J/ψ suppression in Pb+Pb collisions, a conventional description

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We have analyzed the latest NA50 data on J/ψ suppression in Pb + Pb collisions. J/ψ production is assumed to be a two step process, (i) formation of cc pair, which is accurately calculable in QCD and (ii) formation of J/ψ meson from the cc pair, which can be conveniently parameterized. In a pA/AA collision, the as the cc pair pass through the nuclear medium, it gain relative square momentum at the rate of ε² per unit path length. As a result, some of the cc pairs can gain enough momentum to cross the threshold to become an open charm meson, leading to suppression in pA/AA collisions. The parameters of the model were fixed from experimental data on the total J/ψ cross section as a function of effective nuclear length. The model without any free parameter, give excellent description of NA50 data on Eₜ dependence of J/ψ to Drell-Yan ratio. The model was applied to predict the Eₜ dependence of J/ψ at RHIC energy. Much larger suppression of J/ψ, in agreement with other model calculations are predicted.