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Interview of Abraham Seiden by David Zierler on May 21, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
In this interview, David Zierler, Oral Historian for AIP, interviews Abraham Seiden, Distinguished Professor Physics Emeritus at UC Santa Cruz. Seiden discusses his current interests in developing silicon detectors for the high luminosity LHC and sensors for the TRIUMF accelerator, and he surveys the current interplay between theory and experiment in particle physics more broadly. He recounts his birth in a displaced persons camp after World War II and his childhood in Brooklyn and then in California, and he explains his decision to go to Columbia for his undergraduate studies. Seiden describes his graduate research at Caltech and then UC Santa Cruz under the direction of Clemens Heusch to conduct research on deep inelastic muon scattering at SLAC. He discusses his subsequent research on the intersecting storage ring at CERN and he describes how the “November Revolution” at SLAC resonated at CERN. Seiden describes the opportunities that led to him joining the faculty at Santa Cruz and his involvement on the high PT photon experiment at Fermilab. He recounts his interest in Higgs research and the leadership of George Trilling and he explains the origins of the Santa Cruz Institute for Particle Physics. Seiden discusses his advisory work for P5 and the broader state of play of particle physics in the United States and he describes the impact on CERN following the cancellation of the SSC. He discusses the import of the ATLAS upgrade, his involvement with LIGO, and his contributions to BaBar at SLAC. Seiden narrates the run-up and the impact of the Higgs discovery at CERN, and its impact on searching for physics beyond the Standard Model. He surmises how a particle physics approach will help to unlock the mystery of dark matter, and he explains his motivations to write an introductory textbook on particle physics. At the end of the interview, Seiden compares the opportunities in the field that were available to him as a graduate student as opposed to his own students, and he explains why working on the SSC was the most fun he’s had in the field, despite its ultimate fate.
Okay. This is David Zierler, oral historian for the American Institute of Physics. It is May 21st, 2021. I am delighted to be here with Professor Abraham Seiden. Abe, it's great to see you. Thank you for joining me today.
My pleasure. Thank you for making time for this.
Abe, to start, would you please tell me your title and institutional affiliation?
Okay, so two things about the title. I'm a Distinguished Professor of Physics Emeritus. I retired a few years ago. But the University of California has a system where you can be recalled to service, so I'm recalled and continuing my research and the title there is Research Professor. And I'm with UC Santa Cruz, and the Santa Cruz Institute for Particle Physics. For which I was director for thirty years.
Abe, to what extent is "research professor" as a designation, does it allow you to do all of the fun stuff and none of the administrative stuff?
Yeah well you can do pretty much what you want. Typically, people either do this because they want to do some teaching, or they want to do research. So, my focus has been research. So, I can have as many graduate students as I want, get grants, but I don't have to do department meetings, academic senate meetings (laughter). So, as you said, I can do all the fun stuff and not do some of the other things. I can go to department meetings if I want, or not go if I want. So, I mostly don't go, although I keep up with what's happening.
Abe, just as a snapshot in time, what are you working on right now? What's interesting to you in the world of physics?
Okay, so we are working the last few years on a type of silicon detector which allows you to measure the time of a particle hit very accurately. It's a new thing as of the last, I don't know, five years or so. It's going to be in the detectors at CERN to be used at the high luminosity LHC. And we're working on a next version, which not only allows very accurate time measurement, but also very accurate position measurement. So, this would do what we would call four-dimensional tracking. And so, we have a group that's typically fourteen people at Santa Cruz, which includes a lot of students. We have undergraduates, graduate students, postdocs, and a few faculty. And we're having lots of fun with this and I'm giving a talk on this at the upcoming conference called TIPP in Canada next week. And I've talked about it at various other meetings recently. So that's been my main interest, it has been technology. But our group is continuing its work on the ATLAS detector at CERN, where I was involved in the upgrade, like I said, for the high luminosity LHC where they're adding detectors forward-backward to measure time very accurately to help pin down which particles go together in which interactions, because there will be 200 events overlap every crossing on average, so very complicated, difficult environment. We're also working on something very different, a small experiment, which was just proposed for the TRIUMF accelerator in Canada to measure very accurately the ratio of leptonic decays of pions to electrons and muons. We're working on an active target made of these kind of sensors. A very little device, which would tag the pion decays. I assume I use some jargon like muon or whatever is okay?
Oh, I'm good. This is the world I live in.
Okay (laughter). Yeah, stop me if I say something that doesn't make too much sense.
Abe, I'm curious what you think, given what you just mentioned. What's your take on the g-2 muon anomaly at Fermilab right now that's causing so much excitement? It's a purely speculative answer of course, but what do you think about this possibly being new physics?
Well, I think the community of theorists need to pin down whether they believe that their calculation for g-2 is right. There are differing views on this calculation. This has been an issue for a long time, and a lot of it was experimental for a while, where using tau decays or e+/e-, you were getting different answers. Anyway, if they decide it's real, it looks like new physics, which now may be visible in certain other places also. There are anomalous B decays, some which should be calculable pretty accurately like B to D or D-star with a tau, versus with a muon or electron, seem to not agree. And apparently there are some questions about whether the CKM matrix is unitary or not. So, this experiment at TRIUMF is aimed at the same kind of physics potentially, given that we don't know what it is. The experimental team would like to get down to a measurement that is as good as the theoretical prediction. So, we've been working with them. It's a group that I've never worked with before. Very nice people. And we'll see where it goes. So, they're requesting a new beam line at TRIUMF and the committee to look at this recommended it very highly just a few weeks ago.
Abe, as you framed your answer, it brings me to a broader question, and that is, your sense of the general interplay in particle physics right now between theory and experiment. Where do you see this interplay at its most productive level, circa 2021?
Okay, well, really there are a number of things. I mean, very accurate predictions of some of these decays to look for flavor physics violations is one area. We have lots of speculations about dark matter, which is probably the most outstanding issue in particle physics, I would guess at the moment. Since we have discovered the Higgs and so far it looks normal. I mean, normal being what you expect from a single Higgs at the given mass. As those things get measured better, we'll see if there are any surprises or not. The search for supersymmetry so far has not found any. Delineating more places to look is a good thing to do. I don't know whether we'll find anything. So those are some of the areas. I think it's been a difficult time for theory, in that the Standard Model has been very successful but maybe we're entering now a new very interesting time, as we find some funny results. So, for a long time, everything agreed with theory, you found the Higgs, it agreed with theory, and there was no supersymmetry found. So those were, I would say, difficult times, but like I said, maybe we're finding some really interesting new results. And the theorists will follow this out, I'm sure.
To what extent are we stuck by not operating in higher energies that are currently available?
You know, these questions are not high energy questions. You want to keep going to higher energies, but there is not a clear target in this case. I mean, when we went to the LHC, there was kind of a what was called a no-lose theorem, that you would either find the Higgs, or if you don't find the Higgs, that's maybe even more interesting-
Now for higher energies, there isn't a similar thing. It's really to try and test the Standard Model more deeply and see whether there's something at this next energy scale. So, we've been exploring the kind of TeV energy scale. Maybe we can go up to the ten TeV energy scale. You never know when you'll discover something. I mean, there were neutrino oscillation experiments for decades, finding nothing. So, you can conclude, "Oh, there's probably no neutrino oscillations." And then it was just discovered almost by accident. And fortuitously, because the size of the earth was well-matched to what was needed to see neutrino oscillations. And then all of a sudden, all sorts of things happened. We discovered oscillations for neutrinos from the sun, and neutrinos from reactors- the first experiment sets a scale for where you might want to look. So, it's exploratory, the next energy scale, but I don't know that we could say for sure what we would find.
And Abe, it sounds like this past year-plus in the pandemic, it really hasn't slowed you down very much?
