SLAC BEAM LINEWe dance round in a ring and suppose,But the Secret sits in the middle and knows.-Robert Frost

Volume 15, Number 3 March 1984

"2/04/84. 0450. The latest round of measurements gave us 3E-5 rad-m in horiz. We're there!!!!"

A MILESTONE FOR THE LINEAR COLLIDERAt 5 o'clock on the first Saturday morning of February, the Linear Collider passed a major technicalmilestone as physicists accelerated an electron beam with the high intensity and high quality neededin the collider. The quote above, which was taken from a computer logbook, shows how the groupworking on the test felt about it.

These two photographs are images of beams striking a luminescent screen and are enlarged about20 times. The small spot on the right was produced by an SLC beam which had been through thedamping ring to reduce its size. The beam which produced the diffuse spot at left had not beendamped. The story on page two explains more about this achievement.

SLC Milestone . . . 2 SLAC Beam Line, x2979, Mail Bin 94Sir John Adams - In Memoriam .... 3 Editorial Staff: Bill Ash, Jan Adamson,Twenty-Year Service Awards ..... . . 4Twenty-Year Service Awards . ...... 4 Dorothy Edminster, Bob Gex, Herb Weidner.A Slow Road in China . 5 Photography: Joe Faust.National Engineering Landmark Award . 6 Grhic Arts: Water ZawojskiGraphic Arts: Walter Zawojski.Jim Nolan Retires .......... 6 Illustrations: Publications Department.Charlie Kruse Retires .......... 7Oscar Fleisher- In Memoriam ..... 7News and Events ........... 8 Stanford University operates SLAC under

contract with the US Department of Energy.

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LINEAR COLLIDER PASSES MAJOR MILESTONEThe Linear Collider is a completely new way to col-

lide electrons and positrons at very high energies. Itis not a scaled up version of a smaller accelerator, andthere is no laboratory model to compare with. So, thereis great interest to find out as soon as possible how wellit is going to work. With this in mind, a small group ofphysicists and engineers recently set up a crucial testof the chief feature of the new machine: acceleratingan intense electron beam of high enough quality to befocused into the tiny spot needed at the SLC.

Intensity is a familiar idea: it is just the numberof electrons being accelerated. Beam quality is morecomplicated. Roughly speaking, it is like the differ-ence between a laser beam which runs for long dis-tances without spreading out much, and an ordinarypenlight, which starts out no bigger around but spreadsout rapidly. This property of beams, which depends onboth the size of the beam and its tendency to spreadout, is called emittance.

The important test, then, is to accelerate an electronbunch with very high intensity and very low emittance.Unfortunately, the two properties do not happily coex-ist. Intense beams are hard to produce with low emit-tance and even harder to accelerate without losing it.The collider requires both in order to do good physicsat a reasonable rate. Hence, the great interest in thiscombined measurement.

The collider required a new gun and injector systemto get the required high-intensity of around fifty billionelectrons squeezed into short bunches a few millionthsof a millionth of a second long. These devices are shownas points 1 and 2 in the rough sketch below.

This produces a beam which is intense enough andshort enough, but the emittance is too high. This fuzzi-

1 2

ness can be cleaned up by storing the beam in a ring,where the natural radiation processes damp it down.At point 3 the beam is taken out of the linear accel-erator, bent around a long arc, and injected into thedamping ring at point 4.

As the beam circulates around the ring (5), it shrinksdown to a smaller size. After about 30 thousandthsof the second (faster when running at the final designenergy), the beam is taken out of the ring at point 6and reinjected into the linac at point 7. The beam isthen accelerated to about the one-third point of thetwo-mile linac for the final measurements at point 8.

The intensity is determined using a loop which mea-sures the charge of the beam, and hence the numberof electrons. The emittance measurement is more dif-ficult, since it depends not just on the size of the beamat a point but also on how it is spreading out. Thephotograph on the right of the cover shows the beamsize at a luminescent screen. The spot is electroni-cally scanned along the two lines to determine the sizequickly and accurately. Then a focusing magnet aheadof the screen is varied, changing the size of the spot. Inthis case, a beam of good emittance is not as sensitiveto changing this focusing magnet as one of poor emit-tance. The emittance value is extracted from a plot ofa series of these measurements.

The final measurements came after weeks of study-ing the effects of changes in the injection system, thedamping ring, the transport lines between the linac andring, and the new precision controls of the acceleratoritself.

The result is that the intensity and emittance areboth at the desired values for this stage of the project.The collider is well on its way.

S-1

/"' 25'SCRAPERS& COMPRESSOR

DAMPINGRING -- ,

3-84

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SIR JOHN ADAMS - IN MEMORIAMSir John Adams, former Director General of the European re-

search center CERN, died early this month at the age of 63. Thefollowing description of his illustrious career was written by AlbertHofmann, who worked for many years at CERN. The reflection atright is by SLAC Technical Director Burton Richter.

He began his scientific career with radar develop-ment in England during the war, and later worked atthe Atomic Energy Research Establishment at Harwell.In 1953 he joined the newly founded center at CERN inGeneva, becoming Director of the Proton SynchrotronDivision.

John Adams was an excellent project leader andnot only completed the machine ahead of schedule butbrought its performance to a level beyond the originalexpectations. This success brought him wide recogni-tion and gave a big boost to the young organization.In 1960 he became Director General of CERN at age40.

He later accepted a position as Director of Cul-ham Laboratory in England, doing plasma physicsresearch. Meanwhile, CERN had begun planning amuch larger accelerator named the Super Proton Syn-chrotron (SPS), and called him back to lead the newproject.

From 1969 to 1975, he was Director General ofCERN II and led the center through the construc-tion and successful operation of the new machine. By1976 the two CERN laboratories were combined withJohn Adams serving as Executive Director General un-til 1980.

He was an outstanding leader for scientific

I knew John Adams for many years and have alwayshad the greatest respect for his abilities as an acceler-ator builder and as an organizer of great projects.

The machines at CERN and the experiments thathave been done with them are monuments to those abil-ities.

With his death, high-energy physics has lost one ofits important leaders. We shall all miss him.

