Sequential Regeneration of Charmonia in Heavy-Ion Collisions

We investigate the production of psi(2S) in nuclear collisions at RHIC and LHC energies. We first address charmonium production in 200 GeV d-Au collisions at RHIC; the strong suppression of psi' mesons observed in these reactions indicates mechanisms beyond initial cold nuclear matter effects. We find that a more complete treatment of hadronic dissociation reactions leads to appreciable psi' suppression in the hadronic medium of an expanding fireball background for d-Au collisions. When implementing the updated hadronic reaction rates into a fireball for 2.76 TeV Pb-Pb collisions at LHC, the regeneration of psi' mesons occurs significantly later than for J/psi's. Despite a smaller total number of regenerated psi', the stronger radial flow at their time of production induces a marked enhancement of their R_{AA} relative to J/psi's in a momentum range p_t \simeq 3-6 GeV. We explore the consequences and uncertainties of this "sequential regeneration" mechanism on the R_{AA} double ratio and find that it can reproduce the trends observed in recent CMS data.