Physics is Fun Memoires of Richard Wilson Version of September 25th 2009

Colliding beams of electrons and positrons

The fact that operation of the Harvard cyclotron was cheaper than operation of other accelerators was instrumental in my trying, in the 1960s, to keep all parts of a high energy physics program, accelerator, apparatus, and data analysis, at Cambridge, MA, with Harvard as a leading participant. It was one of the several reasons that I rejected offers from other places, Stanford, Manchester UK and Cambridge UK that were made about this time. I failed in this endeavor for a number of reasons, many of which are outlined in the previous section on the CEA. But the failure to keep high energy physics firmly in the Universities has led, in my view, to a decline in the field itself. Since this has been one of the most difficult and painful parts of my life the failure must be described.

In summer 1956 funding for high energy physics seemed limitless and the launching of Sputnik in 1957 ensured that it would continue - as it did for a time with an increase of 20% per year. Funding was made available for two University size accelerators, the CEA and the Princeton-Penn accelerator at $5 million each plus $2 million contingency for each of the two accelerators. Funding for SLAC seemed likely although that took another 7 years In the mid west it was proposed to build colliding proton beams - the “Synchroclash”. Then G.K (Gerry) O.Neill proposed a simpler arrangement. He proposed to store protons in a smaller ring and to allow the stored protons to collide. Norman Ramsey and I both saw that this could be fine for electrons. We discussed this among ourselves and with AEC people. We all agreed that it seemed premature to plan a detailed experiment on electron-electron collisions using the CEA because construction was just beginning, and we agreed that we would return to the idea when CEA began working. Norman wrote to Pief at Stanford suggesting that he try to make a colliding electron-electron facility using the 1 GeV accelerator. I have Pief’s reply, in a letter, which I abbreviate: “The idea is not very interesting because you can only do one experiment”, namely. electron-electron scattering. But Gerry O’Neill persuaded him to go ahead anyway.
In my view it was the vision and enthusiasm of Bruno Touschek which made the difference. Indeed, anyone who takes the trouble to examine his carefully written notes, in a couple of books owned by his widow Elspeth, will recognize the breadth of his vision and his thoroughness. Bruno was always also faithful in praising others. He pointed out that one could make electron-positron collisions and proceeded to do so in a small ring ADA in Orsay about 1962. I was convinced. He pointed out to me that the idea came first from the Norwegian physicist, Wideroe with whom Bruno had worked in Hamburg on a betatron in 1941. Bruno also pointed out that it was Ken Robinson at CEA who showed that keeping electrons stable against all three instabilities, vertical betatron oscillations, horizontal betatron oscillations and horizontal synchrotron oscillations was possible. The sum of the squares of all three oscillation times is constant and positive. Bruno Touschek called this “Robinson’s Theorem” and stressed its’ importance. Even now, neither Bruno’s nor Ken’s insights have been adequately recognized. A combined cycle accelerator, with the gradient and the bending field in the same magnet, could not work. The addition of quadrupoles was necessary. Indeed the beam in the CEA, a combined cycle accelerator, expanded in horizontal size when accelerated to the highest energies. It was unstable against synchrotron oscillations..
I am not sure exactly when I was convinced that we should build an electron-positron colliding ring at CEA. Probably in 1961 when I returned from my sabbatical leave and was working on form factors in the space-like region. There was obviously more structure in the time like region. I described this later in a brief conversation that I remembe with David Ritson at Stanford, who had just spent a year’s leave in Rome. He and Fernando Amman had made a very simple calculation of the change in “tune” of the betatron oscillations when electron beams and positron beams collided at a small angle. The change is proportional to the current, and we needed to avoid half integral resonances so we needed to keep )< < 0.5. We made a proposal to build electron-positron colliding beams at the Cambridge Electron Accelerator. This was informally discussed with the Atomic Energy Commission for funding in 1961 and a brief proposal was duly submitted in 1962 I believe. Bill Wallenmeyer, the high energy man at AEC working in the Office of Science at the AEC told me that the funds for our proposal were put in the budget the AEC had already forwarded to Congress for funding, and in the atmosphere of the time would almost certainly have been funded if others did not intervene. But Pief and Burt Richter at SLAC, which had been formally funded in 1962, were also interested in a large colliding rings even though they had not got an accelerator going yet.
