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Interview of Fabiola Gianotti by David Zierler on February 15, March 29, May 12, 2021,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
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In this interview, Fabiola Gianotti, Director-General of CERN, reflects on being the first woman in this position and the multi-layered challenges of maintaining operations at CERN during the pandemic. She recounts her upbringing in Milan and the scientific influence of her father, who was a geologist. Gianotti describes her education at the University of Milan and her formative interactions with Carlo Rubbia at CERN. She describes her work on the LEP and ADELPH collaborations and how the cancellation of the SSC affected CERN. Gianotti narrates the origins of the LHC and parallel concentration on supersymmetry and she describes the ATLAS and CMS teams and her advisory work for P5 in the United States. She discusses her election and responsibilities as Spokesperson of ATLAS and she describes the careful process of detecting and analyzing the signals that confirmed the Higgs. Gianotti describes the unique opportunity to engage a global audience given the magnitude and interest in the discovery, and she explains LHC’s planning, post-Higgs, for new physics. She describes the shutdown period that started in 2013 and the circumstances to her being named Director-General in 2013. Gianotti surveys what has, and has not, been detected at the LHC over the past decade, and how dark matter searches at CERN are complementary to those using Xenon detectors. She conveys optimism about the high luminosity upgrade at the LHC and how she frequently operates in political realms given the international nature of CERN. At the end of the interview, Gianotti observes that current projects at the CERN are reminiscent of the buildup to the LHC, and why this bodes well for the future of experimental particle physics.
OK, this is David Zierler, oral historian for the American Institute of Physics. It is February 15th, 2021. It is my great honor to be here with Dr. Fabiola Gianotti. Fabiola, it’s great to see you. Thank you for joining me.
My pleasure, thank you.
All right, so to start, would you please tell me your current title and institutional affiliation?
I’m currently director-general of CERN, the European laboratory for particle physics, and I am a particle physicist.
When were you named director-general?
I was appointed for a first term of office in November 2014, with the term of office starting on 1st January 2016 and until the end of 2020. And then at the end of 2019, I was appointed for a second term of office starting on 1st January 2021 for another five years.
Fabiola, when you were named to this position of leadership as the first woman director-general of CERN, in what ways was this important for you personally, and in what ways do you think it was important for the field?
So, for me personally, it was not important at all, as I believe that the selection criteria for the director-general are gender-neutral. So, I think that the CERN council chooses the director-general on the basis of the scientific accomplishments, competence, scientific vision, the capability of leading a complex organization like CERN, and the capability also of establishing and maintaining relations with a large number of stakeholders from the member states to the public, etc. Now, how important is for the field the fact the CERN director-general is a woman? I think that having a woman in this position gives a very good message to the many girls and young women who would like to undertake a professional life in science, and sometime hesitate because they’re not sure to have the same opportunities as their male colleagues. So, I think it can be an encouragement for the younger generation of potential women scientists.
Fabiola, before we go back to the beginning and develop your personal narrative, I’d like to ask a very present and in-the-moment question. Of course, for you, we can have a whole discussion on the logistical challenges in normal times for what it means to be director-general for CERN. But over these past 10 months, I’d like you to reflect on what have been some of the most profound difficulties of keeping CERN going with its research agenda during this time of the pandemic, and in what ways do things like Zoom and remote data analysts and theoretical physics generally have made CERN well-prepared for the emergency that we currently find ourselves in?
Yes, it’s a very good question. So, first of all, the challenges have to do with the fact that CERN is a very complex organization.
In the pre-COVID period, every day we had something like 9,000 people on our site, including staff (these are CERN employees), contractors’ personnel, and users from all over the world. This is the first thing. The second thing is that a large part of CERN’s work requires on site presence, so the work that has to do with our technical and scientific installations, accelerators, laboratories, workshops, as well as the development, construction and assembly of accelerator and detector components. So, it was clear that whereas part of the CERN scientific population could continue to work from home, actually very effectively, because, for instance, the data analysis and the production of physics results have continued at a very intense pace during the past 16 months, other activities that require the personnel to be on site were subject to some restrictions.
We had a period of “safe mode”, meaning that we only admitted on site the people who were necessary for the maintenance and the safety of the installations, about 300 people in total, and that period was in March – April 2020, when most of Europe was in lockdown.
But then already in May 2020, we started to bring back our personnel, starting from those whose work can only be done on site. And at the end of the summer, we were again back to something like 5,000 people on site daily. But then the second wave hit Europe, and we had to reduce our population again and now, Summer 2021, we are at the level of 4,500 people. So, all this to say that it it was a very difficult and very challenging period, as for everyone on the planet of course.
CERN did very well, I must say, because we were able to introduce very effective COVID-19 specific health measures in a very timely way, and those measures have been, at any moment in time, well-tuned and adapted to the situation and the risk. There was no point in locking CERN down while the rest of the world was still active or, on the contrary, to open CERN when the rest of the world was in a difficult situation. So, I think that this, coupled with the scrupulous compliance of the personnel to the rules, had, as a result, that, a) we have no evidence of any spread of the infection on site. Several members of personnel have been infected, but they got COVID outside. And b) that most of our work — we are at the moment in a shutdown period for technical maintenance and upgrade—most of the shutdown work was minimally delayed, more or less by the same period as the duration of the safe mode, so, two-three months. Unavoidably, due to the pandemic we are a bit late but I think we managed to contain the impact of COVID on our scientific activities. And, at the moment, we are restarting the accelerator complex link-by-link after a two-and-half-year shutdown.
Fabiola, of course, science is a fundamentally human endeavor, and so much of collaboration happens informally, over coffee, in the hallway at a conference. There’s so much important about the value of interpersonal and in-person communication in science, and so, with that in mind, what, if anything, has been lost at CERN that otherwise may have happened over the past 10 months?
Well, I think what you said, the human touch and the human interaction. CERN is really a place where people get together. We use to say that our best ideas develop in the CERN cafeteria, a fantastic place where Nobel Prize winners meet with students, and a place very conducive to ideas, new initiatives, etc. So, that of course was lost. And, fortunately, the tools we all have, from videoconferencing systems to massive computing infrastructure, allowed the interactions and the work to continue. What is called “business continuity” was ensured in the technical and administrative departments as well as in the scientific community.
People tried to compensate for the lack of human relations with zillions of videoconference meetings, but it’s not the same thing. It’s also very tiring and can be a bit alienating. But one thing we did was to allow access to site to the people living here in the region who were particularly suffering from the lockdown.
In particular the young people, students and post-doc, who are far away from their families, very often live in very small flats, and so they really need to be on site to interact with people. But in general during the peak of the pandemic we have missed our human exchanges. It is so crucial and so important for CERN and for CERN activities to re-establish them. But I’m an optimist, so I hope that we can get back to this kind of exchanges very soon, in a few months.
On that point, the big question on everyone’s mind now is with a hopeful eye toward a post-COVID world as vaccinations ramp up, I’m curious for you and your vision at CERN, what are some aspects of remote work that might remain for CERN even after the pandemic is over?
Clearly, we have to learn from the pandemic. It would really be a total waste not to learn from this dramatic experience, in particular to revisit the way we work. Of course, the extremes are always bad. I think we should not say, OK, let’s continue in telework full-time. That doesn’t work, we know very well.
On the other hand, there are perhaps activities that can be handled remotely. We used to travel a lot, we as humanity in general but also in our field. Of course, we are scientists, so we attend conferences, meetings, and traveling is a way of meeting people. But we have perhaps to rethink a little bit about this model, and, again, not banning travel completely but perhaps be more moderate, try to make better use of the technology, and be also a little bit more flexible in the way we organize the workplace procedures and practices. At CERN, for instance, we have a telework policy, but it can be extended.
So, I think we have to learn from the pandemic to evolve the society to a new normality, to a new normal, which is better than the previous normal. Going just back to what we were before, in my opinion is not an option.
