondecay, but they do observe about ahundred interactions of atmosphericneutrinos per year for every thousandtons of detector mass. These neu-trinos are created near the top of theatmosphere when cosmic-ray pro-tons initiate a particle cascade, mak-ing one or more charged pions, eachof which decays into a muon and aνµ. The muon subsequently decaysinto an electron, a νµ, and a νe. Thus,the ratio of νµ flux to the νe flux ob-served in an underground detectorshould be about two. This is quitea strong prediction, regardless ofcosmic-ray rates and the subtletiesof calculating the number of parti-cles produced in the cosmic-ray cas-cades. Underground detectors seemto be measuring the expected num-ber of electron neutrinos, but onlysixty percent of the expected muonneutrinos. This νµ deficit could be ex-plained by νµ → ντ oscillations, withthe ντ too low in energy to producea tau lepton by interacting with a nu-cleus. This deficit seems to indicatea value of ∆m2 betyween 10−3 and1 eV2 (see region labeled “Atmos-pheric Ratio” in the illustration onpage 12).

The distance that atmosphericneutrinos travel before hitting a de-tector varies from 25 kilometers forthose coming from overhead to12,000 kilometers for those comingfrom the other side of the Earth. Thisprovides an opportunity to determinewhether there is any difference in thesignal between the up-going and thedown-going neutrinos. If so, the os-cillation length for typical atmos-pheric neutrino energies (500 MeV)

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

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

The LSND experiment at LosAlamos, unlike the solar and atmos-pheric neutrino experiments, was ex-plicitly built to look for neutrino os-cillations. Operating near the targetof the LAMPF accelerator, it uses avery intense π+ beam. The pions stopin the target, decay into a µ+ and a νµ,and the µ+ decays into 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 numbers of these parti-cles are detected, they probably arosefrom ν–µ → ν–e’s oscillations. 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 SPRING 1998

density should just equal the criticalvalue, though there are recent ob-servational data which suggest onlytwenty percent of that value. Ordi-nary baryons, the stuff that makesup stars and stuffed pizza, is onlyabout five percent of the critical val-ue, based on both observational dataand the rates of light element pro-duction during the Big Bang. Someof this missing matter may well beneutrinos; there are hundreds ofthem in every cubic centimeter ofthe Universe. If they had a mass ofjust 5 eV, neutrinos would outweighall the stars and pizza in theUniverse.

Experimenters want to confrontthese hints of neutrino oscillationswith more definitive measurements.New solar neutrino experiments aredetermining the size, time depen-dence, and energy dependence of thesolar neutrino deficit. New short-baseline oscillation experiments arestudying mass differences in the re-gion of the missing matter problem.The reported LSND effect will besought by another collaboration atthe Rutherford Laboratory in Britain,and there is a proposal for a futurefollow-up detector at Fermilab (seetable on the left for a small selectionof these experiments).

WHILE UNDERGROUNDexperiments will continueto study the atmospheric

neutrino deficit, there is another planto study possible neutrino oscilla-tions in the same region of parame-ter space. These are the long-baselineexperiments. While short-baselineexperiments are typically one kilo-meter from the point where the neu-trinos are produced, long-baseline

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

Unlike the atmospheric and solarneutrino deficits, the LSND signal hasbeen observed in only one experi-ment. In fact, other experiments thatare sensitive to these oscillationsover similar regions of parameterspace have obtained negative results.The region favored by LSND but notruled out by other experiments(labeled “LSND” in the figure onpage 12) suggests a value of ∆m2

around 1 eV2.The final hint, the missing mat-

ter problem, is really suggestive ofneutrino mass rather than oscilla-tions. There is a critical density ofmatter in the Universe (see article byAlan Guth in the Fall 1997 issue ofthe Beam Line, Vol. 27, No. 3), aboutone hydrogen atom per cubic me-

ter, abovewhich theUniverse isclosed andwill some-day collapseback into asingle point.If the densi-ty is at orbelow thiscritical den-sity, the Uni-verse is openand will ex-pand forev-er. Thereare strongtheoreticalargumentsthat the

Select Present/Future Neutrino Experimentsa

NeutrinoExperiments Energy Location Status

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

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

Reactor Chooz 5 MeV France CurrentPalo Verde 5 MeV Arizona Future

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

Long-baseline MINOS 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

BEAM LINE 15

experiments in the United States andEurope will be located 730 km awayfrom the source. And another exper-iment in Japan will have 250 km be-tween neutrino production and de-tector. All three of these choices arematters of convenience—the dis-tances between existing acceleratorsand existing underground facilities.As luck would have it, however, allthree projects will substantively ad-dress the possibility that theatmospheric neutrino deficit is dueto neutrino oscillations.

As an example of one of the mostambitious new neutrino oscillationprojects, I will now focus on theFermilab-to-Soudan long-baselineproject (see map on the right). Thereare three elements to the project: theneutrino beam, a near detector at Fer-milab, and a far detector at theSoudan underground physics labora-tory in northern Minnesota.

