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Credit: Lawrence Berkeley National Laboratory
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Interview of Ian Hinchliffe by David Zierler on April 26, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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Interview with Ian Hinchliffe, Senior Staff Emeritus at Lawrence Berkeley National Laboratory. Hinchliffe surveys the current state of play with the ATLAS collaboration. He recounts his childhood in northern England, and his interests and abilities in science that facilitated his admission to Oxford. Hinchliffe explains his decision to remain at Oxford for graduate school to work under the direction of Llewellyn Smith on deep inelastic scattering and he discusses his postdoctoral appointment at Berkeley Lab. He discusses his work in the theory group led by Geoff Chew and he explains the significance of QCD to reconcile calculations with experiments. Hinchliffe describes the opportunities that allowed him to stay at Berkeley Lab and the key developments of neutrino scattering. He discusses his involvement in supercollider physics and planning for the SSC and his tenure as leader of the theory group. Hinchliffe explains how Berkeley got involved in the ATLAS collaboration at CERN and George Trilling’s leadership of this effort, and he explains how CMS is both competitor and partner in the search for the Higgs and beyond. He conveys his feelings when the Higgs was discovered and how ATLAS has contributed to astrophysical research. At the end of the interview, Hinchliffe prognosticates on the future of CERN, and why he remains optimistic that the Higgs factory will push forward foundational discovery.
This is David Zierler, oral historian for the American Institute of Physics. It is April 26th, 2021. I'm delighted to be here with Dr. Ian Hinchliffe. Ian, it's great to see you. Thank you so much for joining me today.
Thanks for the invitation. It's good to talk to you.
All right. Ian, so to start, would you please tell me your current title and institutional affiliation.
Okay. So, I am now formally retired. I'm Emeritus Senior Staff at the Lawrence Berkeley National Laboratory.
When did you go emeritus?
Well, it's a two-step process because I formally retired in 2016, but I was then recalled, and so I was recalled until 2019. So, I don't know what you think is the cut-off date.
In what ways have you maintained relations with the lab, particularly during COVID?
There's nobody at the lab physically except for a few people who have to work in labs. People who work in an office are not allowed in. And I was working in an office, so I wouldn't have been allowed in anyway. I maintained contact, I'm still attending meetings. I'm attending meetings from CERN also because I'm still a member of the ATLAS collaboration, which is based at CERN. I was head of the Berkeley group on the ATLAS collaboration for many years. I'm still a member. I'm less active than I used to be. It's just a natural phenomenon. But before COVID and after I was retired, I mainly went into the lab three times a week maybe. After we were shut down, of course, I haven't been in since, so it's over a year now. I call in to seminars, I call in to meetings, I talk to people occasionally. So, I haven't disconnected completely.
We'll talk more about your affiliation with ATLAS as we develop the narrative, but just as a snapshot in time, what's going on with ATLAS? What are some of the exciting developments right now?
Well, right now they're in a shutdown period. They're doing maintenance. They're improving the accelerator. And data taking is supposed to recommence sometime next year. It's not completely clear. Part of the problem is, of course, they were also seriously impacted by COVID because they do need people, people have to be physically there in order to do work.
So, there was a period when Switzerland was in lockdown and there was essentially nobody- people over sixty-five are still not allowed into CERN, I believe. So, if I were in Switzerland, I wouldn't be allowed in.
So, some people who are close to retirement are probably working from home if they can.
How has your science been affected one way or the other by Zoom and remote work? Have you found it to be easier to get some stuff done? Is it difficult not being within physical proximity of your collaborators?
We were never in physical proximity in some sense 'cause I was here, and many people are scattered all over the world, so sort of used to video meetings before the lockdown had started. Of course, the local group has regular meetings, and they would always be in person, and they're now by Zoom, of course. And it's different. If you're not at the lab you can't chat with somebody. An off-hand chat with somebody just by walking down the corridor you can't really do. You have to set something up in advance or you have to leave something running like Zoom or one of these other chat things and watch it to see if anybody pops up. It's not ideally convenient. I do find that Zoom meetings go too long. And I think if the meetings were in person, they wouldn't.
In-person meetings that last more than hour are usually a waste of time, and Zoom meetings almost always last more than an hour-
-because there's no natural cutoff.
Maybe it's lunchtime and you go and get lunch, but if it's a Zoom meeting you can go and get a coffee and come back.
(Laughter) And as you indicate, those impromptu meetings in the hallway, they can sometimes lead to good science.
Right. Those are the things that one misses most by not being- and as you saw from my CV, I used to be a member of the theory group. I was head of the theory group for a while. And I think probably the impact on them has actually been greater because they did use this bumping into in the corridors, informal chat things more often. And when they had a seminar, for example, although the seminar would last a fixed amount of time, at the end of the time, people might hang around and talk to the speaker, they might go and talk to each other. And that really doesn't happen. When the Zoom seminar is over, it's over. The speaker doesn't hang around to chit-chat, whereas if the speaker had been visiting for a day or two, he or she would be in the corridor for a few hours. You could talk to them afterwards if you're working on something that was related to what they were doing. And that's been lost.
Well, Ian, 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.
Well, I grew up in a small town in the North of England. The nearest big city is Leeds. It's about 200 miles north of London.
Would this be a Leeds accent that I'm hearing?
No. Because where I come from, the accents are incurred by region, and even though I grew up in Dewsbury ten miles from Leeds, this is not a Leeds accent. And somebody who is from there could tell that I'm not from Leeds.
What would you call your accent?
Well, the generic accent is a Yorkshire accent, but that's inconsistent because that's an even larger area, if you understand what I'm saying.
If you're a Professor Higgins or something, you could've placed it within five miles, probably. And probably still could even today. I still have quite a strong accent. It's less strong than it used to be. The biggest change since I've no longer been living there is that the vocabulary tends to change more than the accent, actually. I haven't lived there since I was eighteen.
Are your parents from that region?
My parents were both from the same- my mother died of COVID just before Christmas.
My father's been dead for some time. They grew up in the same town.
What were your parents' professions?
No. They weren't professionals. My father was a grocery clerk/manager, and my mother didn't work for a while. It was common not to work in the fifties when I was a child. Before she got married, she worked in a shop, I think, as what you call a salesclerk. When I got older and my father became ill, she took a job. She worked as a person making school lunches. So, they weren't professionals. Neither of them went to school beyond the age of sixteen.
And your schools growing up, were they small schools, large schools?
Well, you have to define small and large. I went to three schools. There is no equivalent to kindergarten, so the first level of school was up to age seven. And that had maybe 150, 200 students, pupils as they called them. And then from seven to eleven some kind of equivalent to middle school. That was a bit bigger, maybe 200 or 300. And after that, in those days there was selection in the UK. So that was schools I could walk to. The first school was across the street from our house, actually. The other school was maybe a quarter of a mile away, so I would just walk to school.
After age eleven, the schools were then selected in the UK in the sense that there was academic selection. The closest analogous thing is San Francisco has Lowell High School which still does select people based on some kind of academic or artistic abilities and then pulls people from all over the town. The New York School for the Arts and Sciences, whatever it was called, the one where all the Nobel Prize winners went, like Weinberg and Glashow and so on, that's sort of similar in the sense that its catchment area was quite large. So, the catchment area for my high school was a town that had a population of about 65,000.
Ian, when did you start to get interested in science yourself?
When I was in high school, or the equivalent of high school. It was called grammar school. Before then there were no science classes. There were no science classes below high school. In fact, until high school there were no specialized teachers. The same person taught everything. And the high school- we call it a grammar school, there the teachers were all specialized, and that was the first time I came across specifically science classes.
And when did it become physics specifically for you to pursue?
Immediately, because the science classes weren't general science, they were physics classes and chemistry classes and biology classes.
And what was it about physics for you?
That's a good question. I don't know. It sounds a bit corny, but apparently, I think the teachers. There was one guy who retired while I was there, was very effective, I thought. He was a very good communicator. He hadn't become staid by being there such a long time. He was the one I think I had the closest contact with. And then the person who was the headmaster who started on the same day I did. That was just a coincidence. He was not a scientist, he taught English classes. But his English literature classes I thought were always very enjoyable. And he was very erudite and also a very engaging person. So, he had an influence but not in science. And it just seemed sort of natural after the age of fifteen that I would try to go to university. I was the first person from my extended family to go to a university. But there were no relatives either. My mother comes from a very large family. She had six siblings, but none of them went on to education beyond age fifteen or sixteen.
You must've done exceptionally well to have been admitted to Oxford?
Well, it's difficult to normalize these things, right? I was told by this guy, the headmaster whom I was referring to, that I should be considering applying to Oxford. He was an Oxford graduate. And the grammar school typically sent two or three people a year to Oxford or Cambridge. More went to other universities, but typically it was two or three went to either Oxford or Cambridge, so it was a very small group.
In those days, most people didn't go to university in the UK. The number of people who went was only about ten percent. For example, there were many jobs that didn't require a university education that do now. Nobody working in a bank, for example, would have a university education back then. Many lawyers didn't. Many lawyers became articled clerks to solicitors directly from school; a British equivalent of a lawyer who doesn't argue in court, solicitors are not allowed to argue cases. A friend of mine did that. He became articled to a solicitor and later became a lawyer. But he has no university degree, so you didn't need a law degree, for example, to be a lawyer. So, the fraction of people going through the university education was much lower than it is now in the UK. Now in the UK it's approaching the U.S., but back then it was only about ten percent.
Ian, as opposed to the American system where there's generally a general study requirement before declaring a major in your second or third year, in the British system you focus right away. Do you see any particular advantages to that?
I think it's a plus and a minus. Well, in fact, when I was at school, it was even earlier than that, what we used to call the sixth form which lasted two years. Basically, by then, you already knew what you were going to specialize into. So, by age of sixteen you'd basically already decided. So, I think it's a good thing if you know what you want to do, because you're not distracted by doing things that you're not really interested in. It's a bad thing for somebody who develops late and has trouble making up their mind. That can be a problem.
