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

Abstract

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 $c\bar{c}$ pair, which is accurately calculable in QCD and (ii) formation of $J/ψ$ meson from the $c\bar{c}$ pair, which can be conveniently parameterized. In a pA/AA collision, the as the $c\bar{c}$ pair pass through the nuclear medium, it gain relative square momentum at the rate of $ε^2$ per unit path length. As a result, some of the $c\bar{c}$ 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 $E_T$ dependence of $J/ψ$ to Drell-Yan ratio. The model was applied to predict the $E_T$ dependence of $J/ψ$ at RHIC energy. Much larger suppression of $J/ψ$, in agreement with other model calculations are predicted.