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Robert McKeown

Robert D. McKeown

Experimental Nuclear/Particle Physicist and Laboratory Administrator, and Former Caltech Professor of Physics

By David Zierler, Director of the Caltech Heritage Project

December 18, 2023

DAVID ZIERLER: This is David Zierler, Director of the Caltech Heritage Project. It's Monday, December 18, 2023. It is my great pleasure to be here with Dr. Robert McKeown. Bob, it is great to be with you. Thank you so much for joining me today.

ROBERT D. MCKEOWN: Good to be here. Thank you.

ZIERLER: Bob, to start, please tell me if you have any current titles and institutional affiliations.

MCKEOWN: I have Emeritus status at Jefferson Lab, and I have Emeritus status at the College of William & Mary where I was on the faculty while I was in Virginia. It was a kind of courtesy appointment. I just recently signed up with Lawrence Berkeley Lab as something they call an affiliate, which allows me access to go onsite and attend seminars and things like that. It's about 45 minutes away, so I anticipate going down there maybe a couple times a month. I know quite a few people there. I'm trying to keep in touch with the physics world, in all of these aspects.

ZIERLER: Given your long perspective on these things, what is currently interesting to you in nuclear physics and more broadly in particle physics?

MCKEOWN: I've had a long interest in these ghostly particles known as neutrinos and have studied them quite a bit. I keep up on what is going on with those kinds of things. Also the program at Jefferson Lab, I keep tabs on that. Some of the projects that I managed to help get started when I was there are now launched and things are happening, so I tend to try to keep track of what is happening with those. I'm always still interested in cosmology and in astrophysics, and I try to read the journals. Actually I read articles more broadly than I used to when I was active in research because I was so busy doing my own thing. Now I have time to browse around and read things on my own, which is fun.

ZIERLER: Has your work been more on the experimental side or the theoretical side?

MCKEOWN: Almost all experiment.

ZIERLER: What have been some of the major technologies that have propelled the experiments that you've been involved in?

MCKEOWN: The development of particle accelerator technology was very important. In fact, when I started at Caltech there was the beginnings of a subject called accelerator mass spectrometry where people actually used particle accelerators for the first time to do mass spectrometry. That is actually part of the reason I got the idea for doing this fractional charge search experiment with an accelerator. A lot of the work I did used electron accelerators to accelerate electrons. A big topic that got started back in the late 1970s and early 1980s when I got interested in this was what is called the use of spin in electron experiments. The beams can have spin, so all the electrons in the beam have their spins pointed in the same direction, and also you can make targets where the atomic nuclei have all their spins oriented in the same direction. That was a new concept back then, to utilize these new features of doing experiments with electrons. A lot of my work involved using these spin-dependent effects in electron scattering.

ZIERLER: I wonder if you can reflect on the interplay of theory and experiment in your career. In what ways have theorists provided intellectual guideposts to help you design the experiments themselves and what to look for? Then the converse of that, how have some of the experimental results that you've been a part of propelled the theory forward?

MCKEOWN: These spin-dependent effects of electron scattering were just being written down by theorists in the 1970s and 1980s, so it was like a new field, to be able to study these things. It gave you access to all kinds of new and interesting properties of nuclei, particles, and you could test what is known as the weak force or weak interaction using them. Even more recently, something that I didn't do myself but I helped get started at Jefferson Lab, was you could measure the neutron distribution in a heavy nucleus like lead. This can be related to the properties of neutron stars, which are measured using gravitational wave experiments like LIGO. It ties together these things from astrophysics all the way down to microscopic, atomic, and nuclear physics. It's really quite interesting. It all started with theorists writing down what you can measure. Then of course now the theorists pick up the nuclear physics and the astrophysics and put it together in a very unique way, now that we have all of this information both from the astrophysics experiments and from the nuclear physics experiments.

Studying neutrinos has been very interesting, too, because when I was young—neutrinos were first observed in the 1950s coming from nuclear reactors —we knew they existed, but one of the things that actually Caltech played a very important role in was the prediction of neutrinos from the Sun. A fellow in the Kellogg Lab where I worked before I got there named John Bahcall, who worked with professor Willie Fowler worked out the quantitative predictions for neutrinos coming from the Sun due to the fusion reactions that power the Sun. A radiochemist from Brookhaven National Lab figured out how to build a big liquid experiment underground in South Dakota to detect these solar neutrinos. It was remarkable - he found them, but the theoretical predictions were off by about a factor of three. Only one third of the solar neutrinos were there.

It took many, many years before we found a resolution to this that involved several experiments in the early 2000s. That led to us knowing that actually the neutrinos are not massless as was originally thought. They actually have finite masses, and the different flavors of neutrinos can turn into each other. All of this has been observed. All of it was predicted in a very speculative fashion by theorists, but until we did the experiments it wasn't clear. Now, physicistswant to study this in more detailusing an experiment called DUNE that shoots a beam of neutrinos from Fermilab to South Dakota. They want to try to study whether the properties of neutrinos can explain why the universe contains matter rather than antimatter, or rather than equal amounts of matter and antimatter, which is a big mystery. It all leads to new things, new ideas, that then generate new ideas for new experiments. It's a fascinating subject.

ZIERLER: Of course you came of age scientifically just as the Standard Model was coming together. What do you see as your contributions or what is the relevance of your research both in building the Standard Model, and then of course as everybody is trying to do right now, going to physics beyond the Standard Model?

MCKEOWN: My PhD work involved testing the Standard Model, the weak interaction. We didn't find anything wrong with it there. There's two aspects to how this is done. One is you build the highest energy accelerator experiment that you can, such as is done at CERN these days, and directly attack what's called the energy frontier. The other is to work at the precision frontier, where you do very precise experiments at low energies and look for things to go wrong. I did quite a few of those kinds of experiments [laughs], which constrained all kinds of new ideas about the Standard Model, but we didn't find anything new until we were working on neutrinos in the early 2000s. There was a big breakthrough in 1998, where a large experiment underground in Japan saw an anomaly in the distribution of neutrinos coming from the sky, from cosmic neutrinos. They're generated in the upper atmosphere by cosmic rays. This was the first evidence that the neutrinos could change from one flavor to the other, and it would require that they have mass, because if they were massless they wouldn't do that.

I went to a conference around then, and everybody was excited about this, and I heard about another new experiment being proposed in Japan called KamLAND. This was to build a big scintillator detector in the same underground facility in Japan. I teamed up with some people who had been working with another professor at Caltech doing neutrino physics, Felix Boehm. He was retiring. We got together with the Japanese along with other American collaborators and built this KamLAND experiment. That actually showed for the first time you could see the pattern of the neutrinos oscillating from one flavor to the other, and it all looked exactly like the theorists would predict except we found that the amount of mixing that caused this effect was much larger than they would have predicted, so it was actually a surprise.

It was clear after that that the next experiment was to do an experiment closer to nuclear reactors, and we did this in China with some collaborators from China and other countries. We measured the last so-called mixing angle in the neutrino matrix in this experiment, which was at a power station near Shenzhen, which is close to Hong Kong, in China. That was very exciting too, because this really cemented this theory of neutrino oscillations together. As I said, it provides the impetus for the new experiments that are being done today.

ZIERLER: What are the big open questions at the beginning of your career that you feel are more or less resolved, what feels as new as when you first encountered it, and from all of that discovery what new questions can we ask today that weren't even possible 50 years ago?

MCKEOWN: Wow, that's big! [laughs] The neutrino story of course was, when I started out, there was no established evidence for neutrinos to have mass or any of these things, and there was the solar neutrino problem for many years. This had been known since the 1960s. I think largely that is resolved, except for these other lingering questions of how does matter-antimatter asymmetry come about, and so forth. There has been great progress but there is still more to do, as is usual. Cosmology has really come a long way. Not that I worked on cosmology, but I was always interested in cosmology. At Princeton, where I went to graduate school, you were encouraged to do independent study, so rather than take all the courses to prepare me for exams, I wanted to take courses in things like cosmology to learn about something really new. So, I would go to cosmology lectures. In fact, once I went to a seminar on black holes by a fellow I had never heard of before; in fact, most people hadn't. It turned out to be Stephen Hawking [laughs]. I was of course astonished when they wheeled him in a wheelchair and his assistant wrote on the blackboard for him.

