Summer 1993 Vol

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SUMMER 1993 VOL. 23, NUMBER 2 FEATURES Editors RENE DONALDSON, MICHAEL RIORDAN A PEOPLE'S GUIDE TO THE STANDARD MODEL Executive Editor A non-technicalintroduction BILL KIRK to the dominant theory of particlephysics. Editorial Advisory Board Patricia Burchat JAMES BJORKEN, ROBERT N. CAHN, DAVID HITLIN STEWART C. LOKEN, RONALD RUTH 8 TWO PREVIOUS STANDARD MODELS WINICK MARVIN WEINSTEIN, HERMAN Scientists of Napoleonic France and Victorian England believed Photographic Services in universalphysical theories TOM NAKASHIMA that were the "standardmodels" BETTE REED of their times.

Illustrations J. L. Heilbron TERRY ANDERSON, KEVIN JOHNSTON 15 POSITRON EMISSION TOMOGRAPHY SYLVIA MACBRIDE, JIM WAHL A promising medical imaging technique Distribution that borrows heavily from nuclear and particle physics is giving physicians TILGHMAN CRYSTAL a valuable new window on the functions of the human body. Mark Mandelkern

DEPARTMENTS The Beam Line is published quarterly by the Stanford Linear Accelerator Center, P.O. Box 4349, Stanford, CA 94309. 24 THE UNIVERSE AT LARGE Telephone: (415) 926-2585 INTERNET: [email protected] Some Faint, ParticularStars: 1 BITNET: BEAMLINE@SLACVM Virginia Trimble FAX: (415) 926-4500 SLAC is operated by Stanford University under contract with the U.S. Department of Energy. The opinions of the 30 DATES TO REMEMBER authors do not necessarily reflect the policy of the Stanford Linear Accelerator Center. 31 TOWARD THE NEXT LINEAR COLLIDER Cover: Image of the brain of an epilepsy patient made using Probing the TeV Energy Scale Positron Emission Tomography (PET). It indicates substantially reduced metabolic activity in the left temporal lobe (blue area Fred Harris and Xerxes Tata at lower right), consistent with an epileptogenic focus, which is the likely source of this patient's seizures. PEOPLE AND EVENTS (This image and that on page 15 courtesy of Peter S. Conti, Director, 34 PET Imaging Service Center, University of Southern California) 39 FROM THE EDITORS' DESK

Printed on Recycled Paper Ah 40 CONTRIBUTORS A PEOPLE TO THE S r

by PATRICIA BURCHAT

A non-technical in to the dominant ti of particle physics.

"THE SI commo around theoret journal articles is so ml usually

BEAM LINE 1 Over the past 30 years or so, this processes are never seen to occur. In very successful model of the many cases, the absence of a subatomic world-a combination of particular type of process leads to a assumptions and mathematical "conservation rule," which tells us theories-has evolved based on the that some property or quantity is work of many experimental and neither gained nor lost in a given theoretical physicists and on data reaction. A familiar example is con- from particle research laboratories servation of electric charge: the net around the world. It has been electric charge at the beginning of extremely successful at describing every reaction must equal the net the interactions that occur between electric charge at the end. This simple the fundamental particles that make conservation rule eliminates many up matter. Two of the central ideas potential processes; they cannot of this model are that all matter is occur because electric charge would composed of tiny constituents called not be conserved. quarks and leptons and that inter- The Standard Model evolved to actions (or forces) between these explain both the observation of cer- particles occur through the exchange tain processes and the absence of of other particles. The Standard otherprocesses. Experimental results Model is used to make accurate quan- have sometimes led to the discovery titative predictions for many proces- of new, previously unobserved con- ses involving elementary particles, stituents of matter, and at other times from their rates of production to how to the discovery of a new rule for how fast they disintegrate. the constituents interact. The Stan- The Standard Model developed dard Model incorporates both the through a complex interplay between constituents and their interactions theoretical ideas and experimental to give a complete description of all results. It has always been con- known processes involving elemen- strained by the particles and pro- tary particles. cesses that are actually observed. At The shape puzzle (see box at left) certain times during its evolution, gives an example of static interac- the Standard Model predicted par- tions between constituents. In particles or processes that had not been ticle physics we are usually studying observed yet.* Experiments were dynamic systems, in which interac- conducted, motivated in part by these tions between particles lead to a sys- predictions. The outcome of the ex- tem that changes with time. Two periments proved or disproved those particles, such as an electron and a particular aspects of the model. positron, might come together and Important constraints are also annihilate each other to create two placed on the Standard Model by new particles. A heavy particle might what is not observed-it must some- disintegrate into several lighter par- how explain why certain particles or ticles. In the Standard Model, these interactions occur through the exchange of other particles called the *Two important examples are the weak neutral current and the charm quark, carriers or mediators of the force or both of which are discussed in the text. interaction.

2 SUMMER 1993 To understand how a force can be who recognized the correspondence mediated by a particle, consider the between the elements of these dia- analogy of two rollerbladers, gliding grams and the mathematical terms along on parallel paths, one of them that appear in calculations giving holding a ball (see illustration at the probability of a particular inter- right). When one rollerblader throws action occurring. Each line (or par- the ball at the other, she recoils ticle) in the diagram corresponds to a slightly in the opposite direction from factor in a theoretical calculation. her toss-much like a cannon re- Each point at which two lines (or coils when it fires a cannonball, only particles) meet corresponds to an- on a smaller scale. If she throws a other factor. These diagrams help ball to her left, she will receive a physicists conceptualize subatomic Particle B small kick to her right. When the processes and develop deeper insight other rollerblader catches the ball, into particle interactions. For par- a similar kick to his ticle physicists, Feynman diagrams he will receive Force-carrying for in- left. If we were to watch this interac- provide an indispensable tool Particle tion but could not see the ball being tuition, communication, and calcu- exchanged between the two, we lation. might well conclude that a repulsive Particle A force is acting between them. This QUARKS AND LEPTONS are force was actually "mediated" by particles that appear to be Interactions between subatomic the exchange of a ball, which "car- fundamental. No matter how deeply particles can be compared to what when two rollerbladers toss a force between them. we probe with the experimental happens ried" the ball between them. The effects of the The Standard Model describes the facilities available today, we see no force between the rollerbladers (or various possible interactions be- structure within them. Quarks and particles) are "carried" by the ball (or a tween particles in terms of the ex- leptons do not appear to be composed third particle). (Drawing by Bayard change of several different particles. of smaller particles. In fact, they do Colyear) The rollerblader analogy has limita- not even have a detectable size. With tions (for example, it can't be used to current accelerators, for example, explain attractive forces), but it is a physicists can tell that the diameter useful one to keep in mind. Often as of a quark is less than a millionth of you walk the halls of high-energy a millionth of a millionth of a meter! physics laboratories or glance into To put this in perspective, imagine offices of particle physicists, you will that an atom is blown up to the size see diagrams similar to the one at of the earth. Then the nucleus is bottom right on chalkboards or scraps about the size of a football field, a of paper. Instead of rollerbladers, the neutron or proton inside the nucleus lines represent the paths taken by is about the size of an automobile, quarks or leptons. Instead of balls, and a quark is smaller than a tiny you see symbolic representations of pebble! the particles mediating the interac- The word lepton comes from the tion between them. Greek root lepto, meaning "small" These schematic pictures of par- or "slender." The leptons were so- ticle interactions are called Feynman named because the first of them to diagrams, after the late Richard P. be found were very light compared to Feynman, the theoretical physicist other particles. However, much more

BEAM LINE 3 massive leptons have since been two "weight classes." The middle- discovered, leading to the non- weights were called mesons and the sequitur "heavy lepton." The leptons heavyweights baryons. In the early include the first elementary particle 1960s, Gell-Mann proposed that all to show up: the familiar electron, the observed mesons and baryons discovered by the British physicist are made of three kinds of quarks, J. J. Thompson in 1897. The next which he called up, down, and lepton, discovered in 1937 in cosmic strange. He postulated that baryons rays, is a highly penetrating particle are made of three quarks and that called the muon. The third lepton, mesons are made of a quark and an discovered by Martin Perl at the antiquark (the antiparticle of a quark). Stanford Linear Accelerator Center Individual quarks are never observed in 1975, is called the tau lepton. The in Nature; they are always bound muon and the tau lepton both carry inside baryons or mesons. As in our the same electric charge as the shape puzzle, only certain specific electron, but they are hundreds and combinations of quarks are observed. thousands of times more massive. This is an important hint about the nature of the interactions between Each of these charged leptons has Three quarks for Muster Mark! an elusive partner called its neutrino, these particles. which has no electric charge and, as At the time, Gell-Mann had a far we can tell, no mass. In fact, the theory with three fundamental principal "signature" of a neutrino particles in it, so the name seemed S FAR PHYSICISTS have evi- in a particle interaction is evidence apt, at least to him. If the connection dence for six leptons and six of energy being carried away by an between this passage and elementary quarks. Actually, only five quarks apparently invisible particle. It was particles is lost on you, however, have been officially discovered, but to explain just such occurrences that don't worry. "The whole thing is just we have strong evidence that the the existence of the neutrino was a gag, " he acknowledged when asked sixth must exist. The quarks and postulated by Wolfgang Pauli in 1930. to explain how he chose the name. * leptons appear to come in three fami- The first neutrino (the electron "It's a reaction against pretentious lies, each containing a pair of quarks neutrino) was finally discovered in scientific language." and a pair of leptons. Just why there 1956 by Clyde Cowan and Frederick Before Gell-Mann came up with are three families, we don't really Reines of Los Alamos. the idea of quarks, the list of so- know. As well as six kinds of leptons called elementary particles had Ordinary matter is made of par- (the electron, muon and tau, and grown extremely long. "If I could ticles from the first (and lightest) their corresponding neutrinos), there remember the names of all these family. Electrons orbit the nucleus are six kinds (or flavors) of quarks. particles, I would have been a of the atom. Neutrons and protons, Five of them have already been botanist," remarked University of found inside this nucleus, are made discovered and the sixth is eagerly Chicago physicist Enrico Fermi in of up and down quarks (plus other anticipated. The name quark was the late 1950s. Using particle particles that help to bind them to- chosen for the constituents of the accelerators, physicists were dis- gether). Quarks have the unusual neutron and proton (and other covering more and more new feature of carrying fractional charge. particles) in 1963 by California particles, which couldbe divided into The electric charge (expressed in Institute of Technology physicist units of the charge of the electron) is Gell-Mann. The word comes +2/3 for one member of each pair of Murray *R. P. Crease and C. C. Mann, The Second from a line in James Joyce's last novel Creation:Makers of the Revolution in 20th- quarks and -1/3 for the other. The Finnegans Wake: CenturyPhysics, (Macmillan, 1986), p. 282. neutron, with no net charge, is made

4 SUMMER 1993 up of two down quarks and an up Elementary Particles in the Standard Model quark. The proton, with a net charge of one, is made up of two up quarks and a down quark (see illustration bottom right).