After I left school, they introduced something that they called general studies at school level, which was much more broad. And these days people wouldn't just study physics for their final pre-university exam, they would have maybe chemistry and biology, as well. I only studied physics and math in the final two years of high school. Apart from all the classes that were sort of for general culture but not really academic in that sense, I mean, I would still take classes in English literature and history, but I didn't take exams in any of those fields. There was no sense that I would've gone on to university to study one of those. English degrees were shorter than they are now. My undergraduate degree was only three years. That's normal back then. Nobody did four-year degrees except at Cambridge. But it was extremely rare to do more than- and so that meant that what we teach undergraduates here in the first two years I learnt in high school. So that's because it was more focused.
It's not necessarily a good thing, as I said. I think if somebody really wants to go into some subject very deeply, it's to their advantage because here you're a little bit held back; if you're some place like Berkeley where you can perhaps audit courses at the university if you're still in high school or take courses in the extension. That's usually not available. And it certainly was not available to me. There is a pretty good university in Leeds, but I knew where the building was, that's all. Didn't know anything about it while I was at school.
Ian, on the social side of things, coming to university in the late sixties, early seventies, was the counterculture, was that part of your reality at Oxford as an undergraduate?
Well, I became an undergraduate in '71, so I remember the Paris riots of '68, as I was a high school student then and I remember there were lots of student demonstrations in the UK. By '71 it had died down a little. I mean, the students were still rather politically active, shall I say, I think more so than they are these days in the UK. But there weren't daily demonstrations. There weren't attempts to disrupt classes. So, it wasn't like the free speech movement in Berkeley, where classes were shut down and there were large scale sit-ins, that didn't happen. It didn't happen at any of the universities in the UK, I think partly because, as I just said, the pool of people at university was much smaller. Only about ten percent of the people went. And it was rather self-selected. There were the people like me who were first generation at university, and then there were the people whose families had always gone to Oxford and Cambridge, mostly from public schools, as we call them in the UK, what you would call a private school. Public school in the UK means a private school, it means you pay to go there. And so that was the first time I really met people from different social groups, I would say.
'Cause growing up it was a small town. Everybody knew everybody, well, not everybody knew everybody but you didn't meet anybody outside of your own class, I would say, except for the schoolteachers and the family doctor. That was it. Everybody else belonged to the same social class. Their parents worked in similar things to your parents. I didn't know any lawyers, for example, and I didn't know any kids who had lawyers as fathers. I didn't know any kids who had senior management positions anywhere. They were all working at similar kind of employment, at the same sort of level.
Ian, what were some of the most interesting things going on in physics from your vantage point as an undergraduate at Oxford?
So undergraduate, it was '71 when I became an undergraduate. And because you're still learning at that point, I didn't really become active and aware of what was really the current hot topics in research. I knew what had happened in the fifties, so twenty years before, fifteen years before maybe, but the undergraduate courses exposing to things that had happened, say, since 1960 only happened in the last year of undergraduate. That's probably still true, since you can't understand many things without a basis.
So, it was only then that I really understood what- I had some vague idea what was going on even when I was in school. But at that point, the limitations were mainly access. Even if you wanted to learn something on your own, it wasn't so easy. Where were you going to get the books from? Well, the local library certainly didn't have them, and the school library, although it was pretty good, didn't have advanced textbooks. It had books appropriate for school, it didn't have books appropriate for college. So, you could ask one of the teachers to recommend something, but then you'd have to buy it, so you couldn't sort of try it out and see whether it was at your level or too high or too low. So, it was only when I got to university that the scope expanded, if you understand what I mean. Because then one could just wander into the university library and open a book on anything. There were no restrictions, and the teachers strongly encouraged that. You were encouraged to go off and think about what you might be interested in.
Were there any professors in particular who became mentors to you as an undergraduate?
So, the Oxford system then, it still exists to some extent, but the Oxford system then was a tutorial-based system. That is to say you would have a subject that you were studying that term, and you would meet with a tutor, usually a faculty member, not always, sometimes it was a graduate student, but I can't think if I ever had a graduate student. I did have postdoctoral fellows once. And they would meet with you and one other student, so there were just two students and the faculty member, and that would last an hour. And they would set problems, they would discuss things with you. They didn't care whether you went to the lectures. The lectures were optional. I went, but they were sort of optional. And they would teach from textbooks, or books that- maybe articles even, and they would make you read certain things, explain it to them, set problems, discuss science directly with them.
So, I had two tutors who were in the same college that I was. They were not in the same branch of physics that I subsequently went into, but that didn't really matter. They were doing real research. They were a typical academic researcher like a U.S. faculty member, like somebody on the Berkeley faculty who would be spending half their time doing research and half their time teaching. And so once in a while they would talk about their own research. They didn't really like to do this because I think they thought it was taking time away from you. And you're not supposed to be learning about their research, you're supposed to be learning about what's being taught.
So, in that sense, they tended not to talk about their own research, not at least until they got older. I did have occasional tutorials from people from other colleges, one faculty member of who later moved to Cambridge and was promoted. He was influential, I think, because his style of teaching was different. He was much more nervous, much less self-confident. He was a really good person. He was a really strong researcher. He didn't lecture. We had something called a readership which is a high-level position where you don't give university lectures, so the only teaching he did was in courses, being one-on-one with students. That was very beneficial. I think later it was more beneficial that I realized at the time because he was so nervous it tended to rub off on the students, you understand. He was very reticent. Once you got through that barrier, he was very communicative, but there was always this and he's the one, after I left, apart from my thesis advisor, who I stayed in contact with the most.
Ian, was your sense that there was a hierarchy between theory and experimentation at Oxford?
No. No. In those days, they were separate departments. The theoretical physics department had this terrible old Victorian house that was basically almost falling down across from the parks which is where the cricket ground is. And there were two main physics buildings in those days, the old Clarendon Laboratory, which had been there since the end of the nineteenth century, and the nuclear physics building, which had been built only a few years earlier. That was a really new building. And that was right next door. We used to go there for seminars when I was a graduate student.
The theoretical building had no seminar room. It was just like somebody's house that people sat in what used to be somebody's bedroom. And the faculty cars were parked on what used to be a garden, including a Ford Galaxy, which took up three parking spaces, three British parking spaces. Because the head of department then was an Australian who had spent many years at the University of Chicago. And when he moved to Oxford from the University of Chicago, he brought this Ford Galaxy with him, so the steering wheel was on the wrong side. But the rest of the staff were not too happy because it took up such a giant space- he was another shy guy, but really, really nice person. People used to refer to him as "Uncle Dick." He wasn't anybody's uncle. His name was Dick, but he wasn't related to anybody. But he was always referred to behind his back as Uncle Dick, and I think sometimes even to his face, but that said something about his personality. And he cared about students.
Was there a senior thesis at Oxford?
As an undergraduate, no, except for chemistry. Chemistry was a four-year course, and the fourth year was a research course. So, the fourth year you did research, and you wrote a senior thesis. Undergraduates then in physics did not do research as undergraduates. Now they do, but then, no.
Were you committed to theory as you were considering graduate programs?
Yes. Well, you had to decide back then. The way to dodge it a little bit is to go to Cambridge for a year and do something that they call part three, which is like a master's degree. That enabled you to wait a bit longer to decide what you wanted to do if you weren't sure. I decided I'd had enough of exams, so I wasn't willing to take part three. So that was the main reason I didn't go to Cambridge to do part three. I stayed in Oxford.
Now, was that encouraged, to stay at Oxford, or was that generally discouraged, and you should move on?
I think they were neutral. The way it works in the UK is that because- back then, at least, it's still true for graduate students, college was free. I didn't pay anything and didn't take any loans out. The local authority, as it's called, which the equivalent of local government, had to pay the university fees for anybody from their town who got into university. And there was also something called the maintenance grant, which doesn't exist, which paid living expenses. So, I didn't work when I was an undergraduate except during the summer. But during the academic year it wasn't necessary to work. I had enough money, even though my parents didn't have any money, it didn't matter.
How did Llewellyn Smith come to be your advisor?
So, you get admitted to graduate school. I was admitted to more than one, but I decided to stay in Oxford, partly because I wasn't sure who I wanted to have as a thesis advisor. I didn't know people well enough as an undergraduate, so it was too early to decide, except for this guy who I already told you about, the one who was rather shy, John Taylor. I thought I might want to work with him as a graduate student. Llewellyn Smith arrived in Oxford a week before I became a graduate student. Llewellyn Smith previously had been at SLAC, Stanford, and at CERN. He was English, and he'd been an Oxford undergraduate, I believe. I'm not sure about that. And he was looking for graduate students as he'd just arrived. He didn't have any students.
And so, I talked to him first, I think, and then decided he seemed to be more in contact with what was going on in the rest of the world, if you understand, partly because he'd just come back from the States. The other one with the largest exposure was Uncle Dick, as we called him. So, I asked Smith whether he would take me as a graduate student, and he agreed. If it had been a year later, he would've had students already, I don't know what would've happened. There were two of us who were taken at the same time. Those days, you only got funded for three years, so you had to get a PhD in three years. Well, you could stay for longer, but you had to find money.
What was Smith's research at the time you connected with him?
While Smith had been at SLAC, it was when SLAC was doing the early experiments on what we called deep inelastic scattering, scattering of electrons off protons to look at the inner structure of protons. And these experiments mainly done in about 1968 onwards demonstrated that quarks existed, that the proton wasn't a blob, it was made up of point-like objects. And Smith was working on that in the early stages. And that was kind of a hot topic at the time, because before there wasn't a theory of strong interactions. Strong interactions were strong and there was no way you could calculate anything, so it was hopeless. But there were certain experiments that were easier to interpret and predict other things for, and these were these types of deep inelastic scattering experiments. And then e+e- annihilation, which was also done at SLAC and later in Europe; and neutrino scattering, which was then getting going. And there was a neutrino scattering group in the nuclear physics department. I knew some of them while I was a graduate student. I wasn't working in their group, but I knew what they were doing and what they were doing was sort of an interest to me.
