Nuclear structure and saturation effects from diffractive vector meson production

TL;DR

This paper investigates how exclusive vector meson production in ultra-peripheral collisions can reveal details about the small-$x$ structure and saturation effects in oxygen and neon nuclei, using a color glass condensate framework.

Contribution

It presents predictions for vector meson production in oxygen and neon UPCs at LHC energies, incorporating Bayesian-constrained parameters and analyzing model sensitivities.

Findings

Saturation effects increase with nuclear mass and energy.

t-differential observables are sensitive to nuclear structure models.

Predictions can guide future measurements at LHC and Electron-Ion Collider.

Abstract

We study exclusive vector meson production in ultra-peripheral collisions (UPCs) of a wide range of nuclei, and assess the potential of measurements to constrain the small-$x$ structure of oxygen and neon nuclei. We employ an impact-parameter-dependent color glass condensate framework incorporating JIMWLK evolution, with parameters constrained by a recent global Bayesian analysis of $\gamma+p$ and $\gamma+\mathrm{Pb}$ data. We present predictions for coherent and incoherent $\mathrm{J}/\psi$ production in $\mathrm{O}+\mathrm{O}$ and $\mathrm{Ne}+\mathrm{Ne}$ UPCs at LHC energies, and quantify theoretical uncertainties using posterior samples from the calibration. We employ several nuclear structure models and find that $t$-differential observables are sensitive to the chosen model. We further study the mass-number dependence of saturation effects through nuclear suppression factors for coherent and incoherent vector meson production. Saturation-induced suppression increases systematically with both nuclear mass number and energy. Our results provide a unified framework for the systematic study of the onset of gluon saturation and nuclear structure at high energy, accessible in future UPC measurements at the LHC and at the Electron-Ion Collider.