A PERIODICAL OF PARTICLE PHYSICS

SUMMER 1998 VOL. 28, NUMBER 2

EditorsRENE DONALDSON, BILL KIRK

Contributing EditorsMICHAEL RIORDAN, GORDON FRASERJUDY JACKSON, PEDRO WALOSCHEK

Editorial Advisory BoardGEORGE BROWN, LANCE DIXON

JOEL PRIMACK, NATALIE ROEROBERT SIEMANN, GEORGE TRILLING

KARL VAN BIBBER

IllustrationsTERRY ANDERSON

DistributionCRYSTAL TILGHMAN

The Beam Line is published quarterly by theStanford Linear Accelerator Center,Box 4349, Stanford, CA 94309.Telephone: (650) 926-2585INTERNET: beamline@slac.stanford.eduFAX: (650) 926-4500Issues of the Beam Line are accessible electronically onthe World Wide Web athttp://www.slac.stanford.edu/ pubs/beamline.SLAC is operated by Stanford University under contractwith the U.S. Department of Energy.The opinions of the authors do not necessarily reflectthe policy of the Stanford Linear Accelerator Center.

Cover: Computer simulation of the pair production of thetau sneutrino, the supersymmetric partner of the tauneutrino, at 500 GeV center-of-mass energy in a futureelectron-positron linear collider (see the article byJohn Ellis on page 14).

(Courtesy Richard Dubois, SLAC)

Printed on recycled paper

FOREWORD

2 James Bjorken

FEATURES

4 REFLECTIONS

SLAC’s Deputy Director

reflects on a 50-year career

as a scientist and

statesman.

Sidney Drell

14 THE NEXT STEPS IN

PARTICLE PHYSICS

One of CERN’s leading

theoretical physicists

discusses future options

for particle physics.

John Ellis

20 A PHYSICIST IN THE

WORLD OF VIOLINS

A physicist applies well-

known principles to the

construction of violins

in order to understand

techniques for shaping

their sound.

William Atwood

28 A Possible FutureMICROFABRICATION FOR MILLIMETER WAVE ACCELERATORS

Large and small scales are intertwined

throughout physics. Huge accelerators

produce beams for atomic, nuclear, and

particle science. In an interesting, new twist,

microfabrication could be the key

to the accelerators of the future.

Heino Henke & Robert Siemann

DEPARTMENTS

35 THE UNIVERSE AT LARGE

Can’t You Keep Einstein’s Equations

Out of My Observatory?

Virginia Trimble

41 CONTRIBUTORS

44 DATES TO REMEMBER

CONTENTS

page 28

page 35

page 14page 20

IDNEY DRELL and SLAC have histories which areinseparable. Right from the beginning, when SLAC wasno more than Project M housed in a warehouse on theStanford campus, Sid left the more familiar and comfort-

able world of academe to join the adventure of cre-ating a great new laboratory. A major challenge hefaced, as a theorist, was to create the kind of intel-lectual climate more typically found in universitydepartments, and in those days not commonlyfound within this country’s accelerator laborato-ries. This turned into an incredible success story.Quickly the SLAC theory group became very wellknown, not only for the variety of talent itattracted, but especially for its unique personality.To this day this personality persists: uncompro-misingly high intellectual standards, a good mix ofapplied and formal theory, a close interaction withthe experimental community, a breadth of vision,an essential humanism, and an informality andlack of pretension which keeps the pursuit ofphysics something not only deeply satisfying butalso just plain fun to do. It is no accident that this“SLAC style” is a mirror of Sid’s own persona.

Generations of students and postdocs who have passed through the laboratory—such as John Ellis of CERN who discusses future options for particle physics in thisissue—as well as we old-timers, will attest to his overwhelming influence in creat-ing this environment.

Sid’s research contributions, within and beyond the SLAC program, havebeen legion and broad-ranging, of fundamental importance. And his impact on SLAChas extended well beyond that of theoretical physics. From the beginning of SLAChe was invaluable in the building of the laboratory, its staff, and its program. Hehas, as deputy director, played a quiet, but vital role in the overall management andorchestration of the SLAC program. His calm guidance, based on the highest scien-tific standards, an unwavering integrity, and an astute understanding of humannature, has been in most demand in just those periods of SLAC history that havebeen the most stressful. And his wise counsel is always sought by the internationalparticle physics community on how to deal with the broad issues facing the field.

2 SUMMER 1998

FOREWORD

S

BEAM LINE 3

BUT SID’S INFLUENCE has extended far beyond particle physics, in areal sense to the entire planet. As he himself recounts in this issue, hewas drawn into the public policy issues of strategic defense and arms

control already in the 1960s, and his credo and contributions can better be dis-cerned by his own words than by any of mine. Making headway on politicaland social issues is much slower going than on physics, and Sid’s modusoperandi has been to patiently work “from the inside,” a method which wasstrongly challenged during the Vietnam years. Sid, confronted personally atthat time, responded with steadfastness and great integrity. He exemplifiesfor everyone the value and necessity of his form of public service. One smallexpression of his influence is that some of his students and other physicistspassing through the SLAC environment have chosen to move their careersout of physics and into public affairs. Quite a few others, while stayingwithin physics, have been especially active in the social issues created bythe big-science character of particle physics.

THEN THERE IS SID’S IMPACT on me. I first encountered Sid as anundergraduate at MIT, where he taught courses I took, and in addi-tion sponsored evening informal journal-club seminars for under-

graduate physics majors in his home. We happened to emigrate to Stanfordtogether in 1956, he on the faculty, I as a graduate student. I soon was priv-ileged to be one of his many thesis students, something which then evolvedinto writing our textbooks. It was absolutely natural that I too should joinSLAC, and to continue the close association. Sid has been everything to me,as a teacher and mentor, as a second father, as an esteemed colleague, asbest man, and as simply a dear friend. Sid, it is a time for warm congratu-lations on your long and distinguished career at SLAC, and for best wishesfor many happy retirement years—years which we at SLAC trust willcontinue to be shared with us.

James Bjorken

COHERENT PRODUCTION AS A MEANS OF DETERMINING THE SPIN AND PARITY OFBOSONS.. S.M. Berman, S.D. Drell (SLAC). SLAC-PUB-0010, 1963. 5pp. Phys. Rev. Lett.11:220-224,1963

SPECULATIONS ON THE PRODUCTION OF VECTOR MESONS. S.M. Berman, S.D. Drell(SLAC). SLAC-PUB-0016, Aug 1963. 39pp. Phys.Rev.133:B791-801,1964

ELECTRODYNAMIC PROCESSES WITH NUCLEAR TARGETS. S.D. Drell (SLAC), J.D.Walecka (Stanford U., ITP). SLAC-PUB-0021, Nov 1963. 17pp. Annals Phys.28:18-33,1964

ASYMMETRIC MU PAIR PHOTOPRODUCTION AT SMALL ANGLES. S.D. Drell (SLAC).SLAC-PUB-0035, Jun 1964. 10pp. Phys.Rev.Lett.13:257-260,1964

MESON EXCHANGE EFFECTS IN ELASTIC E D SCATTERING. R. J. Adler (Stanford U.,ITP), S.D. Drell (SLAC). SLAC-PUB-0033, Jun 1964. 6pp. Phys.Rev.Lett.13:349-352,1964

BOUNDS ON PROPAGATORS, COUPLING CONSTANTS AND VERTEX FUNCTIONS. S.D.Drell (SLAC), A. C. Finn, A. C. Hearn (Stanford U., ITP). SLAC-PUB-0039, Jul 1964. 43pp.Phys.Rev.136:B1439-51,1964

DOUBLE CHARGE EXCHANGE SCATTERING OF PIONS FROM NUCLEI. R. G. Parsons,J. S. Trefil (Stanford U., ITP), S.D. Drell (SLAC). SLAC-PUB-0063, Nov 1964. 16pp.Phys.Rev. 138:B847-50,1965

ANALYSES OF MUON ELECTRODYNAMIC TEST. J. A. McClure, S.D. Drell (SLAC). SLAC-PUB-0067, Dec 1964. 18pp. Nuovo Cim.37:1638-1646,1965

PHOTOPRODUCTION OF NEUTRAL K MESONS. S.D. Drell, M. Jacob (SLAC). SLAC-PUB-0065, Dec 1964. 24pp. Phys.Rev.138:B1313-7,1965

ANOMALOUS MAGNETIC MOMENT OF THE ELECTRON, MUON, AND NUCLEON. S.D.Drell, H. R. Pagels (SLAC). SLAC-PUB-0102, Apr 1965. 44pp. Phys. Rev. 140: B397-B407,1965

TEST OF ROLE OF STATISTICAL MODEL AT HIGH-ENERGIES. S.D. Drell (SLAC), D.R.Speiser, J. Weyers (Louvain U.). SLAC-PUB-0138, Jun 1965. 8pp. Preludes in TheoreticalPhysics, ed. by A. De-Shalit, H. Feshbach, L. Van Hove. N. Y., Wiley, 1966, pp.294-301.

SPECIAL MODELS AND PREDICTIONS FOR PHOTOPRODUCTION ABOVE 1-GEV. S.D.Drell (SLAC). SLAC-PUB-0118, Jun 1965. 46pp. Invited talk to the Int. Symp. on Electronand Photon Interactions at High Energies, DESY, 1965. Proc. of the Int. Symp. on Electronand Photon Interactions at High Energies, DESY, 1965. Hamburg, Deutsche PhysikalischeGesellschaft, 1965. vol. 1, p. 71-90

AXIAL MESON EXCHANGE AND THE RELATION OF HYDROGEN HYPERFINE SPLITTINGTO ELECTRON SCATTERING. S.D. Drell, Jeremiah D. Sullivan (SLAC). SLAC-PUB-0145,Oct 1965. 9pp. Phys.Lett.19:516-518,1965

DETERMINATION OF RHO0 - NUCLEON TOTAL CROSS-SECTIONS FROM COHERENTPHOTOPRODUCTION. S.D. Drell (SLAC), James S. Trefil (Stanford U., ITP). SLAC-PUB-0170, Feb 1966. 11pp. Phys.Rev. Lett.16:552-555,1966

PERIPHERAL PROCESSES. A. C. Hearn (Stanford U., ITP), S.D. Drell (SLAC). SLAC-PUB-0176, Apr 1966. 95pp. Burhop, E. H. S., ed. High Energy Physics. N. Y., Academic Press,1967. vol. 2, p. 219-64.

EXACT SUM RULE FOR NUCLEON MAGNETIC MOMENTS. S.D. Drell (SLAC), A.C. Hearn(Stanford U., ITP). SLAC-PUB-0187, Apr 1966. 10pp. Phys. Rev. Lett.16: 908-911,1966

POLARIZABILITY CONTRIBUTION TO THE HYDROGEN HYPERFINE STRUCTURE. S.D.Drell, J.D. Sullivan. SLAC-PUB-0204, Jul 1966. 84pp. Phys.Rev. 154: 1477-1498,1967

ELECTRODYNAMIC INTERACTIONS. S.D. Drell. SLAC-PUB-0225, Sep 1966. 57pp. Re-port to the 13th Int. Conf. on High Energy Physics, Berkeley, 1966. Proc. of the Int. Conf.on High Energy Physics, 13th, Berkeley, 1966. Berkeley, Univ. of Calif. Press, 1967. p. 85-99

ELECTROMAGNETIC FORM-FACTORS FOR COMPOSITE PARTICLES AT LARGE MO-MENTUM TRANSFER. S.D. Drell, A.C. Finn, M.H. Goldhaber. SLAC-PUB-0237, Dec 1966.37pp. Phys.Rev.157: 1402-1411,1967

LAMB SHIFT AND VALIDITY OF QUANTUM ELECTRODYNAMICS. S.D. Drell. SLAC-PUB-0609, Jan 1967. 4pp. Comments Nucl.Part.Phys.1:24-26,1967

PION PHOTOPRODUCTION AT 0-DEGREES. S.D. Drell, J.D. Sullivan. SLAC-PUB-0312,May 1967. 13pp. Phys. Rev. Lett.19:268-271,1967

REGGE POLE HYPOTHESIS IN AMPLITUDES WITH PHOTONS. S.D. Drell . SLAC-PUB-0425, Sep 1967. 8pp. Comments Nucl.Part.Phys.1:196-200,1967

WHAT HAVE WE LEARNED ABOUT ELEMENTARY PARTICLES FROM PHOTON ANDELECTRON INTERACTIONS? S.D. Drell (SLAC). SLAC-PUB-0355, Sep 1967. 50pp. Paperpresented at Int. Symposium on Electron and Photon Interactions at High Energies, SLAC,Sep 1967. Proc. of the Int. Symp. on Electron and Photon Interactions at High Energies,SLAC, 1967. Stanford, Calif., SLAC, 1967. p.3-31

4 SUMMER 1998

MYCAREERINRESEARCHas a theoretical physicistdates back to fifty years ago

shortly after the end of World War II. And ithas been the best of times. Back then, it wasa dream time to have been a graduate stu-dent! There was no need to worry about ajob, unless for some strange reason you feltthat Harvard was the only place to be.

Vannevar Bush had laid out a map forthe support of science in his perceptivereport to President Truman in 1945 enti-tled Science, the Endless Frontier. Withclear and brilliant insight he presentedthe design and foundations of the nation’spost-World War II scientific research pro-gram that has become the envy of theworld. Here was his far reaching, vision-ary blueprint: “Science, by itself, providesno panacea for individual, social, and eco-nomic ills. But without scientific progressno amount of achievement in other direc-tions can insure our health, prosperity,and security as a nation in the modernworld.” Furthermore, he reminded Wash-ington that research is a difficult and of-ten very slow voyage over uncharted seasand therefore, for science to flourish withgovernmental support, freedom of inquirymust be preserved, and there must befunding stability over a period of years sothat long-range programs may be under-taken and pursued effectively. Physicswas then a growth industry with anunreal coefficient of inflation that nur-tured us all.

R E F L E C T I O N S

b y S I D N E Y D R E L L

“ I t w a s t h e b e s t o f t i m e s b u t i t c o u l dh a v e b e e n t h e w o r s t o f t i m e s . ”

Looking back at the particle physics of fifty years ago—which now seemslike the Dark Middle Ages—we had a theory of quantum electrodynamics(QED) with which we could do lowest order calculations that were adequate toaccount for what was observed in processes involving photons, electrons, andpositrons. But beyond that, exceedingly laborious calculations generally gaveinfinity, a result that was usually equated to zero and ignored. The infrared divergences alone were understood, thanks to Felix Bloch and Arnold Nord-sieck. Although fragile, limited, and frustrating to work with, QED was the only “successful” field theory, and was variously, and usually unsuccessfully,used as a model to try and to understand other physical systems. These in-cluded nuclei and nuclear forces and what was occurring in situations where mesons were assumed to be the quanta and perturbation theory was invalid.

The first lightning flashes of real progress came in 1947 from Richard Feynman, Julian Schwinger, and Sin-Itiro Tomonaga, with a thunderous rumble from Freeman Dyson. They turned QED into a beautiful, quantita-tive theory whose divergences would be isolated into renormalization con-stants, and whose predictions could be calculated to very high precision. Feynman propagators turned horrendous calculations by the old methodsinto (well, almost) baby’s play, and Feynman graphs helped us know what we were doing. It was a very heady time as we found theory agreeing with the beautiful precision measurements of the Lamb Shift, the electron g–2 value, hyperfine splitting in positronium, and higher order radiation processes.

Shortly thereafter there was great excitement as we dis-covered that there were two mesons—the cosmic ray one andthe nuclear force one—and large new accelerators produced averitable zoo of strange particles. Not only was the physicsvery exciting but also we were buoyed up by the strong sup-port for science, and physics in particular, inspired by thedemonstrated importance of the contributions that physi-cists had made to the successful conclusion of WorldWar II through development of radar and the atomicbomb. As the cold war intensified there was growingconcern that, perhaps, we would be needed again and so we better be nourished and rejuvenated as a strategic asset.

During the next three decades, into the 1970s, particlephysics sped ahead with what now seems like a dizzyingpace. A number of great laboratories were built in theUnited States and around the world. With the creation of

BEAM LINE 5

THE STRUCTURE OF HIGH-ENERGYLARGE MOMENTUM TRANSFER COLLI-SION PROCESSES. H.D.I. Abarbanel, S.D.Drell, F. J. Gilman (SLAC). SLAC-PUB-0371,Dec 1967. 12pp. Phys.Rev. Lett. 20:280-283,1968

DIFFERENCE OF NUCLEON AND PION ELEC-TROMAGNETIC RADII. S.D. Drell, D. J. Silverman(SLAC). SLAC-PUB-0404, Apr 1968. 11pp.Phys.Rev.Lett.20:1325-1329,1968

REMARKS ON EXPERIMENTS AT NAL. S.D. Drell(Stanford U., ITP). FERMILAB-TM-0108, Jul 1968.18pp.

QUANTUM ELECTRODYNAMICS: THEORY. S.D.Drell, S. J. Brodsky (SLAC). SLAC-PUB-0454, Jul1968. 18pp. Invited talk at Int. Conf. on AtomicPhysics, N.Y.U., Jun 1968. Proc. of Int. Conf. onAtomic Physics, New York, 1968. N.Y., PlenumPress, 1969. p. 53-70.

