Interview with John Ellis Interviewer: Hitoshi Murayama

“A” Higgs Boson or“ the” Murayama: Okay. That’s Higgs Boson? right, according to the of cial Murayama: Great to see you statement... three times in a month. It was Ellis: ...they discovered at the in Berkeley, the BrunoFest,1 LHC. then the Nobel Symposium,2 Murayama: Yeah, so let and now here. us actually follow on that. Ellis: Yeah. It’s great to be Now that‘ a’ Higgs boson is here at Kavli IPMU. It’s been a discovered, what is the future really exciting time in particle for the eld? What shall we physics recently. It’s great to be working on? catch up on a few things. Ellis: I think one thing At Berkeley, obviously, the obviously we want to focus was on supersymmetry understand is whether this which is one of our best is just‘ a’ Higgs boson or hopes in physics beyond the whether it really is‘ the’ Standard Model. At the Nobel Higgs boson as predicted in Symposium, the focus was on the Standard Model. There’re the Higgs boson. a number of theories that Murayama: Right. suggested that something, Ellis: We should be a little bit some sort of scalar particle careful – on‘ a’ Higgs boson. might appear in the LHC but with properties rather different from the Standard John Ellis is Clerk Maxwell Professor Model Higgs boson; some of Theoretical Physics at King’s College London since 2010. He composite models for was Staff Member at CERN from example. 1974, and served as Division Leader of the theory “( TH”) division in I think one can say that all 1988–1994. He received his Ph.D. those possibilities are ruled from Cambridge University in 1971. He was awarded the Maxwell Medal out, unless you adjust the and the Paul Dirac Prize by the parameters of your composite Institute of Physics in 1982 and 2005 respectively. He is Fellow of the Royal models to be rather similar Society of London (FRS) since 1985 to the Standard Model. I and of the Institute of Physics since 1991. He was appointed Commander

of the Order of the British Empire 1 BrunoFest 2013, Celebrating Bruno (CBE) in 2012 for services to science Zumino's 90th Birthday, Berkeley, and technology. He has been May 2-4, 2013 serving as a member of the External 2Nobel Symposium on LHC results, Advisory Committee of Kavli IPMU Krusenberg Herrgård, Sweden May since March 2008. 13-17, 2013

14 Kavli IPMU News No. 23 September 2013 mentioned supersymmetry of stable particle that was earlier. Well, supersymmetry originally in equilibrium with is an example of a theory all the regular particles in the that says that there would universe. In such a theory, not just be one Higgs boson you would expect that dark but actually more than ve of matter particles themselves them in total and one of them would weigh less than about would look very much like the a TeV, less than about a 1000 Higgs boson of the Standard times the proton mass, and Model, but not exactly hence should be within the the same. I think that the range of the LHC. differences between some Supersymmetry is one characteristic supersymmetric example. There have been predictions and the Standard other examples as well. I think Model are too small to have that in order to really probe been seen in the data so far. this possibility, we need to go So, we want to re ne the to the maximum LHC energy, measurements at the LHC, and ramp up the collision maybe other accelerators, rate, increase the luminosity, and try to gure out how and see what we nd. closely this resembles the Murayama: A lot of people Higgs boson of a Standard are curious about this Model, or whether there’s question. What if the LHC some difference. wouldn’t nd anything other Murayama: What are the than what looks like the hopes for supersymmetry Standard Model of Higgs being discovered at the LHC, boson? What are the paths in your mind? for the eld beyond that? Ellis: I think that some of Ellis: I think in that case my friends get a little bit clearly one would like to build discouraged but it’s always an accelerator which would coldest just before the dawn. study the Higgs boson in The LHC is currently in a more detail than it’s possible shutdown period. The energy with the LHC. I should hasten is going to be increased by to say that I think, in my almost a factor of 2. The opinion, it’s premature to collision rate will go up as decide on this because we well. I think there’re good need to see what the LHC prospects for discovering nds at maximum energy. supersymmetry there. There But if indeed it didn’t nd Interview are all sorts of reasons for anything at maximum energy, thinking that supersymmetry then clearly I think a lot of might show up in the LHC priority would go to building energy range. an accelerator that could One of them, for example, study the Higgs boson in is dark matter. There are many theories according to which Hitoshi Murayama is Director of Kavli IPMU. He is also Professor at the dark matter is some sort University of California, Berkeley.

