# Coherent J/$\psi$ photoproduction at forward rapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\rm{NN}}}=5.02$ TeV

## TL;DR

This paper reports the first rapidity-differential measurement of coherent J/ψ photoproduction in ultra-peripheral Pb-Pb collisions at 5.02 TeV, providing insights into gluon shadowing effects in heavy-ion collisions.

## Contribution

It presents the first detailed rapidity-dependent measurement of coherent J/ψ production in ultra-peripheral heavy-ion collisions at this energy, comparing results with theoretical models.

## Key findings

- Gluon shadowing influences photoproduction cross sections.
- Measured cross sections vary across rapidity bins.
- The ψ' to J/ψ ratio is consistent with proton photoproduction.

## Abstract

The ALICE collaboration performed the first rapidity-differential measurement of coherent J/$\psi$ photoproduction in ultra-peripheral Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV. The J/$\psi$ is detected via its dimuon decay in the forward rapidity region ($-4.0 < y < -2.5$) for events where the hadronic activity is required to be minimal. The analysis is based on an event sample corresponding to an integrated luminosity of about 750 $\mu$b$^{-1}$. The cross section for coherent J/$\psi$ production is presented in six rapidity bins. The results are compared with theoretical models for coherent J/$\psi$ photoproduction. These comparisons indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of $\psi'$ to J/$\psi$ coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons.