by Virginia Greco. Published: 20 August 2018

The ALICE collaboration has recently celebrated the retirement of Karel Safarik, a brilliant physicist who participated in the inception of the experiment and played an important role in its development. Born in Bratislava, in Slovakia, Karel pursued his research career first in the Soviet Union, then in France and finally at CERN, where he has spent the last 25 years. 

We interviewed him to learn more about his experience, interests and future plans.



Dr Karel, would you retrace for us the major steps of your career?

Let’s start from the beginning. I graduated from the University of Bratislava in 1967. After completing the military service, I moved to Dubna, in the Soviet Union, where I spent 12 years conducting phenomenology studies and working on an experiment at the Serpukhovaccelerator, placed in Protvino.

In 1989 I decided to return to Czechoslovakia and become a high school physics teacher, because I didn’t want to live in the Soviet Union anymore and the political system of the time did not allow me to leave Eastern Europe. But I was lucky because, a few months after my moving, the fall of the Berlin Wall occurred and the system changed: suddenly I was allowed to go wherever I wanted. I received many invitations by colleagues around the world and I chose to join the College de France in Paris. I spent three years there, during which I visited CERN a few times for meetings and other activities. I worked in the WA77 and WA85 experiments and, at the same time, I carried out some theoretical studies. Emanuele Quercigh, who at that time was spokesperson of WA85, suggested to me to apply for a Scientific Associate position at CERN. So I did and I actually got the job. When I came here, I started working in a new experiment that Quercigh had launched, called WA97, and of which I later became spokesperson. It was the first physics experiment using silicon pixel detectors: it was very interesting.

In the meantime, we started to put together the ALICE experiment. Jürgen Schukraft contacted me and proposed me to join the core group of researchers who were working on that idea: at that moment, we were just 6 or 7 people!

Then, my career followed in ALICE, in which I was software coordinator and then physics coordinator for 11 years. Later I became leader of the ALICE physics group, position from which I stepped down last year in favour of Andreas Morsch. In the meantime, in 1997, I was offered a permanent staff position. It worked well, so I stayed at CERN for so long.

What’s the phase of your career that you enjoyed the most?

There are various, indeed. When I was in Russia, my colleagues and I carried out a very fascinating study. We discovered what is called “ρ0polarization” in the central region and we made some calculations in QCD that could explain that phenomenon, which we named higher field correction. That was very exciting.

Another very thrilling phase was when we started ALICE. Everything had to be decided and planned: from the physics measurements that we could perform to the technologies to use to build the detector.

I also remember with pleasure the period of writing the first ALICE paper. There is a fun story about that. I used to play football and apparently during one match I got biten by some insects and that gave me an infection. When, a few days later, I went to the emergencies, the doctors decided to hospitalize me to treat it. The LHC started working in those days, so I followed it from my room in the hospital, where I was given a computer and internet connection. I recall that, when ALICE recorded the first collisions at the LHC, Jürgen visited me in the hospital and so did other colleagues to share with me their excitement. They started working hard to publish the first paper with LHC data and I collaborated with them even though I was still in my hospital bed. We rushed and succeeded to submit the paper one week later, just before midnight. After submitting the article, the colleagues I had worked with came to the hospital with a bottle of champagne to celebrate. It was crazy! [He laughs] The staff of the hospital came to my room and told us to be quiet because we were in a hospital and it was night…

What was the focus of your interest in ALICE?

At the beginning, I took responsibility for the particle tracking, which is a step of the data taking that requires a lot of computing resources and programming. 

While working on that, it occurred to me that we could make studies of charm particles production in heavy ion collisions. Until that time, nobody had performed this kind of measurements. Federico Antinori and I worked on it and found that it was possible, but some changes in the detector were needed. Thus, we presented our idea to Jürgen, since he was the spokesperson at that time. He asked us to prove that it could work because changing the detector would mean spending extra money, of course. The idea had come to me overnight, but the demonstration of its feasibility took Federico and myself some days of calculations. Anyway, we succeeded to prove it and the detector was changed. That was really a breakthrough. After us, other experiments started doing the same.