-Burton Richter

projects and laboratories. He combined ex-cellent technical knowledge with a great abil-ity for management and administration. Intechnical crises his good judgement and calm,firm leadership always led to a solution. Hewas able to choose the best people for thedifferent tasks of a project and unite themin an efficient team. His sense of humor of-ten helped to discharge a tense situation. Heserved in many panels and committees advis-ing government agencies or promoting inter-national collaborations.

His achievements brought him many hon-ors from honorary degrees to Knighthood,but perhaps the most significant tribute tohis work is CERN itself, which as an inter-nnf tionr.1 nrFO.n i 7f.t irn nr d Ihnrrnrfr .. r.w.r c..allCUvxkaimi vl J1 6aa/IUJvl O1AllAU IlJVli OLUVIJS Vjf/j OV

much of its success to Sir John Adams. Sir-Albert Hofmann his

John Adams, right, chatted with W.K.H. Panofsky duringvisit to SLAC in 1981.

"...originator and devoted constructor of powerfulaccelerators which have made fundamental discov-eries in elementary particle physics possible, in theframework of collaborations of which he has alwaysbeen a strong advocate." - from the Doctorate Hon-oris Causa awarded to Sir John Adams by the Uni-versity of Milan in 1980.

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4SGBmLeMrh9

DICK ALLENBOB BAKERJACK BEARDSLEYROY BORTLEMICHAEL BROWNEJOHN CAREYJOHN COCKROFTJIM COOKGEORGE CRUICKSHANKJEAN FRANCISCHUCK HALEMURRAY HARGAINCLARENCE HARRISHAROLD ITOBILL JOHNSONWALTER KAPICARON KOONTZHELEN MORRISONJAMES MOSSROBERT PEDERSENMARTIN PERLDARYL REAGANFRED ROUSEDUANE SINCERBOXVERN SMITHBILL TOMLINBOB VACCAREZZADIETER WALZDICK WILSONWALTER ZAWOJSKI

TWENTY-YEAR SERVICE AWARDS

Ten years ago, Sid Drell honored the largest groupever to receive awards for completing ten years ofSLAG service. Incredibly, two-thirds of that groupwere present at the ceremony held on January 27,1984, this time for serving SLAC for twenty years.Once again SLAC Deputy Director Drell was the guestspeaker while Dr. Panofsky presided over the awardspresentation. The 60 honorees were feted at the Stan-ford University Faculty Club, enjoying cocktails anddinner with their fellow workers and spouses. Piefhighlighted their history at SLAC by saying, "Col-lectively they represent the contributions of thoseemployees who remained with us for a long timeand literally made this successful laboratory and ourachievements possible. There have been triumphs andanxious moments that we have shared in these twodecades, but the net result speaks well for all of thosewho participated."

GORDON BABCOCKJIM BASKETTMARY ANN BLACKMANADAM BOYARSKIFATIN BULOSBILL CLAYTONTED CONSTANTDAVID COWARDIDA DONALSFINN HALBOROBERT HANSELMANVIRGINIA HARMONDALE HORELICKDAVE JENSENJIMMY JUEFRANK KARASBOB LAUGHEADGEORGE MOSLENICK PAPPISFRED PEREGOYBILL PIERCEBENNY REVILLARWALLY SCHMIDTJIM SIROISWARREN STRUVENDAVE TSANGNICK VASSALLOHERB WEIDNERLARRY WOMACK

Ginny Hale, Bob Laughead, Hedi and Ed Loens, Liz Laughead and Chuck Hale toast thecompletion of twenty years of dedication to the Laboratory. Award recipients and spouses

celebrated the evening with fellow long-timers and each SLAC'er was given an engraved silverkeychain with the SLAC logo. At the right, John Cockroft and his wife, Barbara, display thebooklet which outlines the accomplishments of each awardee. Photographs by Casey James.

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SA B i M 18

SLOW ROAD IN CHINA

Helen Morrison, Gwen Bowen and Janet Zhang wentout into the Chinese countryside near Beijing (Peking)to visit the ruined gardens of the Summer Palace (YuanMien) which had been destroyed by the British andFrench during the Opium Wars of 1860. They wan-dered among those fanciful pavilions and pillars, imag-ining the Manchu court strolling there on just such ablue and gold afternoon.

By the time they were ready to depart no trans-portation was available - the taxi had not waited, thebuses did not come. The three started bravely walkingdown the road to Beijing. The scenery was charming,bullocks plowing in the fields, farmers bringing in thecrops in horse-drawn wagons, wide-eyed children gaz-ing at the foreign ladies and their Chinese friend. Butthere were firm dinner plans in Beijing and not enoughwalking time. They then tried to stop trucks and busesheading in their direction - no luck at all.

At this point Helen, recalling her hitchhiking yearsin the Navy, took a position in the middle of the roadand stopped a big green truck full of farm workers bywaving her hands and just standing there. The driverand his passengers jumped out, explaining excitedlythat his truck was too dirty, already full and was not aproper place for foreign ladies. After much argument,interpreted by Janet, Helen and Gwen were welcomedinto the cab and Janet was helped onto the truck bed,and away they went to Beijing. The truck depositedthem near the West Gate of Beijing University, a 10minute walk from their hotel, and returned to its workafter many thank-you's from Helen, Gwen and Janet.

-Gwen Bowen

Gwen Bowen has beenSLAC's housing co-ordinator for 15 years.She shares Helen'senthusiasm for Chi-nese art and culture.

Where was the horse when needed?

Helen Morrison re-tired in 1980 afternearly 20 years ofservice as Secretaryto the Director ofthe Research Divi-sion. Helen has beena life-long student ofChinese art and cul-ture.

Janet Zhang (ZhangYing-Xian) spent 4months in 1981 asan apprentice to Shir-ley Livengood in theTechnical Data Li-brary. She returnedto Beijing to helpset up a similar li-brary at the Insti-tute of High EnergyPhysics.

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6 SLAG_ Beam Line March 1984

SLAC BECOMES AN ENGINEERING LANDMARK

In a ceremony here on February29, the two large engineering so-cieties in the United States desig-nated SLAC a national historic en-gineering landmark., Many of thelaboratory's engineering alumni andthe present engineering staff werepresent to hear their accomplish-ments praised by representatives ofthe American Society of MechanicalEngineers and the Institute of Elec-trical and Electronics Engineers.