PROTON FORM-FACTORS. S.D. Drell (SLAC).SLAC-PUB-0427, Aug 1968. 9pp. CommentsNucl.Part. Phys.2:36-40,1968

THE STRUCTURE OF HIGH-ENERGY PROTON -PROTON SCATTERING. H.D.I. Abarbanel, S.D.Drell, F.J. Gilman (SLAC). SLAC-PUB-0476, Aug1968. 44pp. Phys.Rev.177:2458-2469,1969

SUPERCONVERGENCE AND THE CALCULATIONOF ELECTROMAGNETIC MASS DIFFERENCES.S.D. Drell (SLAC). SLAC-PUB-0424, Aug 1968.9pp. Nucl.Part.Phys.1:94-98,1967

HIGH-ENERGY LIMIT FOR THE REAL PART OFFORWARD COMPTON SCATTERING. M. J. Creutz,S.D. Drell, E. A. Paschos (SLAC). SLAC-PUB-0499,Oct 1968. 8pp. Phys. Rev. 178: 2300-2301,1969

ELECTROMAGNETIC THEORY AND EXPERIMENT.S.D. Drell (SLAC). SLAC-PUB-0612, Oct 1968.8pp. Comments Nucl.Part.Phys.2:1-6,1968

A FIELD THEORETIC MODEL FOR ELECTRON -NUCLEON DEEP INELASTIC SCATTERING. S.D.Drell, D.J. Levy, T-M Yan (SLAC). SLAC-PUB-0556,Feb 1969. 11pp. Phys.Rev.Lett.22:744-748,1969

A THEORY OF DEEP INELASTIC LEPTON - NU-CLEON SCATTERING AND LEPTON PAIR ANNIHI-LATION PROCESSES. I. S.D. Drell, D. J. Levy, T-MYan (SLAC). SLAC-PUB-0606, Jun 1969. 50pp.Phys. Rev.187:2159-2171,1969

A THEORY OF DEEP INELASTIC LEPTON NUCLE-ON SCATTERING AND LEPTON PAIR ANNIHILA-TION PROCESSES. 2. DEEP INELASTIC ELEC-TRON SCATTERING. S.D. Drell, D. J. Levy, T-M Yan(SLAC). SLAC-PUB-0645, Sep 1969. 96pp. Phys.Rev.D1: 1035-68,1970

A THEORY OF DEEP INELASTIC LEPTON - NU-CLEON SCATTERING AND LEPTON PAIR ANNIHI-LATION PROCESSES. 3. DEEP INELASTIC ELEC-TRON - POSITRON ANNIHILATION. S.D. Drell, D.J. Levy, T-M Yan (SLAC). SLAC-PUB-0685, Nov1969. 62pp. Phys.Rev.D1:1617-39,1970

A THEORY OF DEEP INELASTIC LEPTON - NU-CLEON SCATTERING AND LEPTON PAIR ANNIHI-LATION PROCESSES. 4. DEEP INELASTIC NEU-TRINO SCATTERING. T-M Yan, S.D. Drell (SLAC).SLAC-PUB-0692, Nov 1969. 36pp. Phys.Rev .D1:2402,1970

INELASTIC ELECTRON SCATTERING, ASYMP-TOTIC BEHAVIOR, AND SUM RULES. S.D. Drell.SLAC-PUB-0689, Dec 1969. 42pp. Lectures at Int.School of Physics ‘Ettore Majorana’, Erice, Sicily,Jul 1969. Proc. Int. School of Physics Ettore Majo-rana, Erice, July 1969. NY., Academic Press, 1970.

CONNECTION OF ELASTIC ELECTROMAGNETICNUCLEON FORM-FACTORS AT LARGE Q**2 ANDDEEP INELASTIC STRUCTURE FUNCTIONS NEARTHRESHOLD. S.D. Drell, T-M Yan. SLAC-PUB-0699, Dec 1969. 11pp. Phys.Rev. Lett. 24:181-185,1970

6 SUMMER 1998

CERN in Geneva, we truly became one international community collabo-rating productively on experiments and theories. Parity fell, and welearned the beauty of broken symmetry, spontaneous and otherwise.Muons and neutrinos came into the fold and a theory of weak interactionswas completed. We dispersed, analytically continued, and Reggeized tostudy strong interactions. The proton and neutron revealed their innerstructures and acquired many relatives in a strange particle zoo with newsymmetries and selection rules; eventually quantum chromodynamics orQCD—a non-abelian gauge theory of quarks and gluons, with confinementand asymptotic freedom—was developed as a fundamental field theory ofthe strong interactions. Here at Stanford a new laboratory was createdbased on the peculiar idea that very high energy electron beams were alsovaluable probes for advancing our frontiers of understanding in parallelwith the still higher energy protons. Thus the Stanford Linear AccelertorCenter came to be and soon generated its own miraculous decade of discov-eries—partons, charm, tau leptons—and developed progressively higher en-ergy electron-positron storage rings and colliders as extraordinarily produc-tive new tools for exploration. Our sister labs on the high energy frontiersalso made landmark scientific and technical achievements of comparableimportance.

Today, fifty years later, we have a Standard Model that unifies weak,electromagnetic, and strong interactions. We are able to put to the test ourideas on energy scales that reach back almost to the Big Bang fourteen bil-lion years ago, and on distance scales hundreds of million times smallerthan the Bohr radius. Currently we are awash in a sea of revolutionary andpowerful new, and perhaps even correct, ideas of supersymmetry, strings,branes, etc., that have incorporated gravity into a unified theory of every-thing, as even its most modest practitioners describe it.

The union of our progress in particle theory with the probing by our as-trophysicist colleagues into the farthest reaches of the Universe makes ourextraordinary voyage of the past fifty years even more exciting. We are nowbeginning to read the history of the Universe almost all the way back to theBig Bang. Puzzles abound, but astrology has mutated into a science of cos-mology. It has ceased to surprise us to wake up in the mornings to new pic-tures of clashing galaxies, stars being born and dying or being sucked intoBlack Holes, and other sensational evidence of what was going on far outthere way back when! What a gig this has been! And what fun to have beenringside to so much of the action. The strong interaction with our

BEAM LINE 7

experimental colleagues that has long been a SLAC hall-mark has added greatly to the stimulating and enjoyableclimate for our work.

In recent years we have suffered occasional disap-pointments in receiving less than hoped-for financial sup-port for our activities and plans for the future. Gone aresome of the momentum and optimism of the earlieryears. More patience is required of us in fulfilling ouraspirations. This is especially tough on the younger scien-tists looking for opportunities to spread their wings andfly. But the future remains rich with promise. TheDepartment of Energy and the National Science Founda-tion program offices in Washington, with help from theHigh Energy Physics Advisory Panel, continue theirstrong and enlightened support for our work with duerespect for the principles established by Vannevar Bush’sreport. We have also forged increasingly strong bonds of a single inter-national community, cooperatively at work on a truly international LargeHadron Collider at CERN.

Looking back retrospectively, we cannot forget that, at the same time aswe dreamed of the theory of Grand Unification, there were the nightmares ofwhat could have been the worst of times. Scientific progress had also led tonew technologies of nuclear weapons, missiles in space, and the possibility, forthe first time in human history, that the new weapons we had created had suchgreat destructive potential that they could lead to the end of civilization aswe know it.

THE CHALLENGE TO PREVENT that nightmare from materi-alizing led many physicists to work with the military and the gov-ernment. Their commitment took many forms, some working at

weapons laboratories and others working as technical advisers in the arms-control negotiating and policy initiatives. Some of us had the good fortuneof being able to divide our lives between our academic research trying to un-derstand Nature’s mysteries and our technical efforts to help better under-stand and thereby try to reduce or counter the dangers we face. It is my per-sonal conviction that the scientific community—not each individual but asa whole—bears a responsibility, a moral obligation, to project the implica-tions of the technological changes initiated by our scientific progress, and to

FINAL PARTICLE CORRELATIONS IN DEEP IN-ELASTIC LEPTON PROCESSES. S.D. Drell, Tung-Mow Yan. SLAC-PUB-0718, Feb 1970. 11pp. Phys.Rev. Lett.24:855-859,1970

IMPORTANT PROBLEMS AND QUESTIONS FORTHE NEW ACCELERATORS. S.D. Drell (SLAC).SLAC-PUB-0745, May 1970. 34pp. Invited paperpresented at Int. Conf. on Expectations for ParticleReactions at the new Accelerators, Univ. of Wis-consin, Madison, Mar 30 - Apr 1, 1970. Proc. of theInt. Conf. on Expectations for Particle Reactions atthe new accelerators, Madison, Wis., 1970

THE PRESENT STATUS OF QUANTUM ELECTRO-DYNAMICS. S.J. Brodsky, S.D. Drell. SLAC-PUB-0761, May 1970. 89pp. Ann.Rev. Nucl. Part. Sci.20:147,1970

MASSIVE LEPTON PAIR PRODUCTION INHADRON - HADRON COLLISIONS AT HIGH-EN-ERGIES. S.D. Drell, T-M Yan. SLAC-PUB-0755, Jun1970. 12pp. Phys.Rev.Lett.25:316-320,1970, Erra-tum-ibid.25:902,1970 (Also in *Lichtenberg, D.B.(ed.), Rosen, S.P. (ed.): Developments In TheQuark Theory Of Hadrons, Vol. 1*, 454-458)

PARTONS AND THEIR APPLICATIONS AT HIGH-ENERGIES. S.D. Drell, Tung-Mow Yan. SLAC-PUB-0808, Oct 1970. 82pp. Annals Phys.66:578,1971

PARTONS AND DEEP INELASTIC PROCESSES ATHIGH-ENERGIES. S.D. Drell. SLAC-PUB-0903,(Received Apr 1971). 7pp. Comments Nucl.Part.Phys.4:147-153,1970

ELECTROMAGNETIC INTERACTIONS WITH EM-PHASIS ON COLLIDING RINGS, PARTONS, ANDTHE LIGHT CONE. S.D. Drell. SLAC-PUB-0948,Aug 1971. 57pp. Rapporteur’s report, Int. Conf. onElementary Particles, Amsterdam, 1971. Proc. Int.Conf. on Elementary Particles, Amsterdam, 1971.Amsterdam, North Holland, 1972, 307-32

FEASIBILITY STUDY FOR A 15-GEV ELECTRONPOSITRON STORAGE RING (E(CM) = 30-GEV).S.M. Berman, S.D. Drell, J R. Rees, B. Richter.SLAC-TN-71-022, Aug 1971. 45pp.

SCALING PROPERTIES AND THE BOUND STATENATURE OF THE PHYSICAL NUCLEON. S.D. Drell,T.D. Lee (Columbia U.). SLAC-PUB-0997, Dec1971. 91pp. Phys.Rev.D5:1738,1972

A DYNAMICAL MODEL OF HADRONS WITHFERMION QUARKS. S.D. Drell, K. Johnson. SLAC-PUB-1091, Aug 1972. 22pp. Phys.Rev. D6: 3248,1972

RECENT THEORETICAL WORK ON E+ E- ANNIHI-LATION AND CONTINUATION FROM INELASTICELECTRON SCATTERING. S.D. Drell. SLAC-PUB-1137, Oct 1972. 14pp. Invited talk presented atParallel Session on Currents 1: Electron PositronInteractions at 16th Int. Conf. on High EnergyPhysics,6-13 Sep 1972, Batavia, Ill. Proc. of Int.Conf. on High Energy Physics, Batavia, Ill., 1972.Batavia, Ill., National Accelerator Lab., 1973. vol.2, p. 8-18

PCAC AND THE PI0 —-> 2 GAMMA DECAY RATE.By S.D. Drell. SLAC-PUB-1158, Nov 1972. 57pp.Phys.Rev.D7:2190,1973

SPECULATIONS ON THE BREAKDOWN OF SCAL-ING AT 10**-15-CM. M.S. Chanowitz, S.D. Drell.SLAC-PUB-1201, Mar 1973. 10pp. Phys.Rev.Lett.30:807,1973

K(L3) DECAYS IN A TWO COMPONENT THEORYOF PCAC J.L. Newmeyer, S.D. Drell. SLAC-PUB-1275, Jul 1973. 18pp. Phys.Rev.D8:4070,1973

KNOWN AND UNKNOWN REGIONS IN LEPTONPHYSICS. S.D. Drell. SLAC-PUB-1310, Sep 1973.41pp. Invited paper Int. Symposium on Electronand Photon Interactions at High Energies, Bonn,West Germany, Aug 27-31, 1973. Bonn Conf.1973:493

SPECULATIONS ON THE BREAKDOWN OF SCAL-ING AT 10**-15-CM.M.S. Chanowitz, S.D. Drell.SLAC-PUB-1315, Oct 1973. 43pp. Phys.Rev.D9:2078,1974

HEAVY QUARKS AND STRONG BINDING: AFIELD THEORY OF HADRON STRUCTURE. W.A.Bardeen (Stanford U., ITP), Michael S. Chanowitz,S.D. Drell, M. Weinstein, T-M Yan. SLAC-PUB-1490,Sep 1974. 128pp. Phys.Rev.D11:1094,1975

SURVEY OF THEORETICAL SPECULATIONS ONTHE NATURE OF PSI (3105) AND PSI-PRIME(3695).I. Bars (Stanford U., Phys. Dept.), M.S.Chanowitz (LBL, Berkeley), S.D. Drell,, R.D. Peccei(Stanford U., Phys. Dept.), X.Y. Pham, S.H.H. Tye,S. Yankielowicz (SLAC). SLAC-PUB-1522, Jan1975. 39pp. Informal Notes - not for publicationfrom the SLAC Workshop - Theory Subgroup.

8 SUMMER 1998

help citizens and their governments shape their practical applica-tions in ways beneficial to all society. This responsibility is mostcogently manifest in dealing with nuclear weapons, whose enor-mous destructive potential leaves so little margin for error.

In my case the dual tracks of academic research and teachingand involvement in government work opened in 1960 when theJASON group was organized. Its purpose was to enlist fresh sci-entific talent to work on problems of importance for ournational security. We were in the dawning new age of nuclear

weapons, space and intercontinental missiles, and the challenges they pre-sented to formulating national security policy. At the same time, the greatphysicists and other scientists, whose contributions were so important inthe winning of World War II with radar and the atomic bomb, had other re-sponsibilities and were twenty years older than at the start of that war. I wasinspired and greatly influenced in considering JASON by the example of twoof my heroes. As physicists and wise counselors, Wolfgang K. H. (“Pief”)Panofsky and Hans Bethe had made great personal commitments and enor-mously valuable contributions to informed policy choices by the UnitedStates concerning arms control and national security. I very much admiredwhat they had done. JASON thus became a new component of my scientificwork. It served as an introduction for me to new problems that were oftenscientifically fascinating and strategically compelling. Subsequently manyother doors opened for my involvement, both inside and outside of the gov-ernment. Over time I ended up working on a variety of interesting technicalissues of national security and arms control.

EARLY ON I BECAME INVOLVED in the technical possibilities ofgaining intelligence from space-based satellite systems as a way ofpiercing the Iron Curtain erected by an obsessively secretive Soviet

government. Photoreconnaissance from satellites circling the earth above theatmosphere at altitudes above 100 miles enabled the United States to piercethe shroud of secrecy by means that were effective, and that were accepted asnon-provocative. With the photography brought back to earth we could moreaccurately assess the growing threat of Soviet nuclear warheads mounted onintercontinental range missiles and bombers. Subsequently it also opened thepath to arms control. Since we could count and size the Soviet’s threateningstrategic forces from the satellite photographs, we could negotiate treaties andverify compliance with treaty provisions to limit their deployment and to

PARTONS - ELEMENTARY CONSTITUENTS OFTHE PROTON? S.D. Drell. SLAC-PUB-1545, (Re-ceived Mar 1975). 12pp. Physical Reality andMathematical Description, Ed. by C. Enz, et al.,NY., Reidel, 1974, p. 111-123.

QUARK CONFINEMENT SCHEMES IN FIELD THE-ORY. S.D. Drell. SLAC-PUB-1683, Nov 1975. 41pp.Lectures given at ‘Ettore Majorana Int. SummerSchool’, Erice, Sicily, Jul 11 - Aug 1, 1975. EriceSubnucl.Phys.1975:143 (QCD161:I65:1975:PT.A)

VARIATIONAL APPROACH TO STRONG COU-PLING FIELD THEORY. 1. PHI**4 THEORY. S.D.Drell, M. Weinstein, S. Yankielowicz. SLAC-PUB-1719, Feb 1976. 99pp. Phys.Rev.D14:487,1976(*Title changed in journal*)

STRONG COUPLING FIELD THEORIES: 2. FERMI-ONS AND GAUGE FIELDS ON A LATTICE. S.D.Drell, M. Weinstein, S. Yankielowicz. SLAC-PUB-1752, May 1976. 62pp. Phys.Rev.D14:1627,1976

FEASIBILITY STUDY FOR A 15-GEV ELECTRONPOSITRON STORAGE RING: E(CM) = 30-GEV.S.M. Berman, S.D. Drell, J.R. Rees, B. Richter.PEP-0005, (Received Dec 1976). 45pp.

QUANTUM FIELD THEORIES ON A LATTICE:VARIATIONAL METHODS FOR ARBITRARY COU-PLING STRENGTHS AND THE ISING MODEL IN ATRANSVERSE MAGNETIC FIELD. S.D. Drell, M.Weinstein, S. Yankielowicz. SLAC-PUB-1942, May1977. 44pp. Phys.Rev.D16:1769,1977 .QUARK CONFINEMENT. S.D. Drell. SLAC-PUB-2020, Oct 1977. 78pp. Lecture presented at SLACSummer Insitute, Stanford, Ca., July 11-22, 1977.SLAC Summer Inst.1977:81 (QCD161:S76:1977)

FERMION FIELD THEORY ON A LATTICE: VARIA-TIONAL ANALYSIS OF THE THIRRING MODEL.S.D. Drell, B. Svetitsky, M. Weinstein. SLAC-PUB-1999, Aug 1977. 45pp. Phys.Rev.D17:523,1978

FIELD THEORY ON A LATTICE: ABSENCE OFGOLDSTONE BOSONS IN THE U(1) MODEL INTWO-DIMENSIONS. S.D. Drell, M. Weinstein.SLAC-PUB-2026, Oct 1977. 29pp. Phys.Rev.D17:3203,1978

ELEMENTARY PARTICLE PHYSICS. S.D. Drell..SLAC-PUB-2043, Nov 1977. 18pp. Daedalus,Summer 1977.

