Oral History Transcript — Dr. Gerson Goldhaber
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Interview with Dr. Gerson Goldhaber
Gerson Goldhaber; June 23, 2005
ABSTRACT: Gerson Goldhaber (1924- ). Early training at Hebrew University in Jerusalem (1942-1947). Graduate work at The University of Wisconsin. Research at Columbia University (1950-1953); memories of Rabi. Research at The University of California at Berkeley and at Lawrence Berkeley Laboratory (LBL). Took part in first experiment at Bevatron. Worked on K-mesons, the tau and theta mesons; measured the radius of interaction, and the difference between the behavior of like and unlike pion pairs; contributed to the design effort of SPEAR (Stanford Positron-Electron Asymmetric Ring) accelerator at SLAC; co-discovered, and named the Psi particle with George Trilling; Goldhaber found the naked-charm mesons; with colleagues, measured the lifetimes of a number of particles, including the tau lepton, the D mesons, and the B meson; at SLC (Stanford Linear Collider) did measurements of the mass and width of the Z particle, measuring how much of the Z decay went into neutral leptons. With colleague Robert Cahn, he wrote and published the textbook ďThe Experimental Foundations of Particle Physics.Ē Part of The Supernova Cosmology Project (SCP) since 1989. 2004, ĎGersonfestí held in his honor.
TranscriptSession I | Session II | Session III | Session IV | Session V | Session VI
Discussion on "The Experimental Foundations of Particle Physics" by R. N. Cahn and G. Goldhaber
Goldhaber:The idea of writing this book was that students learn about theory and somehow think if youíre smart enough or if they can imitate Einstein they will just figure it all out. I wanted to show that that is not true, but that it all depends on the experiment and then the theory can interpret something but itís not that somebody can figure it all out. Though Einstein seemed to have managed to do some of that. So, how I started this was with the discovery of the neutron. And first of all it was my idea, which perhaps nowadays is not so important, which is to show the original articles. Here is the discovery of the neutron in 1932. Now I started with the neutron because I had some connection to that. I only started with what happened in my lifetime. I didnít go back before then. I started with the neutron because my brother was working with Chadwick. They did an experiment, which we quote somewhere here later. So there was the neutron and soon thereafter was the positron which Anderson discovered at Caltech.
Pavlish:May I ask you how you first heard about these discoveries? Was it through the news? From your brother? Did you read the original papers? How did you first become aware of particle physics?
Goldhaber:Iím not sure how I became aware of the positron, the neutron I became aware of through my brother. I was in touch with him. And he had the idea to do the photodisintegration of the deutoron which gave the first correct mass measurement of the neutron. So my brother and Chadwick, Chadwick was the professor then and he was a graduate student but he proposed this experiment to Chadwick and they did it and it worked.
Pavlish:How is that done exactly?
Goldhaber:Itís done that you take some deuterium and bombard it with gamma rays, at that time the only source of gamma rays was the decay of radioactive thorium which had the energy of 2.6 MEV and that was sufficient to photo disintegrate the deuteron. And so thatís what they did.
Pavlish:That was a tabletop experiment?
Goldhaber:Yes, tabletopÖ there were no, well there was one accelerator, there was the Cochrost-Waltar accelerator but basically it was tabletop. And the positron electron, positron, was from cosmic rays. Cosmic rays are available and people put cloud chambers in cosmic rays and thatís what Anderson did. And discovered the positron and later on with also the same method he discovered the muon.
Pavlish:With cloud chambers?
Goldhaber:With cloud chambers, yes.
Pavlish:You have a containerÖ
Goldhaber:You have a box, an air tight box where you have water vapor or alcohol vapor and then you expanded it and then it becomes sensitive. When you expand it, it cools and the water droplets want to form, come out of the vapor into droplets. And they form on a track on a charged particle track. This is how you get these charged particle tracks. Anyways this was the early work which we discussed. Then there was great confusion at the time because Yukawa, the theorist, had predicted the pion, the particle that is responsible for the nuclear force at least it was thought to be so, of mass about 200 electron masses and it looked like the muon satisfied that criteria and then there was a lot of work, there was the work by Piccioni that distinguished between the muon and the pion. It showed that the muon was not strongly interacting, it was weakly interacting. It wasnít the Yukawa particle. And later on in 1947 the pions were discovered. First it was the negative pion that Perkins discovered and then the positive pion which Occhialini and Powell discovered which explains the whole business that there was a strongly interacting particle which decayed into the muon.
Pavlish:May I ask: at this time in science was this big news for all physicists, what was going on, or was it just a select group of people only who were following this?
Goldhaber:I should say that I was not advanced enough at that point; in 1947 I was still in college. I canít answer that for these particular particles. Later on, yes, it was, as soon as something was discovered it was discussed by everybody. But this was still before my time as a physicist. I got my PhD in 1950 so that was a few years later. So I heard about it but I canít answer that question. But yes it is true that every one of these discoveries made a big splash in the physics community. I heard discussions about it but I was still a graduate student. Then there was the discovery of the neutral pion the pi zero. That was an experiment here in Berkley by Steinberger, Panofsky, and Stellar and also at the same time my friend Ekspong saw it in emulsion. He saw the production of an electron positron pair which was a conversion of a photon from a pi zero decay. And his name was Carlson and apparently there were so many Carlsons that he changed his name as an adult to Ekspong. So this was still published as Carlson. So that completes all the pions and muons, their discovery. There was an important experiment by Panofsky studying the pions and muons.
Pavlish:Could we return to this image here, so it says an emulsion event showing an electron positron pair created by conversion of a photon from pi zero decay. So this is an emulsionÖ
Goldhaber:This is a cosmic ray coming in from above.
Pavlish:Itís like the cloud chamber whereÖ
Goldhaber:This is an emulsion. In an emulsion you are able to see the particles, it is a similar effect. When you have a charged particle going through it, it activates some of the silver grains and then when you develop it you get a track. As you can see the track is proportional to the ionization; there are these very dark tracks which are protons.
Pavlish:Thatís not drawn?
Goldhaber:Oh yes, thatís what it looks like.
Pavlish:These are protons?
Goldhaber:Protons or alpha particles. And there was this one particle which looks like a track which starts sort of, so you have a neutral particle coming out and making this track and then as you follow it you see this track divides into two and that is an electron positron pair. The proton produces an electron positron pair. So there were these two experiments which show the discovery of a neutral pi zero.
Pavlish:This could not have been done with cloud chambers? You needed the emulsions for this?
Goldhaber:It can be done with cloud chambers, but it happened that the first one was done this way. So there, these emulsion experiments, the pion and the pi mu decay was discovered in emulsions and that was, people used to take the emulsions and climb up on a high mountain and leave them there for a few weeks and then develop them. This is how the cosmic ray work was done in emulsions. Cloud chambers, they also took the cloud chamber up to the mountain because the atmosphere absorbs these cosmic ray particles, and so at sea level you donít get as much as you get on top of the mountain.
Pavlish:All of your work with the emulsions was done in a lab?
