I give a sketch here of the discovery of SU(3) symmetry and quarks. I first review three failed attempts to use dynamical models directly; these were replaced by the quark model, once the SU(3) pattern was identified in the phenomenological hadron spectrum. I then analyze the factors that led to SU(3) and discuss the related roles of classification in mathematics and in physics. I describe the emergence of the quark model and conclude with a discussion of the present form of the “flavor” and generations problem.

The structural or dynamical attempts

There are no real prescriptions in the construction of science, since it is truly an exploration of the unknown, rather than an engineering feat. Some years ago, I realized that the entire endeavor of scientific research precisely fulfills the role of the randomized mechanism necessary in any evolutionary machinery. Since the advent of “man the toolmaker,” evolution has become the evolution of human society, rather than the Darwinian evolution of genetic features of man the primate (although the two may soon merge again, with the development of genetic engineering). Society “mutates” through technological innovation, and the random process characteristic of any mutationary mechanism is, in this case, scientific research. “Good” mutations, such as the invention of flint tools or of computers, survive and turn the evolutionary wheel.

It is thus presumptuous of me to try to systematize the scientific method, and yet some broad lines may be drawn, with the qualification that things often work out differently.

The spectacular progress in high-energy physics during the 1950s and the 1960s was due in large part to the availability of four large particle accelerators: the Cosmotron, the Bevatron, the AGS, and the CERN PS.* Although the history of the design, construction, and first operation of each of these machines is an adventurous saga in itself, relatively little attention has been devoted to it.

Many of the machine builders who could detail these histories for posterity are no longer with us. Ernest Lawrence, Leland Haworth, Stanley Livingston, George Kenneth Green, Nicholas Christofilos, Hartland Snyder, John Adams, Frank Goward, and many others are gone, leaving very little beyond journal articles in the way of records of their eventful careers. For the most part, all were too busy with the future to spend much time recording the past. Livingston and I provided a sketchy history of the development of the accelerator art in our book Particle Accelerators. But very many of the colorful events in accelerator history remain unrecorded.

In this chapter I attempt to provide a little background for accelerator history during the 1950s. At Brookhaven, we were in touch with all important accelerator projects and observed at first hand many of the unsung tribulations that beset accelerator builders, as well as the uplifting moments when their machines performed as they should.

Autobiographical note

My career covers the first thirty-two years of Brookhaven's existence. I joined the staff in the summer of 1947, Brookhaven's first year.

I should like to begin by expressing regret for not having been able to be present for the last Fermilab meeting, at which I had been asked to give the final talk about what it was like to be a student of theoretical physics in the late forties, the end of the period covered by that meeting. I still hope to present that material somewhere. Between that conference and this one there were two others, one in Paris in the summer of 1982, where I gave a talk about my experiences with strangeness, and one in 1983, in Sant Feliu de Guíxols in Catalunya, where I spoke on the subject “Particle Theory from S-Matrix to Quarks.” That second conference was called a “trobada” in the Catalan language, a word that reminds us of the troubadours of the Middle Ages who flourished in Catalunya. It reminds us also that we have become much like those medieval minstrels. We spend a great deal of time now traveling from one orgy of reminiscence to another, each one held in the capital of some princely state. Here I am helping to close another “trobada.”

Let me repeat something I said in Catalunya: I shall once again commit the sin of hindsight in the eyes of some of those historians of science who come from the historical tradition.

I believe the antiproton story starts with P. A. M. Dirac, who in 1930 published his paper “A Theory of Electrons and Protons.” Later, the positive particles in the theory were identified as antielectrons (we call them positrons). Dirac's theory started out with electron energies that were both positive and negative. He considered the possibility that the negative-energy states were completely full, or were full except for an occasional missing electron, understanding very well that the missing electron would appear to be a positive charge. Thus, the theory called for positive particles of electron mass, namely, the positron.

