J/Psi Suppression Revisited

The production of J/Psi's in nuclei is re-examined and the critical role of Feynman x distributions in the study of photoproduction and hadronic production of both J/Psi's and Drell-Yan dimuons is expatiated. The need to consider both initial and final state interactions and the key effect of initial state interactions on the total J/Psi cross section are demonstrated. We use a Woods-Saxon Monte Carlo simulation to obtain distributions of the numbers of collisions prior and subsequent to the charmonium production. With those results we relate the mean number of nucleon-nucleon collisions, $<n>$ to $A^{1/3} + B^{1/3}$, and give a new analytic functional form for the A dependence of the suppression. Finally we carry out a full Monte Carlo calculation of S, including an initial state prior energy loss in keeping with the measured Feynman x distributions in $\pi$-A and p-A interactions. We use an energy loss parameterization which is consistent with the energy loss from minimum bias data fitted in ISAJET. We also use an open charm absorption cross section, $\sigma_{oc}$, constrained from photoproduction of J/Psi's, to analyze the latest data on the J/Psi suppression. The role of color screening, the time evolution of off-shell charmonium to the on-shell J/Psi, and the energy dependence of the charmonium-nucleon inelastic and absorption cross sections are discussed. We find no anomalous suppression when comparing our results to published data.