No, actually, it's been quite interesting. We have meetings every week. I have too many meetings, probably. We managed to get people back into the lab. Kind of two people at a time. So mostly our very excellent postdoc, and maybe a student. And now things are opening up more. We were just talking about maybe getting together in June and going out for lunch for the first time.
Oh wow, that's exciting.
It's been- so over the last year, I've been to campus I think only twice, would you believe, in a year? But we have our meetings and are making lots of progress on our novel sensors and electronics. You know, maybe it's conducive to thinking harder in its own way.
Well Abe, let's take it all the way back to the beginning. Let's start first with your parents. Tell me a little bit about them and where they're from.
Okay, so I will give you my history insofar as I know it (laughter). So, I was born in a displaced persons camp in Berlin in 1946. And my parents were from Poland, from a small town in the area not that far from Warsaw and Lublin, I don't know if you're familiar with that part of Poland?
And they left Poland going east into Russia when the Germans invaded Poland and were wandering around. So, number one, they never wanted to talk about it. So, I can't tell you too much. It's quite interesting. My brother was three years old when this started, so he's ten years older than I am. And so, he made it through six years of wandering. What you would think of as very formative years for someone. And he never wanted to talk about the war either. Which was really interesting. So, the only thing I pretty much know is they were for a while in Tbilisi, Georgia. And they found that a rather positive place to be for part of the war. I don't know how they got back to the displaced persons camp. Most of their relatives were killed in the war, during the war. So, when they got to this camp, my mother was very depressed, not surprisingly. And the rabbi in the camp recommended that they have another child, and so that's why I was born (laughter). And then we got to the U.S. in 1948. So, they were in this displaced persons camp for three years. So, they were wandering six years, and then displaced three years, which was nine years, and then we got to Brooklyn, NY, where we lived for something like fourteen years or so I guess. So, my younger years were there.
Abe, so your parents were married before the war, obviously?
Yes, yes, indeed. They both passed away a while ago.
Do you know if they were ever imprisoned? Were they ever in any of the camps?
No, they were not, but they got separated a few times and met again later. So, my mother with my young brother, it was easier for them without my father, to get help while wandering around. So, they were separated sometime and then got back together. But I don't know the details. But they were never in a concentration camp. My wife is from Romania. Her parents met in concentration camp. They were from the Hungarian-speaking part of Romania, and were sent to concentration camp in 1944, so a short period of time compared to people from Poland, and they survived and more of their relatives survived than in my parents' case.
Abe, do you know if your parents came from more secular or more orthodox backgrounds?
More orthodox, but not extremely orthodox. So, my father was a shoemaker, and he was apprenticed at the age of eight or nine years old. So very young. But you know, all the people in these small towns, they learned to read Hebrew, to read Yiddish, and kept the holidays pretty, you know, faithfully. And this continued in Brooklyn for my parents. My brother went to Yeshiva there. I didn't. I went to the public school because my parents didn't have enough money to pay for the Yeshiva for me. So, I have kind of a different background than my brother in that sense. It was a pretty tough neighborhood. I went to John Marshall Junior High School, where there was an undercover reporter, the principal committed suicide. A lot of things going on. Very crowded. You could only walk on one side of the hallway, and then they had arrows where you could make a U-turn. And they had hall monitors. But they had a program called SP classes, where you did three years in two years. So that was the program I was in, which was at the junior high school. And then I went to Stuyvesant for a year, and then my parents moved to California, so I finished high school in California. And I found California to be really wonderful, actually, I have to say. So, I think going to a high school there where you had both boys and girls was a better environment. Stuyvesant had only boys then. That's changed, I believe. And just the natural environment with mountains and trees and stuff, I found to be a good change. And I had several very good teachers in high school, in physics and math, who had a strong influence on my interests.
Why California? What brought your parents to California?
Yeah that's an interesting story. They had some friends from their town in Poland living in California, and they were interested in maybe starting a business together. You know, like a fast food restaurant or something to get away from what they were doing in New York. And in the end, it didn't work out, so they moved back to New York after two years.
But you stayed?
So, I finished high school in California, and then they moved back. I actually stayed on my own over the summmer after they moved, working at the Purex Bleach Corporation (laughter). I got a job which was recommended by our high school math teacher, trying to optimize the timing of when they would do promotions and things. That was also very different and interesting. And I came back a few times in the following summers. I used to go back and forth from California to New York by Greyhound bus.
Because we didn't have any money. Terrible experience (laughter). Three days, three nights by bus. It was- I prefer not to do that again (laughter).
Abe, when did you start to get interested in science, and was it physics specifically when you were young?
Okay. I was interested in a lot of things. There was a book called the Microbe Hunters, I think, for example. That was very interesting. My brother was a chemical engineer, and so he had all sorts of chemicals at home. That was interesting. I remember making bromine, would you believe? Which smelled terrible. Just on a day when my parents were having visitors. This was not good (laughter). So, I was interested in science, but not yet physics and math specifically. I would say in high school, that's when I got pretty much mostly interested in that. Perhaps even math more than physics. I don't know. In physics, we had some great demonstrations. I remember this demonstration where you would have a kind of a gun shooting a bullet, and a can dropping at the same time from the ceiling and then the bullet lands in the can, because everything falls at the same rate. That was a great, dramatic demonstration. So, there were things like that. Our school participated in a math contest and I can't tell you, I don't remember, all the places that entered this contest. Whether it was just Southern California or more statewide. By the way, we lived in Downey, CA, which is in Southern California. Anyway, I won the contest with a partner. It was a two-person thing. My partner’s name was Bob Cooley. I still remember who. So, I got a briefcase and a slide rule (laughter).
You're all set.
Yeah so that was fun, and then I went to Columbia University.
Now did you specifically want to be in New York? Did you want to be closer to your folks?
Yeah. Yes, is the answer to that. And I got a scholarship because my parents probably couldn't afford to pay. It was probably twenty times less expensive than now (laughter). I believe. And so, I actually majored in applied physics, so I was in the engineering school, but I took all the wonderful classes in humanities, civilization, art. We had some very famous physics teachers. My first class was with Jack Steinberger. I had Leon Lederman. I had Polykarp Kusch who did a very good E&M class. Henry Foley, who did quantum mechanics, a very good class. So very interesting classes. I was the valedictorian of the class in the engineering school when I finished.
Now did you think you were going to be an engineer? Was that the original plan?
Yeah, maybe. Maybe. Although I picked applied physics. With my brother an engineer, and I didn't know very much about anything (laughter). And so, it seemed like a possibility. Maybe nuclear engineering, then? Which was then a popular subject. But I picked applied physics, and I was very happy with that choice actually. And then I went to Caltech, and I have to say that that was an easy choice, after reading the Feynman books. The famous red books on the lectures on physics.
Abe, as an undergraduate, were you set on experimentation? Did you think about theory?
Yeah, I thought about both, yeah, I wasn't sure with that.
Particularly because you liked math, so I was curious about that.
Yeah. Yeah, I was not sure. I wasn't sure. Anyway, at Caltech I had two classes from Feynman, so that worked out well. Quantum mechanics and particle physics. You can imagine how good these classes were.
What was it like to take classes from Feynman?
He prepared very carefully for every class, and the particle physics class eventually became this lepton- I think it was called Lepton Photon Interactions, a book. Where we talked about deep inelastic scattering and what happens in the final state. All sorts of stuff which guided a lot of my thinking afterwards, I have to say. It had a very strong impact on what I was interested in. So, I eventually somehow drifted into- I had other good classes. I had Kip Thorne for general relativity. And eventually, I decided to do experiment, to just see the stuff in action, let's say, rather than just thinking about it. And I got started on an experiment at SLAC which involved deep inelastic muon scattering. And my advisor, Clemens Heusch, moved actually in the middle of this experiment to Santa Cruz, and so I moved.