At that time Pief had already got a reputation at the AEC, particularly with Paul McDaniel, Assistant Secretary for Science Research, for being single minded and partisan about physics. They even laughed about it in Washington, so I was warned and did what I could to prevent a confrontation. That the AEC should laugh about this was reciprocated by Pief who several times then and since compared Glenn Seaborg to a tall reed that bends, rather than a tall firm post. I never knew what to say about Pief’s remark because I think that in politics one should be willing to bend - except of course when someone threatens to use nuclear weapons. I proposed that we should build colliding beams of 2-3 GeV, and then when SLAC was finished, they could build one at a higher energy of 20 GeV or so. Thus we could be sequential, be cooperative and avoid unnecessary competition. But that was not to be. Again, Pief wrote me a letter, which I still have, saying that he did not think a ring of even 10 GeV was possible. This is interesting in view of later developments at SLAC and competition with DESY and Cornell. In Frascati they were building a ring, ADONE, where beams of electrons and positrons at 1.5 GeV each would collide. My MIT colleagues, accepting that a confrontation was inevitable argued that we keep the higher energy of 3 GeV in each beam rather than 2 GeV in each beam to be competitive and distinct from Frascati. I suspect that was a mistake. If we had shifted our sights downward to 2 GeV, at least on paper, we might have been accepted. We were to suffer for it.

The AEC set up a small committee, chaired by Jackson Lazlett of Lawrence Berkeley Laboratory to make a recommendation. I discussed that with Pief. He insisted, and I agreed, that we do not involve politicians in the process. At that time our local Senator (Edward Kennedy) and representatives were proud of CEA and visited us. I was very careful not to mention this ongoing decision. I heard later that someone at SLAC had discussed it with politicians from California, and my colleagues in the CEA were appalled. But I doubt whether that had any influence on the scientific committee. It did, however affect morale in Cambridge. The committee had their first meeting in Cambridge, and a second in SLAC. I well remember with horror the meeting at SLAC, about May or June 1964 where John Rees and I were defending our proposal. The words are seared into my memory. They seemed to be the opposite of the idealism that George Chapman had mentioned at the APS meeting some 6 years before. Burt Richter and Gerry O’Neill had not yet got their small electron - electron ring going, and Burt said: “If I was on this committee I would vote against any ring at this time”. I was flabbergasted and almost speechless. I was confident that the skilled CEA team, of Ken Robinson, Gus Voss, Tom Collins, Euan Patterson and John Rees could make a storage ring work, even if all the answers to problems were not immediately available. I said just that. Also I asked if Burt Richter’s statement meant that he was withdrawing the proposal. Alas, no. The committee was certainly divided. Bob Wilson, who was on the committee told me later, in 1965, that he had expected fighting words from me. I failed at this, and John Rees was even more at a loss, suggested to me that we give up the fight.