15 more detail than the LHC. particle that is completely some scale. Now, something recommendation actually But remembering that the different from anything else has been discovered which that we have to be involved LHC has lots more capabilities you’ve ever seen before. It’s a looks like a point-like scalar in accelerator-based particle for exploring a Higgs boson boson, but it is the rst boson particle, at the level that has physics. We are actually than have been done so far without spin. been probed so far. I think taking part in Belle II, that’s – as the energy goes up, also Murayama: Right. this really focuses attention. the forthcoming B-factory the production rate goes up, Ellis: All the other bosons So, many of these composite experiment. What is your the collision rate goes up, have a unit of spin. This Higgs models, one could now put view on this direction in and there’s many other decay boson is certainly unique in on one side. I think it just accelerator-based particle modes of the Higgs boson that respect, and that way focuses much more clearly physics? that would come within it has all sorts of theoretical the question many of us Ellis: One of the big issues in reach, and the ones that have issues, theoretical problems. have been worrying about, particle physics is what we been seen so far could be Also, the Higgs boson could including you, the problem call the problem of avor. measured more accurately– be linked to some of the of naturalness. It also offers Why it is that there’re so one shouldn’t forget that, in solutions of some of our perhaps the prospect as I many different types of some sense, we already have cosmological problems. So, mentioned of the connections quarks and leptons and why a Higgs factory in the form of I think this is opening up with cosmological issues, they mix in the ways that the LHC. an entirely new era in both ination for example, and it’s they do. The Belle II project is Murayama: Some people theoretical and experimental a very challenging suggestion very de nitely aimed at trying even argue that maybe the particle physics. that actually cosmological to understand that better. accelerator particle physics is Murayama: So, speaking of ination might be due to There’s also work being done coming towards the end. We the theoretical side, I know ‘the’ Higgs boson; I don’t on that at the LHC. I think have to think of something that couple of young people think that works. that Belle II and what can be totally different to probe may be sort of disappointed Murayama: Right, that’s very done at the LHC complement physics beyond the Standard these days that there’s no ambitious. each other very, very nicely. Model, dark matter and other signal of new physics yet, and Ellis: It’s very ambitious but, There are some experimental things. What is your take of all the progress you really nevertheless, you know, measurements that you can this question? talked about are pointing one has to be ambitious in make at the LHC that you Ellis: I think that that’s to more experimental order to get anything done. can’t make at Belle II and premature. How many times activities trying to measure I think that just in probing vice versa. I think it’s great have physicists said that the the properties of this‘ a’ that outrageous suggestion, that Belle II is going ahead. end of theoretical physics or Higgs boson and something I think we may learn a lot It’s worth mentioning that, experimental physics is within beyond. What are the more both about scalar perhaps, the second most sight? theorists’ roles at this stage boson physics and also about important discovery at the Murayama: Like even in the in the development of the cosmology. LHC in the rst phase of its 19th century by Lord Kelvin. eld? Murayama: You do think that operation was actually in Ellis: Right. One or two minor Ellis: I think that previously theory has a role to play in the area of avor physics little details could be gured people could have had here. and that is the rare decay of out which, of course, led to reasonable doubts as to Ellis: It’s certainly keeping me bottom strange mesons into quantum mechanics and whether such a thing as an busy! µ+µ-, which is expected in the relativity. elementary scalar particle Standard Model. Evidence Murayama: Exactly. existed. Flavor is one of the Big for that has now emerged Ellis: I am sorry. I don’t buy Murayama: Right, myself Issues in Particle Physics from the LHC, which is that argument. I actually included. Murayama: Oh yeah, quite conclusive. It’s roughly think, in contrast, this is now Ellis: Of course when we that’s good. That’s very in agreement with the a very exciting period because say elementary, it’s always important. Another thing Standard Model. I think that’s the LHC already, in its initial provisional. It’s something we’re getting involved in something that we have to operation, has revealed a new that looks like that down to now actually–based on your push on to see whether it