What we've learned about cosmology—I remember back in the early 2000s, experiments were just measuring the cosmic microwave background radiation with precision, some of them at Caltech. It was very exciting. That subject, again, it's astonishing how much we know about cosmology and have determined over the last few decades. As you may know, there's still more to do, because there's a problem, because if you determine the Hubble constant for the expansion of the universe using cosmology, you get a slightly different answer than if you measure it directly in astrophysical objects, so there's a puzzle there that everyone is concerned about. I think what was really interesting, too, when I first went to Caltech, they had hired at about the same time—he was a senior professor, I came in as an assistant professor—a fellow by the name of Ron Drever, who Caltech hired to develop the idea of measuring gravity waves with a laser interferometer—it was just an R&D project. Nobody thought you would be detecting gravity waves anytime soon [laughs], but he just wanted to learn how to develop the technique. He built a lab at Caltech on campus there and studied how to make the interferometers work, and he had many of the ideas that went into eventually what was LIGO. I watched this whole LIGO thing develop as a spectator. It was amazing. Who would have thought 40 years later that they would actually see events where neutron stars coalesce and black holes and so forth? That has opened a whole new field, and it's just amazing compared to where we were back in 1980. It is astonishing.

ZIERLER: For all of the advances in cosmology—of course there's dark matter and dark energy—over the long term, what do you think the potential impact of the neutrino research, neutrino oscillations, might be in possibly understanding dark matter or dark energy?

MCKEOWN: That's interesting. When I was young and starting out, people imagined that neutrinos might have mass and that they might be dark matter. Even back then, you had what they called galaxy rotation curves, where Vera Rubin and others were able to determine that there was dark matter around galaxies. There were lots of speculations about what the dark matter could be. One was neutrinos but it was soon established, studying more about cosmology, that the neutrinos were not a good candidate for dark matter, so people started looking for other things, these heavier things called weakly interacting massive particles, WIMPs. There were also axions, which were another new idea when I was just starting out. In fact we even did a little experiment down in the basement of Kellogg Lab looking for axions at one point. Didn't see them, but—and nobody else has seen them [laughs] since, either, but they're still looking! There were lots of speculations about dark matter, and we're not there yet. It's a very interesting subject, but it's going to take a while, probably, to figure that one out. There's dark energy as well, which is even more mysterious.

ZIERLER: You mentioned the importance over the course of your career of building ever-bigger colliders and accelerators. A counterfactual, a what-if question—had the SSC been built, in what ways might that have been relevant for your research? And, if you could use your imagination, what might we know today as a result?

MCKEOWN: That's interesting speculation. I did not work at the so-called energy frontier myself, so although the accelerators I needed got bigger and higher energy, I never worked quite at the frontier as you would if you were working at CERN today at the LHC. The SSC was designed to be higher energy than the LHC. Very famous physicists would go and testify to Congress about why you needed this higher energy. [laughs] When the SSC got cancelled, the LHC was proposed, and it went in an existing tunnel, and so the size of the tunnel was fixed. Then, depending on how strong the bending magnets you can make, that determines the top energy, so that's what determines the energy of the LHC, and it is lower than the SSC. The LHC has not found the new phenomena beyond the Standard Model that people had hoped that the SSC would find or that the LHC would find. Perhaps those famous theorists who testified to Congress were right [laughs] and you really just need more energy, and if we had built the SSC, who knows, maybe we would be closer to figuring out how this actually works and what the mystery of the Standard Model is, why it works so well and where it must break down. It's an interesting question. [laughs] I don't know for sure.

ZIERLER: What about supersymmetry? Where is supersymmetry in all of this for you?

MCKEOWN: I don't really work on that topic, but it's another way of trying to fix some of the problems with the Standard Model. I think back in the day, Murray Gell-Mann was quite enamored with this topic, and he had always been right before, so maybe he's still right—

ZIERLER: [laughs]

MCKEOWN: —and it was just harder to find than people had thought. It's still a possibility, although much of the parameter space that people had worked on to try and use supersymmetry to solve the problems with the Standard Model, a lot of the parameter space is now ruled out, so it's looking less likely that this is the correct answer. But you can't be sure until you do more experiments. I'm sure that one is going to need even higher energy accelerators to continue to explore these ideas.

ZIERLER: Of course you are well positioned to reflect on the role of national laboratories in fundamental physics, the way that they work on their own, the way that they work with the academic community of physicists. What is that best possible partnership to move physics forward between academic physicists and physicists working at the national laboratories?

MCKEOWN: I am always amazed, when I think back, the way we did experiments in the earlier part of my career. We had technical people, people who knew how to design things, and machinists who could build things and so forth, and electronics people. So, we could build things, and they were complex for the time, but as scientific instrumentation has become ever more complex—and expensive, is another issue—you need a structure for people to work together as a team to build these larger, more complex things. I must admit that in the early days, it was just a pleasure to not have to deal with it—it's kind of a form of bureaucracy that you have to deal with, and it was a pleasure to work without that. But eventually, as things got bigger and bigger, and as you had to do your experiments at facilities, at these national laboratories, where they insisted that you have what's called project management, this became the way things were done.

It was interesting, when we built KamLAND in Japan, the Japanese didn't do things that way. They were also able to do things very quickly. The government just gave them all the money, we just went out there and built it, and it was amazing. The next experiment I did was this experiment in China, where we had two U.S. national laboratories that wanted to insist that this run like a U.S. project, so they tried to impose all of the rules and bureaucracy of U.S. projects on this. It was a big struggle because the Chinese physicists wanted to work in a somewhat different way.

Another interesting example is LIGO itself, which I think started out trying to do things the old-fashioned way, and eventually the NSF, who was going to fundLIGO, realized that this thing really needs some project management. I think that is when they brought Barry Barish into the project, who had a lot of project management experience from particle physics experiments and accelerators, and that made all the difference in the ability of LIGO to go forward. It's one of those things that has just been a fact of life, that things get more complex and you need a more organized structure for people to be able to effectively work together. Actually a major part of this is also safety. I think back on all the things we did in the lab in the early days; we were careful, but we didn't have the supervision and the structure to be able to really make sure that everyone worked safely. I am very thankful that over all those years we worked without the oversight of safety experts that no one got hurt or injured. That's one of those things that is also a good byproduct of having this—it's bureaucracy, but it really is kind of necessary to be able to build these kinds of experiments and facilities.

ZIERLER: Given all of your service, all of your devotion to the APS, the American Physical Society over the years, what is so important to you about the APS? What functions does it fulfill? What community does it help build in physics?

MCKEOWN: I remember back when I was a first-year graduate student. I had done some research as an undergraduate, at my undergraduate institution, Stony Brook, and I got the chance to give one of these—they called them 10-minute talks—at the April APS meeting in Washington, D.C. That was a big moment in my life, that I got to give this talk. The APS meetings are kind of unique that way. They give a lot of opportunities for young people to give talks that are not elaborate talks but they're small talks on what they are doing. I always felt that it gave me a home for my physics work. They had the journals where I could publish. They held the meetings where I could report my results. Things have evolved since then, but it is just a sense of belonging, that you belong to something. It's a great organization. So many people are so passionate about the subject of physics.

It has actually been a real privilege for me to work in some leadership roles at the APS and try to help make things better and move things along. It's still very challenging. The workforce in physics is not what you would call diverse by modern standards. It does not represent the society that supports it. There's a lot of work to do to try to improve that. There's a whole range of people in society that don't participate in physics, and physics is not better for that. Physics needs more people with more opportunities and more diverse viewpoints. That is a big challenge, and a lot of what the APS is doing is to work in that area. But especially giving young people the opportunities and a place where they can hang their hat as a physicist [laughs] and say, "I belong in this place," and "This is where my people are," it's great to have that feeling, and I've always felt that way about the APS.

ZIERLER: Let's go all the way back to the beginning. Tell me about your family, your family background, where your parents came from.