Ah, that's the question. Why would you leave Caltech in the middle of graduate school?
Yeah, totally because of that (laughter).
What was the circumstances of his move to Santa Cruz?
I think he in the end didn't get tenure at Caltech. I don't know if the decision was final or not, but it was a chance to start a totally new group, because it was a new school, with very close links to SLAC, because it was very close to SLAC. I mean, within an hour drive roughly. And so, this was quite interesting. We were interested to see whether the final states change with q-squared and a bunch of things. It was a very different period for doing experiments than now. I mean groups, we had a large group which was maybe ten people (laughter). So those were the sizes of groups then. And you got to do a lot on the experiment. I designed the beam line for the experiment, I designed the collimation system. We used a streamer chamber. I didn't design the streamer chamber, but I actually built the streamer chamber. The other groups, you know, did the gas system- I designed the scintillator system for the trigger. So, you really got to do a lot of things including piling lots of lead bricks and things like that. And so that was my experiment. It took a little longer to finish with this move, although not that long. And then I went to CERN afterwards. CERN, again, was kind of a somewhat new lab. They had just opened their intersecting storage ring, which was the highest energy collider. It was a proton-proton collider. And I was a fellow, so you could go around and decide what you wanted to do. It was the first, the only time in my life I was so careful. I took a notebook and wrote down what each experiment was doing. There were some that had lots of interesting instrumentation, but I decided I really wanted to focus on a physics idea I had, which was to use an experiment that was starting to look for high PT hadrons, and look for the signature of quark fragmentations. And we published the first measurement of that, actually, in hadronic scattering and found that it looked like what you saw in e+/e- final states. So that was very exciting, you know, to see first-hand the signature of a quark. The way I would put it. Because you don't see them on their own.
Abe, what was it like being at Santa Cruz in its earliest iteration? Did you feel like you were part of a building campaign?
Yeah, yeah. I mean we had a few faculty members. The department was small. What happened was in 1980, we started a new research unit, it's called SCIPP. Santa Cruz Institute for Particle Physics. It's an organized research unit, which is another thing that UC has, and you can have campus-wide units or you know, units that transcend the given campus. So, the Lick Observatory is actually a very large multicampus research unit. We did a campus one, which I think was a very good decision. And these normally need to be interdisciplinary or have some special reason. So, our special reason is that we had a unique access to SLAC. That was the special reason. And it was interdisciplinary in that even back then, we had a certain number of people in particle astrophysics. And that connection has grown a lot. We've done other things. So, I was the founding director, actually, in 1980. And I was the director for 30 years, where we added the whole large number, or some number, of faculty in particle astrophysics. We broadened out to neurobiology. Where the connection is instrumentation. And we've always maintained a very strong interest in instrumentation besides physics analysis. So that's been one of the things we've done in our experiments at SLAC. Now at CERN. It would have been at the SSC, which unfortunately got canceled. And that's been one of our trademarks.
Abe, tell me a little bit more about how you developed your thesis research in graduate school.
Well, the idea for the experiment was my advisor's, not mine. But I found it to be really intriguing given the interest in deep inelastic scattering with this new theory that had just come out where what we're measuring in the q-squared dependence and energy loss in the scattering is the x distribution of quarks in the proton. The fractional momentum or fractional energy distribution leading to scaling in the distribution. So, this was the new hot idea in a way. So, some of the other ideas that were out there had never gotten much traction at Caltech. So, for example, Regge theory, which was a hot topic then, was not very popular at Caltech. There was more of an interest in field theory, really, and it was the era of Murray Gell-Mann and Feynman. And Feynman had just come out with this parton model to explain the deep inelastic results, so this was intriguing to do an experiment like this. The other experiments to measure scaling, had already been done using the electrons, and so doing this muon experiment was a way to look actually more at the final states. Because the other experiments just looked at the scattered electron and measured the distributions that way, without looking at the final state. So that was the reason for my interest.
Abe, to go back to an earlier question, it sounds during graduate school that theory was providing a tremendous amount of guidance for this work.
Oh yeah, without a doubt, yeah.
In what ways were you contributing to what would become the Standard Model, do you think? What was being built with the Standard Model with this research?
Well, basically what became of interest was QCD, the underlying theory for the strong interactions involving quarks. It's quite interesting. The year that the Higgs mechanism was proposed, and nobody paid attention to it, the hot topics involved quarks, color, and things like this. Measuring the quark fragmentation in my CERN experiment was the other angle on quarks in the proton, and I actually wrote a paper on- a theory paper on a model for quark fragmentation, which included the contribution of decays of mesons and things. So, it was one of the early papers on that. And then that whole topic was taken over by more theory theorists than myself. So, I would say that was our contribution there. I've worked subsequently on the BaBar experiment at SLAC. And that contributed to nailing down the CKM matrix, with the phase in the matrix giving you CP violations. I've had an interest in flavor physics going back to graduate school, besides the high PT hadron physics. I worked on, unfortunately I didn't publish it, on what you should look for to find a heavy lepton. Which I wrote up and I had it ready, and then I left Caltech and it never became a report, unfortunately. It would have been a nice addition to things I had done.
Abe, who was on your thesis committee?
Who was on my thesis committee? Well I can tell- being advanced to candidacy, which happened at Caltech, I had George Zweig (laughter). I had John Matthews, who unfortunately died in a boating accident. I had my thesis advisor. I was very nervous during that (laughter). I remember being asked about the case of two particle going to three particle reactions, what are the invariants? I decided I would be very clever and discuss two goes to n instead of two goes to three and got myself into hot water (laughter). I should have answered the question which I knew the answer to. Anyway, on my committee when I finished my thesis, it was Joel Primack, I recall, my thesis advisor, I'm trying to remember who else. Probably Michael Naunberg. That was about it.
Were you around SLAC during the November Revolution?
No, I was at CERN.
Oh, you had already defended and gone to CERN at that point?
Yeah, yeah. A little before. A little before. I liked CERN a lot. I also did a sabbatical at CERN in 1985, where I worked on an experiment, but I spent a lot of the time working on my ideas on silicon trackers. Where I developed a lot of things which our group has focused on ever since. So yeah, I think CERN is a really great lab. It was really nice when I went in '74 because it was smaller, there were no crowds in the cafeteria, it was easy to go eat. They had steak and french fries til late at night, so you could work all day and go eat something at near midnight (laughter). And they had this very nice tradition. All of the groups went for a coffee break once or twice a day, pretty much, to go sit and talk, and of course everyone was coming, visiting CERN on and off, so you got to see lots of people. It's, I have to say, amusing in this particle physics class that Feynman taught, whoever visited would go to that class. So, you'd have Cabibbo would be there, you know (laughter). To listen to Feynman, I mean, for a day or so, I mean they'd come all the times while visiting. But anyway, so that's a little bit of the history of our interest.
What group did you join when you got to CERN initially?
Okay, the group was led by Pierre Darriulat, who eventually became the research director at CERN. He had worked with Carlo Rubbia and formed his own group. There was a lead glass array that Rubbia had used for something else, which we swiped, and used to make a trigger to look at very high- what was then very high, two or three GeV PT pions. That was the trigger for the experiment and then we looked at the hadrons produced. So, it was again a group of like ten people maybe. Very nice group. I enjoyed the group quite a bit. I was there for one year, and then came back to Santa Cruz, where I eventually got a faculty position. Fairly soon after.
Abe, I'm curious how the November Revolution registered at CERN when you were there.
