Gluon shadowing in nuclei and the role of the $c\bar{c}g$ state in the coherent photoproduction of $J/\psi$ in nucleus-nucleus collisions

Abstract

In this brief note, we confront our results on diffractive photoproduction of $J/\psi$ mesons with the putative gluon shadowing ratio defined as $R_g=\sqrt{\sigma (\gamma A\to J/\psi A)/{\sigma }_{IA.}}$, where ${\sigma }_{\mathrm{IA}}$ is the result in impulse approximation. Building on our earlier description of the process in the color-dipole approach, where we took into account the rescattering of $c\bar{c}$ states only, we demonstrate that the inclusion of $c\bar{c}g$-Fock states improves the description at small $x$ commonly associated with gluon shadowing.

8 pages, 2 figures