Burt Richter’s comments made it very difficult for the committee and the AEC to do anything but delay the storage rings. The committee therefore recommended not to fund a storage ring at that time, but they also decided to express a preference for building one at SLAC. I was very concerned about the delay. I was convinced that electron-positron storage rings were the clear future for experimental particle physics and one must be built somewhere. The CEA staff agreed. They, in particular, were more willing than I to move to the location where the beam was to be built - as several did. Tom Collins, probably John Rees, and I went to see Jackson Lazlett at LBL and we met in the office of Andy Sessler in Berkeley who, we found, was the most pessimistic person on the committee. We tried to persuade them that the physics was exciting and that we wanted to see it happen as soon as possible, whether it was at SLAC or at CEA. Andy kept repeating that he recognized that we wanted to build a storage ring at CEA and thought we were trying to get him to reverse the committee’s view that the best place was SLAC. We, particularly Tom Collins, kept reiterating that although we preferred a ring in Cambridge, we wanted one somewhere soon, preferably in the USA. We pointed out that a delay would put a request for construction funds in to the AEC while FERMILAB, the country’s first priority, was being built. As a result colliding beam projects had lost a window of opportunity and there was a six year delay. I spent a little time looking for other sources of money - a wealthy Texan perhaps. But I was no good at that. Rumors came back to us that SLAC scientists were accusing us, particularly me, of trying to upset the decision to build a ring at SLAC. Taking advantage of a family visit to us by Pief and Adèle in fall 1964, we invited the CEA staff to a small party in the garden to explain individually their views which I believed, and still believe, were close to mine. But the incorrect rumors persist to this day. Indeed a Professor at SLAC quite recently justified his behavior to Andrée by saying: “You know what he did.” Andrée knew no more than is written here, and I knew little more about what I did. I strongly suspect that lies were being told about me. Andy Sessler more recently has commented on the fact that at the time CEA had the best group of accelerator physicists in the world. Alas, that was not enough.
It was probably in early summer 1964, while the AEC committee was still pondering the issue, that Burt Richter, Matthew Sands and David Ritson came to try to persuade us to abandon the idea of building a storage ring at Cambridge, but to join them at SLAC where the injection was easier (but see a note later about Cornell). My argument, then and now, was that we had more scientists interested in using such a facility in the Cambridge area than they had at SLAC. The presence of the CEA had stimulated the formation of high energy groups at the University of Massachusetts at Fall River, (where Richard Panofsky later became Dean), at Tufts University, Brandeis University, Northeastern University, Brown University and even Yale University. SLAC could not claim this diversity for many years. It would have helped keep high energy physics in the Universities. This was a strong battle of mine for many years, which I lost. For many years SLAC operated in the LBL Berkeley mode where visitors had fewer rights than at Brookhaven. One of the three said outright, and the others did not contradict: “If you don’t agree now, we will never let you work on the colliding rings”. I was once again taken aback and said that our view was different. If the AEC gave us the funds we would allow all interested scientists to join. But whether or not it was because of the clearly stated threat, I unfortunately was never able to work at SLAC.
Since the colliding beam proposal was postponed sine die, we presented two possible proposals the following year. One was a full proposal, including a detector, the other was for a “stripped down” version for the rings only, costing half the amount. Gus Voss and Ken Robinson were full of bright ideas. Ken had on his blackboard the Luminosity formula L = 2Ie) I made no secret about my enthusiasm for storage rings in my discussions in Europe. Pierre Marin, who I had known and helped as a graduate student in Oxford, built a ring of about 500 GeV at the linear accelerator at Orsay. There they did fine work on the rho and omega resonances. I also lobbied my friends, particularly the Director Dr Willi Jentschke, at the Deutche Electron Synchrotonen (DESY). On the way to the 1964 Dubna meeting I made a special visit to DESY and waxed enthusiastic about the possibilities. At the lepton-proton conference at Hamburg in 1965, Bob Wilson made an enthusiastic appeal. But it was not till 1968 that DESY began to build an electron-positron storage ring (DORIS) at 3 GeV. The budget was considerably larger than we had asked for but he was very slow, and DORI S was not finished till 1974 after the SLAC (SPEAR) finally became operational. The CEA staff became imaginative. Although both John Rees and Gerry Fischer left us (for SLAC) and Tom Collins for Fermilab (where he became Deputy Director), Gus Voss and Ken Robinson were still full of ideas. Why not collide the beams inside the CEA itself, or in a special "by-pass" straight section? This they did. We then built the simple, non magnetic, “Bypass On Line Detector” (BOLD) and Louis Osborne of MIT set out to built a superior detector, with magnets, to replace BOLD when it was ready. Unfortunately Osborne’s detector was finished too late. Already in 1971 the Italians in ADONE had found an unexpectedly large, and exciting, cross section for electron-positron annihilation (150, 152, 155, 158). We found an even larger one, just in time for the “Rochester” conference in FERMILAB. We did not immediately realize it, but this was the first measurement of the extra "charm" degree of freedom.

