What is Next for Supersymmetry and Dark Matter? | Interview with Dr. Joseph Incandela

0:00:28.0Getting into physics

Jed Macosko: Hi. This is Dr. Jed Macosko at Wake Forest University and AcademicInfluence. And today, we have with us Professor Joe Incandela from out on the West Coast, a professor of physics at UC Santa Barbara and somebody who does a lot of different things.

So, the first question I’d like to ask you is, how did you get into physics?

Joseph Incandela: So, it was interesting because my family, it was very artistically oriented, and I studied art at the Art Institute of Chicago every Saturday from when I was 6 until I was 18 and planned to become an artist. Studied all kinds of art and got very interested in glass sculpture, and my favorite sculptor was a chemist, and I decided I needed to study chemistry. And went into chemistry and discovered physics.

That’s usually the story I give. But actually, the more I thought about it, I realized that actually when I was very little, I had thought a lot about spacetime and the universe, and I was very deeply interested in that, and I didn’t discover until I was... I took my first physics course, that there was a discipline that actually studied those things, that that was... One could get a real job doing that. And I think at the end of my first physics course, I remember I was 18, I decided I was gonna get a PhD in physics, and that’s what I did. Yeah.

Jed: So, not everybody who comes to our website will have thought things as through as carefully, but it’s good for them to get to hear your back story.

And then, how is it that you ended up where you are right now? Can you guide us through your trajectory to Santa Barbara?

Joseph: Yeah. I went into physics, I had originally wanted to do theoretical physics ’cause I really didn’t like lab courses as an undergrad. But then when I got into grad school, presumably to do theoretical physics, an experimentalist asked me to try experimental one summer, and I discovered that actually doing experimental physics is completely different than lab courses. And I really liked the combination of understanding the physics and the theory, but actually connecting more with the data and seeing the physics itself and the variety of things you did, where you work with engineers, you build things, you analyze data, you have to become somewhat of a jack of all trades.

And my thesis experiment was a search for magnetic monopoles, which using superconducting detectors, I don’t know if you know, but in 1982 or ’83, there was a candidate event with a superconducting detector at Stanford that really kinda lit the world on fire, it looked like it had to be a monopole. It was exactly what you’d expect.

So my experiment basically was 200 times the scale of that, and we didn’t see anything, but we did show that there was a singles rate and we had coincident loops and we basically killed the party, so to speak. But I then wanted to go into more standard particle physics with accelerators, and I did kind of a stint for 10 months on that, kind of an in-between experiment with an underground experiment at the Gran Sasso mine in Italy, which used standard equipment but was still looking for monopoles and cosmic rays, and then I got a CERN fellowship.

And I joined the UA2 experiment shortly after they discovered W and Z particle, and ever since then I’ve been trying and I worked very hard to be... I really wanted to be part of... Having joined this experiment with people who had just been part of a major discovery made me really want to be a part of a major discovery.

So, I focused on that for a while, I chased after the top quark in Europe and then moved back to the US to look for that, and I led the team that actually had the strongest signature signal for the discovery of top quark. And I did that with silicon detectors, semiconductor detectors, which you can do very high-precision tracking, you can detect the B quarks coming from the top quark decay by their long-lived pathways, because you can project the particle tracks back with such precision that you can see that there’s a decay that’s displaced from the primary vertex.

And that got me into the silicon business, and I worked on that ever since and have been building bigger and bigger silicon detectors. So, part of... I think what got me to where I am in the field was a strong interest in going after major discoveries. Certainly wanted to go after the Higgs, looked for the Higgs already in the ’90s, but we really didn’t have the accelerators we needed, and the LHC was the first real accelerator that would make that possible.

I joined the CMS experiment and helped them build the largest silicon detector ever built. We built 7500 meters of semiconductor detectors at Santa Barbara. Considering the entire world production before that was maybe 5 meters, that was a big job, and then the whole system was 200. But that was crucial and I think I played a big role in that, and that was crucial to our ability to do a lot of the kind of physics we were able to do at the LHC with the CMS experiment.

And then I got into the physics coordination and then the management of the team, and then I was the spokesperson during the discovery of the Higgs. And since then, I’m still on the LHC. I’m still at CMS. We’re now building a 700-square meter silicon calorimeter, but I’m also using silicon and silicon calorimetry to look for dark matter with a 4 GeV and 8 GeV electron beam at Stanford. And so that’s my whole career in a nutshell.

Jed: That was really amazing. Oh, my gosh. Well, lots of connection points in my mind that I’m thinking about. First of all, in high school, I remember my friend, Brian Goldhaber, now Brian Goldhaber-Gordon at Stanford, said that his grandfather looked for the monopole. So this struggle to find the magnetic monopole has been going on for a long time and you are the one who killed it.

Joseph: Well, I killed one of them. They looked originally for what they called just Dirac monopoles. They didn’t know what the mass would be. They knew what the charge would have to be. And no one found them and so it petered out. The interest came again because... And in fact, it was really killed when it was shown with grand unified theories that you didn’t need monopoles to quantize electric charge, which was one of the main motivations for them.