W.K.H. Panofsky, who acceptedthe award on behalf of the labora-tory, spoke on the great importanceto SLAC of its engineers.

A brochure describing SLAC's en-gineering accomplishments and thelandmark program was prepared bythe Beam Line and is included as aspecial supplement to this issue.

This one-foot by two-foot bronze plaque, which commemorates SLAC's land-mark award, will be mounted for public view in a suitable place at the labora-tory.

JIM NOLAN RETIRES

It's time for Jim Nolan to throw away his alarmclock. After more than 18 years at SLAC, he's retiring.

Jim came here from Food Machinery Corporation inSan Jose in 1965. He joined Crafts Shops in the PlantEngineering Department as a rigger-operator.

Jim later became rig-ging supervisor. Duringhis days in the riggingdepartment Jim used hisknowledge and talents allover SLAC. His help wassought by those who hadlarge apparatus to moveor delicate instruments toinstall. Jim was directlyinvolved with procuring,maintaining and operat-ing all the heavy movingPneiinment now in uise here.

He went to Texas to attend school for the operationof the 40 ton LeTourneau forklift and in turn taughtother operators to use this indispensable machine. InOctober of 1978 Jim joined EFD as coordinator of IR-6at PEP which became home for the Free Quark Searchand the High Resolution Spectrometer (HRS).

He was instrumental in the move of the old 2000ton 4-meter bubble chamber magnet from Argonne Na-tional Lab to SLAC for use in HRS. The convoy whichcarried the 105 ton superconducting magnet coil acrossthe country made the national news. Jim managed theloading and unloading of the coil, the assembly of themagnet and detectors and the move into the interac-tion region.

Early in 1982, Jim took a brief 'vacation' from IRSto assist in the move of the Crystal Ball from SLAC toDESY in Hamburg, Germany. It was flown there by theAir Force in a C5-A and Jim went along to supervisethe rigging and the installation at DESY.

In his career Jim has faced many unique riggingproblems and has provided some elegant solutions. Hehas a marvelous ability to get along with people and togain their respect and confidence. He leaves a host offriends and admirers at SLAC.

Jim and his wife will retire to Sonora, California, topursue the good life - fishing, hunting, and caring fortheir ranch. His many friends wish him well. GoodLuck Jim!

-Ed Keyser

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SLA Bea Lie Mac 198 7 ~_

CHARLES J. KRUSE RETIRESCharlie Kruse retired from SLAC on January 4, 1984

after almost 22 years of service. For almost 20 of thoseyears, Charlie was head of the RF Drive Group in Ac-celerator Physics and at the same time took care of theadministrative tasks of the Accelerator Physics Depart-ment. In addition, in the early 1970's, Charlie inheritedresponsibility for the linac laser alignment system fromRill THrrmannsfplft.a_.aaa ...A .. .. · aaa,.1111a A V.

During all these years,what characterized Char-lie was his loyalty to SLAC,his dedication to whateverhe was responsible for, andhis good will toward peo-ple. I think it is fair to saythat he leaves only friendsbehind him. More thaneighty people attended theluncheon in his honor on7',~,- ....nr.r 1 0

r uiluarly 1O.

It was both gratifying to honor him and sad to seehim leave after so many years. I am excerpting a fewof the tongue-in-cheek remarks I made about him atthis luncheon. Those who know Charlie (most peopleat SLAC !) will realize that these were just vignettes.

"Charlie Kruse was born to SLAC in the M-1 Build-ing on Lincoln's Birthday, 1962. He arrived that day at8:06 AM and continued, with one exception, to arriveat that time for the next 22 years. The exception hap-pened in 1973 when one morning, as he was bicyclingto work he discovered that he had a cold and pedalledback home to pick up a handkerchief. That day, hearrived at 8:16 AM. The rest of Charlie's - 1600 hoursof sick leave was wasted!

"As head of the RF Drive Group, Charlie's biggestjob was probably to procure and then to install thetwo-mile main drive line and the thirty sub-drive lines.

"Like most of us, Charlie survived the mid-sixties,the turn-on of the linac, the Beatles, beam breakupand all the other turmoil. But then, in April 1968, theForces of Evil descended upon the Klystron Gallery,and one fine morning, the entire main drive line brokedown. This was a major catastrophe which broughtSLAC to a grinding halt. As Charlie's family assem-bled here can probably testify, for three weeks Char-lie, with Dick Wilson and his crew, lived, breathed, ateand slept with the drive line. As Winston Churchillwould have said, 'This was his finest hour,' for afterthree weeks of blood, sweat, tears and a bit of Rhodiumplating, the war was won and SLAC together with theMain Booster came back on triumphantly!

"Then somewhere in the late 1970's, back in theBusiness Division, Gene Rickansrud asked Charlie tobecome the SLAC Patent Administrator, and in a mo-ment of weakness he agreed. ... What most peopledo not know is that in this position Charlie had toread through thousands of pages of RenormalizationTheory, Quantum-chromodynamics and all the othermundane stuff we write!

... "But let me abandon the curricular and switch tothe extra-curricular. What would Accelerator PhysicsChristmas parties have been without Charlie's IrishCoffee? What would SLAC families have become with-out Charlie organizing SLAC's Family Day? And whatwould Santa Claus have done at SLAC all these yearswithout Charlie's cookies?"

Now we are all going to miss Charlie very much,on the job and off. The only consolation we have isthat some of his social skills will now become usefulto his wife Marge and to their kids. Think about allthe Family days and Christmas parties he can have athome now!

-Greg Loew.... _ . . . . . . . . . _~-

OSCAR FLEISHER -- IN MEMORIAM

Oscar Fleisher passed away on March 1, within a fewdays of his 58th birthday. Oscar joined us in August1969 as the Associate Purchasing Officer. He retiredin March 1981, but returned in the last few monthsof 1983 to help out as a part-time consultant, due toan upsurge in the Purchasing work load. He broughtSLAC a wealth of business and purchasing experienceat a time when we really needed the help.

