by Virginia Greco. Published: 12 March 2018

A member of the ALICE collaboration since 1995, Andreas Morsch is Deputy Physics Coordinator of the experiment as of January 2016. We talked with him to know more about his scientific activity and interests.

Andreas studied physics at the Universities of Kaiserslautern and Saarbrücken in Germany and took his degree presenting a diploma thesis on acoustic imaging and holography. Thanks to contacts of his diploma supervisor, in 1989 he landed at CERN, where he pursued his PhD studies working in the UA1 experiment at the SppbarS collider. Even though at that time he didn’t have a solid background in particle physics, he was welcome in the group because of his programming skills. “I participated in the last run of UA1 and then I devoted my time to data analysis and to catching up with the theory” he explains. Once he completed his PhD thesis on J/ψ -tagged beauty production, he had to change field again, since he obtained a fellowship in the CERN accelerator technology division to work with his thesis supervisor Karsten Eggert on the LHC experiment-machine interface. In particular, he performed simulations to determine how energy from pp collisions would deposit in machine elements.

It was my first contact with the Fluka transport code,” comments Andreas, “and I was surprised that I could immediately produce something that had an impact, since I found some effects that enhanced the local energy deposition in the magnets. They actually had to change the design because of that…”.

He also worked on the beam lifetime for heavy-ions, which was his first contact with heavy-ion physics. “This was a fortunate twist”, he adds. “At that time, ALICE needed to make a major effort to upgrade the baseline with a muon spectrometer, so my combination of knowledge of J/ψ production in pp collisions and of Fluka simulations made myself a very good candidate to work on the muon spectrometer proposal”. Thus, he spent his third year of fellowship in ALICE, working mainly on the simulation of the absorbers for the muon spectrometer and on the study of its physics performance. This work evolved in more responsibilities in the muon spectrometer design optimisation and in the muon offline organization.

At a certain point, though, the ALICE CERN group left the muon spectrometer project, thus Andreas had to change focus once again. “It was probably another lucky circumstance, because I was obliged to look for something else to work on and I found jet physics,” he admits.

So, jet physics became one of his main fields of interest, together with J/ψ and heavy flavour physics, and it is still so. “More recently I became also interested in correlations between soft and hard processes,” Andreas adds, “in understanding how one can extrapolate elementary processes that happen at high pT to low pT and how complex event structures at low pT can be explained by superposition of higher pT processes.” This way of thinking was very useful to understand better p-Pb and Pb-Pb data and, last year, he could write together with Constantin Loizides a paper on the interpretation of very peripheral collisions in Pb-Pb.

As a deputy physics coordinator (together with Andrea Dainese) he has to follow the activities of all the physics working groups and take part in the approval process of the experimental results. “Marco [van Leeuwen, the Physics Coordinator], Andrea and I share responsibilities but we also take into account the specific expertise of each of us. I think we make for a good team,” comments Andreas.

Of course, the physics coordination has to get a broad view of all the analysis carried out and the results in each branch. This is something that requires a lot of time but can also lead to new ideas: “You get a pretty nice overview of the field and being forced to do so you actually make some interesting connections between the different results”.

New ideas are what is needed the most, according to Andreas, in order to interpret the large amount of data that ALICE is being collecting and to “make the data speak”, as he says. “On one hand the whole field has reached a certain maturity, in the sense that we make measurements with high precision, in particular in the field of collective flow effects,” he explains. “Certain macroscopic parameters of the medium are very well measured, such as the viscosity to entropy density ratio and the transport parameter related to jet quenching. We also know that there is deconfinement and colour conductivity, because of the suppression patterns of J/ψ and Upsilon production observed at lower energies and the LHC. But, on the other hand, we also know that the degrees of freedom of the QGP are not free quarks and gluons. Thus, there is still a big task ahead, which is determining what these degrees of freedom really are”.

We have also seen in small systems (pp and p-Pb collisions) effects that are very similar to those attributed to the QGP,” he continues. “Does it mean that our concepts are wrong? Or is this the chance to get some very elementary understanding of the processes that lead to thermalization or to the effects of collectivity? We need to dedicate time to brainstorming for more ideas, as well as to keep investing in people, to give great minds the possibility to stay in the field and think freely without being concerned about their next job or career step”.

After various twists and turns, Andreas has clearly settled in ALICE and will certainly continue working in the collaboration until his retirement: “After that, who knows? Maybe I will change again.” Apart from physics, he enjoys many other activities, “but I am not very proficient in any of them” he says smiling. He plays guitar, both classical and electric, he likes to practice sports and learn languages. “I also have a family, which of course is a very important part of my life as well.”