16 Kavli IPMU News No. 23 September 2013 really does agree at the level sort of a breakthrough down see whether the paradigm for things that I am excited of theoretical accuracy that the line or what do you think mixing that we have in the about. we can make a prediction is the future in the avor moment really works at the or whether there’s some physics era? next level. I think this is where Connection between Particle discrepancy. Ellis: I think it’s certainly clear on the one hand LHCb, the Physics and Cosmology Murayama: Right. I was also that our experimental friends LHC is taking this, and on the Murayama: Now, you also very impressed by the Bs are, in some sense, well ahead other hand Belle II will take mentioned the connection oscillation study by the LHCb. of us. First, I don’t think we this. between particle physics It’s such beautiful data that have good ideas about avor. Murayama: One sort of a and cosmology. Clearly, dark clearly shows the oscillatory We got lots of ideas, but frontier on the side is the matter is the prime topic behavior of the B-mesons. there’s nothing which is very lepton avor violation, which of discussions in trying to That’s fantastic. convincing. I think it’s true in you worked quite extensively connect these areas. How do Ellis: Right. I think that the the quark sector. I think it’s on in the past̶like µ → eγ, these elds go together? Is decay of the Bs meson into in a way even more true in µ → e conversion. Do you dark matter the only thing? µ+µ- is a success, so far. Well, the neutrino sector because think that it’s also a fruitful Is there anything else? certainly a success for the neutrinos seem to mix in direction to pursue? What is the future of this experimentalists, but also so a way which is completely Ellis: Yeah, well, I think that’s intersection? far a success for the Standard different from quarks. Well, in some sense the unexplored Ellis: I think that to really Model. But, there were a you’ve got ideas about what frontier in avor physics. resolve the dark matter number of other puzzles. might be going on but... We’ve seen the avor mixing issue is going to involve There may be matter- Murayama: Which you didn’t amongst the quarks, we’ve a collaboration between antimatter asymmetry in like. seen avor mixing amongst accelerator physicists and charm meson decays above Ellis: Which I don’t like neutrinos. In fact, we’ve non-accelerator physicists. I the level which might be because basically your model seen avor mixing amongst can well imagine that non- expected in the Standard is to say there’s no model. different types of quarks– accelerator experiments Model, although both the Murayama: Right, exactly. those with charge two-thirds might nd some sort of signal theory and the experiment Well, I am testing the and those with charge minus for some sort of dark matter are unclear on that point. hypothesis that some very one-third– we’ve seen mixing particle. But depending on its There’re a number of other peculiar type of model is and avor effects everywhere nature, I think that you’ll need sort of anomalies in the really needed to understand except for the charged to study it in the laboratory. physics of b quarks and the data. So far the data don’t leptons. That’s where the accelerator charm quarks, which Belle II show any sign of that. That’s Murayama: Right. experiment comes in. can address. how I am using this idea of Ellis: The lepton, the µ, and Conversely, I can imagine that Murayama: One of the random matrices. the τ. It is clear to me that this some accelerator experiment criticisms that had been in Ellis: Yeah. I think that we is something that one has to might observe events with the community is that we really need more clues. push to the very limit of what an anomalous amount of have been making actually a You might have thought one can. That’s a place where missing energy. huge stride in understanding we got enough clues by Belle II could have something Murayama: That’ll be exciting. forces, in symmetries, by now because lots of avor to say because SuperKEKB Ellis: That will be exciting. It going to energy frontier, mixing parameters have been will produce, you know, would be exciting anyway. Interview but on the avor side we measured. But, we feel it’s enormous numbers of τ Murayama: Right. actually have gained relatively apparently too stupid apart leptons, for example. Ellis: But if you really wanted little new grounds in our from you to come up with. Murayama: Right. to identify that as dark understanding because we Murayama: Especially me, I Ellis: There’s also possibilities matter, then you’d need to still don’t know the origin of guess... that at J-PARC in a xed pin down that this is a very the patterns of the quark/ Ellis: To come up with models target experiments of using long lived particle which is lepton mass and mixings. Do for what’s going on, I think muons, to offer muon avor obviously not possible in an you think this would lead to a the way to go is to look to violation. Yeah, those are accelerator experiment.

