My own career in science has been intimately tied up in the transition from the old fixed-target technique to colliding-beam work. I have led a kind of double life as both a machine builder and as an experimenter, taking part in building and using the first of the colliding-beam machines, the Princeton–Stanford Electron–Electron Collider, and building the most recent advance in the technology, the Stanford Linear Collider. The beginning was in 1958 and, in the more than three decades since, there has been a succession of both electron and proton colliders that have increased the available center-of-mass energy for hard collisions by more than a factor of 1000.

The history of that advance for both electron and proton colliders (constituent center-of-mass energy is plotted versus time of the first physics experiment) is shown in Fig. 15.1. The important number for the experimenter, the constituent center-of-mass energy, has increased by about a factor of 10 every 12 years for both kinds of systems. On the electron line, one can see a kind of complete cycle in accelerator technology from the birth of the colliding-beam storage ring, to its culmination in LEP II, and the beginning of the next technique for high-energy electron collisions, the linear collider. On the proton line, one has gone from the first bold initiative, the ISR at CERN, which used conventional magnets, to the superconducting magnets that are used in all proton colliders built today.

I begin this chapter with the period 1965–1974 when my colleagues and I worked experimentally on the e–μ problem and I became immersed in the then hypothetical world of heavy leptons. I go on to describe the discovery, in the period 1974–1976, of the tau lepton by myself and my colleagues using the SLAC–LBL I detector at the SPEAR e+e− storage ring. I then recount the verification of our discovery by ourselves and others, research that occupied the years 1976 through 1978. In the final section I describe the period 1978–1985, in which the transition was made in experiment and theory to the modern phase of tau research. I have told much of this history in a paper given at the first Workshop on Tau Lepton Physics and so I have repeated here quite a bit of material from that paper. A beautiful description of the discovery of the tau was given recently by Gary Feldman. The discovery of the tau was the subject of a doctoral thesis by Jonathan Treitel at Stanford University.

Before the tau: 1965–1974

The e-μ problem

The history of the discovery of the tau lepton begins in the late 1960s, when my colleagues and I and other experimenters worked on the problem, “How does the muon differ from the electron?” In fact, that was the title of a paper I wrote for Physics Today in 1971.

Professor Murray Gell-Mann told us how, in 1963, in a submission to Physics Letters, he “employed the term ‘mathematical’ for quarks that would not emerge singly and ‘real’ for quarks that would.” Three years later he offered an improved “characterization of mathematical quarks by describing them in terms of the limit of an infinite potential, essentially the way confinement is regarded today. Thus what I meant by ‘mathematical’ for quarks is what is now generally thought to be both true and predicted by QCD.” But in using the term “mathematical” Professor Gell-Mann got himself into some hot water, for “up to the present, numerous authors keep stating or implying that when I wrote that quarks were likely to be ‘mathematical’ and unlikely to be ‘real,’ I meant that they somehow weren't there. Of course, I meant nothing of the kind.”

How did Gell-Mann get himself into this little predicament? “I did not want to call [confined] quarks ‘real’ because I wanted to avoid painful arguments with philosophers about the reality of permanently confined objects. In view of the widespread misunderstanding of my carefully explained notation, I should probably have ignored the philosopher problem and used different words.”

At the conference Gell-Mann told us about the doctor's prescription he kept posted in his office admonishing him not to debate philosophers, suggesting that his choice of the word “mathematical” was his effort to follow the prescription.

This is the history of the proof of renormalizability of gauge theories as I perceive it. It is a personal account.

The importance of the proof of renormalizability is well known to all. Personally I have always felt that the proof was much more important than the actual construction of a model, the Standard Model. I felt that, once you knew the recipe, the road to a realistic description of Nature would be a matter of time and experiment. There some may disagree with me; I think, however, that a careful study of the recent history of high-energy physics will lead to this conclusion. Seldom has there been such a clear watershed. Old models, truly “dormant” (as Steven Weinberg put it), became credible and popular. Quantum chromodynamics came into being almost overnight. The proof of renormalizability also provided detailed technical methods such as, for example, suitable regularization methods, next to indispensable for any practical application of the theory. In longer perspective, the developments in supersymmetry and supergravity have been stimulated and enhanced by the renewed respectability of renormalizable field theory (including the absence of anomalies). If anything “turned the wheel,” as SLAC people have put it, it is this proof of renormalizability. Of course, the theory needs experimental verification, and whether people were convinced after the discovery of neutral currents, or after the discovery of charm, or W and Z, is another matter.

