Charmonium suppression from shadowing effects

The extent to which geometrical effects contribute to the production and su ppression of the J/psi and q (q) over bar minijet pairs in general is inves tigated for high-energy heavy-ion collisions at SPS,RHIC, and LHC energies. For the energy range under investigation, the geometrical effects referred to are shadowing and antishadowing, respectively. Due to those effects, th e parton distributions in nuclei deviate from the naive extrapolation from the free nucleon result: f(A)not equal Af(N). The strength of the shadowing /antishadowing effect increases with the mass number. Therefore it is inter esting to see the difference between cross sections for,e.g., S+U vs Pb+Pb at SPS. The recent NA50 results for the survival probability of produced J/ psi's has attracted great attention and are often interpreted as a signatur e of a quark gluon plasma. This paper will present a fresh look on hard QCD effects for the charmonium production level. It is shown that the apparent suppression of J/psi's must also be linked to the production process. Due to the uncertainty in the shadowing of gluons the suppression of charmonium states might not give reliable information on a created plasma phase at th e collider energies now available. The consequences of shadowing effects fo r the x(F) distribution of J/psi's at root s=20 GeV, root s=200 GeV, and ro ot s=6 TeV are calculated for some relevant combinations of nuclei, as well as the p(T) distribution of minijets at midrapidity for N-f=4 in the final state. [S0556-2813(99)04205-3].