AC BEAM NE 'There are therefore Agents in Nature able to make the Particles of Bodies stick together by very strong Attractions. And it is the Business of experimental Philosophy to find them out.'--Isaac Newton, Opticks (1704) ... __- _ November 1976 V Burton Richtcr 1976 Nobel Laureate in Pysics 2 SLAC Beam Line, November 1976 2 SLAC Beam Line, November 1976 Contents Of This Issue DISCOVERY OF THE J PARTICLE Discovery of the psi particles: 3 Since the experimental work for which Pro- A personal perspective fessor Ting shared the Prize with Richter is (Burton Richter) mentioned only casually throughout this issue, Burton Richter: A scientific 7 we want to take a few lines here to give a sim- autobiography ple description. In collaboration with a phys- icist from Brookhaven National Laboratory, Ting's SPEAR: A review of the facility S1-S16 MIT experimental group carried out an experiment and the SLAC-LBL experiments at Brookhaven in which high-energy protons were Discovery of the psi particles: One 9 directed against a beryllium target. The pur- researcher's personal account pose was to search for pairs of electrons or (Gerson Goldhaber) muons emerging from the proton-nucleus collis- ions--presumably as a result of the decay of Iliopoulis wins his bet 14 some parent particle produced in the collision into these e+e and p+V- pairs. Editor's Note Such an experiment at a proton accelerator presents formidible problems, most notably the This issue of the Beam Line is intended to fact that the electromagnetically produced elec- commemorate the award of the 1976 Nobel Prize tron and muon pairs tend be swamped by the flood in Physics to Burton Richter of SLAC and to Sam- of particles such as pions that are created much uelC. C. Ting of MIT . The telegram that Richter more copiuosly by the strong interaction. Ting received reads as follows: met this and other potential problems with a Stockholm superbly designed detection instrument (a 10/18/76 "double-arm spectrometer") that was capable not Professor Burton Richter only of excellent momentum resolution and of Stanford Linear Accelerator Center handling intense beams, but also of rejecting P. 0. Box 4349 unwanted pairs of pions or other hadrons by an Stanford University, California 94305 incredible factor of 106 to 108 The Royal Swedish Academy of Sciences to- The process studied by Ting's group, day awarded 1976 year's Nobel Prize in Physics pn or pp e e or p I equal shares to Professor Burton Richter, in (hadrons) - (leptons) USA, and Professor Samuel C. C. Ting, USA, "for their pioneering work in the discovery of a is in a sense the opposite of that studied at heavy elementary particle of a new kind." SPEAR: e+e- + T+7-, K+K, etc. C. G. Bernhard + Secretary General (leptons) (hadrons) The complementary nature of the two experiments is in fact one of the main reasons why such sim- ilar results were achieved. The MIT-BNL group used the symbol J to iden- tify the resonance at 3.1 GeV that the SLAC-LBL called i. For a time there was a friendly com- petition, in which tee shirts mysteriously ap- peared emblazoned with bold strokes:J(3.1) or (. But now, in recognition of the independent achievement of this great discovery by the two groups, the 3.1 GeV particle is often referred to in publications, and even in speech, as J/1 (3.1) The Prize seems well-earned and well-shared. Three of Stanford's four Nobel Laureates Acknowledgments: The cover photo is from in Physics are shown here. From the left, the Stanford News & Publication Service. The Robert Hofstadter (1961), Burton Richter articles by Burton Richter and Gerson Gold- (1976), and Felix Bloch (1952). The fourth haber originally appeared, in slightly differ- is Willis Lamb (1955). Hannu Miettinen took ent form, in Volume (5) of Adventures in Ex- this picture during the October 20 celebra- perimental Physics (1976). tion at SLAC. ~~~-~~~~~~ ~~~ ~~~ ~~~ ~~~ ~~~ ~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ SLAC Beam Line, November 1976 3 SLAC Beam Line, November 1976 3 DISCOVERY OF THE PSI PARTICLES: was too small to handle the construction of both storage ring and the detector, so I began to PERSPECTIVE the A PERSONAL look around for some collaborators for the exper- iment. William Chinowsky, Gerson Goldhaber and By Burton Richter George Trilling of the Lawrence Berkeley Labor- atory (LBL) and Martin Perl of the Stanford Lin- of the psi particles marks for The discovery ear Accelerator Center (SLAC) joined our exper- 17 years of scientific work me a high point in iment with their groups, and the large detection This work began with the on colliding beams. apparatus was completed by the time that the of the first col- start of