Energy dependence of J/ absorption in proton-nucleus collisions

Abstract

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/ψ production cross sections measured in proton-nucleus collisions in fixed target experiments, with proton beam energies from 200 to 920 GeV, and in d-Au collisions at RHIC, at (1/2 = 200 GeV, 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/ψ and on the collision energy. Extrapolating the observed patterns we derive the level of absorption expected at E = 158 GeV, the energy at which the heavy-ion data sets were collected at the CERN SPS.© 2009 SISSA.