Interview with Fabiola Gianotti Interviewer: Hitoshi Murayama

An Intense Month toward unblinded our analyses of the Announcement of the 2012 data at the beginning of Historic Discovery June and the announcement Murayama: You announced was made at the beginning of the historic discovery of the July. Higgs boson at the CERN LHC Murayama: July 4th, right? last July 4th. I watched that Gianotti: Exactly. So, 4 over the web and that was weeks in total from our rst really a moving moment. But look at the“ signal region” how were you feeling just with the 2012 data and before the announcement— the announcement. Do you before the seminar? remember that by the end of Gianotti: I think the prevailing 2011 we had some little hints, feelings were satisfaction, 3σ? concentration and... Murayama: I was there at the exhaustion. We had been December meeting (of the working night and day over CERN SPC1). the previous 4 to 6 weeks. We Gianotti: We had a 3σ excess around 125-126 GeV. But, of Fabiola Gianotti received her Ph.D. course, excesses at the level from the University of Milan in 1989 of 3σ are mainly uctuations, and became CERN Staff Member in 1996. She has been working in and so they come and go. the ATLAS experiment since the The December 2011 hints beginning of the project (early‘ 90s) contributing to detector design were not at all conclusive nor and construction and to detailed convincing. After the winter studies of the physics potential. She served as ATLAS Spokesperson from shutdown, the accelerator 2009 to March 2013. In 2012 she resumed operation at the was awarded the title of“ Grande Uf ciale al merito della Repubblica” beginning of 2012 ramping by the Italian President and the up in energy to 8 TeV (in 2011 Special Fundamental Physics Prize of the Milner Foundation. In 2013 she the centre-of-mass energy was awarded the Enrico Fermi Prize was 7 TeV). That additional of the Italian Physical Society and the Niels Bohr Institute Medal of Honor. TeV was one of the crucial She has honorary doctoral degrees elements for the discovery. from the University of Uppsala and the Ecole Polytechnique Fédérale de Although data-taking started Lausanne (EPFL) and she is Honorary Professor in the School of Physics 1 The SPC (Scienti c Policy & Astronomy, the University of Committee) is one of two subsidiary Edinburgh. She is member of the bodies to the CERN Council. Hitoshi Italian Academy of Sciences Murayama has been a member of “( Accademia Nazionale dei Lincei”). the CERN SPC since 2010.

12 Kavli IPMU News No. 24 December 2013 in April 2012, following good data, and with an scienti c practice we did not independent data set. look at the data in the region I remember a of mass not yet excluded by particularly“ crisp” previous results (the so-called exchange of mails with “signal region”) until we had the ATLAS colleague that optimized our analyses on had sent me the results. I simulated events. On the wrote him“ Oh my God” other hand we studied and he replied“ Indeed.” That the main background was it. processes very carefully One-two weeks later with data, and validated the we unblinded the Higgs simulation against data in the → 4-leptons analysis. You background regions. It was know, for Higgs → 4-leptons only at the beginning of June, we expected a handful of after recording about 1 - 1.5 candidates. We had four fb-1 (inverse femtobarn) of events in the mass region integrated luminosity, that we around 125 GeV at the end unblinded the signal region. of 2011. But, there were no We had two main analyses, new candidates in the 2012 Higgs → γγ and Higgs → data when we rst unblinded. 4-leptons, and I remember So, we were quite puzzled. that the rst analysis to be Then nine candidates came unblinded was Higgs → γγ. all of a sudden at the end Murayama: The best places to of June, a good example of look. statistical uctuations with Gianotti: When we unblinded small numbers. the Higgs → γγ analysis, Murayama: Wow. around June 10, I was at Gianotti: So in the end we Fermilab to take part in had signals in both channels. a symposium celebrating It was a very very intense Interview the history of the Tevatron month. We were very excited, Collider. When I saw the but focus and concentration results I made a jump on my prevailed. We have been chair. There was an excess working so hard to record around 125-126 GeV, i.e., at the same mass as the 3σ Hitoshi Murayama is Director of Kavli IPMU. He is also Professor at the excess observed in the 2011 University of California, Berkeley.

13 the highest-quality data, to Gianotti: I was not really Gianotti: The CMS a seminar here at CERN.”We improve the reconstruction nervous...it was rather...an spokesperson, Joe Incandela, then discussed the date and ef ciency and detector intense moment. and I had been in touch agreed tentatively for July 4th. performance for electrons, Murayama: Certainly you all the time. We were not Murayama: There was actually muons, and photons, and to looked very relaxed and discussing the results in detail, a discussion at the SPC at that understand all possible issues con dent. but we knew more or less time, that the announcement of the analysis. Every detail Gianotti: I was very how things were progressing should be done on site, rather was scrutinized; we made all motivated...beyond the in the other experiment. We than at Melbourne. sorts of checks in time for exceptional result, I was had agreed that we would Gianotti: Exactly. On the the seminar. When I entered so proud to show how not disclose any information Friday before the seminar, the auditorium...there were well ATLAS, I mean the about the other experiment June 29th, the DG called Joe so many people there—many whole experiment, had to our Collaboration. and me in his of ce and said of my ATLAS colleagues (and been functioning in all its Murayama: How much “Now I want to have the I knew that many more were components (detector, data- information did you share at numbers of σ.” We put the following from other rooms taking, software, computing, that stage? numbers on the table. It was or from Melbourne2 where analysis), thanks to the Gianotti: We knew that the 5.1 for ATLAS. the ICHEP Conference was hard and competent work other experiment had an Murayama: CMS, I remember, taking place), many summer of hundreds of talented, excess in the mass region had 4.9. I am sure that was students, and many of the dedicated people, among around 125 GeV also in the really exciting. scientists who have made the which were many young 2012 data. We knew that the Gianotti: I will never forget history of the LHC, like Lyn people. The contribution excess was growing with time those days. Evans and Giorgio Brianti. of every individual was and that it was there in the Murayama: So, until that There were also many of the crucial, and at the same two main channels (γγ and moment Rolf (CERN Director key people from the LHC time the ensemble worked 4-leptons). This was the kind General, Rolf-Dieter Heuer) infrastructure and operation as a perfectly synchronized of information we shared. We didn’t know how signi cant teams, with Steve Myers, the orchestra. also kept the Director General the signal was? head of the Accelerators. And Murayama: That is wonderful. (DG) informed. I think you Gianotti: Actually on June there were previous CERN Gianotti: A great time...and were at CERN for the June 23rd, when it was decided to Directors General, including the accomplishment of more SPC week? hold a seminar at CERN, he Chris Llewellyn-Smith, Luciano than 20 years of efforts of Murayama: Yes, I was. knew that by combining the Maiani, and Robert Aymard, thousands of people. Gianotti: That week was results from both experiments and CERN Management, really something...it was a the signal would be above obviously. Council week and I remember 5σ, but he didn’t know Told by CERN Director Murayama: So you were kind General to Postpone Travel on June 23rd, at the Council exactly how much we had of tense and nervous? to Melbourne dinner, the DG took Joe individually. Murayama: When did you and me aside and told us, Murayama: Interesting. When 2 The 36th International Conference actually learn that CMS also “Guys postpone your trip to did he invite Peter Higgs, on High Energy Physics was held in Melbourne on July 4-11, 2012. had a comparable signal? Melbourne. The council wants François Englert, and Tom

