Charmonium dynamics in nucleus–nucleus collisions at SPS and FAIR energies

Abstract

Charmonium production and suppression in In + In and Pb + Pb reactions at SPS energies is investigated with the HSD transport approach within the ‘hadronic comover model’ as well as the ‘QGP threshold scenario’. The results of the transport calculations for J / Ψ suppression and the Ψ ′ to J / Ψ ratio are compared with the recent data of the NA50 and NA60 Collaborations. We find that the comover absorption model—with a single parameter | M 0 | 2 for the matrix element squared for charmonium-meson dissociation—performs best with respect to all data sets. The ‘threshold scenario’—within different assumptions for the melting energy densities—yields a reasonable suppression for J / Ψ but fails in reproducing the Ψ ′ to J / Ψ ratio for Pb + Pb at 158 A GeV . Predictions for Au + Au reactions are presented for a bombarding energy of 25 A GeV in the different scenarios which will allow for a clear distinction between the models from the experimental side at the future FAIR facility.