For reasons I never understood, the large cross section was not believed. But even before the data were publicly available, the High Energy Physics Advisory Panel (HEPAP), chaired by Sidney Drell, Deputy Director of SLAC recommended the complete abandonment of CEA. Abandonment began in 1973. We had time for one more run at a higher energy 5 GeV c.m. energy. According to my notes, our next run was to have been an energy scan. Would we have seen the J/Psi? I think so. It would have been hard to miss.

Although the fact that we could not get a storage ring at CEA was a great personal disappointment to me, I do not believe we could have done better that the SLAC group, with its extra three persons from CEA. Indeed we might well have done worse. There was a set back in the role of Universities in High Energy Physics. But the most serious problem in abandonment of the CEA was the failure to keep it as a synchrotron radiation facility. As noted, a machine of the same size was completed 20 years later for 100 times the cost at the Argonne National Laboratory.

Earlier in 1967, my younger colleagues, Assistant Professors Lou Hand and Eugene (Gene) Engels persuaded me to join them in a small experiment at Brookhaven National Laboratory. We produced muon pairs from a 12 GeV pion beam using spark chambers and absorbers to detect the and measure the muons. We showed that there was a peak at the rho resonance, showing the inverse of electron scattering, and a very small one at the phi resonance (116). But then we missed a golden opportunity. Leon Lederman suggested we put a 30 GeV proton beam into the apparatus and look for higher energy muon pairs. We would have done this if we could have let the apparatus stay in place. But the habit in those days was to continually move apparatus around. Another experiment was scheduled the next month in our place. Should we propose to reassemble a year latter? Since the mu pair cross section from pions dropped so much from the rho resonance to the phi, we argued that we would be unlikely to see anything and it was not worth submitting a proposal. We were wrong. Lou Hand and I have calculated that If we had put the 30 GeV proton beam into our apparatus we would have easily found the J resonance 4 years before it was found independently by Ting and collaborators and the Psi by Richter and collaborators. So I missed participating in the discovery in two separate ways. Such is life!

In 1968 the Rochester conference was held in Vienna. Pief presented the first exciting results from SLAC. Everything had worked well Their reputation in the community was justifiably high. Then in early 1999 SLAC proposed to AEC that they be allowed to divert promised “equipment” funds to build a simpler colliding beam (the Stanford Proton Electron Accumulation Ring or SPEAR) than previously proposed. This obviated the “freeze” on equipment funds till FERMILAB was finished. I was on leave in Frascati but I immediately wrote to the AEC, in hand writing, stressing the importance and urging the AEC to support SLAC. Of course I sent Pief a copy of the letter and still have one. In my mind then and now the “Bypass” was only a “stop gap”, not to inhibit the real proposal we had constantly urged at some location preferably in the USA. I do not believe that the by-pass did in fact inhibit the real proposal athough some critics have argued that it did.
In spring 1969 I went on leave to Frascati, Italy to work with and help to commission the electron-positron storage ring ADONE. I do not know the etymology off ADONE but Bruno Touschek argued that ADONE had the sme realtionship to his small ring ADA that Minestrone had to miestra. This ring was to produce center of mass energies of 3 GeV. Although I feel sure that ADONE was largely Bruno Touschek’s conception, it was left to Professor Fernando Amman to be in charge of construction and commissioning. Fernando was working hard on commissioning and spent many evenings trying to store the beams and make them collide. I would go in and help as much as I could. My help was mostly by keeping the notebook. Bruno did not turn up at Frascati and then only for an hour or two. So one day I called to see whether I could discuss some problems with him. There were aspects of the design that I did not understand. I hoped that he could help me understand them as my discussions with Ed Purcell and Bob Pound had often clarified matters in my mind. But either Bruno would not, or could not, concentrate on the problems, details of which I have now forgotten. When I arrived at his house on Via Pola Bruno said, not unreasonably: “I must pick up my son from school.” So we did. On the way back he said: “I always stop at this bar for a drink on the way home. “ So we did. Then we got back and Elspeth had prepared a fine supper, with of course one, or maybe two, bottles of Chianti. We still had not got to my problems and it was time to leave. Bruno and Elspeth said that it was too late to drive to Frascati that night so they suggested that I stay the night on their sofa. I had driven on the Rome to Frascati road on a Saturday night before and seen three serious crashes in one night, and as I had been drinking, even though only one glass to Bruno’s two, I accepted. The following morning Bruno and Elspeth took me out for lunch to a restaurant north of Rome with more Chianti. We never got to my problems. I realized then that Bruno would not make any more contributions to electron positron scattering till his addiction was cured. Alas, I was right and he drank himself to death 10 years later.
