J/ψ production in indium-indium collisions at SPS energies

Abstract

The NA60 experiment collected data on dimuon production in indium‐indium collisions at 158 GeV/c per incident nucleon, in year 2003, to contribute to the clarification of several questions raised by previous experiments studying high‐energy heavy‐ion physics at the CERN SPS in search of the quark gluon plasma. Among these previous results stands the observation, by NA50, that the production yield of J/ψ mesons is suppressed in central Pb‐Pb collisions beyond the normal nuclear absorption defined by proton‐nucleus data. By comparing the centrality dependence of the suppression pattern between different colliding systems, S‐U, Pb‐Pb and In‐In, we should be able to identify the corresponding scaling variable, and the physics mechanism driving the suppression. In this paper, we will present the ratio of J/ψ and Drell‐Yan production cross‐sections in indium‐indium collisions, in three centrality bins, and how these values compare to previous measurements. We will also present a study of the transverse momentum distributions of the J/ψ mesons, in seven centrality bins.