Nuclear absorption of charmoniums in pA and AA collisions

We have analyzed the latest NA50 data on J/ψ production in pA and AA collisions. The J/ψ production is assumed to be a two step process, (i) formation of cc̅ pairs, perturbatively calculable, and (ii) formation of J/ψ from the pair, a nonperturbative process which is conveniently parametrized. In a nuclear medium, as the cc̅ pair passes through the nuclear medium, it gains relative square momentum and some of the pairs can gain enough square momentum to cross the threshold for open charm meson, leading to suppression in nuclear medium. A few parameters of the model were fixed from the latest high statistics NA50 pA and NA38 SU total J/ψ cross sectional data. The model then reproduces the centrality dependence of J/ψ over Drell-Yan ratio in 200GeV/c S+U and 158GeV/c Pb+Pb collisions.