Nuclear absorption and anomalous $J/\psi$ suppression in Pb+Pb collisions

We discuss $J/\psi$ suppression in a QCD based nuclear absorption model. Centrality dependence of $J/\psi$ suppression in S+U and in Pb+Pb collisions are explained in the model. However, the model fails to explain the centrality dependence of $\psi\prime$ suppression. $\psi\prime$ suppression in S+U or in Pb+Pb collisions require additional suppression. Additional suppression of $\psi\prime$, due to hadronic comovers or due to QGP formation could not be distinguished in Pb+Pb collisions. We then show that the centrality dependence of the ratio, $\psi\prime$ over $J/\psi$, could possibly distinguish two scenario (e.g. QGP or hadronic comover) at RHIC energy.