N OUR ANALOGY, the rollerbladers represent quarks and leptons. What do the balls represent? What are the particles, that is, that The strong interaction is medi- mediate the interactions between the ated by eight massless, electrically Proton quarks and leptons? neutral particles called gluons. Any two objects that carry elec- Whereas the photon does not carry tric charge-all quarks and leptons the charge of the interaction that it except the neutrinos-interact via mediates (that is, the photon itself is Total Charge = +1 the electromagnetic force. This is not electrically charged), gluons do the interaction responsible for many carry the charge of the strong inter- phenomena of everyday life: heat, action. Gluons themselves have color light, radio signals, electricity, chem- charge. This feature of the strong istry, almost every common phenom- interaction (and the fact that the enon except gravity. What is the car- strong interaction is so strong) makes Nenutron rier of this interaction? You may precise calculations of processes in- have noticed that a very common volving the strong interaction par- particle has not been mentioned yet ticularly difficult. The strong force as one of the fundamental constitu- binding quarks together has the pe- Total Charge = 0 ents of matter: the photon. Photons culiar feature of becoming even stron- in a particular energy range are the ger as the quarks are separated- particles that make up visible light. similar to how a spring pulls back In a broader sense, they are the me- more forcefully the further it is stretched. Because of this effect, diators of the electromagnetic inter- Protons and neutrons are composed action; they are the "balls" that carry quarks are trapped inside mesons of quarks, which are bound together the electric and magnetic forces be- and baryons; they are never observed by gluons. tween charged particles. by themselves. Any two objects that have a spe- All quarks and leptons, even the cial property called color charge will neutrinos, interact via the weak inter- interact via the strong interaction. action, which is responsible for Quarks carry color charge; leptons phenomena such as radioactivity and do not. Therefore, only quarks feel permits the sun to shine. This the strong interaction. This is one of interaction is feeble compared to the the primary differences between strong and electromagnetic inter- quarks and leptons. The strong in- actions at everyday energy scales. teraction is what binds quarks to- But at the energies of particle gether in the neutron and proton and accelerators currently operating at binds neutrons and protons in the SLAC and CERN, the weak interaction nucleus of the atom. actually dominates the electro-

BEAM LINE 5 Interactions in the Standard Model will be attracted toward each other by the gravitational interaction. When considering fundamental particles, the gravitational interaction between them is completely negligible because they are so light. We need not consider it any further, at least in discussions of the Standard Model. Processes involving the electromagnetic, strong, and weak interac- e- e magnetic interaction. It is through tions can be represented by Feynman the weak interaction that heavy diagrams that illustrate how quarks Photon quarks and leptons can turn into and leptons interact through the ex- p P lighter ones. change of mediators (photons, glu- This interaction is mediated by a ons, W and Z particles). In these pair of electrically charged particles diagrams, quarks and leptons are rep- called W+ and W- and an electrically resented by straight lines, the pho- neutral particle called the Z. Large ton by a wavy line, gluons by springs, numbers of Z particles are currently and the W and Z (usually) by dashed being produced and studied at SLAC lines. Some simple Feynman dia- and CERN. The W and Z particles are grams (shown at left) depict impor- very heavy, almost a hundred times tant interactions predicted by the e- heavier than a proton. In our roller- Standard Model. W-- IVe blader analogy, these heavy media-

Niurnd '' U tors of the weak interaction corre- Neutron u u Proton spond to extremely heavy balls, such A T THE HEART of the Standard d d) as bowling balls. Although the im- Model are two theoretical ideas pact of the exchange of a bowling called "local gauge invariance" and ball would be great, the probability "spontaneous symmetry breaking." Feynman diagrams for interactions that either rollerblader can muster These theories provide predicted by the Standard Model. The a mechanism top diagram is an electromagnetic enough strength to throw it very far by which the observed world of mas- interaction between an electron and a is small, but this likelihood increases sive quarks, leptons and mediators proton, mediated by a photon. This as they get closer together. Likewise, of the interactions between them interaction, which is responsible for interactions mediated by the W and can be generated from a simpler binding electrons in atoms, is respon- Z particles are rare due to their huge theory involving only massless par- sible for all of chemistry. The middle mass, and the weak interaction has a ticles with no interactions. When diagram illustrates quarks bound very short range. But when this in- local gauge invariance is imposed on together by gluons, for example in a proton. The bottom diagram illustrates teraction does occur, it can have a a theory that contains only massless the weak interaction leading to radio- very significant effect. In an interac- quarks and leptons, interactions me- active decay of a neutron. One of the tion involving a W, for example, a diated by massless carriers, such as down quarks in the neutron emits a W-, quark or lepton turns into a com- photons and gluons, occur. Spontan- changing into an up quark. The W- turns pletely different particle. eous symmetry breaking then pro- into an electron and an antineutrino, There is another force I have not vides a mechanism for the quarks, while the neutron turns into a proton. yet mentioned. Any two objects that leptons, and the W and Z particles to have mass (or, more precisely, energy) acquire mass. This theory has two

6 SUMMER 1993 attractive consequences. It actually it at experimentally accessible unifies the weak and electromagnetic masses or energies. Part of the moti- interactions, and it predicts specific vation for building the SSC is to search relationships between the strengths for the Higgs boson. of these interactions and the masses of the W and Z particles. In the Standard Model, the electromagnetic HE STANDARD MODEL of par- and weak interactions are actually ticle physics has been so suc- two different mixtures of two other cessful because it predicts, or at least interactions. The "mixing" occurred accommodates, so many aspects of during the symmetry breaking the fundamental interactions: three process. Because they are different massive carriers of the weak inter- mixtures of a common set of ingre- action, one massless carrier of the dients, many of their features are electromagnetic interaction, eight intimately related. They are not two massless carriers of the strong totally independent types of inter- interaction, relationships between actions, as might seem to be the case the strengths of the electromagnetic at first glance. and weak interactions, and the The Standard Model makes defi- masses of the W and Z particles. Of nite quantitative predictions for how equal significance, and interest, the fundamental particles interact however, are the questions that the via the strong, weak and electromag- Standard Model does not answer. netic interactions. Many of these Why do the quarks and leptons have predictions have been tested experi- a family structure? Why is there more mentally. The most precise tests in- than one family? Why do there seem volve the electromagnetic and weak to be only three families? What interactions. So far, no experimental determines the masses of the quarks measurements deviate significantly and leptons? What is the exact from the predictions of the Standard strength with which the W particles Model. change one type of quark into If you have read about the Super- another? What is the mass of the conducting Super Collider (SSC) to Higgs boson? Because the Standard be built in Texas, you have probably Model does not answer all our ques- heard about the Higgs boson. Where tions, it cannot be the final, ultimate does this particle fit in our picture of theory describing particles and their fundamental particles and interac- interactions. We build new acceler- tions? The theory that gives mass to ators to try to find solutions to the particles predicts that the Higgs bo- unanswered questions and to deter- son (or something like it) should ex- mine if there are any flaws in its ist. Although the theory can be used predictions. In this way, we hope to to suggest how this Higgs boson come closer to developing the might be created in particle interac- ultimate theory of matter. tions and how it would decay, it does O not predict its mass. Therefore, we don't really know exactly where to look for it. All we can do is search for

BEAM LINE 7 AVING SLIPPED SO FAR DOWN THE CHAIN of being-from physicist to historian to l administrator-I was very much flattered by the invitation to present this paper. I shall not abuse the invitation by discussing the Standard Model itself, for you all know much more about it than I do. Instead I shall discuss two earlier physical theories-or, rather, sets of theories-that may be considered standard models of their time. My purpose is not to place the modern version in perspective-for what larger setting is possible for a theory that covers all time and all space? My purpose is to remind you that others have had the same intellectual impulses that drive contemporary particle physicists and cosmologists, and that they could point to persuasive evidence in support of their own standard models.

(Adapted from The Rise of the Standard Model, proceedings of the Third International Symposium on the History of ParticlePhysics, Stanford Linear Accelerator Center, June 24-27, 1992, to be published by Cambridge University Press)

8SUMMER 1993 To qualify as a discarded standard perhaps the most effective, were to model, a theory must have been subvert both Napoleon and the stan- deemed fundamental and universal; dard model of his time. also, it must have enjoyed a wide Chief among the modelers and, consensus among physicists and pro- likewise, a great favorite of duced quantitative results testable Napoleon's, was the Marquis de by experiment. These criteria are Laplace, Senator of France and prince satisfied by two and perhaps only of the world's physiciens geometres. two previous models, which I'll call Napoleon showered blessings on the Napoleonic and the Victorian. Laplace and once, on the theory that mathematicians with money can do everything, appointed him Minister THE NAPOLEONIC of the Interior. Laplace lasted six STANDARD MODEL weeks. Later Napoleon explained why: "Laplace did not look at any I call the standard model of the years question from the proper point of around 1800 Napoleonic not because view; he looked for subtleties every- he had anything to do with creating where, had only problematic ideas, it, but because he patronized its prin- and carried into administration the cipal architects, because it rose and spirit of the infinitely small." * * Hav- fell coincidentally with his own ca- ing set down the burdens of office, Charles Augustin Coulomb reer, and because it operated with Laplace could devote himself entirely 1736- 1806 the same mixture of the aristocratic to standard modeling, or, as he put it, and the democratic, the chauvinistic to making physics as perfect as as- had at least one such fluid as its and the cosmopolitan, that charac- tronomy by importing into it the carrier. The polar forces had two each: terized his regime. As in war and mathematics and the method of the a positive and a negative fluid for politics, law and culture, France took theory of gravitation. * * electricity, and austral and boreal the lead in standard modeling-in The fruitfulness of this approach ones for magnetism. Since no one particular, French mathematicians, had been demonstrated in 1785 by could detect a change of weight at- or, to use the term they sometimes Charles A. Coulomb, whose famous tributable to electrification or mag- applied to themselves, physiciens measurement of electric and mag- netization, physicists characterized geometres, or mathematical physi- netic forces rested on several results the associated fluids as "impon- cists. Napoleon recognized the intel- of the gravitational theory. Perhaps derables." lectual power of this set of savants the most important of these was the and worried that they were not all theorem that a uniform gravitating "It's dangerous to give shell acts outside itself as if its mat- gentleman. *Letter of March 23, 1805, quoted by people who have no money too wide ter were concentrated at its center. Joachim Fischer, Napoleon und die an acquaintance with mathematics," Coulomb's invocation of this theo- Naturwissenschaften (Stuttgart: Steiner, he once said, thinking, perhaps, of rem assumed what his measurement 1988), p. 198. * *Notes on conversation on St. Helena, the talented impecunious students was intended to show: that elements quoted ibid., p. 110; see also Maurice of the Ecole Polytechnique, who had of the supposed electric fluid, and of Crosland, The Society of Arcueil won their places by competitive ex- the magnetic, attract and repel one (Cambridge, Mass.: Harvard University the law Press, 1967), pp. 63-4. aminations and were inclined toward another in accordance with * **Details about the Napoleonic standard democracy.* Some of these men, of of inverse squares. These fluids were model can be found in J. L. Heilbron, whom Augustin Fresnel, the archi- a capital feature of the Napoleonic QuantitativeScience Around 1800 (Berkeley, 1993). tect of the wave theory of light, was standard model: every distinct force

