by Loic Henri Antoine Manceau. Published: 08 July 2012


From the 2nd to the 6th of July, the QCD12 international conference took place in the Montpellier medieval town in the south of France. It has been the 16th in a series of conferences in Quantum Chromodynamics that started in 1985. The QCD12 conference was conjointly organized by the CNRS (Centre National de Recherche Scientifique) of Montpellier, the LUMP (Laboratoire Univers et Particules de Montpellier) and the University of Montpellier. The conference involved about 100 participants representing laboratories from all over the world. The medium size of the conference allows strong scientific interactions and is suitable for oral contributions from PhD students and young scientists.

The program of the conference was balanced between theoretical and experimental physics. On the theoretical side, many fields were covered including Standard Model, new physics, form factors, nucleon structure functions, Parton Distribution Functions, non perturbative QCD and chiral symmetry. On the experimental side, worldwide facilities were represented from the Tevatron and the CEBAF in the U.S.A. to the HERA and the PETRA in Germany through the Japanese B-factories and the Chinese BEPC. As for the CERN facilities, new results from the 4 main experiments of the LHC together with results from the NA48 and the NA62 experiments at the SPS were highlighted. A place of choice was held to the Higgs hunting with several oral contributions and the live broadcasting from the CERN of the historic seminar carried by the ATLAS and the CMS collaborations. ALICE physics was not left behind with a half day exclusively dedicated to the new results of the experiment and to the recent theoretical headways made on the Quark and Gluon Plasma.

The session dedicated to the ALICE experiment was opened with an overview of results from lead-lead collisions at 2.76 TeV per nucleon pair. Studies of the particle multiplicity have shown that the temperature of the medium created at the LHC should be twice the critical temperature of deconfinement. As for RHIC, the strong elliptic flow of light particles indicates the creation of a medium behaving as an ideal fluid. The non-zero elliptic flow and the suppression of open heavy flavours are hints for charm quark interactions with the medium. Finally, results from jet production which highlight large opacity were presented during this session.

The second presentation was focused on the resonance production at mid-rapidity in proton-proton collisions at 7 TeV. Such a study should allow a proper tuning of the QCD-inspired production models implemented in Monte Carlo generators as PYTHIA or PHOJET for instance. The good capability of the ALICE central barrel for the measurement of resonances was confirmed and it was shown that there is still room for the improvement of Monte Carlo generator tuning.

The next presentation was dedicated to the J/? production in pp collisions up to 7 TeV and in lead-lead collisions at 2.76 TeV per nucleon pair. In proton-proton collisions at 2.76 TeV and 7 TeV, NRQCD NLO models reproduce cross sections at forward and mid-rapidity. In lead-lead collisions, the relatively moderated J/? suppression could be explained by J/? regeneration as this mechanism is largely involved in models providing a successful description of data.

Finally, the last presentation summarized the ALICE results on open heavy flavours. In proton-proton collisions at 2.76 TeV and 7 TeV, the cross sections of D mesons and heavy flavour electrons at mid-rapidity as well as the cross section of heavy flavour muons at forward rapidity are reproduced by FONLL pQCD calculations. In lead-lead collisions, a suppression of D mesons and heavy flavour leptons was observed beyond that expected from cold nuclear matter effects. Models including radiative and collisional energy loss of heavy quarks in the deconfined medium reproduce the suppression while models including elastic collisions only overestimate the suppression.

The ALICE session ended with a five minutes discussion with the speakers from the collaboration. Participants were particularly interested on charmonium results and a question about the performance of the ALICE muon spectrometer for the measurement of the ?(2S) was raised. This gave us the chance to emphasize the fact that the muon community was working on this measurement in proton-proton collisions as it should be more difficult to obtain results in lead-lead. The concluding question from the chairman invited the speakers to sum up the theoretical conclusions which can be drawn from the presented results.

The visibility brought to the LHC results and in particular to those of the ALICE experiment has contributed to make the QCD12 conference a nice and rewarding event.