His background included inventory management;duty as Purchasing Superintendent at the CharlestonNaval Shipyard; support services on the USS Proteus;head of Contracts Division in the Naval Plant Rep-resentatives Office, Lockheed, Sunnyvale; and Directorof Purchasing Division, Navy Purchasing Office, Wash-ington, D.C. He was a graduate of Pennsylvania StateUniversity.

Oscar was a very enthusiastic and devoted person.He would always roll up his sleeves and get into the jobhimself. He was particularly adept at training peopleand enabling them to take on increased responsibilities.

Oscar is survived by his wife Ruth, son Andrew, anddaughter Beverly who reside in Cupertino. Burial wasat Arlington National Cemetery, Arlington, Virginia.Friends may contribute to the American Heart Associ-ation, Santa Clara County, in his memory, if they wish.We shall miss a dear friend.

-Ralph Hashagen

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8 ~ ~ I__ SLA Bea Lie arh18

SLAC GOLFERS

For several years a SLAC golf league existed quit(happily but faded away under a pile of paperworkThere is now a good possibility that a new set of volunteers can be found if enough people are interested irforming a new league.

The rules of the old league were approximately afollows:

* A nine-hole tournament played each week on thefront nine of the Stanford Course any afternoonTuesday through Friday.

* Round must be played in the company of one omore other members of the league.

* League membership will be divided into tw(flights.

* Weekly prizes will be as follows:

1 ball for low net high handicap flight1 ball for low net low handicap flight1 ball for closest to hole on Number 8

If you are interested in participating, please contacBob Eisele (ext. 2582, Bin 60).

CO-ED SOFTBALL

Sign-ups have begun for the newly formed SLAC CoEd Slow Pitch Softball team. Please contact Tom Kamakani at SLAC ext. 2371 for registration informationand practice times.

TO CONTRIBUTE TO THE SLAC,EMERGENCY RELIEF ASSOCIATION

(SERA), PLEASE INDICATE VUJURCHOICE ON THE FORM bELOW.

I WANT TO DO MY PART TO HELP.

o MY CHECK IS ENCLOSED.I WOULD LIKE TO DONATEs _ TO SERA.

o I AUTHORIZE PAYROLLDEDUCTIONS' OFPER MONTH FOR SERA,TO CONTINUE UNTILFURTHER NOTICE.

(Signature)

(Please print nme*)

(Date)

(Employee number)

ALL CONTRIBUTIONS TO SERA ARE

TAX DEDUCTIBLE

mail to BIN 70

BOOKMOBILE

The Bookmobile which has been coming to SLAC formany years now is in danger of being discontinued dueto lack of patronage. If you are interested in keepingthis service to the laboratory, visit the Bookmobile onalternate Wednesdays from noon until 1:00 beginningMarch 7th. It is conveniently parked near the firehouse.

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FIRST ANNIVERSARY

Pictured above is a partial group of those who cele-brated one-year-less-one-day of running of the dampingring. The damping ring is a major component of theSLAC Linear Collider and figured prominently in themilestone test which was passed in February (see story,page 2).

SLAC EMERGENCY RELIEF ASSOCIATION

The SLAC Emergency Relief Association, SERA, isa personal assistance organization formed in 1968 bySLAC employees to aid those of the SLAC communitywhose financial condition has become desperate due to

> emergencies beyond their control.

Unlike most assistance groups, SERA's operating ex-penses are less than one percent! This is possiblebecause the entire effort is carried on by volunteers.SERA is a charitable corporation whose three direc-tors, elected semi-annually by the membership, to-gether with a secretary and treasurer do the necessarywork.

In these hard times disbursals have increased andthere is a greater need for your support. SERA's in-come is primarily from the donations of its members.A payroll deduction of 50 cents or more per month willmake you a full voting member. You may, of course,wish to make the $6 fee a lump sum donation or au-thorize a larger monthly donation (our current averageis $1.47). In any case, we hope you will join us in thisworthwhile enterprise.

Please indicate your donation on the adjoining formand drop it in the mail today.

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SLAC Beam Line, March 19848

OF QUARKS, ANTIQUARIS,

luIII. uy mIIieiiauili

which balls miss thobject, which hit it,and at what angleand speed theybounce off it, onecould reach someconclusions aboutthe location, size,shape, and textureof the object.: :

28 / FALL 1983

ERRATUM: The phrase "three quarksfor Muster Mark" appears in JamesJoyce's Finnegana Wake, not Ulyete,.

hat is the world made of?That simple question has fas-cinated mankind since the

earliest recorded philosophers. The an-cient answer of "earth, water, fire, andair" does not satisfy us today. Particlephysicists seek a moder answer to thisage-old question, using sophisticatedtools to study matter at ever finer res-olution. As these tools have been de-veloped we have learned that all matterconsists of structure within struc-ture-molecules within cells, atomswithin molecules, and further structurewithin the atoms.

We have also found that, to under-stand the structures at each level of de-tail, we need to ask two kinds of ques-tions. First, what are the buildingblocks from which the structures aremade? Second, what are the rules thatgovern how these building blocks fit to-gether? These two questions-the build-ing blocks ("constituents") and therules governing their interactions-areintimately linked in the study of par-ticle physics. An improved understand-ing of either one allows progress inlearning about the other. Until we finda theory that satisfactorily explainsboth, we cannot say that we understandthe structure of matter.

To get some idea of the type of think-ing involved in particle physics, try tosolve the puzzle shown at right. Theblack pieces represent some of the "al-lowed objects" in the two-dimensionalworld of the puzzle. The white objects,however, have never been seen. Now, thechallenge of this backwards jigsaw puz-zle is to figure out the answer to thetwo questions: What are the constitu-ent pieces (shapes) from which all theallowed objects are made? and What arethe rules for putting them together?There are only two types of constitu-ents in this puzzle and the rules are verysimple. (The answer is given on page 31for you to check yourself.) You will findwhen you try to solve this puzzle thatthe set of white shapes-those that donot exist-tell you as much about howthe pieces are put together as do theblack shapes. This is also true in thestudy of particle physics: sometimesthe physicist learns as much from thethings that do not occur in an experi-ment as he does from the things thatdo occur.

