Fifty years ago, the leaders of two experiments performed at accelerators on opposite sides of the US convened for a long-scheduled committee meeting and realized that they had made the same momentous particle discovery. The approaches and time scales for the detections could hardly have been more different: MIT’s Samuel Ting and his group had accrued and scrutinized data from a hadron-smashing accelerator at Brookhaven National Laboratory (BNL) for weeks; Burton Richter and his team at the Stanford Linear Accelerator Center (now the SLAC National Acceleratory Laboratory) had pinned down the particle at an electron–positron collider in a single weekend, 9–10 November 1974.
Announced publicly by both teams at a SLAC symposium on 11 November, the discovery of the J/ψ particle would provide ironclad evidence of the existence of a fourth quark—the charm quark—and spur what would come to be called the November Revolution in high-energy physics. Ting and Richter shared the 1976 Nobel Prize in Physics.
What follows are lightly edited excerpts from oral histories conducted between 2005 and 2021 by the American Institute of Physics (and one by the Stanford Historical Society) of Ting, Richter, and other researchers who participated in the J/ψ discovery. The accounts focus on the events of 9–11 November 1974. For additional background on both discoveries, see pages 262–292 of historian of science Michael Riordan’s 1987 book, The Hunting of the Quark.
A narrow peak emerges
Samuel Ting (MIT): When I proposed this J-particle experiment, it was rejected by CERN and rejected by Fermilab. Most theorists believed it was a useless experiment, and most experimentalists believed it was too difficult to carry out. In the proposal of this experiment to Brookhaven National Laboratory, I didn’t use the search for new quarks as the motivation. I used the fact that when I was at DESY [the German Electron Synchrotron], my group did a series of experiments on the relationship between photons and vector mesons. Vector mesons are particles—rho, omega, and phi—which have the same quantum number as photons but each with a mass of about 1 billion electron volts. … After completing this series of experiments, I thought, “Why are there only three vector mesons?” and “Why do they all have a mass of 1 billion electron volts? Shouldn’t there be heavier vector mesons?”
Beginning on 31 August 1974, Ting and his team tuned detectors at Brookhaven’s Alternating Gradient Synchrotron to search at energies of 2.5–4.0 GeV for vector mesons. If they existed, some of the particles would be expected to decay into electron–positron pairs. “Immediately we saw clean, real electron pairs,” Ting said in his Nobel Prize lecture. “But most surprising of all is that most of the e+e– pairs peaked narrowly at 3.1 GeV.”
Ting coordinated a series of checks, including assigning two groups in his team to conduct the entire data-analysis process independently. By mid October, both groups agreed that there was a discovery. Ting considered announcing the results on 20 October at a retirement celebration for theorist Victor Weisskopf but decided against it because he wanted to do additional checks. On 6 November, he started drafting a paper to report the discovery.
A crucial decision
The action at SLAC centered on a recently completed electron–positron accelerator called SPEAR. Richter was leading a team of researchers from SLAC and the Lawrence Berkeley Laboratory (LBL) in a search for new physics at several billion electron volts.
Burton Richter (SLAC): We started … at 3 GeV. Then we went [with] 3, 3.2, 3.4, 3.6, 3.8. Finished that, came back, and then we were going to fill it in with 3.1, 3.3, 3.5. We started to fill it in, and very strange things started to happen. We couldn’t get consistent results at 3.1.
Roy Schwitters (SLAC): While analyzing these data over the summer of ’74, Richter was largely away from SLAC at meetings and doing other things. … I found that one energy data point there, again, out of these half dozen or dozen or so runs, two of them were anomalous. One was a factor of seven too high, and one was a factor of five too high. And the statistics were overwhelming. They had to be real. They could not be faked.
Richter: Gerson Goldhaber came in to see me one day, and he says, “Burt, we’ve looked at these events, and in the ones where you got the big yield, there’s more K mesons than in the other ones.” I said, “OK, Gerson. That’s it. We’re going to go back, and we’re going to look again.”
Gerson Goldhaber (LBL): One thing that convinced [Richter] was that I had found that there seemed to be more K mesons produced in that region, in that data. That was probably a fluke. But anyway, it looked that way.
David Fryberger (SLAC): Initially, Burt said, “Well, that’s probably a background, and pursuing it will waste a lot of beam time. Forget it.” He really wanted to get to our exploration of higher energies. But we finally persuaded Burt that we should scan more closely above 3 GeV. He gave us a weekend for our search.
An action-packed weekend
The physicists at SPEAR clocked more events on Saturday, 9 November. The real excitement started the next morning, when the researchers began a run at 3.11 GeV.
Gary Feldman (SLAC): We were using spark chambers in those days, and the spark chamber gives out a pulse that would get picked up … by the speakers in our control room. So you could hear when we triggered. It was, you know, “click.” And as we were running on the peak of the ψ, it was going, “Click, click, click, click, click.”
Schwitters: I mean, it was just the most startling noise and, you know, your whole being was buzzing with it; I mean, it was incredibly exciting. And then, oh, a few hours later, we figured out what we had discovered. It was a much larger cross section than I ever expected, in terms of its peak size and narrowness. Nobody, nobody predicted a resonance would be so narrow.