17 there may be some sort of a Ellis: But that’s something nearby astrophysical source which should be pushed on. that is pumping in additional I think that’s a potentially positrons that are not taken interesting signature. into account in conventional Another thing, obviously, is models of cosmic rays. The to look for other types of other possibility is that those particles that might come conventional models of from astrophysical sources Murayama: That’s right. dif cult to think that it has cosmic rays are somehow or dark matter sources. One Ellis: You know, 50 a dark matter interpretation. inadequate and the number obvious thing is antiprotons. nanoseconds and it’s gone You could get a spectrum of positrons that you see And in fact many models of right and you can’t tell that has that sort of shape in is due to some interplay the AMS signal–even if you whether it lives for a 100 some dark matter annihilation between how they diffuse forgot about the fact that the nanoseconds or 10 billion models. The trouble is that out of the galaxy and how rate is very, very big–predict years. the signal is just very, very rapidly they lose their energy. that there should also be Murayama: Right. big. A signal had been seen It may be that one should antiprotons, which have not Ellis: You really need to by previous experiments. The tweak those parameters been seen. correlate what you see in AMS experiment has done and in that way, one could Murayama: That’s right. the accelerator experiment a fantastic measurement perhaps get a spectrum that Ellis: AMS will presumably with what you see in the which really pins down the rises in the way that’s seen. I sometime in the relatively dark matter experiments. In shape of the spectrum and think the jury is out on that. near future come out with the dark matter experiments, tells you that some of those Murayama: One thing that’s a new measurement of the there’re different types. One dark matter models are ruled not clear about this question antiproton spectrum. That of them is looking directly for out just on that ground. But, is when or how we can may give us more information. scattering in an underground the magnitude is I think very actually settle these potential Another possibility which laboratory. Then, there’s dif cult to understand. interpretations because some people have suggested looking for annihilations of If you take the very general relatively very little we is looking for anti-deuterons these dark matter particles arguments about how big know about the cosmic ray in the cosmic rays. There, that are supposed to be ying the annihilation cross section propagation, the origin of the the signal from dark matter around the galaxy. Maybe, could be, and if you take positrons and pulsars and so annihilations, if there is one, some will get stuck inside the the conventional estimate on. What exactly can we do? might be easier to pick up Sun or the Earth and they of what the density of these Ellis: One thing that clearly from the background from annihilate. They form particles dark matter particles is you could be done looking at normal cosmic rays. That’s that you can perhaps see. cannot reproduce the data. the positrons is to look for another thing which we’ll be There’s a whole range of I think the only way to do it some sort of anisotropy. I looking out for. different non-accelerator would be to postulate that think that if you had nearby Murayama: Obviously, experiments. As I say, they these dark matter particles sources then, at some level, another big major puzzle in really have to work in tandem are clumped, but clumped to you would expect the arrival cosmology is dark energy. with the accelerator ones. an unbelievably big extent. directions of these positrons What do you think we Murayama: Speaking of Murayama: Right, like packs to remember that. As they might learn by studying dark that kind of signal, AMS of 100. wander around through energy? has reported a tantalizing, Ellis: A pack of 1,000, 10,000... the galaxy they forget from Ellis: Dif cult to tell. Clearly, actually beautiful piece of So, I think that’s really tough. where they came from, but there’s the density of dark data, looking at the positron I think that probably it’s due there should be some sort of energy itself and then there’s fraction in the cosmic rays. to some sort of astrophysical statistical memory. AMS and a question of how that What is your take on this source. I guess there’re two other experiments so far don’t density might have varied as piece of data? schools of thought on that. see any sort of anisotropy. a function of time. I think that Ellis: I think it’s really very One school of thought is that Murayama: That’s right. we’re getting–and you are