WHEN IS A PARTICLE: THE RICHTMYER MEMOR-IAL LECTURE. S.D. Drell. SLAC-PUB-2074, Jan1978. 33pp. APS/AAPT Meeting, San Francisco,Jan. 23-26, 1978. Am.J.Phys.46:597-606,1978,Phys.Today 31:23,1978 (issue No.6)

EXPERIMENTAL STATUS OF QUANTUM ELEC-TRODYNAMICS. S.D. Drell.. SLAC-PUB-2222, Oct1978. 29pp. Talk given at UCLA Symp. honoringJulian Schwinger’s 60th birthday, Feb 18-19, 1978. Physica 96A:3,1979

QED ON A LATTICE: A HAMILTONIAN VARIA-TIONAL APPROACH TO THE PHYSICS OF THEWEAK COUPLING REGION. S.D. Drell, H.R.Quinn, B. Svetitsky, M. Weinstein. SLAC-PUB-2122, Jun 1978. 64pp. Phys.Rev.D19:619,1979

RELATIVISTIC QUANTUM FIELD THEORY. (GER-MAN TRANSLATION). J.D. Bjorken, S.D. Drell.1979. Bibliograph.Inst./mannheim 1967, 409P.(B.i.-hochschultaschenbuecher, Band 101).

DYNAMICAL BREAKING OF CHIRAL SYMMETRYIN LATTICE GAUGE THEORIES. B. Svetitsky, S.D.Drell, H.R. Quinn, M. Weinstein. SLAC-PUB-2453,Jan 1980. 54pp. Phys.Rev.D22:490,1980

APPROXIMATE DYNAMICAL SYMMETRY IN LAT-TICE QUANTUM CHROMODYNAMICS. M. Wein-stein, S.D. Drell, H.R. Quinn, B. Svetitsky. SLAC-PUB-2486, Mar 1980. 26pp. Phys.Rev.D22:1190,1980

BEAM LINE 9

initiate reductions. Photoreconnaissance satellites were the first big step to-ward achieving the Open Skies that President Eisenhower had first called forin 1955.

Working in this area of technical intelligence was compelling for its ob-vious strategic importance. The more accurately we can gauge the natureand imminence of developing threats from our perceived or potential foes,the more responsibly and confidently we can act in crises and plan for ournational security. This truism is consonant with the fundamental tenet ofan academic career—the more we learn and the better we understand a situ-ation, the better prepared we are to address it and act wisely. I also foundthis work, continuing up to the present, extraordinarily fascinating on tech-nical grounds as I interacted with scientists and engineers from both theacademic and the industrial world whose accomplishments were remarkable.

Throughout the cold war the issue of how best to discourage, deter, ordefend ourselves against the use of nuclear weapons was on center stage,front and center. Debates about the potential value, versus the dangerous il-lusions, of nationwide anti-ballistic missile (ABM) defenses were ongoing,with periodic crescendos, for more than three decades. Though often drivenby political considerations, these were serious debates about strategic policythat touched a fundamental instinct of all human beings to protect our fami-lies and homes. Nuclear warheads with their enormous destructive poten-tial had greatly changed the requirements of an effective defensefrom the pre-nuclear era. But how different, and what constitutedsensible programs and goals? Was it practical to try to defendsociety with ABMs? What was the best way to maintain a sur-vivable missile force in order to establish a strategic stability thatrelies on mutual assured destruction to deter a would-be attacker?There is an essential technical core to any informed debate be-tween defense and deterrence. It has commanded the attention ofmany scientists for a long time, and I did not escape involvementin this important issue of national security.

At the root of this issue are two technical realities: the rela-tive ease and economy of designing and deploying offensivecountermeasures to overpower any conceivable defenses; andthe requirement that a missile defense against nuclear-tippedmissiles must be near perfect if it is to be effective in protecting society. Inaddition, and of utmost importance, one has to consider the almost certainlyharmful impact of an arms build up between competing offenses and

10 SUMMER 1998

defenses, and their countermeasures andcounter-countermeasures, on strategic stabil-ity and future prospects of reducing the nu-clear threat.

These considerations are still central tothe continuing debate about ballistic mis-sile defenses in 1998. Technology haschanged enormously over the years andnew ideas have come to the fore, such asdirected-energy weapons and space-basedsensors. Furthermore we face new strate-

gic challenges in the post-cold war years. However, I stillsee the situation pretty much as stated by President Eisenhower in 1953 inhis “Atoms for Peace” speech at the United Nations: “Let no one think thatexpenditures of vast sums for systems and weapons of defense can guaranteeabsolute safety. The awful arithmetic of the atom bomb does not permit anysuch easy solution. Even against the most powerful defense, an aggressor inpossession of the effective minimum number of atomic bombs for a surpriseattack could place a sufficient number of his bombs on the chosen targets tocause hideous damage.”

Simply put, as much as one would like to have an effective defenseagainst nuclear attack, one cannot escape limitations dictated by laws ofNature in a futile effort to achieve a policy goal that is technically unrealis-tic, even if desirable.

In his famous “Star Wars” speech in March 1983, President RonaldReagan sought to escape these limitations and build an effective nation-wide defense by relying on the new and emerging technologies of beamweapons and advanced space-based sensors. Some of the most ardent sup-porters of his proposed Strategic Defense Initiative indulged in hyperbolewith claims that they could and would create an “astrodome,” or impene-trable defense, of the entire nation against a massive attack by interconti-nental ballistic missiles. In the absence of a careful analysis of the practicaltechnical realities, fanciful claims preceded more measured judgments, anda largely political and highly acrimonious debate ensued. Subsequently,much more modest, but more realistic, goals for a limited ABM systememerged after a lot of hard work and careful analyses by many physicists inacademia, think tanks, and industry, who analyzed the broad repertoire ofnew and prospective technologies along with relevant operational issues.

THE ANOMALOUS MAGNETIC MOMENT ANDLIMITS ON FERMION SUBSTRUCTURE. S.J. Brod-sky, S.D. Drell. SLAC-PUB-2534, Jun 1980. 27pp.Phys.Rev.D22:2236,1980

THE RUNNING COUPLING CONSTANT INQUANTUM ELECTRO

DYNAMICS. S.D. Drell. 1981. Cambridge 1981,Proc., Asymptotic Realms Of Physics, 32-36.

ASYMPTOTIC FREEDOM.S.D. Drell (Oxford U. &SLAC). SLAC-PUB-2694, Feb 1981. 9pp. Recd asreprint. Trans.N.Y.Acad.Sci.Ser.2 v.40 1980:76(QCD113:G6)

QUARKS, UNIFICATION, AND BEYOND. S.D.Drell (SLAC). SLAC-PUB-2856, May 1981. 5pp.Reprinted from J. of College Science Teaching,May 1981.

SUMMARY TALK GIVEN AT 1981 LEPTON PHO-TON SYMPOSIUM. S.D. Drell. SLAC-PUB-2833,Oct 1981. 15pp. Invited talk given at 1981 Int.Symposium on Lepton and Photon Interactions atHigh Energy, Bonn, West Germany, Aug 24-29,1981. Lepton-Photon Symp.1981:1003(QCD161:I71:1981)

COMPOSITE MODELS OF QUARKS AND LEP-TONS AND STRONG COUPLING LATTICEGAUGE THEORIES. H.R. Quinn, S.D. Drell,S. Gupta. SLAC-PUB-2920, May 1982. 30pp.Phys.Rev.D26: 3689, 1982

ENERGY LOSS OF SLOWLY MOVING MAGNETICMONOPOLES IN MATTER. S.D. Drell, N.M. Kroll(SLAC & UC, San Diego), M.T. Mueller (StanfordU., ITP), S. Parke (SLAC), M.H. Ruderman (Colum-bia U.). SLAC-PUB-3012, Nov 1982. 13pp.Phys.Rev .Lett. 50: 644,1983

EXCITATION OF SIMPLE ATOMS BY SLOW MAG-NETIC MONOPOLES. N.M. Kroll (UC, San Diego),S. Parke (Fermilab & SLAC), V. Ganapathi (UC,San Diego), S.D. Drell. FERMILAB-PUB-84-25-T,Jan 1984. 32pp. Invited paper Monopole ‘83 Conf.,Ann Arbor, MI, Oct 6-9, 183. Monopole ‘83:295(QCD161:N15:1983)

CONSTRAINTS ON RADIATIVE Z0 DECAYS. S.D.Drell (SLAC), Stephen Parke (Fermilab & SLAC).SLAC-PUB-3308, Mar 1984. 12pp. Phys.Rev.Lett.53:1993,1984

Har

vey

Lync

h

BEAM LINE 11

This experience was the most compelling andclearest case I know for restoring a high-level non-partisan presidential science advisory mechanismthat is actively engaged in technical national securi-ty problems. President Eisenhower created one in1957 following the Soviet launch of Sputnik anddevelopment of long-range missiles as a potentialthreat to the United States. The scientists involvedin this mechanism were his resource for direct, in-depth analyses and advice as to what to expect fromscience and technology, both current and future, inestablishing realistic national policy goals. Theywere selected apolitically and solely on the groundsof demonstrated achievements in science and engi-neering. Two things set them and their work apartfrom the existing governmental line organizationsand cabinet departments with operational responsibilities, and from non-governmental organizations engaged in policy research. First of all, they hadWhite House backing and the requisite security clearances to gain access toall the relevant information for their studies on highly classified nationalsecurity issues. Second, the individual scientists were independent and pre-sumably, therefore, immune from having their judgments affected by opera-tional and institutional responsibilities. Therein lay their unique value.Unfortunately the advisory mechanism that served the White House andthe nation well when it was created, eroded in the late 1960s during thepolitical strains and public discord of the Viet Nam conflict and has notbeen reenergized effectively in national security matters.

Most recently I have been involved in helping to provide the technicalbasis for the U.S. decision to sign, and to lead the effort to ratify, a world-wide Comprehensive Test Ban Treaty (CTBT) that would, once-and-for-all,end all testing of nuclear weapons of any yield, anywhere, anytime aftermore than fifty years and more than 2000 nuclear test explosions. The politi-cal and strategic importance of such a treaty for accomplishing our non-proliferation goals was made clear in the debate in May 1995, at the UnitedNations. One hundred and eighty one nations signed on to the indefiniteextension of the Non–Proliferation Treaty based on the commitment of thenuclear powers to work toward the cessation of all nuclear weapons tests.Before committing itself to honor this commitment, the United States had

THE CASE AGAINST STRATEGIC DEFENSE:TECHNICAL AND STRATEGIC REALITIES. S.D.Drell, W.K.H. Panofsky. Print-85-0835, 1984. 23pp.Issues in Science and Technology, p.45-64. Fall1984.

JOHN WHEELER: A PERSONAL TRIBUTE. S.D.Drell. SLAC-PUB-4035, Oct 1986. 3pp. Reprint. Found.Phys.16:681-683,19??

A QUANTUM TREATMENT OF BEAMSTRAH-LUNG. R. Blankenbecler, S.D. Drell. SLAC-PUB-

4186, Jan 1987. 47pp. Phys.Rev.D36: 277, 1987 THE MANY DIMENSIONS OF T.D. LEE..S.D. Drell.SLAC-PUB-4201, Jan 1987. 10pp. Invited talkSymp. Commemorating the 13th Anniversary ofParity Nonconservation and Celebrating the 60thbirthday of T. D. Lee, NY, Nov 22, 1986. T.D. LeeSymp.1986:85 (QC16:L4S9:1986)

THE BETHE-MAXIMON RESULT. R. Blankenbecler,S.D. Drell. SLAC-PUB-4271, Mar 1987. 15pp.Phys. Rev.D36:2846,1987

A QUANTUM TREATMENT OF BEAMSTRAHLUNGAND ITS APPLICATION TO RIBBON PULSES. R.Blankenbecler, S.D. Drell. 1987. *Batavia1987/Ithaca 1988, Proceedings, Physics of particleaccelerators* 711-757.

QUANTUM BEAMSTRAHLUNG FROM RIBBONPULSES. R. Blankenbecler, S.D. Drell. SLAC-PUB-4483, Nov 1987. 41pp. Phys.Rev.D37:3308,1988

QUANTUM BEAMSTRAHLUNG: PROSPECTS FORA PHOTON-PHOTON COLLIDER. R. Blankenbecler,S.D. Drell. SLAC-PUB-4629, May 1988. 15pp. Phys.Rev.Lett.61:2324,1988, Erratum-ibid.62:116, 1989

FEYNMAN MEMORIAL LECTURE. S.D. Drell. VT-7,V.15 (VIDEOTAPE), Jul 1988. 0pp. Lecture givenat SLAC Summer Institute, July 1988.

QUANTUM BEAMSTRAHLUNG: PULSE SHAPINGPROSPECTS FOR A PHOTON-PHOTON COLLID-ER. R. Blankenbecler, S.D. Drell. SLAC-PUB-4810,Nov 1988. 11pp. Submitted to Proc. of 1988 Sum-mer Study on High Energy Physics in the 1990s,Snowmass, Colo., Jun 27 - Jul 15, 1988. Snow-mass: DPF Summer Study 1988:683(QCD161:D15:1988)

PAIR PRODUCTION FROM PHOTON PULSE COLLI-SIONS. R. Blankenbecler, S.D. Drell, N.M. Kroll.SLAC-PUB-4954, Mar 1989. 53pp. Phys.Rev.D40:2462, 1989

Nin

a S

tola

r

12 SUMMER 1998

to determine what would have to be included aspermitted activities in a negotiated CTBT, so thatwe could retain confidence in the safety and reli-ability of our enduring nuclear warheads intothe future.

A JASON study was organized to answer thisquestion in 1995. It was our finding that confi-dence in the safety and reliability of the endur-ing stockpile can be maintained, even if verylow yield tests are banned under a true CTBT,so long as the United States sustains a strongscientific and technical infrastructure in nu-clear weapons. Simply put, with a strongscience–based stockpile stewardship andmanagement program, equipped with ad-

vanced diagnostic equipment and led, as it presently is,by first–class scientists and engineers at the national weapons laboratories,there is no need to continue nuclear testing at any level of yield. Instead wewill rely on enhanced attention to surveillance and diagnostic information,and accurate simulations that will be made possible by major advances incomputational speed and power to deepen our understanding of the physicalprocesses in a nuclear explosion. By filling in the substantial gaps in that un-derstanding that we could accept so long as we could directly monitor theperformance of our bombs by testing, we will establish a basis for retainingconfidence in our ability to hear whatever warning bells may ring—howeverunanticipated they may be—alerting us to evidence of deterioration of an ag-ing stockpile. There will also be facilities to provide for warhead refurbish-ing or remanufacture in response to identified needs. This program is consis-tent with the spirit, as well as the letter of the CTBT: without testing theUnited States will not be able to develop and deploy with real confidencemore advanced weapons at either the high or the low end of destructivepower.

Our conclusion was endorsed by the weapons laboratories and proved tobe persuasive in Washington. It provided the technical base for PresidentClinton’s decision for the United States to support and seek a true, zero-yield Comprehensive Test Ban Treaty in August 1996. The scientificchallenge to develop and successfully accomplish this mission is a majorone for the weapons labs, and for all involved in the process.

NUCLEAR WEAPONS SAFETY: REPORT OF THEPANEL ON NUCLEAR WEAPONS SAFETY. S.D.Drell, J.S. Foster, Jr., C, H. Townes. 1990. 44pp.Sidney D. Drell, Chairman.

STATEMENT TO THE JOINT MEETING OF THESUBCOMMITTEES ON ARMS CONTROL, INTER-NATIONAL SECURITY, AND SCIENCE AND EU-ROPE AND THE MIDDLE EAST. S.D. Drell. Jun1990. 13pp.

ANDREI DMITRIEVICH SAKHAROV. S.D. Drell, L.Okun (Moscow, ITEP). SLAC-PUB-5448, Aug 1990.8pp. Phys.Today 43:26-36,1990

SAKHAROV REMEMBERED: A TRIBUTE BYFRIENDS AND COLLEAGUES. S.D. Drell, S.P.Kapitza. 1991. 303pp. AIP, NY, Ed. S.D. Drell andS.P. Kapitza.

FERMION MASSES IN THE STANDARD MODEL.I-H Lee (Rockefeller U.), S.D. Drell. SLAC-PUB-5423, Feb 1991. 8pp. In Memoriam M.A.B. Beg. In*Islamabad 1990, Proceedings, High energyphysics and cosmology* 13-20. In *Islamabad1990, Proceedings, High energy physics and cos-mology* 13-20 and SLAC Stanford -SLAC-PUB-5423 (91/02,rec.Apr.) 8 p and Rockefeller Univ.New York - RU-91-B-005 (91/02,rec.Apr.) 8 p.

ACCELERATOR PRODUCTION OF TRITIUM(APT).S.D. Drell. JSR-92-310, Jan 1992. 56pp. AMITRE Corp. Jason report, S. Drell, Chairman.

THEORETICAL ASPECTS OF LEPTON-HADRONSCATTERING. S.D. Drell (SLAC). SLAC-PUB-5720,Jan 1992. 41pp. Presented at 1991 SLAC SummerInst. on Particle Physics: Lepton Hadron Scatter-ing, Stanford, CA, Aug 5-16, 1991. SLAC SummerInst.1991:47-67 (QCD161:S76:1991)

IN THE SHADOW OF THE BOMB: PHYSICS ANDARMS CONTROL. S.D. Drell. 1993. 358pp. AIP, NY

Har

vey

Lync

h

BEAM LINE 13

LOOKING BACK, it has been the best of times. SLAC has been andremains a wonderful home with great science, colleagues, students,and friends. Indeed it is one of the great pleasures of a career in

physics to have such wonderful colleagues worldwide. The future of ourfield—and of SLAC too—depends on the continuing extraordinary inventive-ness of its scientists—the accelerator builders and experimentalists onwhom we rely for data, the lifeblood of science. By all signs the future looksbright, with no end in sight. With amazing inventiveness, theorists have in-troduced new concepts that one couldn’t even have dreamed of fifty yearsago. The questions we must still answer are certainly sharper and at least ascompelling as they were fifty years ago: Where has all the antimatter gone?What is the origin of CP violation? Of particle masses, especially for fermi-ons? Whether or whither sypersymmetry and sparticles?

On the nuclear front we have had the good fortune to avoid the worst oftimes, but much work remains to be done. The end of the cold war hasgreatly reduced the immediacy of the nuclear fear that was a recurrent ele-ment of that long contest. But that danger persists, inherent in what weknow how to do, concrete in the between 20,000 and 30,000 warheads pos-sessed today by at least eight nations, and present in the ambitions of oth-ers. And new threats are emerging, involving other weapons of indiscrimi-nate destruction—chemical and biological—in the hands of sub–stateentities and terrorists. They can no longer be ignored, as the attack in theTokyo subway system by the Aum Shinrikyo reminded us in 1995. The com-munity of scientists will have to remain strongly involved, as we have beenup to now, in efforts to build a safer twenty-first century as we advance ourunderstanding of Nature.

REDUCING NUCLEAR DANGER: THE ROADAWAY FROM THE BRINK. McG. Bundy, W.J.Crowe, Jr., S.D. Drell (Council on Foreign Rela-tions, NY). 1993. 107pp.

VERIFICATION OF DISMANTLEMENT OF NU-CLEAR WARHEADS AND CONTROLS ON NU-CLEAR MATERIALS. S.D. Drell. JSR-92-331, Jan1993. 119pp. A MITRE Corp. JASON report,S. Drell, Chairman.

ANDREI DMITRIEVICH SAKHAROV (21 MAY 1921- 14 DECEMBER 1989). S.D. Drell (SLAC). 1994.6pp. Proc.Am.Phil.Soc.138: 177-182,1994

TECHNICAL ISSUES OF A NUCLEAR TEST BAN.S.D. Drell (SLAC), B. Peurifoy. 1994. 43pp.Ann.Rev.Nucl.Part.Sci.44:285-327,1994

HIGH ENERGY PHYSICS ADVISORY PANEL’SSUBPANEL ON VISION FOR THE FUTURE OFHIGH-ENERGY PHYSICS: SIDNEY D. DRELL,CHAIRMAN. S.D. Drell. DOE-ER-0614-P, May1994. 89pp.

SCIENCE BASED STOCKPILE STEWARDSHIP.S.D. Drell. JSR-94-345, Nov 1994. 113pp. A MITRECorp. Jason report, S. Drell, Chairman.

SAFETY IN HIGH CONSEQUENCE OPERATIONS:KEYNOTE ADDRESS. S.D. Drell. Dec 1994. 8pp.Proc. High Consequence Operations Safety Sym-posium, Jul 12-14, 1994 (SANDIA report SAND-94-2364).

SCIENCE AND SOCIETY: THE TROUBLED FRON-TIER: ADDRESS ON RECEIVING SIGMA XI’S 1995JOHN P. MCGOVERN SCIENCE AND SOCIETYAWARD. S.D. Drell. 1995. 16pp. Published in Van-nevar Bush II, Science for the 21st Century: Forumproceedings, Mar 2-3, 1995, p. 92-107.

ACCELERATOR PRODUCTION OF TRITIUM: 1995REVIEW. S.D. Drell. JSR-95-310, Jun 1995. 52pp.A MITRE Corp. Jason report, S. Drell, Chairman.

NUCLEAR TESTING: SUMMARY AND CONCLU-SIONS. S.D. Drell. JSR-95-320, Aug 1995. 9pp. AMITRE Corp. Jason report, Sidney Drell, Chairman.

THE LANDAU-POMERANCHUK-MIGDAL EFFECTFOR FINITE TARGETS. R. Blankenbecler, S.D. Drell(SLAC). SLAC-PUB-95-6944, Sep 1995. 48pp.Phys.Rev.D53:6265-6281,1996

14 SUMMER 1998

ARTICLE PHYSICS IS NOW POISED to take its nextsteps. A well-established framework is provided by the Stan-dard Model, which has been tested in experiments at CERN’sLarge Electron Positron (LEP) accelerator and the SLAC Lin-ear Collider (SLC) to a precision approaching the tenth of a

percent level. According to the Standard Model, the fundamentalforces are due to the exchange of intermediate vector bosons, such as

The Next Stepsin Particle Physics

P

b y J O H N E L L I S

the Z boson probed at LEP and theSLC, analogous to the photon respon-sible for electromagnetism. These in-teract with the fundamental matterparticles—the strongly-interactingquarks and the non-strongly-interacting leptons. Experiments atLEP and the SLC have established alimit of six each on the numbers ofconventional quarks and leptons.The sixth and last quark—the top—was found at Fermilab in 1995 with amass consistent with predictionsbased on its quantum effects in theprecision electroweak data (see“Discovery of the Top Quark” in theFall 1995 Beam Line, Vol. 25, No. 3).Higher-energy experiments at LEPare now producing pairs of thecharged vector bosons W+ or W− thatcarry the weak nuclear forces, withthe aims of measuring their masses

and couplings to the photon and Z tosee, in particular, if they agree withthe predictions of gauge theories. Bythe end of its operations in the year2000, LEP will also have searched sys-tematically for all possible new parti-cles weighing less than about100 GeV. Meanwhile, the Fermilabproton-antiproton collider will beexploring masses up to a few hun-dred GeV for some new particles.

The very success of the StandardModel in describing to date all con-firmed accelerator data raises funda-mental problems to be addressed bythe next generation of experiments.Foremost among these is theProblem of Mass—What is the originof the different particle masses, andin particular how do the Z and Wacquire masses around 91 and 80GeV, respectively, while the photon

BEAM LINE 15

remains massless? Newton taught us that weight is proportional to mass,and Einstein taught us an equivalence between mass and energy, but neithersaid anything about the origin of mass itself. In the initial formulation of theStandard Model, particle masses were generated by an unseen field permeat-ing the Universe, named after one of its proponents, Peter Higgs. Thereshould be a particle associated with this field, corresponding to quantumfluctuations, which has been the quarry of searches at LEP and elsewhere.The absence of such a Higgs boson, at the time of writing, implies that itsmass must exceed about 90 GeV.

Theoretically, this picture of a simple Higgs field and its accompanyingelementary boson is unsatisfactory. Some theorists have suggested that itmight be composite, and one of a multitude of new strongly-interacting parti-cles, but the precision electroweak data disfavor many of these hypotheses. Al-ternatively, an elementary Higgs boson may exist accompanied by a plethoraof supersymmetric particles—one for each known particle, with identical elec-tric charge but different spin. Experiments at LEP and Fermilab have soughtsuch supersymmetric particles, which should weigh less than about 1000 GeV,but to no avail so far. The search for a Higgs boson and its colleagues, be theycomposite or supersymmetric, and the elucidation of their properties, is one ofthe main items on the agenda of the next generation of particle accelerators.

Another key concern is that of the Problem of Flavor: Why is there such aproliferation of quark and lepton species, and what explains their bizarre pat-tern of masses and couplings to the W, including the appearance of CP viola-tion? The Standard Model has no explanation for the number of particlespecies, and just rewrites the couplings of the W boson in terms of the cou-plings of the Higgs boson. This is unsatisfactory and has led some theoriststo postulate that quarks and leptons are composite. However, despite recentalarms from Fermilab and the HERA electron-proton collider at DESY inHamburg, there is no experimental evidence for this radical hypothesis. Thenew generation of experiments on mesons containing bottom quarks, at Bfactories at SLAC and KEK as well as other laboratories, may elucidate themechanism of CP violation and help us understand flavor.

Finally, there is the Problem of Unification: Can the gauge theories of theelectroweak interactions be combined with quantum chromodynamics (thetheory of the strong nuclear interactions) in a Grand Unified Theory (GUT),and perhaps with gravity in a Theory of Everything? Data on the vector-

16 SUMMER 1998

ton-proton collisions at a center-of-mass energy of 14 TeV, with a lumi-nosity of 1034cm−2s−1. In the longerterm, the LEP machine componentscould be combined with the LHC tomake electron-proton collisions at acenter-of-mass energy of 1300 GeVand a luminosity of 1032cm−2s−1.

The LHC proton-proton collisionswill provide the first exploration ofphysics at an effective scale of 1000GeV or more. At the top of the agen-da in this energy range is the reso-lution of the Problem of Mass. TheHiggs boson, or whatever replaces it,is expected to weigh less than 1000GeV. Indeed, the precision elec-troweak data from LEP, the SLC andelsewhere indicate that the Higgsboson may weigh around 100–200GeV. In this mass range, the Higgsboson of the Standard Model shouldhave observable decays into photonpairs or four charged leptons. Twomajor detectors for discovery physicsat the LHC are under construction:ATLAS and CMS (see companion ar-ticles by M. G. D. Gilchriese and DanGreen respectively in the Winter 1997Beam Line, Vol. 27, No. 4). Each isdesigned to be able to explore all thepossible range of Higgs-bosonmasses, and particular attention isbeing paid to the precise measure-ments of photons and leptons.

The range of Higgs-boson massesfavored by the analysis of precisionelectroweak data coincides with thatpredicted in supersymmetric mod-els, giving encouragement to theiradvocates. The major LHC experi-ments should be able to find strongly-interacting supersymmetric particles—the squark partners of quarks and thegluino partners of the gluons ofQCD—if they weigh less than about

boson gauge couplings favor GUTswith supersymmetry, and there arehints that neutrinos might havemasses, as predicted by many GUTs,but it may be difficult to accumulatedirect evidence for GUTs, or for amore ambitious Theory of Every-thing based on string theory.

Several accelerators have programsthat address these fundamental prob-lems. I have already mentioned thecontinuing runs of LEP and the Fer-milab collider, and HERA will alsocontinue to run for several moreyears. And, as already mentioned,about to start operation are the B fac-tories at SLAC and KEK in Japan thatwill address the Problem of Flavor(see “Why Are We Building B Facto-ries” in the Spring/Summer 1996Beam Line, Vol. 26, No. 1).

IN ADDITION, constructionhas started on the Large HadronCollider (LHC) at CERN,which is

scheduled to come into operationin 2005. The LHC will provide pro-

+++++++++++++++

++++++++

++++++++

++++++++

++++++++

++++++++++++++++

++++++++

++++++++

++

+

+++

+

++

+

+

+++

+

+

++

+

+

+

+++++

++++++++++++++++

++++++++++ ++++++++

++++++++++++++++

++++++++++++++++++

++

++++++++++++++++

++++++++

+

++++ +++++

++++++++

++++++++++++++++

++++++++++++++++

++++++++++++++++

++++++++++++++++

++++++++++++++++

+++

+

++

+++

++++++++++

++++++++++

++++

++

++++++++++

+++

+++++++++++++++++++++++++++++++++++++++

++++++++++++++++

++++++++++++++++++++++++++++

++

+++++++++++++++

+++++++++

++++++++++++++

++++++++++

+ +++++++++++++++++++

++

++++++++++++++++++++

+++

++++++++++++++++++++++++

+++++++++++ ++++++++++++++ ++++++++

++++++++++++++++++++

++++

++++++++++++ +++++++++ ++++++++++++++++++++++++++++++++++++++

+

++++++++++

++++++++++++++++++

++++++++

++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++

++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++

++ +++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++

++++++++++++++++++++++++

++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++

+++++++++++++++++++++++++

+

+++++++

++++++++++++++++++++++++++++++++

+

+

++

+++++++

++

+++

+++++++ ++ +

++++++++++++++++++++++++++++++++++

+++++++

+++++++++++++ ++

+++++++++++++++++++++++++++++++++++++++

++

+++++

+

++++++++

+++++

++++++++

++

++++++++

++++++

++++++++++++++++++++++

+++++++++++++

+

+++++++

+++++++++++++++++++++++

+++++++

++++++++++++++

++++++

+

++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++

++++

++++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++

+++++++++++++++++++++

++++++++++

+++++++++++++++++++++++++ ++ ++++++++++++++ ++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++

+

++++++++++++++++++++++++++++++++

++++++++++++ ++++++ ++++

++++++++++++++++++++++++++++++++

++++++

+++++++++

++++++++++++

++

+++++++++

+++

+

++++ ++ ++

++

+++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++

+++++

++

+++++

++++

++++

+++++++++

+++++

++ ++

+++++

+++++

++++++

++++++++++++++

+

++++++++++++++

+++

+ ++++++++

++

+++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++ + ++ ++

+

++

+++++++++++

+

+++++++

++++

+++++

+++

+

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++

+++++++++++++++++++++++++++++++++++++++++++

++++++++++++ +++++ +++++

++++

+

++++

+++++++++

++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++

++++++++++++++++

+++++++++++++++++ + +++++

+++++++++++++++

++

+++++++++++++++++

++++++

+++++++++++++++

++++++++++++++++ +++++++++++++++++++++++ +++++++

++++++++++

++++++++++++++++

+++++++++++++++++

++++

+++++++

+++ ++++++++++

+++++

+

++++++

++++

++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++

+++++

++++++

++++++++++++++++

+++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++

+++++

++++++++++++++++++++++

++++++++++++

++++++++++++++

++++++++++++++++++++

++++ ++++

+++++++++++

+

+++++

++

++++++++++

+

++++++++++++

+++++++++++++++++++++++++++++++++

+++

++++++++++++

++++++++++ + ++++++++

+++

+++++++

+ ++++

+++++++

++

++++++

+++++++++++++++++++++

+++++++++++++

++++++++++++++++++++++

+++

+++++ +++++++++

++++

+

++

+++++++

+++++++++

++++++++++++

++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++

+++++++++++++

++++++++++++++++ +++ +++++++++

++++++

++++

+++

+++++++++++++++++++++

++++++++++++++++++++++

++++ ++ +++++ ++

+

+

+

+++

+++++++++ ++++++++

++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++

++

++++++

+

+

++

++++

+++++++++++++++++

+++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++

+

++++++++++

++++++++++

++++

++

++++++++++

+++

+++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++ +

+++++++++++++++++++++++

++

+++++++++++++++

+++++++++

++++++++++++++

++++++++++

+ +++++++++++++++++++

+++

++

+++++++++++++++++

+++

++++++++++++++++++++++++

+++++++++++ ++++++++++++++ ++++++++

+++++++++++++++++++++++++

+++++++++++ +++++++++ ++++++++++++++++++++++++++++++++++++++

+

++++++++++

++++++++++++++++++

+++++++++++++

+++++++++++++++++++++++++++++++++++++++

++++++++++++++++

++++++++++++

++++++++++++++++++++++++++++++++

+

++++++++++++++ +++++++++++++++++++++++++++++++++ ++++++

++++++++++++++++++

+++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++

++++++++++++++++++++++++++++++

+++

++++++++++++++++++++++++++++++++

+

+

++

+++++++

++

+++

+++++++ ++ +

++++++++++++++++++++++++++++++++++++

+++

++

+++++++++++++ ++

+++++++++++++++++++++++++++++++++++++++

++

+++++

+

++++++++

+++++

++++++++

++

+++++++++

++++

+

++++++++++++++++++++++

+++++++++++++

+

+++++++

+++++++++++++++++++++++

+++++++

++++++++++++++

++++++

++++++

+++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++

++++

+++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++

+++++++++++++++++++++

+++++++++++++++

++++++++++++++++++++ ++ ++++++++++++++ ++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++

++++++

+++++++++++++++++++++++++++

++++++++++++ ++++++ ++++

++++++++++++++++++++++++++++++++

++++++

+++++++++++++

++++++++

++

+++++++++

+++

+

++++ ++ ++

++

+++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++

++

+++++

++++

++++

+++++++++

+++++

++ ++

+++++

+++++

++++++

++++++++++++++

+

++++++++++++++

+++

+ ++++++++

++

++++

++++

++++++++++++++++++++++++++++++++++++++++++++++++++ +++++ + ++ ++

+

++

+++++++++++

+

+++++++

++++

+++++

+++

+++++

+

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++

++++++++++++++++++++++++++++++++++

+++++++++

++++++++++++ +++++ +++++

++++

+

++++

+++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++

++++++++++++++++

+++++++++++++++++ + +++++

+++++++++++++++

++

+++++++++++++++++

++++++

+++++++++++++

+++

+++++++++++++++ +++++++++++++++++++++++ ++++++++++++++

+++

++++++++++++++++

+++++++++++++++++

+++++++++

+++++ ++++++++++

+++++

+

++++++

++++

++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++

++++++++++

+++++++++++++++

+++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++

++++++++++++++++++++++

++++++++++++

++++++++++++++

++++++++++++++++++++

++++ ++++

+++++++++++

+

+++++

+++++++

+++++

+

++++++++++++

+++++++++++++++++++++++++++++++++

+++

++++++++++++

++++++++++ + ++++++++

+++

++++++++++++

+++++++

++

++++++

+++++++++++++++++++++

+++++++++++++

++++++++++++++++++++++

+++

+++++ +++++++++

++++

+

+++++++

++

+++++++++

++++++++++++

++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++

++++++++++++++ ++

+++++++++++++ +++ +++++++++++++++

++++

+++

+++++++++++++++++++++

++++++++++++++++++++++

++++ ++ +++++ ++

+

+

++++++

+++++++ ++++++++

++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++

++

++++++

+

+

+++++++

++++++++++++++++

+++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++

++

++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++

++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++ ++++++++++++++++++++++++++