But a week later Fernando got ADONE working. I was working with him that night and he was about to give up for the day when I noticed that there was twice as much bremsstrahlung from the regions where the electron and positron were interacting than from the others. “You’ve got it” I exclaimed to Fernando. Once there was a signal Fernando skillfully optimized it and Alone was ready for experiments. Four detectors were planned by various Italian groups in four interaction locations to look for various secondary particles . At that time everyone was still thinking of single particles. They had not realized the importance of a detector with close to 4B coverage. Nor had I. I had been helping a research fellow of Jerry O’Neill who had proposed such a detector but that proposal was in abeyance. We set up a scattering apparatus for luminosity measurement. But then the floor fell in under Fernando.
Workers at INFN were asking for higher pay and in June 1969 went on strike, a “sciopero bianco”. They came to work, punched the time cards and did nothing all day. The laboratory management did nothing. A couple of excellent young accelerator theorists left and never came back. Enthusiasm had gone. A year later, in 1970-1971, the strike was over they operated and came up with interesting results. By postulating symmetry of the interaction cross section, they were able to predict the total hadronic cross section. They found a ratio to the electromagnetic cross section of about 2. Bruno ran a summer school in Varenna that July 1969 which I attended with the family. I got the NSF to fund two fellowships from CEA. No accelerator physicist wanted to go so Alan Litke and Ron Madaras went to the conference. Alan Litke went on around the world. To Novosibirsk to see Budker, to Vladivostok, Japan and then home. At that time we were all thinking about single particle experiments: e+ + e- -> P + Pbar. From the form factor measurements in the space like region I had predicted that the cross section was small and, as noted earlier, Nino Zichichi had confirmed this with the antiproton beam at CERN. The smallness of the predicted cross section was one reason that the AEC committee in 1965 had recommended postponement of colliding beam projects. But in Varenna both Burt Richter and I (125) had realized that one could get production of pairs of excited nucleons with a similar cross section to the elastic process, making a total cross section 200 times greater than production of proton-antiprotons in the ground state. But neither of us had realized the simplicity of the quark model predictions. That realization was due primarily, I believe to Bjorken a little later. The ratio of hadronic to electromagnetic cross sections would be given, to first approximation, by the sums of the squares of quark charges . (½)2 + (1/3)2 + (2/3)2 = 2/3. The three fold discrepancy with the experimental value of 2 is attributed to the idea that there are three flavors of quarks
In spring 1972 the CEA colliding beam had its’ first results, with the ratio equal to nearly 3. We were asked to justify our very existence before HEPAP. Sid Drell, chairman of the committee asked us directly what the answer was. I did not answer directly because we were still analyzing the data, but I told him that the problem created by the Frascati data remained. It was another 18 months before SPEAR operated and produced the same results. We were allowed one more run at 6 GeV c.m energy and had to shut down in 1993 for good.