The two-mile-long Stanford LinearAccelerator, which gits in the Stanfordhills not far from the main campus, isa tool for particle physics research.

Think of it as a gigantic microscope.By using high-energy electrons as aprobe, physicists at the Stanford LinearAccelerator Center (SLAC) can "see"deep inside the nucleus of an atom andlearn about the structures buried there.This method is roughly comparable toshooting tennis balls at an unidentifiedobject in a dark room: by measuringwhich balls miss the object, which hitit, and at what angle and speed theybounce off it, one could reach some con-clusions about the location, size, shape,and texture of the object.

Our understanding of the structure ofmatter has grown enormously in theyears since SLAC began operations inthe early-1960s. SLAC and other accel-erators around the world have played acrucial role in confirming some earliertheories about matter and in generatingsome important new developments.

THE FIRST STEP INSIDE THE ATOMAll atoms consist of a central core,called a nucleus, that is surrounded bya cloud of particles called electrons. Thenucleus of an atom is made up of twokinds of particles, protons and neu-trons. The neutrons, as one might guessfrom their name, are electrically neutralobjects-that is, they have no electriccharge-while the protons each carry apositive electric charge. The circlingelectrons each have a negative chargethat is exactly the opposite of that of a

THE STANFORD MAGAZINE / 29

Permission to reprint this articlegranted by The Stanford Magazine.The report is being circulated as a spe-cial issue Number 6 of the Beam Line,March 1984.

The Stanford Linear AcceleratorCenter, SLAC, is a national laboratoryfor basic research in high-energy physics.Its facilities are used by scientists fromuniversities and other laboratories inthis country and abroad. Stanford Uni-versity operates SLAC under contractwith US Department of Energy throughthe Department's San Francisco Opera-tions Office in Oakland.

HOW SLAC WORKS"In high-energy physics you have to have bigger and biggermachines to see smaller and smaller things."

Wolfgang K.H. Panofsky, director of SLAC

The heart of the Stanford LinearAccelerator Center (SLAC) is apieced-together copper tube fourinches in diameter and two mileslong. This is the "linac" itself,the conduit down which elec-trons (the particles that normallyswirl around the nucleus of anatom) travel before colliding witha target in an experiment area,where the results of the colli-sions are studied.

SLAC separates electrons outof their atoms and propels themin a way not much different fromthe way an ordinary televisionset does. In a television set, anelectron gun at the back of thepicture tube shoots a beam ofelectrons forward while magnetsdirect the beam around to makepictures on the screen. SLAC'selectron gun in the foothills be-hind Stanford evaporates elec-trons out of the atoms in a fila-ment of hot tungsten and shootsthem straight down the two-milelinac. The electrons travel inbunches or pulses, up to 360pulses per second, with billionsof electrons in each pulse. Mag-nets surrounding the first ten-foot section of the linac act aslenses to steer and focus thebeam of electrons. Radio wavespiped into the linac from devicescalled klystrons carry the elec-trons along. (The two-mile-longbuilding visible above-ground atSLAC is only the shed housingthe series of 240 klystrons. Thelinac itself is in a tunnel 25 feetunderground.) The electronsride the radio waves and gatherenergy from them in much thesame way surfers ride oceanwaves: a cluster of electronstravels with each peak of theradio wave energy. The farther

along they travel, the faster theygo, approaching ever closer tothe speed of light.

It takes two millionths of a sec-ond for an electron to reach theend of the linac, where powerfulmagnets steer it into any of sev-eral research areas. In one re-search area, End Station A, theelectron enters a stationary tar-get such as a tank of liquid hy-drogen or deuterium. Like all at-oms, those in the target consistmostly of empty space, so theelectron bullet may pass cleanthrough the atoms of the target,missing any subatomic parti-cles altogether. If the negativelycharged electron does comeclose to any charged particle,the electrical interaction betweenthem will cause it to changecourse. A detector records whathappens, counts how many par-ticles go in which direction, atwhat speed, and so on. Com-puters analyze this information.

Two other research areas,SPEAR (Stanford Positron Elec-tron Asymmetric Ring) and PEP(Positron Electron Project) areboth based on the principle ofcolliding moving particles head-on, thereby achieving higher-energy density than is possiblewith a stationary target. This canreveal phenomena that couldnever have been seen before.

SPEAR, the older of the tworesearch areas, is a 200-foot-diameter oval-shaped ring at theend of the two-mile linac. SPEARworks with both electrons andtheir antimatter equivalents, pos-itrons (which SLAC can also ac-celerate). Magnets steer elec-trons into the SPEAR ring to runone direction, and steer positronsto run in the opposite direction.

The beams of particles are keptcirculating at high energy, andmade to cross where detectorscan record what happens. Mil-lions of electrons and positronsmeet each second. Sometimesthey simply deflect one another.Sometimes they collide and anni-hilate one another, thereby creat-ing a burst of pure energy thatlasts for only about one ten-tril-lionth of a trillionth of a second,before it rematerializes into ashower of all kinds of subnuclearparticles and antiparticles thatregister in large electronicdetectors.

Successes at SPEAR and thedesire for even more powerfulcollisions led physicists at SLACand the Lawrence Berkeley Lab-oratory to build a ring ten timeslarger, called PEP. It works onthe same principle as SPEAR,but because it is larger (one anda half miles in circumference),electrons and positrons withmuch higher energy can bestored in this ring and thereforecollide with greater force. HencePEP allows physicists to exploreregions inaccessible at SPEAR.

Plans are now under way tobuild the Stanford Linear Collider(SLC), which will collide elec-trons and positrons at energiesmuch higher than can be storedin PEP, but without putting themfirst in a storage ring. This willrequire new developments in ac-celerator technology, somethingSLAC has continued to producealong with its contributions tobasic physics research.

SLAC is the most powerfulelectron accelerator ever built.Though operated by Stanford,it is a national facility ownedby the Department of Energy.

When particles at by a quark and anSLAC's highest- antiquark. Particleenergy research jets from lower-area, PEP, collide energy facilities thanand shatter, detec- PEP are not as nar-tors such as the one row or well-defined,at left, top, record so they cannot bewhat happens. Left, as easily interpreted.bottom is a typical Right, top and bot-computer plot of a tom: different por-resulting scatter pat- tions of one hugetern. This particular detector at SPEAR.plot would be inter- People are notpreted as two jets of around while detec-particles, produced tors are operating.