A high-intensity neutrino beamfrom Fermilab will be made possibleby a new high-intensity 120 GeV pro-ton source called the Main Injector.Scheduled for completion in 1999,this facility is being built to replacethe present Main Ring as one stageof acceleration. The Main Injectorwill also allow a very high-intensityneutrino program, known as NuMIfor “Neutrinos at the Main Injector,”to be run simultaneously with otherexperiments . The intense protonbeam makes a neutrino beam by hit-ting a target to make the maximumnumber of pions and kaons, whichare focused forward to give a beamwith as little divergence as possible.Then they travel through a one kilo-meter pipe where many of them de-cay into neutrinos, which continuemoving forward. The kinematics of

the pion decay results in an averageangle between a neutrino and theoriginal beam of about 1/20th of adegree.

One obvious concern in aiminga beam at a target so far away is theprecision required to hit it, but thisturns out to be only a minor prob-lem. Hitting the target is a similar toaiming a flashlight at the moon.Most people could hold the flashlightand point accurately enough. Theproblem comes in seeing the flash-light while standing on the moon.This could only be accomplishedwith a powerful enough light. Thelong-baseline neutrino problem issimilar. The neutrino beam spreadsout as it recedes from Fermilab, los-ing its intensity. And, neutrinos arevery weakly interacting, so one needsa very massive target in order to de-tect just a few of them. In order tostudy such long oscillation lengths,the detectors must be far away fromthe source and can only intercept asmall fraction of the beam. Thus itis 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 the deepestlevel of a historic iron mine—is theexisting Soudan 2 fine-grained de-tector. The mine, which operated foralmost one hundred years, is currentlybeing maintained for tourists by theState of Minnesota Department ofNatural Resources. Scientists plan tobring ten thousand tons of iron tobuild the MINOS detector, which willjoin the one thousand tons already inSoudan 2, to study neutrinos fromFermilab. It’s a bit like taking coal toNewcastle.

12 km

SoudanLake

Superior

Lake Michigan

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 SPRING 1998

new MINOS detector in 2002. Givenall the other neutrino experimentsaround the world, I can promise thatthere will be substantial progress inunderstanding neutrinos and the pos-sibility of neutrino oscillations dur-ing the next decade. But I suspectthat progress will come slowly andgradually. The large and growingeffort being devoted to neutrino ex-periments is indicative not only ofthe interest in these ghostly particlesbut also the difficulty of doing pre-cision work in this field. Even if wedefinitively show that neutrino os-cillations exist, there will be a largeset of neutrino mass and mixingparameters to determine. And if neu-trino oscillations do not turn up, wewill need alternative explanations forthe present observational hints. Inone form or another, the experimen-tal study of neutrino oscillations willprobably continue for the nexttwenty years!

The new MINOS (for “Main In-jector Neutrino Oscillation Search”)detector will measure about twelvethousand neutrino interactions peryear out of the five trillion that passthrough. It will consist of six hundredlayers each of scintillation countersand magnetized iron. If the atmos-pheric neutrino deficit is due to νµ →ντ oscillations, MINOS will observedifferent rates of events, differentfractions of events with muons, anddifferent energy distributions fromthose seen in the near detector.

A small version of the MINOS de-tector at Fermilab is a necessary partof the experiment. This detector willbe used to understand the beam andcalibrate its intensity, by measur-ing the interactions of neutrinosbefore they have had any chance tooscillate into other species.

Physicists hope to begin takingdata with the existing Soudan de-tector and the first sections of the

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

Physicists recognize that

the Standard Model

conceals as much as it

reveals about the ulti-

mate workings of

matter. Might the study

of the charm quark help

open the way to the

physics beyond the

Standard Model?

BEAM LINE 17

AYBE WE SHOULD CALL IT somethingdifferent. “The Standard Model” sounds so def-inite, so final. Perhaps another name wouldbetter describe the part-monument, part-

punching-bag nature of the world’s best theory of how mat-ter is put together at the smallest scale. The Standard Modelis a monument—a monument to the power of theory and ex-periment to explore and explain the seemingly trackless in-ner reaches of the matter around us. But it is a punching bag,too, the so-far intact target of experimental jabs and thrustsattempting to expose its weaknesses. The punches haveincluded searches for forbidden processes, neutrino mass,and other symmetry violation. Now, in a dizzying mix ofmetaphor, the 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 the StandardModel conceals as much as it reveals about the ultimateworkings of matter. We know that marvelous scenes will un-fold before us, if only we can find which rope to pull to makethe curtain rise.

Most of the theoretical and experimental energy of thefield of particle physics at the end of the twentieth century isconcentrated on raising the Standard Model curtain on thedrama that will be twenty-first century physics. And most ofthese efforts are devoted to pulling on two ropes: high-energysearches for the origin of mass and the quest to find matter-antimatter asymmetry in the behavior of mesons containingthe bottom quark. But besides these mainstream efforts,might there be another way to raise the curtain? Might we atleast lift its corner by using—charm?

Physics with Charmby JEFFREY A. APPEL

M

18 SPRING 1998

at fixed-target experiments (wherebeams of moving particles hit sta-tionary matter, instead of collidingwith beams of particles coming theother way) has elucidated the dis-tribution of the gluons inside garden-variety hadrons containing up anddown quarks, and even within lessordinary hadrons containing strangequarks. (A hadron is a particle madeof quarks held together by gluons.)