MCKEOWN: I think one of the interesting things is my dad—I think it was during World War II, when he was in the Navy—learned about electronics. After the War, he worked for aerospace companies on Long Island, in New York, as an electronics technician. He never went to college. He worked his way up, learned lots of new things along the way, learned about computers and so forth. He ended up working on what is called the Lunar Excursion Module which was part of the Apollo project. It was built by Grumman, when he worked for Grumman, and he worked on that. Then [laughs] he had a hobby in the evenings; he would go down in the basement and repair television sets for friends and family. He had the vacuum tube tester and all of that stuff.

I learned about electronics and got interested in that kind of stuff from him and what he was doing. In fact, in my teenage years I got interested in amateur radio. He helped me a lot, so I learned enough electronics that I could get my license and so forth. It was a lot of fun. I really enjoyed that. But I think it also gave me the opportunity to learn some technical things when I was pretty young. I think that probably gave me a lot of confidence that I could learn this kind of stuff. Of course I was always good at math and science at school, so that helped too. I think that was a very formative experience for me. If he didn't do what he was doing, I think my life might be very different. [laughs]

ZIERLER: Where did you grow up? Where did you spend your childhood?

MCKEOWN: Mostly in a place called Huntington, New York, on the North Shore of Long Island. We moved there when I was two years old. Then when it came time to go to college, I applied to a few places, and I got into a few schools around the country, but it was a terrific thing back then—the state of New York had—first of all, Stony Brook, the school that I ended up going to, it was called then State University of New York at Stony Brook—they wanted to be the "Berkeley of the East", as they called it. It was a pretty new school. It had been established only a few years earlier. They were still building the buildings and campuslike crazy. It was quite a place. I remember that the tuition was $150 per semester. On top of that, I got something called a New York Regents Scholarship, which paid the tuition. [laughs] So I got to go to college basically for free, which was great. I lived at home most of the time—the first three years—and I would commute. They had a fairly large commuting student population. I would commute about 25 minutes each way. I could live at home, and it didn't cost me anything to—I didn't have living expenses other than buying myself lunch or whatever.

They had hired an amazing Physics Department. I took a physics course in high school, and I had a very good teacher of course. I had always enjoyed physics. I was always reading about physics, so I really loved it. Then when I got to college, I decided I would probably stick with it. I had some other ideas, but—the faculty at Stony Brook was—they had hired this fellow, C.N. Yang, who had a Nobel Prize, so that upped the reputation of the place quite a bit. The faculty were excellent. They were really good teachers, really excellent physicists. I was very lucky to be able to go there. It was a wonderful experience for me.

ZIERLER: Before college, was the draft something you needed to contend with?

MCKEOWN: During college it was an issue. They had a lottery and I came within about a dozen of the cutoff for people that got drafted, so I was a little bit lucky that I didn't end up going in that direction. It wasn't like I went to school because of that or anything. I went to school because I wanted to learn all this stuff and have all these opportunities. It was just something that could have derailed my education for sure. It didn't, but it was definitely an issue at the time. In fact, when I first went to Stony Brook, we would have exams in the evening, and the first physics exam, we go into the physics lecture hall, and everybody is sitting there starting to work on the exam, and somebody called in a bomb scare. This was a very common thing back then, during the years of the Vietnam war. So, we got moved to another lecture hall, and they got us all started again, and of course there was another bomb scare.

Eventually, the professor said, "Okay, just go work on the exam. You can collaborate. Whatever. Just go." This was all new to me, and I was a little bit intimidated because I didn't really know where I stood relative to the other students in my class. This was an eye-opener, because I sat at a table with a bunch of the other students and started working on these problems, and I realized I was helping them a lot more than they were helping me! [laughs] That was one of the first inklings I had that, hey, I'm going to be pretty successful even in university. It was interesting. I guess the Vietnam situation had a little bit to do with that. Mostly I really enjoyed all my classes at Stony Brook. We used to have lab courses in the evenings and so forth. Being a commuter, I needed to have dinner, and so the other students, I would help them with homework, and they would feed me dinners. We had a lot of fun. It was very nice. A lot of nice people I met there when we were students.

Then in my sophomore year, a very important thing happened. I was working part-time also during all this time. In fact, I had an interesting job then. I was working in a liquor store right close to the Northport Long Island Rail Road station. I would work there in the evenings, and people would get off the train and they would stop and buy their hooch on the way home. Mostly I would sit there and work on my homework for my college classes. Occasionally, when the train would come, these people would come in, and I'd have to take care of them. I asked my sophomore physics professor if there was any chances for employment at the university. He right away said, "Yeah, why don't you come down to the nuclear physics lab in the basement, and we'll get you started?" They gave me a job, and I worked for three years, part time, doing nuclear physics research. That's how I started doing nuclear physics.

ZIERLER: Was Vietnam protest, civil rights protest, a big issue on campus when you were an undergraduate?

MCKEOWN: Yeah. At the beginning, like I said, these were all Vietnam protests. People were really against the War, and it was a big issue on the campus of Stony Brook, certainly the first year or two when I was there. Civil rights, not so much. That was earlier, I guess. But the War was something that was very relevant to the students, especially because they were the age to be drafted and so forth, so it was a personal issue. Yeah, it was definitely there. By the time I became a senior, I think 1974, it was almost over, and we were pulling out at that point. Nixon had already resigned.

ZIERLER: Were there any opportunities between partnering from Stony Brook and Brookhaven National Laboratory when you were an undergrad?

MCKEOWN: Not so much for me—I worked on campus—but some of my friends had jobs at Brookhaven. In fact I remember I was visiting them—for some reason, I don't remember what—but there was a lounge where the students could stay on site at Brookhaven. Things were easier then; I could just go there without having any status at the lab. I remember we were in that lounge and watched TV the night that Nixon resigned. [laughs] It was amazing. We watched his resignation on TV at Brookhaven. I remember that. I didn't do any research at Brookhaven then, but I had friends in my physics classes who did.

ZIERLER: What were the big ideas in physics that captivated you as an undergraduate?

MCKEOWN: As an undergraduate? Not so much as I just really enjoyed learning physics. It was a fascinating subject. I do remember that in I guess it was my sophomore year, we had a course in electricity and magnetism. It's the book that I used with freshmen at Caltech many years later. It's the Berkeley text on electricity and magnetism by Purcell. It had a really great treatment about how relativity, special relativity, required—if you had electricity and you had special relativity, you would have to have magnetism, that they were all related. It had a really great treatment of this. I thought that was so deep. It was just amazing to me. It's comparable to the ideas of the Standard Model, where you could unify electromagnetism and the weak force, weak interaction. These are very deep things in physics, and I just really thought that was wonderful. That's one of the kinds of things I remember. The cutting-edge new stuff, I was not so aware of. We were doing nuclear physics stuff in the basement, but it wasn't stuff that was really all very exciting. It was fun to do, but—

ZIERLER: Is that to say that things like grand unification at Harvard, or the November Revolution at SLAC, the building of the Standard Model, did that not really register with you so much as an undergraduate?

MCKEOWN: Not so much, not that I recall anyway. It was stuff that we probably were aware of—you'd read about it in Scientific American and things like that—but these are pretty advanced things for an undergraduate. We pretty much stuck to the basic material of the undergraduate curriculum and didn't have so much of that. There were colloquia and stuff, so I would occasionally go to colloquia about black holes and things, but the Standard Model and all that and the November Revolution—I guess that was 1974 or so—that was actually I guess when I was just getting to Princeton. I started being aware of that—I remember there was this fellow, Frank Wilczek there, and I knew Professor Gross as well [laughs], who both got Nobel Prizes many years later, along with David Politzer, who I didn't know because he was a Harvard guy. I kind of knew these guys back then; it was interesting. Also, Jim Peebles was teaching cosmology, and I would sit in on his lectures, and he was talking all about the formulism for writing down the angular distribution of the sky, which eventually became the power spectrum for cosmic microwave background. I didn't know why he was teaching us these things but I thought it was interesting. Like I said, I also stumbled intoStephen Hawking. There were lots of things like that that went on, that were fun. I got to work in the nuclear physics lab again.