L30 / FALL 1983

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aluurlu LitI nuuleusin neat symmetricalorbits (like planetsaround the sun) isincorrect. Electronstravel in irregularorbits, sometimespassing through thenucleus, sometimesstraying out of theatom entirely.

The scale in allthese illustrations isnecessarily quite dis-torted. If the nucleuswere the size shownhere, the electronswould be invisiblysmall and on an av-erage of one and ahalf miles away.

proton. Matter viewed on this scale (orthe even smaller scales we will discussshortly) is never static. The electronsare constantly in motion around the nu-cleus, and the protons and neutrons arein motion around one another withinthe nucleus. The electrons are held tothe nucleus rather weakly by the at-traction of the protons' opposite elec-trical charges.

In the early twentieth century, sci-entists regarded the atoms themselvesas the smallest building blocks of mat-ter, hence they named the set of possibleatoms "the elements." In fact, scien-tists thought it would be impossible tosplit an atom-that is, to break apartan atomic nucleus into smaller pieces.We now know, however, that this is ex-actly what happens naturally in radio-active decay.

Once they understood the structureof atomic nuclei, physicists thoughtthat the proton, neutron, and electronmight be elementary particles. Thesedid seem to provide a very satisfactoryanswer to the first question, What arethe building blocks?-three types ofparticles from which all types of atoms(all the "elements") can be made. Butinvestigation into the second question,the nature of the forces between protonsand neutrons, led us to conclude thatthe situation was in fact much morecomplicated. Rather than having threeelementary particles, we found a consid-erably larger number- a hundred or so,which had to be regarded as at least asfundamental as the proton or neutron.

Particles play two distinct roles inphysics. Some are the constituents ofmatter, as already described, but otherscan be viewed principally as the car-riers of interactions between constit-uent particles. The "carrier" particles:ravel back and forth between the con-tLILucntl pairicles. Particles that have

electrical charges interact with eachother because of those charges. For ex-ample, it is the electrical attraction ofthe positively charged nucleus thatbinds electrons to it to form an atom.The electrical interaction between pro-tons in the nucleus and electrons canbe viewed as a continual interchange ofparticles called photons-the carriersor, more correctly, the quanta of theelectric field. (The true meaning of themuch-overused term, "quantumjump," is here. When an atom makes atransition from one possible configu-ration to another lower-energy config-uration, it does so by emitting a quan-

THE STANFORD MAGAZINE / 31

turn of electromagnetic energy-aphoton. This is a quantum jump and itis, despite the popular usage, a very tinythough sudden change in energy, not alarge one.)

WHAT HOLDS THE NUCLEUSTOGETHER?Electromagnetic interaction explainshow electrons are held to the nucleusbut does not explain how the nucleusitself is held together. In fact, the elec-tromagnetic interactions might be ex-pected to push the like-charged protonsof the nucleus apart and have no effecton the neutrons. Yet the protons andneutrons do hold together. Why? It isbecause a much stronger force over-powers the electromagnetic interaction.Unimaginatively, physicists call thisthe "strong interaction" or the "strongforce."

A theory of this force was first pro-posed in 1935 by the Japanese physicistHideki Yukawa. He predicted the exis-tence of some particles about a tenth themass of protons and neutrons, calledpions, which would play the role of thequanta of the strong force. The discov-ery of pions during the early 1940s notonly verified Yukawa's ideas, it alsotouched off the rash of discoveries of"elementary particles" mentioned ear-lier. The search for pions was compli-cated by the fact that pions are unsta-ble. When they decay they produceanother particle, which we now call themuon. The muon is like an electron, inthat it has no role in the strong inter-action, but it is much heavier, almostas heavy as the pion. In fact, when phys-icists were searching for Yukawa'spion, the first new particle they foundwas the muon. The fact that the muon'smass was close to that predicted by Yu-kawa for pions led to some initial con-fusion. No one had expected the muon,and to this day we know of no reasonwhy this "heavy electron" exists.

Many additional particles were dis-covered in early accelerator experi-ments in the 1950s and 1960s. Somewere heavier cousins of the pions. Pionsand all their cousins are genericallycalled mesons. Similarly, heavier cous-ins of the proton and neutron werefound. Protons, neutrons, and all theircousins are generically called baryons.(I call these particles cousins becauseeven as they were discovered physicistsrecognized that the particles could begrouped together on the basis of certainproperties. In particular, all the parti-

cles of a given group have the samespin-a property that can be roughlythought of as an internal rotation of theparticle. The spin of mesons can be 0or 1 unit; the spin of baryons is t or 3

units.)

SHORT-LIVED PARTICLESMany of these particles are highly un-stable. This means that they do not nor-mally exist in nature. There are prob-ably no muons anywhere in the roomwhere you are reading this. They comeinto existence only in high-energy par-ticle collisions such as those producedby an accelerator, or in radioactive de-cays. You can think of them as beinglike music, which is not there until youturn on the radio. A fraction of a secondlater the unstable particles themselvesdecay; that is, they fall apart into lighterparticles. Most unstable particles arenot constituents of any normal matter;they are not around long enough for any-thing lasting to be made of them. None-theless, they are just as real as morestable particles.

Many of these unstable particles canbe "seen" at SLAC-that is, their ef-fects can be recognized in experimentshere. For example, at SLAG we may firea beam of electrons into a target thatis a container of hydrogen. (See the side-bar on page 30.) The electrons that passclose by a hydrogen nucleus (whichconsists of just a single proton) will in-teract electrically with that proton. En-ergy is transferred from a passing elec-tron to a proton. By observing theenergy and direction of the electronemerging from the target, we can re-construct what energy and momentumwere transferred to the proton. Or wemay turn our attention to other parti-cles produced by the encounter, such aspions. Noting the pattern of energy andangles at which these particles comeout of the target is another way we canreconstruct what went on in the target.For example, if just the right amount ofenergy is transferred to the proton, wemay transform it into a particle calleda A+-a delta plus. This particle is veryunstable. After a tiny fraction of a sec-ond (10 - 23 seconds to be more precise)it decays into other particles. Acceler-ator experiments of this type were re-sponsible for the discovery of many ofthe unstable particles now known toexist.