My mind was already turning to the thought expressed most clearly by my father-in-law Jesse DuMond . “If you can’t lick em, join ‘em.”. I looked for opportunities to do this. I was unwilling to abandon any of the scientists I had encouraged to come to work at CEA, but in 1972, I informally suggested immediately moving our working detector, BOLD, to SPEAR at once to put in the spare interaction region. This was not accepted but in a formal call for proposals to fill a second interaction region in 1973 we submitted again a detailed proposal to SLAC. We were rejected. I was told that then that the only two “outside” members of the committee, one being Sam Ting, had voted for us. Among other interesting subjects our proposal had suggested looking at - gamma and gamma -gamma interactions using the virtual gammas from the electrons.. Burton Richter suggested that we build detectors for adding that capability to his main detector, and then we could publish together those results, but only those results, using our additional apparatus. Although I duly brought this to the attention of the group, this limited collaboration was unappealing and almost insulting. If the Harvard/MIT/CEA proposals to SLAC had been accepted, we would have had an immediate team to work in one of the interaction regions. But I could keep the team together no longer. Our team disintegrated. There was no way I could hold it together. The CEA budget was gone, and instead of raising the Harvard high energy budget because we would now have to travel, the AEC cut it.
I was very despondent. In a fit of disgust I took all of my notebooks, reprints and most of my letters on colliding beams and destroyed them. I had to take sleeping pills. Andrée’s reaction was worse. “If you submit another proposal to SLAC I will divorce you” . She meant it, but a year later she relented and I submitted another detailed proposal on parity violation in electron proton scattering looking for ( - Z interference. One of Howard Georgi’s graduate students, whose name was also Wilson, explained that the asymmetry would be of the order of q²/M_z² multiplied by sin² 2w where 2_w is the Weinberg angle. That proposal was also rejected. Lou Hand, who I believe was on the SLAC program committee and supporting me, commented later: “Don’t bother to submit a proposal to SLAC again. The better and more interesting it is the more likely they are to reject it.” He had in mind the reputation NASA had developed in its first years: calling for proposals, and then doing the work themselves, I was emotionally unable to visit Pief and Adèle for another 5 years although I visited the Bay area. Andrée did visit, because she loved and loves her sister (as do I and do all my family) but she got extraordinarily angry with Pief one night because he completely failed to understand the problems he had created for me. To calm herself she polished off a whole bottle of Adèle’s sherry. Several times Andrée said to me that I married the wrong lady - a statement with which I strongly disagreed then and now. She had known of the possible problems with Pief’s approach to physics many years before as a teenager from one of Pief’s fellow students (from 1941) Alex Green. Rightly or wrongly I did not want our children to be involved with all of this although they knew something was going wrong. Our children had their own problems as teenagers. It was the Vietnam war, and Christopher did not want to be called up. It was also a time when two of Pief and Adèle’s children, Margaret (Margie) and Carol were in Boston for their music studies (Viola de Gamba and Cello respectively) and we had them round to our house many times. I don’t know whether they know even now (2009) about my personal difficulties.
A year or so later, Joe Ballam, then Director of Research at SLAC took it on himself to encourage me to submit another proposal. But not only could I not face it, but I could not think of another really interesting thing to do at SLAC at the time. Were my proposals really bad? Was I as incompetent as the rejections implied? My mind started to think of other matters. Maybe I could prove myself in another field. As noted elsewhere I did prove myself in another field and the honors others have given me come from these secondary and part time activities. But try as I could, I could not forget high energy physics and the electron positron storage rings which were the cutting edge. I went to a meeting in Frascati, Italy, in about 1975 to discuss with the Europeans a collaboration on the DESY ring, but after a tentative OK my overtures to join were rejected. It seemed that my name was poison. But the opportunity to work with colliding beams again became possible when a 5 GeV accelerator (CESR) was proposed, with a modest budget, at Cornell. Frank Pipkin already had been working there on electron scattering and he and I made a joint group which worked at Cornell, using the CLEO detector, for 25 years. Cornell had already taken the CEA’s linear accelerator injector that I had ordered in 1964! It was nice to see it again. In view of Burt Richter’s 1964 claim that you must use a linac to inject into a storage ring I note that the highest luminosity of any storage ring until the B factory was commissioned in 1995 was continually achieved at Cornell. The CLEO group was a very agreeable one. Disagreements were always talked through. But it was still 350 miles away from Harvard.