In a scientific discipline that went from experiments with less electronics than a videocassette recorder to 105 channels and from collaborations with 5–10 members to 300 during the years 1964–1979, the notion of what high-energy physics is, or what constitutes being a high-energy physicist, cannot be viewed simply as an immutable category that is “out there” – that remains fixed despite these and other developments. What high energy physics is as a discipline and what it means to be a high-energy physicist are renegotiated by participants relative to the experimental and theoretical practices of the field at any given time. In this chapter I will explore some of the sociological consequences of the decisions made by high-energy physicists as they constructed the edifice that has come to be known as the Standard Model.

Many of these physicists' decisions about the Standard Model have already been carefully documented in Andrew Pickering's sociological history of the development of particle physics, as well as numerous chapters from this volume.

The electroweak sector of the Standard Model contains three logically and historically distinct elements:

1. 1. A chiral gauge theory of weak interactions with an exact SU(2)L symmetry;

2. 2. The Higgs mechanism for spontaneous symmetry breaking, giving some of the gauge bosons finite masses, while maintaining renormalizability;

3. 3. Electroweak unification through W0—B0 mixing by sin θw.5

This report is concerned with the early history of the electroweak sector of the Standard Model. I first recall the history of gauge theories in the 1950s and my own motivation for publishing the first chiral gauge theory of weak interactions, predicting weak neutral currents of exact V–A form and approximately the weak strength observed fifteen years later. Then I discuss the evolving appreciation of the fundamental distinctions between global and gauge, partial and exact symmetries, in the weak and strong interactions. Finally, I emphasize that exact gauge symmetry is necessary for the Higgs mechanism for symmetry breaking, but that electroweak unification is not required theoretically: Within the Standard Model, the electroweak mixing angle, sinθw, is not determined, but could have any value, including zero. This leads to an interesting difference between the sin θw = 0 limit of the unified electroweak theory and the original SU(2)w gauge theory of weak interactions alone.

Theoretical consistency requires that a field theory be renormalizable, not necessarily unified.

There are two questions I want to address in this chapter. First, what is the evidential status of entities such as quarks and theories such as quantum chromodynamics, or QCD? In particular, is there a special problematic associated with just these entities and this theory?

But that leads to the second question of a more general nature: What is the evidential status of any theoretical entities and their properties and relations as encoded in some area of theoretical discourse? The second question touches on a central concern of general philosophy of science. But let me start with the first question.

Quarks first came into the physics vocabulary via the fundamental representation of the SU(3) symmetry introduced into hadronic physics in 1964 by Murray Gell-Mann and George Zweig. The actual known particles were associated with higher-dimensional representations of the symmetry, such as the octet, the original Eightfold Way. The quarks were at first a somewhat shadowy substratum for building up the particles actually observed in Nature (in particular the famously predicted Ω−). I say shadowy because one could, for example, abstract from the quarks an algebra of currents, take this algebra seriously and discard the quarks – throwing away the ladder after making the ascent, so to speak. But then, in the late 1960s, came the deep-inelastic electron scattering experiments at SLAC, the verification of Bjorken scaling, and its immediate interpretation in terms of pointlike constituents, the parton model of the nucleons.

I do not claim any deep understanding of Finnegans Wake, but I believe that, had Murray Gell-Mann known the existence of more than three elementary constituents of hadronic matter, he would have chosen a different name. This paper is my recollection of the events that led to the conjecture about a lepton–hadron symmetric world. I want to warn the reader that, as I discovered experimentally, my memory is partial and selective. I would have been particularly worried by this discovery, had I not discovered at the same time that I share this human defect with practically all my colleagues. The difference is that most people are not aware of it, as I was not a couple of years ago, and, furthermore, different people forget or distort different things.

As far as I am concerned, the story begins around 1967 or 1968. I was on a postdoctoral fellowship at CERN coming from the University of Paris at Orsay, where I had done my thesis work under the direction of Philippe Meyer and Claude Bouchiat. I came to CERN in September 1966 and started working on current algebra, one of the most fashionable subjects at that time. Together with other postdocs and visitors, we formed a band of joyful youngsters, enjoying tremendously both physics and skiing, mountaineering, eating, drinking, and so on. We were not doing much in terms of physics, but as David Sutherland, a member of the band, put it, we were doing it in great style.

There is a remarkable similarity among the modern collider detectors operating at many diverse facilities. For example, the experiments running for the past several years at LEP, the SLD detector just beginning to operate at the SLAC Linear Collider, the detectors now coming into operation at HERA, and those planned for the SSC and CERN's Large Hadron Collider all look quite similar to one another even though the colliders on which they function are quite different. I believe that there are simple and understandable reasons for this similarity.