18 Kavli IPMU News No. 23 September 2013 getting through the activities we are today. What is your here at Kavli IPMU–tools impression about this? which could measure the Ellis: There’s a technical term dependence of that energy for that which is gangbuster. density over a large range of I think that Kavli IPMU cosmological time, extending certainly established a very from the present day back to enviable brand. I think that when the red shift was similar people recognize that it’s to one–maybe even more. It indeed a worldwide center that are already happening, it, but it is certainly true could be that the dark energy of excellence which was your it’s also getting involved that all of electronics, lasers, density is absolutely constant. mission that was given to you in other things like we etcetera, etcetera, you could Then that really would be by the Japanese government. already mentioned, Belle make a big incredibly long cosmological constant that Murayama: That’s right. II, improvements to Super- list depends on 20th century will be somehow–well, I Ellis: I think that Kavli IPMU Kamiokande, and the dark physics and, in particular, was going to say the most is driving many of the energy experiments. quantum mechanics. Even boring possibility. From the interesting theoretical and It’s not clear to me at the relativity is now used in experimental point of view, experimental developments, moment what more you could satellite navigational systems, it’s maybe boring but from a and not just here in Japan do in terms of the science. GPS, and so on. Antimatter, theoretical point of view, it’s but also in international But, there’s another aspect a very abstruse discovery, maybe the most challenging. collaboration. I think that the of our work and of your postulated by theorists in I mean a number for that... Japanese government should work; I think that we need to the late 1920s, discovered in Murayama: Right, featureless be pretty happy. They got convince governments and cosmic rays, and now is used number. quite a lot of bang for their other funding authorities routinely in medical diagnosis. Ellis: How could you explain yen. that fundamental science is Thousands of people every that? Right. I think many Murayama: Okay. That’s great not something that you can year have PET scans. theorists like the idea that to hear. Of course, one thing dip your toe in for 5 minutes I think these examples this dark energy density is we are still worried about is and then go off and do show that advances in actually varying slowly. Maybe how we can make secure the something else. fundamental physics do eventually, it’s going to relax future of this institute when Murayama: That’s right. bene t society in general away to zero and that’s a very the WPI funding may ramp Ellis: Fundamental science is and the economy but on a seductive idea. I think the down, possibly, in 4 years something that has payoffs timescale of decades. I think ongoing experiments should from now, maybe with a 5 on the timescale of decades. it’s the role of government tell us whether that really year extension. What can we Murayama: Maybe even to support that. I think it’s works or not. do actually to strengthen our centuries. unreasonable to expect position to the government Ellis: Well, maybe even an industrial company to How Can We Make Secure and what should we be centuries but I mean if you do so. I think the Japanese the Future of Kavli IPMU? working on? look at 20th century physics, industrial companies are Murayama: Excellent. Now Ellis: What should you be so quantum mechanics, there maybe further sighted than switching to gear to why working on? At the purely is some anecdote out there European or American you are here this time, and scienti c level, I think that on the internet that over 30% industrial companies. But, Interview you come for the External Kavli IPMU has a very good of the US economy at the you can’t expect them to be Advisory Committee for Kavli program of being in the beginning of the 21st century looking much further than a IPMU, and you’ve actually most exciting developments was based on 20th century decade in terms of their R&D been on this committee in particle theory and also physics. program. already from the very particle experiment, both Murayama: Interesting. You have to look to beginning, and you saw how in accelerators and non- Ellis: I don’t know whether governments to take the this institute has got started accelerator experiments. it’s true or not and I am sure longer view. The fact that the and evolved and where In addition to the things you can get a big ght about payoff takes a longer time

