Nuclear beta decay has played a very important historical role in the development of our present understanding of weak interactions. For more than 20 years these reactions were the primary source of information on the weak force. In the first part of this chapter, the theoretical ideas developed to account for the experimental measurements on beta decays (and later on the weak decays of hadrons) are reviewed, leading to the V – A theory of weak interactions. This theory, however, gives badly divergent cross-sections at high energy and, moreover, does not account for the weak neutral current interactions which are observed in nature. The standard model of Glashow, Salam and Weinberg, which is based on the principle of local gauge symmetry, predicted such currents and, indeed, successfully explains the bulk of all experimental measurements on weak and electromagnetic phenomena. After discussion on the basic framework of this model, the problem of the introduction of particle masses is reviewed. Non-zero masses would appear to violate the required gauge invariance of the theory. However, if the underlying group symmetry is spontaneously broken, then the particle masses can be generated at the price of introducing one or more fundamental scalars (Higgs particles) into the theory. The predictions of the standard model, for a wide class of reactions, together with a comparison of the experimental results, are discussed in subsequent chapters.

STRONG, ELECTROMAGNETIC AND WEAK INTERACTIONS

One of the main objectives of physics is to find out what, if any, are the basic constituents of matter and to understand the nature of the forces by which they interact. Fundamental particles appear, at present, to be of two distinct types. The first group consists of quarks and leptons. These are spin ½ particles obeying Fermi–Dirac statistics (fermions). The second group consists of the so-called gauge bosons. These are integral spin particles obeying Bose–Einstein statistics (bosons). The gauge bosons appear to be responsible for mediating the interaction forces between quarks and leptons. Existing results show clear evidence for four types of interactions in nature. These are the strong, electromagnetic, weak and gravitational interactions. Our knowledge of these interactions stems, to a great extent, from our understanding of the underlying symmetries which appear to exist in nature and in the way in which they appear to be broken.

The world is made up of ninety-two naturally occurring chemical elements. The properties of a given isotope of an element do not, as far as we know, depend on its origin. These elements are composed of electrons and nuclei, which are in turn composed of protons and neutrons. The electrons are fermions and obey the Pauli exclusion principle. This leads to an elaborate shell structure and important differences in the chemical properties of the elements. Prior to the development of particle accelerators, studies in particle physics were limited to indirect means.

This statement, from Newsweek (22 April 1985), epitomizes the political economy of postwar high-energy physics. Its practitioners have had to allege that more than “mere scientific findings” will result from the construction of their atom smashers – the ultimate dream machine has changed with time – in order to satisfy their federal patrons. The increasingly energetic and costly machines built since the war have testified to the physicists' success in linking their own with the national purpose. There has been, inevitably, a trade-off between scholarly and state purposes that can be understood by an historical analysis of the political economy of high-energy physics in the late 1940s and early 1950s, when the modern patterns of patronage of particle physics first manifested themselves.

Introduction

The history of CERN is of considerable interest, not only for highenergy physics but also more generally, because CERN is the first example of an intergovernmental research laboratory created in Europe that has been operated successfully for more than thirty years – a remarkable model for the creation of international organizations.

Armin Hermann, with the help of a few younger historians, is preparing a complete history of CERN in two volumes.* From this extensive presentation, John Krige of Hermann's group, with the help of his colleagues, will extract a more concise CERN history, contained in a single volume of 300 pages and addressed to a wider public.

My account here is of a completely different nature. I did not consult the archives of the foreign ministries or of the research councils of the member states of CERN or of other intergovernmental organizations. The material here is based on a few well-known documents, on my personal diary of that period, and on a few reports and lectures prepared years ago by Lew Kowarski or by me.

Everyone agrees that the early history of CERN can be divided into three periods. The first period encompassed the first initiatives and extended from the middle of the 1940s to 15 February 1952. On that date, the representatives of eleven European governments signed in Geneva the agreement established ing a provisional organization with the aim of planning an international laboratory and organizing other forms of cooperation in nuclear research.

