Small x gluon from exclusive J/psi production

TL;DR

This paper uses exclusive J/psi production data from HERA to determine the gluon density in the proton at very small x, providing insights into its behavior and reducing uncertainties in this region.

Contribution

It introduces a method to extract the gluon distribution from exclusive J/psi production data, focusing on the small x and low Q^2 region where uncertainties are large.

Findings

Gluon density is approximately flat at low Q^2

Results are consistent with recent global analyses

Provides new constraints on small x gluon distribution

Abstract

Exclusive J/psi production, gamma* p -> J/psi p, offers a unique opportunity to determine the gluon density of the proton in the small x domain. We use the available HERA data to determine the gluon distribution in the region 10^{-4} <~ x <~ 10^{-2} and 2 <~ Q^2 <~ 10 GeV^2, where the uncertainty on the gluon extracted from the global parton analyses is large. The gluon density is found to be approximately flat at the lower scale; it is compared with those of recent global analyses.