Actually, it was interesting—when I went to Princeton, they gave you a form and said, "Here's the fields of physics you could study. Fill out the form and let us know what you think." I rated cosmology the highest, and a few other things, then eventually got down to nuclear physics. But of course they admitted me with the idea that I was going to work in the nuclear physics lab [laughs], so that's where I ended up! I often think, I could have worked with David Wilkinson, who was a big man in cosmology. It would have been interesting to maybe go in that direction, if I could have. Maybe I needed to be a little more assertive, but again, you just get into these places, and you feel like, "Oh my gosh, do I really belong here?" You don't know yet, so it's hard to be very assertive. Other people have more confidence, I guess, but I didn't have so much then. But it all worked out for the best in the end.

ZIERLER: When it was time to think about graduate schools, what was attractive to you about Princeton?

MCKEOWN: You know, I had no idea. And it was very different, then. Now, the students all go around and visit all these places, and you have parties for them, and [laughs] you try to impress them of what a fun place it is. It wasn't like that then. You just mailed your applications and you got an answer back. I got into good places—Caltech, Berkeley, Princeton, MIT, Cornell. What happened to me was I talked to my professors at Stony Brook and asked them their advice, and they all said, "Go to Princeton." I'm not really sure why. And, there was a fellow one year ahead of me that graduated from Stony Brook that went to Princeton, too, so I said, "Well, he seems to be surviving. I guess I can do it there." Also it wasn't so far away. I think at that time I was dating my future wife, so I was in a relationship that it would have been nice to stay close to Long Island. Princeton seemed like the natural place.

ZIERLER: Tell me about getting to Princeton. How did it feel for you coming from a state school in New York?

MCKEOWN: Well, it was amazing. The graduate students at that time lived up on a hill, a little bit off campus up on a hill in a place called the Graduate College, which was this big, gothic-style building with a big chapel in it. It had a big carillon that they rang on Sunday mornings and stuff. It was a bizarre place. I got a room in this place, and it was beautiful. It had all of these windows that looked out on a golf course. I hear they're tearing up the golf course to build something new, so it won't be there forever, but it was amazing. All the other students were kind of in the same boat. I think everybody was a bit intimidated by the place. What was interesting was the graduate students were completely separate from the undergraduates. I don't know if it's still like that. The undergraduates, we always thought that they were sort of upper-class [laughs] kids, and they were all—I guess they had just started admitting women a few years before that, but it was very dominated by males. The undergraduate population was like a whole foreign thing to us. They lived a completely different social life than the graduate students.

I settled into the Physics Department and it was great. Lots of friends with the other students. Like I said, they stressed independent study, so I didn't have to take too many classes. I could study things on my own for the exams and so forth. The exams were very intimidating. They had oral exams as part of the general exams. I didn't think they were quite fair, the way the professors asked the questions, but you know, that was the way it was. [laughs] It was just more of the same thing of feeling, "Oh my gosh, this is difficult."

I think actually most of these places are very different now. This is part of the whole thing about physics, and we talked about the APS before, is it's a much more friendly place. In fact, the last few years I have been on the board of directors of the APS, and was lucky to sit there. You go to these meetings, the board meetings, with the president and president-elect and so forth. It's clear that the APS is quite committed to improving the culture of physics and has changed considerably over the years. There are substantial efforts to make physics more welcoming and inclusive. I think physics departments are like that, too. They're much friendlier. I think it's a much different experience than when I was a student. That's good. That's good for physics. I think we all hope we can develop a more diverse workforce in physics. Maybe that's still to come. But I think it's a necessary aspect of changing the culture in physics from what it was when I was a student, which was I think somewhat intimidating.

ZIERLER: When you started graduate school, did you have a good idea of what kind of physics you wanted to focus on?

MCKEOWN: Like I said, I thought I'd try to do something different like cosmology, but they didn't cooperate! [laughs] So I tried to learn things on my own, and I would go to classes and seminars. But I was lucky; I think the physics I ended up working on in the nuclear physics lab was very enjoyable. I got to meet some amazing people—it was kind of a special time there, then. There was a large group of amazing visitors that were visiting the lab. Two of them were recent Caltech PhDs, it turns out—Eric Adelberger, who ended up at the University of Washington; and Art McDonald, a Canadian physicist was visiting also at the time. I got to meet these people when I was very young. Art McDonald won a Nobel Prize many years later for a neutrino experiment, in the Sudbury Neutrino Observatory. They both graduated from Caltech around 1969 or so. Then there was Hamish Robertson from Michigan State. These people were very accomplished—young, at the time—experimental physicists. Even more than the professors, we learned a lot from them. It was a very productive, fertile environment to grow up in.

An interesting aspect of all of it was computers were just getting going at the time. In fact when I was at Stony Brook, we had computers, from Digital Equipment Corporation—they were pretty nice computers at the time. Some of the other graduate students wired up little boxes with switches on them and programmed the computers with a game called Space War, and there would be little spaceships orbiting around a star, and you would shoot at each other. It was like video games, back in 1972! There was no color; it was just green stuff. Then when I went to Princeton we actually took a step back, because they had a Xerox computer. I don't think Xerox makes computers anymore, for good reason. This was amazing. There were all these circuit cards in them. I remember I actually fixed the thing once, because it wasn't working, and I actually took the card out of the computer, and I took a soldering iron and replaced the transistor on the card. I figured out somehow that the transistor was blown, put it back in, and fixed the computer, and it started working. It was like, holy smokes, I actually fixed this thing! [laughs] But that was a really different world.

Once I left Princeton, things got very different. That was an anomaly. They were kind of backward in their use of computers. But it was amazing, because we were just learning how to use computers. Princeton had an IBM mainframe, probably an IBM/360 or something. Most of the other students that did theory or cosmology or whatever would have these big decks of cards, and they would do their computing on this big IBM machine. I didn't do very much of that, but it was very interesting. It seems like a really different world than we have now. It's hard to believe.

ZIERLER: Who was your thesis advisor at Princeton?

MCKEOWN: His name was Gerry Garvey. He was working on these experiments that—as usual, there were these experiments to test the weak interaction, and there was some experiment somewhere—I think it was in Japan—that showed an anomalous result. This happened just as I got to Princeton. Everybody got excited about this and they were inventing all kinds of new experiments to test and see whether it was right and so forth. That's what I got swept up in. It was actually very exciting. It was very different from the environment I had at Stony Brook. Stony Brook, they were just measuring energy levels of nuclei, and there wasn't too much excitement about it other than when you were done you could publish a paper. But the stuff going on at Princeton, there was real excitement, and there were all these visitors that were also all excited about this stuff. It was just—it was fun. I really enjoyed that.

Garvey decided after my second year that he was going to take a job as the director of the Physics Division at Argonne National Laboratory outside of Chicago. He invited me to come there and work on my thesis experiment there at Argonne. It was nice, because they had more professional staff, they had real engineers, and they had much better computers. They actually had staff to run the accelerator for you. At Princeton, you did everything yourself. The middle of the night, you would be taking things out of the middle of this big cyclotron magnet. Actually, very hazardous [laughs]. I don't think it should have been done that way, but that's the way we did things!

He invited me to go to Argonne, so I moved out to Argonne and spent four years there. I took about two and a half to three years to finish the experiment. We had to build it first, and we used the accelerator in the basement. I was there four years. The Chicago weather, which is normally not very nice in the winter, was very extreme those four years, it turned out. [laughs] I started doing some work in Los Alamos using the Meson Physics Facility there. I remember once I went to the Chicago airport, and the roads were covered with inches thick of ice, and I came back like three weeks later and the same ice was there, only there were ruts where the car tires were going. It just stayed cold. Of course in 1980 when I was approached for a position at Caltech, that sounded very good. Chicago winter was really getting to me! [laughs]

ZIERLER: What were the results of your thesis work?

MCKEOWN: It was beta decay, so it was studying the weak interaction. Boron-8 and lithium-8 are two—they are called mirror nuclei. They are mirrors of each other if you turn all the protons into neutrons and vice versa. They both decay to beryllium-8 by emitting a beta particle and a neutrino. In beryllium-8, there would be alpha particles emitted, and we studied the correlation between the beta particles and the alpha particles, and you compare it between the electron decay and the positron decay. The prediction was—there was a variation of the weak interaction know as second-class currents. The Japanese experiment I mentioned earlier had claimed to see second-class currents, and that was what everybody was excited about. We were looking for these second-class currents in this experiment. It turned out the experiment showed exactly what you would expect from the Standard Model of the weak interaction, so we didn't see anything abnormal, but it was a really nice experiment. It was fun to do.