So that's partly the reason, is he seemed to be more, shall we say, "cutting edge" than some of the others. Uncle Dick was one of the early pioneers of the quark model, so it was a bit of a triumph for him in a sense when the SLAC experiments demonstrated that quarks were real. But there were a lot of other people working on physics of lower energy and low momentum transfer scattering of protons and hadrons mainly. There were lots of people in Berkeley doing that, to be fair. And Berkeley in the fifties, when Geoff Chew was still around, was the center of that. That was the hot topic. That was where people said the future of understanding fundamental physics was going. And there were a few of those in Oxford. It wasn't passé yet, but it was viewed to be kind of stuck, if you understand what- they hadn't made much progress. All the action was over here in the quark model world. And as a student, you want to go where the action is. I think it's as simple as that. You don't really want to work in- I won't use the word "backwater," but you understand what I mean. You want to work in a field that's expanding and not a field that seems a bit stuck. So that was basically what drove my- Smith, at that time, there were only a few other people in the UK, actually, who were doing similar things.
What was the process for you like developing your thesis research?
Well, the process is not that much different than it is in the U.S. And a thesis advisor the first year will guide you. But even in the first year, I still would've started research along with course work. So typically, what would happen is the thesis advisor gives you a topic, you would work on something, you might work with him. I actually worked- although there was no paper. I did meet this guy we were working with who subsequently became the director of DESY in Germany. That's a large laboratory outside Hamburg. He was a young faculty member at the time. He was in Germany. And I didn't meet him until I went to a summer school, but he knew who I was since Smith and he worked- there was no internet in those days. He and Smith were using the telephone all the time. So, in some sense, I worked with him. We didn't write any papers together, but in some sense, he knew who I was when we met him, let me put it that way, and he said, "Oh, I'm glad to meet you. I'm going show some of your stuff in my talk." But in those days, because communications were rather limited- it's not like today, you had to work with somebody locally. You were dependent on locals.
Again, that was partly another reason for choosing Smith, because he had the contacts. And conferences were more important, summer schools and conferences where you broadened your experience. And at summer schools, particularly, where you would learn from faculty members from other institutes and other countries exposing you to a wider range of topics. These days it's easier. You can look at some talks on the web that might have been given at some summer school. Back then, if you were lucky, somebody would've transcribed the notes and maybe a year later you could look at it. But it was a slow process. And so, having a thesis advisor who was connected mattered more.
How did you know you had enough to defend ultimately?
Well, you have to rely on the thesis advisor. That's true everywhere. And as I said, in the UK it's a little bit different because there's this cut-off driven by funding. If you want to stay for more than a certain amount of time you have to arrange for more money. But I think Smith and I assumed at the beginning of the third year I would graduate that year. Smith didn't say that. What Smith said is, "You ought to be thinking about what you're doing next," which was not the same statement as you ought to be writing your thesis. So, sort of a year before graduation, Smith started discussing, "What are you gonna do next? Are you gonna stay in the field? Are you going to take a postdoctoral position? Are you gonna move, maybe going to industry? Are you gonna do something else?" So that conversation started a year before I left.
What were some of the conclusions of your thesis?
So my thesis was about what we now call deep inelastic scattering, so it was basically all neutrino scattering, understanding whether or not you can predict things properly, take measurements from one experiment, extrapolate, can you predict something that can be measured in another one? So, I was using data from deep inelastic scattering. And in those days there was a mystery which, in fact, we had got the right answer to but we didn't know it, about production of muons in hadron colliders at CERN. And nobody knew where they were coming from. Some people thought they were charm particles, but it didn't really make a lot of sense. Turns out that's what they were because charm hadn't really been discovered then. So, I was trying to understand that; what was the source of these muons, what were they coming from, could we get some reasonable rate, could we predict them at the sort of rate that were being measured?
As I said, there wasn't enough information, and we didn't have enough fundamental facts 'cause nobody really knew whether a charm existed then. It hadn't been discovered. It was discovered at SLAC by people from Berkeley, actually. The discovery was contemporary with my thesis, but things moved slowly in those days, so you had to wait for the paper to be published, show up in the post. I became a graduate student in the year which you sometimes refer to as the "November Revolution" because that was the year that SLAC discovered the J/psi meson and e+e- annihilation, and Brookhaven also in a different experiment, and that kind of turned the world over. After that, everybody believed in quarks. Before that there were still the skeptics, such Geoff Chew who didn't believe in quarks until 1990.
So, it was an exciting time to be a student because there was a lot going on. There was really a lot going on. There were lots of experiments running, there were lots of measurements being made that people couldn't understand but didn't know whether they were right. Maybe the experiment is screwed up or we didn't really understand what was going on and the theory was screwed up. It was both, actually, in some cases. I was at a conference once where the speaker- there was a famous experiment done at Fermilab, which turned out to be mostly wrong, and until a definitive experiment was done at CERN which sorted it out, there was a lot of mystery about this. And the spokesperson of this experiment, the Fermilab experiment, said at a conference, after listening to the CERN experiment, "X and Y are in trouble now." X and Y being two of his collaborators. It was rather disingenuous. He became director general of CERN afterwards, so it didn't do him any damage.
Proof, I guess, that fame is irreversible. But that was a time when there were lots of new experimental results floating around, some of which turned out to be right, some of which turned out to be wrong. We hadn't entered what I call a period of consolidation, which high-energy physics entered starting in the eighties. And it was a time when it was a bit like the wild west in some sense. Crazy ideas came up every five minutes, most of them were wrong, but occasionally somebody would have an idea that was actually not wrong. That was partly, as I said, why I decided to work with Smith, because he was sort of in the thick of that.
You mentioned muons. Just to go to something happening right now, all of the excitement with the g-2 experiment at Fermilab. If you had to take a wager, would you say that this is new physics?
The issue then is the following: There's two things you have to believe. Do you believe the experiment's right? I think, yes, I believe the experiment's right. They got an answer which is consistent with the previous measurements from Brookhaven, although it's not really independent because the apparatus is the same and there's a lot of the collaborators are the same. So, I have to be a little bit careful saying that their results confirmed. But before you can claim there's any new physics, you have to understand what the old physics predicts for muon g-2. And that's a bit controversial at the moment. As you're probably aware, there are recent new calculations which don't agree with the old calculations and are closer to the experimental numbers. So, if you believe the new calculations, then there's no new physics.
Do I believe them? Well, I'd like another- these calculations are in lattice gauge theory. I'd like another independent lattice gauge theory group to do a calculation and get the same answer. There are other lattice gauge theories. They are consistent with what these guys say, but they are much less precise, so you can't really draw any conclusion. But I would like another lattice group to do another calculation of comparable power. If they get the same answer, I will probably say there's no new physics.
How did the postdoc at Berkeley Lab come together for you? Who was the point of contact there?
So, again, as I said, I started this conversation with Smith when I was a graduate student, and his advice was- which was good advice, actually is unless there's somewhere you won't go you should apply to as many places as you can. Now, again, and it's different back then because we had to write letters, we had to put stamps on envelopes. It was a big hassle. And also, for the people writing your letters of reference. There were no emails. So, he knew many of the U.S. groups. That was an advantage. So, he knew which were the groups in the US. that were active. In the UK it was easy.
So, I applied to some positions in Europe. I was a bit nervous about that because I don't really- my French is awful, and I don't speak any German at all. I was offered a postdoc position in Munich and I was told that you don't need it to go there, only socially do you need any German, you don't need any German professionally. I didn't really believe it. It was right, actually, but I didn't really believe it. Courses are often given in English, for example, particularly toward Northern Europe where Scandinavia these days almost all science undergraduate courses the lectures are given in English. Even in Switzerland the lecturer has a choice, he can lecture in any of the Swiss languages or in English, and they almost all lecture in English.
But anyway, so apart from this language issue- I did apply to CERN where there isn't a language issue. I didn't get into CERN, but before I applied, Smith told me, "Don't take it if you get it because it's a very large group. You can get lost rather quickly. Unless you can latch onto somebody or you know somebody already don't go there." His advice was, take another postdoc first and then go to CERN if you can, when you have a bit more experience, when you've functioned independently for a while. In those days, postdoctoral fellowships were only two years, so just after a year you'd have to apply for another position. So, his advice was don't apply to CERN. I ignored him and applied anyway but I didn't get in, so it was irrelevant.
Had you traveled to the States before?
No. I'd been to France once when I was a school child. And I'd been to conferences when I was a graduate student, so I'd been to Italy and I'd been again to France. I'd never traveled outside the UK on vacation. Couldn't afford it.
What were your impressions of Berkeley when you first arrived?
Well, it was October when I arrived, so it was one of those typical Berkeley boiling hot October days, what we now call a fire day. I didn't know anything about fires. The only thing I knew about Berkeley was the San Francisco earthquake. I knew about the physics department, but I knew very little about the area. So, I stopped in New York on the way because one of the people who was a postdoc in Oxford had a position at the Rockefeller University in New York and he invited me to stay there for a few days, and that was a good idea. So, I'd got over the jetlag a little bit. I landed in the middle of the afternoon from New York. It was really boiling hot. And I didn't really know what to make of it. I checked into a hotel and then the next day I went to the lab and checked in there. And then day after I found an apartment.
What group did you initially join?
I joined the theoretical physics group in Berkeley, and Geoff Chew was the group leader then.
What were some of the big topics that the group was discovering and working on at that point?
The theory group then was still- I won't use the words "stuck in the past" but it perhaps the premier group in the fifties and early sixties. It was still doing the sort of stuff that it had been doing then. It was a big group.
You mean Bootstrap?
Yes, Bootstrap. So, Chew was still doing that. There was a guy at the lab still doing that who worked with Chew. You know who Stanley Mandelstam is?
Stanley Mandelstam was there then. He was not doing Bootstrap, he was doing more formal field theory, but he was not related very closely to experiments, shall we put it that way. The person I worked with when I arrived wasn’t in Berkeley when they offered me the job. He was a young tenure-track person at the lab who was at CERN on leave. He knew Smith so, again, maybe that's some reason why they offered me the job. I don't know. I knew Dave Jackson. You know David J. Jackson, the one who wrote the famous textbook?