Oh, very exciting for everyone, yeah. Yes, certainly. We had all sorts of talks. I remember Sam Ting also gave a talk. In his way on the board where you use very large letters and write three words and then erase it and start over. Yeah so this was very exciting for people. There were initially questions about what was being seen, but I think it narrowed down reasonably quickly to being charm. We actually did a charm search before I left SLAC. What we did is we took my muon scattering experiment and we used a pion beam. We used the trigger and tried to see if we saw charm. It was probably one of the first charm experiments. And we didn't. The rates were just too low at the energies we were running at. So that was too bad (laughter). But that was in the air. I mean that was an exciting idea. It had the elegance of cleaning up some questions. Of course, at that time, few people thought that there were six quarks, including bottom and top quarks, but this four-quark generation model with charm was very nice.
What were the outcomes of the research during your time at CERN?
Well, I think it was a transition time. So, I mentioned what we were doing. I was only there a year. I think they transitioned into more experiments looking at charm eventually. Eventually they, motivated by deep inelastic electron scattering, looked at deep inelastic scattering of neutrinos. So, neutrino scattering became a very important part of their program led by Jack Steinberger. And so, there was a transition away from standard hadron physics, which involved at time things like looking at diffraction and measuring total cross-sections into physics having more to do with the structure of the proton and quarks and neutrinos and stuff. I think there was a similar transition at Fermilab probably as well. For a period of time, I would say that the CERN experiments were executed better than those at Fermilab, because they had a lot more money. They were quite well-funded, whereas we had more problems in the U.S. But they had similar types of goals.
Did you specifically want to go back to Santa Cruz? Were you looking more broadly for faculty positions at that point?
No, I specifically wanted to go back and continue what we were doing.
There was unfinished work, essentially?
Yeah, yeah. I had an interest from SLAC, actually. I think from Martin Perl. And I got other unsolicited interest, but I didn't pursue it.
And was it a faculty position initially, or it was more like a second postdoc?
It was like a visiting faculty kind of position. So not a tenure track position for a couple of years.
What did you do when you got back to Santa Cruz? What was the research at that point?
Well we were looking at actually doing a high PT photon experiment at Fermilab, which we eventually did. But again, it kind of got overwhelmed by people looking at charm decays and then we switched to the Mark III experiment at SLAC, which was in fact measuring very accurately lots of charm decays. So that was the physics interests at the time. And then SLAC eventually proposed the first linear collider. I was quite involved in studies for the detector. I led the studies for large drift chambers at the time. Actually, for a period of time, I was the manager of the construction of the drift chamber for the Mark II upgrade for the SLC. All these construction things are very tense I have to tell you (laughter). That is, till things work, the chance of failing the- I often wonder why anyone would do more than one such construction project after seeing how tense it is, but you come back for more basically motivated by advances, possible advances in physics. And then we transitioned into worrying about silicon detectors instead of drift chambers, with the goal of using them as the tracker at the SSC. So, I joined what was called the SDC collaboration, led by George Trilling, who was really great to work with. I feel really sorry that experiment, you know, that the whole thing got canceled.
What were the goals of the Trilling experiment? What was the aim there?
Search for the Higgs.
Yeah. But a very broad experiment. I mean, very similar to the goals of the experiments that are now at the LHC. You know, calorimetry, tracking, vertexing. When we started, it was not clear how you would build the tracker at these luminosities, and so I was leading the effort on silicon detectors, and we did the measurements, a lot of measurements to show that it was more radiation hard than thought at the time. We discovered some failure modes. This thing called reverse annealing, if you don't keep it cold. The possibility of thermal runaway, which I actually figured out theoretically before we measured it. I was pleased with that. And we did a design of the geometry, figured out what was needed for tracking and this and that. And we had a lot of groups participating, very strong Japanese participation in this. So, we had a meeting in Japan every year, once a year, which we had for a while. I went to Russia twice with Trilling and Gil Gilchriese to try to raise some money. The Russians were interested in providing steel, so we went to a steel factory. I went to their Institute for Space Device Engineering, because they were interested in providing silicon detectors. And I have to say, by the second visit you could really see a negative change in what was happening in Russia. It was during the period they had lots of problems where lots of scientists lost their jobs and funding. The problems really took off afterwards.
At what point were you offered the faculty position at Santa Cruz?
1978, I think? I'm not sure that I remember exactly. Yeah.
And you were happy to stay? It was a good place?
Oh yeah. Yeah, it was a great place because all sorts of new things were happening. We had very good contacts with astronomy and astrophysics also. When we started our institute, you know, members included George Blumenthal, Joel Primack. George became the chancellor at Santa Cruz eventually. And they were working on theories of galaxy formation and eventually the dark, you know, ideas about dark matter came about. So, it was a very nice environment. I eventually had some interesting decisions. I had several times job offers at SLAC, including becoming the research director under Jonathan Dorfan. After mulling this over for quite a while, I decided to stay at Santa Cruz. And partly it was because I wanted to continue the things we were doing. It was clear that SLAC needed to go into a very different direction. Namely into photon physics.
Why was that clear at the time, Abe? Why photon physics?
Because they had the possibility, and they didn't have the possibility to lead an effort for the linear collider, which would have been the interesting thing they could have done in particle physics. Although even then it was looked at as probably being built at Fermilab. But if it had happened, SLAC would certainly have had a major role. So, it just seemed to be clear that that- and they were beginning to have lots of discussions with groups who were interested in photon science. And certainly, that's completely taken off at SLAC as the main thing for the lab. So, you know, it was a decision. Do you want to lead things in kind of this new direction, or do I want to stay with the science I have been used to? But also, the individuals who I had worked with for a long time who I liked very much, and so in the end I decided to stay. And the campus agreed to augment the program in astrophysics if I would stay. So, I actually got four faculty members added. That was part of the package. And I made them write a letter saying they would do this, because I don't trust the follow through of university administrators because they can change over time and new people don’t necessarity have the same interests as the original administration.
Of course. Of course.
And we did add the faculty members.
Abe, tell me about the creation of the Santa Cruz Institute for Particle Physics. How did that come together?
Okay so that was led by the senior scientists, actually. So, it was my advisor, Clemens Heusch and Michael Nauenberg, who was the senior theorist. And so, you write a proposal, the campus has to decide whether to back it or not. There are all the campus committees, many of whom were not wildly in favor of this because the campus was quite different. I mean, it was very college oriented. It was not too science focused. But the chancellor who had arrived from Caltech, Robert Sinsheimer, who was a famous biologist, he was quite in favor of forming the institute, and so with lots of arguments and last-minute things, it got approved. In '79, I think. And then it really started in 1980 and based on the recommendation of the dean of natural sciences and the chancellor, I ended up being the director. Founding director. Which was kind of bold, since I didn't have tenure yet, actually.
But I got tenure a year later. Yeah, so there had to be an exception made, because the director had to be a tenured faculty member normally (laughter). So that's the story. As I said, a major argument was that we had a totally unique opportunity in this new, reasonably new, lab. SLAC that was very close by. And where we had extremely good connections. Lots of people complained that it was hard to work at SLAC. You know, because they favored their in-house groups or whatever. But we never had that problem. I think we worked very well with a large number of the groups. When I led the effort to complete the drift chamber for the linear collider, actually, Martin Perl agreed to teach my class in return, so I had more time. So that was again pretty good connections.
Abe, the title "Institute for Particle Physics" sounds deliberately ecumenical. That it didn't emphasize theory or experiment. Was that the idea? That it would be a home for both?
Oh yeah, absolutely. Absolutely. And even the astrophysics, you know, was kind of particle astrophysics, it was called. Although I think once it was formed, I don't know that we paid too much attention. Whatever the astrophysics of most interest was fine.
Was the Institute set up more as a place to host senior people, or as a place for postdocs? Or a combination of both?