BEAM LINE 9 In chronological as well as logical whether there existed two, one, or parallel with the fluids of electricity zero electrical fluids. As the stan- and magnetism, the substance of dard textbook of the Napoleonic stan- heat, or caloric, became a Napoleonic dard model put the point, the objects imponderable fluid. At the phenom- of physical theory had their place in enological level, strong analogies the heads of mathematicians, not in existed between tangible and latent the course of nature. The system of heat, and heat capacity, on the one distance forces and their specialized hand, and electric charge, the un- carriers had the merits of intelligi- charged normal state, and electrical matical parallel with baryonic matter bility, mathematical convenience, capacity, on the other; and, on the that carried the forces of cohesion, universality, and, sometimes, fit with modeling level, between the ex- affinity, and gravity. As the experiment; it would be asking too pansivity of the several hypothetical Napoleonic standard modelers liked much to require that it also repro- fluids. It was therefore obvious to to say, they had tied together duced God's blueprints. suppose that the particles of caloric astronomy and microphysics; a great The system aroused some oppo- interacted among themselves and strength of their system, according sition among physicists, particularly with the molecules of matter ac- to them, was the mutual reinforce- in Germany and England, and among cording to a force whose dependence ment of their theories of the very the proletariat of the educated, for its on distance experiment might seek. large and the very small. rigidity of form and its mathematical We now have five imponder- The system had its successes: demands. In order to retain the ables-two each for electricity and Poisson's work on the distribution model's formal coherence, the model- magnetism, and one for heat-and of electricity on conductors, and on ers had to introduce some very com- ponderable matter, all interacting the behavior of magnetized shells; plicated formulas, particularly for the directly by forces dependent only Biot's and Ampere's on electromag- interaction of polarized light with upon the distance between the netic forces between wires; Laplace's birefringent crystals. In Biot's version interacting elements. We need only and Poisson's on adiabatic processes; of this complication, the optical force two more to complete an eightfold Dulong and Petit's on specific heats; depended on the angle between the way. One of these was light, then Malus' on light; Laplace's on refrac- direction of the light ray and the still conceived in Newton's terms as tion and capillarity; and Gay-Lussac's optic axis of the crystal; and also on streams of particles, regulated in their on the combination of gases. Around the shape, orientation, and rate of commerce with ponderable matter 1810, the Napoleonic standard rotation of the light particles.* As for by a direct distance force that caused model, like Napoleon himself, the off-putting demand on mathe- reflection, refraction, and diffraction. seemed capable of absorbing every- matics, many natural philosophers The capstone, or omega-minus, of thing. In both cases, the result was a of the time complained that they the system, the seventh imponder- juxtaposition of disparate elements could no longer follow fundamental able and the eighth constituent of tied together by overarching laws physics because these standard the natural universe, was discovered and institutions constructed on the modelers insisted on writing it in the around 1800, when physicists found same pattern. The physicists recog- language of exact astronomy. And radiant heat beyond the red end of nized explicitly that the union was previously interested laymen ignored the visible spectrum. Radiant heat formal rather than substantial (the altogether a line of thought that they made a fine middle term between functional equivalent of the require- considered stifled by the oppressive light and heat; heat tied all three to ment that all descriptions be renor- electricity and magnetism, via the malizable, gauge-invariant quantum analogies I've mentioned; and these field theories), and they conceded *J. B. Biot, "Sur de nouveaux rapports entre la reflexion et la polarisation a la lumiere," seven imponderables, or leptons, that they could not affirm, in the Societe philomatique, Bullctin des were associated through a mathe- prototypical case of the theory, sciences, Vol. 3 (1812), pp. 209-16, 226-9.

10 SUMMER 1993 requirements of mathematical analysis. Further afield, the scientific re- spectability of imponderables appeared to some optimists to open a place for the human soul among the substances constituting the world. I leave the last word on this matter to the first man of his age. In his retirement on Saint Helena, Napoleon declared his faith as follows: "I believe that man is the product of the [imponderable] fluids. . . that the brain pumps them around and gives life, [and] that they constitute the soul." *

William Thomson (Lord Kelvin) James Clerk Maxwell THE VICTORIAN 1824-1907 1831-1879 STANDARD MODEL and execution, and because it per- that was required to make a world The Napoleonic standard model did fectly fit the materialism, clutter, was an incompressible aether not long survive Napoleon. During and complacency supposed to have possessing mass and independently the 100 days between the Emperor's characterized Victoria's reign. It may mobile parts; and, also, mathematical return from exile on Elba and his also count that she elevated its chief physicists clever and patient enough definitive abdication after Waterloo, spokesman, William Thomson, to to extract from long hydrodynamical Fresnel was busy perfecting the wave the peerage (as Lord Kelvin) just as calculations some analogies between theory of light. At about the same Napoleon had distinguished Laplace. the behavior of vortex atoms and time Fourier was putting the final The Victorian standard model had laboratory results. One encouraging touches on his quantitative theory as main ingredients an omnipresent finding was that no more than six of heat, which accomplished won- aetherial continuum and discrete vortex atoms could move together as ders without requiring the concept material particles. The interactions a vortex molecule, which seemed of caloric. At the mid-century, the of the continuum and the particles relevant to the periodicity of work of Joule, Mayer, Clausius, and were a prime subject of discussion. Mendeleyev's ouija board, or table of William Thomson destroyed caloric The most radical scheme tried to the elements. As Maxwell observed altogether, and made heat a mode of dissolve matter itself into an aether. of this form of the Victorian standard motion of ponderable molecules. In the best elaborated form of this model, "[its] difficulties ... .are Then came James Clerk Maxwell, grand unifying theory, atoms became enormous, but the glory of sur- who reduced the remaining six lep- vortex rings, or, to give sufficient mounting them would be unique." * * tons to one, the electromagnetic variety, chains of linked vortex rings, Another elaborate form descended ether, whose motions brought forth in a universal frictionless fluid; they from Maxwell's machinery of the the phenomena of electricity, mag- moved about like smoke rings in air, netism, light, and radiant heat. By or superstrings in vacuum, collided *Quotcd by Fischer, Napoleon (1988), 1880 the basis of a new standard and parted like the particles of a gas, p. 283. model had been set. I call it Victorian or stuck and moved together like **J. C. Maxwell, Encyclopedia Britannica, because it was British in inspiration atoms combined into molecules. All 9th edn (1875), s.v. "Atom."

BEAM LINE 11 electromagnetic aether and J. J. speeches. The president of the French Thomson's discovery that a body has Physical Society, Alfred Cornu, greater inertia when charged than adroitly wedded Gallic foresight when uncharged. The most refined with British achievement; the me- exercise in this form was Joseph chanical reductions that had suc- Larmor's theory of aether knots, per- ceeded across the channel, he said, manent, mobile centers of strain in a and especially the attempts at a grand universal plenum having no proper- unified theory of aetherial vortices, ties but rotational elasticity and a promised nothing more, or less, than capacity for internal motions. Just as the imminent realization of the

the kinetic theory had made heat a Ue dream of Descartes, to explain the mode of motion of matter particles entire physical world with a little and the electromagnetic synthesis FO geometry and lots of brain power. had made electricity, magnetism, and 03 Then Henri Poincare put this project light modes of motion of the aether, in its proper epistemological place. a<3E now inertia arose from the move- Uj The making 0. of models and the ment of Larmor's aether knots. He reduction of all physical phenomena found that he could do without the Joseph Larmor, 1857-1942 to matter in motion might be, and concept of mechanical, or rest mass, even do, very well, he said, but that and aetherialize inertia; moreover, workings of springs, flywheels, did not signify that theoretical since he could find no reason that all universal joints, and rubber bands, physicists were approaching the his knots should be twisted in the which Kelvin and his colleagues truth. According to Poincare, a same sense, he allowed two types, deemed essential to their compre- theorist properly regarded is no more differing chirally, that is, with op- hension of physical theory, gave their than a librarian, who arranges the posed helicities, which he called posi- enterprise the air of a Victorian collections of science-that is, tive and negative electrons. The ro- factory; or so its primary critic, Pierre confirmed experimental results-in tation of an electron of one type Duhem, liked to say in deprecation the way most convenient for around one of the other, or a circulat- of the system that had superseded overview and retrieval. It makes ing ring or rings made of positives his ancestors' scheme of impon- sense to ask if a library catalogue is and negatives symmetrically placed, derable matters and distance forces. useful and reliable, but not whether constituted an atom. These ideas date No more, however, than Laplace's it is true. The physicists of 1900 from the 1890s, that is, from before school did Kelvin's insist that their approved Poincare's talk as "one of the discovery of the electron, and standard model was true of nature. the most perfect expressions of the long before the invention of the Rather, they rested the priority of state of mind of the masters of nuclear atom.* mechanical reduction on its modern science."**** These parsimonious theories, visualizability, on its conceptual, if which invoked no more than the not mathematical, convenience and *Joseph Larmor, Aether and Matter on their conviction and experience, (Cambridge: Cambridge University principle of least action and a Press, 1900), pp. 26-8. substrate with a very few general that the human mind can reason **More on the Victorian Standard Model mechanical proprieties, were the exactly only about mechanical in J. L. Heilbron, "Fin-de-siecle processes occurring in absolute space physics," in C. G. Bernhard, E. ideals to which, in theory though Crawford, and P. Sirborn, eds., rarely in practice, the various and time.** Science, Technology and Society in the mechanical analogies fancied by This epistemology was nicely Time of Alfred Nobel (Oxford, 1982), Victorian physicists might be caught at the International Congress pp. 51-73. **C. E. Guillaume, "The International reduced. The analogies between the of Physics held in Paris in 1900. The Physics Congress," Nature, Vol. 62 machinery of the aether and the French, as hosts, gave the opening (1900), pp. 425-8.

12 SUMMER 1993 his mother's tears not as expressions of her sorrow [about his career choice] but as solutions of muriates and car- bonates of soda . .. , and he will reflect that they were caused not by his selfishness, but [by] cerebral pressure on her lachrymal glands."* * Very likely these attacks helped to recommend that meekness, which, however uncharacteristic of physicists, Poincare expounded to applause before his peers as the or- thodox epistemology of the standard model of 1900. That was the way several perceptive critics of the time regarded the matter. The philoso- pher Eduard von Hartmann can speak for them all. "The more physics keeps its completely hypothetical character in mind [he wrote], the better will 1854-1912 Henri Poincare, be its scientific reputation in public It turned out that the relations of the goal, or even definition, of phys- opinion.* ** aether and matter could not be ics as the expression of all natural catalogued conveniently by the phenomena in terms of mechanical physicist-librarians of 1900. One day quantities, the trouble-maker could THE ATLANTIC MODEL Lord Kelvin, looking up from the infer that modern science taught that springs and rubber bands wherewith those quantities, and the physical A few symmetries may be discerned he was wont to fashion aethers, spied and chemical properties built up from in the decay processes of Napoleonic two clouds over the dawning twen- them, were the only things that truly and Victorian physics. For one, the tieth century. He reminded physi- and objectively exist. Champions of demands of unalterable character- cists that, despite the labors of a yesteryear also found it convenient istics of the theories came into flat dozen Larmors, they had no accept- to foist on physics the doctrines that contradiction with experiment. In able account of the interaction of the brain secretes thought like the the earlier case, the conception of aether and charged bodies in motion kidneys do urine, that the soul is a heat as a conserved fluid could not be and that an inescapable consequence mistake, that religion and poetry are reconciled with Carnot's analysis of of the kinetic gas model, the equi- bunk, that man descended from the workings of an ideal engine and partation of energy, failed before the monkeys, and so on. "Bring up a Joule's measurements of the behavior facts. These were profound obser- woman in the positivist school [they of real ones. In the later case, the vations. As we know, it took rela- said], and you make of her a monster, tivity to dissipate the first cloud and the very type of ruthless cynicism, of *W. S. Lilly, "Materialism and morality," quantum theory to knock down the all engrossing selfishness, of un- FortnightlyReview, Vol. 46 (1885), second. bridled passion."* In an article en- pp. 575-94. Like the Napoleonic standard titled, "The scientific spirit of the **E. P. Cobbe, "The scientific spirit of the age," Contemporary Rcview, Vol. 54, model, the Victorian inspired or sup- age," published in the Contempo- (1888), pp. 126-39. ported a general philosophy that out- rary Review for 1888, you can read ***Hartmann, Die Weltanschauung der ran it and darkened its name. From that a man bred to science "will view modernen Physik (Leipzig, 1902), p. 219.