Dave Jackson, the day I received the offer in Oxford from Berkeley, Dave Jackson was giving a seminar in Oxford. He was on sabbatical in England and showed up in Oxford to give a seminar, so at least I was able to ask him about Berkeley. That was sort of fortunate. He was moving in the direction of, shall we call it, the new physics. So, he and Mandelstam and Chew were the senior faculty members.
Ian, did you ever engage with Chew and ask him why he hung onto Bootstrap longer than other people had?
Yeah. I don't want to say- I have a lot of respect for Chew. I thought he was a great guy. He was very smart. He was very interactive. He had an enormous number of students, many of whom went on to great- including David Gross, who went onto win the Nobel Prize. He was Chew's student. David was a generation a little bit ahead of me, so I didn't know him until I got older. So, Chew was incredibly influential, and he encouraged his students to go off and do what they thought was interesting. He didn't force them into the Bootstrap. So, in that sense, he was an old-style academic. He was interested in what everybody was doing. When I showed up in Berkeley, he asked me to give a course of lectures about what I was doing, 'cause there was nobody doing anything like that in Berkeley. And he wanted to know. He didn't want to work on it himself, he just wanted to know what was going on. So, in that sense, yes. And he fostered the real sense of there being a group. He encouraged people to talk to each other, he encouraged people to collaborate with each other. He wanted everybody in, and he wanted everybody around. So, he created this atmosphere. Even though I never worked with him, the atmosphere had an effect; let me put it that way. He only just died. I don't know whether you're aware of that. Chew only died a couple of years ago.
He was in his nineties. And I used to talk to him occasionally into his late eighties, and he came to the lab two or three times a week until the last six months or so. He did eventually reconcile to quarks existing, yes, but not for a very long time. At first, he thought they were a useful mathematical artifact, a useful tool. They weren't physics but they were a useful tool in order to understand and predict things. That he was willing to concede. He wasn't willing to concede that they were physical.
Who else was with him on this topic? Was he by himself?
At the end, yes. But when I got there, no, there were other people still- as I said there were people at Oxford, faculty members at Oxford working on this sort of stuff, and there were still people in Berkeley that were postdocs doing it then. It wasn't that unusual. It was only in the early '80s when it really started to become a niche thing. People were still working on it even into the early to mid-eighties. The difference was when QCD- when people could actually start calculating things with QCD, and we're getting agreement with experiments, it was a bit difficult to argue that it was wrong. You couldn't say this is wrong. It just worked, after all. You calculated something and you measured it and it's agreed. You might believe it was just a mathematical tool, but you couldn't say it was wrong, whereas part of the problem with the stuff that Chew was working on was that computationally it was impossible, so you couldn't really get any answers that you believed.
Or another way of putting it is you couldn't make a prediction with a well-defined uncertainty You couldn't say, “do this experiment I expect to get three plus or minus one”, you could say, well, “I expect to get between three and twelve,” that's not very useful. And so that was really why people stopped doing it. There was a perception that it was stuck. There were pieces of it that were useful, and in fact many of the mathematical techniques went on to be used in string theory. In some sense, string theory came out of the Bootstrap.
Many of the techniques that were used came from the Bootstrap, although the string theorists may not be willing to admit that, but it's true. So, it wasn't useless. They did lots of important- and they did guide some experiments, particularly in the fifties and sixties. You know, it was go and measure this; maybe we'll learn something.
So, it was influential. It's just that after QCD became established in the eighties, it didn't have any predictive power and you could continue to do long energy experiments, pion nucleon scattering and measure the cross section, but then what did you do with it? Nobody could predict it. And once it became everybody agreed that QCD was right in some sense, then the argument about the stuff that Chew was working on was, well, that's in a strongly coupled regime, I just don't have a calculational technique. So, we, know the answer, we just can't calculate it. A bit like chemistry. You know, we know the answer to chemistry, but you can't calculate it 'cause it's calculations- it's quantum electrodynamics. All of chemistry is QED. But you can't calculate it. It's much too complicated. Now you can. But you had to make models and approximations which were very powerful and extremely useful, but there wasn't really anything fundamental about that.
Once you got computational chemistry, everything changed, of course. And to some extents, for QCD everything changed once we got the lattice gauge theory people, 'cause they were able to calculate in a regime where perturbation theory doesn't work. So, you can do calculations even though the theory is strongly coupled. We still can't calculate cross sections, but, for example, we could calculate masses of particles. which we couldn't do. We had quark models but that's not the same thing. We could calculate particle masses directly starting with QCD. I think the people who might still hang onto the Bootstrap would be people who said, well, we are trying to understand how you might be able to calculate in a regime where other methods don't work. That's really what they were focused on.
Now, your initial appointment was a two-year postdoc?
That's right. That was normal there. All postdocs were two years. In Europe, it was driven by CERN and still is to some extent because the CERN fellowships are written into the CERN constitution. They can't be longer than two years.
And at what point did you realize that this was not a short-term visit for you?
Okay. So that one is not so easy to answer. So, I always assumed after I came, I would apply for another postdoc and move somewhere else. I didn't know where, but it was just an assumption.
Not necessarily the States, though, you're saying?
No. Going back to Europe. I did apply to CERN then.
So, after one year I applied to postdocs, 'cause you have to do. There's a one-year lead time. So, after being here a year, I started applying for postdocs again. And somebody said, well, you might want to apply for faculty jobs. So, I applied for some faculty jobs in the U.S. There were no faculty jobs in England that year. It was a particularly bad time. There were three years in a row where there were no faculty jobs. But I did apply to CERN. I didn't apply for any postdocs back in England. I figured if I got into CERN, I would go there. Otherwise I would stay in the U.S. or go to somewhere else in Europe, maybe Germany.
So, I was offered postdoc positions and then maybe it was January or February, LBL started this search for a more senior position, and so Chanowitz said, "You should apply for that." This was the guy who came up from CERN. He's still around. So, I applied for that not knowing whether I would get anything else. I have mixed feelings about people hiring their own people. I think it's not a good idea generally.
And you felt like this was an internal hire, you were well integrated enough that you would be hired from within, so to speak?
No. Because they made a big speech about, "we don't hire internally," and that was basically true. And in the time since I've been here since then, we've hardly ever hired internally, so basically it is true. So, I didn't draw any conclusion one way or the other. I was interviewed in several universities in the U.S. I was interviewed in Michigan, Columbia, and I've forgotten- there was somewhere else at that time, and in Berkeley. And there was no formal interview in Berkeley. I guess they decided it was a waste of time. These days there would be a formal interview. but I think then they just decided, well, we know this person, it's just a waste of time. Sort of ironically, they hired two people that year. They only had money for one person. The other person who was hired, Bob Cahn, is still around also. He's older than me. He was then faculty at UC Davis, so senior to me having been faculty at Michigan before he went to UC Davis. He told me, "Before you make any decision about Michigan, go there in January." That was good advice. I was interviewed twice. The second interview was the first week of February. It was freezing cold, snowing like hell, and they offered me the job the week after. Fortunately, I didn't have to decide because Berkeley offered me the position, so I stayed.
(Laughter) Now, divisional fellow is a staff position?
It's the labs equivalent of a tenure-track position at a university.
So, it's a fixed-term position. It's not indefinite. It's a fixed-term position in the same sense that a junior faculty member, say, at Berkeley or any other U.S. university is a tenure-track position. It's a fixed term. They consider you for tenure at some point. They might keep you, they might not. It took me a while to understand this because the UK universities don't operate that way. There's no such thing as a tenure-track position in the UK where they hire you, that's it, you're there forever. So, when they explained it to me, I understood what was going on. So, it was like a university assistant professorship except the term is a bit shorter. Normally tenure reviews in assistant professors are after five or six years.
Tell me about some of the big research projects that were happening in your group in the late seventies and early eighties.
Are you still there?
Yeah. Yeah. You cut out for a second.
Well, I got disconnected temporarily. I don't know what happened.
That's okay. My question was: What were some of the big research projects in your group in the late seventies, early eighties?
So, one of the largest areas of interest was weak interactions because, at that point, this was before the W and Z gauge bosons were found. The Glashow-Weinberg-Salam model was being tested, mainly in neutrino scattering. So, people were working on weak interactions, trying to reconcile experimental measurements. That was a hot topic. There were lots of people working on hadron spectroscopy, particle masses, particularly associated with charm quarks. That's what Dave Jackson was working on at the time. They called them models. Well, they weren't really models, but they were QCD inspired, calculating the spectrum of charm/anticharm ground states. This was a large, important thing. After SLAC discovered the J/psi, it discovered a cascade of states and it was able to measure how the states decayed one into another, what their mass spectrum was, and so there was an enormous amount of data there that needed to be understood, and lots of people were working on that.
And there were people in Berkeley working on that. Dave Jackson was working on it. I didn't work on that. I worked on other aspects of weak interactions. And then, once it has become sort of clear that the Standard Model was perhaps right, as we now call it, QCD and weak interactions were right, there were still these mixtures about what other sort of things might be going on, and there was the question of, did the Higgs boson exist or was it just an artifact- to use Chew's analogy, was it just a calculation technique? Nobody saw Higgs boson. We had no idea what the mass was. So, there were people working on where to look for Higgs bosons. That was going on in Berkeley, as well, in the early eighties. I worked on a little bit of that. The group got bigger with the arrival of two people from Europe, Mary K. Gaillard is still here, and Bruno Zumino, who died a few years ago.
Mary K. is American, but her education was French, and she lived in France for many years. She's a very interesting person to talk to, partly because she can tell you about the difficulties- women in France have it worse than anywhere else.
And they still do. They still do. But when she was in, it was really tough.