The fusion of a photon with agluon from a target hadron is thedominant process for producingcharm-anticharm pairs with a pho-ton beam. The fusion of two gluonsin hadron-hadron interactions is thedominant process for creating charmquarks in that environment. Bothof these processes depend on the dis-tributions of gluons in hadrons. Bycarefully studying the characteristicsof charm production, we work back-ward to the way gluons are distrib-uted in target neutrons and protons,as well as in beam hadrons, such aspions, kaons and protons. Gluon dis-tributions in pions and kaons (eachcomprising a quark and an antiquarkheld together by gluons) appear to besimilar. In protons, which are madeof three quarks, the gluons are

Since its famous discovery almosta quarter century ago, the charmquark has intrigued particle physi-cists as a unique particle, the firstof the heavy quarks—and more. Itis the only quark with charge +2/3that is both unstable (unlike the upquark) and yet survives long enough(unlike the top quark) to bind withother quarks and form observableparticles. Thus the charm quark of-fers a unique way to discover effectsthat may occur only in this “up-quark” neighborhood of the parti-cle world. Such effects might nevershow up in the down, strange andbottom quarks, with their −1/3charges. Charm might give us alonged-for peek beyond the StandardModel curtain.

FASCINATION OF CHARM

Until 1974, three kinds of quarks hadappeared in experiments: up, downand strange. But theorists, reasoningthat quarks should come in evennumbers, predicted a fourth kind,dubbed charm. If it existed, besidesevening up the quark score, charmwould explain a puzzle: why do neu-tral kaons decay only very rarely intoa pair of muons? Charm did indeedmaterialize, simultaneously on theeast and west coasts of the UnitedStates, and it proved to have the prop-erties the theorists had said it would.Since its appearance, the charmquark has taught physicists muchabout the strong and weak nuclearforces and how they interact.

Charm also teaches us about or-dinary matter. Most of the matterthat we see is made of quarks, heldtogether by gluons, in neutrons andprotons. Producing charm particles

“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 windowinto what is going on in the main-stream matter of the Universe.

In the story of charm, as in thestory of all particle physics, tech-nology is the deus ex machina thatmoves the plot forward. Advances inaccelerator, detector, and computingtechnology have let us make the ac-quaintance of charm, and advancesin technology will take us still fur-ther in the study of its character.Learning more about charm will notonly help us understand the gluons,but illuminate the differences be-tween the quarks and—and!—get tothat physics beyond the You-Know-What. For charm particles may holdclues to why, for example, charm isone of only six quarks, and why thosesix come two by two, like creaturesfrom Noah’s Ark.

THE DISCRETE CHARMOF FERMILAB FIXED-TARGETEXPERIMENTS

The fixed-target run that ended inSeptember 1997 may have seen thelast dedicated charm experiment atFermilab. This moment—the end ofan era of charm—is a good time tolook at where we have come so far incharm research and at where wemight be going.

Today, precision results on charmphysics come from electron-positroncollision experiments at Cornell’sCESR and from Fermilab’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

first of the heavy

quarks—and more.

BEAM LINE 19

of fully reconstructed decays ob-served and the cleanliness (with re-spect to background) of the experi-mental signals. The Fermilabexperiment with the most prodigioussample of clean, reconstructed charmdecays now has 200,000; but it willsoon relinquish its title to a charmexperiment from the last fixed-targetrun that projects a million or more,all told. When we consider thatcharm appears only once in every 200relevant photon interactions andonce in every thousand hadron in-teractions, and add in the fact thatexperiments typically reconstructonly about half a percent of these, werealize that experimenters are look-ing for one clean decay in about100,000 interactions.

The nature of fixed-target experi-ments can lead to clean charm sig-nals. Most of the charm particles pro-duced move rapidly in the directionof the incident beam. They live longenough (about a picosecond) to movea few millimeters beyond their pro-duction point before they decay.Experimenters can observe this dis-tance, but it requires precision mea-surement of the trajectories of thedecay products, uncluttered by a lotof distracting “junk” in the way.Depending on how the charm par-ticle decays, knowing the identity ofthe decay products leads to the clean-est signals. In the electron-positronmachines used so far to study charm,the charm particles are at rest ormoving slowly at production, so theydecay on top of the productionpoint—a much messier situation. Infixed-target experiments, physicistscan use the decay topology to selectonly those interactions that couldcontain charm particles. For those,

they then examine only those par-ticles coming from single vertices.

The combination of these stepshelps to select the precious charmevents from the more copious, un-interesting false candidate events.Applying selection criteria using ver-tex separation and particle identifi-cation reduces background muchfaster than signal. The more certainwe are that a charm decay vertex can-didate is separated cleanly from theevent’s interaction vertex, the morecertain we can be that we have ob-served a real charm decay.

The methods developed for thesefixed-target experiments have notonly bagged many a charm particle,but have influenced the design forhadron colliders doing bottom andtop quark research and for asym-metric B factories where we need tomeasure the separation between thedecay sites of the particles contain-ing bottom quarks.