BEAM LINE 13 conception of electrons as charged perhaps rightly, that his soul was an or as an ingredient, of a theory of billiard balls subject to the rules of imponderable fluid, and the materi- everything? Or as a hodgepodge of Victorian mechanics and electro- alists of the 19th century seized on mathematics and phenomenology dynamics prevented physicists from mechanistic reduction to prove that requiring the insertion of ad-hoc con- combining them into stable atoms no one had a soul. This similarity stants that will almost certainly al- or accounting via a visualizable seems to extend to the current most never be deducible from first model for spectroscopic and other Standard Model and its fellow trav- principles? If this skepticism repre- data. Second, the resolution of these eler, the Big Bang, which have sents the dominant view, the parallel and associated difficulties was prompted declarations from physi- holds. If not, if physicists truly believe accomplished through new and far- cists that sound theological. In his that they have found the truth or reaching discoveries: in the examples Nobel prize lecture, one of the chief some of it, we have a broken symme- just mentioned, the second law of architects of the Standard Model, try of great interest to historians. thermodynamics and the elementary Abdus Salam, acknowledged his I have decorated the standard quantum of action. Third, the privilege in being chosen to reveal models of 1800 and 1900 with the overthrow of the standard models the portion of God's plan that related names of Napoleon and Victoria; that resulted at first in important savings to weak interactions; a professor of of 2000 remains unattributed, await- in mathematical effort: the wave theoretical physics at Oxford, John ing, as we say in the fundraising theory of light arrived at conclusions Polkinghome, quit his post to become game, the naming gift. Unfortu- about the optics of birefringent pastor of theological physics for the nately, no single individual now gives crystals more directly than the Anglican church; and the contri- the tone to an age. In view of this sad complex theories of Laplace's school; butors to Physics, Philosophy, and decline in the human race, and be- and the old quantum theory, for all Theology, a volume published a few cause the current Standard Model its faults, allowed computations of years ago by the Vatican, show, has been purchased by the taxpayers spectral series much simpler than among much else, how to square the of Europe and the United States, I the classical theory of radiation did. Big Bang with St. Augustin and propose to call it the Atlantic model. A fourth point worth dilating is creatio ex nihilo.* The recent dis- This choice may have the further that neither model ever had the covery of large scale inhomogeneities recommendation that the ancient allegiance of all the good physicists in the background radiation was an- island of Atlantis was ruled by a of its time. Although the opponents nounced in phrases that might have decuplet of five pairs of twin broth- could not duplicate the full range of come from the pulpit. One astro- ers all from the same parents;*** exact descriptions available to the physicist called the discovery "the that, although it did not exist, it had consensus physicists, they could holy grail of cosmology." The dis- its place on medieval maps of the make important discoveries by coverer himself, George Smoot, who world; and that, in the hope of going looking where the standard models works for the spiritual University of beyond it, Columbus discovered did not point. Thus the so-called California at Berkeley, observed that, America. romantic physicists of Napoleon's "if you're religious, it's like looking O time set in motion the discovery of at God."* * the magnetism of current-carrying A sixth point of symmetry, very wires by Oersted,and the detection necessary to complete the scheme, of thermal electricity by Seebeck. might be dragged from epistemology. *Polkinghorne, Science and Creation Opponents of the Victorian standard The spokesmen for the previous (Boston, 1989), pp. 84-98; Robert John Russell et al., eds., Physics, Philosophy, model, the so-called energeticists, standard models explicitly dis- and Theology (Vatican City: Vatican played an important part in the claimed that they had found the Observatory, 1988), pp. 283, 375-8, 405. prehistory of relativity. truth. No doubt they were right. And **Los Angeles Times, April 25, 1992, p. B.7; San Francisco Chronicle, A fifth similarity concerns wider how is it with you? Do you regard the April 25, 1992, p. A16. applications. Napoleon fancied, Standard Model as the foundation, ***Plato, Critias, 113.

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::::ij:Liiiii-l::e8, gwenaM~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~hasin ...... subsid ician suspcts ti havhehad a stroke which has partially resolved, b ut confirm this diagnosis b r t i ith anti. drugs. X-ray computed netic rei imaging of your bwn He o. pos~itron emissiontmgahscnose if~there is .your brain that hasreducedmetabolicactivity.: due t tory loss Of cir Positron Emission Tomography images are normal, your physician or PET is a new technique increas- would probably conclude that a ingly used in clinical medicine to stroke was not the cause of your create images that tell physicians symptoms. how effectively certain tissues are In addition to its clinical role, PET performing their physiological func- is extensively used in physiological tions, such as metabolizing sugars or research to study the functions of synthesizing proteins. It does this by normal organ systems, especially the determining the spatial distribution brain. Studies using radioactive glu- of radioactive nuclei that emit a cose and radioactive water as a tracer positron the antiparticle of the elec- for brain blood flow have identified Ca'l tron. In contrast to X-ray computed the parts of the brain responsible for tomography (CT) and magnetic reso- certain higher level thought pro- nance imaging (MRI), which give cesses such as recognition of sounds high-resolution images depicting the and association of related words. PET PET images of a normal brain. The more intense areas represent gray matter anatomy of human tissues, PET ac- research also has shown that certain consisting of cell bodies. The less curately measures how tissues are abnormalities, such as susceptibil- intense areas are other tissues-mostly functioning. In the case described ity to spontaneous panic attacks, can white matter, consisting of the axons of above, the PET scan was performed be localized to well-defined areas of nerve cells, and cerebrospinal fluid. after giving the patient a radioactive the brain. Areas of the brain that are not function- sugar analog, and the resulting im- One of several new medical- ing normally have decreased intensity, ages show the rate at which the brain imaging techniques that have been while epileptic foci and tumors may have developed over the past two decades, increased intensity. tissue uses the sugar glucose. As the

16 SUMMER 1993 PET represents a big departure from functions, it gives information that the projection images of conventional is very different from all the others. nuclear medicine. These new Because physiological changes methods give computer-generated usually precede anatomic ones and "parametric images" that represent reflect the nature of a disease process some property of tissue as an inten- more specifically, PET offers the sity. Most of these methods are tomo- possibility of early and more accurate graphic, producing pictures of a three- diagnosis, which will certainly lead dimensional object as a sequence of to more effective therapies and higher slices. The first to be developed was likelihood of cure. X-ray Computed Tomography (CT), which gives pictures that have the same kind of anatomical information A LTHOUGH THEY EXPLORE very as ordinary radiography, but with far different realms, PET and high better contrast and freedom from energy physics are technological artifacts and backgrounds. X-ray CT cousins. Now a hundred million dol- is the first technique that generated lar industry and growing rapidly, PET accurate images of soft tissue struc- uses particle accelerators to produce tures and allowed physicians to short-lived radioactive isotopes that diagnose diseases of the brain, liver, are incorporated into substances kidneys and other organs without called radio-pharmaceuticals, which invasive procedures. Another new are then administered to patients. technique is magnetic resonance The PET scanner consists of a cylin- imaging, or MRI, which uses nuclear drical array containing thousands of magnetic resonance to produce scintillation particle detectors and a images that give the density of powerful computer readout system, protons and the properties of their both similar to those used in high chemical environment. MRI is a energy physics experiments. valuable technique in distinguishing The first step in a PET scan is the normal from abnormal tissues. A preparation of a tracer, which requires third technique, ultrasound, is used a cyclotron bombardment to produce to make images based on how sound the radioactive isotope. Chemical penetrates various tissues. These synthesis then incorporates this images give mechanical information isotope into radio-pharmaceutical such as the presence of kidney stones molecules. After the patient is or fluid-filled cysts. They indicate positioned in the scanner and injected the abnormal enlargement of such with the tracer, the scan begins. As organs as the gall bladder or kidneys. the tracer molecules circulate These parametric imaging tech- through the body and are taken up by niques are complementary. They cells, the radioactive nuclei emit measure distinctly different proper- positrons that travel up to several ties. Frequently, scanning of an organ millimeters in tissue and annihilate by several different techniques is with electrons they encounter. Each required to make an accurate diag- annihilation produces two gamma nosis. Since PET is the only imaging rays of equal energy, both 511 keV, method that measures physiological which emerge from the body in nearly

BEAM LINE 17 opposite directions and hit detectors The images obtained after admin- on opposite sides at almost exactly istering the PET tracer can be ana- the same instant. The gamma rays lyzed to determine metabolic prop- must be detected nearly simul- erties of tissue. FDG competes with taneously, essentially guaranteeing glucose for transport into the cell that they come from the same and for the first step of metabolism. electron-positron annihilation. A It is a better tracer than radioactive straight line drawn between the two glucose because there are no radioac- Cross-sectional view of a patient inside detectors passes through the point of tive metabolic products (such as car- a PET scanner. Positrons emitted by a annihilation. The computer records bon dioxide). PET measures the time- radio-pharmaceutical travel a short millions of these "coincidences." dependent concentration of the tracer distance (exaggerated in the drawing) Tomographic reconstruction, per- in tissue. The model gives the rate at before annihilating with an atomic formed by special-purpose high-speed which FDG is transported and me- electron to produce two back-to-back computers, determines the distribu- tabolized, which is directly re- gamma rays, which are recorded by tion of annihilation points from all lated to the rate at which glucose is detectors on opposite sides of the patient. The spatial distribution of many the coincidence lines recorded. Be- metabolized. such electron-positron annihilations is cause the positron has a short range, The FDG model is used in func- reconstructed with the aid of a powerful this distribution approximates that tional brain imaging, in which stimu- computer, giving a three-dimensional of the decaying nuclei. The spatial lation by sensory or intellectual image of processes occurring inside the distribution of annihilation points is means activates specific brain areas, body. (Drawing adapted from a corrected for gamma ray attenuation thereby increasing their metabolism. brochure of the Siemens Corporation) in the body and can also be corrected It is used to quantify the glucose for scattering. For the brain the at- metabolism of damaged heart tenuation correction is computed muscle, which is used to determine using the image of the scalp as re- whether bypass surgery would be corded by the scan. For the body the effective. In some cancers, the glu- correction is measured by perform- cose metabolic rate is a measure of ing a PET scan using externally placed the malignancy of the disease and positron-emitting sources. gives physicians valuable prognostic The corrected PET image, which information. shows how much tracer has been incorporated by cells, gives a quantitative map of how this tracer is me- ET IS OF PARTICULAR interest tabolized. A mathematical model of in physiology and medicine cellular physiology then relates this because of its unique ability to tracer uptake to the metabolic activ- characterize many processes non- ity of the tissue for real biological invasively. Its tremendous advantage substances. We can determine the is the ability to image the positron- rate at which cells utilize glucose emitting isotopes of carbon, oxygen, (the simple sugar fueling most of our nitrogen and fluorine. These isotopes tissues) from the uptake of the radio- are used to radiolabel water, carbo- active sugar analog FDG. Similarly hydrates, proteins, fats, vitamins and we measure perfusion, the rate at drugs-in short, nearly all the com- which oxygen and nutrients are de- pounds that living things metabolize livered to cells, by studying how tis- but cannot be effectively imaged by sues absorb radioactive water. the single-gamma technique.