Well, Fabiola, let’s go all the way back to the beginning, to happier times perhaps. Let’s start first with your parents. Tell me a little bit about them and where they’re from.
My father is from Northern Italy, from Piemonte, which is a northwest region; my mother from south, from Sicily. Unfortunately, they both passed away recently, fortunately not of COVID. My father was a geologist. My mother studied literature and music. So, my father passed on to me and my brother his love for nature, for, you know, understanding how things work, and he was really a great lover of nature. And I remember very, very long hikes out in the mountains when we were kids, my dad would stop at every single flower or rock or insect to explain us what kind of flower, rock or insect we were seeing.
My mother was a very warm person, and what she gave me, well, she gave me many, many things. But perhaps the one thing I am most grateful for is the passion for music, and the fact that she forced me when I was 7, 8 years old to start to study the piano which, at the time, I hated. I could not really stand it.
because I had to subtract 20 minutes every day from playing with my friends to practice. So, for me, it was a drama, those 20 minutes of practicing every day. But, of course, now I am really grateful to my mom for that because not only she gave me an interest that I have been cultivating all along my life, but also because music taught me a lot also for what I am today as a physicist.
Indeed there are many strong links between science and the arts, and between music and physics in particular. The rigor, the discipline, the creativity and the curiosity that you have to develop when you play, when you do music, these are the same things that I found later on in physics. Well, so these were my parents. Of course, the reason why I’m most grateful to them is because they taught me and my brother good values, they were examples of integrity, humility and generosity, not only to the family but also to people in general. Very honest, very transparent, very fair. I had great parents.
Being from two extreme ends of Italy, where did your parents meet?
My father was a geologist, and used to work for some US oil companies, and his task was to find oilfields. He had concluded that there must be oil south of Sicily in the so-called Canale Sicilia. It’s the sea strip between Sicily and North Africa, and he thought there was oil there, and so he went to southern Sicily to start to dig. And actually they found the oil, and that field has been for many decades one of the main sources of oil for Italy. My mom lived in Sicily and they met through a common friend.
Growing up, given how culturally different Sicily is from Northern Italy, what were some of those differences that you were exposed to either in terms of food or religion or even language?
So, one thing I remember is that my dad was used to have lunch at noon. My mom would start thinking of what she could possibly prepare for lunch at noon.
So, you see, that required a little bit of [laugh] convergence between them—they had two different cultures. I don’t think it was just due to their different geographical origin; they were two very different people. My father was a very quiet person, very serene, and my mom was, you know, very dynamic and—how to say—a lot of fantasy, a lot of initiatives. But, all in all, they compensated each other very, very well.
As a geologist, would your father involve you in his work? In other words, did you have a good sense of what it meant to be a scientist, even as a young girl?
Yes, I did. Actually, initially I wanted to become a geologist. I shifted to physics later on. I remember once my father took me and my brother up to the Etna, a volcano in Sicily, to have a look at one of the craters. For me, it was a shock, you know, it was like seeing hell, all the flames and dust and smoke coming out.
I was 10 years old, and I was scared to see something that looked to me like the end of the world. At the same time, I was so fascinated to see what happens deeply inside the Earth. And so he really conveyed to me the passion for science, the passion for observing and learning.
One thing that I like also today in my job is learning. I feel satisfied, it gives me a real sense of joy when I learn something new in my job or in other fields, not just in science. Now, in my current job, I’m exposed not only to science but to many other aspects and challenges, from administration to budget, relations with various stakeholders, and many different things. And every day when I go home in the evening, I tell myself, gee, how much did I learn today. And for me, that’s the thing I value mostly, and I think it comes from my father.
Fabiola, where did you grow up? Where did you spend most of your childhood?
Milano, yes. I was born in Rome because my father’s office was originally there. And then when I was 6-7 years old, the family moved to Milano because my father’s work shifted to Milano. So I grew up there. I did most of the school there, from elementary to middle school, high school, and university up to and including my PhD. And then I applied for a fellowship at CERN, and I came here originally for two years, which was the duration of the fellowship, but I’ve been here ever since.
[laugh] What kind of schools did you go to as a girl?
So, the elementary and middle schools are the same for everybody in Italy. Then for high school, I went to a humanity school, so a school where you learn everything except physics and math, so history, philosophy, Latin, ancient Greek, literature, art, history of art, all these things; but very little math and very little physics. At the time, it was considered to be the best school in terms of giving children a broad, all-encompassing culture.
I must say that I consider those five years at high school the foundations—together with my music studies at the conservatory— of what I am today, even if I did study very little physics at that time. But, you know, that school gave me the tools, the intellectual tools. And later, I could apply them to another field, physics. Once you have the tools, then it’s a matter of just using them.
I think this applies also to today’s society. We live in a world where, due to the fast development of technology, also the skills required by the job market evolve very quickly. And we are in a kind of paradoxical situation because, on the one hand, the job market today requires very specific knowledge. And so one would be tempted to give the young generation those kind of narrow, very specific and very pushed skills.
On the other hand, because of the evolution of the job market and the technologies, God only knows what society will need in 30 years from now, and most likely a large fraction of the current jobs will not exist. So, the best education we can give to the young generation is to provide them with the tools, including an open mind and a critical spirit, as these are perennial skills that survive through the change of society.
So, it’s fair to say as a teenager, you had very little idea of all the amazing things that were happening at CERN in the 1970s-1980s?
I didn’t know anything about CERN and physics, nothing. But many things happened in my life later on. One was that despite the little physics that we were taught at the humanity school I attended, which is called Liceo Classico in Italian, just a couple of hours of physics classes per week, I had a very good teacher who managed to generate passion, in me at least, by explaining us things that are very, very complicated because they require knowledge of quantum mechanics which, of course, at the time I didn’t know at all. But he was able to explain physics in a very simple and appealing way, and that was my first attraction into physics.
The other thing that pulled me into physics was that I was a very curious child. I would ask myself, my parents and the teachers all kinds of questions. But, of course, at the time, the web did not exist because the web was developed at CERN [laugh] later. And most of the times the answers I received were not satisfactory. So I wanted to understand how things work and contribute, in my little corner, to push backward the limits of knowledge. The wish to understand how the universe works became, with time, an increasingly stronger push toward science. And this desire to understand how things work at the most fundamental level brought me into particle physics, which is the most fundamental of all science because it studies the elementary constituents of matter and of the universe.
Fabiola, a cultural question from your childhood, between your early interests in geology, and then thinking about science in undergraduate, of course, you received support from your parents, but I’m curious if as a girl and as a young woman if you were ever made to feel at any point that science was not appropriate for you, that there were other fields that you should pursue?
Never. I must say I was lucky enough to live in an environment at home, where nobody ever told me that science was not a job for women; nor at school. So, I never heard arguments like, “That is not good for you, for your future”—not at all. My parents gave me their advice when they were asked; sometime also when they were not asked. But they have always been telling me, “You do what you like and what you think is good for you.”
What were the schools that you were considering for college? Did you ever think about going farther away from home?
I studied six months at ETH in Zurich during an exchange of students before starting at college. And then I came back to Milano where actually, in the meantime, I had decided to study physics. You know, the University in Milano was very good. In general, Italy has a very strong tradition in particle physics, which dates back to Enrico Fermi and many other great scientists of the last century. So, that school of excellence has been transmitted and propagated over the years. And still today, Italy trains some of the best physics students and young scientists in the world. For this reason, I decided to stay in Milan.
Fabiola, last question for today, given that you were not necessarily on a physics track when you started college, what was it for you? How did you catch the bug, as we say? Was it a professor? Was it a field? What got you so interested from the beginning?
You mean at the beginning when I started college if I had any difficulties because I was coming from a non-scientific school?
No, not difficulties, but because your plan was not originally to study physics—
—usually those things are—those things often develop in high school. But for you, it sounds like they really came in college, and my question is what was it? Was it a—?
No, it came in high school.
Oh, it did?