TECHNOLOGY OF CHARM

Advances in three areas of tech-nology have produced today’s large,clean samples of charm in fixed-target experiments. Silicon micro-strip detectors (SMDs), videotapestorage, and computer farms—alllinked together—have taken charmphysics to new levels.

The figure above right shows howthe history of production and decayof charm particles in one event canbe reconstructed from the trajectoriesof the resulting charged particles.Tracks (the records of particle tra-jectories) emerging from the primaryinteraction vertex and the two charmdecay vertices (one for the charm andone for the simultaneously produced

–22

–20

–18

–10.4 –10.2Y-Coordinate (mm)

–10.0

Z-C

oord

inat

e

(mm

)

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 these

regions.

Silicon Microstrip Detectors

MODERN MICROELECTRONIC TECHNIQUES make possible

the silicon microstrip detectors that have brought charm physics such a

long way. How do SMDs work? When a charged particle traverses a thin

crystal of pure silicon, it deposits energy that frees electric charges to

migrate.

If an appropriate voltage is applied across the crystal, the migrating

charges will produce signals on metal electrodes. The signals, suitably

amplified by sensitive electronics off the silicon plate, are digitized and

recorded for later analysis. On SMDs, the electrodes are closely spaced

strips, typically 25 to 50 microns from center to center, with amplifiers

attached to each strip. The large number of strips allows experimenters to

record the passage of many charged particles through each detector,

reduces the capacitative load on the fronts of the amplifiers, and improves

the achievable spatial resolution. The SMD signal collection takes just a

few billionths of a second, making SMDs useful in the intense, high-rate en-

vironments that characterize more and more particle physics experiments.

20 SPRING 1998

anticharm) appear to emerge fromdistinct vertices. This is only possibleif the charm particles live longenough, if they are moving fastenough, and if the 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-dent beam and 150 microns in thetransverse direction. SMDs provideresolutions about ten times moreprecise than these distances. Thisprovides powerful separation be-tween combinations of tracks thatemerge from charm decay verticesand background.

Over the past fifteen years, theraw data from fixed-target experi-ments has gone from a few gigabytesto 50,000 gigabytes. It would havecost a fortune to handle so much datausing the old open-reel magnetic tapesystem. Fortunately, new technologyin the form of 8 mm videotape cameto the rescue with greater capacity ata far lower price. However, becauseof the less-than-lightning speed of anindividual 8-mm tape-writing device,one fixed-target charm experimentused 42 of the tape drives writing outevents in parallel. The data-acquisitionarchitecture supported this paralleltape writing, along with parallel-pathdata accumulation from the front-end electronics.

Massive new data sets also re-quired greater economy in analysiscomputing. Charm experiment E691first used massive parallel-processingcomputer farms at Fermilab for thispurpose. At that time, experimentersused laboratory-designed, single-board computers (over a hundred inone system) with commercial CPUchips and home-built control software.

5 cm

5 c

m

~ 1000 Collecting Strips

50 µm Pitch

300 µm

ParticlesA silicon microstripdetector.

BEAM LINE 21

Later, commercial workstations tiedtogether with custom software be-came more cost effective. This ap-proach of using large data sets com-bined with simple early eventselection offers certain advantages,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 better than theuse of only the cruder informationavailable at data-taking time, whichnecessarily throws away some of theinteresting charm events. It alsohelped that the price of computingpower dropped rapidly in the inter-val between the purchase of systemsfor on-line and those for off-line use.

CHARM OF THE FUTURE

Massive data storage, massively par-allel computing and silicon micro-strip detectors have all become partof the standard tool box for modernhigh-energy physics experiments.The experiments that discovered thetop quark at Fermilab’s Tevatron col-lider, the experiments that study bot-tom quark physics in Z decay atSLAC and CERN, and experiments

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.

But now, whither charm physicsitself? Have the present technologiesrun their course for charm? A lookat the likely landscape of futurephysics experiments shows few ifany long runs of sufficiently ener-getic beams to produce great num-bers of charm particles. Would-becharm investigators will need somesort of new environment to pursuetheir explorations. Two possibilitiessuggest themselves: asymmetricelectron-positron colliders and theforward regions of hadron colliders.Both remain to be explored, althoughboth offer the promise of openingnew realms of charm.

As in the past, we will need newtechnologies to deepen our knowl-edge of charm. But if we are inven-tive enough, and alert to new tech-nical opportunities, it is possible thatwe may look to charm for its uniquepotential to raise the curtain on theopening act of that riveting all-starproduction, “Physics Beyond theStandard 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 Decays

1980–81 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

Vis

ual M

edia

Ser

vice

sD

on S

umm

ers

22 SPRING 1998

This Was the Year That Was(Astrophysics in 1997)

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

THE PROGRESS of

science is not generally

much like that of a

kangaroo. Rather, we tend to

advance amoeba-like, cautiously

extending pseudopods in some

directions and retracting them

in others. 1997 witnessed at

least its share of advances and

retreats, with perhaps a

leap or two. The following

sections are meant to be

logically independent and

readable (or at least no

less readable) in any

order.