THE QUARK REVOLUTIONBy grouping particles into families, one

sees a pattern emerge. In the mid-1950sthis pattern led Caltech physicistsGeorge Zweig and Murray Gell-Mannto make a proposal that, at the time,seemed quite revolutionary: that themesons and the baryons were all com-posites, made from objects they called"quarks." Gell-Mann picked the namefrom the phrase "three quarks for Mus-ter Mark" in James Joyce's book Ulys-ses. (In German, quark is something be-tween sour cream and cottage cheese-which of course is a poor choice for thebuilding blocks of anything.)

Zweig and Gell-Mann suggested thatquarks come in three types: up, down,and strange. Each of the three differenttypes of quark has its own pattern ofcharges and strangeness. (We particlephysicists have a bad habit of takingeveryday words and giving them tech-nical meanings that bear little relationto their usual meaning. "Strangeness"is one such word. When particles withthis property were first found, some oftheir behavior was hard to understand,so we called them strange particles.Later we realized that their behaviorcould be understood and quantified, sowe assigned them a label or quantumnumber. The name "strangeness" waslater attached to this quantum number.)

For each kind of quark there is alsoan antiparticle, called an antiquark,which has opposite charge and strange-ness from the corresponding quark.From just the three types of quarks andtheir antiquarks, Gell-Mann and Zweigshowed that they could describe each ofthe known particles as a different com-bination of quarks. For example, in theirquark model, mesons (such as the pion)are all made of combinations of onequark and one antiquark. The baryons(protons and neutrons and their cous-ins) are combinations of three quarks;antibaryons are made of three anti-quarks.

Why was the quark idea revolution-ary? After all, the history of particlephysics was to look for structure withinstructure. The idea was revolutionarybecause, in order to equal the chargesof each known particle by adding up thecharges of its quark constituents, onehad to assume that the quark chargeswere e and -e (where e is the chargeof the proton). No particle with chargeother than integer (whole) multiples ofe had ever been observed. If fractionallycharged particles exist, they exist onlyin those combinations that add up to in-teger charges, never any others, or alone.

32 / FALL 1983

(Only one experiment, performed atStanford under the supervision of Pro-fessor William Fairbanks and publishedin 1979, claims evidence for isolatedparticles with charges that are consis-tent with +2-e or + -e. The question isgenerally regarded as unsettled. How-ever, if isolated fractional charges do in-deed exist, then the rule of combinationwill need modification to accommo-date them.)

At the time the quark model was firstproposed, it was believed that protonsnever fall apart-and in fact no suchprocess has ever been observed. But ifa proton is made of pieces-quarks-why doesn't it fly apart into thosepieces if you hit it hard enough? Allprevious structures had worked thatway. So strong was the prejudice againstthe existence of fractional charges thateven the inventors of the quark modelwere at first reluctant to call quarks realobjects. Perhaps, they suggested, thequarks represented only a mathemati-cal device to explain the pattern of the"elementary" particles.

BUT ARE QUARKS REAL?A series of early experiments at SLACin the mid- 1960s provided a major pushin the direction of accepting quarks asreal physical objects. Carried out by ateam under the leadership of RichardTaylor of SLAC and Henry Kendall ofMIT, the experiments consisted ofshooting high-energy electrons throughthe accelerator at a target containinghydrogen or carbon. By measuring howmany of the electrons scattered off thetarget in a given direction and with agiven residual energy, one could look forevidence of structure within a protonor a neutron. James Bjorken, a theoristat SLAC, showed that results of the Tay-lor-Kendall experiments could be ex-plained if the proton was assumed tohave constituents that, when interact-ing with the very-high-energy elec-trons, behaved essentially indepen-dently-as if they were separate, freeparticles, rather than particles tightlybound in a proton. SLAC's evidence,taken in conjunction with later work atproton accelerators in Illinois andSwitzerland, gradually made physiciststhink of quarks as real objects.

Once we reach the point of acceptingquarks as real particles, the other ques-tion must be asked: What is the natureof the interaction between them? Animportant clue to the nature of theirinteraction-and in fact one of the most

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substantial pieces of evidence for ourpresent theory of matter-comes alsofrom the Taylor-Kendall scattering ex-periments. The clue is that, to describethese experiments in terms of quarks,one had to assume that the quarks be-haved as if they were free while inter-acting with the very-high-energy elec-trons fired at them. Most of the particletheories (mathematical structuresknown as field theories) studied up tothat time would not produce such a re-sult. This Taylor-Kendall clue led to asearch for theories that would accountfor this free behavior of quarks. Theclass of field theories so identified hasthe general name of Non-AbelianGauge Theories. (Algebras are classi-fied as Abelian or non-Abelian follow-ing the work of the nineteenth-centurymathematician Niels Henrik Abel. Thecharges in these theories have a non-Abelian algebra.)

The particular non-Abelian GaugeTheory that is believed to describe theinteractions of quarks is called Quan-tum Chromo-Dynamics-QCD forshort. According to this theory, quarkscarry a charge other than their electricalcharge. This we call their color charge,or just color. Here is another adoptionof an everday word for a totally differentmeaning. Color charge has nothing todo with the colors we see. It simplymeans that these particles participatein QCD interactions.

Each type of quark can come with anyof three possible color charges. Further-more, the quantum particles that carryout the interaction of color chargesthemselves carry color charges. Thesequantum particles are called gluons be-cause they are responsible for "gluing"the quarks together into combinationsthat constitute, for example, protons orpions (which have zero net color charge).Whereas electrical charges add up ac-cording to the rules of ordinary arith-metic, the mathematics of colorcharges is somewhat more complicated(because it is non-Abelian): it turns outthat only the combination of quark plusantiquark, or the combination of threequarks can form particles of zero colorcharge. Two quarks or four quarks cannever give zero color charge. Thus, theparticles we observe are those that canbe understood as combinations for whichthe total combined color charge is zero.