Goldhaber:Yes, I did not work with cosmic rays I only worked with accelerators. But the emulsion techniques were developed and then I was able to benefit from that. Now the muon was actually first discovered also by Anderson. Anderson not only discovered the positron but also the muon. It was Nedermeyer and Anderson who discovered the muon. Ok, so letís move on. Now we are around 1948, 49, 1950. Now we have strange particles. The first evidence was obtained by my good friend Leprince-Ringuet. I met him later when he came to Berkeley to expose emulsions at the Bevatron. And I exposed them for him and developed a stack and gave him all the emulsions. What he discovered was a track; letís see do I have a picture? So they found a particle of mass 990 electron masses. That was in 1944. That was the first evidence. It was a positive particle and that gave people some doubts because it could be a proton badly measured. A proton would be 1800 electron masses. Twice as much, but if you measure it badly... if they had seen the negative K meson it would have been definite but this is how it happened. They saw the positive. And then there was a cloud chamber experiment by Rochester and Butler, this is now in 1947, quite a few years later. They saw two, what are called strange particles, they were then called strange particles because they showed one was a V that was a neutral particle that decayed into two particles and the other was a charge particle which decayed. And these were just calledÖ it comes in at A and goes out at B and it changes direction so that was a decay from the right hand side of the cloud chamber. So they saw these two particles, there was a whole slew of particles which got discovered in cosmic rays. One important one was a tau meson; Ms. Brown found this in Powellís group. Powell got the Nobel Prize for all these. Powell was the photographic emulsion expert in Bristol, England and he demonstrated a lot of these new particles. Now the tau was interesting, because it decayed into three particles, one two three, now the other one was called theta and theta decayed into just one charged particle and presumably a neutral one; decayed into two particles. And it was slowly shown that the tau and the theta have the same mass and the same lifetime. This is where I began also to make some contribution here at the Bevatron they produced these. They were seen in cosmic rays but also at the Bevatron. At the Bevatron the Richmond group made an even better measurement of the mass and showed that these two objects had the same mass and I was involved in showing that they also have the same lifetime. In particular, Sula my first wife and Luis Alvarez did an experiment to measure the lifetime of the tau. So you had something that had the same mass and the same lifetime and this was a big puzzle, Dalitz in England was a theorist who studied this in great detail and pointed out what happened there was not allowed that something decays into two particles and three particles. And we showed and also the cosmic ray people showed that it was a lot of evidence that they were the same particle. That they did not differ in lifetime and in mass. This is what led Lee and Yang to propose Parity violation in the weak interactions, so it was a very important piece of work. Here I show the mass measurements by the people in the Richmond group. I guess I should say it was Birge and coworkers.
Pavlish:So by this time you had received your PhD and you were here.
Goldhaber:I received my PhD. I had spent three years at Columbia University working on essentially the positive and negative pions, their properties and how they interact with Hydrogen and with deuterium and then I got the position here in Berkeley and came to work at the Bevatron. And it was very fortunate as I came the Bevatron started operating and so I was able to expose emulsions at the Bevatron this is discussed in one of the early papers ďThe Early work at the BevatronĒ which you have. So you can fill in from that.
Pavlish:At this time did you have an awareness of what the interaction between theory and experiment was? I know thatís something that you mentioned in some of these papers. What was the interaction at the time and was it different later on, in particle physics?
Goldhaber:Well, it was sort of a race between experiment and theory. Sometimes experiment was ahead, sometimes theory was ahead. And it sort of oscillated in that way. There were experiments, and then theory managed to explain it. The big thing about theory is that it has to explain what has been found and predict something which can be checked or not. So a correct theory is one that predicts something which later can be observed experimentally. Sometimes it was the prediction and sometimes it was the experiment whichÖ what I discussed here these were all experiments with no predictions. It was just found in cosmic rays. People looked and made these observations. And then there was this puzzle why does this one particle go as a theta and as a tau; theta with two particles and tau as three particles and Dalitz showed thatís an impossibility.
Pavlish:According to quantum mechanics?
Goldhaber:Yes, quantum mechanics. And then Lee and Yeng showedÖ the assumption was that parity was conserved up to this point. Lee and Yeng showed that if it was not conserved that this could be happening. That was a very important theoretical development and they got the Nobel Prize within the same year of this prediction.
Pavlish:Were there competing theories?
Goldhaber:Yes, there were. I remember the one that worked but I donít remember the ones that did not work. But yes, Iím sure there were some suggestions of particle doubling, etc. The one that worked was this parity violation. That brings me to 1955. Now the Bevatron was designed to find antiprotons. In other words the energy was sufficient to produce antiprotons if they existed. So there were a number of groups here that wanted to find them. And in particular in the Segre group which I belonged to at that time we made these two approaches: one was the counter experiment the other was my emulsion experiment. Together with Amaldi; we made this agreement that we would do the emulsion work together with Amaldi in Rome. And it turned out that Chamberlain and Wiegand designed a beam and built equipment that allowed them to measure to find antiprotons. And in fact in October this year weíre having a fiftieth anniversary of the antiproton celebration. So theyíre having a symposium here for the fiftieth anniversary. So it was what Chamberlain and Wiegand built and in the Segre group who made this, designed a beam which could measure the antiprotons. They measured the time of flight; they showed that antiprotons took a longer time to go from one counter to another than pions. This is the time, this is the signal, this is the first counter, this is the second counter. This is longer than that one. Here the time is plotted. This is in microseconds. The pions took something like thirty-five microseconds and antiprotons took something like fifty microseconds to go from one counter to the other. And they simply recorded it on an oscilloscope. They took pictures on an oscilloscope.
Pavlish:I was going to ask that, soÖ you have the beam coming from here?
Goldhaber:The beam coming from here going all the way to here. And then, they had counters here and here so there was a certain distance and it measured the time of traversing this distance. So they found then that there were negative particles which had the mass close to the proton. And the emulsion experiment took longer because of the scanning. Actually my emulsion experiment was exposed before they had this beam. They only had the front part of the beam and I exposed right over here before it was completed. But it took so long to scan the emulsions that this was completed, this was observed before I was able to show that we had this annihiliation.
Pavlish:So you actually had it there it just hadnít been exposed?
Goldhaber:It was in the emulsion but hasnít been found. So, I think I mentioned already yesterday that we made a second exposure with a magnet that selected negative particles.
Pavlish:And that was your idea?
Goldhaber:Yes, and then we found some forty antiprotons. Also, besides us exposing them, the lab wanted the other emulsion groups. So they all put in photographic emulsions there. We later on wrote a paper of the antiproton collaboration experiment. Thatís not in here which showed that we had something like 40, 35 antiproton events which were found.
Pavlish:From all of the emulsions?
Goldhaber:Yes, from all of the emulsions. If we had done this to begin with, we would have found it within a week. But we were too clever. We put an absorber in (I mentioned that yesterday) and that killed the antiprotons. So, anyhow, so there was that experiment. But when it started it could have been that we would have found it first in the emulsion.
Pavlish:It was so close; it was just chance thatÖ
Goldhaber:Yes, then the next paper here deals with the discovery of the antineutron. Another experiment which started out with antiprotons and then did a charge exchange, got the antiprotons to interact and change into antineutrons. And then they discovered, they saw the antineutrons. Now there was some controversy about the antiproton experiment, that Piccioni originally had made some suggestions that it needs focusing magnets and he was going to calculate them but then Chamberlain also wanted focusing magnets and did the calculations himself and so they did have focusing magnets and later on Piccioni said, ďAh but it was my idea to have focusing magnetsĒ and he actually made a lawsuit after they got the Nobel prizeÖ but Piccioni was a good physicist. I mean, thatís just aÖ but the main thing of this experiment was also to measure the time of flight but also with a Cerenkov counter. They had a Cerenkov counter which only recorded pions. They couldnít distinguish between pions and antiprotons so they had two ways to measure this.
Pavlish:So as you were doing these experiments with the emulsions, was there a lot of interaction or was it kind of a competition. What was the atmosphere in the lab?
Goldhaber:It was a good atmosphere. We just plowed away but in the meantime they found these particles. So it was clear that they had them first. But later on, there was another attempt also to put another counter at the end of this beam to see the pulse height, to show the annihilation. This was in Moyerís group. They showed that there were large pulses but they were never able to show that there were pulses of energy greater than the mass of the proton. See, thatís the signature of annihilation. At that time one didnít know about any mesons that would have such a high mass but later on we found the charmed mesons have a much higher mass than the proton. So it was not so unreasonable to think that maybe this was some meson which happens to have the mass of the proton and then makes a big splash but not bigger than the mass of the proton. Ok so that takes care of the antiproton and the antineutron. And then for later on. Every particle that was discovered, one discovered the antiparticle for it as well. One which we discovered was the antiomega minus. The omega minus was a very important particle and we discovered a positive version of it, which is the antiomega. So, essentially every baryon. You know what a baryon is?
Pavlish:That was going to be my next question. I have this little particle booklet with a lot of the data in it. And I was wondering, for somebody who is not a particle physicist, if you would be willing to give a briefing on well, here these the Meson summary Baryon Summary table.
Goldhaber:Maybe later. Because now we think these are all quarks. At the time we thought those are all elementary particles. But we now think these are all built out of quarks. Yes, we can discuss that. Sure. The next thing I have here, starting from 1952 to 1964. Here we put always these time periods.
Pavlish:Yes, thatís wonderful.