THE UNIVERSE AT LARGE

MICRO- AND MACRO-MARS: WATER,WATER, EVERYWHERE

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

year’s announcement 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 curmudgeonlypessimism has been justified. After several months ofrat-like gnawings on the edges of the evidence by otherexperts, the original proponents have essentially with-drawn the suggestion. Tactfully, they switched from Science to Nature for the recantation.

BEAM LINE 23

Meanwhile, a number of Martianshave acquired personal names. But it’sno use calling them, because, like catsand Victor Borge’s children, they don’tcome anyhow. In fact, they all seemto be rocks. And while reports from theSagan Memorial Station indicate thatthe said rocks have carefully washedtheir hands for dinner, there doesn’tseem to be anything to eat. Continuedanalysis of Pathfinder data will proba-bly yield additional information onMartian geology,* but more advancedprobes will be needed to dig below thesurface and look for possible relics of early pre-biologicalor biological evolution. If you happen to have someold slides of the Viking lander site lying around, you cancheck my impression that the topography of Mars haschanged less in the last twenty years than that of ourfaces.

Liquid water continues its role as the probable lim-iting factor for the development of chemically based life.It may, however, not be so very rare. Besides the Earthand Mars, wet places in the solar system appear to in-clude subsurface regions of two moons of Jupiter, Europaand Ganymede. Lots of images are already in from theGalileo mission, which, after staring at Jupiter for awhile, has begun contemplating the moons, and willcontinue to do so into 1998.

Gaseous and solid water are all over the place. Wehave always suspected this from their prominence incomets and other reservoirs of local volatile material,but the inventorying has not been very easy. The prob-lem is terrestrial water—a very good thing in its way,but given to smearing its absorption features across anyspectrogram you take from Earth’s surface. ISO, the In-frared Space Observatory, a mostly-European effort withgood resolution in both wavelength and position onthe sky, has finally climbed above even the very highest

terrestrial ice crystals and water vapor molecules. It seesH2O emission and absorption features in star forma-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 clump together. The water features are often sostrong and numerous that they in effect constitute thenoise in investigations of other species that emit and ab-sorb primarily at infrared wavelengths. Just what youwould have expected in retrospect.

Nevertheless, not all water is created equal, at leastnot in its ratio of deuterium to hydrogen. That ratio hasnow been measured in three bright comets, Halley,Hyakutake, and Hale Bopp. In all three cases, D/H isabout twice the ratio in terrestrial ocean water. Thismeans that water supplies from comet impacts cannotbe the primary source of terrestrial water, unless thereis a comet reservoir not yet probed by the observations.The old-fashioned source of volatiles was outgassingof material trapped when the Earth formed.

*Areology would seem to be the obvious word, but it justhasn’t caught 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 SPRING 1998

THE FAT LADY BURSTS

I have been told on equal authority (that is, none) thatthe pulchritudinous person in question was either KateSmith rendering “God Bless America” to end a baseballgame or a Sutherland-like soprano expressing the desireto leave Paris shortly before the end of La Traviata (notat all a bad thing to do, particularly if the performancehappens to be in Paris). I would not presume to choosebetween them. But we were told with equal authorityabout three years ago* that the gamma-ray bursters werelocated either in the halo of our own galaxy or in oth-er galaxies at distances comparable with the size ofthe observable Universe. This choice is now easy. Theyare at cosmological distances.

GRBs are, tautologically, bursts of gamma rays (mean-ing anything above 50 keV or so) that come to us at com-pletely unpredictable times from completely random di-rections in the sky, at a rate of about one per day (giventhe sensitivity of the detectors now orbiting on theCompton Gamma Ray Observatory). Most last from atenth of a second to a few hundred seconds, show sub-structure and complex spectra, and dump from 10−8 to10−4 erg/cm2 at the top of the Earth’s atmosphere, withthe faintest ones being commonest. Oh yes. And untilFebruary 1997, none of them 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 distributionin space, despite seeming to be at the center of it (seebox on the next page). Thus the edge was supposed to beeither the edge of an enormous halo of our own galaxy(not host to any other known sort of object) or an opti-cal illusion, introduced by the redshifting of the energyof sources far enough away that cosmic expansion isimportant.

In the last year, a suitable satellite, the mostly-European BeppoSAX, began picking up X-ray tails to the

40

30

20

10

04,200 4,600

λ (A°)

5,000

F ν (1

0–29 e

rg c

m–2

s–1 H

z–1)

Fe II Fe II Mg II IMg II

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.

*At a 75th anniversary restaging of the Curtis-Shapleydebate, whose proceedings appear in the December 1995issue of Publications of the Astronomical Society of thePacific.

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events are and roughly how much energy each must putinto gamma rays (1051 ergs or more, unless the pho-tons are strongly beamed) has triggered a new round ofsimulating . Most of the simulees involve at least oneneutron star or black hole, or sometimes two in a binarysystem. Given the sub-second time scales of many bursts,there aren’t really a lot of other possibilities.