Quarks exist inside particles, butthere is only an extremely small prob-ability that one single quark could everbe observed very far distant from the

Dimensions in centimeters

others. (A comparably improbable eventwould be finding all the air moleculesin a room in one corner while the restof the room was empty. Such things,though theoretically possible, are so im-probable that for all practical purposesone calls them impossible.) Physicistsrefer to this property as confinement:the quarks are said to be confined tothe interior of the zero color charge par-ticles.

DISCOVERIES AND CONFIRMATIONSI said earlier that quarks come in threetypes: up, down, and strange. That wasthe belief until the early 1970s, whenparticles containing a fourth type ofquark, the charm quark, were discov-ered independently and more or less si-multaneously by Burton Richter ofStanford and Samuel Ting of MIT. Thiswas one of the most dramatic particlephysics discoveries of the decade. WhileRichter and his colleagues worked atStanford, Ting and his colleagues wereworking on the other side of the countryat a proton accelerator at BrookhavenNational Laboratory on Long Island.Ting's Brookhaven experiments wereactually performed a little earlier thanthe Stanford experiments, but the groupheld up the announcement while mak-ing careful checks of their results. Fi-nally the two groups, Brookhaven andStanford, announced their results atSLAC on the same day in November1975. The two group leaders, Richterand Ting, shared the 1976 Nobel Prizein physics for the discovery. (Particlescontaining a fifth type of quark havesince been discovered by Leon Leder-man and his collaborators at Fermilabin Illinois.)

Richter had done his experiments ata new colliding beam research facilitybuilt at SLAC under his leadership inthe early 1970s, the Stanford PositronElectron Asymetric Ring (SPEAR; seesidebar, page 30). His was not the onlyexciting discovery at SPEAR. At almostthe same time that Richter and Tingwere doing their experiments, a groupat SPEAR led by Martin Perl discoveredanother particle, the r-lepton. Whereasthe charm quark had been predicted bysome theorists because it was necessaryfor the theory of some radioactive de-cays, the new lepton was completely un-expected. It was another copy of theelectron and muon, but many timesheavier than either. Why this repetitionoccurs is one of the outstanding puzzlesof particle physics today. The discovery

of the new lepton was unique to SPEAR,though it has since been observed atother accelerators. As a result of the dis-

covery, Perl shared the 1983 Wolf Prize(with Lederman, the discoverer of the

fifth quark).Other experiments at SPEAR gave

further confirmation for the QCD the-ory of quarks and gluons. Gail Hansonof SPEAR found that the scatter pat-terns produced when electrons collidewith positrons fit those that would beexpected according to the QCD theory.It remained for PEP (a later and higher

energy version of SPEAR that began op-eration at SLAC in 1980) and a similarfacility in Germany to carry this studyof patterns to a level of detail not pos-sible at SPEAR.

Another expectation of the QCD the-

ory is that, in addition to the particlesthat can be made of combinations ofquarks, there should be some particles,called by the silly name of glueballs,that are made of combinations of

gluons. Some of the possible glueballparticles have properties that could notbe achieved from quark combinations.Physicists at SPEAR are currently fas-cinated by recent evidence for particlesthat could be glueballs. Further infor-mation is needed before they can con-

sider this evidence conclusive, but at

present the existence of glueballs seems

to be a possible interpretation.The most widely accepted theory de-

scribing the electromagnetic interac-tion and also the force responsible forsome radioactive decays (called theweak interaction) is also a non-AbelianGauge Theory. It received a very im-portant confirmation from a set of pre-cise experiments made in 1980 by aStanford group headed by Richard Tay-lor. They used the original.SLAC facil-ity, but with a new particle source ca-pable of producing polarized electrons.As previously mentioned, electrons,photons, and many other particles have

a property called spin, which can bethought of as an internal rotation of the

particle. The spins of particles in a

beam can be aligned or polarized. (Pho-tons, for example, are polarized whenlight passes through Polaroid sun-glasses. You can observe the effect of

this polarization by putting anotherpair of sunglasses at right angles to thefirst and seeing that no light comesthrough, whereas when the two lensesare aligned the lighf comes throughboth.) In a beam of polarized electrons,the direction of the spin rotation for the

majority of the electrons coming downthe accelerator is aligned in a predeter-mined fashion. By detecting a tinyasymmetry in the number of electronsscattered to the left or right (relative tothis direction of polarization), theSLAC group demonstrated that the pre-dictions of the non-Abelian weak in-teraction theory were correct. It wasonly after these SLAC experiments thatthe theory was regarded as well enoughestablished to award a Nobel Prize tothe theorists who had developed it tenyears earlier.

THE FUTUREWe have now reached a picture of mat-ter in which all those particles thathave strong interactions are compositesof quarks and gluons. The strong inter-actions are now seen as a residual effectof their internal color charge structure.Other particles, called leptons, have nointernal color charge structure andhence no strong interactions; they par-ticipate only in the weak, the electro-magnetic, and the gravitational process-es. The fact that all the interactions,even gravity, are now described by gaugetheories has given much impetus to the

idea that we can find a single unifiedtheory of all forces-an idea which Ein-stein pursued without success in thelatter part of his research. Perhaps we

are now on the verge of formulatingsuch a theory. Certainly, many peopleare trying. Another equally fascinatingdirection of research is to try to explainthe repeating sets of leptons and quarksby looking for yet another level of struc-

ture within them. Perhaps quarks are

the fundamental building blocks of na-

ture, perhaps not. Only time and fur-ther study will tell.

For SLAC's part, the next major stepwill be to construct a new higher-en-ergy facility, the Stanford Linear Col-lider. One of SLC's goals will be tostudy the particle called the Z-boson,but perhaps other results from SLC willprove as exciting as whatever it can tell

us about Z-bosons. When one pushes to

a new and unexplored frontier, one oftenlearns more than one can predict. i

HELEN R. QUINN, '63, MS '64, PhD

'67, is a research fellow at SLAC, andone of nine permanent members of theSLAC theory group. A native Austra-lian, she has worked in Germany atthe Deutsches Elektronen Synchro-tron and been an associate professorof physics at Harvard.

THE STANFORD MAGAZINE / 35