ZIERLER: What were the circumstances of you joining the faculty at Caltech?

MCKEOWN: At Argonne, there was the graduate student office where there were maybe seven or eight desks where graduate students would sit. That was your place. Most of them were University of Chicago students. I was from Princeton. I was the outlier. I think I just came into the office one day, and—in those days, we didn't have email; you had these little yellow message slips. [laughs] I got this message to call this guy Professor Koonin at Caltech, and left a number. I called him up, and he asked if I would be interested in a faculty position at Caltech. Hmm! [laughs] Sure, I think so! [laughs] I remember I went out for a visit. They took me around and I talked to lots of people. I didn't really know too much about the process—these days, I think people are much more aware when they interview for a job, what it's about.

ZIERLER: Do you remember who met you, who was taking you around on that initial visit?

MCKEOWN: I don't remember for sure. I know this guy Koonin was involved. He was a nuclear theorist that I hadn't heard of because he didn't work in the area that I worked in. We ended up later becoming good friends, and we still are. I remember giving a seminar, and it seemed to go pretty easily. Even at Argonne, there were people like John Schiffer and Gerry Garvey, and if you gave a talk, they would challenge you. I'll put it that way. [laughs] This was like kind of a walk in the park. They seemed to think it was okay! They didn't give me too much of a bad time. I thought, "Okay, I guess that went okay." The next thing I know, I got an offer.

The only other thing I had cooking—a good friend of mine from graduate school had graduated with Gerry Garvey as well, but he went to Los Alamos afterwards. He went to Argonne with us for a while as a postdoc but then he went to Los Alamos. He was at Los Alamos, and he got his boss to invite me to interview at Los Alamos for a job. So, I go out there, and it's actually very interesting, because the guy, his boss, who was the director of the Physics Division then at Los Alamos, was a fellow named Jay Keyworth, who was a nuclear physicist. This is 1980. If you fast-forward two years to 1982, Jay Keyworth was Ronald Reagan's science advisor, pushing a strategic defensive initiative otherwise known as Star Wars! [laughs] But I sat with this guy, and he's trying to talk me into going to Los Alamos. It was a very interesting conversation.

In the end, I really felt Caltech had a much stronger draw. They were offering me, by modern standards, a pittance in the startup package. I think it was $35,000 and I spent much of it on an oscilloscope [laughs]. What was interesting was the people at Argonne and my PhD advisor did not want me to take this job at Caltech. They didn't want me to. I think part of the reason was—well, Caltech wanted to hire me because the experimental nuclear physics faculty was getting pretty long in the tooth and they wanted to bring somebody new in, which is good, but being that they had been long in the tooth and all these people had been there for a long time, a lot of the equipment was very outdated. Talk about computers; they did not have a computer in the nuclear physics lab when I went there. I told you that I had nice computers when I was an undergraduate back at Stony Brook, eight years earlier, and there was no computer in the Kellogg lab! It was amazing! All the oscilloscopes were these really old, kind of like what would be relegated to undergraduate laboratories for undergrads to use because they weren't state-of-the-art oscilloscopes. But, they had just convinced the NSF to build a new accelerator, so they had a new accelerator that was under construction when I went there. I felt like this was a real challenge to try and build a modern laboratory doing physics in this environment where these old guys thought the old way was the good way. It was kind of interesting.

To back up a little, the lab, the Kellogg Lab, gained a lot of notoriety—their hallmark was studying what's called nuclear astrophysics where you measure nuclear reactions in the laboratory that are relevant to the production of elements in stars. The big bang produces hydrogen and helium and pretty much nothing else, and everything else—the carbon, the oxygen, the iron to make steel, everything—is made in stars. Figuring out how that all happens was a big deal. Willie Fowler was an icon in that business and he had a postdoc—this was all before I got there—named John Bahcall who was the guy that calculated the solar neutrino flux, so the place was famous for this nuclear astrophysics stuff. That was the scene I walked into. Just a little aside—I still remember, 1983—we had a house up in Altadena, and I used to wake up in the morning and make coffee and listen to the radio, listen to some classical music, and of course the news would come on. I still remember the day in October of 1983 when the news came on and they announced that Willie Fowler had won the Nobel Prize! [laughs] Here's this guy right in the lab where I work who got the Nobel Prize. Boy, that was quite a day. That was quite a day, I'll tell you. It was amazing.

Anyway, back at the ranch—so they had this new accelerator. As I mentioned earlier, there was this kind of new technique that people had been developing called accelerator mass spectrometry where you use an accelerator like that as a mass spectrometer. That was one of the possible future uses of this things. The guys there thought they were going to do more nuclear astrophysics, and that's fine, but there was this experiment at Stanford by this guy Bill Fairbank that seemed to show that there were fractional charges in a material called niobium. In the very early days, Millikan, who was famous from Caltech, the first president I guess, he established that all charge is quantized in units of the electron charge. Then Murray Gell-Mann and another guy named George Zweig came up with this idea of these quarks, that they could explain the array of particles and relationships by saying that the protons and neutrons and other elementary particles were made of these things called quarks, and these quarks had to have fractional charges in multiples of one third of the charge that Millikan found. This guy at Stanford seemed to be seeing fractional charges in this experiment with superconducting niobium spheres.

I had the idea that, well, we could use the technique of accelerator mass spectrometry but we would use an ion beam to basically disassemble pieces of niobium into atoms—it would just kick atoms off the surface—and then you would take any charged objects that came off the surface and run them through the accelerator system. If it were a completely electrostatic system with no magnetic fields, it would be able to determine the charge without regard for the mass of the particles, since we didn't know what the mass was going to be. We started this experiment, and this was kind of the first thing I did at Caltech. It was interesting. It was a fun experiment. It was kind of challenging. I had a graduate student and some postdocs that helped me. We did the experiment on niobium and didn't see anything. Then we did some other experiments. I got to know some of the people in the Geology Department, geochemists—one was Gerry Wasserburg who was a wonderful scientist—and some others. They gave me meteorite samples and said, "Let's look in meteorites." [laughs] We just started doing random things like that.

One of the interesting stories was, the student that searched for these fractional charges in the experiment wrote his thesis, and had to do his oral exam for the thesis defense. They set up a committee like they usually do and on his committee he was privileged to have Dick Feynman as a member of his committee. It was like, "Huh! This is going to be interesting. Wow!" [laughs] We go in, and the student starts talking, describing the experiment, and Feynman starts asking kind of random questions. They weren't very good questions. It was clear he had not even read the thesis. [laughs] (I should have known because even for my PhD defense, that was something I learned in the room of the oral exam, was that none of these people actually read the thing! [laughs]) Anyway, what was really interesting was Feynman, as time went on, started asking—the questions got better and better and better. [laughs] They got to be pretty good! [laughs] So you get to the point where, gee, hopefully he doesn't find something we overlooked or something! That would be very embarrassing, right? Not only bad for the student but it would probably end my career, right? [laughs] But in the end, all went well. I still remember to this day how Feynman came up to me afterwards and complimented me that this was a clever experiment and he really liked it. That meant a lot, at the time. That was really interesting. That night, I went out with the student and his wife and my wife—there used to be a restaurant in Pasadena called the Chronicle; it was a very continental kind of place—we went for a fancy dinner—we never had gone there before—[laughs] and celebrated. That was really interesting. I like these Feynman stories. There's a lot of those. It's interesting. He was quite a guy.

ZIERLER: Those initial misgivings from people at Argonne, your thesis advisor, about not taking the job at Caltech, how had that aged by the time you were a faculty member for a couple years? Were you glad you joined the faculty at Caltech?

MCKEOWN: I was having a great time, yeah. Actually, it was going very well. When I got reviewed after three years or so, I think the problem was they thought I was doing too many things, which was probably true, so I had to kind of restructure my research program a little bit. But I was just having so much fun. Being among all of these people—Willie Fowler, Dick Feynman, Murray Gell-Mann—people like Murray Gell-Mann, and George Zweig was there at the time too, they were so supportive of this quark search thing, because they thought—it was a problem, then, because nobody really understood that—we hadn't been living very long with the idea that a proton is made up of quarks but you can't take the quarks out. Nobody has ever seen the quark! I think they thought this was going to be the thing that really—maybe the quarks are really there, and this guy Fairbank found the magic formula, and maybe this guy McKeown is gonna verify it! Everybody was very supportive, so it was very nice.