The symposium on which this volume is based was the fourth large meeting sponsored by physicists and devoted to the history of nuclear or particle physics. Many of the historians who attended earlier meetings came away with the impression that their hosts considered them to be passive receptacles for the true stuff of history (namely, reminiscences and recollections) or active clerks, able to look up bibliography, spell, and get dates right. This was a violation of parity between physicists and historians in the study of the past, and it resulted, of course, in weak interactions. I shall take the opportunity provided by the democratic action of this symposium's organizers to say a few words about the methods and objectives of historians. I shall then mention a few aspects of the history of particle physics particularly interesting to historians.

Although physics and history aim at different things, there are important parallels between them. Classical physics may have its analogue in dynastic history, the concern with rulers, courts, diplomacy, and wars characteristic of the historians of the nineteenth century, a concern that eventually made some people as impatient, and showed itself as limited, as the physics of mass points. While physicists extended their work to the domains of relativity and the quantum, historians brought social, economic, and institutional forces to center stage. Historians of physics underwent this revolution – which took them from exclusive concern with great men and battles of ideas to consideration of the milieu as well as the content of science – about twenty-five years ago.

With the benefit of hindsight, I would like to speak on certain theoretical developments that occurred during the late 1950s. The subject matter I shall discuss centers around the views regarding the meaning and role of symmetries, or the lack thereof. I shall talk in particular about the happenings in Chicago, not only because they are what I experienced at first hand but also because one of the participants, Jun John Sakurai, unfortunately cannot be heard any more. Let me begin by stating that, at the risk of oversimplification, I regard Ernest Lawrence and Hideki Yukawa as the two founding fathers of particle physics, in that they respectively established the basic experimental and theoretical methodologies in this field. That these are the basic methodologies still holds true, with some qualifications that I shall come to in a moment.

Limiting myself to the theoretical side only, Yukawa's way was to freely invent (or postulate) new particles in order to explain phenomena that are new or not yet understood. Although Yukawa stopped pursuing this direction after his success with the meson theory, the philosophy behind it was articulated and practiced by his collaborator Shoichi Sakata, yielding further successes. The two-meson theory was one such example. At any rate, Yukawa's approach was phenomenological and ad hoc, in that it lacked a theoretical guiding principle of its own, which was perhaps the reason why he stopped pursuing it. This contrasts with the current situation in which gauge theory has established itself as the supreme principle.

Jones: The discussions are organized as follows: first some remarks on the subject of particle accelerators in the 1950s, then some remarks on particle detectors. Although people like Luis Alvarez bridge both fields, generally the two fields are more or less discrete. Robert R. Wilson deals with aspects of particle accelerators from the Cornell perspective; in a separate chapter in this volume, Donald Kerst summarizes the MURA developments in the 1950s;* Robert Hofstadter discusses detectors, in particular the development of solid inorganic scintillators. Ugo Amaldi and Alvarez then take up other aspects of particle detectors. The panel concludes with a general discussion, including responses to questions from the floor.

It may be useful at this point to summarize the accelerator and detector technologies that were available at the beginning of the 1950s, and then briefly catalog the conceptual advances and inventions during that decade. Electron acceleration techniques evolved rapidly during the 1940s, beginning with the invention of the betatron by Kerst and, following the war, the development of the electron-synchrotron by Edwin McMillan. Meanwhile, William Hansen and others invented and developed the electron linear accelerator, substantially in the form it has retained to the present. The proton accelerators before 1950 were at first high-voltage machines, developed by John Cockcroft and Ernest T. S. Walton, then electrostatic generators developed by Robert J. Van de Graaff and Raymond G. Herb, followed by Ernest O. Lawrence's cyclotron. Postwar developments included the synchrocyclotron of McMillan and Vladimir Veksler and the Alvarez proton linear accelerator.