  We have analysed the latest NA50 data on $J/\psi$ production in pA and AA
collisions. The $J/\psi$ production is assumed to be a two step process, (i)
formation of $c\bar{c}$ pairs, perturbatively calculable, and (ii) formation of
$J/\psi$ from the pair, a non-perturbative process, which is conviniently
parametrized. In a nuclear medium, as the $c\bar{c}$ pair passes through the
nuclear medium, it gain 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. Few parameters of the model were fixed from the
latest high statistics NA50 pA and NA38 SU total $J/\psi$ cross sectional data.
The model then reproduces the centrality dependence of $J/\psi$ over Drell-Yan
ration in 200 GeV/c S+U and 158 GeV/c Pb+Pb collisions. We also discuss the
centrality dependence of $J/\psi$ suppression at RHIC energy.

Nuclear Theory