19 also means that the research the message, and we just CERN, showing up in media on one or two“ ambassadors” programs are not things that discussed what I think the and being very visible. to do the job. I think it’s are done in 5 minutes or 5 message is. But then I think Ellis: I think that there particularly important months or 5 years. Right. that we have to get out probably is an LHC effect. In that the young people get They take longer. the message. I think it’s an fact, it was interesting that a involved. The young people Murayama: Right. absolutely essential part of few years ago, the UK science obviously have a lot of Ellis: I mean we’re talking a a physicist’s or a scientist’s minister came to CERN, and credibility with other young lot about the LHC. The LHC work to engage with the he said that he thought that people. Well, after all it’s was rst conceived in 1984, public. We can’t just all sit in LHC startup could have an people that we’re trying to and it’s probably going to go our ivory tower and expect impact similar to the Apollo inuence. I mean one of on for at least one, maybe yen to rain down. We have to moon landings. the things that–one of the two more decades. All these explain what it is that we’re Murayama: Wow! deliverables, I think, that we other projects that we’re doing, and we have to learn Ellis: Then I thought this is have is an increased interest mentioning, these also have to explain it in terms that bullshit. But, now I think of young people in science, long time scales. I think that the person in the street can he was right. I think history technology, engineering, and the Japanese government understand. has proven him to be more mathematics. Are you talking like any other government Sometimes it happens. or less correct. I mean, I to a bunch of young people? has to come up with a I think that in Europe and certainly know that in the That’s one thing. But, I got mechanism for funding long- at CERN, we’ve been very UK enrollment in physics a lot of gray hair. You’re term forefront research in fortunate that the person generally has gone up. beginning to have some fundamental science. Physics in the street has noticed Murayama: Wonderful. grays... is not unique. We’re talking about the Higgs boson. Ellis: The quality of the Murayama: Yes, I do. about physics but it’s not the I think we’ve got the ear students has gone up. In fact, Ellis: It’d be good if we could only example. Govenment has of governments. They are I was just talking with one nd some young people who to understand that it’s not basically sympathetic. But, I of my colleagues at King’s don’t have so much grey hair, something that you can leave. am sure that in Japan that’s College London. He was who also are naturally very It’s not like a quickie divorce. the case to some extent also. marking exam scripts earlier energetic to join in this effort. It’s something that you’re in Murayama: Yeah, absolutely. on this week. I walked into Murayama: Right. That’s for the long run. Ellis: I know that you, his of ce. He said“, These something we should be personally, have been very kids are too good.” Not only working on. Great. Any sort much engaged in that. I think are their numbers but also of last message you would Engaging with the Public Is an Essential Part of a we just have to, perhaps, also that the quality is going up. like to give to us? Scientist’s Work convince our colleagues that Certainly at King’s, we have Ellis: I don’t think so. I think Murayama: So, we have to they have to – some of them, decided to increase the that Kavli IPMU is doing a communicate these bene ts maybe work harder on this. threshold for students to great job. I think that you of basic research and, as you Murayama: That’s true. come in to study physics. should have con dence say, not just in physics, but You spend a lot of time Murayama: Good. Sounds in what you’re doing. You, in all areas as a long term communicating the like that your advice to us is personally, certainly have bene t to the society and importance of science as basically the same, namely, con dence in what you’re human kind which needs sort of scienti c ambassador “Do great science and get the doing. I think that let’s go to be supported by the to the general public. I’m word out.” out and communicate our government. How effectively sure that has a huge impact. Ellis: Yeah, but I think that excitement to the rest of the can we communicate these Somebody told me that you and I have to, like I said, society. points to higher levels, enrollment for young students convince our colleagues to Murayama: Okay, let’s do politicians, governments, and in science, in mathematics participate in this. that. Thank you, John. the general public? How do in Europe, overall have been Murayama: That’s tricky Ellis: My pleasure. we do that? improving like 20% or so, actually. Ellis: I think one thing is partly thanks to this impact of Ellis: Yeah, you can’t just rely

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