14 Kavli IPMU News No. 24 December 2013 Kibble? exciting moment. All the ATLAS Members but actually they didn’t Gianotti: I don’t know exactly, Gianotti: We owed it to Worked in Full change much. So, this really Synchronization I think he invited them a few team work and team spirit. shows that all the people days before the seminar. We worked all together, Gianotti: Another reason I working at the various steps Murayama: I see. So he was experiments and accelerator was very proud on that 4th of of the chain—and it’s a very really con dent about that, groups, in a very harmonized July was our accomplishment long chain from the detector wasn’t he? and ef cient way. as an experiment. ATLAS to the nal plots and numbers Gianotti: I think he was Murayama: I was watching worked in a superb manner —had done their work in the con dent that it would be the announcement over over the past years, and best way, impressively fast, above 5σ by combining both the web from my home in in particular in the weeks and fully synchronized with experiments. So, enough to Berkeley. That was after preceding the discovery and the others. Really fantastic. I announce a discovery. midnight, but I couldn’t sleep the announcement. The was very much impressed. Murayama: Individually you at all. It was so exciting, and data included in the results Murayama: Then right after had 5σ. That was amazing. I your last slide said 5σ...and I shown by ATLAS and CMS on you nished the last slide wasn’t expecting that. wept. I literally wept. It was so July 4th were recorded until there was a standing ovation, Gianotti: We had convincing moving. June 18th. June 18th was right? signals in both channels. Gianotti: The excitement a Monday, and on Sunday, Gianotti: That was a very When at the beginning of is also due to the mass of June 24th, we already had touching moment...the June the 2012 ATLAS data the new particle. Nature the preliminary results based awareness that the LHC, were showing an excess in the has been very kind to us on the full data set that we and by LHC I mean Higgs → γγ channel, but we because a Higgs boson of would show on July 4th. It the experiments, the had no new Higgs → 4-lepton 125 GeV decays into many means that the data taken up accelerator, the international candidates, I told myself“, We different nal states (γγ, to 6 p.m. on June 18th had collaborations, and CERN, will not go public if we don’t ZZ, WW, bb, ττ) and so we been calibrated, processed, had accomplished something see it in the two main decay can study it in a variety of reconstructed, distributed all great and memorable. channels.” Then, gradually, topologies both at the LHC over the world, analyzed, and Murayama: There is a famous with more data, the signal and future accelerators. If it gone through the statistical picture of you and Mr. Peter built up in both channels. I had been heavier, only WW combination of the various Higgs together and he is would like to stress that the and ZZ decay modes would Higgs boson decay channels. blessing you for this incredible accelerator really performed have been experimentally Murayama: That is so fast. achievement. That was Interview in a superb way that month accessible, thereby reducing Gianotti: Amazing. So, on probably the rst time you of June, the best month dramatically the June 24th, I already had met him? of operation of all 3 years. opportunities of measuring its the complete results on my Gianotti: It was. I Without that performance, properties. laptop...not nal, there were congratulated him on his we would have not discovered Murayama: We are so lucky still... brilliant idea. the Higgs boson so quickly. that we can actually study all Murayama: Some re nement. Murayama: He was right. Murayama: Fantastic, I am of them. Gianotti: ...some re nements Gianotti: Yes he was right. sure it was a really, really and cross-checks to be done, Peter Higgs is a very modest,

15 switched off my cell phone during the press conference and had forgotten to switch it on again. Immediately I received a call from Paola Catapano (from the CERN communication group) who asked“: Where are you hiding? The journalists are looking for you.” I replied I was at the LMC meeting. nice person. I was really of stimulating questions. There of surreal atmosphere—no She shouted at me“ Are you impressed by him, not only I had some presentiment, for one mentioned the morning’s craaaaazy? You are going to for his scienti c stature but the rst time, of the impact events; no special celebration; the LMC meeting the day of also for his human qualities. our discovery would have on we did not congratulate each the Higgs discovery, when the He congratulated ATLAS on people’s minds. We nished at other. Nothing. Business as press from all over the world the great achievement. I gave 1 p.m. Then I went to the LHC usual, back to normal life. is on site?” I replied“, Paola, credit to him, and he gave Machine Committee meeting Murayama: Really? That’s we discovered a new particle, credit to the experiments. (LMC), which takes place amazing. that’s fantastic, but now let’s Murayama: That’s fantastic. every Wednesday afternoon. Gianotti: Steve Myers move on.” Gianotti: An unforgettable The LMC is a meeting where started the meeting as Murayama: Back to business. moment. the accelerator experts— every Wednesday: minutes Gianotti: After the LMC Murayama: A word on including the operation, of previous meeting, action I went home to prepare François Englert? and infrastructure teams— items, etc. The only allusion to my luggage for the trip to Gianotti: I had met and representatives from the the discovery was on the rst Melbourne. I failed to forget François Englert before. experiments get together slide of the status report given that it was winter in the He has a completely to review achievements and by Mike Lamont, the head southern hemisphere... different personality, very problems of the previous week of the LHC operation team. Murayama: No champagne sparkling.“.. amboyant” you and to plan for the following The title was“ Report from that day? would say in French. week. That Wednesday, July the Higgs factory operation” Gianotti: There was a little Murayama: Then you moved 4th, was no exception, and I instead of the usual“ Report champagne party in building to the press conference. attended the LMC meeting as from the LHC operation.” 40, but it was during the press every Wednesday. British humour.....That was it. conference. Murayama: Wow. Business as Murayama: That’s a nice Murayama: So you missed it. Returned to Business as Usual Right after the Press usual! touch, though. Gianotti: I missed it. I was told Conference Gianotti: Business as usual Gianotti: It was. At some that it was a nice moment, Gianotti: The press conference —and that meeting was point during the LMC and an informal one. People was very interesting with a lot something special, with a kind meeting I realized that I had had gathered together