Goldhaber:The discovery of resonances. In 1952 it was Fermi and coworkers who discovered the first resonance, namely that the proton when you impinge the proton on hydrogen. Sorry, no Iím saying it backwards. We now had these pions were produced in beams at the cyclotron for example. And later at the Bevatron. At the Bevatron it was in 1954. We had beams of pions and we did experiments of shooting pi-plus on protons and pi-minuses on protons. And they found that the cross-section was rising. Here is a picture of the cross-section. For the pi-minus they were able to show (this is what I mentioned yesterday), that for pi-minuses they came out of the cyclotron so you could go to higher energy. The pi-pluses were pushed into the cyclotron so they didnít have high energy pions. And this is where Lederman and I did an experiment of finding higher energy pi-pluses. We filled in some points over here. Looking for the resonance but as I said yesterday we missed it. Because we had two points on the two sides. You see here, we only had these two points and not this one. Something like that.
Pavlish:May I ask how a figure like this is produced.
Goldhaber:Yes, this was a counter-experiment. What you do is you build a hydrogen target. Take liquid hydrogen for example in a bottle, and you shoot pions onto it and then you measure the scattered pions with counters. So you have counters measuring the scattered pions coming out. And so this was the first instance of a resonance.
Pavlish:Whatís a resonance?
Goldhaber:A resonance is just like a particle but itís not bound. A particle is a bound system. However, itís not stable. It can decay. A resonance is something with well-defined quantum numbers but the energy is such that itís not a bound state. It can decay directly. Resonances and particles are really indistinguishable. Itís just that theyíre observed in different fashion.
Pavlish:Do you remember how the name resonance was chosen. Nuclear Magnetic Resonance is completely different, right?
Goldhaber:Thatís completely different, yes. This was aÖ
Pavlish:It had to do with the mathematics of it?
Goldhaber:Itís that essentially a state is produced which is very short-lived. A particle is a long-lived state. A resonance is a very short-lived state. I donít know how the name resonance was chosen. I didnít choose it.
Pavlish:Thatís very helpful. That clarifies it.
Goldhaber:Then, this period starting in about 60, in the Alvarez group here, Luis Alvarez who later got the Nobel Prize for this work, showed that you getÖ This is now done with a bubble chamber. With a bubble chamber you measure all the tracks and then combine them and show the effective mass of two tracks. You combine them and show that there was a peak at some energyÖ in phase space it would have been like this curve here. And the peak showed that there is something special happening. And so they discovered several resonances. A resonance of theÖ this is a lambda pi resonance
Pavlish:This one here?
Goldhaber:Yes, this one here. Itís called a Y-star. And so on. And they found a number of resonances. So, in the Alvarez group the resonances all occurred in the K minus proton system. So, I then concentrated on the K plus proton. The Alvarez group was doing K-minus protons so I concentrated on the K plus proton. And to my chagrin I did not find any resonances. And that was explained later on. We will come to that.
Pavlish:So that in itself was an important finding.
Goldhaber:It was an important finding, yes. Gell-Mann and Neíeman called this the Goldhaber gap.
Pavlish:Is that the paper about the chance meeting on the bus? That references the Goldhaber gap.
Pavlish:Iím going to turn the tape over because it looks like itís about to be done.
Goldhaber:We did however find a K-star resonance. Even though it was positive strangeness, the K-star was a positive K-star. They had worked on negative K-stars. And we were able to measure the spin of the K-star which was an important measurement at the time. Spin 1.
Pavlish:So how did you do that?
Goldhaber:In emulsions we found a lot of K-stars which was an accumulation of particles with that particular mass and then we did the angular distribution and the angular distribution indicated that it is a spin-1 particle. There is something interesting about this spin-1. At that point, Heisenberg had a student here in Berkeley, Hans-Peter Durr. And Heisenberg had a theory at that point which wanted spin-0 for the K-star. So every week for about 3 months, Heisenberg sent a letter to Hans-Peter Duerr who came to see us (by the way us included my then wife Sulamith). Heisenberg through Peter said have you tried such and such and could that mean that its spin could be zero. They were all good suggestions and we tried and we said no, itís still spin-1. Next thing, Heisenberg wrote another letter. That went on for about 3 months, which we had this exchange with Heisenberg through Hans-Peter Duerr and he finally gave up and it is spin-1.
Pavlish:That was an example of him developing a theory that wasnít corresponding with experiment.
Goldhaber:Yes, that was late in his life when he had a theory explaining everything but it didnít work. Thatís not to take away from his earlier theories which are very important. Later on, I was invited by Heisenberg to come and give a lecture in Munich and he made a party for me at his house and was very friendly. It was very hard for me to go back to Germany. It was the first time that I went back to Germany and I felt very uncomfortable about that. Since then, Iíve been back many times and Iíve sort of gotten used to it. But that first time it was very uncomfortable for me. Anyhow, these were the adventures with Heisenberg.
Pavlish:Did you know other physicists at the party? Was it a party of physicists?
Goldhaber:Yes, it was a party of physicists. No, I do not remember who else was there. I remember Heisenberg had a tie clip which was an h-bar.
Pavlish:Cool. Do you remember what the talk was that he invited you to give?
Goldhaber:Not in detail, no. It was the work I was doing at that time related to our discovery of Bose Einstein Property of Pions. Around 1960-61. We were in Europe. We were at CERN for a sabbatical for a year. Thatís when it was. OK, so there are these various resonances. Some are very interesting. Maglic discovered a 3-pion resonance. The little omega, which was kind of interesting and other people discovered the phi. But the center was really in Alvarezís group here. He had built this large, six-foot bubble chamber. It may still be at the entrance here at LBNL. You can go and visit it.
Pavlish:I was going to ask you about that. Has Berkeley always been a center for particle physics? Looking at it geographically. Well, thereís CERN now.
Goldhaber:CERN was just starting up then. Well, it started up already, but the main work was here. The Bevatron was the highest energy in the world at that point. Much of the work came from Berkeley. The other place was Brookhaven. They actually had a 3 GeV. The Bevatron was 6 GeV. Brookhaven had a 3 GeV machine, the Cosmotron, which found some of the early K-minus interactions because they started running before we did, they found K-minus interactions in emulsions were quite interesting but that was sort of it at the time. Once the Bevatron got going we were way ahead for the next ten years or so. We discovered the antiproton, we discovered the antineutron. We discovered the resonances. It all happened here. Now, there was at some point I formed a group together with George Trilling. I left the SegrŤ group after seven years and what I said is that there is a law in the Bible that after seven years you release the slaves. And thatís about what happened. And then we formed our own group and went on to make all these studies of interactions of positive K-mesons and did not find a resonance of K-plus proton. And we couldnít understand that. It was only later explained in terms of the quark model. And that was important also about the discovery of the omega minus, the prediction for the omega minus. Gell-Mann predicted it and also Neíeman. Gell-Mann had a chance to say it loud at a conference in Geneva in 1962 while Neíeman said it to me but didnít have a chance to say it out loud but he also predicted it. The omega-minus, which was a very special event. It really proved that their model was correct. Called the 8-fold way. So that was then a prediction. These resonances were all found and nobody knew what it was. But then Gell-Mann and Neíeman had a theory and their theory predicted there should be another particle with triple strangeness, strangeness minus three. And that was indeed found. And this is also here given under Resonances. Here it says observation of a hadron with strangeness minus 3. Ok, so that closes the chapter on resonances for the time being. Then we have a chapter on weak interactions. And here there were these tremendous developments that Madame Wu, at the suggestion of Lee and Yang did an experiment that showed directly that weak interactions violate parity.
Pavlish:So by this time when these were coming out, these papers, you were reading them right away.
Goldhaber:I heard about it before the paper came out.
Pavlish:There was internal communication between the physicists? Usually by word of mouth?
