IMPACT OF STORAGE RINGS ON ELEMENTARY PARTICLE PHYSICS - eScholarship
G. H. Trilling · 2010
IMPACT OP STORAGE RINGS ON E.LEMENTARX PARTICLE PHYSICS George H. Trilling Department of Physics and Lawrence Berkeley Laboratory University of California, .Berkeley, California 9U720 I. Introduction vention s a total c m . energy squared), because many of tha gross properties of hadron interactions such as total cross section, multiplicities, etc. have logarithmic energy dependences. Only large energy jumps can have much impact when such slow variations are involved; in deed, at the time of initial turn-on, the ISR provided a c m . energy increase by a factor of about 8 over the PS and AGS, enough to permit significant tests of ideas developed earlier and to observe substantial departures from uome of these predictions. It is fair to say that as Fermilab came on, the energy advantage of the ISR for this kind of physics became reduced in view of such dis advantages as the inability to vary the initial state, the difficulty of detecting particles in the forward direction, etc. More recently the ISR emphasis has tended to be more what one might call quark and lepton physics for which the high energy still provides unique capabilities. An early surprise from the ISR was the discovery of a rising pp total cross section at high energy. There had been hints, for example, a small rise in the K p cross section measured at Serpukhov and suggestive re sults from cosmic rays, but nevertheless the ISR result was a surprise. More recent work from Fermilab subse quently confirmed with impressive precision that total cross sections increase with energy for practically all hadron-hadron systems. The total cross section gives the imaginary part of the forward scattering amplitude. The real part has now also been measured both at Fermi lab and for the highest energies at the ISR (a tour-de force by the CERN-Rome Group, since the technique in volves Coulomb interference at very small angles for which one has to place detectors perilously close to the full circulating beam). The results are shown in Fig. 1. It is well known that new experimental discoveries often closely follow the development of new technology. There is hardly a better example of this than the close coupling between new discoveries in the frontiers of elementary particle physics and the development of the art and science of making high-energy accelerators. It is almost twenty-five years since the construction of the Bevatron made possible the discovery of the anti- proton 1 and, since that time our knowledge and under standing of particle physics has made enormous strides in step with new developments in both the accelerator and he detector arts. It is therefore with pleasure and gratitude that I, a particle physicist, attempt here to document how intimately many of the recent advances have been tied to your success in the develop ment of storage rings and colliding beams. The history of the development of storage rings is something you know much better than I. As far as I know, the earliest particle physics results from stor age rings were tests of quantum electrodynamics obtained in 1965 by the Stanford-Princeton Collaboration on its 300X voo HeV e e storage ring. Hadron production in e e~ collisions became the topic of primary interest in electrotr-ijiositron storage rings shortly thereafter and was investigated at medium energies by machines at Orsay and Novosibirsk and at higher energies by Adone, CEA, and then SPEAR and DORIS. The next generation of e e machines is just beginning to impact particle physics, the PETRA turn-on having occurred some months ago, and the turn-on's of PEP and CESR being due to occur later this year. In parallel, the large proton-proton intersecting .itorage ring (ISR) at CERN opened its window onto ultra- high-energy hadron-hadron collisions in I970 and has since continuously contributed to the understanding of particle physics. The next generations of hadronic- collision machines will be the modest pp colliding- ', beam facilities at CERN and Fermilab in the early 198ofc, and the large storage ring ISABELLE at Brookhaven a little later. j The expected and perhaps unexpected achievements of the new machines, including those turning on now or in the very near future will be the subject of subsequent. talks by Bjorken and Richter. I just want in this talk . to describe a few physics breakthroughs cade possible by storage ring operations over the last few years. My time does not permit anything like a complete survey, 'and I shall only be able to mention a few highlights. Since a complete list of references would have to be very lengthy and my space is limited, I shall give no : references. I extend appropriate apologies to those groups whose wcrk ia quoted here. I t^Ort'' m P w Felly tl « 1K7 Bnnogth •! a I97J l a t u m M si 1171 Amaldi tt at 197] CCHN-AOITK »7( II. Physics from the ISR I start with pp colllding-beam results. The pri mary raison d'etre of the pp storage ring is its ability to reach, with large luminosities, the highest possible energies for given cost (this advantage may eventually belong to the pp storage rings, but I am talking about present rather than future facilities). Such a machine can then be used to extend the study of known phenomena to the highest possible energies and to look for totally new things. Unfortunately no new thresholds have been observed at the ISR, but the detailed study of various aspects of hadron collisions at high energy has proved extremely interesting. The early ISR work was primarily concerned with what is often referred to as log s physics (by con Fig. 1. Ratio of real to imaginary part of forward proton-proton scattering amplitude. Fits to these data as well as the cross-section data coupled to dispersion-relation calculations provide the best indications about the behavior of the cross sections at even higher energies, and suggest that the rise con tinues up to very high energies. I now want to mention briefly the study of general multiparticle processes which represent the bulk of in- elastic interactions at high energy. If one considers an inelastic process creating particles of mass m, emit ted with momentum P (longitudinal and transverse compo nents P and P relative to the beam line), it is con venient to replace the variable P by the longitudinal L T L