Thermal versus Direct J/Ψ Production in Ultrarelativistic Heavy-Ion Collisions
Abstract
The production of J/\Psi mesons in central collisions of heavy nuclei is investigated as a function of collision energy. Two contributions are considered simultaneously: early (hard) production coupled with subsequent suppression in a Quark-Gluon Plasma, as well as thermal recombination of primordially produced c and \bar c quarks at the hadronization transition. Whereas the former still constitutes the major fraction of the observed J/\Psi abundance at SpS energies, the latter dominates the yield at RHIC. The resulting excitation function for the number of J/\Psi's over open charm pairs exhibits nontrivial structure around \sqrt{s} \simeq 30 AGeV, evolving into a significant rise towards maximal RHIC energy. We study this feature within different (thermal) scenarios for J/\Psi suppression, including parton-induced quasifree destruction as a novel mechanism.