16 Kavli IPMU News No. 24 December 2013 spontaneously. Murayama: Now that you have discovered the Higgs boson, and you stepped down as the spokesperson, what’s next for you? Gianotti: After stepping down as spokesperson, and completing some tails of my previous job, I have been contributing (as main editor) to the ATLAS article describing improvement in theory. some work. As you know particles (including the new the measurements of the Gianotti: Now I am here P5 (Particle Physics Program “entry,” the Higgs boson) will Higgs boson couplings. It was in Japan for a completely Prioritization Panel) is a improve signi cantly. submitted for publication on different reason. I am committee set up by the US Murayama: Good, I am sure 4th July 2013 (exactly one involved in a review of the Department of Energy (DOE) you will enjoy that. year after the announcement Japanese participation in to propose the roadmap for of the discovery!), together the LHC upgrade—both US high energy physics for Studied Humanities in with the“ twin” paper on the the accelerator and ATLAS. the 10-20 years to come. High School and Piano in Parallel determination of the Higgs Japan has made very strong It’s a very interesting and boson spin. contributions to the LHC, stimulating panel, covering Murayama: Now back a little Murayama: They are beautiful from construction of high- the full spectrum of topics bit to your own story. You papers. tech detector and accelerator and facilities in our discipline, actually majored in music Gianotti: The work on the components to physics including cosmic surveys, right? You got a degree at the Higgs boson paper was a analyses (including Higgs neutrino physics, underground conservatory. lot of fun. I had the chance boson searches in the Higgs experiments looking for dark Gianotti: I got a 10-year to work with many young → γγ channel). Giving lectures, matter, colliders, etc. This is piano degree, but in parallel people and to dig into the mostly in the US, has been making my life a bit busy at I have also been studying details of the analysis. By the another intense activity the moment, but I plan to humanities at high school, so way, Hitoshi, in several cases over the past months. I like ramp up my ATLAS activity Latin, ancient Greek, literature, Interview the experimental uncertainties teaching very much, but I again soon, to prepare for the history of art, philosophy... and on these measurements are had to neglect it while I was second LHC run. Indeed, in very little math and physics. becoming comparable to the Spokesperson. 2015 the LHC energy will be One good thing of the theoretical uncertainties. This Murayama: You are also raised by a factor larger than calls for some additional work involved in P5 in the US. 1.5,3 so that the potential for 3 The ongoing LHC upgrade is to increase the energy of each proton from theorists... Gianotti: Yes, and this both discovering new physics beam from 4 TeV to 6.5 TeV (center- Murayama: I know. The is another commitment and performing precise of-mass energy from 8 TeV to 13 TeV). It is expected to be completed data are calling for lots of requiring traveling and quite measurements of the known by early 2015.

17 Italian education system is motivation. physics. But I was very much questions one by one through that no matter what you Murayama: You wanted to impressed by the explanation experiments, observations, study in high school, you have know more. provided by Einstein of this and measurements. So I access to the full spectrum of Gianotti: Yes. Then, when phenomenon: he understood decided to study physics. I disciplines at the University I was 16 or 17, I read a that electrons are emitted was of course not sure that level. So even if you have beautiful biography of Marie from a metal only when the this would be my... studied humanities, you Curie. I was stunned. I was sample is hit by light of the Murayama: Lifetime passion? can move to science. This is particularly impressed by her right wavelength (hence Gianotti: Yes. But the very good, because at the “domestic” way of doing photons with quantized hesitation didn’t last long...as beginning of high school, research. Her small and energy equal or larger than soon as I started to study when you are 13 years old rudimental laboratory was a the electrons’ binding energy mathematics, mechanics, or so, you don’t really know room in her house, close to in the material). I found this thermodynamics, and later what you want to do in life. the kitchen, and she could explanation so obvious, so on quantum mechanics And the years between say check the radioactive samples compelling, so elegant, and so and quantum eld theory, I 13 and 18 are crucial for while she was preparing the simple...that I said to myself, understood that was really my kids to mature. So it’s very soup for dinner. I found this “Physics is what I want to way. important to have exibility simple and familiar way of do!” in the education system, doing science very attractive. Murayama: You were not What Next for Particle and not to be forced to take Of course, what I ended up puzzled by this wave-particle Physics? nal decisions about your doing is completely different...I duality? Murayama: Great! Now professional life when you are could not move ATLAS to my Gianotti: Not much at that looking further into the not even a teenager. kitchen! time because I was not really future, what’s next for particle Murayama: What made you Murayama: And you can’t exposed to it. I am more physics? do that switch? have a kitchen right next to it. puzzled now...but we know Gianotti: It’s really amazing Gianotti: Many reasons. First Gianotti: Well, actually we that quantum mechanics can that this question comes from of all, I have always been a do have a small kitchen at be very little intuitive. you. You are a theoretical very curious kid, asking all the ATLAS experimental site. Murayama: Anyways, that physicist, so you should guide kinds of questions. Why don’t But that’s not what I meant. really sank into your mind. us experimentalists! Seriously, stars fall from their height? Another event that pushed Gianotti: The three elements I think there are three main Why do they stick to the me into physics occurred in I mentioned were very results from the rst LHC run. sky? At that time there was my last year of high school, instrumental to bring me into First, we have consolidated the no Web, so I could not nd when our professor of physics physics. I liked philosophy Standard Model with a huge information easily and quickly. talked about the photoelectric as well, because it also tries amount of measurements I used to ask adults and often effect. Of course, we didn’t to identify and address in a new energy regime. It replies were unsatisfactory. So have enough mathematical the big questions. But, I works beautifully. Second, we I wanted to nd the answers grounds to understand had the impression that have completed the Standard myself, or at least contribute quantum mechanics and physics is more direct, as it Model with the discovery of to nding them. That was one the details of the underlying really strives to answer the a Higgs boson. One of the