In high school already. In the Italian system, you have five years of high school, which ends with a baccalauréat when you are 18. And then you go to university, what you call college. So, when you go to college or university, you have to choose what you want to do, so I decided to study physics and I had already chosen to do physics while I was in high school. Of course, it was a totally—how to say—I had no—
Right, I had no reason whatsoever to believe that I would love physics because I had a very superficial idea about what physics was from my two hours a week of classes—
But I loved the fundamental questions and I wanted to do something in science. I had the impression that physics would satisfy me. But until I started at college, I had no certainty. It was a jump—I don’t want to say a jump into the dark, but almost. I was not 100% sure I would love it.
In retrospect—I never regretted it. Going back to what I said before, I love learning. So, sometime I tell myself that —if I had chosen to do something else, you know, history, which I also love, law or something else, at the end, I would’ve loved it because I like learning. But, I was so happy with my physics studies in college. I really realized after just a few months that I’d found my way.
And did you live at home or did you live on campus?
No, at home. There was no campus, and people coming from outside Milano would find a flat in university’s hostels or homes for students in the area of the university, but there was no real campus. And so I was at home until I left to Geneva with my fellowship.
Who were some of the most important professors as an undergraduate in physics?
Oh, many, many, many—I can mention a few names, like Amaldi, Fiorini, Mandelli, Di Lella and many others. In general, I was never disappointed. I found every single exam, every single class, every single course interesting.
And already in the first two years I was very much attracted by quantum mechanics—so studying the very, very small and I had already chosen to follow that kind of path. And there I had very, very good professors. So, that also had an impact.
When did you get the sense that to pursue an academic career in physics, there was a binary in the field, and that you would ultimately have to choose to focus on either experimentation or theory?
I think it was during my second or third year at the university. As I mentioned, I was very much attracted by quantum mechanics and particle physics because of their fundamental nature. I always preferred to understand the fundamental constituents rather than more complex systems that emerge from them.
Now, between theory and experiments, what happened in the meantime is that Carlo Rubbia, who was a CERN scientist, was awarded the Nobel Prize in physics for the discovery of the W and Z bosons at CERN. And that for me was fantastic, I read everything about Carlo Rubbia’s experiment, and I said to myself, yeah, yeah, yeah, I want to be an experimentalist.
Also because, I like to do things with my hands, since I was a child. I like cooking, I like playing the piano, I like fixing things at home. I really like doing things with my hands. So, I think these two factors together pushed me to become an experimentalist.
When did you first get to meet Carlo?
[laugh] When I was on my third year at the university, and we organized a trip to CERN, my first trip to CERN. And a friend of one of my classmates at the university worked with Carlo, and so she organized a visit to Rubbia’s experiment, whose name was UA1, which stands for Underground Area 1, at CERN. So she took us to the experiment, and it was a fantastic visit, of course. And then we came back to the main building, and she asked whether we wanted to meet Carlo. We said, “Of course”—
—and we were completely in awe and—
Yes, exactly, and we met Carlo, who looked to me … very big, very—how to say? When you are in a room, and Carlo is there, you only see Carlo.
Have you met him?
I know of him. I’ve heard so many stories of Carlo. Fabiola, now, last question because I know we have to wrap up for today—
—your first impression at CERN, did you have a sense right then and there that this would be your long-term academic home?
No, I don’t think so. My first impression was … the smell of the corridors, the smell of plastic because the floor of the corridors had a kind of plastic coverage, I think part of it is still there. I mean, still today, there are some corridors at CERN where it smells the same.
— and sometimes I go there on purpose because I want to [laugh] remember what I felt when I first came—and then the other thing is that when you come to CERN the first time, it’s a kind of labyrinth because all corridors … have you been at CERN?
All corridors look the same, and I remember the first day I got lost because I was trying to go from the main building to the hostel building where I had a bedroom and I got lost. I could not find my way. So, that was my first impression.
For a few years—I’ve been working at CERN being affiliated with the University of Milano, so I would be based in Milano, and I would go to CERN for meetings, data-taking, and other occasions —but not on a permanent basis, until I got my fellowship. Until then, I was not so sure that I would like to be at CERN permanently because I was quite happy with my life in Milano where I had family, friends, music, etc., and also the possibility of going to CERN whenever I wanted for meetings or other events.
So, when I got the fellowship, for which I had applied just because I was encouraged to apply, it was not really my spontaneous choice, I was not sure that I would go. And then I decided to go and try. And after a couple of weeks at CERN, I thought that I wanted to stay there, here, for the rest of my life.
That’s a great place to pick up for next time.
[End of first session.]
[Start of second session.]
OK, this is David Zierler, oral historian for the American Institute of Physics. It is March 29th, 2021. I’m delighted to be back with Dr. Fabiola Gianotti. Fabiola, nice to see you again.
Nice to see you, David.
We picked up from last time where you were talking about meeting Carlo Rubbia, and you were going back and forth between your position in Milano and CERN, and then something changed for you. And we left off where you said, “And then I decided that I wanted to stay at CERN for the rest of my life.” So, first for the chronology, what year are we talking about when you made that commitment to be at CERN full-time?
So, this was 1993—when I applied for what we call a CERN fellowship. This is a two-year postdoctoral position and people who get a fellowship become employed members of CERN. So, I applied for this fellowship, not out of my spontaneous—how to say?—initiative, but because a couple of senior colleagues with whom I was working at the time advised me to do so in order to get out of my group in Milano, my “family environment” professionally speaking, the people with whom I grew up, to have an experience outside my professional home and to walk with my own legs.
So, I applied for a fellowship and I got it. And then I came to CERN on 2nd May, 1994, and that’s when I moved here on a permanent basis for two years. But after those two years, I was expecting to go back to Milano because after a fellowship, the next possibility at CERN is to get a staff position, a limited duration contract. But it’s a very selective, very competitive position.
And after that, even more selective and even more competitive is to get an indefinite contract in the research sector. I knew after a few weeks I was at CERN on a permanent basis that I would like to stay here forever. But, of course, with a lot of question marks, especially for the indefinite contract position because at that time, if you failed, if you’re not selected, you could not apply again. It’s a one-go, a one-off thing. So, that’s how it all happened.
Fabiola, what were some of the big things that were happening at CERN in 1994?
So, there were two important things at the time. The main highlights were the operation of the previous collider, the predecessor of the LHC; it was called LEP, which stands for Large Electron-Positron Collider. It was an electron-positron machine, as the name says, and had started operation a few years before.
LEP had four experiments, called ALEPH, DELPHI, L3, and OPAL, and I was not involved in any of them at the time. Later on I joined ALEPH. And the other highlight, in which I was involved, was the beginning of the work for the Large Hadron Collider, both on the accelerator side and on the experiment side. So, what we were doing at the time was R&D, research and development, on new technologies for this new accelerator and the detectors. The LHC presented very serious challenges for the experiments due to the intensity of the colliding beams. So, completely new concepts had to be developed from the detector viewpoint, new technologies, and the challenges looked unsurmountable at first face.
And that was a fantastic time because, yeah, it was a time of creativity, you know, scratching our heads to understand how we were going to do with the harsh environment like the one that the Large Hadron Collider would present to the experiments. So, that was really a nice time.
To zoom out a little bit, Fabiola, of course, in 1994, this is the official cancellation of the SSC in the United States. How did that affect the feelings at CERN, especially given in the high energy physics community in the United States, people increasingly realized that the only new physics that was going to be done at higher energies was going to be at CERN? So, from your perspective, did that change things at all?
Yes, it did because, first of all, it put the LHC on more solid ground in that the competition from the SSC vanished with the cancellation of the project. Furthermore, we saw a strong immigration of US scientists, some of whom I had worked with previously, coming to CERN to join the LHC experiments. And that made quite a significant difference for us in terms of intellectual contribution, technological contribution, partnerships. Of course, the cancellation of the SSC was not good for physics, but in that difficult and sad circumstances, the fact that many US scientists could join the LHC experiments was great news. It gave a significant boost to the LHC program.