PEOPLE AND PLACES

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

The SAGE detector for solar neutrinos managed to re-sist for another year having its gallium resold for com-mercial purposes, but the HEGRA detector for extensiveair showers partially burned soon after it had confirmedthe second extragalactic source of TeV gamma rays, aquasar previously seen from the Whipple Observatory.SAGE also survived a calibration run with a radioac-tive source, showing that, if neutrinos get to it in theirelectron-flavored garments, it sees them, whileSuperKamiokande came on line in Japan and confirmedthat, for the highest energy neutrinos expected from thesun, only about half the predicted flux is arriving in dueorder and technically correct.

Some important satellite 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 whatthey should, including the 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 with good enough angular pre-cision to swing other telescopes toward their locationsbefore all the fireworks were over. Three events, in Feb-ruary, May, and December, have been recorded—briefly!—in visible light, and the May one as a radiosource. They are not all the same. The February loca-tion has an underlying steady, fuzzy visible object thatis probably a distant faint galaxy. Most important, theMay event (see figure on page 24) had sharp absorptionlines in its spectrum that could be identified 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 (but not beyonda redshift of about 2). And no, I am not going to tellyou how much that is in light years because it dependsVERY much on your favorite values of the Hubble con-stant and other cosmological fudge factors.

Theorists had, of course, modeled most of the pos-sibilities long before February. But knowing where the

*Yes, they really are nearly identical in pronunciation. Theunvoiced vowel “u” may be familiar from “sukiyaki.” Asfor the seemingly-double-valued consonant, about all Ican suggest is that you try saying “rocket flights” and“locket frights” quickly, in alternation, until they startto sound the same.

26 SPRING 1998

The literature contemplated itself, with conclusionsthat Einstein (a) really did write down “his” equationsbefore David Hilbert and (b) had tackled calculationsof gravitational lensing as early as 1912, but thought theresults hardly worth publishing. A couple of colleaguesintroduced into the 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 thermodynamic quantity?” And the grem-lins of typography and copy editing brought us manytreats, of which my favorite is the acknowledgment “tothe TIRGO tune allocation committee for the award oftelescope time. At most observatories, TAC is an acronymfor “time allocation committee,” but having once sharednights at Mt. Palomar with a colleague who kept awakeby singing music of the old Polish church, I can see thatthe other might sometimes also be needed. If only theyhad allocated me “99 bottles of beer on the wall” (thosewere long winter nights), or even La Traviata.

DON’T GIVE UP YOUR DAY JOB

Non-Hollywoodites may need reminding that, alongwith “don’t call us, we’ll call you,” these are words spo-ken to an aspiring actor or musician who may not bequite ready for the big time. Here I have in mind caseswhere somebody went out on a limb (often a very sturdy-looking, oak one) only to have some portion of it sawedoff from under him. Additional examples include theMartian micro-fossils and Type I supernovae as distanceindicators mentioned in other sections.

Our own Local Group of galaxies consists of two bigones (us and the Andromeda Nebula) and a whole bunchof little ones, whose number has seemed to increase atabout one per year of late. But the 1992 and 1996 “dis-coveries,” small, faint galaxies a million or two lightyears away in the directions of the constellations Tu-cana and Antlia were actually catalogued back in 1977.New at least as confirmed LG members? Perhaps noteven that. Antlia is probably further away than themillion-parsec limit of gravitational binding to the LocalGroup.

Accretion disks around proto-stars, white dwarfs, neu-tron stars, black holes, and prominent 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) must be abinary system withan accretion disk ofmaterial from itsnormal star swirlingaround the whitedwarf. The latestword is that AE Aqris actually a net ex-cretor. Accretion ofcourse persists for

most of the other ad-vertised objects, pre-ferentially this pastyear in the form of“advection domi-nated accretion,”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 withmasses like Jupiter but shorter orbit periods, glimmeredout of press releases from the October 1995 announce-ment of 51 Peg onward. Perversely, much of the com-munity embraced with enthusiasm a late 1996 sugges-tion that no such planets were orbiting. 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 like Antlia as galaxies in the first place.(Courtesy Mike Irwin, RoyalGreenwich Observatory, UK)

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shift (that is, its distance) and its angular motion acrossthe plane of the sky (that is, two-dimensional velocity,if you know the distance). The community had beencounting on Hipparcos for quite some time to improveour knowledge of the brightnesses and kinematics of anumber of kinds of stars that are either interesting fortheir own sake orimportant inclimbing up the“distance ladder”to far away galax-ies and the Uni-verse.

The splashiestpress release be-longed to a prob-lem that has beenaround for half acentury, “the ageof the Universe.”The time scale ofthe Universe im-plied by its mea-sured expansionrate (the Hubbleconstant) has spo-radically seemedto be rather lessthan the ages ofthe oldest stars wesee. And this par-ticular example of“old wine in lessold bottles” hasnever been one wewere happy with.Fifty years ago, itled to the inven-tion of the SteadyState model of the Universe. More recently, the faintat heart had been driven to invoking Einstein’s notori-ous cosmological constant or even to doubting the

independent group at University of Texas, will havegiven us back our planets by the time you read this.

Yes, we live in a screwy Universe, but is it also chi-ral? Theorists have predicted and observers not seen fordecades any indication that space-time is rotating 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 sufficiently poor angular resolution that bits of thesources with different intrinsic polarization weresmeared together. Owners and operators of more recent,more suitable data sets rapidly fired back upper limitsto the twisting of space considerably below the positivevalue claimed in the Letter.

