Study of the J/$\psi$ production and suppression in In-In collisions at the CERN SPS

The NA60 experiment aims at measuring the kinematics of the muon pairs produced in ultra-relativistic nuclear collisions. The use of dileptonic probes in the search for quark-gluon plasma formation has been carried on by several experiments at the CERN SPS, which have provided some of the most interesting observations; nevertheless certain important questions remain open. One of them is the interpretation of the anomalous suppression of the J/ psi meson in Pb-Pb collisions with respect to the yields extrapolated from the proton-nucleus data taken by the NA50 experiment. The NA60 experiment has recently taken data on J/ psi production in indium-indium collisions: the comparison of the suppression patterns in the two systems (In-In with respect to Pb-Pb) should help in understanding which is the physical variable driving the J/ psi suppression. In this paper, after briefly summarizing the NA60 physics motivation and detector concept, we present the first results from In-In collisions at 158 GeV/nucleon, focusing on the preliminary analysis of charmonia production and suppression.