Interview with John Ellis Interviewer: Hitoshi Murayama “A” Higgs Boson or“ the” Murayama: Okay. That’s Higgs Boson? right, according to the ofcial 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 rene 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 denitely 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.