A more technical question is that the SSC was conceived to operate at higher energies than even the LHC.
Did that change at all the way that the LHC was conceptualized? Was there additional pressure for the LHC to be operating at higher energies as a result of the fact that the SSC never would?
No, because we were constrained by the existing tunnel. It was clear that the next machine, the LHC, would be installed in the pre-existing tunnel, a 27-kilometer ring, which had been built for LEP. And so, given that the circumference of the tunnel was fixed, the energy was dictated by the available technology for the superconducting magnets. And the technology we were developing at the time, niobium titanium, allowed us to reach something like eight-nine tesla in terms of magnetic field, and so a center of mass energy of 14 TeV, not more than that.
The LHC beams were expected to be more intense than the SSC beams, so the luminosity was larger. Of course, energy counts a lot. But there was no way we could reach the SSC energies, unless we had decided to dig a new, bigger tunnel, which of course would have costed a lot.
Fabiola, was the search for the Higgs always the most important project?
It was one of the leading motivations for the LHC, of course, together with the search for new physics, physics beyond the Standard Model, in order to address the open questions. So the Higgs boson was one of the main drivers but not the only one, and there were many other important goals.
Another important point was that Higgs boson production and decays were, from the experimental point of view, among the most difficult processes to detect, and so searches for the Higgs boson were useful benchmarks for us when we were designing the experiments and developing the necessary technologies.
The reason is that the Higgs boson signal is relatively weak, and the backgrounds are quite large, and that posed a lot of challenges in terms of detector performance. But, at the end, we were able to find it, and much faster than expected. So, this shows how good these detectors are, and how well they have been performing right from the beginning.
What about supersymmetry? To what extent were you focused on supersymmetry?
Supersymmetry was another benchmark process. We hoped that we would discover supersymmetry, for various reasons. First of all, it’s a beautiful theory. Second, it would allow us to answer some of the open questions in one shot, from dark matter to the problem of the Higgs mass stabilization (which is called naturalness or hierarchy problem in physics). Another nice feature is that supersymmetry predicts not just one but a full spectrum of new particles, many, so that would entail plenties of discoveries, and plenties of new things to measure.
But supersymmetry didn’t show up, so the world is not supersymmetric at the energies that we have explored so far. But nobody prevents supersymmetry from being a correct theory at higher energy scales. For instance, string theories are supersymmetric, so supersymmetry may exist at some very high energy.
As the Higgs boson, Supersymmetry was also used as a benchmark for the LHC detector design and development because it predicted a huge variety of topologies and a very rich phenomenology, with many new particles and different final states from their decays. So, these different final states were very useful for us to design the detectors.
But what is important to say is that we were not after a specific theory. We were after, and we are still after, the open questions. Nature may have chosen another answer to those questions than supersymmetry, and nature is more clever than physicists. We should not run behind a specific theory. We should try to address the questions.
Of course, theoretical models are very useful to guide the search, and they were very useful also to design the detectors and the analysis tools. And one very nice thing is that several theories that were not known or not yet developed when we were designing the experiments, and predicted quite exotic topologies, different from those we were expecting, could later on be explored pretty well by the LHC experiments. This means that the detectors we designed in the ’90s are very robust and versatile. Although they were designed primarily having some physics channels as guidance, like Higgs boson and supersymmetry searches, at the end they are so robust and flexible that they provide excellent sensitivity to many other theories.
Fabiola, in the 1990s and early 2000s, who were some of your most important collaborators, both within CERN and visiting scientists from all over the world?
Oh, I had many, many collaborators at CERN. My ATLAS colleagues primarily, but also colleagues from CMS, the competitive experiment. It was a friendly competition. I also had many colleagues in the US at the time, in the early 2000, who were not involved in the LHC. For instance, I was on the Fermilab Physics Advisory Committee, and it was a great experience to be exposed to the very rich program at Fermilab and more in general in the US.
I was also on another panel, P5. This stands for Particle Physics Program Prioritization Panel, and is a panel set up by DOE and NSF every few years to develop the roadmap for the field in the US. I was on P5 twice, and that was a great opportunity to meet many great US physicists. Giving names would be reductive because I would for sure forget some of them.
[laugh] That’s OK.
I’m sure that I would forget some of them.
[laugh] Too many.
Yeah, too many, yes.
Fabiola, when you joined CERN full-time and just to, you know, foreshadow to your present leadership, at what point in your career at CERN did you realize that you were on a trajectory of leadership?
I don’t know if I ever realized that I was on a trajectory of leadership, because of the way things work in our field, or at least the way I perceived them to happen. It was a gradual process. At some point, I was appointed physics coordinator of ATLAS. That was an important role, although the experiment was not yet taking data, but it was quite an important position in such a big collaboration and in a crucial period for the experiment. But I never considered being physics coordinator as a first step in a leadership trajectory.
I considered being physics coordinator as a role that I could play for a few years, which I did actually until 2003, and then, for me, the next step was to continue to do my research work, and leave that role to someone else. This is the regular rotation of roles in our experiments. So, for me, it was not the beginning of a longer path toward more and more important roles, which is what happened ultimately. I was seeing it like a period of time where I was called to have a leadership role in the experiment, which I enjoyed. And then after that, I would go back to continue to do what I was doing before, which I had enjoyed as well.
What were your first affiliations with the ATLAS collaboration? When did you join that?
Oh, I joined ATLAS even before the name of ATLAS existed. I started to work on detector R&D for LHC in the early ’90s. To be precise, it was May 1990, just after I completed my PhD thesis on the previous hadron collider at CERN, the SpbarpS. This was a proton-antiproton collider.
ATLAS didn’t exist yet. ATLAS became an official experiment in 1992. So I was there even before [laugh].
What were some of the theories that were so important for the way ATLAS came about?
Higgs, supersymmetry, at some point extra dimensions became fashionable. Those were the main drivers.
And when were you named spokesperson?
In July 2008, at an ATLAS collaboration meeting in Bern, it was then that I was elected , and I started my term of office on 1st March 2009.
And what were some of the—?
This coincided with the first—
What were some of your key responsibilities in this role?
You know, the spokesperson is someone who oversees the experiment in all its facets, from detector operation to the publication of the physics results, and the relations with CERN’s Management and the collaborating institutes. The period I was spokesperson coincided with the start of operation and the first run of the LHC. So, we had first collisions at low energy in November 2009 and first collisions at 7 TeV in March 2010. The first period of operation, the first results, and the publication of the first articles were new challenges for the experiment, and it was very exciting to be Spokesperson in that period.
But, pretty much as everything else at CERN, managing ATLAS was pretty much teamwork. I had two deputy spokespersons, a technical coordinator and a resources coordinator. And there were coordinators of the main activities: run and detector operation, trigger, software and computing, data preparation and physics. So those responsibilities spanned the full range of activities of the experiment.
Fabiola, I wonder if you could describe how the Higgs was discovered, from the very first moment that people started to realize that this is what the data was showing, to the certainty that compelled the collaboration to announce it publicly. What was that very first moment like?
It was not just a moment. It was a period. So, at the end of 2011, we already had some hints at the level of three sigma. In our field, we provide a quantitative estimation of the probability that what we observe is a genuine new signal and not a fluctuation of the background, and three sigma is not enough as it corresponds to a probability of 0.3% that what you observe is due to a background fluctuation. This is not enough to claim a discovery.
But, nevertheless, it was an intriguing hint around a mass of 125 GeV in the decay channels into photon pairs (gamma-gamma) and into four leptons (muons and/or electrons). At the end of 2011, the CERN director-general asked the two general-purpose experiments, ATLAS and CMS, to show the status of their searches for the Higgs boson in a big seminar at CERN. And I remember that the ATLAS results were very clean, in that if you look at the probability that what we observed in the data came from the background, that probability was large over the full mass spectrum, except for a dip in the mass region around 125 GeV, indicating a possible signal there. All the rest was compatible with coming from the background. CMS had a much less clean spectrum at the time.
