Energy dependence of J/ψ absorption in proton-nucleus collisions

Charmonium states are expected to be considerably suppressed in the case of quark-gluon plasma formation in high-energy heavy-ion collisions. However, a robust identification of suppression patterns as signatures of a deconfined QCD medium requires a detailed understanding of the normal nuclear absorption already present in proton-nucleus collisions, where the charmonium production cross sections increase less than linearly with the number of target nucleons. We analyse the J/psi production cross sections measured in proton-nucleus collisions in fixed target experiments, with proton beam energies from 200 to 920GeV, and in d-Au collisions at RHIC, at root(NN)-N-s = 200GeV, in the framework of the Glauber formalism, using several sets of parton distributions with and without nuclear modifications. The results reveal a significant dependence of the absorption cross section on the kinematics of the J/psi and on the collision energy. Extrapolating the observed patterns we derive the level of absorption expected at E-lab = 158GeV, the energy at which the heavy-ion data sets were collected at the CERN SPS.