Forward J /ψ production in proton-nucleus collisions at high energy

Inclusive production of J/ψ mesons, especially at forward rapidities, is an important probe of small-x gluons in protons and nuclei. In this paper we reevaluate the production cross sections in the color glass condensate framework, where the process is described by a large x gluon from the probe splitting into a quark pair and eikonally interacting with the target proton or nucleus. Using a standard collinear gluon distribution for the probe and an up-to-date dipole cross section fitted to HERA data to describe the target we achieve a rather good description of the cross section in proton-proton collisions, although with a rather large normalization uncertainty. More importantly, we show that generalizing the dipole cross section to nuclei in the Glauber approach results in a nuclear suppression of J/ψ production that is much closer to the experimental data than claimed in previous literature.