Transverse momentum spectra of J/ψJ/ψ in heavy-ion collisions

We investigate J/ψJ/ψ transverse-momentum (ptpt) distributions and their centrality dependence in heavy-ion collisions at SPS and RHIC within the framework of a two-component model, which includes (i) primordial production coupled with various phases of dissociation, (ii) statistical coalescence of c   and c¯ quarks at the hadronization transition. The suppression of the direct component (i) is calculated by solving a transport equation for J/ψJ/ψ, χcχc and ψ′ψ′ in an expanding fireball using momentum dependent dissociation rates in the Quark–Gluon Plasma (QGP). The coalescence component is inferred from a kinetic rate equation with a momentum dependence following from a blast wave approach. At SPS energies, where the direct component dominates, the interplay of Cronin effect and QGP suppression results in fair agreement with NA50 ptpt spectra. At RHIC energies, the ptpt spectra in central Au + Au collisions are characterized by a transition from regeneration at low ptpt to direct production above. At lower centralities, the latter dominates at all ptpt.