Goldhaber:Yes. Word of mouth, yes. At that time we didnít yet have the internet. It was word of mouth. So the one thing was this very important experiment by Wu and Angler and coworkers which proved parity violation in the weak interaction, which Lee and Yang had assumed. And there were two others, one by Galvin and Lederman and one by Freedman and Telegdi which also showed that parity violation in different ways. Then in the weak interaction there was the very important experiment by Goldhaber, Grotzen, and Sunya, one of which is my brother Maurice, where he showed that the neutrinos have negative helicity. They are a left-handed screw. As opposed to a right-handed screw. And that was a very ingenious experiment that made use of one nucleus. My brother used to know all the nuclei. All the isotopes, how they decay and so on, and there was just one that had this property that you could use it to measure the helicity of the neutrino. I wonít go into the details of the experiment, but that was important. And also, then there was the discovery in 1959 by Reimess and Cowan, of actually of seeing a neutrino. An antineutrino from a reactor. One was able to see it interact. Then, in 1962, was the important experiment of Lederman, Schwartz, and Steinberger and others that showed that there were two kinds of neutrinos, nu sub e and nu sub mu. In other words in mu decay, you produce a different kind of neutrino than when an electron is involved.
Pavlish:This work, how closely was it related to your own interests at the time?
Goldhaber:This was not. All of the weak interactions were very important work but I was not involved in any of it.
Pavlish:You were not involved but you were interested as aÖ
Goldhaber:Yes, certainly I was very interested in the results. I worked on the strong interactions and these are all in the weak interactions. These were important developments in weak interactions. Ok.
Pavlish:And were you aware that, I mean when you say that you were working in strong and this was weak interactions. Were you aware that there was a body of knowledge that was developing that you wanted to put the pieces together? Or your own experiments were soÖ
Goldhaber:No, no I was certainly aware of what was going on, particularly because one of these important experiments was done by my brother. And the parity violation was a result of our work on kaons, k-mesons. Not just our work but also the cosmic ray work. So yes, I was very aware and very interested but I didnít do it. Then thatís here we come to Chapter 7 which is 1956-67 and this is a discussion of the K zero system which is very complicated. I donít think that I will try and explain it. It led to two things. First of all it was shown that there are two kinds of k zeros, k01 and k02. Again, they had different decay modes; one was two pi, the other was 3 pi. So it is a very similar story to the tau and the theta. But here things were different. Since they were neutral, you could have mixing between them. And so this led that there was one that there was a k0 short and a k0 long. And they found that some had a longer lifetime and the other has a shorter lifetime. That also led to the experiment of Fitch and Cronin which was at Princeton. Well, it was done at Brookhaven but Fitch was at Princeton. Is he still there?
Pavlish:Yes, I believe so. Iím not sure if he teaches.
Goldhaber:Heís probably retired now. Where they showed CP violation. Before one had parity, P violation. And they showed CP violation by studying these neutral kaons. I wonít go into the details. Itís a long story. So again, several papers are discussed here. Thereís an enormous difference in the phenomenological behavior. They can regenerate and go from one to the other and when you go through a material they regenerate. And all this is discussed in this chapter. Again, I personally did not work on this. I followed it. I was at the conference in Kiev in Russia in 1962 where Fitch and Cronin announced their results. And this was really a very important, epoch-making result. So, you can look at these various experiments in this chapter 7. Oh, thereís one thing I didnít mention but I was involved with, it actually comes earlier in relation to the resonances. Actually, I and my students were the first to look for resonances. We were looking for the rho resonance. Rho was predicted to decay into two pions. And again, this is one that got away. We were the first, as far as I know, to write down the equation for the mass of two particles. And to actually use it to find something. So we were looking for the rho meson which had been predicted by two people here in Berkeley and we didnít find it. The reason we didnít find it, we were looking in the right place but we didnít have enough statistics to show it, to prove it. But, I found something else. So the way I did that is to take pion pairs. In order to see a resonance of pi plus pi minus. So I said ok let me compare pi plus pi minus with pi plus pi plus. And see that pi plus pi plus is not going to have a resonance while pi plus pi minus should have it. So I studied, instead of looking at this fancy mass of the two particles I was just looking at the angle between the two particles. And then I found that pi plus pi plus and also pi minus pi minus, notice this total charge of two has completely different behavior than pi plus pi minus which is total charge of zero. And we found this effect and we published this angular distribution and there was no explanation at first. It was just a very strange effect. Later on we realized that this was the Bose Einstein effect. That itís the Bose Einstein nature of pions and pions are spin zero so you have two spin zero particles. These are two bosons. And it gives you a measurement of the interaction region. It measures the interaction region. Then we wrote a paper together with the theorist Bram Pais which describes this and shows that itís the Bose Einstein effect and this is called the GGLP effect, for Goldhaber, Goldhaber, Lee, and Pais. And this started a whole industry because that effect is found everywhere and particularly now in the high energy heavy gold on gold collisions where people are looking for a quark gluon system, this effect is important in this region in that workÖ Anyway so we discovered the Bose Einstein correlation. Thereís a lot of work done on this. There are books written on it. [shows book]
Pavlish:Oh wow. Oh my goodness.
Goldhaber:Here and it starts with my paper. This is the GGLP effect.
Pavlish:What is the title of the book again?
Goldhaber:ďBose-Einstein Correlations in Particle and Nuclear PhysicsĒ by Richard Weiner. He actually wrote two books. Thereís another book on this. So it became a very big industry. People studied it everywhere. Including, I did some more work on it later. In fact this is where a student Juricic. We did this work. Now, up to 1965 when Sula died, all this work was done together with her. We worked together on all the things I mentioned.
Pavlish:Was it a unique collaboration?
Goldhaber:By unique do you mean husband and wife?
Goldhaber:Somewhat, not completely unique. My brother, his wife was also a physicist. But they didnít work together all the time. They worked together occasionally. But we were sort of in the same group up to the early days and so we actually worked together with students. Now thereís something interesting that I should mention. That Won Yong Lee was my student. He then went to Columbia University where he became a professor. He spent 40 years at Columbia university and this year has come back to join me again. Heís not in just now but he sits in that other chair there.
Pavlish:What brought him back here?
Goldhaber:To work with me. But I should qualify that. His son is also a physicist here in Berkeley. His son is in Berkeley. The other attraction then was his son and his grandchild. But he did come and is working with me. Ok, so well you can find this book in the library Iím sure. So the whole book describes lots and lots of experiments which were done.
Pavlish:Itself a subfield of particle physicsÖ is that what you call this?
Pavlish:Or even a field in itself.
Goldhaber:No, a subfield. And with lots of theories, lots of experiments. Some of them done by me. And now they, for some reason this effect has also been seen, a similar effect earlier with photons. Photons of course are also bosons. And has been seen with bosons byÖI discuss it here in one of these papers by Hanbury-Brown and Twiss. Anyway, for some reason the present day work doesnít refer so much to my work GGLP but they refer to this Hanbury-Brown Twiss (HBT). I donít know why.
Pavlish:Thatís with photons.
Goldhaber:With photons. But we discovered it with pions and the work is all with pions. So anyway, thatís one of those quirks. So there are many papers. I did not put this paper in the book because itís sort of a bit of a side issue. The book really tries to pick the absolute most important papers in particle physics and this was a slightly aside. It went in a different direction. It is used in Nuclear physics more than in Particle physics. Anyway, I just wanted to mention it. If we want some food we may have to go fairly soon. So Iím inclined to stop here.
Ok, good. [continuing in the afternoon] It is Thursday, June 23. Dr. Goldhaber and I, Ursula Pavlish, are in his office here in the Lawrence Berkeley National Laboratory, in Berkeley, California, continuing our conversation about his life and work. And we are in the middle of his book that he coauthored called The Experimental Foundations of Particle Physics. I believe that Dr. Goldhaber and I will continue our conversation from here.
Goldhaber:Well, weíve reached Chapter 8, which is the structure of the nucleon. Now again, we summarized that, again I did not do any work on this subject. While it consists of scattering experiments of electrons on nuclei, and also neutrinos on nuclei, and this was the beginning of some hint that the nucleon is not an elementary particle but rather that thereís some structure inside and that was later established to be the quarks which are the structure of the nucleons. I wonít go into more detail on this chapter unless you have some questions.
Pavlish:I will have to read it over. I didnít get to this chapter.
Goldhaber:As I say, I have no personal insight, since I havenít worked on this subject.
Pavlish:This work was done by many groups or by a few?
Goldhaber:The electron scattering was done at SLAC. And the neutrino scattering was in various laboratories. There were many groups involved. It led to the understanding that there is structure inside the nucleon which wasnít clear before. In the meantime both Gell-Mann and George Zweig had the proposal that there are quarks. That the nucleons, the baryons, are made out of three quarks and the mesons are made out of a quark and an antiquark. And this was based on the analysis of all the resonances I discussed earlier. And was done independently by both Gell-Mann and Zweig.