I think it was a combination of both. There are some major advantages to having an institute. For example, we got our own lab space independent of the allocations for physics or any other subject. In a small place with just not so many buildings having your own lab space was a major advantage. We got a few positions, which were research positions. Long-term researchers, where basically the idea was to get people who could lead their own program. It wasn't meant to be for a postdoc. It was meant to be a major researcher like you would have at a national lab. And so, there were these major advantages to having an institute. We had our own administrative assistant. So those were all really important in getting really going. And having a broad enough program to attract significant funding from DOE, or the NSF, or whatever. Since then, I mentioned, we've done neurobiology. We've even gotten funded by NIH, NSF. NASA. We added people later. Bill Atwood, who was the technical lead of GLAST, which is called Fermi now in space. So that was a very exciting, different kind of project again. I wasn’t involved in all these projects other than being a cheerleader as the director. Or, you know, discussing with people how to design things or whatever. But so, we've expanded over time. I've had other jobs- within the community. I chaired the scientific policy committee for SLAC for a few years. Maybe that's one reason why it was clear to me they were going to be going into photon science. I have been on the scientific policy committee for CERN, during the period where the US joined the LHC. The other U.S. member at the time was Martin Perl. So, we could offer some insight or advice about what's happening in the U.S., which is always hard to discern, because there are so many players. I mean, it's not a unified thing. You have to make it through Congress, you have to make it through the administration. I chaired P5 for a number of years. We developed the first major plan for the field. And that ended up, like the SSC, being disappointing I have to say. That is, when we did our plan, the idea was that the U.S. would build the linear collider, and the DOE was kind of pushing that. One of the guidelines for our report was that that would be the US's next project. And then in the middle of this, it got yanked out and the U.S. decided, or DOE decided, it was too expensive or whatever all the reasons were. I suspect expense was a major one.
What years were you involved with P5?
Pardon? How many years?
What years? What were the years when you were involved with P5?
Well, from the first one through 2007 maybe?
I'm not sure exactly. So, for our initial assignments we had specific projects to look at. For example, should they build a new silicon detector for the Tevatron? Or things like that. And then we did a more global plan, which I think is what we really thought we were going to do initially, and they finally did it. And then after our P5, I think Charlie Baltay was the chair of the next one. It was kind of a recovery plan after the International Linear Collider didn’t happen. And then after that, Steve Ritz, who was our next director at SCIPP, he chaired the next P5, and that one actually made a plan that was very influential. Completely influential in that the community and funding agencies have followed it since then. So it laid out the HL LHC upgrade as the major future project, the neutrino program as being the most important U.S. project, and a number of other projects including particle astrophysics and so that plan actually has been followed and has been very important in guiding the program in particle physics at both DOE and the NSF. Especially DOE.
What was your involvement with the cancellation of the SSC? Where were you in terms of advisory work at that point?
I was not in the advisory chain then. So, I was a victim, not (laughter)- so as I said, we were leading this effort to build the inner tracker as a silicon detector, with lots of layers and then it got canceled and we took the project to CERN. Where we joined ATLAS, and both ATLAS and CMS had both developed silicon trackers which kind of follow the pattern of what we had proposed. They have a more prominent place for pixels. We had proposed strips at the time, because it wasn't clear that you could build a pixel detector, but over the period where ATLAS was being built, it became clear you could build a pixel detector, so that's had a role which has been growing as the rates get larger. So, it's taking over a little bit more of the radius, more layers. But anyway, they're all silicon detectors of one kind or another. For the pixels, the problem was the read-out. Can you build a radiation hard read-out for the devices or not? And what would it be? And it was discovered that small feature-size CMOS is radiation hard kind of by accident almost. That is, as the oxide thicknesses get small enough, the charges that build up go away on their own through tunneling and whatever. And so, you could build a read-out for these pixel detectors that would work, even under high radiation. And that's continued.
In what ways did you have counterparts in this research for CMS?
Well yeah, I mean initially both ATLAS and CMS asked us to join. So, we've had various interactions. We have built a detector, the sensor is by Hamamatsu. Which has been very dominant in silicon detectors going back to the Tevatron I think as well. So that's been kind of in common. I don't know that we interacted too strongly afterwards. Then I think we went our own ways. We're quite familiar with all the individuals in the U.S.
Tell me about your responsibilities as manager of the ATLAS upgrade effort. What was involved with that?
Okay so we had the ATLAS upgrade. Well, let me go back. For the original ATLAS, I was the manager for the silicon for a long period of time. The first manger was Gil Gilchriese, for a short period of time. And then he decided that he wanted to do something different. And so, I took over that for a number of years, seeing the construction through. The pixels were initially in what was called management contingency, because it wasn't- there was not enough money, it wasn't clear if you could build it but we managed to get that out of management contingency and built. And then when that was over, I became the R&D manager for U.S. ATLAS, and that's a role I had for many years. So, there was a certain amount money and we had work to be done on all of the subsystems, and I worked with all of the individual subsystem leaders to develop budgets. We actually built a little upgrade called the IBL. Which is an innermost silicon layer in ATLAS, which is working. And the U.S. part was built through an MRI with the NSF, which I was a spokesman for. And so, we actually even built something during this R&D phase, and then once the HL LHC scope was clear, there was no point to do anymore R&D, so they abolished the position. And I then went over into working on a new detector, called HGTD or High GranularityTiming Detector, which is meant for timing which in the end is being built without U.S. funding because we're too short on funds, and it was kind of late in the process for the US system, where you have to have a schedule, a budget, and know exactly what you're doing before you can go do it. But it's getting built, and we actually participate in the R&D aspects of it in trying to understand how radiation hard the sensors can be made. So, we still have a role, but it's R&D rather than construction.
Abe, I'm curious about your advisory work with LIGO, given that that's a bit of a different field. How did that come together?
Well good question (laughter). I was asked by Barry Barish, who I knew from a number of other times. Our institute has an advisory committee, which has had a number of people. He was on the advisory committee for a while.
Now did you know Barry from Caltech?
Yes, but not very well, being a student. I knew him more from the SSC days. Where he was leading the competitive experiment to ours. Anyway, so he asked if I would be willing to do this. I think the idea was they were going into a phase of, you know, more large-scale construction with schedules and management and various things compard to the early days. And this was motivated by the fact that things were actually not going all that well. There was a committee led by Bill Frasier who was then vice president of the UC system, but was a particle physicist. And he recommended that they, you know, that they needed to make some changes. So, they had this committee that I joined. They also started this LIGO science, I'm trying to remember the exact name, group, which is what the universities belong to. And the project itself was run by Caltech and MIT. It was somewhat like a lab with users. We had to advise on budgets and various technical undertakings. And that was quite interesting. I chaired the committee for a little while. It was initially chaired by Frazier, if I recall. I learned some new things. I enjoyed one thing, they were making a proposal for the advanced LIGO, which they got funded and is really a major success and I still remember Kip Thorne making the presentation. I got a chance to criticize aspects of his presentation (laughter).
Wow. What did you say?
I don't even remember (laughter). But you know, he's done an amazing job. So after having him as my professor of general relativity, it's an amusing opportunity. So yeah, so I think, you know, that's been a major success. We interacted a lot with the NSF. I think we helped them a lot in the interactions with the NSF, of getting funding for the university groups. Focusing the work being done on things that, you know, groups kind of get interested in their own things, but with the limited funds, it was really important to focus on things that would be needed for the project, so I think we helped a little there. And there was lots of interesting work being done on lasers and mechanics. The person who did the initial mechanics, Bill Miller, who we met while doing the silicon detector planning for the SSC. He started his own little company, and he actually did the initial mechanics for LIGO. And he's helped with other projects. He did some SBIRs with LBNL, developing very low mass structures, and low mass foams. Again, various interesting contacts you make. So, I have to say that high energy physics is a great field, partly because it's so international. You get to meet so many people.