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, naturally, went uncit-ed. Probably only two people in the world noticed this,Maurice Goldhaber and yours truly, the authors of thelimit paper!

Some things really do have net chirality, including, un-expectedly, some of the amino acids in the Murchisonmeteorite. Contamination by the 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 THE UNIVERSE,OR, TWO AND A HALF CHEERS FOR OUR SIDE

Hipparcos is an acronym (origins lost in the mists oftime), a slight misspelling of the name of a Greek com-piler of star catalogues, Hipparchus, and a (mostlyEuropean) satellite that scanned the skies for severalyears, establishing a coordinate system made up of pre-cise positions for more than 100,000 stars. In the process,it also determined for each star its 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 SPRING 1998

correctness of the basic picture of a universe expand-ing out of a hot dense state (a.k.a. Big Bang).

Two solutions are possible—make the Universe older(that is the Hubble constant smaller, by deciding thatthe galaxies you used to calibrate it are further awaythan you had thought) or make the stars younger (alsoachieved by shoving them away from you, so that theyare brighter and use up their fuel faster). One way of look-ing at stars measured by Hipparcos seemed to do exactlythese two things. Parallaxes of a set of stars calledCepheid variables (a traditional distance calibrator) werea bit smaller than expected, nominally both increas-ing the time l/H and decreasing stellar ages. Unfortu-nately, equally valid ways of looking at the data, usingyoung clusters of stars to calibrate the Cepheids and sta-tistics of stellar motions to get brightnesses 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 titled “parallaxes and proper motions of pro-totypes of astrophysically interesting classes of stars,” butyou must read the archival literature to find out whatwe learned (other 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 toturn the right sort of telescope or equation in the rightdirection, much like the case in Moby Dick, where Cap-tain Ahab nails a gold doubloon to the mast for thefirst person to spot the whale, or, said Richard Armour,the first person up on deck after dark with a claw-headedhammer. Finding the optical counterpart of the May 8th

gamma-ray burster was one of these. Some other 1997examples follow:

• Radio pulsations from Geminga. This gamma-raysource in Gemini was long a mystery because it seemed(like the bursters) to have no counterpart at any otherwavelength. 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. But all proper pulsars shouldbeep radio signals at us (that is, after all, how they werediscovered in 1967), and Geminga seemed to be a failure.Three groups, all centered in Russia, have finally foundthe radio pulses, more or less simultaneously (and eachhas published the discovery at least twice, 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 sometime, because a spiral or m = 2 perturbation is the nat-ural consequence of having a large point mass off tothe side of a disk (hence the particularly spectacular armsin spiral galaxies with 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 common they no longer make the New York Times.Whoever happens to get the first HST images and spec-tra of the center of a nearby galaxy is just about guar-anteed to find a black hole somewhere in the 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)

BEAM LINE 29

106–109 solar masses. In a few cases, where more thanone technique has been brought to bear on a particulargalaxy, the results for BH mass are in clear disagreement.You can argue about whether this constitutes progress,but it does at least guarantee employment for future gen-erations of astronomers. Our Milky Way is part of thegreat majority with 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 center.

• Broad absorption lines in a radio quasar. Properquasars are strong sources of radio emission (the oth-ers are QSOs or quasi-stellar-objects, unless you are feel-ing lazy). BALs or broad absorption lines are saturatedones with redshifts just a smidge less than the redshiftof the emission lines. They are attributed to gas beingblown out of or around the QSO nucleus. Until 1997, theradio-loud and BAL sets were disjoint. And it took a sur-vey of something like 105 radio sources to find the first,faint overlap (this is a pun; the 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 it is really a QSO.The 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 forming stars like mad (and new, massive stars arethe brightest kind) and partly because it is gravitation-ally lensed and amplified by a foreground cluster atz = 0.23.

• The most distant supernova. Here too records arefalling constantly, and the current one at z = 0.9 or there-abouts is not very important for its own sake. Distantgalaxies contain heavy elements, so we know they mustalready have had supernova explosions. But the mem-bers of one class of supernova (called Type Ia) all seemto have the same intrinsic luminosity and so can be usedto measure very large distances and get global values forthe cosmic expansion rate (H) and its change with time,the deceleration parameter, q0. These, in turn, are al-gebraically related to the mean density of the Universe.Through most of 1997, the supernova method seemed tobe the one hold-out in finding a q0 or density value large

enough to stop the expansion of the Universe in the (veryremote) future, while a number of other methods thatlooked at masses of clusters of galaxies or their distri-bution in space were finding perhaps 30 percent of thatcritical density. But the result came from a very smallnumber of distant Ia’s. With a larger sample of about fif-teen events, the best fit is a smaller deceleration para-meter, or a density of 30–40 percent of the critical value,agreeing with the other methods.