Bruno had been a faculty member at NYU, so he had been living in the US before he went back to Europe. He was Italian, but he'd had a faculty job at NYU before he went back. They came in the early eighties, and that again changed the aspect of the group a little bit because they were doing- well, Bruno was doing supersymmetry, which was a hot topic at the time. I was working on that also. Mary K. was working on Higgs bosons. They were mainstream, let me put it that way, unlike Geoff. And Mandelstam would become mainstream again because of the rise of string theory. So, then there was a lot going on. There were the people like Stanley working on string theory, and Bruno working on supersymmetry. And then, the people working on things closer to experiment like Mary K. Gaillard, Chanowitz, and this other guy, Cahn, the one I referred to, who came from Davis. It was a pretty big group back then, and there were lots of postdocs, as well. Still is a big group. It's not as big as it was, here were more students then than there are now.
Ian, a general question. Perhaps now is as good a time as any. To what extent were you connected with Berkeley's Department of Physics. Did you spend time on campus at all?
Okay. So, I was a lab person, so I didn't have any teaching responsibilities. I did have graduate students and they were Berkeley graduate students and there would be a co-advisor. I occasionally taught courses but only research courses. I was ambivalent about teaching in the following sense: I felt I wasn't being paid to teach. I was paid to do research. If the campus wanted me to teach, they should pay. So, I never taught undergraduate courses. If they wanted me, I might have, but they would've had to have paid, and they would have had to have paid my lab salary so the lab could hire somebody else. I felt it was not reasonable. The DOE was paying me to do research. They weren't paying me to teach students on campus. They never said that but it's true.
So, I did have connections with campus but only with graduate students. The theory group in those days was centered at the lab. We had seminars on campus. We used to do it on days when the faculty would have office hours so they would be down there all day and then, at the end of the day, we'd have a seminar. But I never had an office campus. I didn't see a need for it. I did teach graduate courses. In fact, the first course I taught was with the first Nobel Prize winner that I really got to know very well, he's dead now, Owen Chamberlain; discovered the antiproton. And you have this vision of Nobel Prize winners as being prima donnas and rather difficult to get on with, and it's basically true, but not in the case of Owen. You couldn't have met a nicer guy. And so, I taught a course with him, and that was a fun experience 'cause he knew a lot. And he came out of the 1950s generation of experimental physicists when Berkeley was the place to be for doing experiments when we had the Bevatron and so on. And he came out of the generation of World War II people, as did Chew, of course. Chew was briefly at Los Alamos, I believe. Don't quote me on that, but I believe that Chew was briefly at Los Alamos. And Owen was that generation. So, Owen was directly connected to Ernest Lawrence, for example.
Ian, when did you get involved in supercollider physics?
Okay. So that was early eighties. This was before I had tenure, before I became senior staff but while I was no longer a postdoc. During that period, there was a lot of discussion about what the US should be doing next experimentally, and there was an accelerator under construction at Brookhaven called ISABELLE. I don't know if you know about that.
Which was- what shall we say- technically challenged in the sense that it was behind schedule, over budget, and not clear they could build it. It was in serious technical trouble. And there was a question as to whether or not, also, its energy was high enough to do anything. You need an argument. You can't get somebody to argue for funding or to fund a large project unless you have some well-defined goal in mind. It may not be what you find but you need a well-defined goal if it's very expensive. If it's cheap nobody cares. You can get the money and just do a little experiment and if you don't find anything, so what. That's what experimental physics is all about. But when you're building a major facility, it's almost impossible to get it funded unless you can say, well, we are going to do this. You might end up not doing this, but that doesn't matter. You need a goal. And so, the issue in the early eighties was, what do we do about Brookhaven? 'Cause it started out as a regional project. It had gotten so big that it was going to squeeze out everything else in some sense. And it was also pretty clear that Brookhaven couldn't carry it out, they needed more people.
So, the DOE realized there was a mess, and what should they do with it? So, there was a lot of work going on trying to understand whether or not- how useful it might be even if it were completed. And that was really where I got into this stuff. And out of this came the early discussions about the SSC (Superconducting Super Collider) and why did the energy have to be what it was; why did the luminosity have to be what it was? And I was in very early involvement in all those discussions. And what was the real goal of these things? What were you guaranteed to find or not, as the case may be? But what were you guaranteed to learn, is the way I would put it, which is important. Nobody's gonna spend fifteen years of their life doing something if they have no idea what they are gonna find at the end of it. So that was when I got involved- I did spend some time in Texas during the SSC days and before that.
Were you on leave from the lab when you were in Texas?
I went on leave from the lab. I don't remember when this was. Must've been '82 or '83. And I spent several months in College Station, Texas. I don't know whether you've ever been there. It's real rural Texas there. And then I spent almost six months after that in Cambridge, so I was gone for quite a long time. That was when I considered going back to the UK seriously. My father had just died, and I wasn't quite sure whether I ought to move back to the UK, so I spent a semester in Cambridge. But before that, I was in College Station, Texas, Texas A&M. That was culture shock. Much more culture shock there than in Berkeley.
Ian, what was exciting scientifically about the SSC, at least in the early days?
Well, after all the discoveries of the seventies—the charm, bottom; the W and Z bosons were discovered in the early eighties at CERN- there was a question as to what next. And the biggest question was what's really responsible for the W and Z masses? Is it the Higgs boson? Is it something more complicated? Is there something else? We knew about gravity, gravity had to exist, but how does gravity fit in with anything else? So, there were lots of people working on so-called grand unified theories then, trying to unify all forces, not gravity. And these motivated the various experiments that were looking for proton decay, 'cause they all predicted proton decay, and still do, actually. They all predicted proton decay at some level, which, again, it wasn't seen. But that motivated the early proton decay experiments.
So, a lot of excitement there about how fundamental is what we now call the Standard Model? Is there something more fundamental behind it? Is it supersymmetry? Is it sort of grand unified theory, where there's only one coupling instead of three? How does gravity fit in? And it was clear, to me at least, by the mid-eighties that you were not gonna make any progress on any of these issues without more experimental data. You could go and make models. Maybe you get better calculational techniques, but you weren't gonna really learn, have the ability to find out whether anything was really right without doing experiments. And so, then you were asked the question, what experiment? So, in the case of proton decay of the grand unified theories it was obvious. You went and looked for proton decay. In the case of things like supersymmetry, well, you have to go and look for it. Or in the case of a Higgs boson, you better look for a Higgs boson.
And the problem with the Higgs, of course, was nobody knew where to look for it. Its properties were perfectly well defined with only one exception, nobody knew what its mass was. Could have been lighter than the proton in those days. So, you wanted to be sure of doing an experiment that would guarantee to either find it or prove it doesn't exist, and proving a negative is not so easy. So, you want to search all possible masses, and if you don't find anything, you want to be able to say at the end, it doesn't exist. That's a tough one, because usually people can say, well, it just makes you a little bit heavier to avoid your leads. So that was most of the stuff I was doing while I was there, what we called supercollider physics initially. So, did you need a proton collider? Could you perhaps do it with an e+e- collider, limit it to lower energy? That was one of the questions being discussed. Should you wait until you could build an E+/E- collider of higher energy? How much is enough? Why was the SSC energy chosen; why not some other energy? Well, the answer is you wanted to be sure of either finding something or proving you didn't have it, so that was what was driving it. And that's what I spent a lot of time on in the eighties, early nineties.
Ian, to what extent was the interest in supersymmetry being driven by what possibly could've been seen at the SSC?
I think that's the wrong way around. First of all, there was a lot of interest in supersymmetry from a very formal aspect, the sort of things that Bruno Zumino was working on, because it offered you the only opportunity to have a unified theory which includes gravity. But you can make very general consistency arguments that if you want to make a theory involving gravity, it'd have to be supersymmetric. It could be a string theory, but it has to be supersymmetric. So, there's a strong theoretical argument, and still is, in favor of some kind of supersymmetry. That doesn't tell me anything about where you might find supersymmetric particles. I mean, are we gonna find them on the mass scale of the W and Z, or are they gonna be 10 million times heavier than that; are they gonna be Planck mass things?
So, this general argument about integrating gravity didn't tell me anything about the masses. The argument about the masses comes from the argument that the Higgs boson, if you believe it exists, is unnaturally light. If you start doing calculations with it, rapidly you can't explain why its mass is what it is. I don't know what it is but it's less than a TeV or so before it was found. Why is it so light? Whereas all the other particles, you have an explanation of why they were light. Their masses were protected by a symmetry of some type. So, the proton is naturally light in the sense- we knew where the proton mass came from, comes from QCD. An electron mass is naturally small in the sense that you can put it to zero, it'll stay zero. There's a stable position. If you put the Higgs boson mass to same value, it won't stay there.
So that argument said that you need something to make the Higgs have the mass that it's got or keep it light, a more general way of saying it. And supersymmetry provides that because in a supersymmetric theory, the Higgs mass is protected. It doesn't wander off. And that tells you that all the supersymmetric particles have to have a mass scale roughly similar to the Higgs boson. We don't know what roughly similar is. Nobody has seen any. So, I personally think the motivation for supersymmetry is now less than it was because we haven't found anything. And this argument about the Higgs mass looks a bit contorted. Even if we find supersymmetry next week, the argument's gonna look a bit contorted.
So, I'm no longer convinced by that argument. I mean, there are other options. It doesn't have to be supersymmetry. There are other options. But supersymmetry was attractive because there was a strong theoretical argument that it should exist at some level, coupled with this argument about the Higgs mass. The first argument about that it should exist doesn't tell you anything about the Higgs mass. String theorists are perfectly happy to have it only be a supersymmetric theory at the Planck scale where all the forces are equally strong. But that doesn't tell me anything. The problem I have with that is they can't make a prediction, so I don't know whether it's right or wrong, if you understand what I'm saying. Science for me is something that makes predictions that you can test and if it's wrong we throw it out and do something else. I guess I'm a Popperian in that sense.
(Laughter) Ian, when you're promoted in 1984 to a senior staff physicist, does this change your day-to-day at all?
Well, you're expected to do more management because while you're a postdoc you're only expected to do research. And when I was divisional fellow, nobody asked me to sit on a committee or do anything like that.
And I suppose this only increased when you became group leader of theory?
Yes. And eventually I became experimentalist, of course. That was in the nineties.
