Forward $J/\psi$ production in proton-nucleus collisions at high energy

TL;DR

This paper re-evaluates forward $J/\psi$ production in proton-nucleus collisions using the Color Glass Condensate framework, showing improved agreement with experimental data on nuclear suppression effects.

Contribution

It introduces a nuclear extension of the dipole cross section within the CGC framework that better matches observed nuclear suppression of $J/\psi$ production.

Findings

Good description of $pp$ collision cross sections with large normalization uncertainty.

Nuclear suppression of $J/\psi$ is significantly closer to experimental data.

Glauber approach effectively models nuclear effects in the dipole cross section.

Abstract

Inclusive production of $J/\psi$ mesons, especially at forward rapidities, is an important probe of small-x gluons in protons and nuclei. In this paper we re-evaluate 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 $J/\psi$ production that is much closer to the experimental data than claimed in previous literature.