construction, in 1958, storage ring was ready to operate. Our first machine: the Princeton-Stanford 500 liding beam paper on the l particles contains almost two colliding-beam machine MeV electron-electron authors for each cubic meter of magnetic field. collaboration with W. C. Barber, that was built in The dynamics of such a large group would likely and G. K. O'Neill at the High Ener- B. Gittelman, be as interesting to a sociologist as the exper- on the Stanford cam- gy Physics Laboratory (HEPL) iments are to a physicist. pus. Preliminary design of a large electron- positron storage ring began in 1961 at just Gerson Goldhaber has recorded his impress- about the time that the SLAC project was author- ions of the events surrounding the discovery of ized, and in 1964 the first formal proposal for the first psi particle in a separate article in funds to construct this machine was submitted to this issue of the Beam Line. My impressions government funding agencies. will be somewhat different from his, since each of us perceives from our own point of view. The The effort to gain approval for this project things that stick most clearly in my mind about extended through six years, eventually culminat- that great Sunday, November 10, 1974, are the ing in August 1970 with the start of construct- huge crowd of people in the SPEAR control room, ion of the SPEAR project. In April of 1972 the the smiles on all of the faces, and the general machine was ready for its first operation, and feeling of euphoria that possessed all of us. physics program began early in the experimental Never before had so many members of the collab- 1973. I have taken a few detours along the way oration been present at any one time. The ac- into other kinds of experiments--tests of quan- celerator physicists who had helped to build electrodynamics, high energy photoproduction, tum SPEAR were also there. Machine operators were interactions--but my first love has pion-proton there. Experimentalists from other groups at physics that could be done with always been the SLAC drifted in during the day, as did many of I have been led on by a naive colliding beams. the theorists. All of us were talking and smil- positron and electron, particle and picture: ing and watching the experimental events as they of antiparticle, annihilating and forming a state were analyzed and reconstructed on the computer simple quantum numbers and enormous energy dens- display scope. ity from which all of the elementary particles While many of us felt that we had to find could be born. something new because of the peculiar behavior It has been particularly satisfying to have of the data (described in Gerson's article), witnessed the birth of a new class of particles, Vera Luth was so sure of the outcome that, dur- the 9's with their completely unexpected proper- ing the previous day, she had started to cool ties. Every experimentalist dreams of making the down a magnum of champagne in our refrigerator. great discovery--a discovery that will change the That magnum and quite a bit more disappeared as direction of scientific thought. I don't know the day wore on. yet if the colliding-beam machines and the new particles that we have discovered with them will Gerson, Willy and I discussed publication of cause a sharp change in that direction, but sure- the results and decided not to wait on further ly they have bent it a bit. detailed experiments, but rather to send the information out immediately. All of the collab- experiment The group that collaborated on the orators who could be reached concurred in this very large which uncovered the l particles is a decision. It was clear to all of us that noth- physics one, even by the standards of high-energy ing like this new particle had ever been seen in the ex- It is large because the apparatus used before, so it didn't matter a bit at that point of our de- periment is huge. The basic outlines what the exact cross section was to the last in the first tection equipment were set down 20%. We had used the experimental apparatus be- in 1964. Ad- electron-positron machine proposal fore, our computer codes had all been carefully has since changed the detector vancing technology debugged, and we had already put in a great deal It now had a mag- in detail but not in concept. of work rechecking the whole system when we had over 20 cubic meters and netic field volume of earlier found the peculiar experimental data. equipment, trig- is filled with particle-tracking With no reason to hesitate, we immediately be- devices. ger devices, and particle-identification gan to write up an "on-line" paper describing In 1970, when the construction of the SPEAR stor- the results.