Probing the gluon density of the proton in the exclusive photoproduction of vector mesons at the LHC: A phenomenological analysis

TL;DR

This paper investigates how exclusive vector meson photoproduction at the LHC can be used to better constrain the gluon density in the proton, especially at small x and low Q^2, by fitting models to experimental data.

Contribution

It provides a phenomenological analysis of the gluon density using current parametrizations and LHCb data, highlighting the importance of the gluon distribution's behavior at small x.

Findings

Models with a slowly increasing gluon density fit LHCb data better.

The analysis constrains the normalization and scale of the photoproduction cross section.

Current data favor models with a gentle rise of gluon density at small x.

Abstract

The current uncertainty on the gluon density extracted from the global parton analysis is large in the kinematical range of small values of the Bjorken - $x$ variable and low values of the hard scale $Q^2$. An alternative to reduces this uncertainty is the analysis of the exclusive vector meson photoproduction in photon - hadron and hadron - hadron collisions. This process offers a unique opportunity to constrain the gluon density of the proton, since its cross section is proportional to the gluon density squared. In this paper we consider current parametrizations for the gluon distribution and estimate the exclusive vector meson photoproduction cross section at HERA and LHC using the leading logarithmic formalism. We perform a fit of the normalization of the $\gamma h$ cross section and the value of the hard scale for the process and demonstrate that the current LHCb experimental data are better described by models that assume a slow increasing of the gluon distribution at small - $x$ and low $Q^2$.