Sequential regeneration of charmonia in heavy-ion collisions

Abstract

We investigate the production of ψ(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 ψ′ 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 ψ′ suppression in the thermal medium of an expanding fireball background for d–Au collisions. When implementing updated hadronic reaction rates into a fireball for 2.76 TeV Pb–Pb collisions at LHC, the regeneration of ψ′ mesons occurs significantly later than for J/ψ's. Despite a smaller total number of regenerated ψ′, the stronger radial flow at their time of production induces a marked enhancement of their RAA relative to J/ψ's in a transverse-momentum range of pt≃3–6 GeV. We explore the consequences and uncertainties of this “sequential regeneration” mechanism on the RAA double ratio and find that it can reproduce the trends observed in recent CMS data.