The positron was promptly (in three years) found by Carl D. Anderson. His finding greatly strengthened belief in the importance of the Dirac equation. The question then on people's minds was, Does the proton have an antiparticle? I think most physicists believed that the proton did have an antiparticle, but there was some doubt. I remember someone saying: The proton has a large anomalous magnetic moment. That may be the signal that the proton is very different from the electron.

A number of cosmic-ray papers did mention the antiproton as a possible explanation of certain hard-to-explain events. For example, Evans Hay ward published a paper in 1947 that included three singular events observed in her cloud chamber. One of them (Figure 17.1) was discussed in her paper as a possible antiproton. It showed considerable shower activity attributable to a particle that might have been of proton mass entering her cloud chamber.

The Bevatron started operating in early 1954 at what was then the Radiation Laboratory and is now known as the Lawrence Berkeley Laboratory.

Some personal background

Sula (Sulamith Goldhaber) and I came to Berkeley from Columbia University in 1953. I joined the Physics Department and Emilio Segrè's group at the Radiation Laboratory. She joined Walter Barkas's group and later Edward Lofgren's group. We had been working with photographic emulsions at Columbia's cyclotron located at Nevis, with the help and encouragement of Gilberto Bernardini. Before that, I used emulsions loaded with D2O as a γ-ray spectrometer for my Ph.D. thesis under Hugh Richards at the University of Wisconsin in Madison.

Setting up with photographic emulsions

Whereas in my earlier work I had used 100–600-μm single small emulsions on glass, this was the period in which emulsion stacks began to be used in cosmic-ray work at Bristol and elsewhere; the electron-sensitive emulsions had recently been introduced by Kodak Ltd. of England, followed by C. Waller at Ilford, in close consultation with Cecil F. Powell and Giuseppe P. S. Occhialini.

Thus, I started out at Berkeley to build up an emulsion-processing plant in the Physics Department – the photographic-emulsion arm of the Segrè group. That involved new techniques for marking emulsion sheets, to allow easy track following from sheet to sheet, the modification of microscopes with special stages to hold and manipulate those large emulsion sheets after they were mounted precisely on glass, and the construction of accurate microscope stages for multiple scattering measurements.

Introduction

Study of the formation and propagation of S-matrix theory in the 1940s helps one to understand the rapid development, under radically different scientific and sociological conditions, of the theory of elementary particles in the fifties. The S matrix is a two-dimensional array whose elements are the transition amplitudes between states of atomic or elementary particle systems. According to a standard textbook of the midfifties, “Such a scattering matrix was first introduced by Wheeler (1937) in connection with the problems of nuclear structure and scattering. It has been reinvestigated in great detail by Heisenberg (1943) in connection with the theory of elementary particles.” During World War II and the first postwar years, few people were interacting on problems of pure physics; only on rare occasions, often accidentally, did they meet for discussions, or even exchange letters. Despite these obstacles, they did interesting and original work that led to the resumption of particle physics by a larger group after World War II. The S matrix played a comparatively large role in the discussions around 1945, but was abandoned in the early fifties. Toward the end of the fifties, however, several developments led to renewed interest in it.

The origin of the S-matrix theory of elementary particles

In a paper submitted in the summer of 1937, John A. Wheeler proposed to derive the properties of light nuclei, such as energy levels and transition probabilities, with the help of a unitary “scattering matrix.” The elements of this matrix were connected with the transition from incoming to outgoing groups, consisting of a few protons and neutrons within the nuclei in question.

The physicist's ability to study the properties of strange particles expanded greatly following the observation of machine-produced V particles. Protons were accelerated by the Cosmotron to 1 GeV in May 1952; however, by the time shielding was added and the target, beam, and detector equipment put in place, it was the spring of 1953. At this point, experimenters could begin to collect data. Among the first detectors to be used was the highpressure hydrogen diffusion cloud chamber with an 11,000-G magnetic field. In the first 4,000 photographs, with the chamber exposed to a high-energy neutron beam, several V particles popped up. Two of these had tracks that gave momentum and angle measurements of sufficient accuracy to be convincing. That led to the first studies exploiting the advantages the accelerator had over cosmic rays.