Why the difference with CMS? Why was CMS less clean?
Well, it depends on the statistical fluctuations in your data. When a possible signal is at the level of just three sigma, it is still quite compatible with background fluctuations that can happen here and there in the explored mass spectrum. In the ATLAS case, the fluctuations were very limited.
And then the signal came out very clearly during the following data-taking period. At CERN we take data typically between March and November, and then we have a pause between December and February. The latter is what we call the winter technical stop, and is devoted to the annual maintenance of the accelerator and the experiments. So, the results that we had presented at the seminar in December 2011 were based on the data collected in 2011 at a center-of-mass-energy of 7 TeV. Then, in March 2012 the LHC started operation at a higher center-of-mass-energy, 8 TeV. So, the data sample that we recorded in 2012 was a completely independent data sample, at a different center-of-mass-energy.
With the new data recorded in 2012, we did what we call a blind analysis. Initially, we did not look at the 125 GeV mass region, where we had some signal hints from the previous data, but we used the so-called side bands, so regions of mass away from the region of the presumed signal, to validate the simulation and refine the analysis techniques. And only at the end, we opened the box in the region of the signal.
So, we were looking mainly at two decay modes of the Higgs boson, into gamma-gamma and into four leptons, which are experimentally the most promising decay modes in that mass region. There is another important decay, in pairs of W bosons with both W’s then decaying into a charged lepton and a neutrino, but that is a more difficult channel from the experimental viewpoint because you don’t see a clear peak like for the gamma-gamma or the four leptons channels.
So, at the beginning of June, I think it was the 11th of June, I was in the US, at Fermilab, attending a ceremony to celebrate the end of the Tevatron program. And the Higgs to gamma-gamma analysis group had decided to unblind the analysis that day. And I remember it was early morning. I was in the hotel and the convener of the Higgs to gamma-gamma working group sent me a figure of the statistical probability that the data are compatible with the background. So, it should be flat if the data are compatible with the background, and if there is a signal then there should be a dip around the mass corresponding to the new particle, indicating that the data are very little compatible with the background hypothesis in that mass region. Sorry for being a bit technical.
As spokesperson of ATLAS, would it have made sense naturally that you would be the person to announce it, or perhaps I should ask this on others, but is it possible that your announcement of it was in recognition for your excellence in this project?
No, it was just because I was the spokesperson of ATLAS. I think it’s the role of the spokesperson to announce a big discovery, and of course it was also discussed with the CERN director-general and with the spokesperson of CMS. But that morning was the beginning of the period leading to the announcement.
That figure was based on the data recorded in 2012, and it did not include the 2011 data. So it was a completely independent dataset, which showed again a clear dip around 125 GeV. And I remember that I replied to this colleague in Italian, as he was an Italian physicist, something like “Oh, my god.” And his reply was, “Indeed.”
“Indeed.” I think we both knew at that time that the Higgs boson was there. This was the 11th of June 2012. I went back to CERN after the nice ceremony at Fermilab. We were continuing to accumulate data at the fastest possible pace, and the LHC was working as a marvel, with very high efficiency. If the dip was due to a signal, then it should grow with more data, whereas if it was due to a fluctuation, then it would disappear with more data. And the signal kept growing in the gamma-gamma channel. But we had nothing in four lepton channel. So, at that point I said to myself and to the collaboration: “We should not go out with the announcement if we don’t see the signal in two different channels”.
At that point, I had already informed the director-general of CERN. And the spokesperson of CMS, Joe Incandela, had also informed the director-general of what was going on in CMS. And it was very nice because Joe and I would keep each other abreast of what was happening in our experiments. But we never disclosed to our collaborations what the other experiment had because we didn’t want that the experiments influence each other nor to create useless stress in the community.
And, of course, if you know that the other experiment has similar hints for a signal at the same mass value, the temptation to rush things out would have been large. But we have to do things properly and perform all the numerous, rigorous cross-checks needed before announcing a discovery. The signal in the gamma-gamma channel was increasing in both, ATLAS and CMS. But we didn’t have much in the four lepton channel because the expected number of signal events is small and therefore we were subject to larger statistical fluctuations. But then, all of a sudden, around the 20th of June or so, events started to pop up and in a few days we had a handful of four-lepton events in that mass region.
That was the time when we said “we got it”, and it was great. Those weeks were unbelievable. People working day and night in the building where most of the ATLAS and CMS collaborators have their offices, you could find people having pizza at 3 a.m., you know, working like mad, and not resting, not showering, ... doing nothing else than working hard, doing thousands of checks. For weeks and weeks, it was just an unbelievable period.
And at the end of June, in agreement with the director-general of CERN, we decided to announce the discovery. And by then, both experiments individually had achieved five sigma, which in our field is the threshold to claim a discover, because 5 sigma means that the probability that what we observe is due to an upward fluctuation of the background is only one in 3.5 million. “Individually” means that by combining the results of both experiments, the evidence would be even stronger than five sigma. So, that was—
Fabiola, was it important to keep this work secret until the announcement? Did you attempt not—
—to let this get out into the public?
Yes, yes. It’s very important to keep the result secret because we had to do many checks. You know, when you go public with a discovery, you must be 100% sure that it’s not a fake.
Joe and I asked our collaborations to keep the confidentiality. And I don’t know how because ATLAS and CMS are large experiments, you know, including 3,000 physicists each. But nothing went out. Everybody in the scientific community outside ATLAS and CMS knew that there would be an announcement soon, but nobody knew exactly what we had in the data.
Fabiola, did you work with the communications team in crafting the announcement, or you wrote it essentially by yourself?
No, it was organized centrally by CERN, I mean, the press release, in collaboration with the experiments. All the relations with the press were managed by CERN. So, we had a scientific seminar in the main auditorium. And then after the scientific seminar, we had a meeting of the CERN management, the two spokespersons, and several members of the experiments with the press.
The press release was drafted together by the experiments and CERN. But the scientific seminar was a classical scientific seminar prepared separately by the two experiments. So, I prepared the slides for ATLAS, which were carefully reviewed by the collaboration during a rehearsal session. This is the usual procedure in our field. And in parallel, we prepared the publication, which went out a few weeks later, together with CMS’s publication.
As you were preparing these materials to announce to the world, of course in the world of physics, you don’t have to convey what a big deal this is. And, yet, the whole world was captivated by this discovery, people that are not closely following physics. You heard about it. It was in the television reports. It was in the newspapers. It was a very big deal all over the place.
What were some of the most important things for you and your team to convey as an opportunity to engage with the public about the excitement of what experimental physics can accomplish?
So, various things. First of all, from the physics viewpoint, that it was a very important discovery because the Higgs boson is a very special particle. It’s not like any of the other 16 elementary particles we had discovered before, because it got very special features. In physics, we call them quantum numbers. Also, it does not interact with the other particles through the three forces that we know act at the microscopic level, namely the strong, the electromagnetic and the weak force, but through a new type of force named after Japanese physicist Yukawa. So, this particle is really something special, and also played a very special role in the evolution of the universe. It is also important for our own life because is related to the Brout–Englert–Higgs mechanism through which the elementary particles acquire at least part of their masses. And if the elementary constituents of atoms, the quarks and the electrons, were not massive, atoms would not exist as stable systems. They could not stick together. So, the matter of which we are all made would not exist.
This is what we wanted to convey to the public, we didn’t just discover another lepton or another quark. No. This was really something new and very, very special. So, that was the first message.
Second, that in order to discover that particle, we had to develop and deploy cutting-edge technologies in many, many fields, from superconducting magnets to fast electronics, vacuum technologies, cryogenics, etc., to the benefit of society. So that discovery was the result of the creativity, ingenuity, perseverance and determination of the particle physics community, from the theoretical physicists who predicted this particle in the early ‘60s to the physicists and engineers who built the instruments to detect it: the accelerator, the experiments and the computing infrastructure. We had to face enormous challenges. The LHC at the beginning was considered mission impossible.
Third, being able to discover the Higgs boson so quickly after…only two years from turn on was really a tribute to the work of thousands of scientists from all over the world. So many people from all over the world working together, a great example of collaboration across borders. So, it was a very nice example of what humanity can do when we put aside our differences, and focus on the common good.
I wonder if you could also convey how you described the importance of needing 3000 scientists per experiment coming from all over the world, and the fact that CERN is a collaboration from all of these different European countries. Why the need for this level of resource to discover a particle?
Well, first of all, because the deeper you want to go in the study of matter, the more energy you need. So, if you want to study human cells a tabletop microscope is enough. If you want to discover the Higgs boson, you need a 27-kilometer ring filled with technology, and the detectors and the computing infrastructure, and this is not something that a single country, not even a single region of the world, can do alone. This enormous amount of work is a huge challenge and requires the collaboration of some of the best minds in our field.
Research at high-energy accelerators requires cutting-edge technologies to address very complex problems. Let me open a parenthesis to give an example. Computing developments, including high-speed processors, large storage, etc., are today led by industry, from IBM to Oracle and many others. It’s not in the hands of fundamental research.
And, yet, these big, big players in the field of computing consider that particle physics is unique and very useful to them. Why? Because we have extremely stringent requirements and very complex problems to solve. So, we provide very useful use-cases. The problems that we need to solve, for example extracting a tiny signal like the one due to the Higgs boson from huge backgrounds that are much larger than the signal itself, required new analysis techniques, including multivariate analysis and, more recently, machine learning. We also need to store and analyse large amounts of data. So, the huge complexity of what we do requires advanced technologies and many people.
Fabiola, last question for today. As you described it, initially, LHC seemed like it was mission impossible. Did the discovery of the Higgs, in your mind, justify the creation of the LHC in and of itself? Meaning if nothing else happened at LHC, was it worth it for just the Higgs?
I think so, because it’s such a monumental discovery, and it’s not something that you can discover with other instruments. You cannot use gravitational waves or other approaches to discover the Higgs boson. The Higgs boson, either you produce it in beam-beam collisions at accelerators, or there is no other way.
It is a monumental discovery, which has implications for our understanding of the universe even beyond the Brout-Englert-Higgs mechanism itself. I don’t want to go into details. But inflation, the very fast expansion of the universe at the very beginning of its history, was triggered by a scalar field, so a field associated with a spin-zero particle. And the Higgs boson is the first elementary scalar of which we have evidence in nature. All other elementary particles we have discovered so far have either spin-1 or spin-½. Actually, one of the first mails I received after the discovery was from a famous cosmologist who told me, “Now we have the evidence for the first time that scalar fields do exist in nature. It’s an important experimental evidence in support of inflation.”
But the LHC experiments did many more things than finding the Higgs boson. They discovered some 60 new composite particles in the family of hadrons. They were able to expand our scrutiny of the Standard Model over an unprecedented energy domain and to exclude several scenarios of physics beyond the Standard Model. The impact of the LHC on our understanding of fundamental physics is absolutely phenomenal. But maybe we can discuss this next time.
For next time. OK, Fabiola. Thank you so much.
OK. [End of second session.] [Beginning of third session.]
OK, this is David Zierler, oral historian for the American Institute of Physics. It is May 12th, 2021. I am delighted to be back with Dr. Fabiola Gianotti. Fabiola, thank you so much for joining me again.
Thank you so much, David.
Fabiola, I’d like to return to an earlier exchange we had where you talked about the value of the LHC even if it was only the Higgs that was discovered. We can broaden that out a little bit because, of course, even if the Higgs wasn’t discovered, simply the construction and planning of the LHC was a boon to basic science generally in terms of the engineering, in terms of the computer and data analysis, in terms of all of the detection technology that went into the LHC. I wonder if you can comment more broadly on the value to basic science that only came about as a result of the commitment to constructing the LHC?
Yeah. Well, first of all, the scientific impact of the LHC is of great value for our understanding of fundamental physics beyond the discovery of the Higgs boson. Of course, the discovery of the Higgs boson, as we said, is really a monumental discovery, and all of the measurements of the Higgs boson that have been made since the discovery are of crucial importance. But also understanding the known phenomena with unprecedented precision in a new energy domain, and being able to exclude several scenarios of physics beyond the Standard Model, from the scientific viewpoint are of great value.
And then, as you say, there are also the unprecedented technological developments that had to be carried out to build the accelerator, the experiments, and the computing. And those developments have boosted the impact of our field on society. Examples are CERN’s technologies applications to medicine: detectors and accelerators developed in the framework of CERN’s scientific projects, in particular the LHC, find applications in medical imaging and cancer treatment. And these are just a couple of examples of advanced technological developments that were boosted by fundamental research. In general, fundamental research—not only in our field—is a driver of innovation because the goals are so ambitious that you really need to invent new instruments and new technologies, that go beyond what is known at a given moment in time.
Fabiola, I wonder if you can comment on the ways in which the duality of the relationship between CMS and ATLAS where there were elements of cooperation and competition that were so valuable in terms of how quickly and how successfully the Higgs was discovered. What were some of the lessons learned from this dual relationship that informed how LHC would function after the discovery of the Higgs?
So, in general, the relation between the two general purpose LHC experiments, as also previously in our field with the Tevatron at Fermilab or the LEP collider at CERN, has always been driven by this dual character, as you call it, of competition and cooperation. I use to call it healthy and friendly competition.
Competition is very useful first of all because it pushes us to go beyond, to try to do better and more, but it’s also very useful to produce results on a relatively short timescale because you know that the other experiment may scoop you, so you have to be fast, of course rigorous and solid, but fast. You cannot sit for months on your results as you may be tempted to do if there was no competition. So, this is one thing.
Cooperation is also crucial because results like the discovery of the Higgs boson or other important measurements or findings, by the way CERN works are jointly announced by the experiments. In particular for the Higgs boson, the announcement had been prepared ahead of time by the CERN management with the spokespersons of the experiments. Finally, and perhaps most importantly, the experiments use to work together and combine their data to increase the reach of their results. Historically, this is part of the culture of our field.
So, collaboration is really the foundation of what we do, and on top of this there is some competition that helps us to deliver in a timely way and to do things in the best possible way in order to be “the best experiment” [laugh].
Fabiola, after the initial rush faded a little bit between the discovery and the announcement, and it was time to think about what next, simply by virtue of the Higgs being discovered where it was, what new questions are now allowed to be asked that were not possible before, both theoretically and experimentally, in terms of the future of the LHC?
After the discovery of the Higgs boson, the first things to ascertain were the features of this new particle, namely its quantum numbers and the way it couples to the other particles, and to try to understand from these measurements, which were made possible by the increasing amount of data we were recording, if the Higgs boson really behaves as expected in the Standard Model. So, if it is the Standard Model Higgs boson or something more exotic, if it is an elementary particle or a composite particle. The spin, in particular, is very important because the Higgs boson is the only elementary particle with spine zero, the only scalar, predicted by the Standard Model.
So, that was the first step after the discovery. And today, nine years after the discovery, we don’t observe any significant deviation from the Standard Model prediction, although the current experimental uncertainties are in some cases quite large. The current uncertainties on the way the Higgs boson interacts with the other elementary particles are between 10 and 30%. So, the precision is good but it’s not yet at the level required to detect possible effects from theories beyond the Standard Model. This requires more data from the LHC, as well as future colliders.
The Higgs boson itself raises many questions. This is because the Higgs boson is related to the most obscure part of the Standard Model, and many of the problems of the Standard Model arise from the Higgs boson. If you look at the mathematical formulation of the Standard Model, the so-called Lagrangian, the terms that are still obscure are those where the Higgs boson appears.
So this very special particle is really key to understand the difficulties of the Standard Model and possibly shed light on how to overcome them. We know that the Standard Model is not the ultimate theory of particle physics because it doesn’t explain dark matter, the matter-antimatter symmetry in the universe, neutrino masses, and many other facts. So, there must physics beyond the Standard Model. And because all of the problems in the Standard Model arise from interactions involving the Higgs boson, it’s natural to believe that this particle is key to unveil the new theory that allows those problems to be solved.
So, clearly, the Higgs boson is one of the main avenues of exploration if we want to make progress in fundamental physics, and one that can only be pursued at colliders. Dark matter is different, and several complementary approaches are being deployed to understand its nature, from colliders to underground detectors looking for dark matter particles coming from the intergalactic halo. But the Higgs boson can only be studied at colliders.
Fabiola, is this to say that you see the discovery of the Higgs as a capstone that—
—the Standard Model?
Yes, for sure. It’s the end of something, and the beginning of something else. It’s the end of something because it was the only particle of the Standard Model that had not yet been observed. With the discovery of the Higgs boson, the spectrum of particles predicted by the Standard Model is now complete not only theoretically but also experimentally.
But, at the same time, it’s really the beginning of a new era, the beginning of an era of exploration of what is beyond the Standard Model, using the Higgs boson as a tool.
So, this is to say that anything that might be seen at the LHC now, by definition would be physics beyond the Standard Model?
Yes. But this was true even before the discovery of the Higgs boson. We may not have discovered the Higgs boson first. If supersymmetry existed at the TeV scale, then some supersymmetric particles would have been discovered even before the Higgs boson because some of these particles are easier to detect than the Higgs boson. But yes, if we discover new particles in the future, these particles are not from the Standard Model. The Standard Model is complete.
Fabiola, what was your reaction to the announcement with the 2013 Nobel Prize awarded to Peter Higgs and François Englert, and the suggestion to the extent that this is a recognition of the discovery of the Higgs boson as a theoretical achievement?
So, your question is what was my reaction to the announcement of the Nobel Prize being awarded to Peter Higgs and François Englert? Well, of course, great joy. I was there, watching the screen, and looking forward to the announcement from the Swedish Academy. It was another great day.
Of course, there was no doubt they would get the Nobel Prize, and it was good that they got it the year after the discovery. It’s amazing what those people did in 1964, together with other great physicists like Robert Brout and others who contributed to prepare the intellectual environment for such an intuition. I had the privilege of being invited by Peter Higgs to go to Stockholm—
—to assist to the ceremony. We had a great time in Stockholm.
What were some of the administrative and scientific decisions that led to the so-called long shutdown in 2013 of the LHC?
We use to have periods of shutdown interleaved with runs. So, we typically run the LHC and the rest of the accelerator complex for three years, and then we go into a period of shutdown, typically for a couple of years, to do heavy maintenance work that cannot be done during the technical stop at the end of the year. During these end-of-year stops, we do some maintenance work, but there are some activities that cannot be carried out in just a couple of months and require a longer shutdown.
The long shutdowns are also used to upgrade the accelerators and the detectors and we are now upgrading the CERN accelerator complex and the experiments to run with proton beams of higher intensity. During the current shutdown we have implemented some of these upgrades, and the rest will be implemented during the next long shutdown, planned to start in 2025.
In the middle of this, of course, in 2016, you’re named director-general. I wonder if you can explain mechanistically or operationally how this happens. Is this something that you apply to? Is this something that you’re asked to do? What is the approval process, and what do you have to present as a plan or a mandate in this very important position?
Oh, it goes this way. It’s a process that is managed by the CERN Council, which is the governing body of the Organization, where representatives of the member states and associate member states sit. So, the Council puts in place a search committee, and the search committee broadly looks for candidates. The job is advertised but I didn’t apply, as usually, you know, people from our field [laugh] do not really apply. They are called if they are—if there is an interest upon them.
So, the search committee looks broadly across the community, and solicits nominations of candidates. And then from the long list of candidates that are either suggested or identified by the search committee, the search committee produces an intermediate of candidates, maybe 10, that are called for a first interview. This interview is mainly on science, as the committee wants to see the scientific vision of the person, as well as his/her vision for the future of CERN. And at the end of this process, the search committee provides a shortlist of typically three people.
And these three candidates are then interviewed by the Council where the discussion is more on the strategic level and goes beyond scientific matters. It also covers human resources, budget, relations with various stakeholders, etc. And then the Council votes. So, there are two steps: a first interview with the search committee, and a second one with the Council.
I did not apply. I was called by the search committee. It took a few sleepless nights to decide whether I would go for the interview or not. Of course, it’s a very prestigious job, and several colleagues had encouraged me to accept to be a candidate.
But I hesitated as I thought that this job would be mainly administration, and so not interesting to me since I wanted to do research. I wanted to continue to study the Higgs boson. I had started a nice project with some young post-docs and students to measure the couplings of the Higgs boson, and I wanted to work on that. But I realised that it would be difficult to decline the invitation from the search committee, although inside of me I was hoping I would not be selected. That was my hope, but it didn’t go like that [laugh] and I was appointed.
Today, I am very happy with this job. It’s a very nice job, and it’s not boring at all. It’s not just administration. It has also many, many other interesting facets, including scientific aspects, of course.
On the question of scientific vision, what did you convey, both during the interview and when you introduced yourself in this new role to the enormous community at CERN?
Well, the priorities for the lab and also for the European community were first of all the full exploitation of the LHC, which is a wonderful instrument. When I say “instrument”, I mean everything, the collider, the experiments and the computing. There is still a lot the LHC can teach us, in particular following its high-luminosity upgrade.
But at CERN, we don’t have just the LHC. The LHC is our flagship project, but we have other facilities, including a radioactive isotope facility, an antimatter facility and a broad fixed target program. This is what we call the “scientific diversity program”, a program which is complementary to the LHC. And scientific diversity is very important at a time where we are looking for new physics, and we don’t know how this new physics is going to manifest itself.
It may be through new particles or new kinds of interactions or new phenomena. And we don’t know the energy where new physics will appear. So, we must remain broad. A healthy lab as a flagship project and a diversity program, and so this is what I said. And last but not least, we need to prepare the foundation for the next big facility at CERN by pushing the accelerator and detector R&D, but also supporting design studies for future colliders, linear and circular, hadron colliders and electron-positron colliders. So, these were the three pillars of the vision that I had at the time and actually also today.
When the LHC restarted in 2015, given all of the excitement and optimism about what could be seen, what new physics could be detected at the LHC, I wonder if you might explain what was—what people were most looking forward to when the LHC finally came back on in 2015?
So, in 2015, we had a big jump in energy. The LHC went up from 8 TeV to 13 TeV. And, of course, the most immediate thing we were hoping for was to discover new particles, new massive particles not accessible at the lower energy. So, we were looking for supersymmetry and other predicted particles, but also tried to address the open questions more than a specific scenario.
Also very important was to improve our understanding of the Higgs boson. And the number of measurements of the Higgs boson and the precision the experiments have been able to achieve are truly impressive. The past years showed the creativity of the experiments in studying Higgs boson production and decay modes that years ago were considered to be absolutely impossible to detect or to measure.
But by developing new algorithms, and using techniques like machine learning, they were able to study tiny processes that a priori we would doubt could be extracted from the much larger background of other known processes. And, so, the past years provided—how to say?—another demonstration of the power of the ATLAS and CMS detectors, which were developed in the ’90s and are still performing extremely well. They also showed the ingenuity of the physicists in developing powerful analysis tools.
I wonder if you might contrast the theoretical guidance that the community had about the mass of the Higgs, and where it would be found, and contrast that with despite operating at energies almost at a factor of two, those particles have not yet been discovered. Where is the theoretical guidance or at least the surprise in the fact that new particles at these energies have not yet been discovered?
Yeah. So, we were all hoping that we would discover new physics at the TeV scale, the scale we are now exploring, because new particles would allow us to solve a certain number of problems like the light mass of the Higgs boson, dark matter, etc.
There is no doubt that new physics exists because the Standard Model is unable to answer many outstanding questions. For instance, there is no particle in the Standard Model that has all the good features to be the constituent of dark matter.