The Kellogg Lab was actually great. It was a lot of fun. There was an annual retreat to—I think Caltech has sold it now, but there used to be, east of San Diego, in a place called Fullerton, a ranch called the Capra Ranch. Frank Capra was a Caltech alum and had left this ranch to Caltech, and people were able to use it for retreats and all kinds of things. It was not too far from Palomar so the astronomers used it a lot. We would have an annual Kellogg retreat there. We also would take our group of graduate students to the Athenaeum for lunch on Fridays. It was just a great environment and I really enjoyed it. It was great.

ZIERLER: After that review where you were told that you might be doing too much, did you prioritize? Did you whittle down what was most important to you?

MCKEOWN: A lot of the stuff was collaborating with other faculty, and I had to tell some of them that I was going to have to focus on certain things. It was a little bit difficult but I think it was for the best. Yeah, it was fine. We hired another assistant professor a couple of years later. We had lots of visitors coming all the time. In fact, really interesting, we used to have every winter Hans Bethe, who was one of the fathers of nuclear physics—he got a Nobel Prize I think in 1967—he was the head of theory at Los Alamos, and Dick Feynman worked under him at Los Alamos during the Manhattan Project. He was a big man in the Manhattan Project. He was a buddy of Willie Fowler's, and so he would come in the winter and he would bring his friend from Stony Brook, Gerry Brown. Hans Bethe was from Cornell. It was cold in New York so they came to Pasadena in January. Hans Bethe [laughs]—the joke was he loved explosions, ever since the Manhattan Project.

There was a problem for many years that it was thought that a lot of the heavy elements were made in the explosion of very heavy stars called supernovae, Type II supernovae. Hans Bethe and Gerry Brown thought this was a problem we should be able to solve. They were old-school. They sat down with a piece of paper and started working on equations. They thought they could make these stars explode. They never could. It always failed. It turned out many years later that the key to making these things explode is three-dimensional turbulence that you can't do analytically in a one-dimensional model like they were trying to do. To make the star explode, you really need a numerical simulation with very complex turbulence in it. But they thought they should be able to make this thing explode. They would come every winter and work on this. Actually, when LIGO was getting traction, they came up with the idea that, gee, maybe there are binary neutron stars, and maybe there's a lot of them; we don't know. They started thinking about, maybe there's gravitational waves from binary neutron stars. I'm not sure they had the very first idea, but they had early glimpses of what became true many decades later. It's kind of interesting. It was great having them visit every winter. They were very smart people and it was very inspiring to be around them.

ZIERLER: I'm curious if you ever had interactions with Murph Goldberger, either from your graduate school days at Princeton or when he was Caltech president.

MCKEOWN: Yeah. [laughs] That's interesting! When I decided to go to Argonne from Princeton, he was the department chair. I still remember I had to go into his office, and there was some form he had to sign for me to be able to go to Argonne and still be a Princeton student but not in residence at Princeton. I don't remember what he said. He made some offhand remarks. I don't think he particularly liked this idea. Probably being department chair, he's probably not happy that this guy Garvey was leaving in the first place, and now he's taking students with him. I don't really know—I'm kind of connecting the dots—but he seemed not too happy about the situation. [laughs] Then, I show up a few years later as an assistant professor, and Murph Goldberger is the president of Caltech! I can't remember if he remembered me. He might have? But Caltech is a small place, so you get to know the president a little bit. He was a very impressive guy. I didn't interact with him too much. The division chair at the time was Robbie Vogt, and I interacted more with him. He helped me with the startup package and things like that, getting started. He became provost later, and there were a lot of other things along the way. [laughs]

ZIERLER: Going through the tenure process and coming out the other side, did that influence your research at all, the kinds of things that you felt you could be able to work on?

MCKEOWN: No, I don't think so, other than this sort of mid-course correction of trying to focus more. Other than that, I pretty much did what I thought was important. When I went to Caltech, I didn't know if I was going to get tenure or not. I had no idea. But I didn't really conduct myself in a way that I thought would get tenure. I just did what I wanted to do and what I thought was good physics, good research. I tried to do well at teaching but that, in those days anyway, didn't count as much. But I enjoyed the teaching. As anyone at Caltech will tell you, teaching Caltech students is a real pleasure. I really enjoyed that part of the job. Then of course the graduate students, I had 14 graduate students over the years get PhDs, and something like 30 postdocs came through and worked with me. It was just a lot of great people. Like everything else, the interactions with the other people are what really make it all worthwhile. The physics is great, but what makes it fun is interacting with people and doing the physics with people, so I really enjoyed it.

ZIERLER: When did you start to get involved with advisory work for national laboratories?

MCKEOWN: Too early [laughs]. It was like committees at Caltech; I got onto committees too early too, before I really was prepared. In the eighties, in Los Alamos—well, Gerry Garvey went from Argonne to Los Alamos and became the director of the Meson Physics Facility, and I was on their program committee. I also got to be on committees for other accelerators. There's a thing called the Nuclear Science Advisory Committee, which advises DOE and NSF on nuclear science. They do something called a long-range plan every six or seven years or so. In 1983, I was pretty junior then, and they were doing one of these long-range plans in a place called Wells College, New York, and they asked me to go and be part of this process. That was a real eye-opener, because all the bigwigs in nuclear physics were there, arguing about the future of the field, and there I was [laughs]. It was amazing!

Like I say, I thought it was too early, but these days there's a big push everywhere in academia and at the labs to include early-career people in all of these kinds of processes to get their perspective. I think it's valuable. The problem of course is that these people also need to stay focused on their research. It's hard to learn to do science and then go off and do committees and things. It wasn't so common when I was young, but people seemed to ask me to do things, and of course you always say yes. [laughs] You don't say no. It was valuable. I learned things. I met people. The guy who became the chair of this NSAC in the 1990s was somebody I worked with and was on committees with in the 1980s named Ernie Moniz who became the secretary of Energy back in the Obama administration.

ZIERLER: NSAC is Nuclear Science Advisory Committee?

MCKEOWN: That's right.

ZIERLER: What is its mission? What is it designed to do?

MCKEOWN: To advise DOE and NSF on nuclear physics and nuclear science.

ZIERLER: This has nothing to do with the Nuclear Regulatory Commission?

MCKEOWN: No, that's completely separate. That's regulating safety of nuclear reactors. That's separate. There's the set of national laboratories that all have nuclear physics programs, and all these professors at these universities doing nuclear physics at these facilities. Somebody has to decide which of these facilities get upgraded and which facilities to build in the future. High-energy physics has something called HEPAP, High Energy Physics Advisory Panel, and they were the first ones that first said, "We should build the SSC." The Department of Energy has these different programs in the Office of Science and each program has an advisory committee. That's the process. It was in place back in the early 1980s, and I got roped into it pretty early. Which was fine. You certainly learn a lot, and you certainly meet a lot of people that way, so it was interesting.

ZIERLER: What were some of your interactions early on with Jefferson Lab that might have foreshadowed your decision ultimately to join the Lab?

MCKEOWN: Before the Lab was built, they were running study groups in the summer. This was in the early 1980s and mid-1980s. I would go there with a graduate student, a postdoc, and we would spend a few weeks. We would read all these papers that the theorists were writing on spin-dependent electron scattering and we would come up for ideas for experiments and write them up and they'd go into reports to the Lab before anything was built. It was amazing. Then there was the very first program advisory committee meeting to decide on the priorities of the program for the future accelerator as it was being built in 1988. I remember I was on that committee. Ernie Moniz was on that committee. That was a very interesting exercise.

ZIERLER: What were the objectives of the accelerator and why was this something that was not being thought of at one of the extant national labs?