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

EVERY DOG IS ENTITLED TOONE BITE

This is my attitude, asone of the adjectival editorsof a fairly prestigious jour-nal, toward authors bear-ing papers about whichone is tempted to quotePauli, “It isn’t even wrong.” Because there are lots ofjournals, many of these ideas turn up as “new” yearafter year. Still, isn’t it a sort of relief from the serious-ness of transverse optical phonons to contemplate.

a. A model of star formation that produces cylindri-cal stars.

b. A universe whose metric 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 SPRING 1998

in the sun and for the peak mode of the variable starDelta Scuti (actually 162 minutes).

c. A scenario for making gamma-ray bursters in theheliosphere.

d. Dark matter candidates in the form of a vector-based theory of gravity or solid hydrogen.

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

ACKNOWLEDGMENTS

I asked the editor to perch the amoeba atop the kanga-roo in the first picture so as to have an excuse for men-tioning Robert K. Merton, author of On the Shouldersof Giants (no, Newton was not the first to say it), whohas been an occasional, generous reader of these maun-derings for some time. Reviewers, even more than oth-er scientists, are indeed supported by their colleagues.

The series, Astrophysics in 199x, arose from a sug-gestion by Howard E. Bond, the immediate past editorof Publications of the Astronomical Society of thePacific, who must often have felt like the parent of Rose-mary’s baby, and who also just happens to have been thechap who first spotted the optical counterpart of the May8th, 1997, gamma-ray burst—that was the one that hada measurable redshift, but he couldn’t measure it, becausehe was using a 0.9 meter telescope (it took the Keck10-meter). I am grateful both to him and to my some-timeco-authors, Peter Leonard and Lucy-Ann McFadden, fortheir contributions 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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CONTRIBUTORS

GORDON FRASER studied atLondon’s Imperial College in themid-1960s, when theoretical physi-cists were attacking spontaneoussymmetry breaking under Tom Kib-ble and relativistic SU(6) theory un-der Abdus Salam and Paul Matthews.Fraser also wrote short-story fictionand became side-tracked into jour-nalism. He returned to physics as ascience writer, eventually transfer-ring to CERN. He is editor of themonthly CERN Courier; co-author,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 Quark Machines (Bris-tol, Institute of Physics Publishing,1997). He is also editor of ParticleCentury, a collection of contribu-tions to be published by Institute ofPhysics Publishing later this year.

MAURY GOODMAN is aphysicist in the High Enery PhysicsDivision of Argonne National Lab-oratory. He received his BS from theMassachusetts Institute of Technol-ogy. His 1979 PhD from the Univer-sity of Illinois at Urbana came on aphotoproduction experiment withAl Wattenberg. After a postdoc atMIT working on a Fermilab neutrinoexperiment, he joined the Soudangroup at ANL, where he studies at-mospheric neutrinos and is search-ing for evidence of nucleon decay. Hewas an early advocate of a long-base-line neutrino program at Fermilaband is now a member of the MINOScollaboration.

JEFFREY A. APPEL has been aphysicist at Fermilab since 1975.Most recently he has been spokesper-son for Fermilab experiment E769 andcospokesperson for E791. For eightyears ending in March of this year,he headed the Physics Section andfollow-on Experimental Physics Pro-jects. Appel received his PhD fromHarvard University. He is a Fellowof the American Physical Society andhas coauthored over 120 articles inprofessional journals.

Appel's interests extend beyondthe purely scientific and technical.For many years he chaired the Fer-milab Auditorium Committee thatorganized the arts, lectures, and ex-hibition series there. He also initi-ated a special Illinois Research Cor-ridor summer jobs program foroutstanding science and math teach-ers. His present interests are radia-tion-hard vertex detectors and the BTeVresearch and development program.

32 SPRING 1998

VIRGINIA TRIMBLE is not sure that she was a turtle in a pre-vious lifetime or deserves to be one in the next, but members ofthe genera testudo and pseudymis (order Chelonia) are her favoritecompanion animals. Her graduate days at Caltech (1964–68) werebrightened by the silent sympathy of Triton (a snapper who morethan earned his name), Beauregard (a button 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 printed thesis by the time we came to a parting of theways. Oscillating yearly between the University of California andthe University of Maryland is too hard a lifestyle for a turtle(and sometimes marginal for a human being), but someday I hopeto have another opportunity to listen for the voice of the turtlein the bathtub.

DATES TO REMEMBER

Jul 22–30 29th International 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 Summer Institute on Particle Physics: Gravity—From the Hubble Length to thePlanck Length (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 International Conference on Biophysics and Synchrotron Radiation, Argonne, Illinois (Susan Strasser, Conference Coordinator, APS, bsr98@aps.anl.gov)

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

Aug 23–28 19th International Linear Accelerator Conference (LINAC 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, CERN/DSU, 1211 Geneva 23, Switzerland, or Susannah.Tracy@cern.ch)

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

Sep 6–19 1998 CERN School of Computing (CSC 98), Funchal, Madeira, Portugal (Miss Jacqueline Turner,CERN School of Computing, 1211 Geneva 23, Switzerland, or Computing.School@cern.ch)

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

Sep 14–18 International 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 Organization Workshops, Argonne, Illinois (Susan Strasser,Conference Coordinator, APS, carlson@aps.anl.gov)

Oct 19–20 25th Annual SSRL Users Conference, Stanford, California (Suzanne Barrett, SSRL, PO Box 4349,Stanford, CA 94309, or barrett@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)