But new physics didn’t show up yet. Maybe because it’s at a higher energy scale, which we may explore with a future collider, or maybe because it is light but very weakly coupled to the Standard Model particles and for this reason we have not found it yet. This is why we also have a scientific diversity program which looks for new physics in a way complementary to high-energy colliders.
In terms of data analysis, are we certain that the new particles are not there, and we just ha…are there and we just haven’t seen them?
I think so because, you know, first of all, the analyses are extremely sophisticated. But there are a couple of extreme cases which we may have missed. One could be that the new particles are too light to be observed at the LHC because they would be completely overwhelmed by the backgrounds. But there are limits coming from previous facilities, including LEP.
And it’s difficult for me to believe—although not impossible— that new particles have evaded the LEP limits or limits from other facilities and are still light enough not to be seen at the LHC. It would be like if nature wanted to hide something.
The other case is if the new particles are very heavy, and therefore they are produced with very tiny rates. But then with more data, in particular thanks to the high-luminosity phase of the LHC, we may be able to observe them. If they are too heavy to be produced at the LHC, their detection would be the task of the next facility.
Fabiola, to what extent are we sure that if we operate at high enough energies that we will find supersymmetry, versus the idea that perhaps supersymmetry doesn’t exist?
We’re not sure. We don’t even know if supersymmetry exists. Maybe it exists, but at an energy scale that will never be accessible to an Earth-based collider. But our objective is not to look for supersymmetry, or theory A or B. Our goal is to address the open questions, so to find the new physics, whichever it will be, that will be able to answer those questions.
For this reason, the experiments are extremely inclusive, not only in their analysis strategies, but also in the way events are selected already online, what we call the trigger. Some of the analyses target some specific models and therefore look for specific topologies that are predicted by those models. This is one approach.
But there are also many analyses that are completely inclusive. They do not really target any specific model. They examine all possible final states looking for any possible deviation from the Standard Model expectation: a substantial deviation may indicate new physics. So, we do not run behind any particular theory, we try to be as inclusive as possible.
In what ways do you see the search for dark matter at the LHC as complementary with other experiments, such as the incredible XENON experiments that Elena Aprile is doing?
So, the two approaches are complementary in terms of the mass range that they can cover, the experimental techniques used, the source of a possible dark matter signal, etc. The power of this complementarity is also that if one day the LHC produces a particle that looks like a dark matter particle, or if one day XENON1T or another experiment of a similar type observes a particle that looks like a dark matter particle, then the other approach should also be able to study that particle if it has a mass in the range covered by both.
And by making complementary measures, both approaches will provide useful information on the underlying theory, because discovering a new particle is one thing, understanding the theory that is behind that particle is more difficult and more important. And, so, for that, we need different instruments. We need to crosscheck information. We need to measure the new particle through different processes.
Fabiola, as you know as well as anyone else, there’s a big difference between announcing the discovery of the Higgs, and really learning more about its properties because you’ve been able to discover it. So, with the second run from 2015 to 2018, what do we now know about the Higgs that we didn’t know in 2011/2012?
Well, we have measured its mass with very high precision, at a level of the per mil. Initially we had observed the Higgs boson through its decays into W bosons, Z bosons, or photons. But we had no experimental evidence of the way the Higgs boson would interact with fermions, like the top quark, the bottom quark, and tau leptons.
Over the past years, the experiments were able to measure the interaction of the Higgs boson with W, Z, and photons with much higher precision, and, at the same time, to observe the Higgs boson interactions with the fermions of the third generation, top, bottom, and tau. And that’s a very important result. The next step will be to “attack” the second generation, so to look at Higgs boson decays into muon pairs.
Now that we are in the middle of the current shutdown, what are some of the hopes with regard to the high luminosity upgrade? What might happen as a result of the successful conclusion of the current shutdown we’re in?
So, the high luminosity upgrade will be completed during the next long shutdown, which will take place between 2025 and 2027. The first part of the upgrade has been implemented during the current shutdown and concerned mainly the injectors, so the accelerator links upstream of the LHC: their role is to prepare the beams and accelerate them step-by-step until they’re injected into the LHC for the final acceleration. And during the next long shutdown, we will upgrade also the Large Hadron Collider.
The High Luminosity LHC will allow the experiments to record 10 times more data than what they will have recorded by the end of the LHC operation, which will be completed at the end of 2024. With this much larger amount of data, the experiments can increase their discovery potential for new particles, with sensitivity to masses that are 20-30% larger than what they could reach by the end of 2024. And they will be able to measure the Higgs boson with higher precision, in particular also study rare decay modes such as the decay into two muons.
And last but not least, at the High-Luminosity LHC the experiments will be able to measure the known processes with much higher precision, looking for deviations from the Standard Model expectation that may indicate the presence of new physics. Indeed, the larger the amount of data, the higher the precision of the measurements, and therefore the sensitivity to the tiniest deviations from the Standard Model prediction.
Fabiola, to what extent is planning for the ILC relevant for the LHC? Are there any concerns about redundancy at those energies, or because the ILC is still a possibility, and not a definite, it doesn’t really affect the future direction of the LHC?
Well, linear colliders are complementary to hadron colliders in their capability of measuring the Higgs boson. There are processes that are only accessible or better studied at hadron colliders like, for instance, those involving couplings of the Higgs boson to the top quark, and others that are, on the other hand, much better studied in the cleaner environment of linear colliders.
If two complementary facilities run in parallel, one could imagine that the results from one facility could feed into the other one, that the results could be combined, etc. At the moment, because the ILC is not yet approved, and taking into account that the construction of such a machine will take at least 10 years, it’s not obvious that there will be any concomitant running of the LHC and the ILC.
Fabiola, I will ask you two final questions. In what ways in your tenure as director-general of CERN have you found yourself operating in the capacity of a diplomat, given the fact that CERN is a apotheosis of European collaboration?
Well, of course, there are aspects in my work that have to do with relations with various stakeholders, from CERN’s member and associate member states, so our “family”, to non-member states, other intergovernmental organizations, other research institutions, the private sector, foundations, etc. So, that requires, if not diplomatic skills, you know, some capability of dealing with interlocutors that are not always scientists or that have other priorities, or with whom you have to speak a different language. So, that was very instructive, I must say, and I learned a lot.
Fabiola, last question, administratively, what is most important for you to contribute in your future as director-general? And scientifically, as a particle physicist, what are you looking forward to getting back to if you ever have the opportunity to spend more time doing the science?
So, concerning the last question, I would say that, because I am so much attached to the Higgs boson, if I could go back to science, what I would really like to work on is measuring the properties of the Higgs boson. Administratively, I’m not so sure I understand your question. What do you mean “administratively”?
What are the biggest challenges that CERN is facing right now that require your attention, everything from the pandemic to budgeting—
The pandemic is still with us, but I hope that in a few months we could be out of this nightmare. For me the most important challenge today is to lay the foundation for the future of CERN. Of course, we have to complete the operation of the LHC and build and operate the High Luminosity LHC. These must attract all our attention, they are our priority in the short- and medium term.
But equally important is to understand what we are going to do next. What will be the next collider at CERN. Of course, these facilities are expensive and require technologies that, today, don’t even exist.
It’s very much like at the beginning of the LHC, in the mid ‘80s, when first ideas on a hadron collider in the existing 27 km tunnel were discussed. The LHC looked very much like mission impossible, and less stubborn people than physicists and engineers would have said, “OK, no way. We give in.” So, we are a little bit back in that situation. We have to decide what is the most promising project from the scientific viewpoint, and step-by-step, with motivation, determination, enthusiasm, and also with humility, we have to build the future of CERN and Europe in the global context of the field.
Fabiola, I’d like to thank you so much for spending this time with me.
Thank you, David.
It’s been a great honor for me to this spend time with you.
Thank you for the very good questions.
OK. Fabiola, we’ll be in touch. Take care.