Impact of the nuclear modification of the gluon densities on J/ψ production in pPb collisions at √s_NN=5 TeV

Based on our previous studies, we predict the nuclear-matter effects on J/ψ production in proton-nucleus collisions for the recent Large Hadron Collider pPb runs at √s_NN=5 TeV. We have analyzed the effects of the modification of the gluon parton distribution functions in the nucleus, using an exact kinematics for a 2→2 process, namely, g+g→J/ψ+g as expected from leading-order perturbative QCD. This allows us to constrain the transverse-momentum while computing the nuclear modification factor for different rapidities, unlike with the usual simplified kinematics. Owing to the absence of measurement in pp collisions at the same √s_NN and owing to the expected significant uncertainties in yield interpolations which would hinder definite interpretations of the nuclear modification factor R _pPb, we have derived forward-to-backward and central-to-peripheral yield ratios in which the unknown proton-proton yield cancels. These have been computed without and with a transverse-momentum cut, e.g., to comply with the ATLAS and CMS constraints in the central-rapidity region.