Study of the J/ψ production and suppression in In–In collisions at the CERN SPS

Abstract

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/ψ 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/ψ 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/ψ 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.