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The first phase: 1947-1974

The modern era in Particle Physics began in 1947 in Bristol and Manchester, with the discovery of the tex2html_wrap_inline276 -meson, of strange particles, and of muon catalysed fusion [1, 2]. The first paper that describes the strong interactions of a meson has only one author [2], but very quickly the advantages of international collaboration came to the fore. Within a year a American balloon (from Oppenheimer) was carrying a British emulsion (from Bristol) into the stratosphere to look for cosmic ray interactions.

Heisenberg's Uncertainty Principle gives the key to everything that follows. The search for the ultimate constituents of matter leads to the search for objects of zero size. (Causality and Relativity together dictate that all finite size bodies must have the possibility of internal movement and so must be composite.) In general then, one is looking for constituents which are smaller than the composites that can be made from them, and the Uncertainty Principle tells us that to access smaller distances one needs higher energies. High energy particles are available in cosmic rays, but in a totally random way so that major investment in detector technology would be needed to get beyond what can be learned from the first observations.

Progress therefore required the construction of high energy accelerators and that needed capital investment. At a UNESCO meeting in Florence in June 1950, I.I. Rabi pointed out the ``urgency of creating regional centres and laboratories in order to increase and make fruitful the international collaboration of scientists in fields where the effort of any one country is insufficient for the task." This meeting led eventually to the setting up of CERN, the European Organisation for Nuclear Research, initially with twelve member states, and now grown to nineteen. By June 1952 Geneva had been picked as the site for the laboratory, favoured over Copenhagen, Paris and Arnhem. It is rumoured that the low costs of operating in Switzerland were an important factor.

By the 1960's a pattern had emerged of about ten ``state of the art" accelerators at national and international laboratories around the world. The most sophisticated experiments involved the use of bubble chambers. Each chamber was an expensive capital facility capable of producing exquisitely detailed pictures of the reactions of a beam of particles incident on the liquid in the chamber (usually liquid hydrogen), held momentarily in a superheated condition so that fine trails of bubbles formed along the paths of charged particles. By observing the paths, one could infer the motion of the particles, rather as one can observe the passage of aircraft from the vapour trails in the sky. By varying the type and the energy of the incident particle, a wide range of observations could be made. With a production capacity of millions of photographs per year, such a chamber could support a varied sequence of investigations, rather like an astronomical observatory.

One took the film back home to one's institute, to scan and measure with the assistance of skilled young ladies. Usually a group of laboratories came together to make a common project. By sharing the repetitious labour they could increase their measurement capacity and build up a common library of data. They took the film first, over a few days or weeks, and then shared the reels around the collaboration. Problems of optical distortions and the like, which affected the quality of the results, were different on film taken on different dates. Each site therefore took responsibility for certain reels of film, measuring events of interest not only to themselves, but on processes whose scientific explanation would be elucidated elsewhere. This usually took more than one year, and technical analysis problems had to be solved as they arose during this time. Sharing the development of software tools resulted in both gains and losses in efficiency: some skill in managing a collaborative effort is needed if such a venture is to be coordinated around a set of Universities spread perhaps over two or three countries.

The relatively short time spent at the accelerator taking the film, its transportability, and the fairly standardised nature of the film-analysis technique encouraged collaborative work and allowed the intellectual input of groups from far apart to be brought together to improve the quality of the analysis. The sharing of responsibility for the quality of the data, and the pooling of the data used in each analysis, created a custom that the collaboration publishes its work as a whole. Before one's work can be published, one must convince the collaborators of its validity. There may be competing analyses on the same topics from other groups within the collaboration, and these must reconciled before the work can be made public. This internal refereeing has done more to raise the quality of the field than any other single custom. It also laid the foundations for the thousand-member collaborations of today. As always, the external competition from other collaborations is vital, both as a safeguard and as a spur.

My own entry to the field, in 1966, was in search of a ``one-man" experiment. I was afraid of the dangers of the big-science culture. In the event I did complete a bubble chamber experiment substantially on my own, with the advice and help of my supervisor and a sabbatical visitor, but apart from the facilities in Oxford, where I was based, I used laboratories in three countries - accelerators and bubble chambers at Rutherford (UK) and Saclay (France) and measuring and computing facilities at Berkeley (USA). Apart from an education in becoming street-wise during riots in two countries, I mastered such topics as inventing tape formats that were compatible between computers with 60-bit word length (in Berkeley) and 36-bit word length (in Oxford.) 8-bit bytes had yet to make their mark!

Bubble chambers dominated Particle Physics Research in the 1960's. But another style of work grew alongside it, using electronics and spark chambers. This demanded a different culture. Teams of up to a dozen scientists worked long hours for months at a time at the accelerator, mastering technical problems to get a specialised detector ready to measure accurately and with known efficiency a particular process, probably one not accessible to bubble chambering because it demanded, say, measurement of photons or neutrons or the use of a polarised target. I practised this craft between 1974 and 1978. It teaches one how the quality of the detector instrument dictates the range and usefulness of the studies that can be made.

The style of experimentation is driven by the science to be done. Each generation of machines brings improves in energy or intensity that demand new practices from the experimenters. The start-up of Fermilab (an incremental process around 1972) marks a transitional phase. Experimental teams were still small, but beginning to be challenged by the required advances in technology. I myself went, in common with four other European Research Associates, to work for Columbia - in New York for a year and then at Fermilab, mastering such arts as cable tray and shielding block design! I joined a Columbia-Fermilab experiment led by Leon Lederman, that was looking for the Z and W bosons.

We didn't know then how massive these bosons might be, but we planned to produce them in proton-beryllium reactions at the highest possible energy and intensity and to identify them by their decays to electrons and muons. For the first time we used magnets, calorimeters and presamplers to distinguish electrons and muons from pions that were ten thousand times more common [3]. The work on technique was innovative, and paved the way for much of today's, but our effort was limited to building a spectrometer of modest aperture, and was delayed by poor performance of the accelerator. By April 1974, we had measured successfully inclusive electron and muon production rates as a function of transverse momentum, and we were working to build a second arm for the spectrometer, to detect particles that decayed to a pair of leptons.

We were too late. High energy physics was revolutionised in a single day in November 1974, by the discovery of the tex2html_wrap_inline282 particle [4]. It was found in two separate ways, by hadronic production of lepton pairs, just the method we had developed at Fermilab [5], and by the study of electron-positron annihilation [6]. The Fermilab group recovered, and pushed on to discover the tex2html_wrap_inline284 particle [7], but the success of the electron-positron annihilation work changed not only our philosophy of physics - within a few months the quark model became accepted as the norm - but also the techniques.


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