Accessing transverse nucleon and gluon distributions in heavy nuclei using coherent vector meson photoproduction at high energies in ion ultraperipheral collisions

TL;DR

This paper uses theoretical models to analyze coherent vector meson photoproduction in heavy-ion collisions at the LHC, revealing how nuclear shadowing affects momentum transfer distributions and impacts the understanding of nucleon and gluon distributions in nuclei.

Contribution

It provides a detailed calculation of momentum transfer distributions for vector mesons in ultraperipheral collisions, highlighting the effects of nuclear shadowing on nucleon and gluon distributions.

Findings

Nuclear shadowing suppresses cross sections.

Shadowing shifts momentum transfer distributions to smaller values.

Impact parameter space broadening of nucleon and gluon densities.

Abstract

By using the theoretical approaches describing well the available data on $t$-integrated coherent photoproduction of light and heavy vector mesons in Pb-Pb ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) in Run 1, we calculate the momentum transfer distributions for this process for $\rho$ and $J/\psi$ vector mesons in the kinematics of Run 2 at the LHC. We demonstrate that nuclear shadowing not only suppresses the absolute value of the cross sections, but also shifts the momentum transfer distributions toward smaller values of the momentum transfer $|t|$. This result can be interpreted as a broadening in the impact parameter space of the effective nucleon density in nuclei by 14\% in the case of $\rho$ and the nuclear gluon distribution by $5-11$\% in the case of $J/\psi$.