++++++++++

++++++++++++++++++

+++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++ ++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++

+++++++++++++

+++++++++++++++++++++++++++++

++++

++++ +++ ++++

++++++++++++++

++++++++++++++++++++++++++++

+++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++ +

+++++++++

++++++++++++++++++++ ++++++++++++++++++

+++++++++++++++++++++++++++++++

++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++

+++++++++++++++++++++++++++++++

+++++++++++++++++++++ ++++++++++

++++++++++++++++++

+++++++++++++++++++++++++++

++++++++

++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++

+++++++++++++

+++++

+++++++++++++++++

++++++++++++ +++++ +++

+++++++++++++++++++++++

++++++++++++++++++++++

+++++++++++++

+++++++++

++++++++++++++++ ++++++++

++++++++++++++

+++++++++++++++++

++++++++++++++++++++++ ++++

++++++++++

+++++++++++++++ ++++++++++++

++++++

+++++++++++++++++++++++++++++

+++++++++++++++++++++++++++

++++++

+++++

++++++++++

+++++++++++++++++++++++++++++++++++++++++++++ ++++++++

+++++++++

+++++++

+++++++++++++++++++++

+++

+++++ +++++ ++++

+++++++

++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++

+++++++++++++

+++++

+ ++++++++++++++++++++

++++++++++

+

+++++++

++ ++++++++++++++++

++

++++++

+

+++++++++ ++++++

+++++++++++++

++++++

+++++++ +++

+++++++++++++

++++++++++++++++++++

+++

+++++++ ++++++++++++++++++++++++

++++++++

+++++++

++++++++

++

++++++++++++ +++++++++++

+++++++++++++

++++++++++++++++

+++ +++++++++++++

++++++++++++++++

+++++++++++

+++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++

++++++

+++++++++

+++++++++++++

++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++

+++++++++++++++ ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

This is how a Higgs boson weighing150 GeV might look in the CMS detectorif it decays into four muons. Particles arefirst tracked in the central part of thedetector, and muons then pass throughthe cylindrical calorimeters that absorbother particles, to be measured in theouter chambers.

BEAM LINE 17

2000 GeV, as expected in super-symmetric models. They may alsobe able to reconstruct decays ofsquarks and gluinos, and to identifysome weakly-interacting supersym-metric particles, as well as discoverat least one of the super-symmetricHiggs bosons.

In this way, the LHC should pro-vide a breakthrough in our under-standing of the Problem of Mass. Ifsupersymmetric particles exist, itshould also provide some detailedmeasurements of their spectroscopy,that could provide some hints con-cerning GUTs and perhaps a Theoryof Everything, contributing to our un-derstanding of unification. The LHCwill also make possible measure-ments of mesons and baryons con-taining bottom quarks that are moredetailed than those possible with theSLAC and KEK B factories, continu-ing their assault on the Problem ofFlavor.

The LHC machine and detectorsare being constructed as a global pro-ject, with significant contributionsfrom the United States, Japan, Rus-sia, Canada, China, and Israel as wellas the European member states ofCERN. Indeed, the American con-tingents of experimentalists are thelargest in ATLAS and CMS. It seemslikely that any future major accel-erator project will be realized as asimilar global collaboration.

This is the context in which sev-eral projects for linear e+e− collidersare currently being prepared for pro-posal to governments around theworld. Although we cannot be surewhat the LHC may (or may not) dis-cover, we can already make some ed-ucated guesses as to the stones it willleave unturned. Although it can

discover the Higgs boson, the LHCcannot measure many of its cou-plings to other particles and verifythat it does its job of providing theirmasses. Although it can discoversome supersymmetric particles, theLHC probably cannot discover all thepredicted weakly-interacting ones. Itis also limited in its possible massmeasurements, and hence in the pos-sible tests of unification it can make.Also, the LHC may well be unable todiscover the heavier Higgs bosons ex-pected in supersymmetric theories.There is plenty of scope for an ac-celerator with complementary capa-bilities to complete our picture ofphysics in the range of energies up toabout 1000 GeV.

LEPTON-ANTILEPTON col-lisions offer a cleaner experi-mental environment than

proton-proton collisions, and one inwhich all types of particles—bothweakly- and strongly-interacting—are produced democratically. An ex-ample of the complementarity of e+e−

and hadron-hadron collisions hasbeen provided in the 100 GeV range.Although the Z was discovered in

proton-antiproton collisions, itsdetailed study has been possible onlyin e+e− collisions. These and otherprior experiences convince us thatfuture e+e− colliders are likely tobroaden and deepen considerably ourunderstanding of physics beyond theStandard Model.

The first established landmark be-yond the energy reach of LEP is thetop quark-antiquark threshold around350 GeV in the center of mass. De-tailed measurements of properties ofthe top quark will be possible, andspectroscopic measurements mayenable us to derive indirectly someproperties of the Higgs boson.

Moreover, the fact that presentelectroweak data favor a relativelylight Higgs boson offer the enticingprospects of copious production ata next-generation e+e− collider. Thiswould enable its couplings to the Zboson, the bottom quark, the tau lep-ton and perhaps two photons to becompared in detail with the predic-tions of the Standard Model or its su-persymmetric extension. A lineare+e− collider would certainly advanceour knowledge of the Higgs boson farbeyond its initial discovery.

Another guaranteed physics topicis W+W− production, which will en-able the gauge theory predictions forW+W−photon and W+W−Z couplingsto be tested with far higher precisionthan is currently possible at LEP orFermilab. It may also be possible tomeasure the W mass more precisely,as well as many other properties.

IN ADDITION to this (more orless) guaranteed physics agenda,there is the prospect of a thresh-

old for new physics beyond theStandard Model, perhaps that for

The fact that

present electroweak

data favor a relatively

light Higgs boson

offer the enticing

prospects of copious

production at a next-

generation e+e− collider.

18 SUMMER 1998

supersymmetry. Unfortunately, wedo not yet know what the crucialthreshold energy may be. LEP may beable to provide us with a better hint,or perhaps the Fermilab proton-an-tiproton collider, but we may wellhave to wait for the LHC beforeknowing better where (for example)supersymmetry may appear.

Once one is above the threshold, alinear e+e− collider will enable unpar-alleled measurements to be made. Themasses of supersymmetric particlescan be measured with high precision,and their spins determined. All theheavier weakly-interacting super-symmetric particles can be studied, aswell as the heavier supersymmetricHiggs bosons. Many consistencychecks on the supersymmetric theorywill be possible, and many checks ofunification ideas will be made. Al-though the LHC should be able to dis-cover supersymmetry, and may beable to make many spectroscopicmeasurements, a linear e+e− colliderwill be needed to complete the job.

In view of the uncertainty in thesupersymmetric threshold energy,flexibility in the energy of such a col-lider is essential. We have alreadyseen that a center-of-mass energy of350 GeV provides an interesting ini-tial program of top physics and per-haps the Higgs boson. However, themachine should be able to reachmuch higher energies eventually: ide-ally up to 1000 GeV per beam so as

to cover all the likely range of su-persymmetric particle masses.

To my mind, there is a compellingphysics case for a linear e+e− colliderto cover the energy range betweenLEP and 2000 GeV in the center ofmass. Its complementarity to theLHC would ensure that the Problemof Mass is completely resolved, andthe possible path to related physicsbeyond the Standard Model is clari-fied. Here, personal prejudice and abroad consensus among theoristshave guided me to concentrate on su-persymmetry, but the linear colliderwould surely have similar benefitsfor the study of composite Higgsmodels. During the coming fewyears, as projects for linear collid-ers are finalized around the world,this physics case must be conveyedconvincingly to the world particle-physics community, and beyond. Itseems to me clear that any such pro-ject would need to be constructed ona fully international basis, buildingon previous experiences with HERAand the LHC. In this connection, thepresent cooperations between dif-ferent laboratories around the world,notably between SLAC and KEK, areexcellent first steps. On the otherhand, it is also good that several al-ternative technologies be researchedand developed in parallel, so that theoptimal choice may be made whenthe time comes. Since several dif-ferent options are being studied, onemight wonder whether more thanone project could be proposed suc-cessfully. In my view, it would be dif-ficult to convince the physics com-munity of the need for more than onelinear collider in the energy range be-low 2000 GeV in the center of mass,but politics is another story.

Particle Detector

Final Focus

20 Miles

Electron Source

Pre-Accelerator

Damping Ring

Electron Source

Positron Source

Pre-Accelerator

Damping Ring

Artist’s conception of a TeV linearelectron-positron collider. The individualelements are not drawn to scale.

can be demonstrated, so there isplenty of work to go around! It is at-tractive to consider a demonstrationproject, analogous to the SLC as“proof of principle” for linear e+e−

colliders. From the physics point ofview, an interesting option could bea Higgs factory, which would exploitthe larger coupling of the Higgs bo-son to muons, and the possibility ofa reduced energy spread compared toan e+e− collider.

Finally, let me mention the ideasthat are being discussed for a possi-ble proton-proton collider withbeams in the 50–100 ×103 GeV range.The key technical issues here are thereduction of tunneling and equip-ment costs by an order of magnitudebelow those of the LHC.

IT IS TOO EARLY to saywhich of these possible optionsfor accelerators beyond the LHC

and the linear e+e− collider might bemost interesting.The answer dependson the unknownphysics that theseprior machines willuncover. However,we can already besure that both theLHC and a linear col-lider capable ofreaching up to about 2000 GeV in thecenter of mass will be very excitingphysics projects. Now that the LHCis under construction, I hope that allthe world’s particle physicists willwork together to gain approval andconstruct such a linear e+e− collider.Physics needs it!

BEAM LINE 19

SINCE THE PERIODS be-tween the first discussions andthe realizations of new accel-

erators are long and lengthening—LEP was first studied in 1975 and en-tered operation in 1989, a gap offourteen years, the LHC was firstmentioned in 1978 and first studiedin 1984—it is not too soon to considerwhat might come after the LHC andthe linear collider. Several ideas arecirculating in the United States andin Europe, many of which will re-quire years of research and develop-ment before a specific project can beformulated.

One of these is a higher-energylinear e+e− collider, operating in therange of 2000 to 5000 GeV in the cen-ter of mass. This would probably re-quire a different technology fromthose currently envisaged, operatingat a high accelerating frequency.CERN has been doing research anddevelopment on such a technology,based on the compact linear collider(CLIC) two-beam concept, as part ofthe world-wide linear collider effort.I trust that the CLIC work will con-tinue, with the aim of demonstrat-ing its feasibility for a post-LHCproject.

Another concept for colliding lep-tons at several thousand GeV in thecenter of mass is a muon collider.There are major issues connected, forexample, with source intensity, beamcooling and decay radiation, that willneed to be tackled in an extensive re-search and development program.Aspects of this idea are now beingdiscussed actively in the U.S. and itis desirable that other regions of theworld also contribute to this effort.A lot of work is necessary before thefeasibility of such a muon collider

Linacs

Synchrotrons

Solenoid

Li/Be Absorbers

Recirculation

Linacs

Linacs

Future Collider Parameters

Collider Particles Ec.m. Luminosity Starting(GeV) (cm-2s-1) Date

PEP II e+e− 10 3×1033 1999KEK-B e+e− 10 1034 1999LHC pp 14,000 1034 2005LHC ep 1300 1032 ?

Possible layout of a muon collider.

HE DEVELOPMENT AND HISTORY of the vio-lin covers much the same time frame as contemporaryphysics. While Newton was developing his classicalmechanics and formulating how the planets move in thesky, Antonio Stradivari was creating some of the world’s

greatest and most treasured violins in Cremona, Italy. Thisinstrument had evolved from the viol familyabout one hundred years earlier and was givenits final form by another Italian maker,Gasparo da Salo, and his student GiovanniMaggini. Like the modern-day electric guitar,this evolution was driven by the need for alouder sound to accommodate public func-tions. It was an instrument of the masses,unsophisticated and brash. The viol remainedthe refined favorite of the royal courts.

Salo’s new design was seen and copied by a Cremonesemaker, Andrea Amati, whose sons continued their father’slead and perfected the violin’s design. The question ofwhether Stradivari was an apprentice in the Amati shop restson a single label in one of his violins attributing its style toAmati. What we know for sure is that both lived in Cremonain the second half of the 1600s and that Stradivari began mak-ing violins in the Amati style. He soon branched out,however, and went on to a long and illustrious career duringwhich he produced over a thousand instruments.

By 1750 the violin had gained wide acceptance. Indeed,most famous composers of the day produced works that fea-tured this instrument. It was their demands that led to somelast modifications. The definition of pitch was raised and theneck (and hence the string length) was lengthened, allowing

20 SUMMER 1998

A Physicist in the World of Viby WILLIAM ATWOOD

A physicist applies well-known

principles to the construction

of violins and in the process comes

to a better understanding

of techniques for shaping their sound.

BEAM LINE 21

a greater range in notes.Unfortunately, the originaltechnique of simply nail-ing and gluing the neckonto the body proved too weak to counterbalance the pull ofthe strings. In response, in the late 1700s the maker Man-tegazza developed a method of mortising the neck into thesides and top block for added strength. The modern violinhad been born. However, violins made during the next twocenturies failed to achieve the success of the earlier Italianmakers, leading many to believe that a secret or secrets hadsomehow been lost.

Yet, progress was made during this period in understand-ing how bowed instruments produced their characteristicsound. The German physicist Hermann von Helmholtz iscredited with explaining bowed string motion. The condi-tions of fixed length and tension and of continuous sound(periodicity) mean that the only frequencies present could beintegral multiples of the fundamental (that is, the lowest al-lowed vibration mode). Musically this means that for a givennote, its octave, the fifth above that, the next octave, thethird above that, and so on are part of the sound. Helmholtzrecognized that the timbre of the violin sound must be veryrich in these harmonics, and he became curious as to howthe moving string produced them. The string, he determined,does not just wag back and forth upon being agitated by thebow. Rather a sharp kink makes round-trips between thebridge and the nut, flipping over at each reflection (see theabove illustration). As the kink passes by the contact pointof the bow on its way to the bridge, it first releases the gripof the bow hairs on the string and then an instant later grabsthem again. The result is a continuous plucking action oftenreferred to as “slip stick.” The kink travels in an apparent

lins KinkBridge

Nut

An example of Helmholtz string motionwhere a kink appears to rotate aroundthe string, alternately bouncing off thebridge and the nut.

22 SUMMER 1998

profound influence on the sound butalso are structurally critical as thedownward force of the bridge owingto the tension of four strings is abouttwenty pounds.

The violin body is basically a res-onator driven by the vibrations fromthe bridge induced by the aforemen-tioned Helmholtz-type string mo-tion. However, only those frequen-cies that approximately match thenatural resonances of this systemwill result in any appreciable sound.

The frequency response can bemeasured by vibrating the bridgewith a pure sine wave (no harmon-ics). This is accomplished by at-taching a lightweight transducer tothe bridge and sweeping the drive fre-quency while keeping the amplitudeconstant. The relative sound out-put can then be recorded (see left il-lustration on the opposite page).While the data in this plot are in de-tail complex, some overall featuresare easily understood. First there isa forest of resonances extending fromabout two hundred hertz up to aboutfifteen kilohertz. Although there aremany sharp gaps, most notes gener-ally sit sufficiently close to a reso-nance to be excited. The lower endof this range is quite curious: the bot-tom few notes on a violin (G at 196Hz and G# at 208 Hz) fall off the edgeof the response envelope. Somehowour ears are able to infer these notesfrom the higher harmonics they con-tain. Also, investing money in homeaudio equipment with responsesabove fifteen kilohertz won’t makethe violins sound better!

Each note on a violin has its ownparticular sound. The fundamentalas well as its harmonics will fall invarious places in the response

clockwise direction for “down” bowsand counter clockwise for “up” bows.As a result, when drawn across a lev-el string, the bow tends to skate to-wards the bridge on an up-bow and to-wards the fingerboard on a down-bow.

Following the Second World War,a renaissance in violin making beganwith luthiers bent on recapturing theprecision and artistry of former yearsand a new interest from scientistsabout how the violin works. Sever-al new schools dedicated to the con-struction of stringed instrumentsnow exist in the United States. Andthere are organizations with refereedjournals focused mainly on the sci-ence of the instrument. In this stim-ulating environment, a young and en-thusiastic group of makers is argu-ably producing violins that may infact rival the old Italian instruments.

FUNDAMENTALSOF A WORKING VIOLIN

The illustration at the top of the pageis a cross section of the violin at thelocation of the bridge. The body is es-sentially an empty, thin-walled box.The top plate, or “belly,” that pro-duces most of the sound is typicallytwo to three millimeters thick whilethe back is similar in thicknessaround the edges but can be five mil-limeters or more near the center. Thewalls are approximately one mil-limeter thick except for the liningsthat reinforce the glue joint to thebelly and the back. Under the footof the bridge corresponding to the Estring, a small dowel mechanical-ly couples the top to the back. Un-der the other foot is a longitudinalstiffener called the bass bar. Both ofthese components not only have a

Bridge

Bass Bar

Sound Post

f Hole

A cross section of the violin at thebridge.

