Nuclear absorption and J/ψ suppression in Pb+Pb collisions

We have analyzed the NA58 data on J/ψ suppression in Pb+Pb collisions. J/ψ production is assumed to be a two step process, (i) formation of cc̅ pair, which is accurately calculable in QCD and (ii) formation of J/ψ meson from the cc̅ pair, which can be conveniently parametrized. In a pA/AA collision, a cc̅ pair gains relative square momentum as it passes through the nuclear medium and some of the cc̅ pairs can gain enough momentum to cross the threshold to become an open charm meson, leading to suppression in pA/AA collisions. A new prescription is proposed for the gain in momentum square, consistent with Krammer process. The model could explain the E_T dependence of J/ψ over Drell-Yan ratio.