That aspect of it is a really special thing. Now that may be true in other fields too. especially as they're becoming more international, actually, as well. But that was an aspect even way back. I mean in the 1970s, which I really appreciated having gone to CERN. So anyhow, that's the story there.
When did you get involved with the BaBar collaboration?
Okay that was- Okay, that had a history. We wrote the first paper on how to actually measure CP violation in these b factories. Which is a rather unusual thing where you measure which decay occurs first, whether it's the b or the b-bar, and there's an asymmetry, which comes from this phase in the CKM matrix, if that's the source of the CP violation. So, we actually wrote the first paper on that. Myself and Pat Burchat at Stanford, and Roy Aleksan, who was visiting at Stanford or at SLAC that year. And so that's how we got involved initially, actually. So, I think we had a very important role in understanding how to do the measurement. This got elaborated in a way during the 1988 Snowmass meeting, where I did something different. I was working on electroweak symmetry breaking. I co-chaired the group. I was the experimentalist, and Howard Georgi was the theorist on that study. But anyway, then when the SSC ended, that's when we got involved in BaBar, as well as continuing the work with ATLAS for the LHC program, which was going to be quite a bit later. And so, for BaBar we worked on the silicon tracker with a number of other groups, including Stanford, LBNL, and Santa Barbara, and Pisa, are the big contributors. And so that's how we got involved. I actually chaired the group that finalized the detector, and also the group that picked Dave Hitlin as the spokesman. There were a lot of groups interested in the b physics at the time. We were interested also in measuring D mixing, which had never been measured before, and which we did in fact measure. And it is kind of a one percent effect. The question was, is it larger than you might have expected? So, I think it's hard to predict, but it looks likely to be just standard physics, we didn't make any discovery there. But it was something to measure and look at carefully. It was the meson system not measured yet. The mixing for kaons was very large, for b's it was large. And D's were unknown. But just the conspiracy of all the numbers, it was very small, although the underlying physics was the same for all the mesons.
In what ways going back to the LHC did the silicon tracking research contribute to the discovery of the Higgs? What did it do overall?
Okay, well, it's the main tracking system employed to measure all the charged tracks. And so, for Higgs goes to anything charged, you need to use the tracker. So, it has a role in reconstructing muons where you use also the outer muon system, but you get the mass resolution by- or momentum resolution by using the inner tracker. So, these experiments basically use the entire detector. You can't do the experiment without the calorimeter you can't do the experiment without the tracker. You can't do the experiment very well without doing vertexing to see. So, for example recently, we finally found evidence for Higgs goes to b/b-bar, which is actually the largest branching ratio, and a hard one to measure. And that's dependent completely on the tracker and the vertexing, to know that there's a b there, a displaced vertex. So, it has roles like that. I mean one of the channels measured was Higgs to gamma-gamma, and clearly the calorimeter has the major role in that case. And then there was Higgs to Z-Z, for that the tracker has a big role, as well as everything else. So, it depends on each channel.
Now, Abe, how much did you feel like an insider when the excitement was really building in 2010-2011, as we get closer and closer to the discovery of the Higgs?
Yeah, it was very exciting. In fact, I was at the meeting in Melbourne, Australia, where they had this great announcement and video conference. I even brought my wife to listen to that meeting, or video conference. So yeah, everyone was very excited.
Did you have opportunity to interact with Fabiola Gianotti at all?
Oh yeah, sure. Yeah.
What was her leadership style like from your vantage point?
Well she was very good at pretty much everything. Analysis, detectors, listening to people. I think, you know, she was kind of a good natural choice as the CERN director general when it happened. She, when we had the P5 where the high luminosity LHC was endorsed, I think she was on the committee. And I gave one of the presentations in favor of that project to the committee.
The discovery of the Higgs allowed what new questions to be raised that weren't possible before?
Well, I mean, you could posit there is a Higgs, and then once you say that, you can raise a bunch of questions. So, the Higgs is very odd. It's completely odd. It's the only scalar. It has couplings which follow no pattern. Right? It generates the masses of these objects in a pattern which is not understood at all. So, what is the pattern? Why? Why do you have a scalar? Why not more scalars? Why is it a doublet? You know, why the quantum numbers? Electroweak quantum numbers. Why not a scalar that goes along with QCD color? So, you know, what generates the symmetry breaking at what mass? So, there are a huge number of questions because it's so odd. It has no kind of connection to a lot of the other things, other than through this mass generation mechanism, which it seems to do very accurately and very nicely. So, one of the questions raised was, "Oh, is there supersymmetry, and is the Higgs a part of the supersymmetry pattern?" But then we haven't found supersymmetry yet. And so, the Higgs is still out there as a single object with all these questions. And there are other questions. Why three generations? But that may not be a Higgs question other than the Higgs coupling to each of them in some way. And why are the masses so odd? Why are the neutrinos so light? So, we have a lot of intriguing questions with I would say no good hints at the moment as to what the answer is.
How surprised are you as we're getting close to ten years out, at how little has been seen at the LHC since?
Yeah, I am surprised. I am surprised. I mean you would have thought that- so, at this TeV scale, we have the top quark, which was discovered a lot earlier. Why is that at the TeV scale? We don't know. And then the Higgs. And then the Z and the W. All of those are in the neighborhood of 100 GeV. Okay, so you'd say, okay, let me go up another factor of ten, up to 1 TeV. Will that fill out a number of other things? Fill in there or tell us how they work together, whatever? And nothing has been seen. So, I am surprised. I mean in a way, it motivates going another of factor ten in mass to look further at whether once you get up there, you'll actually start seeing maybe supersymmetry? Maybe other things? A lot of the motivation for supersymmetry, I think, goes away if you go way up in mass scale. Because then it's not necessarily related to this issue that the Higgs- why is the Higgs mass not going off to some huge value? Why did it stay at this 100 GEV scale? And supersymmetry was supposed to fix that. There were cancellations. But if it gets very heavy, then that presumably doesn't work.
Now do you think that these things will be resolved at CERN with upgrades, or are these the kinds of issues that really need something like an ILC to understand?
Well, I think we'll do what we can with the upgrades, but I think, you know, we now see enough that it looks like you need more. And I don't know whether the ILC is at a large enough mass either, although it will certainly measure with greater precision all the things about the Higgs. And sometimes when you do that, you find that there are things which don't fit, and you get some ideas. So, it certainly is a precision Higgs machine. We're getting more, higher and higher precision at the LHC. I think we'll get to branching ratios of a few percent eventually. And maybe we'll see some deviations there.
Abe, how did you get involved with the Sanford Underground Research Facility?
Oh (laughter). I was asked to be on a committee for that. We had one meeting only at the lab. I went down into the tunnel, which was amazing. Kind of scary (laughter). As you hear water pouring on this elevator (laughter). Took a nice walk and then we provided some advice. A little advice, not too much advice. And then they actually chose what they wanted to do, so we didn't really need a committee. I think that unfortunately the NSF version of this project didn't happen. And I think ultimately it was because it was too expensive for what the NSF had historically done. And so, it ended up not happening, and then DOE and the Fermilab neutrino experiment gave it new life. So, at our meeting, they were just debating what kind of detector to build, whether it was going to be a water Cherenkov detector or this liquid argon detector. And there was an initial recommendation for a water Cherenkov detector. And I avoided endorsing that, because it wasn't clear that they would stick with that, so we let it go, which was probably smart. And then they took the liquid argon as a more adventurous approach.
I'm curious what you might think about how particle physics might contribute to understanding dark matter.
Oh, that is a very interesting question (laughter). Well you know if it were supersymmetry, and maybe it still is, but I think, you know, it's getting more and more unlikely.
Wait, why do you say that, Abe? Why is it more unlikely than at supersymmetry?