18 SUMMER 1993 Vascular Metabolic Compartment Ca

Another important advantage is the not found by other imaging tech- great superiority of PET images to niques, and determine their spread the projection images of single- in order to plan appropriate therapy. gamma imaging. PET images have After treatment, it may be difficult Cell Membrane better spatial resolution and much to determine whether the cancer has - Capillary Membrane lower backgrounds, and they can be recurred, because the affected area is for the itself The compartmental model accurately corrected for gamma abnormal due to the disease metabolism of FDG [(F- 18)2-deoxy-2- attenuation and scattering. Because and the therapy. PET can often re- fluoro-D-glucose] in brain tissue. Models collimation of gamma rays is not solve the resulting ambiguity. of this type are used to relate tissue required, PET has a high efficiency A typical application of PET is in activity to metabolic activity, in this case compared to single-gamma imaging the workup of a patient with a lung the rate of glucose consumption. systems. mass that has been identified as can- PET is used for scientific studies cer. If the cancer is localized, the of the normal physiology of heart patient has a chance of being cured and brain, the organization of the by surgical removal of the diseased nervous system, and the abnormal portion. But lung cancer frequently metabolism of ischemic(blood spreads to lymph nodes in the chest starved) cardiac muscle. In clinical and to other parts of the body. Sur- settings, PET helps to diagnose dis- gery is not appropriate for patients eases of the brain such as Alzheimer's with such widespread disease. Che- disease, epilepsy and stroke, and to motherapy and radiation therapy of- diagnose heart disease and determine fer much better prospects for these whether bypass surgery is required. individuals. Especially in patients The importance of PET in the with chronic lung disease, which is study, diagnosis and treatment of particularly common in smokers, it cancer is rapidly increasing. Cancer is usually difficult to identify small cells are likely to metabolize glucose cancerous regions using other imag- faster than normal tissues. Some tu- ing techniques. PET, however, is very mors grow rapidly and require more sensitive to the presence of small sugar to meet their energy needs. cancers. Others consist of defective cells that In the early days of PET the em- use sugar inefficiently, obtaining phasis was on studying small organs energy from anaerobic metabolism such as the brain and heart. But with Projection image made from a PET scan (as opposed to the aerobic metabo- the advent of instruments that can of a patient originally thought-to have a solitary cancer. The large focus in the large parts of the body, the em- lism of normal tissue). Cancerous scan right chest is a primary lung carcinoma tissue usually appears as an area of phasis has shifted to whole-body and the smaller, less intense' foci are increased uptake in a PET scan using scanning, which is particularly valu- metastases to lymph nodes and to the a radioactive sugar as a tracer. Other able for the detection and character- abdomen. (This image and the ones on recently developed tracers include ization of cancers. A projection has pages 16 and 20 courtesy of the PET radioactive amino acids and nucleo- been reconstructed from the Center at the West Los Angeles sides (the building blocks of proteins tomographic data of a PET scan (see Veterans Administration Medical Center) and DNA) that appear to be valuable the photo on the right), made with in detecting cancers and distinguish- FDG as a tracer. There is an intense ing them from benign lesions. These focus of hypermetabolism, represent- techniques can detect cancers that ing a primary lung tumor, plus many are suspected from clinical tests but smaller foci in the lymph node chains

BEAM LINE 19 PET images of the brain of a patient with a form of continuous epilepsy. The dark areas represent neurons that fire continuously and consume much more glucose than normal tissue. During the first scan (top) the patient was lethargic and her EEG showed abnormal electrical activity. Note the dark area to the right of the image, indicating intense activity. During the second, she was fully aware and had reduced abnormal activity. The final scan, made after recovery from the seizure, also shows permanent damage due to a previous stroke. (Courtesy of Adrian Handforth)

of the chest and in the abdomen awareness. The PET scan showed that representing metastatic tumors. the left temporal lobe uptake was Many of the small tumors were not reduced but still abnormally high. A observed using other diagnostic im- third PET scan, at 10 weeks, showed aging techniques. that the left temporal lobe had re- PET is especially valuable in the duced metabolism compared to the diagnosis of epilepsy. Epileptic sei- right one, implying that it was in fact zures occur when nerve cells in the damaged. In this case the PET scan brain begin to fire in a continuous not only showed that epilepsy was and disorganized way. It is truly a the cause of the patient's altered functional lesion. There need be no mental state but settled the scien- structural abnormality although tific question as to whether the EEG there usually is one, frequently pattern seen was characteristic of a subtle. Epilepsy is often difficult to form of epilepsy. diagnose because seizures often occur at infrequent intervals, and the brain is difficult to examine anyway. ET IS A HIGHLY interdiscipli- Electroencephalography (EEG) is nary subject that requires the helpful but it is frequently ambigu- collaboration of physicists, chemists, ous and localizes lesions poorly. A physiologists and clinicians. There PET scan of an epileptic patient us- is a strong relationship between PET ing the sugar analog FDG often has a techniques and the accelerator, characteristic pattern, in which the detector, and computer technologies affected area of the brain has dimin- used in high energy and nuclear ished glucose uptake between sei- physics. Isotope production requires zures and greatly increased uptake particle beams similar in energy and while a seizure is occurring (because intensity to those used for the of the great energy requirement of injectors of accelerators dedicated to the continuously firing neurons). physics. In fact PET isotope pro- Many patients with intractable epi- duction at the Fermilab linac is being lepsy whose lesions are localized by considered. Recent advances in nega- PET are operated upon successfully tive ion acceleration and the devel- and their disease is either cured or opment of new types of linear accel- controlled. erators is directly applicable to PET. One epilepsy patient was an eld- The PET scanner uses precisely the erly woman who had suffered a cere- kind of crystal scintillation detectors bral hemorrhage several years be- and computer-based data-acquisition fore. She was found to be lethargic systems that constitute electro- and her EEG showed a particular pat- magnetic calorimeters in large high tern which was considered ambigu- energy and nuclear physics exper- ous for epilepsy. Her first PET scan iments. Multiwire proportional showed marked uptake of the FDG counters, developed by George tracer in part of her brain, the left Charpak for particle physics, have temporal lobe. During two weeks of been adapted for PET (although this treatment with anti-epileptic drugs, technology is not in the mainstream the patient gradually regained full yet). Rapid image reconstruction

20 SUMMER 1993 ;;; ;; :: iHB

BEAM LINE 21 22 SUMMER 1993 requires special-purpose computers rings, each containing 512 detectors, similar to those used for on-line contains over 12,000 detectors. Use- analysis in nuclear and particle ful PET images must have at least 1 physics experiments. million counts per tomographic The positron-emitting isotopes plane, which requires that the effi- used for PET are all short lived. Thus ciencies of these detectors be high they are usually produced on-site, by and that the data-acquisition system bombarding gas and liquid targets be able to handle high data rates. The with proton and deuteron beams from scintillating crystal Bismuth small cyclotrons in the 10-20 MeV Germanate (BGO) is the current stan- range. Some of the production reac- dard and gives a 90% detection effi- tions need targets composed of the ciency for elements that are 30 mil- rare and expensive isotopes 0-18, N- limeters deep. The need for timely 15 and C-13. Targets and computer- reconstruction of the images has led ized hot cells for automatic produc- to the development of fast proces- tion of radiopharmaceuticals are in- sors that sort the data as it is ac- tegrated with the cyclotron to allow quired and perform the reconstruc- frequent bombardments without the tion in fewer than several seconds operators receiving prohibitive ra- per image. The PET scanner depends diation doses. A PET cyclotron facil- crucially on recent developments in ity is largely self-shielded and detector and electronics technolo- installable in an ordinary laboratory. gies that originated with high energy Operator intervention is not required and nuclear physics, as well as on the from the beginning of bombardment rapid development of computing to receipt of final product. techniques. A useful scanner was The area of tracer development not even possible a decade ago. for PET has attracted organic chem- Medical imaging is now an im- ists and biochemists who use many portant U.S. industry. Its develop- of the techniques developed for phar- ments have led to diagnostic and maceutical design and synthesis. therapeutic breakthroughs in almost They are constrained by the minus- every area of medicine. The develop- cule quantities of radioisotope and ment of the instruments used in short times required for a PET syn- Positron Emission Tomography owes thesis, as well as by the biochemical a lot to the instrumentation used in requirements for a useful tracer. high energy and nuclear physics. New The modern PET scanner is ca- developments, such as smaller and pable of imaging the entire brain or more efficient accelerators, better heart and of performing a whole body particle detectors, improved electron- scan in an hour or less. To do so, its ics and computers, and more sophis- cylindrical array of detectors must ticated computational algorithms are be at least 70 cm in diameter and being actively sought by both disci- 10 cm long. Its spatial resolution plines. The continued vitality of high should be no worse than 5 millime- energy and nuclear physics research ters, which requires that each detec- will certainly lead to the develop- tor have transverse dimensions com- ment of better methods for advanced parable to this. A scanner with 24 medical imaging. O

BEAM LINE 23 SOME FAINT, PARTICULAR STARS Part 1

by VIRGINIA TRIMBLE

Supernovae, quasars, and Big Bangs are all very well, but most astronomers earn their precariouslivings by reading each other's papers about stars, many not much brighter than the sun.

!UCTURE AND EVOLUTION OF NORMAL STARS is the best- derstood part of modern astrophysics.* That is, we can (1) write wn a set of differential equations to describe the run of mass, I nperature, pressure, and luminosity with radius, (2) evaluate the rious functions in those equations on the basis of laboratory data d established theory for nuclear reaction rates, opacity to radiation, equations of state, and the like, (3) solve the equations nu- merically to get model stars, (4) evolve the models forward in time to get either evolutionary sequences for individual stars or snapshots of ensembles of stars with the same age but different rates of evolution, (6) compare the sequences and snapshots with observed properties of stars and clusters of stars, and (7) arrive at the happy outcome that most of our models correspond to real stars and most real stars can be modeled.

* Yes, I hear you out there mumbling "solarneutrino problem," but (a) the weak interaction physicists seem to want to take it away from astronomy and (b) even if it is ours, it corresponds to 10% errors or changes in stellartemperatures, lifetimes, etc., rather unimportantin the great scheme of things as represented on an envelope back or a T-shirt front.