BEAM LINE 23

spectrum and be amplified accord-ingly. In the right-hand figure abovethe waveform of the sound of a vio-lin being bowed on the open E stringis shown fit to a harmonic series. Forthis note the fifth and sixth har-monics are three and two times larg-er than the fundamental. The appar-ent rapid oscillations are the resultof these harmonics, slowly interfer-ing with each other while the (slow)overall envelope modulation is at thefundamental frequency of 660 Hz.Yes, we hear E, but we also veryquickly identify the note as comingfrom a violin. It is the presence ofthese harmonics that identifies thesource of the sound for us. If we re-peated the above exercise for othernotes, similar results will be ob-tained; however, the harmonic con-tent (which harmonics are impor-tant) will change.

To achieve good projection, onewants positive pressure waves to beproduced simultaneously from thetop and back of a violin. You mightvisualize this condition as the violinalternately swelling and shrinking.Jack Fry, another noted physicist,pointed out in the 1970s that thearrangement of sound post and bassbar inside a violin resulted in thistype of radiator. But certainly not allof the resonances can be so simple.Various places on the surfaces of thetwo plates will be moving in and outof phase and hence form higher pole

radiator patterns. For each note, var-ious radiation patterns will empha-size various harmonics when mea-sured at different locations. AsGabriel Weinreich recently observed,“perhaps this is part of the intrigu-ing aspect of the violin sound. . .itseems to dance and sparkle, comingall at once from some place and atthe same time from no place inparticular!”

APPLYING PHYSICSTO MAKING VIOLINS

A physicist’s approach to learningabout a new physical system oftenstarts with fundamentals such ashow big, how small, what controlsthe overall behavior, etc. John Schel-leng pursued this type of dimensionalanalysis and found an overall figureof merit for violin wood: the ratioof the density to the velocity ofsound. One can intuitively under-stand this ratio is important by ob-serving that if, for instance, the topweighs a lot, it will require a hardshove to get it moving. But, just be-ing light is not sufficient. We wantthe entire top plate to move—not justthe local area under the feet of thebridge. Hence, the stiffness is also ofprime importance.

It is interesting to plot the den-sity versus velocity for various typesof wood (see illustration next page).Along straight lines emanating from

90

80

70

600.30.2 0.5 1 2

Frequency (kilohertz)3 5 10

Am

plit

ude

(d

ecib

els)

These two plots illustrate aspects of vio-lin sound. On the left is the frequency re-sponse of a Guarnerius del Gesù violin.A dense “forest” of resonances coversthe frequency band from approximately220 Hz to 15 kHz. On the right, thewaveform of a single note (E) played ona violin is shown. The pronounced rapidoscillations are due to the fifth and sixthharmonics, while the slow, overall enve-lope modulation is at fundamental fre-quency (660 Hz). (Courtesy CarleenHutchins)

0 4 6 82

Time (m sec)

0

–10

–20

–30

10

20

30

Am

plit

ude

(a

rb. u

nit

s)

Ala

n D

. Ise

lin

24 SUMMER 1998

A modern mechanical engineermight view the violin as an exampleof thin shell technology. Violin platesbegin as thick pieces of wood. The fi-nal cross-sectional shape shown inthe figure on page 22 is arrived atthrough a two step-carving process.First the outside is shaped. The curve(called the arching pattern) is usu-ally copied from one of the old Ital-ian masters. While these arching pat-terns may appear the same to theuntrained eye, there can be a widevariety in the maximum height andhow full the curve is. “Height” is ameasure of how much the center sec-tion puffs up from the plane of thesides (usually 14–16 mm). The backof the instrument can have a differ-ent height than the front. The “full-ness” of the arch refers to how farthis puff extends toward the edges.“Swoopy” arches start their descentcloser to the center. Full arches (de-scent closer to the edge) tend to bestronger and more resistance to long-term deformation owing to the sta-tic loading produced by the strings.

After shaping the outside, the in-side is scooped out. Here’s where thefun begins! How thick should thewood be and what thickness patternshould be used. This is complicat-ed and still only poorly understood.Since the material is wood and there-fore anisotropic with variations inphysical properties from piece topiece, any recipes based purely ondimensions will fail. Somehow onemust use the vibrational propertiesof the individual plate to guide thethinning (or graduating) process.

Traditionally makers have use atechnique based on “tap” tones.Holding the free plate off center inthe upper area with the thumb and

the origin the ratio is con-stant: large values being“good.” Balsa wood seemsto be the material ofchoice! Of course we’renot even suggesting thisoption since, as alreadymentioned, the static load-ing of twenty pounds fromthe downward force of thebridge would tax thestrength of balsa. Not farbehind, however, isspruce. This is the mate-rial of choice in practicallyall musical instrumentsthat have a wooden sound

board (pianos, guitars, harps, violins)and for the same reason (high stiffnessper unit weight) was the material ofchoice for aircraft before aluminumwas readily available (HowardHughes’ famous Spruce Goose).

However only the top of a violinis made of spruce. The rest is usu-ally made from curly maple, a highfigured hard wood. The above chartreveals that this material wasn’t cho-sen on the basis of sound productionbut rather for its beauty and perhaps,more fundamentally, its strength (theaxial pull of the four strings combineto over sixty pounds). It also mattershow the wood is cut from the tree.Detailed experiments have revealedthat the velocity of sound decreasesas the alignment of the fibers deviatesfrom being parallel to the surface. Infact not only does the sound velocitygo down, but the rate at which vi-brations are damped-out increases.This becomes a noticeable effect fordeviations as small as a few degrees.Traditional makers have always pre-ferred wood split from logs rather thansawed. Now we know why.

6

7

5

4

3

Vel

ocit

y (

x105

cm

/sec

)

2

1

00 0.40.2

1815 12 10

87

65

4

3

0.80.6Density (g/cc)

1.0 1.2

1

2

3

4

5

6

7

8

9 10 12

1113

14 15

16 17

1819

1 Balsa 8 Pine 15 Sycamore 2 Poplar 9 Larch 16 Rosewood 3 Norway Spruce 10 Walnut 17 Oak 4 Poplar 11 Amer. Mahogany 18 Pear 5 Linden 12 Ash 19 Pernambuco 6 Padouk 13 Norway Maple 7 White Fir 14 Sycamore Maple

Data from Barducci and Pasqualini

The velocity of sound versus the densityis plotted for different types of wood.This ratio (velocity/density) is a goodfigure of merit for acoustical quality of amaterial, high values being best. Thedata points indicate typical values for aparticular wood; however, a variation of30 percent in both sound velocity anddensity is not uncommon.

BEAM LINE 25

forefinger and tap-ping near the cen-ter with the otherhand produces adistinct pitch thatcan be perceived asthe plate nears itsfinal thicknesses.Keeping the sameholding point andtapping at the cen-ter near the bot-tom reveals yetanother pitch.When old Italianinstruments are disassembled forrepair, their tap tones are often ex-amined. In particular, a famousmaker/restorer named Simone Sac-coni, who worked on many of the ex-isting Stradivari violins, reported thatall had tap tones between F and F#,strongly suggesting that this was partof the equation that evolved in Italythree hundred years ago.

Carleen Hutchins, who studiedunder Sacconi, developed a newmethod for measuring tap tone whilemaking instruments. She showedthat they corresponded to eigen-modes of the free plate, which can beseen clearly using the technique ofChladni patterns. Hutchins sus-pended a violin plate horizontallyabove a loud speaker connected to anaudio signal generator. When blackglitter is sprinkled on the surface,at resonance, the patterns shown inthe drawing on the right appear. Thenodal lines are the places where theplate is not moving and hence theglitter tends to accumulate. The tra-ditional tap-tone technique requiredholding the plate on a nodal line andtapping at an anti-node. This simpleprocess is in wide use today.

Tuning the tap tones has now beenreduced to a “science,” but free vio-lin plates are not an end in them-selves. The plates are eventually gluedto the sides, changing the boundaryconditions from free to somewherebetween hinged and clamped. Inves-tigations into the vibration modes forplates both free and clamped haveshown that the thickness of woodnear the edges of a plate is critical indetermining the eigenmodes for theclamped condition but has little ef-fect on the free plate. Wood removalnear the center controls the latter.

SETUP

Completing the violin after graduat-ing the plates involves a great dealof precision woodworking and thencomes the varnishing. The next phasein which physics can play a part isin the “setup.” This includes shapingthe fingerboard and bridge, fitting thesound post, adjusting the tailpiece,and so on. Much of how the finalproduct will sound is determined atthis stage.

The bridge of the instrument con-veys the vibrations from the strings Mode 1 Mode 2 Mode 5

The three main eigenmodes for a freeviolin top plate are shown below. Thefrequencies associated with thesemodes are approximately an octaveapart.

26 SUMMER 1998

While there has been littlequantitative work to detail whatsound a mode-matched instrumentmakes as opposed to an unmatchedone, both players and listeners pre-fer the former. The frequency of theair cavity mode is determined most-ly by the volume of the box and thesize and shape of the f holes. Littlecan be done to alter this “bottle” noteand indeed one finds little variationfrom instrument to instrument. Aclosely related note can be found byhumming into an f hole and findingthe pitch at which the body resonates(usually between C to C#). The firstbending mode has two transversenodal lines running across the widestsections of the upper and lower ar-eas. The pitch of this eigenmode canbe determined by holding the in-strument upside down at the widestpoint in the area next to the tailpieceand lightly tapping on the scroll. Itturns out that the fingerboard can bemodified to vary this note. By addingweight at the end near the bridge orby thinning the fingerboard in thearea where it joins the neck, the notecan be lowered.

The tailpiece also plays an im-portant role. The relative lengths ofthe strings between the bridge andthe nut at the far end of the finger-board and between the bridge and thetailpiece should be six to one. Thislength can be approximately tunedusing a ruler; however, a knowledgeof harmonics gives a simpler andmore accurate technique. A stringwhich is one-sixth the full lengthwill sound a note at the fifth abovethe second octave. Given that violinsare tuned in fifths means that byplucking the string behind the bridge

to the top. In some sense it may beviewed as an audio filter. Its tradi-tional and intricate shape was mostlikely arrived at through trial and er-ror with an eye on the esthetics andan ear on the resulting sound. Ob-servations of which bridges soundgood suggested an experiment us-ing similar tuning techniques tothose used for free plates. A high-power audio tweeter and audio gen-erator revealed that the best bridgeshad a simple bending eigenmodepitched at high F (2800 Hz).

After a final fitting with strings,the vibrational modes of the com-plete instrument can be investigatedand adjusted. When the lowest aircavity resonance and the lowestbody-bending mode have similar fre-quencies, the violin comes alive.

Both Helmholtz and Drell seem fascina-ted with bowed string motion. Here Drellis engaged in a real time analysis of thebow’s slip-stick interaction with thestring.

BEAM LINE 27

and comparing it to the note of thenext higher string plucked in front ofthe bridge an octave should be heard.The pitch of the note behind thebridge may be adjusted by changingthe length of the cord (called the tail-gut) fastening the tailpiece to the end-pin of the instrument. But the tail-piece also has resonances which havebeen found to have optimal values.Changing the tail-gut length changesthese pitches as well. The only re-maining free parameter is to adjustthe weight of the tailpiece: heavierlowers its resonance pitches whilelighter raises them.

PLAYING

One of the appealing attributes of theviolin is the variety of sounds. Thissound palette is manipulated throughthe bowing technique. The mainvariables are the speed of the bow,the downward pressure on the string,and the point of contact on the stringwith the bow hair. (To a lesser extentthe amount of hair which is in con-tact with the string also plays a role.)All this occurs essentially in a three-dimensional space. A two-dimen-sional projection of this bowing spaceis illustrated in the figure on theright. The softest sound is obtainedwith a slow, light bow halfway be-tween the fingerboard and the bridgewhile the loudest notes are producedwith a fast, heavy bow at a similarcontact point. The most variation inspeed and pressure can be found inthe middle of the range. Here too isthe largest range of possible contactpoints. Harsh, biting sounds may beproduced with the bow near thebridge, while soft, fluffy sounds are

obtained with the contact point near-er the fingerboard. By adjusting thesethree variables, the violinist is chang-ing not only the music dynamic butalso the timbre of the sound.

An obvious question is what hap-pens if you go outside the “allowed”region in the bowing space? You pro-duce either an annoying scratchingsound or an equally unpleasantwhistling. The edges of this space aregiven by the boundaries for theHelmholtz-type “slip stick” actionas discussed in the introduction. Pre-ferred violins have a large bowingspace. These instruments allow theconcert artist the greatest range insound color and dynamic. A corol-lary is that cheap violins have a smallbowing space. This explains how thebeginning student, with little bowcontrol, may sound atrocious on a$200 fiddle provided by the parentswhile the teacher (with a great dealof bow control) can sound reasonablygood!

Physics or physics training doesnot give any intrinsic advantage toviolin making. Music is essentiallyesthetic and producing an instrumentnecessitates highly developed wood-working skills. However, physics canbe a tool for understanding what pa-rameters of the instrument controlvarious aspects of its sound, therebyproviding a guide for shaping it. It canalso inspire experiments with nar-row focus aimed at resolving specificissues in violin making. And, final-ly, good experimental science, specif-ically the recording of detailed noteson each instrument, can pay offhandsomely when trying to deter-mine what works or doesn’t work.

Finger Board (Fluffy)

Bridge (intense)

Middle

Middle

Pressure(light) (heavy)

mf

ppp

fff

Spee

d(s

low

)(f

ast)

The bowing space for the violin is illus-trated above. The speed that the bow isdrawn across the string together with thedown pressure changes the musicaldynamic (shown inside the white dia-mond). The point of contact between thebow and string changes the “color” ofsound and has its largest range in themiddle (shown outside the whitediamond).

28 SUMMER 1998

by HEINO HENKE & ROBERT SIEMANN

A Possible FutureMicrofabrication for Millimeter W

Large and small scales are

intertwined throughout

physics. Huge accelerators

produce beams for atomic,

nuclear, and particle science.

In an interesting, new twist,

microfabrication could be

the key to the accelerators

of the future.

INSTRUMENTS AND THEIR CAPABILITIES oftendetermine the frontiers of science. The particle physics fron-tier is the highest achievable energy, and there has beenexponential growth in energy because of breakthrough con-cepts, inventions and discoveries, and application of newtechnologies to particle acceleration. The Fermilab Tevatronis an example—there the earlier breakthrough concepts ofstrong focusing and colliding beams are combined withsuperconductivity, one of the great discoveries of modernphysics, and the application of superconducting technologyto accelerator magnets.

Synchrotron radiation sources are having profound impacton a wide range of sciences from condensed matter physicsto protein crystallography. Those synchrotron radiationsources were made possible by the invention of klystronswhich are efficient high power radio-frequency (rf) ampli-fiers, strong focusing, and sophisticated magnet technology.

What concepts, discoveries, and/or technologies willdetermine the future frontiers of accelerator-based sciences?In the near term the CERN Large Hadron Collider and theNLC—or ILC—the international linear collider beingdesigned jointly by KEK and SLAC, depend on extensions ofmagnet and rf technologies. Superconducting rf is becomingmore and more important for high current applications innuclear and particle physics, for single-pass coherent lightsources and for linear colliders with the TESLA project atDESY. However, none of these are breakthroughs—andwithout breakthroughs the costs of accelerators arebecoming formidable.

BEAM LINE 29

Our interest has been in explor-ing new technologies which are riski-er but have breakthrough potential.One such technology is microma-chining that makes it possible tothink about millimeter-wavelengthaccelerators that have millimeter-size features. These accelerators havepotential for both particle physicsand synchrotron radiation, but theycannot be realized from straightfor-ward extrapolations of long wave-length accelerators like the classicSLAC 10-cm wavelength, S-bandlinac. We do not imply that there arenot formidable problems; rather wesee an opportunity if the problemsposed can be solved either throughtechnological developments or con-ceptual insights.

MICROFABRICATION

In the last few decades microfabri-cation has made impressive progress.High speed milling machines andshaped diamonds allow 2–5 µm pre-cision. Tiny high pressure water jetsand laser beams provide fast and pre-cise cutting. Pressureless wire elec-trodischarge machining reaches theaccuracy limits (below 1 µm) of thebest measuring devices. Ion etchingand lithographic techniques, thework horses of the semiconductor in-dustry, have been modified formechanical manufacturing. Theyoungest offspring is shape deposi-tion manufacturing where metallicpowder is injected into the melt-poolof a scanning laser focus.

Traditionally linac structures arecylindrical, but a more open struc-ture is needed for adequate vacuumpumping as dimensions shrink to themillimeter scale. The planar, muffin-tin geometry shown in the illustra-tion above seems to be the best can-didate. It consists of two separatehalves with a wide gap in betweenthat provides sufficient pumping con-ductance. This simple two-dimen-sional structure has mechanical tol-erances in the 1 to 3 µm range. Thesetolerances and the planar geometrymake wire electrodischarge ma-chining and deep X-ray lithographywith the German acronym LIGA thatstands for Lithographie, Galvanofor-mung, Abformung meaning lithog-raphy, electroforming, and molding.