Pavlish:Was this due to the shapes of the resonances in the baryons and mesons or.
Goldhaber:No, not the shape but the symmetry. How these particles were observed. It turned out you could explain it with three quarks. And an important part was also this Goldhaber gap that you canít have it because the K plus is made out of an anti-strange quark. The K minus is made out of a strange quark and another quark. So this ruled out resonances in the positive strangeness baryon system. And that led to the proposal of quarks by Gell-Mann and Zweig who called them Aces. But the name quark has stuck.
Pavlish:He called them aces?
Pavlish:That was Zweig, you said?
Pavlish:Zweig called them that?
Goldhaber:Yes, George Zweig. But they both came up with that suggestion. Now, I gather that Neíeman also thought of it but it is not generally considered that he made that suggestion. He was close. He had also considered some kind of substructure. So what this meant that all these particles, what seemed to be different elementary particles and there were twenty by now or so by then, are just made out of three quarks. That one set of them is made out of three quarks and another set of them, the mesons, are made out of one quark and an antiquark. And then you had these three varieties of quarks: up, down, and strange, that made up all the possible combinations.
Pavlish:That was in the theory already?
Goldhaber:Yes, well that was the theory of the quarks. So, for instance, you could take three strange quarks and this gave the omega minus, this gave the triply strange particle, you could take three up, three downÖ all combinations. And that accounted for all the known particles. Except for the photon. All the leptons and the neutrinos that was separate. But all these strongly interacting particles. So now I come to this experiment at SLAC, which was a phenomenal experiment because we just had a new discovery every other day, so to speak. Now this came about because Burt Richter built a collider at SLAC, an electron positron collider. It was in a single ring. At Petra they also built an electron positron collider. But they had more money and were clever and so they made two rings. It turned out that positrons go one way and electrons go another way and they collide. That worked but it wasnít as good as the single ring. Originally, Richter also planned to do two rings but he didnít have enough money. So then they figured out that they can make one ring which turned out to be better. As I mentioned it yesterday, we (meaning George Trilling and I, and Willy Chinowsky) were approached by Richter at the time to come and work with them on this experiment. We decided that this was an interesting new field. And the bubble chamber looked like we had already enough resonances. This looked much more promising than the bubble chamber. Of course we had no idea how rich this field would be. We just figured it would teach us something. It was a new avenue. And so we joined in and we worked on the construction of the first collider which was the: SLAC LBL Solenoidal Detector later known as Mark 1. It became known as Mark 1 because we built a second one known as Mark 2. So we started out. This is described in detail in some of the notes I have given you so maybe I should leave it at that that you have those notes unless you have some specific questions.
Pavlish:Iím looking at the notes
Goldhaber:I have there two articles. One is specifically how we came about to do this and the other is just how it went at the accelerator finding the psi.
Pavlish:One is in the Adventures and is the other one the ďFrom Psi to Charmed MesonsĒ
Goldhaber:Yes, thatís right
Pavlish:This is not a very sophisticated question, in your article ďFrom Psi to Charmed Mesons,Ē you wrote in the very beginning of it, ďWe soon learnt how to distinguish cosmic ray events from Babhas.Ē
Goldhaber:Babhas are electron positron scattering events.
Pavlish:My question is how do you distinguish these events from one another? Is it difficult?
Goldhaber:It is quite easy. They look very different. A muon pair is just two minimum ionizing particles going in opposite directions. See, when they produce this pair they have to conserve energy and momentum so they go off exactly in opposite directions and one is positive and one is negative. An electron pair also does the same thing, however the electron radiates and so it looks very different in the counter from a muon pair. A muon just goes through. We had some basically electron detectors which are these chambers with liquid argon where the electrons give gamma rays or X-rays while the muons just went through without any interaction. The device was sufficiently well constructed so it was very easy to tell those apart.
Pavlish:It was specifically constructed to be able to.
Goldhaber:Yes, and then the interactionÖ what do I call it Hadronic production?
Pavlish:Well you have beam gas collisions and annihilation into hadrons.
Goldhaber:Annihilation into hadrons. Then you had more than two particles coming out. A whole bunch of particles.
Pavlish:And that would look just like a big, kind of like a firework?
Goldhaber:Well, yes like four or five particles. You can distinguish two from three, from four and so on.
Pavlish:And was there one person whose job it was to look at these?
Goldhaber:We all looked at them.
Goldhaber:No, not together. Separately. Each of us looked at his own computer. Actually, while we were running at SPEAR. While we were discovering the psi I was looking and I made such a table. Itís in those notes if you have that handy.
Pavlish:In this one or this one?
Goldhaber:In this one. Here. I was just sitting there, looking. We had a display, a Cathode ray display, like a computer. And we just counted. They came in one every minute or so, so one could just count them. And I could see Babhas were clear. And then three particles or greater, those were the Hadronic and then the two prongs were the muon pairs. And I was able to see that the cross section has increased because before we had ten of these guys for sixty-one and suddenly we had fifty-five for one hundred and seventy. So this is one in six and this is one in three or so. The cross section has gone up enormously. Also the rate at which these were coming in was much faster. So, of course everybody was also there, was measuring the cross-section. But I happened to look at this screen and count it how many came in.
Pavlish:Just to recap, how does the cross section, how does that give you the information?
Goldhaber:Well, the cross section is these points. They suddenly started going up. So we were somewhere here when I got this data we were here somewhere. And then the next day we continued and when we got up by a factor of seven, I went to write the paper. Then it had gone up another factor of ten. So that was a very exciting weekend.
Pavlish:So how was it that you had the experiment running and I assume that itís still up, itís still in back?
Goldhaber:Itís still working but not for this itís working for Bremsstrahlung, like one of these photon high energy x-rays and so on the machine produces those, it doesnít do interactions anymore.
Pavlish:But at the time this was the experiment running there and this room wasÖ where you were all together; all the physicists working on the project had a lab on the side?
Pavlish:You had a computer lab where you were working at the incoming data in real time?
Goldhaber:This was both the control room and we looked at the data as it came in. And here we were discussing what on earth this is because we couldnít understand what this is. I had this data table you know, and Vera Luth took this picture and caught us discussing. ďHere, what can the quantum numbers be? Can they be found in the particle data booklet?Ē is what I said, basically.
Pavlish:And thatís after you had seen the resonance curve.
Goldhaber:Yes, as we saw the resonance curve.
Pavlish:And what is the relationship between the quantum numbers and the resonances?
Goldhaber:You have to do further measurements of angular distributions to get quantum numbers. You couldnít get it just from the resonance. But we got those quantum numbers. And so well, at first, we didnít have them. We said, what can the quantum numbers be? And we had never seen any resonance this strong, this big before. And then on Monday morning, I came back to Berkeley and I reported this to a group of people here in Berkeley and Roy Schwitters, who is not in this picture, reported it at SLAC, to a group of people at SLAC, and that morning we found out that Sam Ting had already made this observation of what he called the J particle. This one here. Which is kind of the opposite. We collided positron electron and produced this state and he collided protons on the target and produced the state which decayed into muon pairs. Muons and electrons are related. They are both leptons. So we sort of looked at the reactions in opposite directions. Here was a decay of the state into leptons and here was a collision of leptons producing the state.
Pavlish:Wow. How frequent is that in the history of particle physics that you have two different experiments that come up with the same result?
Goldhaber:Different experiments. But I think that this was unique that they came up with the same result from different directions.
Pavlish:Thatís what I meant.
Goldhaber:I am not aware of any other case.
