Gluon Saturation Effects in Exclusive Heavy Vector Meson Photoproduction

TL;DR

This paper investigates gluon saturation effects in exclusive heavy vector meson photoproduction, comparing linear and nonlinear evolution equations, and finds experimental evidence for saturation effects in lead targets.

Contribution

It provides a comparative analysis of linear and nonlinear evolution equations in heavy vector meson photoproduction, highlighting saturation effects in Pb targets.

Findings

No difference between models for proton targets at current energies.

Data favors gluon saturation in Pb target $J/\psi$ production.

Supports the significance of saturation physics in heavy ion collisions.

Abstract

We study exclusive $J/\psi$ and $\Upsilon$ photoproduction for proton and Pb targets in the high-energy limit, with the energy dependence computed using the linear Balitsky-Fadin-Kuraev-Lipatov and the nonlinear Balitsky-Kovchegov evolution equations. The difference between these two evolution equations can be directly attributed to gluon saturation physics. We find that for proton targets there is no difference between the two approaches at the energies of the currently available data, while for Pb targets in $J/\psi$ production the data shows a clear preference for the evolution with gluon saturation.