MCKEOWN: This was an interesting story. Back in the late 1970s, the NSAC process was not so formal then, but they did write a report and they recommended an electron accelerator. They didn't specify the energy, but I think they anticipated that it would be about one GeV. The main feature of this accelerator was that the beam would be continuous. At the time, you had at Stanford and you also had at MIT electron accelerators, and around the world also. All these electron accelerators were pulsed. The reason is basically there are waveguides that contain radio frequency energy and they're made of copper. The radio frequency energy is so high that if you just let them run, it would melt the copper. Even with the water cooling and everything you can do to keep the copper from melting, you would melt the copper. There's just too much power dissipated in the copper. Copper is a good conductor but the resistance is not zero. So, you pulse the machine. You turn on the RF power for only a short amount of time and turn it off again before the copper melts. So, the beams are pulsed, and when the beams are pulsed that really limits what you can do in terms of experiments, because all the electrons come at once and it's kind of a mess. It just makes it difficult.

It was realized that if you could spread the beam out continuously—and there were ideas for how to do this—that this would enable a whole generation of new experiments. That was the idea in the late 1970s. Then they had a competition for this accelerator. MIT wanted to build it. Argonne wanted to build it. I think the National Bureau of Standards wanted to build it, what became NIST. And, the University of Virginia wanted to build it. There were a couple of people at the University of Virginia—they had a bright, young guy there—and they came up with a design. They had a committee that went around. The chair of the committee was a man named Allan Bromley who became science adviser under I believe Bush the first. They decided that this would go to Virginia. Part of the reasoning was, well, the Southeast needed a facility, and all these other places already had things. Kind of crazy, but that's what happened.

Then they hired a guy from Berkeley who was what you might call a professional accelerator builder. These people at Virginia were inexperienced but they had an idea. The idea was that you would pile up the pulses in a ring and stretch them out and then let them come out. It was kind of a brute-force, simple idea. That was what won the competition. So, they got this guy—his name was Hermann Grunder—to come to Virginia to build this accelerator. He hired some of his people. He was originally Swiss and he hired some of these Swiss guys from Switzerland that knew how to build accelerators. They got enamored with a new idea that was being worked on at Cornell which was, okay, the way you fix this problem of the copper melting is you make these things superconducting. Zero resistance. [laughs] Well! This was a very new thing, and nobody had ever built anything like this before. This guy Grunder made a remarkable decision—okay, we're going to go with the new technology. This was a time [laughs] in the 1980s when the lab director could tell the Department of Energy what he wanted to do. [laughs] These days, it doesn't work that way. They were so desperate to have this professional guy build this accelerator there that they relented and said, "Okay." So he changed the whole design [laughs] that had won the competition, and he built it, and it was a remarkable success.

I was involved early on in the program, in designing experiments. I did for a while work to help them build one of the experimental devices which was a big superconducting torus and I got them started on building that project. But I had other priorities in my own research that did not involve that lab, so I started working more at Bates Accelerator at MIT, and then at SLAC, Stanford Linear Accelerator. We were working also at the DESY laboratory at Hamburg, Germany. I wasn't too involved after a while in the lab in Virginia. Along the way they renamed it to be Jefferson Lab, or Thomas Jefferson National Accelerator Facility. It wasn't originally called that. For a while I was the head of their user group and things like that, but I kind of started going my own way, doing other things. I always was apprised of what was going on there; I just didn't particularly participate in it very much myself. There was one experiment that one of my former postdocs set up there that I participated in for a while, so I had some relationship with the Lab.

In the mid 2000s, I guess it was, I was on an advisory committee at Fermilab, their Physics Advisory Committee that decides which experiments run at Fermilab. I was doing that for a few years, and I got to know the associate laboratory director, a fellow named Hugh Montgomery. In probably 2008 or so, he was offered the directorship of Jefferson Lab, so he became the Jefferson Lab director. He had a number-two man there, and I think they weren't getting along or something. An email came out that the number-two man had resigned. We were working in China at the time on neutrinos, me and a friend of mine. We were chatting and I said, "Gee, that's probably a pretty interesting job now,." Because with the new director—they always had accelerator people in charge of that lab, and he was an experimental physicist. In fact, he was a particle physicist, not even a nuclear physicist. He was actually a very personable guy and I enjoyed meeting with him and interacting with him at Fermi. My friend sent him an email and said, "Hey, why don't you see if Bob wants to take this job?" [laughs]

The next thing I know, I hear from him, and it took the better part of a year to get it all negotiated. I wanted to have a faculty position at the College of William & Mary. That means you have to convince the faculty at William & Mary that this is a good idea. All these things, especially when you get into that situation, take time. Caltech made a good effort to try and convince me to stay, and I can't say they did anything wrong [laughs], but it seemed like maybe it was time for a change. Maybe it was just—it's like you do what your PhD advisor did—at some point you leave the university and go and direct a lab or something. So, I did it. It was a bit of a culture shock at the beginning, because all the DOE stuff was a much different environment than being at Caltech.

ZIERLER: Did you give up your tenure or did you have a leave of absence tryout period?

MCKEOWN: Caltech wasvery nice to me. They gave me two years leave of absence. I really appreciated that, because I wasn't sure [laughs] about this at all. They were very accommodating and I appreciated that very much. But, we were there, and things were going okay, I guess. It was difficult at first, but it was going okay. There were aspects of the job I really enjoyed. I was really helping people get projects started, and it was very rewarding that way. So, I decided to stay there. I was still doing neutrino physics in China for a few years, but then—I was funded by the National Science Foundation, and it was a little too much for them to fund a research project of somebody that was deputy director of a Department of Energy lab. It just didn't fit their portfolio [laughs]—let's put it that way—so they really didn't want to fund me anymore. So, I had to kind of stop doing research.

I had kind of a principle when I went to the Lab and tried to maintain, which was that I wanted to not have any conflicts of interest. You might say, well, why don't you just start doing research at the Lab there? It would have been easy, right? It's just down the street. That's true, I could have done that, but I really wanted to maintain my neutrality. There's 1,500 users that come and work at the Lab, and I thought it was really important to not take sides. It's just the way I operated when I was there. So, I couldn't continue doing neutrino research because NSF didn't want to fund me, and I didn't want to get into a situation at the Lab where I felt like I would have a conflict of interest, so I stopped doing my own research and just concentrated on the administrative work.

But I enjoyed being on the faculty at the College of William & Mary. They were very friendly to me, and they really appreciated my presence there. I had an office and I would come attend seminars and colloquia and come to faculty meetings, and they seemed to really appreciate that I would participate in their academic life there. It actually turned out quite nice. It was good. I got to be heading towards 70 years old and the pandemic hit, and that shook everything up. We had bought a place here in California and wanted to live out here, so decided to take retirement.

ZIERLER: Were you able to keep up an active research agenda when you joined Jefferson Lab, or were your responsibilities really more on the administrative side at that point?

MCKEOWN: I still had this experiment in China. The neutrino experiment in China was just getting going. We were still constructing it in 2010 when I left. In fact, I had a whole team of a better part of a dozen people at Caltech that continued to work on this stuff [laughs] while I was in Virginia. The NSF continued to pay them! Well, a combination of NSF and the DOE project that was building the experiment. The thing just kept going. I was in constant contact with them, obviously, and going back and forth to China. It was Christmas Day, 2011, when the experiment started taking data. It was one of these nice things—in March of 2012, we were able—the result was so clear in the data that we took that we were able to write a paper and publish very quickly. It was very successful. There were several other experiments around the world competing with us, and we beat them all to it, and got a very nice physics result that surprised everybody.

It was really thought that this angle we were going to try to measure was very small and was going to be hard to measure. It turned out to be just below the previous limits from previous experiments, so it actually was very easy for us to make a very definitive measurement very quickly. It was very exciting, actually. It was a lot of fun. That experiment continued to run until probably 2020 or so. Around 2014 or so, when my funding cut out, I drifted away from it. That was it for my research career at that point.

ZIERLER: Then of course COVID happens.

MCKEOWN: Then COVID happened. Sitting in my house in Virginia, working from home—we had the house out here in California already, and I said, "Gee, we should be in California." Of course, everything changed at the Lab. They all of a sudden decided it was very attractive to be able to pay people in other states because you could attract people to work remotely that you wouldn't otherwise be able to hire. They viewed this as an opportunity like many businesses did. So, I got to be able to work from California, remotely, and it was great. We have two children, a son and a daughter, that live in the Bay Area here, so we wanted to eventually retire up here. The pandemic kind of precipitated the whole thing, got us moving on.