24 SUMMER 1993 The main residual difficulties occur in the initial letters followed by the genitive of the constellation stages of star formation, where we don't quite know name, are very common. SS Cygni, U Geminorum, how to choose the dominant few of a very large number W Virginis, SX Phoenices, and DQ Herculis stars are of possible physical processes, and in the death-throes just a few of the kinds I won't discuss here. Still others, of massive stars, when it takes much more than an like the PG 1159 stars, carry names from catalog desig- hour of computing time to follow an hour's change in nations of the prototype. stellar conditions. A practicing astronomer is expected to be able to The stars that follow are not intended to make you recognize half a dozen or so of the commonest and most rush out to Sears and Roebuck in search of a replace- significant types; real pros (mostly of advanced years) ment theory. They are merely a bit weird or unex- may know 40 or 50. The main purpose in learning this pected. And they are all fairly faint, either in the sense or any other technical vocabulary outside your own of being not much brighter intrinsically than the sun or field is to enable you to ask questions in a way that will in the sense of being far enough away that not many provoke a serious answer. For example, think about photons reach us. Helena would probably not have your own potential responses to the questions (a) Could loved any of them. there still be a fourth family of leptons if they are too massive to be produced in Z0 decay? vs. (b) How many A WORD ABOUT NAMES elementary particles are there? With this justification in mind, I feel only slightly The main evolutionary categories of stars carry names apologetic about calling a spade a GD Agricolae imple- describing their locations on a graph of intrinsic lumi- ment fromjhere on. nosity vs. surface temperature, the HR diagram. The most populous, main sequence, region harbors stars VARIABLE STARS WITHOUT A CAUSE? burning hydrogen in their cores. The red giant branch stars burn hydrogen in thin shells; the horizontal Probably no star is truly constant in brightness. Cer- branch and clump stars are core helium burners; and so tainly the sun is not. It is brightening monotonically by forth. a part in 1010 per year. Its rays wax and wane with the More specialized classes are nearly always named 11 year solar cycle (by about 0.1%). And its surface for a prototype. This is not a common pattern in the quivers and shimmers in a rich array of oscillatory physical sciences, though paleontologists and arche- modes with periods of minutes and still smaller ampli- ologists sometimes name assemblages of fossils and tudes. But more conspicuous variability is normally artifacts for type-sites (e.g., Villafranchian fauna and associated with more conspicuous causes. Villanovan pottery). It is also not a very good pattern, The standard inventory includes regular pulsation because the name tells you nothing about the proper- in size and temperature (Cepheid, RR Lyrae, and many ties of the class. The astronomical version has the other variables); formation and dissipation of obscur- additional disadvantage of looking very untidy, being clouds in an extended atmosphere (the R Corona cause the prototype stars can have so many different Borealis stars); bright and dark patches on a rotating kinds of names. surface (BY Draconis and Am stars...and pulsars); sud- Thus there are classes named for naked eye stars like den release of stored magnetic energy (flare stars); and Algol and 6 Cephei (the Cepheid variables, for the companions that periodically block our view or distort fourth-brightest star in the constellation Cepheus). stellar shapes away from spherical symmetry (Algols, Variable star names, consisting of one or two capital W Ursa Majoris stars, and many others).

BEAM LINE 25 Kevin Krisciunas, right, with actor Richard Chamberlain at summit of Mauna Kea, Hawaii, during the filming of the PBS Kevin Krisciunas originally discovered the variability of series, "The Astronomers." (Courtesy Kevin Krisciunas) 9 Aurigae with this homemade 6-in. telescope, built when he was 13, in the backyard of his home near Los Gatos, For a handful of stars, none of these seems to work. California. The photometer and electronics were added ten No companions or dust are in sight; the periods are years later. (Courtesy Kevin Krisciunas) wrong for rotation or radial pulsation; etc. And yet the brightness varies. The most striking case is 9 Aurigae. energy transport. Convective stars are the ones that Marginally a naked eye star, at 5th magnitude,* it most often have spots, flares, and other surface displays 10% brightness fluctuations that are domi- blemishes. But our three "variables without a cause" nated by a period of 2.75 days, too long by a factor of 60 are apparently seen roughly pole-on, so rotation won't or so to be normal radial pulsations [which are driven make them vary. The awkward combination of by gravity and so have P = (Gp)-1/2]. The other members properties drove a recent collaboration (including Kevin of the class are y Doradus and HD 96008. Krisciunas of Hawaii and colleagues from Austin to In addition to their unexpected variability, the three Okayama) to suggest that they were seeing the have in common surface temperatures near 8500 K. spottiness expected for convective stars, but that the This is on the ragged edge between cooler stars (like the time scale was set by active areas forming and decaying. sun), in whose envelopes most of the energy is That isn't the right answer either. A set of radial transported by convection, and hotter stars (like Sirius velocity measurements of 9 Aurigae, made by Roger and Vega), in whose envelopes radiation suffices for Griffin of Cambridge, also shows variability, meaning that the surface of the star must be moving in and out, * Astronomers are especially attached to our strange units of but on a time scale possible only for something much energy received at the earth from cosmic objects-the Uhuru count, the fansky, the milliCrab, and the magnitude. A 5th more complicated than an ordinary breathing mode. magnitude star illuminates us with about 3.8 x 10-11 erg/cm2/ An interesting discovery with a down side. Stars in sec/Angstrom, and a 6th magnitude one (the naked eye limit yet another regime of temperature and luminosity can under favorable conditions) with 1.51 x 10-11.These numbers provide enough information to figure out the whole logarithmic no longer be counted on as standards against which to system, though I cannot imagine why you should want to. measure stars that you expect to be variable.

26 SUMMER 1993 CONTACT BINARIES IN OLD STAR CLUSTERS-WHENCE AND WHITHER? W Ursa Majoris stars are the conjoined twins* of astronomy, pairs of stars orbiting with their outer layers in physical contact, so that gas, energy and angular momentum are easily traded back and forth. V Despite the absence of customs barriers, the paired stars nearly always have different masses, luminosities, and sizes. W UMa's are moderately rare (perhaps one star in a thousand) and moderately difficult to model (the second law of thermodynamics doesn't really like prolonged contact between objects with different equilibrium temperatures). But the real prob- 0.5 1.0 1.5 lems are what comes before and after, and how long B-V does it all take? The problems are similar for the pre- and post-UMa Positions of cluster W Ursa Majoris stars in the HR diagram of of phases. Five billion years from now, our sun will the star cluster NGC 6791. H and R were Einar Hertzsprung Denmark and Henry Norris Russell of the USA, who indepen- expand as a red giant, eventually perhaps engulfing the dently thought of plotting the brightness or luminosity of stars inner planets. Contact binaries clearly can't do this. versus their spectral types (indicating surface temperatures). The first expanding envelope will quickly surround Working in the early 20th century, H and R had only photo- both stars, and the enhanced viscosity will lead to rapid graphic magnitudes as brightness measures and spectral merger of the stars and ejection of the envelope. Some types for temperature. Modern HR (or color-magnitude) other denizens of the astrophysical zoo, the FK Comae diagrams can use an assortment of magnitudes or loga- stars (rapidly rotating, rather unstable giants) are likely rithms of luminosity as the vertical axis, and spectral type, logarithm of temperature as the horizontal one. The post-merger product. color, or candidates for the immediate WUMa stars shown as triangles have a range of colors and There is also a space problem for the precursors of W brightnesses wider than that of the numerous single stars Ursa Majoris binaries. Stars form from collapsing cores shown as small dots in the diagram, but only the brightest W in clouds of interstellar gas and dust that start out as big UMa's have so far been detected as such. as the whole solar system. Thus contact systems present an extreme version of the problem of forming close apart (but still gravitationally bound together) and binaries in general. Solutions come in two classes. spiral gradually inward when angular momentum is First, a rapidly rotating core could bifurcate late in its lost in a magnetic wind, until they come into contact. collapse, giving rise to a zero-age contact system. If this In this case, w UMa's should turn up only when stellar is the right answer, we should find W UMa's among the populations age. They might also be rather short lived. youngest stellar populations, and they will gradually Unless achieving contact automatically turns off the disappear from older ones as the stars attempt to winds or the magnetic field, loss of angular momentum expand. Second, the two stars could form quite a ways will continue, and the stars will merge more rapidly than they would if driven only by expansion. find out the relative numbers *The authoris currently working on hei their Girl Person Scout Obviously we need to merit egalitarianbadge in political correctness. of W Ursa Majoris stars at different ages in order to

BEAM LINE 27 understand what is going on. Only recently has this become possible. Stars have to be in clusters to tell us their ages with any accuracy. And generations of astronomers have believed that the oldest, globular, clusters (Beam Line 22, No. 3, pp. 38-43) contained no binaries at all. The first "large" collection of w UMa candidates (six to be precise) in a globular cluster appeared in a widely-uncited 1984 paper by M. J. Irwin and V. Trimble. Since 1989, Mario Mateo of Carnegie Observatories and others have confirmed several of these and found additional contact binaries in other globular clusters. The numbers probably add up to rather less than one star in a thousand, but not by an enormous fraction. Thus, however contact binaries form, even the 1010 Roger Griffin in his early 20s, not long after the epoch of the year ages of globular clusters do not suffice to deplete variable-star light curves. (Courtesy Roger Griffin) the population drastically. Clusters 1-5 Gyr old also harbor W UMa's. Combing even in the age of the universe. Tempted, but perhaps both the skies and the literature, Janusz Kaluzny wrong. NGC 188, one of the best studied, old, but not (Warsaw) and Slavek Rucinski (Toronto) have found 67 globular, clusters, has seven contact systems, and no contact binaries scattered among nine clusters in that pairs of stars slightly further apart that could spiral in age range. Thus, however contact binaries die, 109 to replace these seven when they die. I don't know the years is long enough to make about as many as there are solution, but I certainly admire the problem! ever going to be at any one time. Only two younger clusters, the Hyades (108 years) and the Pleiades (107 years), have been searched RV TAURI VARIABLES: STARS THAT GO intensively for contact binaries. The brightest stars in BUMP IN THE NIGHT each cluster are naked eye objects, referred to as the head of Taurus the bull and the Seven Sisters (so called RV Tauri was the third of its class to be discovered, because there are six of them-look for yourself). The after R Scuti in 1795 and R Sagittae in 1859, but the first W Ursa Majoris stars are not naked eye objects. In fact, to be watched long enough for the defining property of they are not even telescopic objects, because none has the group to show up. The brightness variations of RV been found in either cluster. Tauri stars, even with charity, can at best be described More work is needed (and the check is in the mail). as semi-regular (see figures at the top of the next page). One is, however, greatly tempted to conclude that very But one clear pattern jumps out at you. The light young contact binaries are rare or non-existent. In- minima alternate between deep and shallow. stead, w UMa's arise slowly, but continuously, in aging Not surprisingly, the unsolved problem is figuring stellar populations, as wider binaries spiral together out the physical mechanism responsible for this alter- into contact systems, and then gradually merge into FK nation. It is quite easy to make a model star exhibit RV Comae stars (or whatever), while their place is taken by Tauri behavior. Robert Christy, who developed the others, the supply of progenitors not being exhausted first fully non-linear stellar pulsation code,* found

28 SUMMER 1993 SS Cygni in recent years, as recorded by members of the American Associa- tion of Variable Star Observers. Com- parison with the graph on the left suggests that averaging the 2 observations of many astronomers will improve the calibration of exact The brightness of RV Tauri and other variable stars from late brightnesses but not the determination of the characteristic 1953 to 1956 as recorded (and interpolated with dotted light curve shape. (Courtesy Dr. Janet Mattei, director, lines) by Roger Griffin (also the observer of radial velocity AAVSO) variations in 9 Aurigae). Alternation of deep and shallow light minima is the defining characteristic of the class of which RV Tauri is the prototype. By contrast, SS Cygni, the prototype of out, imparting red and blue doppler shifts to spectral a very different sort of variable, always returns to the same lines, and these calculated shifts are not good fits to the minimum brightness, though the maxima vary somewhat. data. In fact, spectroscopists working on the problem, from Helmut Abt in 1955 on down to the present, have such alternation in his models when he cranked up the tended to believe that the short, half-period is the basic luminosity too high. Even I, slightly adapting the one. The evidence is that a separate set of absorption Christy code to deal with stars completely lacking lines appears at the end of each light maximum, evolves hydrogen, found "RV Tauri type behavior" for suffi- to larger velocities, and then disappears at the next ciently large luminosities twenty-some years ago. In maximum. This means that a separate shock wave these models, the cause is an alternation of construc- moves through the stellar atmosphere during each tive and destructive interference between the funda- cycle, whether large or small. Predictably, the deeper mental mode and a first overtone with two-thirds its minima go with larger displacements of the stars' outer period. In this model, the fundamental is actually the layers. long, double, period between (for instance) successive Some other suggested mechanisms would accord deep maxima. with the half-period being the basic one. These include Unfortunately, a model is not a star, and correspon- damping of convection in the atmosphere during alter- dence in one property is no guarantee that you have the nate cycles and rotation of a spotted surface superim- physics right, particularly in this case. None of the posed on the pulsation. Neither has been explored in calculations has ever been done with the correct chemi- great detail, and neither prompts one to say gleefully, cal composition to represent stars as old and metal- "That's it. Why didn't I think of it?" deficient as the RV Tauri variables. The code also tells The first person who ever told me about RV Tauri you how the atmosphere of the star should move in and stars described the situation this way. A pulsation cycle lifts the outer atmosphere up so high that it doesn't have time to fall back down again all the way while at Los Alamos, developed *Yes, he is the same person who, outward. Thus the the design sometimes called the Christy bomb. I don't under- before the next cycle starts stand how it works either. downflowing gas bumps against the upwelling gas and

BEAM LINE 29 keeps it from going very far. Then the atmosphere, not having been lifted so far, has time to fall back all the way and follow the third cycle, which is large again, and so forth. I wish I could remember who said this, because it sounds like the right answer, though a few additional calculations may be needed.