The present situation contrasts markedly with that of the detectors employed in the first collider experiments during late 1960s and early 1970s – essentially the same period we are studying at this Symposium. In the early colliding-beam experiments, many different detector architectures were tried; out of all those ideas came a “standard model” of detectors, the cylindrically symmetric, solenoid-magnet detector that so dominates colliding-beam experiments today. For example, the first detectors at the early storage rings – CBX at Stanford, ACO at Orsay, the VEPP machines at Novosibirsk – were visual detectors, involving spark chambers and other techniques; they were designed to study specific final states over limited ranges of solid angle, with little or no particle identification, limited trigger capability, and no momentum analysis. They were not, as one would say today, general-purpose detectors.

In 1978 a team of twenty physicists performed an experiment at SLAC that demonstrated convincingly that the weak and electromagnetic forces were acting together in a fundamental process, the inelastic scattering of polarized electrons. This result showed that the electron was a normal partner in the model of electroweak interactions as first spelled out by Steven Weinberg in 1967.

The work I describe here was done mostly by other persons as part of a team effort. In this paper I have tried to give credit to the many excellent contributions from this group. I had hoped to point out all of the important individual efforts that were so critical to the overall success, but I feel that this summary falls short of that goal. This chapter should be taken as a personal recollection of the work that occurred over a period of eight years at SLAC, Yale University, and elsewhere.

As a part of this chapter, the organizers asked that I summarize the work in atomic physics to seek out parity-violating effects in atomic levels. I reluctantly agreed to attempt this, even though I had no involvement in those experiments. What I present here is only a brief history of the search for optical rotation by bismuth vapor, as reported in the literature. I have not attempted to extend this summary to cover the work on the other atoms – thallium, lead, and cesium – which came somewhat later.

The most striking thing about the papers presented in this session is that, aside from Sharon Traweek, the speakers have tended to gloss over or to ignore completely the presence of controversy and conflict in the treatment of their topics.

Of course, it is always dangerous for an historian to draw attention to this dimension of the way scientists present the past. We lay ourselves open to two kinds of charges. First, that we are simply interested in muckraking, in giving physicists a bad press, in seeking to wash dirty linen in public so as to create a sensation and to boost our own visibility. Second, while physicists admit that they do sometimes disagree, they also insist that the community rapidly converges on a shared understanding of events. Historians who stress controversy are simply exaggerating, blowing up out of proportion what are simply normal, unimportant differences of opinion between rational human beings.

For my part let me say at once that yes, we do perhaps have a tendency to concentrate on controversy. Writing history would be pretty boring otherwise! On the other hand, this is done not to titillate, but with far more important aims in mind. Indeed it amounts to a very different way of dealing with the past than that conventionally favored by scientists themselves.

Put crudely, scientists reflecting on their own history tend to start from the present and to cast their eyes back over the past, identifying highlights and allocating credit.

The period that witnessed the rise of the Standard Model also saw radical change in the science policy and sociology of large laboratories. In the 15-year span from 1964 to 1979 the science policy climate in Europe and the United States evolved from the post–World War II golden age of strong political support and burgeoning budgets to the current era of political vacillation and uncertain funding. As researchers investigating the fundamental nature of matter used fewer mammoth accelerators and larger, vastly more complicated detectors, requiring larger teams and more specialized workers, the social structure of large laboratories also was transformed.

To help illuminate this pivotal moment, the conference organizers convened a panel on Science Policy and the Sociology of Big Laboratories. I chaired the panel, which included two other historians specializing in big science (Robert Seidel and John Krige), philosopher of science Mark Bodnarczuk, and four physicists who helped administer laboratories during these years (William Wallenmeyer, Wolfgang Panofsky, Maurice Goldhaber, and Norman Ramsey). The panel session, which consisted of 15-minute presentations by each panel member followed by a brief discussion period, was videotaped. Panofsky and Goldhaber also gave me written remarks. At the request of the conference organizers, I reviewed the videotape and written remarks and integrated, expanded, and placed into context common themes from the panel discussion to create this chapter. Panelists are quoted from the videotape of the panel session or from their texts, as indicated.

The history of science is usually told in terms of experiments and theories and their interaction. But there is a deeper level to the story – a slow change in the attitudes that define what we take as plausible and implausible in scientific theories. Just as our theories are the product of experience with many experiments, our attitudes are the product of experience with many theories. It is these attitudes that one usually finds at the root of the explanation for the curious delays that often occur in the history of science, as for instance, the interval of 15 years between the theoretical work of Alpher and Herman and the experimental search for the cosmic microwave radiation background. The history of science in general and this conference in particular naturally deal with things that happened, with successful theories and experiments, but I think that the most interesting part of the history of science deals with things that did not happen, or at least not when they might have happened. To understand this sort of history, one must understand the slow changes in the attitudes by which we are governed. But it is not easy. Experimental discoveries are reported in The New York Times, and new theories are at least reported in physics journals, but the change in our attitudes goes on quietly and anonymously, somewhere behind the blackboard.

The rise of the Standard Model was accompanied by profound changes in our attitudes toward symmetries and toward field theory.