J/ψproduction in Au+Au and Cu+Cu collisions atsNN=200GeV and the threshold model

Abstract

Using the quark gluon plasma (QGP) motivated threshold model, where all the $J/\ensuremath{\psi}$'s are suppressed above a threshold density, we have analyzed the recent PHENIX data on the participant number dependence of the nuclear modification factor for $J/\ensuremath{\psi}$'s, in Au+Au collisions, at RHIC energy, $\sqrt{s}{}_{\mathit{NN}}=200$ GeV. Centrality dependence of midrapidity $J/\ensuremath{\psi}$ suppression in Au+Au collisions are well explained in the model for threshold density ${n}_{c}\ensuremath{\approx}3.6\phantom{\rule{0.3em}{0ex}}{\mathrm{fm}}^{\ensuremath{-}2}$. PHENIX data on $J/\ensuremath{\psi}$ suppression at forward rapidity data are not explained in the model. The analysis strongly supports deconfined matter formation in central Au+Au collisions at midrapidity. We have also analyzed the preliminary PHENIX data on $J/\ensuremath{\psi}$ suppression in Cu+Cu collisions. Cu+Cu data are not explained in the threshold model.