PREVIEW OF COMING ATTRACTIONS

"Some Faint, Particular Stars (Part 2)" will include Geminga (the nearest gamma ray pulsar), FG Sagittae (the galloping G giant), dwarf carbon stars, and perhaps some other sorts. It will also explain about Helena and particular stars, in case your copy of Bartlett has disappeared. O

Dates To Remember

Sep 8-10 Workshop on Photocathodes for Polarized Electron Sources for Accelerators, Stanford, California (Maura Chatwell, SLAC, MS 66, P.O. Box 4349, Stanford, CA 94309 or [email protected]).

Sep 19-23 Third International Workshop on Theory and Phenomenology in Astroparticle and Underground Physics (TAUP 93), Assergi, Italy (by invitation) [Laboratori Nazionali del Gran Sasso, 1-67010 Assergi, Italy, phone (862) 437231 or [email protected] or FAX (862) 410795].

Sep 20-24 13th International Conference on Magnet Technology, Victoria, Canada (P. A. Reeve, TRIUMF, Depart. Physics and Astronomy, University of Victoria, Box 3055, Victoria, B.C., Canada V8W 3P6 or [email protected]).

Oct 4-8 RF Superconductivity, Newport News, Virginia (Julie Oyer, CEBAF, 12000 Jefferson Avenue, Newport News, VA 23606).

Oct 13-21 5th International Workshop on Next-Generation Linear Colliders, Stanford, California (Kathy Asher, SLAC, MS 24, Box 4349, Stanford, CA 94309 or [email protected]).

Oct 31-Nov 6 IEEE Nuclear Science Symposium, San Francisco, California (E. J. Lampo, Lawrence Berkeley Laboratory, MS 29-100, 1 Cyclotron Road, Berkeley, CA 94720 or [email protected]).

30 SUMMER 1993 * \A A 1 A . X X A A , . A A A A A IA A e t ... -fc* N. -...... - a:-S . M -l

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Probing the TeV Energy Scale

by FRED HARRIS and XERXES TATA

A review of the Second Workshop on Physics and Experiments with Linear e+e- Colliders by two of its participants.

LMOST TWO HUNDRED PHYSICISTS from North b P America, Europe and Asia met to discuss the / physics possibilities of linear electron-positron / - colliders at the Second International Workshop on Physics and Experiments at Linear e+e- Colliders. This meeting was held during the last week of April at Waikoloa on the Big Island of Hawaii. It was the second in a series of international workshops that began north of the Arctic Circle in Saariselka, Finland, in September 1991. Organized by the High Energy Physics Group at the University of Hawaii, the gather- ing was sponsored by SLAC and KEK with additional support from the Department of Energy, the National Science Founda- tion, the International Science Foundation, and the University of Hawaii.

BEAM LINE 31 The main theme of the workshop was the physics present and future accelerators such as the SSC and reach of-and the feasibility of experiments at-linear LHC. The status of the SLC, important to the develop- e+e- colliders operating in the center-of-mass energy ment of the technology needed for the NLC, together region from -300 GeV to 2 TeV. Also discussed were with physics results from the SLD experiment, was the prospects for physics at ey, yy, and e-e- colliders. reported by Martin Breidenbach of SLAC. Then Bj6rn The program included both plenary and parallel ses- Wiik of DESY described the various linear collider sions. While the plenary sessions focussed on over- designs being pursued, including their problems and views of the major issues and summaries of new re- progress. He predicted that by 1996-97, it should be sults, the parallel sessions allowed ample opportunity possible to write a proposal for a 500 GeV linear collider for specialized discussions among experts. A variety of including a reliable cost estimate. topics were discussed at the meeting, including top The opening session was followed by a busy day and physics, extended gauge sector, gamma-gamma phys- a half of parallel sessions, where results of many de- ics, the Higgs boson, QCD, properties of gauge bosons, tailed studies were presented. These discussions mainly supersymmetry, and strong symmetry breaking inter- focussed on experiments to study physics at or beyond actions. the electroweak scale, and on a comparison of the In his opening talk, Daniel Treille of CERN dis- physics capabilities of linear colliders and hadron cussed the physics potential of a linear collider in light supercolliders. A central issue was the search for phys- of current knowledge and possible new results from ics beyond the Standard Model, which, together with the Higgs boson search, constitute the principal raison Pisin Chen of SLAC, Guy Coignet (center) of LAPP Annecy, d'etre for the exploration of the TeV energy scale. and Daniel Treille of CERN participate in a group discussion. While much of this exploration can indeed be done at the hadron supercolliders, the cleanliness of events at high energy e+e- colliders make them ideally suited for experiments that elucidate the nature of any "new physics," demonstrating the complementary aspects of electron-positron and hadron-hadron supercolliders. The feasibility of yy, ey, and e-e- colliders and the physics merits of these machines were also addressed in these sessions. Workshop participants concurred that linear colliders operating at 250-500 GeV are optimal for studying the Standard Model Higgs boson in the intermedi- ate mass range. For example, it should be possible to discover at least one of the Higgs bosons in the minimal supersymmetric model at these machines. And, with an integrated luminosity of aboutlO fb- 1, it should be possible to distinguish between the Standard Model and supersymmetric Higgs bosons over a wide range of parameters. The high luminosity together with the cleanliness inherent in e+e- collisions will allow for experiments to make precise measurements of the

32 SUMMER 1993 ¢ I+ I Martin Breidenbach, William Ash, and Robert Messner of SLAC enjoy a leisure Peter Zerwas, left, of DESY and Stanley Xerxes Tata, left, of the University of moment during a break in the workshop. Brodsky of SLAC. Hawaii and Michael Peskin of SLAC. top quark and W boson properties (masses, rare decays, the major physics topics discussed at the meeting: anomalous couplings, etc.), permitting stringent tests topquark physics, gauge boson properties, Higgs boson of the Standard Model at the scale of electroweak physics, supersymmetry, and yyinteractions. The pos- symmetry breaking. sibility of extended gauge sectors as well as of strong Another subject discussed extensively concerned electroweak symmetry breaking sector was also re- the prospects for discovering supersymmetric particles. viewed. Representatives from the various laboratories Participants addressed the feasibility of using the prop- discussed the development of linear colliders at CERN, erties of such particles, as measured in experiments at DESY, KEK, Novosibirsk, and SLAC. New develop- linear colliders, to study the physics of supersymmetry ments in polarization were reported by Charles Prescott breaking. of SLAC, while William Ash of SLAC summarized Other subjects discussed at the meeting included: experimentatal issues. extra gauge bosons of extended gauge groups, the pos- In his summary talk, Seigi Iwata (KEK) emphasized sibility of strong symmetry-breaking interactions, and the importance of linear e+e- colliders, as not only a the importance of the hadronic structure of the photon stringent testing ground for the Standard Model but for the design of the beams and detectors. In the session also a facility where spectacular new physics discoveries on yycollisions, Z° pair production was identified as a might be possible. Extending an invitation to the next potentially important background for studies of Higgs workshop in this series, which will be held in Japan in boson properties. Participants considered the possibil- the fall of 1995, he thankfully contradicted the earlier ity of constructing a low energy rycollider for a study extrapolation of banquet speaker Richard Taylor of of resonance physics and perturbative QCD. SLAC, who used the location of the previous and present The final two days of the workshop were devoted to workshops and a globe to predict that it would be held an overview and summary of the multitude of results in Antarctica. presented during the parallel sessions. There were 0 separate experimental and theoretical plenary talks reviewing the status and new developments of each of

BEAM LINE 33 PEOPLE AND EVENTS

Lederman Receives Fermi Award

Leon Lederman, Director Emeritus of the Fermi National Accelerator Laboratory, is a winner of the 1992 Enrico Fermi Award. He received this award, which includes a gold medal and a $100,000 honorarium, from Secretary of Energy Hazel O'Leary on July 29, 1993. It was presented to Lederman "for his pioneering scientific achievements in high energy physics, exemplified by his discovery of the upsilon particle and the muon neutrino; for his leadership in the creation of the world's first major superconducting accelerator at Fermilab; and for his leadership in science education at all levels of society." The U.S. Government's oldest and one of its most prestigious awards for science and technology, the Fermi Award is given for a lifetime of achievement in the field of nuclear energy. Past winners include Ernest Lawrence (1957), J. Robert Oppenheimer (1963), Wolfgang K. H. Panofsky (1978), Robert R. Wilson (1984), and Victor Weisskopf (1988). Also receiving , 1 1_1 d £...... O 1- ..£ .f. . -TT n .1n.1DnR .. , Tc,-1, tne awaru tnis year were rormer secretary uir Leclnise naruiu Drouwii diiu Ju II S. Foster, for their contributions to nuclear deterrence and their leadership of the Lawrence Livermore National Laboratory.