Vera Lüth (SLAC): Soon it got crowded in the control room, and the first corks of champagne bottles popped. There were smiles on everybody’s face and a general feeling of euphoria. I remember the SLAC director, [Wolfgang] Panofsky, pacing back and forth with his hands on his head, uttering, “Oh my God! Oh my God!”
Feldman: They were just coming up, “Click, click, click, click, click”—like that. And [Panofsky] looked at it and he said, “My God. What we’ve been telling people all these days is actually true.” What he meant was that e+e– was the way to do some fundamental physics as opposed to proton collisions, which was the sort of standard of the day.
Lüth: While data-taking continued, many of us were speculating what kind of new resonance this was. It decays to hadrons; what is the decay rate? What are its quantum numbers? What inhibits its decays and makes it so narrow? And how should we name this particle? We checked the Greek alphabet, but there were not too many choices. Iota was not considered because it implies insignificance. So we quickly agreed to call it ψ, even though some theorists objected: “No, that’s for the wavefunction. You can’t use it.”
James Bjorken (SLAC): Burt Richter phoned me while I was having dinner: “We have discovered a very narrow resonance.” I went back to dinner in a daze. It was roast beef with a sharp horseradish sauce. After I wolfed down the horseradish with no effect whatsoever, my wife Joanie said, “You had better go to the lab now.”
Feldman: It was a very exciting time. In 24 hours, we took the data, analyzed it, wrote a [manuscript for] Physical Review Letters, and submitted it sort of the next day. Actually, you couldn’t submit things that fast in those days. There was a meeting going on, and we gave it to one of the Brookhaven people who was at the meeting, and he took it back to the headquarters of the Physical Review, which was near Brookhaven.
An extraordinary meeting
On 10 November, four days after he had started work on the paper reporting the discovery of the J particle, Ting boarded a flight to San Francisco to attend a meeting of SLAC’s Program Advisory Committee. Ting learned about the SLAC discovery that evening by phone from members of his team at Brookhaven.
Ting: Panofsky had a program committee meeting at SLAC and invited me to be a member. Panofsky is a person I cannot say no to. I had never accepted to serve on any committee before.
Stanley Brodsky (SLAC): Sam and I were very good friends. He called me from his motel and said, “Stan, guess what?” And then he told me about an amazing discovery by his group at the Brookhaven laboratory. They had created a new heavy particle which he called the J. … I said, “Sam, I have to tell you something that has just happened at SLAC.” I had been told that day about the discovery of the ψ particle at SLAC, and I realized it could well be the same particle that Ting had described to me.
Ting: On November 11, I went to SLAC to attend the committee meeting, and then I learned that Richter’s group had the exact same result that we had.
Brodsky: A joint colloquium at SLAC was then arranged … for both Sam Ting and Roy Schwitters. Sam announced his group’s discovery of the J at BNL, and Roy announced the discovery of the ψ at SPEAR. It was clear from both talks that the J/ψ was a vector meson, a bound state of heavy quarks—which we now know is a charm–anticharm quark pair. So I was part of this amazing moment when the two groups came together to make a joint discovery: the J/ψ particle and the new fourth quark flavor, charm.
Lüth: Roy described our experiment and showed the data, and Sam Ting sketched the experiment at BNL and their results on the blackboard, showing a narrow peak centered at a mass of 3.1 GeV. The news of this unusual event had spread, and the auditorium was packed not only with physicists, experimenters, and theorists but also technicians and engineers, secretaries and machinists. I was not sure if they all understood in detail what was reported, but they clearly realized the enormous excitement among the physics community.
Richter: Sam had gotten in first, and we’re second. But here we were with something not allowed to exist, done in two separate experiments at two different laboratories 3000 miles apart with very different methodologies and very different detectors, and we both have the same thing.
Implications of a charming discovery
The Brookhaven and SLAC teams’ papers reporting the discovery of the particle appeared in the same December 1974 issue of Physical Review Letters, which also included a confirming report from researchers at an electron–positron collider in Italy. The discovery of related particles soon followed, aiding theorists in interpreting the particles’ structures. “The world of high‐energy physics has been set afire by the discovery of a new particle with very narrow width at 3.1 GeV,” Physics Today reported in January 1975.
Ting: After the discovery of this particle, which I called J and Richter called ψ, a family of new particles was discovered. The members of this family have a lifetime 10 000 times longer than the rest of the elementary particles. This is equivalent to if someone went to a village somewhere in South America and found in that village that everyone has an average age not around 100 years old but a million years old. This means the people in this village are definitely different from the rest of the population. It means something new and unexpected has happened. … Before this discovery, physicists thought there were only three types of quarks. This is because three types of quarks [up, down, and strange] can explain most of the existing physics phenomena at that time. With this discovery, we’re at four, and later on, a fifth type [bottom] was found followed by a sixth type [top].
Feldman: This discovery really cemented the quark model as being real and not just a mathematical artifact, which I think [Murray] Gell-Mann thought it was when he first proposed it. And many people questioned, “Is it real, or is this just some mathematics that turns out to be modeled in this way?” And … the quark was so heavy that you could build a nonrelativistic model and understand exactly what was going on. A potential and so forth. And it was so much larger than the scale of the strong interactions, which was around 100 MeV, that everyone at that point understood that the quark model was really real.