In the summer of 1950, several groups were experimenting with continuously sensitive diffusion cloud chambers, and Ralph P. Shutt recognized their potential use for Cosmotron experiments, in particular if high-pressure hydrogen could be made to work. Great enthusiasm and a wide variety of skills existed at that time in Shutt's cloud-chamber group, and very shortly two 20-atm hydrogen diffusion chambers had been constructed. Through the effort of Gilberto Bernardini this equipment was moved to the Nevis cyclotron, where exposures to pion beams demonstrated the usefulness of this new tool. With the addition of a new magnet, the high-pressure hydrogen diffusion chamber was on the floor of the Cosmotron when the first experiments began.

Introduction

Japan changed considerably during the decade of the 1950s, and research in science and technology was no exception in this regard. World War II came to an end in August 1945 with the surrender of Japan, which in 1950 was still under occupation by the allied powers. The economic situation was miserable: Inflation was rampant, black markets were thriving, and people were literally starving. However, the morale of theoretical physicists was high, for during the 1940s they had produced the two-meson theory, the super-many-time theory, and the covariant renormalization theory. In 1949, Hideki Yukawa was honored with the Nobel Prize in physics. In contrast to this flourishing theoretical culture, the level of experimental particle and nuclear physics was very depressed. For example, on 23 November 1945, all the cyclotrons in Japan – two at the Institute for Physical and Chemical Research (Riken) in Tokyo, one at Osaka University, and one under construction at Kyoto University – were dismantled by order of the occupation forces, who threw the dismembered parts into the sea (possibly also into a lake). On 30 January 1947, the Far Eastern Committee, which was the organization for policy making of the allied powers in Japan, decided that “all research in Japan of either a fundamental or applied nature in the field of atomic energy should be prohibited.” This prohibition, which obviously put severe restrictions on the resumption of research in nuclear physics, was in force until the peace treaty became effective in 1952.

Over the ten years after the signing of the peace treaty in 1952, by which Japan recovered its independence, economic conditions improved significantly.

This volume is the second in a series based on the lectures and discussions of historians and physicists at a Fermilab international symposium on the history of particle physics. The first volume, The Birth of Particle Physics (New York: Cambridge University Press, 1983), was based on a symposium held in May 1980 that traced the emergence of the field out of cosmic-ray and nuclear physics in the 1930s and 1940s and also examined the extent to which relativistic quantum field theory could serve as a theoretical structure for the new area. All the lectures were given by physicists; historians of science participated in panels and in audience discussions, but did not serve as speakers.

The present book, more complex than the first, grew out of the International Symposium on Particle Physics in the 1950s: Pions to Quarks, held at Fermilab on 1–4 May 1985. Whereas the first symposium and volume dealt with the birth and infancy of particle physics in the 1930s and 1940s, the focus of this book is the period in which the field found its identity, became established, and turned into a big science – the adolescence of particle physics, with all the problems and anxieties that term evokes. At the second Fermilab history symposium, and in the present volume, historians of science played a major role, delivering talks and preparing chapters based on their presentations.

The book is divided into ten parts, each containing chapters based on symposium talks, a few also contain articles on topics that could not be addressed in the three short days of the symposium, but which the editors felt deserve a place in the volume.

Although some of you already know about the CERN history project, please allow me a few words of description. Like the object of our study, the history team is supranational: John Krige from the United Kingdom, Ulrike Mersits from Austria, Dominique Pestre from France, and myself from Germany. The funding comes from science foundations in several European countries. CERN is not financing the project, but provides offices and other help.

Our results are being issued in a series of reports called Studies in CERN History, to stimulate criticism and discussion before the final manuscript is produced. The prehistory, up to the official foundation of CERN on 29 September 1954, is nearly finished and will be published as the first of two volumes.* One part is an analysis of the emergence of the idea to create a European laboratory from scientific needs and the desire for European unity. The two principal champions who struggled for the laboratory were Pierre Auger and Edoardo Amaldi. Amaldi's account at this symposium is included here as Chapter 35.