ZIERLER: When did you buy the house?

MCKEOWN: 2019.

ZIERLER: So that was always the retirement plan.

MCKEOWN: Yeah, but I figured it was three or four years. I was talking to the director and said, "I'm not going to do this too much longer." I said, "Now that I bought the house, the writing is on the wall." So, he knew it was coming. Once 2020 hit, the pandemic—the whole idea was we would go back and forth a lot. We'd have a house on each coast. But you couldn't travel. It wasn't working so well. We were stuck in Virginia. We said, "Okay, let's just sell that place and we'll be stuck in California." The Lab cooperated. They had to do some paperwork with the state of California to be able to pay me, but they did it, because they were doing it for other people. They had 11 other states that they were working on. Boom, there I was! As I said, I have Emeritus status at the lab, and at College of William & Mary, and so I still have contact with the Lab a lot. I'm starting up with Berkeley. I'm going to go down to Berkeley. In fact the person who signed me up at Berkeley was one of my ex-PhD students—

ZIERLER: Oh, that's great.

MCKEOWN: —and has been at the lab here for quite a while now. I have all these ex-students all over the place. I run into them everywhere. It's great.

ZIERLER: We'll bring the story right up to the present. What are you interested in? What do you want to do with your new affiliation at Berkeley?

MCKEOWN: I don't think I'm going to actually participate in research very much, as much as just try to keep up with things, go to seminars, maybe hopefully once in a while have something useful to say that they would find helpful. You never know. I don't think that they will ask me to be on any committees or anything like that. I'm not getting paid.

ZIERLER: Although they might know that you have trouble saying no.

MCKEOWN: Yeah, who knows, we'll see. I was a little reluctant to get into this just for those kinds of reasons. The Division of Nuclear Physics in the APS has an annual fall meeting, and it floats around, but every five years or so, it goes to Hawaii. This year, it was in Hawaii right after Thanksgiving. Even though I am not supported by the Lab or anybody, my wife and I, we had so many friends who were going to be there, and it's Hawaii, so we said, "Let's just go." We went at our own expense to the meeting in Hawaii, and I saw all these people from Berkeley there that I know, and every one of them said, "Why don't you get an affiliate status at the Lab?" I'm going, "I don't know. I don't know." I realized afterwards that I enjoyed seeing them so much that I should do it. One of the problems is, it's only 45 minutes away if there's no traffic, but there's never no traffic. There's a bus and a BART that I can do, so I'm thinking that maybe that's the way to go, is take public transportation. We'll see. It's still a work in progress. [laughs]

ZIERLER: Let's wrap. I want to ask a few retrospective questions about your work and career, and then we'll end looking to the future. On the physics side, I wonder if you can reflect on what it all means, your very important work on nucleon structure. What do we now know, and how has a new generation of physicists taken that research in new directions?

MCKEOWN: I think the one thing I did that had the most impact was I—it was kind of an interesting thing, because—I've always been interested in the weak interaction. Back in 1988 some theorists came up with an idea that you could try to figure out if there were—you know that a proton or a neutron, you could make it up only of what are called up and down quarks, and you don't need the other flavors of quarks, but some theorists speculated that actually, there could be a significant number of strange quarks in protons. It'd be strange quark, antiquark, because you have to make pairs. They wrote a paper in 1988 that said, well, maybe you could measure this using the weak interaction with neutrinos. I read this paper. I had actually studied this subject before; it just wasn't interesting before! Now they're saying it's interesting!

I said, okay, I think that the way to measure this is by using the spin-dependent electron beam using what is called parity violation. I published a paper in 1989 that said that, and it spawned a whole program of people working for 20 years to try and measure this. In the end, we showed that the number of strange quarks is very small and the theorists were wrong. Which sounds like a bit of a dud, but it allows people to now continue to develop the theory without having to worry about the uncertainty of these strange quarks. They can just work with the up and down quarks and not worry about it, so actually it was an important development.

It also pushed the technology of studying these very small—these are part-per-million asymmetries; they very small and hard to measure—pushing new technology that led to subsequent generation of experiments, like the one that I mentioned earlier, where you could measure the neutron skin in a lead nucleus using the same parity-violating effect. That's something that is relevant to LIGO and all kinds of things, which is interesting. There's a new experiment that is a successor to one we did at SLAC back in the 1990s to measure the parity violation in electron-electron scattering, something called Møller scattering. That's just being built at Jefferson Lab. I had a lot to do with helping my friends get it all approved through the process and getting funded by DOE, and they're well on their way to building the experiment. It is supposed to start up in 2025. I think pushing the technology has led to this new generation of these experiments that do things other than study the nucleon structure.

ZIERLER: On the administrative side, what do you feel at Jefferson Lab that you helped put in place that is securing Jefferson Lab's significance and relevance well into the future?

MCKEOWN: I would say two things. One is I initiated something called Laboratory Directed Research & Development, LDRD. All of the other big labs like Berkeley and Oak Ridge and Argonne have had this for a long time, but Jefferson Lab didn't have it. They had some weird argument that, well, we're just a nuclear physics lab so we don't need it. But it's a way of developing new technologies and new ideas, so I decided to try to start it at the Lab. It was really interesting, because people would come forth with all kinds of interesting ideas! I haven't really seen anything pan out to be fantastic yet, but some of them have been pretty significant. If nothing else, it actually is really good for the morale of the staff, because they feel like they have this new program that they can pitch their creative ideas. It actually was very successful, and the Department of Energy gave us high marks for starting this. When I went there, it was just poo-pooed—"No, we don't do that." I thought that was good.

The other thing I would say is the people I managed to hire and put in place. It's very talented people that are really moving the lab forward, including especially we hired the head of Computer Science and Technology—we stole her from SLAC, and her presence at Jefferson Lab has enabled them—just a couple months ago, they were told by the Department of Energy that they are getting a new project to build a high-performance data facility which is probably a $300 million computer facility. This is broadening the program of Jefferson Lab away from nuclear physics to do other things in the computational space, and that will enable them to have connections with all the other programs beyond nuclear physics in the DOE complex. I think just putting some of these key people in place has really enabled the Lab to go new places and do new things that they hadn't been able to do before. I'm very proud of that.

ZIERLER: Looking to the future, and especially because you now have this special opportunity at Berkeley to stay connected, what excites you as you look ahead? What are the frontiers where you think there's a real chance for breakthroughs and discovery?

MCKEOWN: Cosmology, dark matter, dark energy—Berkeley has always been deeply involved in these things. I have friends working on experiments in those areas. I'm hoping we will see some startling new results that will shed some light on these remaining puzzles that we have in cosmology. That's something I'd really like to see.

ZIERLER: Are there any experimental or observational efforts currently in existence or planned for the future that you're most bullish on for helping achieve these breakthroughs?

MCKEOWN: There are these big liquid xenon dark matter detectors. The most recent one is LZ. I used to be on an advisory committee for them. They have a big presence from Berkeley. Actually it is co-managed by Berkeley and SLAC. HEPAP just had their version of long-range plan that they call the P5 report, and they have recommended two interesting things. The next generation of that type of experiment, bigger one, would push it to [laughs]—people always have these funny terms—push it to the limit of what you can do given that the universe is also full of neutrinos and that would then confuse you, called the neutrino fog. There's another generation of those, but that will probably take 10 years. And, there is new—what is called the fourth-generation cosmic microwave background experiment—to study polarization of the microwave background. One of the experiments had a hint a few years ago but it turned out it was due to cosmic dust—called the BICEP experiment. This will be the next generation of that. Hopefully we'll see polarization that is indicative of gravitational radiation generated right after the big bang. That would be a fundamental discovery. They have approved this as the highest priority thing to go forward in high-energy physics. I'm sure Berkeley will be involved in that. The leader is a guy named John Carlstrom. He used to be at Caltech in the early days when I was there. He's at University of Chicago now. I still remember a colloquium back in 2001 or 2002, and Andrew Lange and John Carlstrom got up and showed us the pictures of the early universe, and it was stunning. It just sent chills down your spine. I'm hoping to get another experience like that or two.

ZIERLER: That's great. Bob, on that note, this has been a wonderful conversation. I want to thank you so much for spending this time with me.