Goldhaber:At least it doesnít come to mind. Maybe there is. And then, when the people in FriscottiÖ Friscotti was also an electron positron collider but they had designed it to go up to 3 GeV and this was 3.1. So when they heard about it, they ran all their magnets hot and they also found it. So in the Physical Review, these three papers were published together. Now, there are several things of importance here. The Physical Review had a rule that youíre not allowed to go to the newspaper before you publish in the journal. But from my talk here in Berkeley, somebody told the student newspaper. And they published it. Although I asked them, please donít. They didnít care. They published it. And then the New York Times came along and said, how come you told them and you didnít tell us. And they were mad. And so then there was a big article in the New York Times with both teams reporting there. And then the Physical Review was bypassed and they wrote an editorial why this was such an exciting thing that they couldnít be held back. And they warned you; in the future donít think thatís a license to do that. Thatís all discussed in my paper here. Well, and then we went on. If there is such a resonance maybe there are more. And we went on, went in very small steps and within the next week we found the second peak, the psi prime. And then we went on and on and on and on and there was nothing more, at least not as narrow as these two. There were some wider peaks which were found later. Much much wider. The difference, again, these were particles. The very narrow thing is what one can consider as a particle, meaning that it lives for finite time though the time is still in the microseconds, still very short. But then, we started to produce resonances. Then we went above a threshold and then you produce things which are resonances.
Pavlish:So thereís a wider peak?
Goldhaber:A wider peak means that they live for a shorter time, an even shorter time. So this was relatively long time.
Pavlish:So is there a cutoff point between what is considered a particle still and what is a resonance?
Goldhaber:Itís basically whether thereís something it can decay into. And what this turned out to be decaying into was charmed mesons. And then I set out on this search and I found the charmed mesons.
Pavlish:So when you saw the peak, did you know that because its narrow that it decayes into other particles.
Goldhaber:We had no idea what it was at first. Charm was one of the contenders. And its only when I found the charmed mesons that it became clear that charmed quarks were real. My coworker Francois Pierre and I found these charmed mesons independently.
Pavlish:Was he at Brookhaven, or?
Goldhaber:No, no here he was a visitor in our group. But he independently analyzed the data and also found this effect. So we jointly got the Panofsky award. Ah, here. Francois Pierre. And we published it together.
Pavlish:So what did that involve to analyze the data? What kind of work? When the data came inÖ
Goldhaber:It involved reading all the data tapes and plotting all kinds of combinations of the various tracks. Here two tracks combined gave a unique mass. That was the signal. Here Iíll show you. Where was it? Well here, you combine the two particles pi, k and suddenly you see a peak in the distribution. Thatís what was involved. Itís discussed in detail in this document. So there were these various steps. Then on top of everything Martin Pearl discovered the tau lepton. Tau is the same name that we used before but this is different. This is the tau lepton. In other words, he found that the electron and the muon which was discovered earlier in cosmic rays, that thereís a third member of the family. Tau stands for third. The third lepton. And that paper is here also. So you see there was a discovery every few weeks which was just epoch-making. So two of those discoveries got the Nobel Prize: the psi and the tau. Charm, not yet. So this was a very exciting time and it all happened within a year or so. Within one year we made all these discoveries. Then we went on for another nineteen years and we made other discoveries that were not as epoch-making. We went to higher energy and we discovered that there was a long lifetime to the B mesons. By long, I mean 10-12 seconds as compared to 10-18 seconds. And so on. So there were other discoveries. Then finally we saw the Z zero. The Z zero is a member of the photon family, which was discovered at CERN. Rubbia discovered that. But we were able to see it in a new machine which was a linear collider that Richter built. So we went away from SPEAR, which was the original machine. Went so to the PEP and then to the linear collider. So this whole process took about twenty years. I worked; I collaborated for about twenty years with the people at SLAC. There is coffee now, which Iíd like to get. Would you like some? Then come along.
Goldhaber:OK, so letís see, where are we?
Pavlish:Shall we continue the conversation with the discovery of charmed mesons?
Goldhaber:Yes, well charmed mesons are described in great detail in this so I think we can maybe I can just addÖ I really donít know what to add because itís so detailed in there.
Pavlish:It is, yes. May I just ask you if you were to describe this to a lay person? You say on page 23 that charmed mesons, you put this together as a kind of explanationÖ
Pavlish:I guess if you could just describe it for a lay person. And then also the results that you came close to or that you actually did discover but because of the statisticsÖ you mention it at the end. But more, Iím interested in how did you come up with these reasons. Did they all come at once or did you have to think for many weeks?
Goldhaber:This was a long story. I spent two years. The discovery happened in one weekend. Also for the charmed mesons I saw it in one weekend and so did my colleague here, Francois Pierre. But the proof that this is really charm took two years to complete. So this was, yes, so I just go through all the reasons why this is a charmed meson. The first one is the threshold which means if you make a K starÖ what would be the alternative? The alternative would be that itís a K star, not a charmed meson. Then meaning a strange meson. Then you can make a K star together with a K meson. You didnít have to go to this high energy. And this threshold shows that it was above twice the mass of 1865.
Pavlish:Of the K star?
Goldhaber:Of this object. A K star you just have to conserve strangeness. So you have to have positive strangeness and negative strangeness. So there was no reason that the second one had to have the same mass as the first one. The fact that they have the same mass meant that thereís some new quantum number thatís involved. Not strangeness. Otherwise it looked like a strange particle. Ok, so that was the threshold. So thatís really the same argument that you had to produce a pair of them. So thatís the same argument. Then, there was a charge decay mode. All of these arguments are saying, what if this was a K star and now, let me see. But then it also decayed into K pi pi and there was a mode that was missing here, that for a K star should be there. Then, remember I was telling you that the width for a resonance you have a wide width whereas for a particle you have a narrow width. So this had a narrow width while a K star you wouldíve expected a larger width: 50 to 200 MeV. This was one less than 2 MeV. Actually itís much less but we could prove itís less than 2. So the width of the particle. Then there was evidence for parity nonconservation. Just like the tau and theta this one also shows parity nonconservation which means that itís a weak decay, not a strong decay since the particle can decay. A particle has a weak decay, while a resonance corresponds to a strong decayÖ and we had evidence for parity nonconservation. I donít know if I show it here or not. But anyway there was such evidence; we have a paper on that.
Pavlish:So all of these results you can tell from the initial experiment?
Goldhaber:No, no from further study. We studied it for two years.
Goldhaber:Until we had conclusive proof. Otherwise weíd say maybe.
Pavlish:What did you change in the experimental setup?
Goldhaber:We studied angular distributions. We did whatís called a Dalitz plot. When you have a three particle decay you can get a Dalitz plot. And so forth. Then there was a prediction that there should be higher mass states and indeed we found higher mass states. If itís a new quantum number, charm, then there would be higher mass states and we found that. This all took a lot of time.
Pavlish:And these were published in subsequent papers?
Pavlish:How many of these were published together in one paper or was it each point was published in a separate paper?
Goldhaber:Originally only the psi, sorry the charm discovery was published in a paper without knowing anything about the quantum numbers. So that was the discovery of charmed mesons. Then the discovery of the charge decay mode. The evidence for parity violation was another paper. Spin analysis was another paper. Study of the D star decay was another paper. D star, another paper. So each of these were separate papers and they went on. Finally also the lifetime was measured. That was much later. So, thatís the story.
Pavlish:I have one more question but Iíll turn the tape over.
Goldhaber:So basically, the idea is that we found this particle but then we studied it in great detail. And each one was sort of a separate experiment. And we came to the conclusion that it must be charm. People didnít doubt it from the beginning but again, there was the question of making it a real proof as opposed to possibly.
Pavlish:So this was after you had looked for other peaks, right? Then you said that you had looked. Iím just trying to understand how this time it was so fruitful. You know, in this experiment. Like you mentioned that this was two years but for eighteen years afterwards, it wasnít asÖ
Goldhaber:It wasnít as exciting.
Pavlish:No discovery was as big.
Pavlish:And I was just wondering was it the energy, was it the precise setup, was it just that here you had something to find whereas otherwiseÖ
Goldhaber:We struck the right energy of e plus e minus. There were other people who but worked at different energies and didnít get very much. So we happened to have the right energy and the right team to be able to exploit it and the right apparatus. The detector was right. Then we built a better detector which was much better but nothing as exciting happened with the new detector.
Pavlish:When the detector was being built, how was the energy chosen? Was it because you were going to subsequently higher energies?
Goldhaber:It was just chosen of what was the convenient thingÖ it just happens that this energy contains these resonances. If we had chosen to work at a higher energy we would never have seen it.
Pavlish:So has particle physics spanned a continuum of energies?
Goldhaber:To some extent, yes. But thatís what we did here. We went on and on and on in energy, all the way up to 7.6 GeV. Starting at 3.2 GeV. And only one such narrow peak (which means a bound state) was found.