Tell me about that transition. How did that happen for you?
I was invited. So, while the SSC was around, I had strong connections with the experimental groups preparing experiments at the SSC. The spokesperson for one of the two experiments was a Berkeley faculty member, George Trilling, who unfortunately died a year ago. So, George, who I already knew quite well, and there were lots of other people from Berkeley involved in one of the two experiments. So, I naturally spent a lot of time working with them. I'm not somebody who could build apparatus, but I could discuss the physics motivation with them. I could talk to them about what should be being measured and how things perhaps could be improved. And they could ask me, can this be measured? Can you do anything with this? We think we can measure this; can you imagine doing anything useful? That sort of discussion was very, very useful.
So, I spent some time again in Texas, but now in Dallas, Waxahachie, as it was. It wasn't Dallas, it was just south of Dallas. Although the original site was not in Waxahachie, the original site was in Dallas itself in some warehouse. So, I spent some time there when the SSC started up. So, I had some disruption around about 1990 'cause we lost our house in the Oakland firestorm of '91. So, when the SSC was canceled, we were living in San Francisco, refugees. We're back in Berkeley now, but we were living in San Francisco then. So that period was kind of a bit stressful dealing with architects and various other kinds of things. And so, the last year or so before the SSC died, yes, I was still doing research, but I wasn't going to Texas anywhere near as often as I had before. They asked me to move to Texas permanently. You're old enough at this point you can decide whether or not you can live somewhere for an extended- when you're a postdoc you don't care. If I'm only there for two years what's the difference? And I decided I wasn't willing to live there. It just wasn't me.
It's a good thing. That didn't work out very well for anybody.
Well, most of the people that went there, a lot of them went back to where they came from. So, I think if I had gone there, Berkeley probably would've taken me back. We don't know that, of course, but I think it's probable that they would've done. The people came from SLAC; most of them went back to SLAC, for example. So, after the SSC was canceled, the Berkeley group joined one of the experiments at CERN, the ATLAS experiment. I did not join at that time though.
What were the circumstances originally? How did Berkeley get involved?
Well, the Europeans- the LHC had been approved initially as a rival project. Smith was the director general at CERN at the time. So, it was approved partly as a rival project. In fact, an interesting question as to whether the LHC would've been approved had the SSC not been approved first. But let's not go there. But it's an interesting thing to think about. How much did that pressure of competition make a difference?
But in any case, after the SSC was canceled, CERN is a rather fortunate institution. Unlike any US lab, it can indulge in long-term planning because its budget is fixed 10 years at a time, so you can plan ten years ahead.
And you can borrow money from one year to pay in the next. It's not like the U.S., where you can't move money across the fiscal-year boundary. There you can get all the money and spend it. So, in particular, when they built the previous accelerator to the LHC, they borrowed money from the CERN pension fund to build the accelerator and then paid it back afterwards. That you could never do in the U.S. because you couldn't be guaranteed of getting the money later.
Anyway, so the Europeans realized that the project was much bigger than they thought. Maybe they already knew this, but they didn't want to admit it. So, when the SSC was canceled, they realized that they needed expertise from the U.S., not just accelerator people, they also needed experimentalists, and they needed money and resources.
And Berkeley lab was a natural place to go for this expertise?
Well, because George Trilling had been the spokesperson of one of the two experiments at SSC lab, everybody knew who he was. And there were a core of other university groups and labs who worked with us on that project. So, they were a natural core group; the people who have already been working together. It was a natural core group for that group, at least most of them, to try to move to CERN. There was some reorganization but generally speaking a large fraction of what we then called the SDC collaboration joined ATLAS. So, there was a lot of negotiations with CERN at a very high level about how much money the US was willing to pay, both for the experiment and to construct the accelerator. It was clear the Europeans didn't have enough money. So that political discussion- Smith was director general when that was going on. So, they recruited US people because they wanted not just expertise, they also wanted cash. I mean, research people come with money and they come with postdocs, so they wanted these people.
So, the US joined the LHC experiments pretty quickly after the SSC was canceled in '93. I did not join at the time. I decided CERN was too far away. I wasn't sure what I was gonna contribute. It didn't look to me a particularly useful thing at that point. I was gonna go back and do QCD, think about theory. And that lasted until 1996, when the then spokesperson of the US ATLAS group- George, had stepped down. The spokesperson was Bill Willis who was then a senior faculty member at Columbia. He called me up and asked me if I'd join the experiment. He said they were having some trouble because they kept getting questions and things they couldn't answer. They needed people to go to large meetings to explain the program, to defend the issues. And in particular, there was a problem with the US in that SLAC was pushing an e+e- machine which then nobody knew whether or not it could be built. But the obvious question was, well, if you could have either e+e- or proton collider, which one would it be? And nobody could answer that question. So that's partly why I reengaged.
Why not? What was so difficult about that question?
Why they couldn't build it?
Well, they couldn't build it- it was a technical issue. Just purely an engineering issue. I don't want to pooh-pooh it too much, but it was a technical issue as to whether or not they could actually build the accelerator that they wanted to. And that discussion is still going on, to be honest. But I think now I'm convinced they could build it. But let's not go off down that road. So, there was a lot of discussion about how much resources- now, I'm not just talking about money; how many U.S. people might be involved in CERN experiments versus experiments at SLAC, perhaps an experiment with Japan. So, would it be best to just wait a bit until these accelerator problems are solved so the LHC might turn on first, but you might have a better experiment later? These were all valid questions. And that's partly why Willis drew me back into the process. Of course, he knew what answer he wanted, but that's a different problem. I didn't know what answer I was gonna get. Then after that, more or less immediately after that, I was asked by the Europeans actually, not by Willis, if I'd like to do more on ATLAS. And my involvement on ATLAS initially was these arguments about how the detector should be designed and then discussions of computing. I never knew much about computing, but I was always-
This is when you got involved with the Monte Carlo group?
Right. But I also got involved with the ATLAS computing, the early staging of the ATLAS computing structure. What we called the ATLAS computing model, how data was going be processed out, was going be analyzed, distributed- so I spent some time working on that before there was data, so in the early-to-mid 2000s. By this time, I was out of the theory group. It made no sense to have somebody attending the theory group who was spending half their time traveling around to meetings.
What were some of the big goals of ATLAS at these early years?
Well, we're back to the Higgs boson again.
After the SSC died, there was an interesting question as to whether LHC had enough energy to find the Higgs since we didn't know what the mass was and how long it might take. Now, the mass turned out to be smaller than it could've been, so, in fact, we found it.
But the most interesting thing- one of my colleagues at CERN (Daniel Froidervaux) said this to me afterwards, since I worked with him in the early stages trying to understand how long it might take to find the Higgs, what you might need, what capabilities the experiment might need to have. And after it was found, he sent me an email and said, "Did you go back and look at the old reports that we wrote in 1997 and how close we were?" And we got it right. Once we knew what the mass was, we got it right. We got the channels right, we got the rates right, everything was right. It was a bit surprising, but maybe not. But he said, "You know, we didn't know what the mass was, but we knew what to do once the mass was what it was." So that was the primary goal.
And then there was the goal to look for supersymmetry, look for something else. That hasn't panned out. We haven't found anything else. And so far, lots of detailed measurements have been made on the Higgs. And it looks like a Standard Model Higgs. It's been observed in many final states. Its couplings are known, many of them, and they're sort of what we expected once I told you what the mass was. Some people started to say it's disappointing. I think that’s wrong. We found the Higgs boson earlier than most of the skeptics said we would, despite the fact Daniel Froidevaux pointed out that we got the amount of data that would be needed and the time scale right. I was still a little bit surprised. You tend to be over-optimistic, maybe. It's a natural phenomenon. And did I think we would find the Higgs? Yes, sooner or later. Did I think it would happen as early as 2012? No. And the early evidence wasn't all that convincing, to be honest.
Ian, where is CMS in all of this? Is it redundant? Is it complementary? Is it a competitor?
It's somewhere between a competitor and a complement, more of a competitor, I would say than a complement. There's always a problem, and you mentioned g-2. And this was always a problem for somebody who was nervous about g-2. I use the word "nervous." Because when Brookhaven found the g-2 anomaly, there's only one experiment, there's only the Brookhaven experiment. So, suppose there was something that they didn't understand or something that wasn't right. If you had another experiment, you would have been able to get another measurement from a different group of people with a different apparatus and it would've given you great confidence that they'd gotten the same value.
Now, as I say that, forty-five minutes or so ago, there is an overlap between the Brookhaven people and the people at Fermilab, but the experiment was taken down and it was rebuilt. So, it's not quite a new experiment but it's close. So, there's always a problem when somebody sees something that's unexpected or marginal, which the Higgs was at the beginning; do you believe it or not? And having another experiment is useful, there's no question about that. It gives you much more confidence that it's right. As I said, the thing about the Higgs boson was nobody knew what the mass was, so you measure the mass. Two experiments come back, and they say the mass is the same thing, then you're pretty sure it might be right. And there were issues at CERN during the previous experiments at CERN with an e+e- collider called LEP, and that had four detectors. We can debate whether four were too many, but anyway, it had four detectors. And there were cases there where one detector would see something odd, and the others didn't. And so, discrepancies were resolved much more rapidly. Also, once measurements started to be made that tested the details of the Standard Model, and some of us, me included, questioned the errors that they were reporting, the uncertainties.
Having another experiment justifies their errors to some extent; if they get a number from another experiment that's consistent within the error with the first experiment, you have some belief that maybe not only is the value right, that maybe the errors are right, as well. That was one of the big question marks I always had about g-2, were they understating the errors, the experimentalists. And again, if you'd had another experiment that might've helped you. Turns out I don't believe they were underestimating the errors, but I think it was a legitimate question. CMS has different capabilities than ATLAS. It's better for some types of physics than it is for others. For the Higgs, they had a slightly easier time because the mass is rather low. If the mass had been higher, we would've had an easier time. I don't know what the mass is. So, for some physics studies that are being done now, ATLAS is more powerful, for some CMS is more powerful. And it's the complementary experiment LHCb which is really different because it has different capabilities than ATLAS and CMS do. Also, the geometry is completely different. But it's a different style of experiment, so that's not really complementary, I would say. That's different. And it's certainly not competitive. It's very difficult. CMS can do some measurements which are competitive with LHCb, but very few. So, they don't have really any competition. CMS and ATLAS, yes, they have competition.