Charm particle production was certainly a topic of interest for me. Later I became physics coordinator, so I had to follow all the topics.

[Photo: Andrej Barát, Pravda]


What did attract you towards heavy-ion physics?

As I mentioned, I joined ALICE because I was invited by Quercigh, thus basically I entered this field by chance. At the beginning, I was attracted by the technological challenge rather than the physics implications. That came later.

Actually, when I had just started working in ALICE, I was contacted by Peter Jenni, the first spokesperson of ATLAS, who invited me to join the experiment. I refused because I had already accepted Quercigh’s proposal and normally, when I start doing something, I go on with that.

What do you think the future of heavy-ion physics is?

I see that there are two developments ongoing. From one side, there are people focusing on low energy and then there is the research at high energy, which is what we are doing with ALICE. 

We have a programme for studies to perform during the Run 3 of LHC and then, I believe, it makes sense to continue working with heavy ions in future accelerators. 

Do you mean at the Hi-Lumi or beyond it?

Certainly with the Hi-Lumi, but also beyond, at the Future Circular Collider (FCC).

If it is built…

Yes... I think the problem is that we do not have precise indications of the energy scale at which we can discover something that would allow us to make a jump in our present knowledge. We know for sure that the Standard Model is not the end of the story and that it actually does not work at the scale of 1010 GeV. Of course, we cannot even imagine building an accelerator of such an enormous energy. But the breaking point can be anywhere between the LHC energy and that value, thus it makes sense to build a machine that can go to higher energy. However, we do not have proof that we will be able to find that breaking point at the scale of 100 TeV; this means that, with our present knowledge, we cannot guarantee that the FCC would allow us to find what we are looking for. 

It’s the same with QCD and heavy-ion physics. Something has to happen closer in time to the Big Bang, i.e. at higher energy, but we do not know the precise point.

Nevertheless, I still hope and think that we will discover something at the LHC that will make the physics case for the FCC. Indications can also come from dark energy and cosmic ray experiments.

What are your plans for your retirement?

I got a position at the Prague University, which I will join as of next October.

I am very interested in a project that they are developing, the Extreme Light Infrastructure (ELI), which will provide ultra-short and very high intensity laser pulses. I have some ideas about using that for fundamental physics research, we could perform some tests of relativity.

What are and have been your hobbies and passions outside physics?

I love sports, I have been practicing various. In particular, I used to play football and I was organizing the experiment Sunday football matches: it started in the Slovak community, but then it involved many other ALICE members. Now I have some problems with my legs, but I still play when I can.

I also was one of the founders of the CERN ice-hockey club, some years ago.

When I was young I used to play badminton, I even got into the junior category Slovak team. When I came here I joined a badminton club in Prévessin and we entered the regional league: I got a few medals for that.

I also loved to go to a chalet on the Jura mountain a few times per year: we would go hiking there and then stay overnight.

You have had quite a busy and eventful life and there are many anecdotes about you that people tell. For example, it seems that you have been driving for many years without having a driving license…  

[He laughs]Well, people are telling this story without mentioning the context, so it seems crazier than it actually is. What really happened is that, when I was in the Soviet Union, at a certain point I decided to buy a car. As a normal citizen, six months before buying it I subscribed to the driving school in Dubna. You couldn’t start the lessons whenever you wanted, though. You were included in a list and they would call you when a new round of courses began, but they used to send a letter of call only one week before starting. At that time, I was working on an experiment at the Serpukhovaccelerator, so from time to time I had to go to Protvino. They sent the call to my address in Dubna just a few days after I had left for one month. When I returned home, I found the letter, so I went to the driving school and asked to be included in the class. But they refused because it was too late and invited me to subscribe again and wait. I got frustrated and, since I had already bought a car, I ignored the system and I started driving without license. 

Didn’t you ever get stopped by the police?

Of course I did, I was stopped various times, but I was a foreigner, so I showed them my passport and they would not understand what was written. They didn’t know what to do and let me go.

When I came to CERN and decided to buy another car, I finally got a driving license in France. Everybody was surprised discovering I didn’t own a license already. [He laughs again]