Pavlish:May I ask you about this image of the psi, when you connect the points. What exactly are you connecting there? Is that just a cute thing? Why are these crosses and these dots, for example?
Goldhaber:The crosses are measurements; each one is a measurement as it crosses a wire in the chamber. So these are measurements. So there were measurements in the wire chamber. These are counters which got hit by the electrons, and these are counters which got hit by the pions. This is the reconstruction of the track. Itís not fake, as a picture. Itís the actual reconstruction of the tracks. Well, I had called it a psi to begin with and then we found that it looked like that.
Pavlish:So do you think youíre psychic that you knew from before that it would like that and then it did?
Goldhaber:No, I donít think Iím psychic. I just happened to pick that.
Pavlish:It is just a funny coincidence?
Goldhaber:A funny coincidence, yes. These points are just some points in the chamber so theyíre really not relevant. Itís really just the xís and the counters.
Pavlish:Maybe from a philosophical vein, part of the enterprise of physics is that you expect nature to behave in measurable ways, wouldnít you say? And the data that you collect from experimentsÖ
Goldhaber:I just noticed a mistake here. These are pi. Somebody wrote them as etas. Pi plus, pi minus.
Pavlish:So, go ahead.
Goldhaber:This is a cartoon that Dave Jackson made because there were one hundred theories coming out about what this might be. Just like now there are one hundred theories coming out on what dark energy is. And we donít know. And here, there were a few experimental papers. And Roy Schwitters but them on a balance to show that experiment is much more important than all these theoretical papers. You had a question.
Pavlish:This isnít directly related but I would like to know your opinion about this. As a physics researcher you found these truths about nature. Some people who arenít of the scientific bend donít understand how is this possible. Some humanists, they think, how is nature so to be ordered and arenít there things that only happen once in an experiment or in nature. I was wondering, have you ever encountered such a happening? Do you believe that such happenings can exist or is that antiscientific?
Goldhaber:The only one I know about is the big bang, which may have happened only once. However, we donít know that it happened only once. My point of view is that however strange it is itís obvious that itís allowed. Things can only happen if the laws of physics allow it. If itís allowed then maybe it happened many more times. People talk of other universes which are not connected to us. We cannot find out about them. It may have happened many times but elsewhere, outside of our... We can only know what happens within 14 billion light years. If you take a sphere, we only have information on what came to us. Now who says that the universe is not much bigger than that. And other things can have happened there. Some people speculate that there may be other universes. What makes it plausible to me is that if the laws of physics allow the big bang, then why should it occur only once. Because in general in physics if something is allowed to happen, it happens. Itís not a fluke and itís not unique.
Pavlish:So what was it, in those two years when you were looking, were those two years a heightened time of excitement because you had to come up with all these proofs?
Goldhaber:I wouldnít call it quite so dramatic. It was sort of findingÖ People were pretty much convinced that thatís what it was but I feltÖ In fact, I was challenged by my friend Gosta Ekspong. Can you prove that this is charm? And I accepted that challenge and proved it. But it wasnít the same excitement as finding charmed mesons.
Pavlish:How would you relate the excitement of finding the charmed mesons with the rest of your work in physics? Is it somehow apart? Most physicists donít have the privilege of witnessing or producing such a great discovery. How is it continuous but also discontinuous from the rest of your life in science?
Goldhaber:Well, you move along. You work every day and nothing happens and you work for a month, you work for a year, nothing exciting happens and then all of a sudden you get this tremendous excitement of a major discovery and Iíve been fortunate that Iíve had some of those. But the rest of the time you sort of keep on working with the hope that maybe something like this will happen. But it doesnít happen often. It happens a few times in a lifetime. But when it does happen, it makes the rest worthwhile.
Pavlish:Would you say that it is these discoveries that complete the life in science? Or letís say we erase all the great discoveries of your life in physics, would you be just as satisfied, as happy with your work?
Goldhaber:Yes, I enjoy my work as a physicist. Even when I work all day and donít make a major discovery, I enjoy what Iím doing. The major discovery is the extra that you get if youíre lucky. I enjoy the steady work in physics. Like weíre just now looking for supernovae and so on. Itís fun for me to search for them. You donít always get a major discovery like this.
Pavlish:Do the major discoveries, in your experience, come in clumps, as this seems to have?
Goldhaber:This was a very exceptional period. No, they usually... well, sometimes they can. Like the Alvarez group had a very exceptional period: they found a lot of resonances. That was a very exciting time. So in some sense, maybe clumps is the right way and then there are fallow periods when you donít find anything.
Pavlish:Could we talk a little bit about the personal interaction. Itís very important to have people who work well together. People who are all smart. Do smart people who are going to be making these greatest discoveries, do they naturally become attracted to one another, naturally become friends, become colleague?
Pavlish:There are better physicists and worse physicists. Are there different skills that are not so easily measured as good or bad?
Goldhaber:Sometimes there are different skills and you need different skills. Some people like to build equipment; some people like to use the equipment. Some people like to think about the equipment, think about the results. So there are all these different specialties. In some sense you need the other people; you need the knowledge, while you pursue what you do best.
Pavlish:So in your group what was it like, what was the dynamic? Who was doing what kind of work?
Goldhaber:I was always working on the analysis of the data. We had people who worked on building. We built part of the detector together with our colleagues at SLAC.
Pavlish:So you were doing analysis but also building, when necessary. You came up with the idea of the magnet.
Goldhaber:No, that was not my forte. Only this one time, the magnet for the antiproton that I came up with. In general, in this equipment building my colleagues did more of it than I did.
Pavlish:Would you say that you were more theoretical than they?
Goldhaber:No, no, not theoretical. Just not in building equipment. We had John Kadyk and Gerry Abrams and George Trilling. Those were the main people in our group. They spent more time on the building. Then there was also even the writing of programs, how to fix the data. They also worked on that aspect. But I worked on actually looking at the data. I somehow have the ability to look at the data and get something out of it. So in a group thereís a natural division of what people concentrate on.
Pavlish:If one division is lacking, would you recruit somebody?
Goldhaber:Possibly yes, yes you might have to. If you donít have anyone who knows how to do Öthat was the sense in which the people at SLAC asked us to join in their experiment. They were lacking this ability, this experience I should sayÖ thatís how it happened.
Pavlish:When you say that youíre very good at data analysis, would you ever come up with something and then somebody else would do the analysis separately and then you would compare? Were there people whom you were particularly good at working like that with?
Goldhaber:Yes, whenever I found something, I always felt that it needs to be checked by somebody else. I never feel confident that thatís it. I can make mistakes. There were always checks in our group. And similarly I checked when Martin Perl found the tau lepton, I checked the data and I agreed with it. I did not agree with his interpretation although he was right. I wasnít convinced that it was a new lepton. But I was convinced that something was happening there.
Pavlish:In this particularly extraordinary time, what was your interaction with theorists? Your group didnít have any theorists?
Goldhaber:We did not have a house theorist. But we had theorists. I had a close interaction with Shelley Glashow. I interacted with him. In fact he claims that he set me up to find charm. Thereís some truth to it but not completely. There was a meeting in Madison, Wisconsin where the major topic was why we didnít find charm. We had found the psi already but why didnít we find charmed mesons. At that meeting I decided Iím going to spend the next month looking for charmed mesons and find out why we donít find them. On the way home I met Shelley. At the airport, on the plane, he was trying to convince me that I should go and measure, and find out whatís going on with this charm. He takes the credit that he suggested it to me. Itís true that he had suggested it to me, but itís also true that I had already decided it beforehand.
Pavlish:You had already had the inspiration yourself.
Goldhaber:Thatís what Iím going to do. It was such an obvious thing that was missing in our data.
Pavlish:How hard was it to go back?
Goldhaber:Then I went back and the first weekend I found it. My colleague Francois Pierre also found it independently at about the same time. Then we wrote a note together to the group stating what we had found. So I didnít have to work a whole month on it.
Pavlish:With the people in the group, did you go to lunch together, dinner together? Was it a very close-knit collaboration or was it, you would work together but the personal element was not very important?
Goldhaber:We went to lunch sometimes but it wasnít a must. You saw today, people get together at lunch. Sometimes we donít. But we did have group meetings where we discussed our work, and the progress of our work.