Ian, as you became more involved, how much time were you spending at CERN versus at Berkeley on any given year?
So, I would go to CERN maybe once a month and stay there for about a week. There was a brief period when I was physics coordinator, and at that point I was perhaps spending more time at CERN than at Berkeley. I didn't move to CERN, partly because Marge was teaching, and I didn't want to move alone. So, then I was perhaps spending two weeks at CERN and a week and a half in Berkeley, kind of maximally inconvenient 'cause you just get over the jetlag and you're moving again.
So, it is sort of maximally inconvenient. I knew I was in trouble when I boarded a United Flight at San Francisco once and the flight attendant on the door inside the plane greeted me by name without looking at the boarding pass. I knew there was a problem flying too much. I think it's not necessary to travel as much- forget about COVID. Even before COVID, I'd only been going to CERN two or three times a year. I felt it wasn’t necessary to go any more often. When I was group leader, I felt I had to go because we had people based at CERN, and somebody had to look out for them. So, I would still be going at least once every six weeks. But when I was no longer group leader in 2019, I felt really no reason to go.
Ian, you said earlier that you were surprised that the Higgs was found as early as it was. Is that retrospective? In other words, were you even surprised in 2011 where things stood?
So, first thing, remember, there was a delay at the beginning because there was this famous explosion in the tunnel when a magnet exploded right at the beginning. So, the start of it was delayed essentially by a year. But even accommodating that delay- before the delay, I thought 2012, '13 was a reasonable date. After the delay, I thought it was more like '14, '15. The thing that did surprise me was how quick it was. There was a lot of discussion in the US particularly about how long it would take the LHC experiments to start producing results. After they've had the collisions then you have to analyze the data. How long does it take before a paper appears in the journal? And I had no experience in this 'cause I'd never been on an experiment before, so personally I couldn't tell you. There was always skepticism in the U.S. People said it would be three years. After you've had collisions, it can be three years before you ever have any data. Well, that three years would've taken you past the discovery of the Higgs, so that's why some people were surprised. I thought this sounded a bit ridiculous to me but, anyway, they claimed it would take you a year to understand your detector, it won't perform exactly and really need to be calibrated. All this sort of made some sense, but I still didn't believe it.
But there was the experience of Fermilab. I don't know quite how to put this, but when Fermilab upgraded the Tevatron it was an extremely slow process, and probably seeing data from either the two Fermilab experiments after the upgrade was extremely slow. And I'm talking about the period in the '90s. And I think people looked at that and said, oh, that's a no. So, it took Fermilab two or three years to get papers out. It didn't take the LHC experiments the same amount of time. Now, was never true of SLAC experiments, and it was never true of other experiments at Fermilab, either. So I didn't really have any reason to understand it, but one of the arguments that the e+e- people always used to make was it might take us longer to build the detectors, but as soon as we turn it on, we'll know what we're doing immediately because it's a cleaner environment. It's a much easier thing to do. There's less junk coming out. It's easier to measure. The energy is well defined, which it's not for a proton collider 'cause you don't know what the energy of the fundamental scattering process is. You only know what the energy of the protons is.
So, there was a lot of skepticism about how long it would take, and I think that fed into the surprise. As I said, I wasn't really surprised how fast we got papers out. Papers came out within months of the first collisions. And that's why I wasn't too surprised about it. I just thought the Higgs was very difficult. It needed a lot of data, first of all, 'cause the cross sections are so small. And you knew what to look for, but you didn't know where to look for it, and it was very sensitive to detector calibrations. So, these things that people were complaining about, about understanding the detector, that was important. And people said the detectors won't perform as well as you expect. Well, I don't know what the basis of that statement was. If you knew there was something wrong with a detector you were building, you'd build something else. So, it was either people who didn't know anything just saying, oh, well, it'll turn out to be worse, or people wanted it to turn out to be worse. I'm never sure which it was, the pessimist or the- I always found it a little bit disturbing. You would always get these statements made; the detector won't be as good as you think. And when you ask them for something concrete, they never give you anything concrete. It was, well, we all know it's like that.
So not having been on an experiment before, when we turned it on and started getting data, I was pleased. It works. Results are coming out. The machine's working very well. It is fair to say that the accelerator worked much better initially than anybody expected after the explosion. Once they got that fixed, the machine people did a really good job of bringing up the luminosity. It didn't take them years and years and years to get the thing to work. And I think some of the skepticism beforehand was that. It's a very complicated machine, that was true. They don't really know how difficult it's going to be. And then there were the people saying the magnets won't work. Well, in some sense they were right, because one blew up. We ran at half the design energy initially, and we have not yet reached the design energy, so in that sense they were right there also. The LHC is still running below its design energy, and that is primarily due to the performance of the magnets, the dipole magnets. But nevertheless, if the Higgs had been heavier, we'd have needed more energy at the start.
To what extent, Ian, did the discovery of the Higgs represent institutionally a success for Berkeley Lab?
Well, we were responsible- not me personally 'cause I'm not a hardware person, but we were responsible for building a large part of the tracking detector for ATLAS, the thing that's closest to the beam, closest to the interaction point, both the pixel detector and the silicon strip detector that sits outside it. Particularly the pixel detector was a very challenging technical project, and there were real questions there in the early stages as to whether it would work. I mean, that's a fair comment. It did work. And how long it would last is another issue. Because it's close to the beam. There's a lot of radiation coming from the beam itself. It's silicon, it gets damaged. You can't put your iPhone next to the beam. It won't last more than thirty seconds, and the chip will be fried. The detector would degrade too fast. You'd have to replace it after a year or two, which isn't really practical. You can't keep going down there and replacing it every year.
So, I think there were legitimate questions about this. How well would the pixel detector perform? How long would it last? It performed as expected, I would say, and it's lasted longer than we expected. I mean, it is suffering from radiation damage now but ten years old. And it will have to be replaced and will be replaced, so not next week but in the next five years or so. So, its performance is degrading but its performance is still good enough at the moment. Won't be good enough eventually, but it's good enough at the moment.
So that was one of the areas where I think I was very nervous. Is this thing really going work? And it is going to last if it works? Is it going to last long enough? 'Cause if the Higgs had had a larger mass, it might've taken us until 2016, for example, to find it. Well, it turns out, yes, the pixel detector did last that long. It's still going. But it wasn't obvious when we turned the machine on that it would last that long. I mean, we had conservative plans to replace pieces or to just switch off the layer that's closest to the beam, assuming it wouldn't perform anymore. We couldn't take it out but just ignore it. And that never happened. So, in that sense that was good news, so that was a surprise, yes. And that was, I think, again part of some of the skepticism. You're building detectors that are in an environment that's much more demanding than people have built before; how do you really know it's going to work? And then, we're back to how long it takes to understand it. Well, it took less time to understand it than we thought.
Ian, did you see the discovery of the Higgs as the capstone to building the Standard Model?
Yes. It's not the end in the sense that it proves that the Standard Model is in some sense complete. There could be other bits that we haven't seen, but there's no evidence. If we don't find any more bits- let's forget about supersymmetry then, if we don't find any more bits, there aren't any things that you can't explain outside the Standard Model. Now, I have to be careful. There's the g-2 situation, and there's some anomalies seen by the LHCb collaboration. And there we'll get the real answer if they're right or not, because the e+e- collider in Japan is starting up again. And that is measuring the same thing. So, if there's something funny going on in B decays, we will know for sure. There might be. We don't know for sure yet. There are some odd-looking things. So, in that sense, there might be things that don't fit in the Standard Model, but there's no bits of the Standard Model that are missing. There's no things that we see that we know are there that we don't see. There's the complicated issue about what's going on in the neutrino sector, but that's something about which the LHC and colliders can't say. We know that there's something complicated going on there. And there's a lot of useful experiments there.
Ian, I'm intrigued by your invited talk at the Cashmorefest in Oxford in 2015 where you asked provocatively, "Where is the new physics?" Six years out, we could still ask the question, where is the new physics?
I think you can still ask the same question.
Well, the LHCb people would answer that that it’s in B-decays, and the G-2 people would've given the answer in 2016 it's in g-2, 'cause the Brookhaven experiment already had results then. I was being deliberately provocative. Cashmore, I'd known as a student. He was an experimentalist. I'd known him as a student and later as sort of a drinking buddy, so it was appropriate, I guess, to tweak him a little bit. He wasn't too happy about some of my jokes. We got married in the same town, not to each other. They didn't like that joke. We both got married in Reno. He was at SLAC at the time.
How did ATLAS change following the Higgs discovery? What were some of the new questions that were able to be asked only after this event?
Well, the people looking for supersymmetry and other new physics weren't really impacted because there has to be a Higgs boson, at least one, in supersymmetric theory. So, they viewed it as just the first thing. There's more coming. We found the Higgs. That's the first thing. We'll find more Higgs and we'll find supersymmetry. It didn't affect their program at all, I would say. The Higgs program itself was affected, because instead of searching over a vast space of possible masses—you knew there was this particle. You wanted to measure its properties. You wanted to know whether it was the real Higgs or did it look like a Higgs. And so the Higgs program changed. It changed from being a search program to being a measurement program rather rapidly. Now, there's still searches going on for Higgs-like resonances at different masses, and there was a brief fuss where there was a statistically insignificant excess at 150 GeV. I don't know whether you remember that. That was in the New York Times also. But that one I never believed. CMS didn't have it, in my opinion. I'd better be careful here. You're recording this. But the CMS evidence was never as convincing. Turned out there was a reason it was never as convincing; it was a statistical fluctuation.