The present chapter is based on an analysis of the decision-making process in four of the participating countries – the studies by Krige for the United Kingdom, Pestre for France, Lanfranco Belloni for Italy, and Hermann for Germany. The work is based (as are all the studies of the team) on source material in many governmental and private archives, as well as in the CERN archives, and will form part of the first volume of CERN's history.

The title of this essay is taken from Robert Oppenheimer. He had three types of excellence in mind: first, for the theoretician, the excellence of new ideas while he attempts to read Allah's design; for the experimenter, the excellence of new discoveries, the sheer pleasure of the search of carrying an experimental technique to its limits and beyond; and, finally, of the desire to spite the theorist. Oppenheimer had these forms of excellence in mind, but also much more: He emphasized the opportunity physics affords to come to know internationally a class of great human beings whom one respects not only for their intellectual eminence but also for their personal human qualities – a reflection of their greatness in physics. In addition, he had in mind the opportunities that physics uniquely affords for involvement with humankind – in the parlance of today, in engaging in problems of development and of enhancing the human ideal.

I wish to speak here on some aspects of Oppenheimer's thoughts from a personal point of view. I shall illustrate these by recalling my induction into research on the renormalization of meson theories and the excellent men I was privileged to meet while pursuing this research. I also wish to speak on excellence through world development. In particular, I want to speak about the International Centre for Theoretical Physics, whose creation, under the auspices of the United Nations, I was privileged to suggest in September 1960. The Centre came into being only in October 1964 – beyond the cutoff date of this symposium's coverage.

The neutrino, neutron, positron, and muon were discovered in the 1930s. The pion and strange particles had their turn in the late forties. During the fifties, which saw the change from dependence on natural sources to accelerators in the study of particles, the particles and their properties were sorted out, the strange particles were systematized, the first particle resonances were seen, and parity was found to be violated, with a concomitant clarification of the weak interaction. It was an exciting time. The field advanced rapidly. I was young and played my part in this adventure.

Cosmic rays and muon decay

For me, particle physics began in 1947, when I was a graduate student at the University of Chicago. Enrico Fermi gave a seminar on the results of the Conversi, Pancini, and Piccioni experiment in which he explained that because the negative mesotrons rapidly find their way to the atomic K shell, the observed long lifetimes were incompatible with the role of these mesons as Yukawa particles. It was a beautiful and important experiment, and Fermi's explanation was extraordinarily lucid, as well as stimulating and exciting. The puzzle was at least in part cleared up a few months later when the Bristol group discovered the pion in nuclear emulsions.

It was a great privilege to be a student in that department at that time. There were excellent teachers: Fermi, Edward Teller, Willie Zachariasen, and Maria Mayer, to name a few. Fermi's courses, in particular, were models of transparent and simple organization of the most important concepts.

The photographic method

The use of photographic plates to record ionizing radiations dates back to Henri Becquerel, who in 1896 discovered radioactivity from the blackening of plates by uranium salts. In 1910–11, M. Kinoshita showed that it was possible to record individual tracks due to a particles at both verticle and tangential angles to the emulsion plane. During the 1920s and 1930s, experiments by M. Blau and H. Wambacher in Germany, G. Zhdanov in the USSR, H. J. Taylor in England, and R. Wilkins and H. Rumbaugh and A. Locher in the United States recorded particles both from cosmic rays and from accelerators, on occasion achieving sensitivity to protons by use of organic sensitizing dyes (e.g., pinakryptol yellow). The general nonreproducibility of the results, however, placed the technique under something of a cloud. Indeed, in 1935, Taylor, at Cambridge, using Ilford Rl and R2 emulsions, concluded that it was “impossible to deduce with any accuracy the energy of individual particles from range in emulsion.” Similar remarks were voiced by M. Stanley Livingston and Hans Bethe in 1937.

This situation was transformed for two reasons. First, Cecil F. Powell and F. Fertel in 1943 showed that the energy resolution in the study of (d, p) reactions in boron, using the proton range in emulsion, was at least as good as that obtained with counters and absorbers (Figure 5.1); the method could be made quantitative.