Towards a determination of the low $x$ gluon via exclusive $J/\psi$ production

Abstract

We discuss how the stability of the theoretical prediction for exclusive $J/\psi$ photoproduction has been improved through a systematic taming of the known $\overline{\text{MS}}$ coefficient functions by accounting for a formally power suppressed, but numerically significant, correction encoded within a $Q_0$ cut. The phenomenological implications of this will be emphasised meaning, ultimately, the possibility to include the exclusive data into a global fitter framework to provide constraints on the small $x$ gluon.

5 pages, 5 figures. Proceedings of the XXVII International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2019), submitted to PoS