Signatures of the Color Glass Condensate in J/Psi production off nuclear targets

TL;DR

This work analyzes J/Ψ production in high-energy proton-nucleus collisions within the Color Glass Condensate framework, focusing on how gluon saturation (via the saturation scale $Q_s$) and the charm mass $M_\psi$ delineate coherent and incoherent production regimes. It derives a quasi-classical cross section linking the cc̄ propagation through the nuclear color field to the vector-meson overlap, and shows how quantum evolution drives $Q_s$ with energy, predicting a transition from enhancement at backward rapidities to suppression at forward rapidities. The study reveals limiting fragmentation and hidden parton scaling, compares predictions to RHIC data with a phenomenological evolution model, and provides clear LHC-era expectations where exact $x_1$-scaling should emerge due to proton saturation. These results highlight how CGC mechanics control hard quarkonia production in nuclei and offer experimentally testable signatures across rapidity, centrality, and energy.

Abstract

We consider the J/Psi production in proton (deuteron) -- nucleus collisions at high energies. We argue that the production mechanism in this case is different from that in pp collisions due to gluon saturation in the nucleus and formation of the Color Glass Condensate. At forward rapidities (in the proton fragmentation region), the production of J/Psi is increasingly suppressed both as a function of rapidity and centrality. On the other hand, at backward rapidities at RHIC (in the fragmentation region of the nucleus) the coherent effects lead to a modest enhancement of the production cross section, with the nuclear modification factor R(J/Psi) increasing with centrality. We find that the J/Psi production cross section exhibits at forward rapidities the limiting fragmentation scaling established previously for soft processes; in the energy range studied experimentally, it manifests itself as an approximate "xF scaling".