18 Kavli IPMU News No. 24 December 2013 ngerprints of a Higgs boson spectrum. are not able to formulate can only be provided by an is that it is a scalar particle, Gianotti: Exactly. Or very quantum theory of gravity, e+e- accelerator, like the ILC. i.e., it has zero spin. All our exotic signatures. Obviously, and therefore to reconcile Also, only an e+e- collider observations are in very we have already scrutinized gravity with the three other allows measurements of the good agreement with this our data extensively and forces. For these and other absolute Higgs couplings hypothesis. We don’t know looked at as many topologies reasons, we know the to be made in a model- yet if the new particle is THE as we could. And the most Standard Model is not a independent way. Higgs boson of the minimal obvious scenarios have been complete theory and there Another crucial study in the Standard Model or an object ruled out. But we cannot must be new physics. The years to come, an essential belonging to a more complex completely exclude that question is“: Where is this new “closure test” of the Standard theory. It looks very much new physics is hiding in physics?” Is it at an energy Model, is related to WW like the Standard Model some dif cult corners of the scale accessible to the LHC scattering at high mass... Higgs boson, but the present parameter space. For sure or to a future higher energy Murayama: Demonstrating measurements by ATLAS and operation at 13 TeV will collider? Or is this scale far unitarity of scattering. CMS are affected by large be extremely bene cial for too high to be explored by Gianotti: Does the Higgs uncertainties (at the level of searches (and not only for any conceivable accelerator boson x the bad behavior of typically 20%). Anyway, all searches). built by mankind? the Standard Model for large particles predicted by the What can we expect to In any case, it’s very nice masses of the WW system? Standard Model have now see? Well, we know that the that we now have a new Or is there a new dynamics been observed experimentally. Standard Model is not able to particle, a Higgs boson, coming into play? This is a The third important result address in a satisfactory way which requires detailed very interesting territory to from the rst LHC run is all questions in fundamental studies and measurements. study, which again calls for that we have no evidence so physics. We don’t know the It might be a door into new full LHC energy because... far for physics beyond the composition of dark matter physics, as the latter could Murayama: The cross section Standard Model. It doesn’t and what is the origin of the modify some properties of is so low. mean that new physics does matter-antimatter asymmetry this particle (production and Gianotti: Right. So, interesting not exist. It may well be in the universe. Dark energy is decays modes, strength of the times ahead. accessible at the LHC in 2015 an even bigger question, for interactions with the other Murayama: Let’s hope for the or later, when running at which we have no clue. Is the particles, etc.). For instance, best. 13 TeV. It may even be that accelerated expansion of the the LHC can reach an ultimate Gianotti: Yes, let’s hope for Interview new physics is in our present universe due to a modi cation precision on the measurement the best, Kanpai to new data and we haven’t nd it of gravity or to an unknown of the Higgs boson couplings physics! yet because it manifests itself form of energy? Actually the at the level of 2-5% (based Murayama: That is right, in a less obvious way than Higgs eld exacerbates the on some assumptions). This thank you Fabiola. expected, hence requiring problem. would allow some scenarios Gianotti: Many thanks to you, more work and more time to Murayama: It’s part of dark of new physics to be excluded. Hitoshi. be identi ed. energy. To do better, a precision of a Murayama: Like a degenerate Gianotti: Moreover, we few permil is needed, which

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