Hawaii's Vincent Peterson Retires

Thirty years ago Vincent Peterson, Wolfgang K. H. Panofsky's first Ph.D. student at the University of California, Berkeley, formed the University of Hawaii's High Energy Group. Until this year he served as its Principal Investigator. The original group included Peterson, Robert Cence and Victor Stenger. Today, it includes 17 physicists, 9 staff members, and 8 graduate students. To date it has produced 31 Ph.D. physicists. In 1965 Peterson organized the first of a successful series of Summer Schools in High Energy Physics as a way to put Hawaii on the high energy physics map. Four outstanding speakers were invited to present a series of talks to recent graduates from all over the world. The tenth and last Hawaii Summer School was held in 1985. In the early 1970s, Peterson led the group into a bubble chamber collaboration with a Berkeley group under M. Lynn Stevenson. They built a device using delay line proportional chambers to identify muons from neutrino interactions in the bubble chamber. It was so successful that the Hawaii- Berkeley team was invited to collaborate on a series of six experiments with

34 SUMMER 1993 many other groups, leading to a twenty-year program in neutrino bubble chamber physics with Ha- waii recognized as one of the leaders. Building new hardware as an entree into new experimental efforts became the modus operandi for the Hawaii group under Peterson. The group built proportional chambers for a free quark search on the PEP collider at SLAC. State-of-the-art silicon strip detectors with large-scale integration readout chips became the entree into the MARK II experiment, which finished taking data at the Stanford Linear Collider in 1990. Sherwood Parker of the Hawaii group became a recognized world expert on f- f vr ini AT , rt- an -41,llCtl - -UseolI'I -r 1 I 1 oiKIUelCL;LUIIIcL UeCVIC;S 111 high energy physics. Peterson and Vince Peterson flanked by friends and colleagues at the recent th Linear e' e - Parker received a grant from the Workshop on Physics and Experiments wi TexasNational Res h L y Colliders. Left to right, Mike Peters, Steve Olsen and Peterson of Texas National Research Laboratory Hawaii, and Gert Harigelof CERN. Commission to develop silicon pixel devices with on-chip readout for use in SSC detectors. Initial prototype tests of these devices have been very successful. In the middle 1970s, a meeting held in Hawaii explored the possibility of building an underwater detector, dubbed DUMAND for Deep Underwater Muon and Neutrino Detector, to detect high energy neutrinos coming from astrophysical sources. Thus began the entry of the Hawaii group into non- accelerator particle physics. Within a couple of years, John Learned and Arthur Roberts joined the Hawaii group to begin studies along with Peterson and Stenger on the feasibility of such a detector. This experiment did not fit into the usual funding scenarios. It is a tribute to Peterson and the others involved that-through hard work, patience, and dogged determination- approval for phase one of DUMAND was recently given by DOE. The first three strings of detectors will be deployed in the ocean off the Big Island late this year. Far from enjoying the surf and sand in Hawaii, Peterson will continue to work with Sherwood Parker on silicon pixel development. Stephen L. Olsen, formerly of the University of Rochester, will replace Peterson as the group's new Principal Investigator.

BEAM LINE 35 SLAC Scientist GerhardFischer Dies Suddenly

Gerhard Emil Fischer, a senior scientist and one of the leading innovators of the Stanford Linear Accelerator Center, died February 7 of a heart attack. He was 64. Fischer came to SLAC in 1965 to work on the design and construction of the SPEAR electron-positron storage ring and had a major role in the development of the Stanford Linear Collider. Fischer, called "Gerry" by his colleagues, was born in Berlin, March 1, 1928, the son of a biochemist and the grandson of Emil Fischer, who won the Nobel Prize in chemistry in 1902. His family fled Nazi Germany in the late 1930s, settling in Canada. He received his undergraduate degree from the University of Toronto in 1949 and went to the Radiation Laboratory at the University of California, earning his doctorate in physics in 1954, with a dissertation on proton scattering. At Berkeley he began his life-long interest in accelerator physics. Fischer taught at Columbia University for five years and continued his research at Columbia's cyclotrons. In 1959, he moved to the Cambridge Electron Accelerator at Harvard, for a time the highest-energy electron accelerator in the world. Fischer believed the future of high-energy physics Gerhard Emil Fischer, 1928-1993 would be at electron-positron colliders and worked with a group to have one constructed in Cambridge, Massachusetts. When the Atomic Energy Com- mission decided to build such a device at Stanford rather than Harvard, he moved west to work on the SPEAR ring with Burton Richter. Fischer was a key member of the storage ring research and development team, and while the ring was being built, he participated in a series of fixed- target experiments. He was responsible for the injection system into the SPEAR ring, and designed the large solenoidal magnet for the MARK I particle detector used to carry out the experiments. He also was among the authors of the papers that announced the discovery of several elementary particles and was a ranking authority on understanding beam motion and instabilities in storage rings. Fischer was one of the first to recognize the significance of SPEAR as a source of synchrotron radiation. He also was key to the development of the PEP collider, a joint program between SLAC and the Lawrence Berkeley Laboratory. In the 1980s, Fischer moved to the linear collider project, in which electrons and positrons could be accelerated simultaneously, separated and then collided together, an innovative tool for particle physics. Fischer was project manager for the first damping ring and designed the unique alternat- ing-gradient magnets that make up the curving arcs of the collider. At the

36 SUMMER 1993 time of his death, he was working on research into the next generation of linear colliders. Gerry Fischer was our colleague and close friend. He was exceptionally skillful at what he did, helpful to others in more ways than can be recounted, and a friend and mentor to many.

Jackson Laslett Dies at 80

On May 7, 1993, Lawrence Jackson Laslett passed away at the age of 80. One of Ernest Lawrence's graduate students, Laslett went on to make important scientific contributions to the design of particle accelerators. His generous, gentle spirit will be missed as much as his scientific contributions. Laslett was born in Boston and grew up in Southern California. He completed his undergraduate education at the California Institute of Tech- nology, and his graduate work at Berkeley. Following the completion of his Ph.D. in 1937, he went to Europe where he and Sten von Friesen built the first European cyclotron, in Copenhagen. Following the war, Laslett joined the faculty of Iowa State University. He made many significant and meticulous contributions to weak-focusing synchrotron design, and was active in photo-nuclear research, gamma-ray and electron spectroscopy and spectrometer design. As a participant in the Midwestern Universities Research Association (MURA), he was a leader in the development of the theory of strong-focusing accelerators, whose design principles are still used in modern particle accelerators and colliders. In 1955 Laslett became interested in digital computation, a tool that he used with precision and delight for the rest of his career. In that year he did the first digital computations of magnetic fields with James Snyder and Richard Christian, using an ingenious system to include magnet currents. The three of them developed an integrated series of programs to calculate magnetic fields and particle orbits. These programs, and their descendants, now play a crucial role in the design of accelerators. At MURA, Laslett began work in the field of stochastic phenomena. By very careful attention to detail, he was the first to show by digital computation that there is a real phenomenon of chaos, beyond any roundoff or truncation errors. He continued to work in this field well beyond his retirement. Laslett was also active in government service. During World War II he worked on development of airborne radar at the MIT Radiation Laboratory. He was a member of the Office of Naval Research in Washington in 1952-

BEAM LINE 37 1953, and later in London in 1960-61. From 1961 to 1963 he worked at the Atomic Energy Commission, where he established the Office of High Energy Physics. In 1963 Laslett returned to Berkeley, where he worked on the 200-BeV accelerator design. He also made major contributions to the Electron Ring Accel- erator design and to all aspects of the Heavy Ion Fusion accelerator program. His landmark work on collective instabilities, written in collaboration with Andrew Sessler and V. Kelvin Neil, opened an entirely new aspect of accelerator physics. Laslett retired in 1987 but continued to work at the laboratory until just before his death. At the time of his retirement, his most important papers were collected 0oo an and published by the laboratory. The sheer volume of (a the work was startling-many hundreds of papers and

a) (1)a reports touching almost every topic in accelerator o c physics. co On a personal level, Laslett's contributions and _j influence were immense. He was exceedin plv modest Jackson Laslett, left, Bob Thornton, top, and John Bakus in but quietly shared his insights, work and perspective. the dee stem tank of the 60-inch (Crocker) cyclotron before it Numerous figures in the field today revere him as a was assembled at the old Radiation Laboratory on the mentor. He was a splendid scientist and person; he will University of California campus. biebe sorely missed.

38 SUMMER 1993 FROM THE EDITORS' DESK

D URING THE PAST FEW YEARS the Beam Line has gradually been finding its way beyond the immediate scientific community for which it is intended and the into the hands of people in government, commerce and education who want to know more about what particle physicists do. Articles such as Patricia Burchat's lead article on the Standard Model, which appeals to an educated but not necessarily scientific readership, help us reach this expanded audience. She explains the insights of particle physics in language these new readers can readily understand. Others, such as Mark Mandelkern's article on page 15 about Positron Emission Tomography, appeal to scientists and general readers alike. Both audiences will probably be interested in learning how recent advances in nuclear and particle physics are being adapted for use in modern medical-imaging equip- ment that allows physicians to observe physiological processes as they occur within the human body. Articles like these help communicate the benefits of basic research-be they advanced technologies or a deeper understanding of Nature. With the need for basic research coming under increasing attack in Washington and elsewhere, it is helpful to remind readers about its positive impact on their lives. We think the Beam Line can play a small role in helping to communicate the value of basic research. We look forward to your help and suggestions in achieving that goal.

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BEAM LINE 39 CONTRIBUTORS

J. L. HEILBRON, Professor of History and the History of Science, MARK MANDELKERN is a is Vice Chancellor at the Univer- Professor of Physics at UC Irvine sity of California, Berkeley. He and the Principal Scientist of the PAT BURCHAT, currently an writes about the history of the PET Center at the West Los Ange- Associate Professor of Physics at physical sciences and their institu- les VA Medical Center. He is also UC Santa Cruz, is working on the tional settings during early modern Clinical Professor of Radiological development of a design for a times and also during the 20th Sciences at UCLA. He earned his silicon-based vertex detector for an century. His work on the earlier Ph.D. in physics from the Univer- asymmetric B factory detector. She period includes Electricity in the sity of California, Berkeley and an her B.S. in applied science earned 17th and 18th Centuries: A Study M.D. from the University of from the Univer- and engineering in Early Modern Physics (1979), Miami; he is board certified in sity of Toronto and a Ph.D. in Elements of Early Modern Physics nuclear medicine. In addition to physics from Stanford University (1981), and Physics at the Royal his PET research on cancer and the in 1986. Pat is currently a member Society during Newton's Presi- brain, Mark is currently working of the Fermilab E791 collaboration, dency (1983). His work on more on a Fermilab experiment studying studying the production and decay recent subjects includes Dilemmas the production and decay of of charmed hadrons. She has two of an Upright Man: Max Planck as charmonium. He has three chil- children, Matthew (4 years old) and Spokesman for German Science dren, India (10), Benjamin (8), and Michael (1). (1989), and in collaboration with Seth (5). R. W. Seidel, A History of the Lawrence Berkeley Laboratory, Vol. I, Lawrence and his Laboratory (1990).

40 SUMMER 1993 VIRGINIA TRIMBLE divides her time between the Physics Depart- ment at the University of Califor- nia, Irvine, and the Astronomy Department of the University of Maryland, College Park. Her degrees are from UCLA (B.A.), California Institute of Technology (M.S., Ph.D.), and Cambridge University (M.A.). She was the 1986 recipient of the U.S.National Academy of Sciences Award for scientific reviewing and currently serves as editor of Comments on Astrophysics and associate editor of the Astrophysical Journal.

Xerxes Tata, left, San Fu Tuan, and Fred Harris, colleagues at the University of Hawaii, during the recent Workshop on Physics and Experiments at Linear e e- Colliders.

FRED HARRIS is a Professor of Physics at the University of Hawaii, which he joined in 1970, after receiving at Ph.D. from the University of Michigan. He helped to build the external muon identifier for the 15-foot bubble chamber, which led to his participation in a long series of neutrino bubble chamber experiments at Fermilab. In 1978, he joined the free quark search at PEP, followed by the Mark II upgrade experiments at PEP and the SLC. Since the finish of Mark II, he has worked on B Factory computing R&D. Fred served as Chairman of the Local Organizing Committee for the recent Hawaii Workshop.

XERXES TATA is an Associate Professor in the Physics Department at the University of Hawaii, which he joined in 1988 after postdoctoral stints at the University of Texas, the University of Oregon, CERN, and the University of Wisconsin. He has also been a visiting scientist at KEK. Tata is a theoretical physicist with broad interests in theory and phenomenology of the Standard Model and beyond. His recent work has mainly focused on devising strategies for the detection of new physics in experiments at high energy colliders, with emphasis on Higgs boson searches and supersymmetry.

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