Electrodischarge machining (EDM)is a relatively cheap and conceptu-ally simple process, and the toler-ances achieved are remarkable. Theworkpiece and an electrode are im-mersed in a dielectric fluid, and ahigh voltage pulse produces an arcbetween the electrode and workpiecewhich erodes the surface. Since theelectrode is eroded as well, it has tobe replaced, and a wire electrodis-charge machine uses a thin, spooled

Beam Axis

Cooling

RF Input

Vacuum

A muffin-tin accelerator structure.

aveAccelerators

30 SUMMER 1998

required for accelerator applications,and they have relative advantagesand disadvantages that could provecrucial. Two drawbacks of EDM arethat the structure must be con-structed in layers and diffusion bond-ed together and that the process isnot well suited for mass production.LIGA is expensive for prototype fab-rication since it requires an X-raymask which typically must be man-ufactured in three steps, a synchro-tron radiation beam line for a many-hour exposure of the plastic resist,and facilities for developing the re-sist and electroforming the structurewhich proves to require care and ex-perience. It should be much cheaperwhen producing large numbers ofidentical structures because moldingcan be used. Open questions dependon the application and relate to sur-face quality and the suitability of elec-troformed copper for high gradients.

mm-WAVE POWER SOURCES

In many ways the availability of highpower sources is critical for accel-erator development, and at the pre-sent time such sources for mm wave-lengths are scarce. The only real highpower sources are gyrotron oscilla-tors with up to 1 MW power, and theyare large and expensive. Modifyingthem to be amplifiers reduces thepower rating and efficiency dramat-ically. The Naval Research Labora-tory, working in collaboration withCPI and Litton, is developing a100 kW gyrotron amplifier. Anothercandidate for high power at shortwavelengths is the ubitron, but it isbetter suited as an oscillator, and sig-nificant development is needed for itto be a high power amplifier.

tungsten wire that cuts through theworkpiece like a fretsaw. The cuttingspeed strongly depends on the thick-ness of the workpiece and the desiredsurface finish. Today, the best ma-chines cut 1 mm per minute in a1 mm thick copper sheet with sub-micron precision and 1 µm surfaceroughness. A nearly optical surfaceroughness of 0.1 µm is possible atlower speeds.

LIGA has been developed primar-ily at Karlsruhe, Germany, for fab-ricating microstructures with ex-treme height to width ratios. In a firststep (Lithographie) a thick resist lay-er of plastic is irradiated through amask by synchrotron radiation (seeillustration on the left). By develop-ing the exposed resist layer, a tem-plate is produced which can be filledwith a metal by electroforming(Galvanoformung). After strippingthe unexposed resist a metallic mi-crostructure is obtained. A third andfourth step allow for mass fabrica-tion. A negative of the microstruc-ture is obtained by injection mold-ing of thermoplastic material(Abformung). This negative serves asa template for subsequent electro-forming processes. Many structurescan thus be made from the originalmaster.

Today LIGA is an advanced tech-nology. Many components such asacceleration sensors, microturbines,electrostatic motors, and linear ac-tuators are being manufactured byindustry. The achievable accuracy isaround 1 µm or better, and structuredepths of 600 to 800 µm are possible.This is exactly what is needed for amuffin-tin structure.

Both EDM and LIGA have thepromise of meeting the tolerances

X-ray Sensative Plastic

Injection Molding

Substrate

Metal

X-rays

Material

Expose and Develop Plastic

Electroplate

Remove Plastic

Injection Molding

Simplified lithography process.

20 mm

A 94 GHz muffin-tin accelerator fabri-cated with LIGA by Argonne NationalLaboratory scientists (top) and thecenter of a 25-cell, 91 GHz acceleratormachined with EDM at Ron Witherspoon,Inc. (bottom).

BEAM LINE 31

Microfabrication offers a new anddifferent approach to a mm-wavepower source—a large number ofsmall, simple, and cheap tubes witha minimal power distribution net-work in contrast to the usual con-figuration of a small number of highpower tubes with a complex distri-bution circuit. A mm-wave klystronshould be able to generate up to150 kW and would have good effi-ciency. Using permanent magnet fo-cusing, developed at SLAC for X-band(3 cm wavelength), such klystronswould meet the goal of being small,simple, and cheap.

A 150 kW klystron would be anideal power source for compact, lowenergy accelerators, but high energyaccelerators require substantiallymore power. Possible ways to achievethat are discussed in the high energyaccelerator section.

COMPACT, LOW ENERGY ACCELERATORS

An advantage of mm-wave accelera-tors is the small, planar geometry.Complex structures can be realizedwith lithography on a single supportwith no extra fabrication costs, andthe designer’s skill—rather than costor space—becomes the limiting fac-tor. This leads to new ideas for com-pact, low energy accelerators thatcould include a small, light linac formedical applications, a space-basedaccelerator, or a compact synchro-tron radiation source.

Some applications require stand-ing wave cavities where forward andbackward traveling waves conspiresuch that the accelerating gradientshave alternating signs from cell-to-cell. It isn’t possible to feed many

cells of a standing-wave cavity froma single input coupler, and thesestructures are also sensitive to fab-rication errors. The solution is to usespecially designed coupling cells thatdo not contribute to the accelerationbut increase and symmetrize the cou-pling. Such a structure is normallycomplicated and expensive, but withlithography one gets it for free.

Klystron Amplifier Principle

RF In

Cathode

CollectorAnode

Input Resonator

Output Resonator

Solenoid

Drift Space

Electron Beam

RF Out

Basic klystron arrangement.

THE PRINCIPLE OF THE KLYSTRON AMPLIFIER is shownin the figure above. A heated cathode emits a continuous electronbeam of relatively low density. The beam is accelerated and at the

same time focused by an electrostatic anode before entering an input

resonator that is fed by a low power in-put signal. There the beam receives avelocity modulation that depends on theinput signal. This dependence makes theklystron an amplifier, as opposed to anoscillator. This is critical because it al-lows control of the multiple klystronsneeded in an accelerator. After a driftspace, where the beam is focused mag-netically, the originally continuous beamis bunched which corresponds to a large

rf current. It enters the output resonatorwhere it loses energy to an external load(usually the accelerator). The leftoverbeam with a strongly reduced kinetic en-ergy is dumped into the collector. Theklystron as described would be fully op-erational, but it would have low efficiencyand low gain. High power klystrons haveadditional idling resonators between theinput and output resonators to improvethe bunching process.

32 SUMMER 1998

a klystron, beam monitors, and mag-netic focusing devices are mountedon a single support and all fabricatedlithographically. A module thenneeds only connections to the pow-er supplies, vacuum pumps, and lowpower electronics to become a work-ing accelerator.

PARTICLE PHYSICS

The potential advantage of mm-wavelength accelerators for parti-cle physics is a higher acceleratinggradient. It is known from experiencewith 1–10 cm wavelengths that gra-dients are limited by dark currentcapture, which is the acceleration offield emitted electrons to relativis-tic energies, and by rf breakdownwhich is a complex phenomenoninvolving field-emitted electrons,X rays, ions, rf fields, and surface con-ditions. The maximum gradientsfrom these phenomena scale approx-imately inversely with wavelengthas shown in the figure on the left.

These wavelength dependenciesgive mm-wavelengths breakthroughpotential, but short wavelength, highgradient accelerators require muchmore than a straightforward extrap-olation from longer wavelengths.Our colleague Dave Whittum ofSLAC has a lighthearted, but also se-rious, transparency that summarizesthe situation were such an extrap-olation made, “The power sourcedoesn’t exist; the accelerator wouldmelt in one shot; the beam densitydilution is unacceptably large; thebeams destroy themselves during thecollision; and the collider wouldrequire a dedicated power plant.”This is fertile ground for imaginativesolutions.

A mm-wave rf undulator is underdevelopment at Argonne NationalLaboratory’s Advanced PhotonSource. When a relativistic electronbeam travels through an rf undula-tor, it is subjected to transverse forcesfrom the rf fields, and it radiates co-herent, quasi-monochromatic radia-tion similar to that from a conven-tional magnetic undulator. At around100 GHz the undulator period can beas short as 1 mm. This is substan-tially smaller than possible with amagnetic undulator, and the electronbeam energy can be lowered for thesame photon energy.

Scientists at the Technische Uni-versitaet in Berlin are interested inlow energy accelerators with gradi-ents between 1 and 10 MV/m, and themain concerns are small size, lowweight, and low cost. One exampleis a compact 50 MeV linac that couldpower either an undulator or a freeelectron laser and generate tunableradiation down to 50 nm wavelength.The figure at the top of the pageshows some details. The klystronand beam focusing device are inte-grated such that the whole acceler-ator fits on one table apart from pow-er supplies. For the future it wouldbe attractive to have integrated ma-chine modules. That means a certainnumber of rf structures together with

Source Quad

Bend

Mirror

Klystrino

Acceleration

~ 3.5 m

~ 0.

6 m

A compact, tunable radiation source.The linac is composed of 16 cm long rfstructures with 140 cells each. Everystructure is powered by a 100 kWklystron.

▲

▲

■✚★

●

0.01

0.1

1

10

0.1 1 10 100

Gra

dien

t (G

V/m

)

Wavelength (mm)

RF Breakdown

Dark Current Capture

■

▲

✚

●

★

SLC JLC-ATF NLC CERN-SLAC CLIC (lower limit)

Gradient limits from dark current captureand rf breakdown together withachieved gradients.

BEAM LINE 33

Begin with pulsed temperaturerise and associated destructive ef-fects. Radio-frequency losses are con-centrated on the surface, and theresultant heat does not diffuse sig-nificantly into the metal during therf pulse. The surface volume is re-peatedly stressed beyond the yieldstrength and eventually the surfacecould fail. This has been seen with40˚C temperature rise in high powerlaser mirrors where surface qualityis critical.

Forty degrees is far below the tem-perature rise for interesting acceler-ating gradients, but there is anecdo-tal evidence that pulsed temperaturerises well above that do not causeproblems for rf cavities. An experi-ment using power from the X-bandklystrons is in progress to study thissystematically. The first run had thetentative result that rf properties ofcopper were not affected after 107

pulses with over 100˚C pulsed tem-perature rise. This apparatus will alsoallow testing of materials with higheryield strength and testing of ideas toreduce pulsed temperature rise suchas a thin diamond coating that istransparent to rf but serves as a heatsink thereby reducing the tempera-ture rise by up to a factor of three.

Beam-induced fields, or wake-fields, reduce the beam phase spacedensity. If the reduction is suffi-ciently large, it is impossible to fo-cus tightly at the interaction point.Wakefield effects are proportional tocharge, offset of the trajectory fromthe center of the aperture, and varyinversely with the cube of the wave-length. The latter is obviously badfor short wavelengths. The best wayto reduce wakefields is to preciselyalign the beam and accelerator.

Experiments with a prototype X-bandstructure have demonstrated thatwakefields can be detected and areprecise position monitors. Awakefield-derived signal can be usedas the input to a feedback loop thatmaintains alignment. Such feedbackloops could provide the wakefieldcontrol that is needed for millimeterwavelengths. To the degree they donot, the charge will have to belowered.

But, since luminosity depends onthe beam charge as well as phasespace density, this is also bad. It ispossible to get high luminosity withlow charge individual bunches by ac-celerating a large number of bunches,one behind the other, with a long rfpulse (see the illustration at the topof the page). This cannot be extendedto millimeter wavelengths becausethe pulsed temperature rise is pro-portional to the square root of therf pulse length. Dave Whittum hasconceived of a simple, elegant wayto accelerate multiple bunches: let

RF Energy Beam Bunches Accelerator Structure

RF Energy

e–

The conventional and matrix acceleratorapproaches to multiple bunchacceleration.

34 SUMMER 1998

SOME OF WHAT we havewritten about is futuristic;some is not. Some will come to

pass, and some will not. The 150 kWklystron and low energy compactaccelerators could be realized in thenear term. When they are, they willbe direct results of thinking aboutand applying microfabrication toaccelerators.

A millimeter-wavelength, 5 TeVcollider is an ambition to studyphysics at a new energy frontier. Itwill take originality and creativity tomake it possible, and even so it maynever be. It is a promising direction,and, as with all basic research, onepursues it for that reason while at thesame time realizing that the unex-pected is expected.

the rf and beam travel in perpendic-ular rather than parallel directions.This “matrix accelerator,” shown onthe previous page, accelerates mul-tiple bunches while keeping the rf ina single cell for only a short time.Like many conceptual breakthroughs,this solves a problem but introducesnew ones which, hopefully, are eas-ier to solve. Parallel beams must becombined; the rf structure remainsto be designed and shown to be prac-tical (lithography could be the key);and a source for the required highpower rf needs to be invented.

To put a scale to the rf power, thegradient depends on the square rootof the rf power, and a muffin-tinstructure requires 40 MW inputpower for 200 MV/m gradient. If suchpowers are possible they require botha power source beyond the 150 kWklystron we discussed and pulsecompression. A high power ubitronmay be the right power source. Wewill know better when the klystrondevelopment is further along. Witha ubitron one could reach multi-megawatt power levels for severalmicroseconds. This must be com-pressed down to a few nanosecondsto have the appropriate peak powerand pulse length for the matrix ac-celerator. Pulse compression is rou-tine; it is used in the SLAC LinearCollider and is part of the NLC rf sys-tem. The new aspects are the degreeof compression and the almost cer-tain need for active switching of highpower rf which has been demon-strated at moderate powers.

BEAM LINE 35

THE UNIVERSE AT LARGE

Can’t You Keep Einstein’s Equations Out of My Observatory?by VIRGINIA TRIMBLE

LL SPECIES ARE ADAPTED to the environ-ment that has been around for a while (some ad-mittedly better than others). This includes Homo

scientificuss and its subspecies H. scientificuss astronomische.Thus even we, committed though we are to Progress andAdvancement, tend to resist changes in our surroundings.Such resistance is by no means completely foolish. Most ofthe inventions patented never worked very well; most newideas are wrong; and most of the people who tell you how toimprove your research want to start without the second lawof thermodynamics. Hence, betting against neat, new thingsis nearly always the winning strategy. But when you lose,you lose spectacularly, and virtually all the achievements ofastronomy over the last few centuries can be traced prettydirectly to changes in technology, demographics, or theoreti-cal constructs.

New widgets include amplifiers, detectors, telescopes,launch vehicles, computers, and much else. The communityconstantly recruits not just new people but new kinds ofpeople. And I hope at some future time to explore how wehave (often reluctantly) incorporated these. Today (Wednes-day), however, the focus is on interchanges of ideas betweenastronomy and other parts of science. An oral presentation ofsome of the material, at the 150th anniversary meeting ofthe American Association for the Advancement of Science,

Fish and guests start

to smell after three days.—Old Country Saying A

Part I

36 SUMMER 1998

was originally entitled “How physics came to visit andtried to take over the house,” but I soon realized thatthe real situation is a good deal more complex. Notice,however, that even the name of the society includes “de-fend our territory” words as well as “reach out” words.

Both the domains of thought and the specific ideaswithin each of the following sections are as chrono-logical as I could make them (which isn’t very). And theapproach is relentlessly Whiggish, making use of high-ly collimated hindsight, emphasizing contributions thatwe perceive as moving the subjects forward, and draw-ing distinctions between disciplines that probably didnot exist when some of the ideas were being formulated.

NEWTONIAN GRAVITATION

Sir Isaac, in assembling his theory of universal gravita-tion, made direct use of astronomical observations ofthe motions of the moon and planets. He promptly re-turned the favor by providing the first estimates of themass of the sun: 29.7 earth masses in 1687 and 226.512earth masses in 1713. Notice he shared the fondness ofmodern, calculator-owning freshpersons for carryingaround more (in)significant figures than necessary! Thecorrect value is actually 332.9 earth masses, but nearlyall of Newton’s error the first time out arose from us-ing a distance to the sun that was not the best avail-able even then, not from the content of his theory. As-tronomers soon fell in with the idea, and improved “solarmasses” came from Lalande (a cataloguer of stars) in 1774and Encke (who found an interesting comet) in 1831. Es-timates for the masses of Jupiter and the other planetswith satellites followed and gradually improved in par-allel as the distance scale for our solar system improved.

The next step obviously was masses for other stars,but this required recognizing that many of them orbitin gravitationally bound pairs. John Michell, the Eng-lish polymath, had said so on statistical grounds asearly as 1767. He was perhaps more ignored than dis-believed, and the recognition of the reality of bound sys-tems had to wait for William Herschel’s efforts to mea-sure stellar parallax. He thought that close star pairs

in the sky were accidental projections. But, after morethan twenty years of looking for changes in separationangles due to the motion of the Earth (parallax), he con-cluded that the real motions were orbital and the pairsnot accidents.

Masses for stars followed slowly (most visual bina-ries have orbit periods of many years, and you need a dis-tance estimate as well). And, meanwhile, Herschel heldto the view that only solid bodies could exert gravita-tional forces and therefore the sun, though perhapsgaseous on its surface, must have a cooler, solid interi-or, of which we catch glimpses through the sunspots.He also expected that interior to be inhabited, and wasby no means alone in either opinion. A gaseous (and un-inhabitable) sun had to await advances in spectroscopyand thermodynamics, which brought their own con-troversies and misunderstandings.

CERES, STATISTICS, AND THE PERSONALEQUATION

The discovery of Ceres in 1801 (by Giuseppe Piazzi, aSicilian astronomer) was very nearly followed by theundiscovery of Ceres, when it disappeared behind thesun with too little of its orbit observed to permit cal-culating where it should reappear. Carl Friedrich Gausscame to the mathematical rescue, with an improvedmethod of orbit computation that made use of what wenow call the method of least squares to incorporate dis-cordant data. And to this day, the least squares methodis the only bit of statistics the average astronomer hasheard of. We nearly all think Gauss invented the idea,which is also only approximately true.