Well they looked at a large part of the phase face and don't see it. But it can still be there. It could be like the situation with neutrino oscillations. You look and look and look and see nothing and you can conclude, "Oh, it doesn't happen." And then all of a sudden you have a surprise. That's still possible, and the experiments are pushing the limit to go as far as they can before you have backgrounds in the experiment from neutrinos. So, they'll eventually, I assume, get to that new limit, and we'll see if we see something. So, I think the fact that they haven't seen anything yet has motivated looking very broadly at all options. So, there are various- I mean, we already had experiments looking for axions. I think there will be more of those and looking in more clever ways. There are other things happening, which I don't keep abreast of well enough probably to even tell you. I think this is, you know, the forefront to somehow get at this. It's a very sneaky situation where you see dark matter in its effect on galaxies and the effect of clumping to actually make this structure of the universe. Yet you can't distinguish between a larger mass and fewer of them and a smaller mass and more of them. The particles. So, we haven't had a technique within astrophysics to actually pin down, say, what is the mass? If you had a mass, you would know maybe where to look. So, it's got to be these other experiments that look for it, and there's the supersymmetry ones which involve scattering. There are other ones with axions which involve interactions with the magnetic field. This has generated an interest in looking for dark objects, like a dark photon. More generally is dark matter part of a whole new generation of things of some kind? So those experiments will continue. We have some people in our group who are involved in an experiment at J Lab, to look for dark photons. It's an experiment led by John Jaros at SLAC. And so, there will be more of those until a discovery is made. Kind of a broader look. And none of them have found anything either yet, so it's not just supersymmetry. And I mean what would be really nasty is if the dark matter has absolutely no interactions other than gravity (laughter). That would make life very hard. But I think the particle physics is all a search for what this might be, and I'm very supportive of a very broad look. These have often been quite modest, small experiments, so we should be supporting and doing them, which I think the community does in fact support strongly.
Abe, long term, do you see neutrino physics as one area where the United States will remain a leader in experimental physics?
Yeah, I think so. I think so.
Why? What do we have here that's not happening elsewhere?
Well, I mean, the competition is mostly in Japan, actually. In fact. So I think maybe we'll both remain leaders, because neither country wants to give up the experiments they've pioneered, so what we have is a long baseline to a mine, which you can do experiments in, and a very high intensity neutrino beam, which you need an accelerator for, so you get that from Fermilab. There's a different energy range possible at Fermilab than in Japan. I think it's good that Japan has gone in the direction of a water detector. You know, it's good to have different techniques. So, I think we'll remain a leader, but I think so will Japan. I think it won't be like they drop out and we just do it. I think CERN has come to the conclusion that they will be supporting efforts, rather than leading efforts, as much as possible. Based on various discussions with the DOE management, saying, well, you know, if you want us to support your program, we need you to be more active supporting our program. And that has worked. I mean that kind of rational discussion has worked pretty well.
Abe, what were your motivations in undertaking the major project of writing the textbook Particle Physics: A Comprehensive Introduction?
Oh, writing a textbook is a way to clarify your thinking about things.
So, it was as much for yourself as it was for students, you're saying?
Yeah. And I had taught the class a few times. And I had a certain point of view. So, I mean one of my goals is to have lots of calculations for experimental physicists to look at to get a chance to see, how do we calculate things? Why are things the way they are? And to broadly include flavor physics, HiPT physics. And also, the physics that was historically done, about resonances and now not covered often, and so that was the motivation. It's a lot of work to do a thing like this (laughter). I'm old fashioned. I hand wrote everything first. And then got it translated into tech and sent it away to Addison-Wesley. The publisher.
So, in what ways, Abe, did it clarify your thinking? What needed to be clarified?
Oh, just when I found the connections between things. Organized various calculations in one place. I don't think there was... I mean, it helped in one set thing, the section on the Higgs made me sit down and work through that more carefully than I had in the past. So, it helped in things like that here and there.
Abe, were there some textbooks that you saw there was a gap in the literature where this kind of a textbook, a comprehensive particle physics textbook, was necessary? Did the field need that update?
In my mind, yes. But you know, there are other textbooks. There was one by Don Perkins, which was popular. It was at a little lower level in terms of calculating things. There was one by Halzen and Martin where I had a different point of view, so I wanted to get my own point of view in. So yeah, I think so. I think now it's out of date, in the sense that we actually found the Higgs and certainly that should be included in any textbook now. But as I said, we haven't found a framework for it.
Yeah. It's unfortunate that it probably doesn't need to be as updated as you would have hoped.
Yeah, I mean, you can take the book and put down, oh, the Higgs mass is 125 GeV and you’re kind of done (laughter). Yeah. Yeah. So anyway, that was- it was also a period where we were still kind of getting the LHC going and so I had time to do something different and engage my thinking. Which you typically don't have the time when you're taking data and in the middle of analyzing data and worrying about your students. So, it was kind of a specific period of time.
Abe, when you stepped down as director of the institute in 2010, I wonder if you reflected on your accomplishments in that role? What you had built and where the institute might be headed next?
I was very happy with where we were. I felt that I was handing it off to Steve Ritz, a very good person, with some different directions, and that we were in very good shape in terms of projects we were doing, new things. Basically, I hired almost all the people that are still there. We had built an institute with a very good collection of people. Some are retiring. I mean we had a very good electrical engineer who retired, who I had found toward the start of the institute. Most of the people in our lab, because we can't pay competitive salaries with industry, have usually some different reason to be with us. You know, they like it there. This engineer was the best student in my E&M class (laughter). And then I hired him. And he learned on his own slowly and he did a lot of great work for ATLAS and other projects, and unfortunately, he retired, so it leaves a hole which is hard to fill. Because again we can't really be competitive with a salary in Silicon Valley. So, we still have, other than one person leaving, we still have this very good technical staff. One person who retired, Hartmut Sadrozinski, I work with very closely. He also has been recalled. So that scheme works for more than just myself.
And so yeah, I'm quite pleased. We now have our third director who just started. Jason Neilson. Who now is back in the particle physics area. Steve Ritz was in the astrophysics area. Jason is the leader of our participation in the ATLAS experiment. I'm still our team leader at CERN, but I really need to change that and have him be the team leader. With this pandemic, I have things I didn't have time to worry about.
Abe, when you retired, what did you want to do before the recall? In other words, before any formal thing and you just wanted to work on the things that were most interesting to you, what was it at that point?
Well, when I retired, I had the recall in mind, that I would do this.
Oh, you did?
Oh yeah, yeah. When I was recalled, I was still quite involved in ATLAS, and that was my goal, and then we discovered these detectors called LGADs, by the way. Low Gain Avalanche Detectors. Which we've been quite involved in developing in collaboration also with someone from the University of Torino, Nicolo Cartiglia, who was our student once upon a time. And so that kind of took our attention, or took my attention, because here- you know, ATLAS has I don't know how many thousand people. Here was something you could do on your own and contribute in a unique way, pretty unique way. So that's why several of us went more and more into hardware technology development, really. We're quite well supported by DOE for this work now as a separate part of our grant. They have a detector R&D program. And we have two SBIR proposals, which we'll find out about in about two weeks, three weeks, I guess?
What are you proposing? What's on the docket?
