Charmonium suppression in lead-lead collisions: Is there a break in theJ/ψcross section?

In the framework of a model based on nuclear absorption plus comover interaction, we compute the $E_T$ distribution of the $J/\psi$ in PbPb collisions at SPS and compare it with available NA50 data. Our analysis suggests that the existence of new physics (deconfinement phase transition) in the region $E_T\lesssim 100$ GeV is unlikely and that signals of new physics should rather be searched in the region $E_T\gtrsim 100$ GeV. The $E_T$ dependence of the $J/\psi$ transverse momentum has been computed. At large $E_T$ it turns out to be much flatter in the comover approach than in a phase transition framework. Estimates of the $J/\psi$ suppression at RHIC and LHC energies are also given.