Charmonium Suppression in Lead-Lead Collisions: Is There a Break in the $J/\psi$ Cross-Section?

Abstract

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 $E_T\text{lsim}100$ GeV is unlikely and that signals of new physics should rather be searched in the region $E_T\text{gsim}100$ 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.

Comments: 31 pages, LaTeX, 9 postscript figures included using epsfig; references updated and comments added; final version to appear in Phys. Rev. C