But then, Gerard 't Hooft showed that in all grand unified theories, there were monopole solutions, but they were very massive, kind of GUT monopoles. And so they were so massive, they would not have been detected by any of the previous experiments and the only sure way... One of the few sure ways was to use just a magnetic charge and detect the current in a superconducting loop.

So when that was seen at Stanford, people got very excited that that was the new, very heavy, massive monopole. Those are not entirely ruled out. It’s ruled out that we would see them very easily on Earth. That’s probably true, but we can’t rule them out completely and believe it or not, there could be just one in the universe and they could be...

[laughter]

Jed: We just met with Gerard yesterday and so...

Joseph: Oh, really?

0:08:31.9Supersymmetry

Jed: Yeah. He was fantastic and it was interesting to compare his feelings about supersymmetry compared to Mikhail Shifman , who we earlier interviewed. Misha, of course, was sad that the LHC didn’t find supersymmetry and he was holding on to hope that a bigger super collider would find it. And Gerard was more circumspect and said that just because a theory is beautiful doesn’t mean it’s true. True theories are beautiful, but it doesn’t always work the other way around.

So what are your thoughts about supersymmetry since you spent so much time at the LHC?

Joseph: Yeah. And in fact, one of the things that I’ve been doing is searching for supersymmetry since, along with the Higgs, that was my main interest then and probably ever since the Higgs was discovered, my main focus has been supersymmetry. And it looked... But I should say the reason I was interested in supersymmetry personally was not that it was such a beautiful theory or that it was such a nice symmetry that it completed this group of symmetries or... There’s many reasons to like supersymmetry, theoretically. It solved some very basic problems as well with the standard model, as you know, perhaps with the gauge hierarchy problem. You can’t really easily explain why the Higgs mass is as low as it is, for example, without supersymmetry or something like that.

So there are a lot of theoretical motivations, but the reason I like to... When I focus my effort on something experimentally, which can be 10, 15 years of work, you have to have lots of reasons to do it. So I needed something more than just theory and I think it was dark matter and the fact that supersymmetry predicted a candidate for dark matter. So that’s what I’ve been looking for, is that dark matter candidate at the LHC, and we have ruled out almost everything we could possibly look for in this simpler, more beautiful supersymmetry model. Now, we’re looking at less beautiful supersymmetry models where the symmetries are broken a little bit or you have like a... The R-parity is not perfect, it’s partially violated and things like this.

So I like to hear that Gerard was saying what he did because I often say the same thing, we have to be careful not to be too much swayed by the beauty of the theory. We have to go after practical things and so dark matter, though, is really there. We know it’s out there. We don’t know what it is and so that’s also why I’m looking, for instance, at this experiment at Stanford. It turns out that in the mass window between about where the electron mass is and the proton mass is, no one’s ever really looked. It’s dark matter and supersymmetry would not necessarily predict it there, unless you introduce a new force.

But I found that very compelling because that’s where the stable matter in the visible universe is, the electron, the lightest quarks, the proton, and nature likes to find reasons to do things in a symmetric way and also above that, the LHC has ruled out a lot, there’s a lot of other experiments. Direct detections has ruled out dark matter above that, in many classes and models below that. Cosmic microwave background has ruled out a lot. So there’s this window that is pretty much untouched where stable visible matter lives that nobody’s looked, whereas we’ve looked, to some extent, everywhere else. So that window really has to be closed and I’m working on that now.

Jed: And if you close that window, would you say it’s safe to say that dark matter is what? Just comets? Reactive light?

Joseph: No, it could still be... Feels like it could be axions. There are many things dark matter could be. The problem is, there’s not, there’s a wide... If you look at the spectrum of possibilities, it’s something like 88 orders of magnitude. We’ve ruled out maybe, I don’t know, 10 orders of magnitude perhaps, or 20 or, whatever. I can’t do that off the top of my head, but we ruled out a fair amount, but there’s a lot left. The problem is, there are wide ranges of dark matter that we would not be able to detect, so we’re going after what we can at the moment. We need stuff that would interact even very, very, very weakly with the standard model particles to see it, ’cause we’re made of standard model particles.

If it’s not detectable in that way, we may never be able to definitively say what it is, so the hope is that we will find it with experiments like this, and there’s a wide range of experiments going on right now. The fact that the LHC didn’t find it actually opened up a huge array of new ideas for looking elsewhere, so there’s still some hope we’ll find it.

Jed: And when you find it, it doesn’t necessarily resuscitate supersymmetry, ’cause as you said, supersymmetry wouldn’t even predict the kind of dark matter you’re looking for right now.

What do you think are the chances that supersymmetry will turn out to be true?

