Charmonium suppression and regeneration from SPS to RHIC

The production of charmonia is investigated for heavy-ion collisions from SPS to RHIC energies. Our approach incorporates two sources of J/Psi yield: (i) a direct contribution arising from early (hard) parton-parton collisions, subject to subsequent nuclear absorption, quark-gluon plasma and hadronic dissociation, and (ii) statistical production at the hadronization transition by coalescence of c and (c) over bar quarks. Within an expanding thermal fireball framework, the model reproduces J/Psi centrality dependencies observed at the SPS in Pb-Pb and S-U collisions reasonably well. The study of the Psi'/Psi ratio at SPS points at the importance of the hadronic phase for Psi' interactions, possibly related to effects of chiral symmetry restoration. Predictions are given for the centrality dependence of the N-J/Psi/N-c (c) over bar ratio at full RHIC energy. We also calculate the excitation function of this ratio. The latter exhibits a characteristic minimum structure signalling the transition from the standard J/Psi, suppression scenario prevailing at SPS to dominantly thermal regeneration at collider energies. (C) 2002 Elsevier Science B.V. All rights reserved.