ATLAS had never had any more evidence. When we took more data, it wasn't there. So that was nothing wrong with the measurement. Nobody made a mistake. It was just a fluctuation. They happen from time to time. But the rest of the Higgs program became focused on measuring the properties of the Higgs. And I started to work on measuring the properties of Higgs decay, in particular the coupling of the Higgs to the top quark, which you measure by observing the production of the Higgs in association with the top quark, and then you measure the rate and that enables you to infer the coupling between the Higgs and the top quark. So that I wouldn't have done if supersymmetry had turned up; let me put it that way. If somebody found supersymmetry, I'd be looking for more supersymmetry.
In what ways have you seen ATLAS become relevant in astrophysics?
Well, there's the issues of dark matter. I guess that's astrophysics. There are some models of dark matter which would cause particles to be produced at the LHC and therefore would leave behind signatures. It's very difficult- if you don't see anything, you can perhaps rule out some model. If you do see something at LHC, which would be essentially the production of particles in association with missing energy, you don't really know whether the thing that's coming off the missing energy is a dark matter particle. It might be, but you don't know whether it's stable. If its lifetime is fifteen minutes, as far as ATLAS is concerned it's stable, but it's not a dark matter candidate 'cause it would've decayed in the early universe. If somebody comes up with that evidence of dark matter and fits it into some model, you might be able to test that model at LHC. It might already have been tested. You might be able to rule it out.
So, in that sense, there really is complementarity. There are things that the LHC can do that the direct detection experiments can't do. But if the direct detection experiments saw something, gave you some pretty good idea what the masses were you were looking for, and also the cross sections- 'cause the process is reversed—so if they can tell you what their rate is, you can constrain the rate at the LHC, at least, you could check whether or not there were things that were consistent with it or not. So, in that sense, yes, it's really complementary.
Now, again, they haven't seen anything, so, well, we don't know. I did spend some significant time before there was data at LHC thinking about whether or not- how much the LHC could say about dark matter. And there have been LHC publications on searches for dark matter, but they're extremely model dependent. You have to make lots of assumptions in order to interpret them. So, from the point of view of a theorist building a dark matter model, the current publications are quite useful, 'cause they might tell you you'd ruled out already, and they might tell you where we might be able to look. But the LHC is not a dark matter experiment. You might say that their looking for dark matter was a serendipitous thing. Nobody thought about it back in the early nineties when the experiments were being designed and when the LHC was being thought about. Nobody stood up at a conference and said, build this detector and, by the way, we'll measure dark matter. You would've been laughed out of the building, rightly so. So, it's one of these things that once you have the detector, you think about things you can do with it that you didn't realize beforehand.
Given your interests in experiments that operate theoretically at much higher energies, what is your sense of the prospects of this? Where might they happen, CERN included?
Well, I have two issues. I'd like to set aside the politics, 'cause I can't comment on the politics. So that's just- you should know that. I think there's a sociological problem. These experiments take a very long time to build and to bring to fruition. We talked about the timescale of the LHC. The SSC timescale is probably a better one. We started talking about the SSC in 1982, and the Higgs was discovered at the LHC in 2012; it took thirty years for the Higgs to be discovered. Now, it was discovered at LHC not SSC; that doesn't matter, the timescale does. There were people who worked on that for thirty years, people building stuff. They may have been doing other experiments in the sideline, but they were really dedicated to it, like the person, Peter Jenni, who was the spokesperson of ATLAS for almost its entire life. He was no longer the spokesperson when the Higgs was discovered. That was unfortunate. He'd stepped down a year or two before. But that sort of commitment people are going to have to be willing to make.
So, the question is, how long does it take? It's a long time, longer than anybody would estimate. That's another problem. You probably can't give a realistic estimate because then nobody would say I want anything to do with it. I remind you that when the SSC was approved in '85 or '86, it was supposed to give beam in 2000, so fifteen years. That's about right. When it was canceled, it was supposed to give beam in 2007, I think. And the LHC was delayed, even forgetting about the magnet. So, I think there's a problem. You have to convince people that the science is sufficiently important that you're willing to spend the largest part of your professional career working on it. It's that kind of a commitment. And this isn't a trivial commitment.
It's a career.
And so, order to do this, you have to have a pretty convincing argument to convince yourself because if you're going to be the one who's doing it- to convince yourself that it's worth it. You can always do something else. You're not forced to do this. And so, the question is, are you willing to take that effort and is the goal of the experiment enough? That for me is the question that matters. Now, for some people, it may not be that. It may be, well, this is an interesting technical project to build. I like to build pieces of apparatus. It's a strong technical motivation. That motivation alone is enough. And it doesn't take me fifteen years, it maybe takes me ten, and other people will finish afterwards. That's okay. But that's not my motivation. And I think in order to convince enough people, you have to convince my type that the possible science output from what you might learn is enough to justify the costs and the expense, the costs in terms of human bodies, not the cost in terms of money. And I think this argument was convincing in the case of the LHC. Of course, that's a self-satisfying statement because I made the argument to some extent, so I don't want to sound too obnoxious. But it is fair that there was a real argument. And it turned out to be right. But even if there had not been any Higgs, we would still have learnt something from the LHC experiments. Suppose it had found absolutely nothing. I mean, that was always a possibility; you find absolutely nothing. What would that have told you? That would have told you that the Standard Model was wrong.
In some ways, that's almost a more exciting development.
Right. So, I'm being proper again. But it would've told you that it was wrong, and that's something that's very useful. So, I'm not sure now I can make an argument for another facility, because I don't know, there's a lot of discussions about e+e- facilities and there are two types of those. There are ones that are relatively low energy or concentrating on measuring the detailed properties of the Higgs boson, in particular measuring channels that the LHC can't see like Higgs decay to charm, although I'd be a bit skeptical about that. Maybe we'll figure it out eventually. We've got plenty of time. But there are some channels for which the- Higgs goes to nothing, which is not very easy to measure. Higgs goes to nothing can be measured- Higgs decays to things you don't see. That's easy to measure to a e+e- collider because it's a fully inclusive thing. You know what the energy was, you know what else has been produced, you know there was a Higgs there, you didn't see anything. Therefore, you see the rate of producing nothing, you can calculate the decay rate. So that's a very useful direct measurement. You can do measurements of the same thing at LHC, but they're much less direct, the environment is much less clean, and we don't know what the initial energy is. We only know what the proton energy is. So that is a strong argument in favor of relatively low energy e+e- machines. That raises a philosophical question. If you see some non-standard Higgs decay, then what? The people who proposed these machines believed that this is the way to go, and they believe that if they see anomalies from branching fractions that are not quite what we expected because of the result of precision regiments it will tell you something. I'm a bit skeptical as to whether it will tell you anything.
Why is that a philosophical question, then?
Well, I'm back to g-2 again. I was at a meeting somewhere in Minnesota, it was, in Minneapolis in the summer of 2013. The DPF had a large meeting at one of the so-called Snowmass things. The anomaly from g-2 was already known. The Brookhaven results were out, and everybody was doing this; you know, what's this? We don't understand it. And there were lots of proponents of e+e- saying, you know, how much of these precision measurements- how much data will you have to have, how precise the experiments will have to be in order to find convincing discrepancies from the Standard Model. Forget about what we would do with them. And somebody in the audience asked, what's a convincing discrepancy? Now, the standard measure is five sigma. Well, the speaker was being a bit more aggressive and saying, oh, four sigma is enough. And three people from the audience shouted out, what about g-2? Which is already more than four sigma. And I don't think there was a single person in the room who believed at that point that new physics had been discovered in g-2.
So, it was an interesting question as to if you did find discrepancies in Higgs properties, how much would you really learn? I think if you only saw one discrepancy, you'd learn almost nothing. I think if you saw many you might be able to see a pattern and put it together. So, the sum of the measurements will be worth much more than any one individual measurement. So, I think there is a strong motivation for so-called Higgs factory. Higher energy e+e- machines I really don't have any motivation because I don't know what the energy should be. In the case of the SSC and the LHC, we knew what the energy had to be. It had to be energetic enough to answer this question; is that a Higgs or not? So, you need a comparable question that you can guarantee that some one of these higher machines can answer. It can't, in my view, be a fishing expedition. You're not going to get somebody- I wouldn't work for thirty years on a fishing expedition. Maybe at the end we get something that's not what I was expecting, but that's okay. But to go on an experiment and thirty years later you measure nothing, and you haven't learnt anything, I don't think that's very useful.
Ian, as a capstone to our discussion, so for my last question, let's remove all of the real-world inhibitions and focus exclusively on a platonic pursuit of new physics. We're not worried about career timespans, we're not worried about budgets, we're not worried about politics. You have in this fantasy world everything that you need to design the experiments that are optimized for new physics. With that golden ticket, what is the experiment and what would you be most optimistic to find?
So, I would first spend the money on the Higgs factory, the thing we talked about, because I think you can get that going fast, you can get people involved, it will produce a lot of results. Even if it just confirms the Standard Model, it's still very useful. So, I think that's a bit of a no-brainer. Beyond that, it's not clear. Would I wait until somebody can build a muon collider? Give all the money to the accelerator physicists and tell them to build a muon collider. Maybe that's the answer. Maybe that's a better answer than an e+e- collider because a muon collider could reach higher energy maybe. Would I just say best thing to do is build the highest energy hadron collider I could think of? Maybe that's the answer. But, again, the problem is I don't know- there are technical limits, of course. There's no point discussing something you can't build, and the muon collider- I first heard the talk about the muon collider in 1985, and there's been a lot of progress but we're no closer to building a muon collider now than we were in 1994. The similar comments apply to things like plasma wakefield accelerators. These could be very useful, but we're a long way away. I could build a higher energy LHC more or less now, and I could build this Higgs factory now, and I could build an e+e- machine of maybe a TeV now. I can't build a muon collider now. So, if I had to choose now and told build something, I would build the Higgs factory and then I would build one hundred TeV proton collider.
Okay. Well, it sounds like a plan to me.
But I would have a great difficulty convincing some colleagues to go and build an experiment.
(Laughter) Ian, it's been a great pleasure spending this time with you. I'm so glad we were able to do this on behalf of Berkeley Labs, so thank you so much.