Joseph: Well, it’s interesting, I mean, I think there’s a good chance that the universe does make use of supersymmetry. It’s... For all the reasons I mentioned before, the theoretical reasons, it’s very troubling if you don’t have something like that to explain, for instance, the gauge hierarchy problem. I mean, you could argue that maybe this... There’s a multiverse, this is the anthropic universe and so forth. That may be the truth, but I like to say as an experimentalist, that’s not something I can test, and so it’s kind of irrelevant to me at the moment. We have to rule everything else out first.

But, supersymmetry may be part of the universe in a way that we can’t ever detect. And supersymmetry is not a fixed theory, it’s a parameter space that’s incredibly broad, and there’s even many classes of supersymmetry that we haven’t even begun to study. It’s a symmetry. That’s what it is, so the universe may use that symmetry, but it doesn’t mean it has to do it in a way that we detect it.

Jed: And even if you never detect it, don’t you think that it has provided a lot of good, helpful ways of seeing the universe that have led to good real discoveries since the 1970s?

Joseph: Absolutely. It’s driven a lot of great thinking and methodology, both experimentally and theoretically, and it’s used a lot, as you probably know, and there’s something called the AdS/CFT theorem, which uses supersymmetry, supersymmetric Yang-Mills theories and there’s a lot of work going on with supersymmetric theories, theoretically, that are more tractable, you’d have to talk to a theorist to get this straight, of course, but it’s a great model for understanding just some of the methods and mechanics and what universes could be, and I think it’s helped drive a lot of major breakthroughs in our understanding of fundamental theories or the...

But we’re a long way away from... I think we’re still probably a century away from where theoretically physics needs to get to really start answering some of these questions, perhaps, with string theory and things like this. This has happened before, where it takes time to develop the mathematics and really understand things.

Jed: Yeah, and Gerhard was saying that string theory depends even more on supersymmetry than some of the other ways of explaining the universe.

Is that how it works? If supersymmetry never finds the confirmation in any of our experiments and the string theorists are gonna be kind of scratching their heads, is that how it works?

Joseph: No, well, that’s an interesting point. I think... I don’t wanna contradict a Nobel Prize-winning theorist about theoretical physics, but I know Gerard well, we spent some time together traveling and lecturing at one point, and he’s brilliant, and he’s also very good at kind of probing the tough questions and looking at things from all sides.

But I would say from my limited understanding, certainly supersymmetry for most part, requires... I mean, string theory requires supersymmetric or it has supersymmetry in the solution, most of the time. Not all cases. I think there are classes of string theory that don’t require supersymmetry, to my understanding, but most does, and it could be that if we never find supersymmetry, that makes some people doubt a little bit string theory, but there’s another way to flip that around.

What if string theory develops to the point where it makes predictions that we can confirm in other ways? For instance, we don’t know why the masses of the particles are what they are. What determines the Yukawa couplings? Suppose string theory at some point can predict that? I don’t know, or can predict other parameters of the standard model, and at the same time says there has to be supersymmetry, that might be a reason to believe there is supersymmetry and it might be able to explain why we don’t find it. I think there’s a long way to go on these things.

Jed: And I think a century is probably about right. I mean, who knows? Somebody really smart could come along tomorrow. But yeah, I don’t think it’s something that we have to rush because there’s so much left to know.

Do you ever feel like Indiana Jones looking for archaeological entities when you’re looking for these top quarks and monopoles and things like that? Do you feel like a real, "I’m gonna find this thing. It’s gotta be here somewhere?"

Joseph: Yeah, I think you do feel that, especially when it takes a long time, you start really getting an intimate sort of connection with what you’re chasing. Though, I think the more incredible thing is when you see these things. So for the top quark discovery in particular, that was the first big discovery I was involved in, and we did a blind search, a blind analysis, and we got permission to open the box and there were like a handful of us, and you open this... You look at the distribution and you say, "Oh, my God, it’s there!" And it’s hard to convey what that feels like, you’re looking at something that really is a characteristic of the universe, this is part of spacetime, it’s something that hasn’t been produced copiously in the universe since the Big Bang, and you’re seeing this thing, and it’s a pretty amazing feeling to be part of that, but it’s pretty rare and it’s slow. Our research in particular is very slow, I like to tell people, "Think of a glacier and then slow it down."

Jed: [chuckle] Oh, gosh, that’s depressing. But it’s still exciting. I mean, again, with the Indiana Jones analogy. Indiana Jones’s dad was looking for the Holy Grail his whole life, you know, writing down in his little notebook and finally got to see it, so I bet that model...

Joseph: I have like 15 or 20 logbooks just going back years and all the studies and preparations and ideas. And many of us in the field are like that, but it is hard. We’re in a field where it’s getting very hard to make further progress, you can see the size of the machines we need. Hopefully with dark matter, we can get by with some much smaller experiments now, and find it. That might give us clues also about supersymmetry, by the way.

0:20:56.3Sign off

Jed: It has been such a pleasure to have you here and to hear your story.

Joseph: Well, thanks, thanks. Yeah, thanks for having me, it’s been a pleasure.