by Panos Charitos. Published: 19 November 2012


Marcelo Gameiro Munhoz from the University of Sao Paolo

A.M. When did you start working with the ALICE experiment?

M.G.M. I started working in relativistic heavy ions with the AGS E864 experiment in 1995. I took my PhD in this experiment and then I moved for a postdoc in STAR in 1999. My involvement with ALICE started in 2006 when our group was accepted as full member by the Collaboration Board. Paolo Giubellino was a great supporter of our involvement with ALICE. Following that we started progressively to move from STAR to ALICE and getting more involved with the experiment. I would say that we got more involved in ALICE since 2009.

A.M. How did you start your career in high energy physics?

M.G.M. I did a master degree in low energy nuclear physics in the accelerator called PELETRON in our university; this is an 8 million Volts accelerator for heavy ions. I then took my PhD from the University of Sao Paolo but I spent most of my time in the U.S. In the AGS experiment called E864 that was led by Jack Sandweiss from Yale University. My advisor then was Claude Pruneau, so I spent part of my time in Detroit and part of my time at Brookhaven National Lab. I finished my PhD in 1998 and the next year I started my post-doc in STAR.

A.M. What is your current research in ALICE?

M.G.M. Our group consists of 4 faculty members, 6 PhD students and 3 master students in ALICE. There are also two post-docs here who come from our institution in Brazil and they are now working for other institutions.

We are mainly involved in heavy flavour analysis and jet physics while we are also involved with the Electromagnetic Calorimeter project. One of our students is doing J/psi reconstruction using EMCal triggered events. He has also worked in the development of a proposal for an electron trigger using the HLT and the EMCal. Another student is working in correlations between electrons and hadrons trying to separate the contribution from charm and bottom quarks. We also have a student working with electron v2 by using the EMCal triggered events. Another one is working with jets trying to develop a procedure to separate background from signal in the full jet reconstruction. We also have plans to start looking at jets from heavy quarks with different techniques and I hope that you will hear from us soon.

We are also involved in the elaboration of a proposal for a forward calorimeter for the ALICE upgrade program. We have two master students working on the simulation for this proposal.

We are trying to get more and more involved in instrumentation following a long tradition that our university has in low energy nuclear physics. We built many systems like a large scattering chamber, a neutron wall, several small telescopes for particle identification and for measuring the energy of charged particles. So we have a long tradition and we would like to make the next step and work in instrumentation for CERN. In that respect we are starting a collaboration with the Engineering School from our University where a large group is interested in working with us at CERN. I hope that they are coming here soon for a visit and based on their large experience with electronics I think that something interesting will come up.

A.M. What is so important about jets?

M.G.M I think that these two observables, namely the scattering of high momentum partons and heavy quarks are the most interesting and the clearest observables for studying the properties of the QGP. This is what is called tomography of the QGP. You can use these probes to measure the energy loss in the QGP and therefore extract information about the properties of the plasma. I think that heavy flavour, charm and bottom quarks are very interesting for that. In addition, quarkonia states like the J/psi are of interest because through the screening effect you can try to understand better the properties of the plasma.


Heavy Ion Groups from the University of Sao Paulo, Brazil

These particles travel through the plasma interacting with it and hence they loose energy. The mechanism and the intensity of this energy loss will depend on the properties of the plasma. If you know the behaviour of these particles in the case that you have no plasma (as in proton-proton collisions) and then you compare with what you see in heavy ion collisions, you can extract information about how these particles interact with the plasma and also the properties of the plasma.

A.M How can we imagine jets produced in QGP?

M.G.M. If you have a high energy scattering of a parton during your collision, because of confinement this parton will never come free. It will always go though the process of fragmentation and hadronization hence will produce other hadrons. When we have the scattering of two high energy partons in the medium, they interact with the medium and hence the jet will be modified. In proton-proton collisions there is no interference of the medium in this process. However, when the scattered parton is in the QGP, it interacts with the plasma, so it can lose energy so we expect that the jet will be different because of the presence of the QGP. That is what we call jet quenching. From this measurement we can try to extract information about the plasma.

A.M What is new in ALICE compared to the jets we observed in previous experiments?

M.G.M. Because of the higher energies of LHC we expect them to be more frequent. They will prevail and will be easier to measure and extract information. We have seen that more heavy quarks are created in the energies of LHC as well and there is also higher energy partons scattering, therefore it is possible to extend the range of the phenomena that we are studying.

A.M. I would like to ask you about the GRID since your institution in Brazil is part of it.

M.G.M. In Brazil we have a cluster of approximately 300 CPU cores running in the GRID. This means that we contribute to the ALICE needs for data processing and we are planning to increase the size of our cluster. We have already finished the construction of a new building and this infrastructure will allow to accommodate something between one and two thousand new CPUs. Moreover, we have just hired a new staff member in a full time position that will make sure that everything runs smoothly. I should also mention that we are applying for funding to buy more cores and we have already got a grand for additional 300 CPU cores.


Masterclass students at the University of Sao Paulo, Brazil

It is our aim to carry on with some developments and get more and more involved in new things that can be done in terms of computing. As a matter of fact, I just had a conversation with John Harvey from the CERN software group and since we are both in the project EPLANET that supports exchanges between Europe and Latin America, we arranged to have someone from CERN in Brazil for a two-week workshop on computing and to discuss the possibilities of doing more computing development.

A.M. What do you think that your university and your students are getting back from their participation in a large European Organization like CERN?

M.G.M. The involvement of Brazilian institutions with CERN is very important. The know-how that is being developed here is very important for any country that wants to advance in terms of technology. In Brazil we have this paradox: if you look at the number of publications, Brazil is in the 13th place in the world but if you look at technology development we are in a very low position. So currently, the big debate in Brazil is how academic knowledge can be transformed in wealthiness. I believe that CERN is a very good example on how you can do that. CERN has a large experience in technology transfer and in building tight bonds with industry so we can learn a lot.