Well, the proposals are for the electronics development to go with the detectors. So, all these detectors need electronics. That is, you don't see the signals on their own. And that's another totally challenging thing, because to do fast time measurement typically requires a lot of power. You need very high bandwidth. So, it takes a lot of power if you're not careful. So, to try to have electronics that minimizes power but gives you very good, fast signals with low noise, those are all challenges. So, one of the SBIRs is to use silicon germanium technology. Which is something we looked at, I don't know, twenty years ago or so, I guess. So, we're getting back to looking at that, and the other one is with a company in Hawai'i called Nalu. And they're interested in a full system. So, the one on the silicon germanium with a company called Anadyne that’s just a front-end. It would need then supplementing with a back end, but I see the key to this being the front end. So, we're working on that. Those are very interesting projects. We're part of a U.S.-Japan collaboration, also on these detectors. Which I believe was just funded. So, we have lots of things going on. One of our colleagues is heavily into x-ray detection using these detectors as well as diagnostics at future accelerators. We just joined in a proposal led by SLAC and involving a bunch of labs, and Stanford and ourselves. Again, for electronics development. That's aimed at X-ray science, so it's a proposal not focused on high energy particularly.
Well Abe, now that we've worked right up to the present, for the last part of our talk, I want to ask a few broadly retrospective questions about your career, and then we'll end with a look to the future. So, one thing we haven't talked about yet is your career as a mentor to undergraduates and graduate students. On the undergraduate side, what have been some of the courses that have been most enjoyable for you to teach over the years?
Okay, so what I really liked, were either electricity and magnetism or quantum mechanics, these are my favorite classes for undergraduates.
What are some of your favorite textbooks for both?
So, for graduates, I've used Jackson. For the undergraduates it is textbooks by David Griffiths. However, I do a lot of the class on my own, I have to say. In every case. I mean I do my own notes, I do my own thing.
Now are these classes are more for physics majors or more general classes?
No, for physics majors. For graduate classes, I’ve especially enjoyed E&M and particle physics and quantum mechanics. So, these are kind of the subjects I've liked most. They are kind of subjects that most follow the mysteries. What I see as the most mysterious aspects of the universe (laughter). Which is always intriguing. And so that's been my most interesting classes. So, I got the award in the natural sciences division one year, actually. I don't remember actually what it's called. The faculty member who gets an award once a year. But that includes a teaching component. It's a teaching, service, and research award. So then at least I was doing, you know, some useful teaching, unlike right now (laughter). So, I've enjoyed teaching, except I think almost no one enjoys making up tests, grading, and doing that part of it, but that's just part of it. But giving lectures and interacting with students is really fun. The last class I taught was math methods, actually. Which I really enjoyed also. I got, after I don't know how long a time, got to look back at all these things with more of an eye of understanding, you know, so it was things like Fourier transforms, differential equations, things like that. Which were fun to look back at. And so that's been my reaction to teaching.
What have been some of your most satisfying moments as a mentor to graduate students? Either a really successful thesis project or what some of your graduate students have gone on to do?
Well, typically, you know, we've mentored students somewhat as a group. So, one of the best students I mentioned is in Torino, Nicolo Cartiglia. We worked on an experiment at DESY in Germany developing some of the technology we actually were aiming at the SSC. It was almost like a demonstrator. It was to measure leading protons. Leading proton spectrometer. But it used silicon detectors, and our own designed electronics. And they worked very well. We never had to calibrate anything. The initial calibration worked for the whole experiment, which was pretty good. And it was the fastest silicon detector at that point in time. So that's one thing. We've had a lot of students who have gone on to industry, actually. I would say the majority of students have gone on to industry. I had a pair of students who eventually got together and got married, who worked BaBar. And then they went off to CERN and she actually, Christian Flacco, she continued working with me on finishing up the measurements that we were involved in for BaBar, and he went off to work at CERN, and they've since gone on to industry. So that's been quite positive, I have to say. We see some of our students periodically. And I think they've generally been quite successful. I think they've been quite happy in industry. A lot of- I mean we're in a part of the country where there are a lot of possible jobs in industry. In terms of testing electronics, equipment, and so you could always feel really good that you're getting someone a job which pays fifty percent more than a postdoc when they take that job (laughter). Yeah.
Abe, for yourself, reflecting in your career when you came of age professionally during such a fundamental time of discovery in particle physics, is your sense that those opportunities still exist for the younger generation of particle physicists?
Not as easily, I have to say. I mean people are still excited about the potential, but I mean when I was, you know, in the middle of my PhD, finishing my PhD, taking graduate classes, etc., the number of exciting ideas were incredible, and the number of experiments being done were quite a lot. And so, it was a very, you know, golden age, really. And now it's gotten harder. So, I think as I said when I was doing my experiment, we had like ten people so you could do everything. And the students now are doing things in a more restricted area but are still very well-known within the group in that restricted area. So, I don't think it's a problem for people being recognized doing really good work. And the work is much more challenging. So, when I was a student, I designed our trigger system, which was a whole bunch of scintillation counters. Very simple, really. So, you'd do a coincidence of a few counters and that would say there's probably a track, and then you would trigger the streamer chamber, which recorded the data using film. Now, the trigger is incredibly complicated. The computing is incredibly complicated. I wouldn't be able to keep up with these people at this point in time. So, I found my niche, which has to do with sensors and innovative work there. But on this nitty gritty stuff of making the experiment work, it's really very, very complex. So, I think people can still get very good jobs if they decide to go into industry, having done these very interesting, you know, neural networks, and AI are very popular. People are learning about all of that. So, I think that's fine, but in terms of new physics things, all of a sudden popping out, you have to remember when we discovered quarks, it wasn't known that there were quarks. In fact, I have to say that when I got to CERN and I was interested in this question of fragmentation functions, some of the people told me, "Come on, this is nonsense. Can't possibly exist" (laughter). So yeah, so it was interesting. So, I think it's harder from the physics point of view, and I think it's harder for theorists too. That is to do something and have it, you know, transform our thinking, in a way. It may happen.
In surveying all of your research projects, all of your collaborations, everything that you've been a part of, what sticks out in your memory as the most fun you've ever had in physics?
Yeah, I hate to say it. It's the SSC, which never happened.
The SDC experiment was maybe the most fun. The most exciting was finding this quark fragmentation function at CERN. That was really exciting.
In what ways? What was so fundamental about it?
There it was.
Everyone at CERN was telling me quarks don't exist (laughter). And there it was. And it fit with what Richard Feynman told me was there (laughter). This was the era where later Feynman and Field had these collections of papers about quark fragmentation. Actually, I got referenced in one of their papers. I was really proud of that (laughter). So that was in a way the most exciting in terms of, you know, finding physics. More so than BaBar, which also found something really new, but somehow being in this smaller group and proposing what we measure in that case, and never having experienced a discovery myself. I mean all this. I had lots of classes that were fun, but I had never seen, you know, you roll the- then we had tapes. You know, you roll the data and there it was. It was really great. Really something wonderful. I suspect a lot of people at CERN, especially for the younger people, when for the first time they saw the Higgs, probably had a similar experience. I hope so.
Abe, last question looking to the future. What do you want to accomplish personally? What's most important to you as you look ahead to your career?
Uh-huh. Boy, that's a tough question (laughter). Well, I'd like to see these devices we've been working on have a big role in future physics experiments broadly. I'm giving a talk next week, and I have a compendium of people who are looking to maybe use these. So, there's the electron-ion collider, which is going to be built at Brookhaven. There's someone who wants to use it in space, there's someone who wants to use it in Darmstadt, heavy ions. So, I'm hoping that it ends up having a role in lots of different things, and that we continue working on it and refine what we're doing. And I think in terms of our own participation, it will I hope be this pion-leptonic decay experiment at TRIUMF, where we actually do an experiment ourselves with this, besides the technology being employed by other groups. So, I think that is a kind of realistic assessment of what I can do individually. And of course, I look forward- this is one thing by being in physics, you can appreciate everyone else's discoveries. I look forward to appreciating myself what other people find. And I'm hoping that they do someday find dark matter, because that will be really exciting (laughter).
Indeed. Well, Abe, it's been a great pleasure spending this time with you. I'm so glad we were able to do this. So, thank you so much.
Yes, thank you.