Pavlish:Were those every week, or every month?
Goldhaber:For a while it was weekly. Weekly group meetings. Let me see if I can find the Gersonfest pictures. Youíve seen those?
Pavlish:The ones online?
Goldhaber:Thereís a picture of some students and I, well, youíve seen it, are working on a, are having a seminar at my house. And we had those frequently.
Pavlish:And you had also technicians who were. How many?
Goldhaber:It varied. First when we were working on photographic emulsions, we had quite a few technicians, as many as fifteen or so scanning the emulsions. Then when we worked on bubble chambers we also had technicians who helped analyze the bubble chamber film. Then when we worked at SPEAR, basically we did not have technicians. Just the physicists worked on the programs. So there is a slow transformation from emulsions to bubble chambers, bubble chambers to colliding beam electronic machines, different electronic machines at different detectors, at different colliders, and finally I went into astrophysics. So there are all these, the techniques change.
Pavlish:Has this change baffled you, has it amazed you, the rate of change of the technological sophistication available to physicists? Or, do you see it as natural, with all the discoveries being made, that physics would produce technology, technology would show new physics, new physics would lead to new technologies.
Goldhaber:Yes, the latter. I just went along with the flow. It didnít amaze me.
Pavlish:So if you look back to when you were a boy, you didnít know what was to come but you were going to be a part of what was to come.
Goldhaber:Certainly not. I was interested in physics. I was influenced by my brother being in physics. He was in nuclear physics at the time. It just seemed fantastic that I could do that work and even get paid for it.
Pavlish:Well, this is another drawing of the psi.
Goldhaber:Yes, here it happened differently. There it didnít look like a psi.
Pavlish:Well, it still has that shape.
Goldhaber:This one needed to be on this side, this one on that side to make a psi. Sure, it is that same phenomenon. Although these are kind of hard to see.
Pavlish:So these are computer plotted?
Goldhaber:No, those are hand plotted.
Pavlish:So you still did some hand analysis.
Goldhaber:This is not my plot. This is made by various people who found evidence which made us look back to find out what was going on. There was this funny point here. And similarly funny points here. This was the original, Kadike found this which showed some anomaly here. There was a tiny indication. I explain in there why that happened. Actually, I explain it in the other paper.
Pavlish:So, once you knew that you had found something extraordinary, you took pictures or?
Goldhaber:One of the physicists, Vera Luth came prepared and took photographs and brought along some champagne even. [opening of filing cabinet] These are all my papers. Hereís a biography. So, what else would you like to know?
Pavlish:Perhaps, if you would talk a little more about this in context of the history of particle physics. Maybe about how your discoveries were so important for the formulation of the standard model.
Goldhaber:The early work, the introduction of the quarks was a result of the resonances which were discovered. Our contribution there was not finding any positive strangeness baryons. And then from the quark model, the standard model was built up. And we havenít reached the next chapter where Leon Lederman discovered another object, like the charmed mesons, which were the bottom mesons. There are more chapters. Thereís much more stuff. The bottom mesons were discovered. Which behaved just as another quark. Charm was the fourth quark. Bottom was the fifth quark. Later on they found the top which was the sixth quark. Now we think there are six quarks. With the bottom, essentially the same story repeated only of course it was different. That was all happening at Fermi Lab and at Cornell. So they found first of all the resonances like the psi, only it was the Upsilon. Then there were the bottom mesons, which just like the charmed mesons. And later on at FermiLab they found the top meson. Top pair production. Itís a little different because itís much heavier so the situation was different but itís the continuation of the same story. That really engrained the six quark model; six quarks but coming in three families. Up down is one family. Strange charm is the second family. Top bottom is a third family. It was kind of a repeat of the same story. But we were fortunate in finding the first time around the charmed meson. The repeat wasnít as exciting anymore as the first time around. But the bottom meson is very important. Right now theyíre set up in SLAC and in Japan to study bottom mesons and study CP violation. It turns out you can study CP violation with bottom mesons. Theyíre doing that. Thatís happening and theyíre getting a lot of new information there.
Pavlish:May I ask a question, a more basic question. Is it the quantum numbers that distinguish the charm from the bottom? Why would you be able to study CP violation with bottom but not with the charm?
Goldhaber:I can answer the first part of that question. They have different quantum numbers which are called flavors. We now know, for whatever reason that the quarks come in three different flavors. There are three different pairs of quarks. Thereís up down that protons are made of. The others, you have to go to high energies to produce them.
Pavlish:So would you say that the up, down are the only naturally occurring ones at our energy scale?
Goldhaber:Yes they occur at relatively low energies so one can produce them easily. Then one found only the strange quark. And thatís where Glashow predicted that there should also be a charm quark to complete the same pattern of up, down.
Pavlish:Thatís at higher energy.
Goldhaber:Yes, at higher mass. At even higher mass you get top and bottom. Top is very high mass. And we donít know why those exist, why nature decided to replicate it three times.
Pavlish:Could it be that other flavors exist at higher energies or lower energies?
Goldhaber:Lower energy, no but higher energy we donít know. Thatís what this new machine at CERN, the Large Hadron Collider at CERN will tell us what happens at higher energy.
Pavlish:What is the energy limit at this point?
Goldhaber:Energies up to 2 TeV. 2 x 109 electron volts, at Fermilab. At the Hadron Collider it will go to 14 TeV. So we are looking forward to finding out whatís happening. We donít know. There are many theories, like the Higgís and so on. But we really donít know. It may turn out completely different. And whether there could be a fourth family of quarks, who knows.
Pavlish:The theory allows it.
Goldhaber:Let me think. The theory has now been built into three families. But Iím sure it can be accommodated. If found, it can be accommodated. And there are all kinds of theories of Technicolor and supersymmetry and Higgís. All kinds of things are expected, but the experimentalist has to stay within whatís actually being seen.
Pavlish:How important are the theories to you as an experimentalist?
Goldhaber:Actually, my approach has been I just want to find out whatís there without being prejudiced by theory. The exception was looking for charmed mesons. There was a theory and we were specifically looking in that direction.
Pavlish:Was the discovery in that case different?
Goldhaber:Yes, itís a little different. Actually, I should correct that. Also when I was looking for the antiproton there was a definite prediction. And the answer would have been yes or no. We found it or we didnít find it. But otherwise I have always, well it varies. I shouldnít be so categorical. I have mainly tried to find out whatís there as opposed to whatís predicted to be there. But there are exceptions. Also when I looked for the rho meson I was looking for something specific and didnít find it and found this Bose-Einstein effect instead.
Pavlish:Thatís the case of another.
Goldhaber:Thatís a case of just looking.
Pavlish:But you wouldnít say that the different kinds of discoveries feel any different or in your mind is there any further classification?
Goldhaber:I like them all, whether itís predicted or not. It is a thrill to find something.
Pavlish:Have you found that depending, maybe not in the phases of your career, but in different years that thereís a different balance betweenÖwhether itís better to be working on experiments at a certain time based on the balance with theory. I donít know if my question is clear. Because you had the theorists and the experimentalists working. Was it more exciting when the theorists were waiting for you to produce something or more exciting when you had new equipment and you could look for whatever you wanted and maybe show something to the theorists that they didnít expect?
Goldhaber:I tried to work on whatever my equipment was capable of doing. I try to do that. From time to time I pursued specific ideas that were around then. The antiproton was one. The rho meson which I didnít find was one. The first resonance, the Fermi resonance where we looked specifically and we missed it, which was one. So as I think back, I have followed, part of my work has followed theoretical ideasÖ the psi was a total unexpected discovery. More recently, dark energy was a totally unexpected discovery.
Pavlish:With nothing in theory?
Goldhaber:The theorists said no, it canít be. So it varies, thereís a mixture of finding things because you expect them or just finding things. Like the Bose Einstein statistics. We didnít know what it was until later.
Pavlish:So you donít think in physics thereís ever a chance for experiment and theory to diverge too much. That thereís usually this coherence that one goes ahead, then the other gets ahead.
Yes, sometimes one is ahead, sometimes the other is ahead. Donít forget also that sometimes there are one hundred theories and only one of them or none of them is correct. Sometimes itís a question of deciding between different ideas, different theories. Like what we are planning now.Session I | Session II | Session III | Session IV | Session V | Session VI