J/psi suppression as a function of the energy of the zero degree calorimeter : can it discriminate between deconfining and comovers interaction models ?

The ratio of $J/\psi$ over Drell-Yan cross-sections as a function of the energy of the zero degree calorimeter in $Pb$ $Pb$ collisions has been computed in a comovers interaction model and compared with the results of a deconfining model. The predictions of the two models are different both for peripheral events and for very central ones. These differences are analyzed and the results of the models confronted with available data -- not only for $Pb$ $Pb$ but also for $pA$ and $SU$ collisions.