The personal equation is a statistical idea that arosewithin astronomy and has not, so far as I know, everseemed applicable anywhere else in science, though itturns up occasionally in detective fiction. It arose fromthe method by which positions of stars in the sky usedto be measured. Start with a telescope that is free toswing in only one direction, perpendicular to the hori-zon, in the north-south (“meridian”) direction. Then theprecise time a star passes through the center of your field

BEAM LINE 37

of view provides its east-west position (right ascension)and the distance above the horizon at which it passesprovides the north-south position (declination), at leastafter a bit of additional arithmatic. Standard operatingprocedure involved two astronomers, one with a listof stars to be observed, an accurate clock, and a pencilto keep records, and the other with his eye to the tele-scope, to say “now” each time the next star passed thecross-hairs in his eyepiece. Feel free to replace the pen-cil by a pen in this narrative and “now” by “nunc” orsome other one-syllable equivalent.

Comparison of positions obtained by different as-tronomers at different observatories soon showed thatthe identity of the record-keeper didn’t matter verymuch, but the identity of the now-sayer did, especial-ly for the east-west coordinate. In the words of a 1926text: “Even the best observers habitually note the pas-sage of a star across the fixed wires of the reticule slightlytoo late or too early, by an amount which is different foreach observer. This personal equation is an extremelytroublesome error, because it varies with the observer’sphysical condition and also with the nature and bright-ness of the object. Faint stars are almost always observedtoo late in comparison with bright ones . . . ” Thus Prof.Apple’s right ascensions for a given set of stars could eas-ily be systematically larger or smaller than Dr. Berry’sby several seconds of arc, enough to matter in many ap-plications of positional astronomy.

In the end, the way around the problem of the per-sonal equation was that of Rutherford, “Don’t do betterstatistics. Do a better experiment.” Other measurablequantities that, over the years, have revealed systematicoffsets from one observer to another include stellarand galactic brightnesses, Doppler shifts, and classifi-cations of stars and galaxies. And increased automationand mechanization, from photoelectric detectors toautomated neural networks, have gradually made resultsmore repeatable and impersonal (which is not quite thesame as more correct). There must surely be similar casesin other sciences (the average number of species assignedto a newly-discovered genus?), and examples would beappreciated.

THE SPEED OF LIGHT, MAXWELL’S EQUATIONS, AND THE REST MASS OF THE PHOTON

Ole or Olaus* Roemer (1644–1710) actually participatedin 1672 in one of the sets of observations that put thesun much further away than the distance Newton choseto use in the first edition of Principia, but astronomersknow him as the first person to measure a reliably-finitevalue for the speed of light. Even before universal grav-itation, Roemer had enough confidence in the unifor-mity of nature to suppose that the orbit periods ofJupiter’s moons were constant from year to year. He thusattributed late and early sightings of their eclipses byJupiter to light having more or less distance to travel,

*Or any of several other spellings, but it doesn’t matter which youchoose because the sound is one of those Danish phonemes notavailable to the rest of us. It is, as Victor Borge said, a long wayfrom “ugghrl” to “thhhh.” Incidentally, Roemer also invented thetransit circle and meridian circle instruments whose use revealedthe “personal equation” of the previous section, and the mercurythermometer, whose use was germane to the discovery of the“mechanical equivalent of heat” of the next section.

SunJupiter

MoonEarth 2Earth 1

Each of the four Galilean moons of Jupiter is eclipsed onceevery 1.7 to 16.7 days. When the Earth is at E1, we see theeclipses occurring too early by about 8.5 minutes. You can’tquite observe Jupiter when we are at E2 (the sun is in theway), but the eclipses will seem to be occurring somewhat toolate any time we are in that part of the orbit. The Earth’s orbit isreally only one-fifth the size of Jupiter’s, not about one-third asshown.

38 SUMMER 1998

depending on the relative orbital positions of the plan-ets. The data available to him slightly over-estimatedthe range of early-to-late and slightly underestimatedour distance from the sun, leading to a number for c with-in ten percent of the current best value (which can neverbe improved again, since it is now a definition!).

Halley (who also had a comet) updated Roemer’s num-bers in 1694, and uninterest flowered for another gen-eration. Then James Bradley found the same sort of num-ber by a very different method. Bradley (like Herschel)was looking for stellar parallax, but discovered the odd-ly-named aberration of starlight. Think of photons asraindrops descending upon a moving observer. The an-gle you have to tilt your umbrella (telescope) forward tocatch the drops (photons) is the ratio of your speed tothe speed of light. Bradley saw this 20.5 arcsec tilt in1725, had understood it by 1729, and, armed with a bet-ter idea of the size of the solar system and the Earth’sspeed in it, improved on Roemer’s number for c.

Notice that sufficiently accurate versions of Roemer’sand Bradley’s observations could, in principle, take theplace of the Michelson-Morley experiment, because onecan carry them out with the Earth’s orbital velocity makingvarious angles with the incoming light. In fact, the physi-cists finally took over, and the first laboratory value of ccame from Fizeau in 1849. It was about as good as theastronomical ones, but improved methods, from Cornu,Foucault, and (of course) Albert Abraham Michelsonquickly took the lead in providing additional significantfigures (1850+) and, eventually, evidence for non-depen-dence on the motion of source or observer (1887+).

Meanwhile, back at the Cambridge ranch, James ClerkMaxwell was busy writing down the four equations,knowledge of which is frequently taken as the minimumrequirement for calling yourself a physicist. Constan-cy of c is built in, along with the absence of magneticmonopoles. Astronomers quickly came to terms withthe former; the latter you may well wonder about. Wequite blithely ascribe polarization of radio (etc.) radia-tion to synchrotron emission in magnetic fields strungout for kiloparsecs and more along the arms of spiralgalaxies and the jets and lobes of quasars. If an experi-mental physicist wise in the ways of laboratory plasmascomes along and asks where are (or at least were) theelectric currents that sustain (or at least produced) thesemagnetic fields, the answer is quite often, “eh?” On theother hand, you get back the curious fact that the restmass of the photon must be less than 10−47 to 10−57 g,in order for fields to persist over large scales from Jupiterto a galaxy.

The corresponding limit on the mass of the gravi-ton (from the existence of gravitationally-boundsuperclusters of galaxies at least 100 million parsecsacross) is about 10−63 g. Both are considerably smallerthan laboratory limits, and occasional free spirits havetaken them as real, non-zero masses.

WHAT MAKES THE SUN SHINE?

The source of solar and stellar energy was the mostimportant unsolved problem in astronomy/astrophysics

20.5 arcsec

East

An astronomer unclear on the concept of aberration ofstarlight attempts to shield his telescope from photons byholding an umbrella over it at an angle of 20.5 arcsec to thevertical. 20.5 arcsec = 10-4 radians = ve/c, where ve is theEarth’s orbital velocity.

BEAM LINE 39

for half a century or more, 1880±10 to 1938±2. Of course,it couldn’t be a problem until conservation of energywas recognized as a universal phenomenon, which itwas not by Galileo or Newton or even William Herschel(though he speculated on the role of chemical interac-tions in the atmosphere above the solid(!) surface of thesun).

Energy conservation became part of laboratory physicssometime between 1798, when Benjamin Thompson(Count Rumford) reported to the Royal Society (London)on “Experimental inquiry concerning the source of heatexcited by friction” and 1849, when James Joule reportedto them “On the mechanical equivalent of heat.” TheGerman physician Julius Robert Mayer is generally cred-ited with the first proposal of energy conservation in fullgenerality in 1841. By this time, the Earth was alreadyat least tens of millions of years old, according to Hut-ton, Lyell, and other uniformitarian* geologists who hadthought about how long it must have taken to buildup sedimentary rocks, make the oceans salty, and soforth. Chemical reactions, which might sustain the sunfor a few thousand years, were, therefore, never seri-ous contenders, except on Archbishop Ussher’s chronol-ogy, and, even then, the end would be at hand.

In fact, Mayer soon proposed a solution to the solarproblem he had identified. It was gravitational potentialenergy, liberated by infalling meteors. Independently,the Scots engineer John James Waterston recognized theproblem of solar energy in 1843 and proposed as a solu-tion the continuous contraction of the sun, followingon from its origin in a Kantian rotating nebula. Mayer’spaper was rejected by the Academy in Paris, Waterston’sby the Royal Society in London.

A contracting star can live about GM2/RL years ongravitational potential energy, a number that should ob-viously be called the Mayer-Waterston time scale, butis actually called the Kelvin-Helmholtz time scale, forthose who put forward the same ideas in about 1854

(Kelvin with meteors initially, Helmholtz with overallcontraction). Both had encountered Waterston’s work,in a two-page abstract arising from an 1853 meeting ofthe British Association for the Advancement of Scienceand containing both the meteoric and the contractionpossibilities. Kelvin and Helmholtz were, therefore, pre-sumably at least guided by their predecessors, but theyhad better credentials, better press agents, and better for-mal mathematics at their disposal.

There followed a brief era of good feeling, in whichmost geologists squeezed hard on their layers of sedi-ment to compress them within 20–40 million years,though a few refused, including T. C. Chamberlin ofChicago (whom we recognize as the first half of theChamberlin-Moulton hypothesis for the origin of thesolar system, once a popular competitor to Kantian con-traction). Chamberlin and Kelvin faced off at the 1900meeting of the American Association for the Advance-ment of Science, neither, of course, changing his mind.

In any case, the solar boat was soon set further rock-ing, this time by the biologists, who had taken the ideasof Darwin to heart (and head). They insisted on at least109 years for evolution from slime molds to Kelvins. Thephysicists clambered back aboard starting in 1905, whenRutherford and Boltwood (independently) reported rockages of many gigayears after considering the decay ofuranium and thorium to lead. The numbers settled downaround 3–4×109 yr in 1913, when Soddy weighed in withthe concept of isotopes.

A PAIR OF JEANS (Sir James)

You might think at this point that we are well poisedto romp home with Eddington, Bethe, and all to hy-drogen fusion as the primary source of stellar energy.But real events took several detours, which it would notbe fair to blame entirely on James Jeans.* Jeans was, how-ever, the person who most strongly insisted that the realage of stars and stellar systems was more like 1012–13

*Uniformitarianism is not, at least in intention, a religion, but justthe notion that we see in continuous operation now all theimportant processes that have shaped the Earth. The opposite iscatastrophism, and, as usual, the truth is somewhere in between.

*After all, it was Eddington who declared that the sun was mademostly of iron, silicon, and oxygen, so that radiation pressure andgas pressure were equal at its center.

40 SUMMER 1998

years than 109–10. This “long chronology” arose whenJeans tried to account for the relaxed appearance of stars,clusters, and (after 1925) galaxies and for the observeddistribution of the shapes of orbits of binary stars. Thebinary star case, at least, was an example of the theoremthat most mistakes are made before you ever put pencilto paper. Jeans postulated that all binaries had formedwith circular orbits, which were gradually distorted intoellipses by encounters with other stars. Stars are VERYfar apart, and so this will take a VERY long time: in fact,just about the time Jeans calculated. Like most Britishastronomers of his and later generations, he had a back-ground in formal mathematics, and did not often makemistakes after putting pencil to paper. Modern obser-vations of binary systems of different ages show, how-ever, that they form with eccentric orbits that are grad-ually circularized by tidal interactions between the stars.

Meanwhile, however, Jeans’ time scale led him to re-quire a source of stellar energy in which mass was com-pletely annihilated and 100 percent of mc2 made avail-able. That physics knew of no process to do this was not,to him, a fatal objection. Indeed, at the time, experi-mental physics was not very clear on how to liberateany form. of “subatomic energy” except through spon-taneous radioactivity.

There were even times when the long chronologyseemed to be winning. Rutherford’s definitive 1929 state-ment on the age of earth rocks from uranium decay(3.4 Gyr) includes the remark that this number provesthe sun must be making uranium more or less currently,since the total solar age is 100 times longer. Similarremarks appear in other papers and books by both physi-cists and astronomers up until about 1935 when the“short” time scale of a few ×109 yr triumphed. This seemsto have come from approximate agreement among (a)the age of the Earth, (b) the expansion time scale of theUniverse, and (c) the time stars could live on nucleartransformations without annihilation. Even Jeanscapitulated, in the last, 1944, edition of one of his pop-ular books.

E. A. Milne, whom we have not met before in thesepages, was an equal muddier of the waters of stellarphysics in the 1920s and 30s, and his ideas are even harderfor the modern reader to appreciate than those ofEddington and Jeans. Leon Mestel has made the in-triguing suggestion that it would all have been sortedout much sooner if Karl Schwarzshild had survivedthe Great War and had been available to bang their re-calcitrant heads together.

BACK ON TRACK

A second seeming detour was actually the path backto the main highway. This was the association of thestellar energy problem with that of the origin of theelements. Heroes of the tale include Aston with his massspectrograph (1922+), Atkinson and Houtermans withcyclic nuclear reactions that both built up heavy ele-ments and released a few MeV per nucleon (1929), andGamow, Condon, and Gurney with barrier penetration.They and others are hymned at greater length in an ear-lier Beam Line (Spring 1994, Vol. 24, No. 1), ending withtwo choruses by Hans Bethe, the first dated 1939 (whenhe wrote down most of the details of the hydrogen fu-sion reactions that we now call the CN cycle and proton-proton chain), the second dated about 1990 (when headded his voice to the choir proclaiming that the solarneutrino deficit is a problem in weak interaction physics,not in astronomy or argon chemistry).

Nucleosynthesis (the formation of complex atomsfrom simple ones) and the production of energy in starsare now solved problem, though much input wasrequired from nuclear physics and from the area of spec-troscopy, to which we will turn in Part II in the Win-ter issue.

BEAM LINE 41

Educated in England, JOHN ELLIS obtained his BA andPhD from Cambridge University. After one year each atSLAC and the California Institute of Technology as re-search associate, he settled at CERN in 1973, where heled the Division of Theoretical Physics for six years, andis currently a senior staff member. He is the author ofover 500 scientific articles, mainly in particle physicsand related areas of astrophysics and cosmology.

Most of his research work has been on the possibleexperimental consequences and tests of new theoreticalideas such as gauge theories of the strong and electroweakinteractions, grand unified theories, supersymmetry, andstring theory. He was awarded the Maxwell Medal of theInstitute of Physics in 1983 and was elected a Fellow ofthe Royal Society in 1985. The University of Southamp-ton awarded him an Honorary Doctorate in 1994, and hehas held visiting appointments at Berkeley, Cambridge,Oxford, Melbourne, and Stanford.

CONTRIBUTORS

SID DRELL was educated at Princeton and the Uni-versity of Illinois. After short stints on the faculty atStanford and MIT he returned to Stanford as a physicsprofessor in 1956. When it was created in 1963, he trans-ferred to SLAC where he served as head of theoreticalphysics from 1969 to 1986, and Deputy Director.

An advisor to the U.S. government on technical is-sues of national security and arms control for many years,he is currently a member of the President’s ForeignIntelligence Advisory Board and chairs the council over-seeing the Livermore, Los Alamos, and Berkeley NationalLaboratories for the UC president. He is a member of theNational Academy of Sciences, was President of theAmerican Physical Society in 1986, and was head ofthe High Energy Physics Advisory Panel from 1974 to1983. Among his awards was a MacArthur Fellowship in1984. He is an avid amateur string quartet player.

Sha

ron

Kin

der

-Gei

ger

42 SUMMER 1998

HEINO HENKE is Professor and head of the ElectricalEngineering department of the Technische Universitaetof Berlin. He was educated at the Technische Hochschulein Darmstadt where he also received his doctoral degree.Beginning his career in biocybernetics, he later switchedto accelerator physics when he became a staff memberat CERN in 1977. Recently, he spent six months at SLACworking on millimeter-wave radio-frequency structures.His research interests include rf technology, electro-magnetic fields, beam-coupling impedances, new accel-erating techniques, and linear colliders.

During a research stay in the radio-frequency groupof the Advanced Photon Source at Argonne NationalLaboratory the idea was born to combine modern micro-technology with accelerator physics. Since then,millimeter-wave radiofrequency structures are one themain research topics in his Berlin group.

BILL ATWOOD has been a physicist at SLAC since1975. He received his BS from the California Instituteof Technology and PhD from Stanford University. Hehas co-authored over 130 articles in the field of parti-cle physics.

Raised in the greater Boston area, he began playingthe piano when he was six years old and the violin ateight. Because his father was a part-time furniture makerwho specialized in copies of French Provincials, he re-ceived early training in wood working. He became in-terested in violin making in 1976 and began makinginstruments in 1983. He has made more than forty vio-lins and violas which are being lovingly played by BayArea musicians. Recently a young violinist from theUniversity of California, Santa Cruz, won a concertocompetition on an Atwood violin.

Rai

ner

Pitt

han

BEAM LINE 43

ROBERT SIEMANN is a Professor at SLAC and Headof Accelerator Research Department B. He was edu-cated at Brown and Cornell Universities and spent sev-enteen years on the faculty at Cornell before comingto SLAC in 1991. He has worked on a number of highenergy accelerators, including CESR, the Tevatron, andthe SLAC Linear Collider, and has written extensivelyon accelerator theory, experiment, and technology. Hispresent interests are advanced accelerator techniques,and he is involved in development of mm-wave accel-erators and experiments on laser and plasma basedacceleration. He is the Founding Editor of the newlyestablished journal Physical Review Special Topics—Accelerator and Beams.

VIRGINIA TRIMBLE continues to oscillate amongappointments at two universities (University of Cali-fornia Irvine and University of Maryland), vice presi-dencies, and council memberships and such in at leastsix professional organizations, an assortment of editor-ial boards, peer review panels, and lectures. She is cur-rently feeling a bit frazzled but hopes it doesn’t show toomuch in this quarter’s column.