# Coherent photoproduction of $J/\psi$ in nucleus-nucleus collisions in the color dipole approach

## TL;DR

This paper models the exclusive production of J/ψ mesons in ultraperipheral heavy ion collisions using the color dipole approach, comparing theoretical predictions with experimental data to understand nuclear shadowing effects.

## Contribution

It applies the color dipole model with Glauber-Gribov theory to calculate nuclear diffractive amplitudes and compares results with recent collider data.

## Key findings

- Good agreement with data at certain energies
- Indicates potential for additional shadowing corrections at high energies
- Highlights the importance of real part contributions in the amplitude

## Abstract

We investigate the exclusive photoproduction of $J/\psi$-mesons in ultraperipheral heavy ion collisions in the color dipole approach. We first test a number of dipole cross sections fitted to inclusive $F_2$-data against the total cross section of exclusive $J/\psi$-production on the free nucleon. We then use the color-dipole formulation of Glauber-Gribov theory to calculate the diffractive amplitude on the nuclear target. The real part of the free nucleon amplitude is taken into account consistent with the rules of Glauber theory. We compare our results to recent published and preliminary data on exclusive $J/\psi$ corrections in ultraperipheral lead-lead collisions at $\sqrt{s_{NN}}=2.76 \, \rm{TeV}$ and $\sqrt{s_{NN}} = 5.02 \, \rm{TeV}$. Especially at high $\gamma A$ energies there is room for additional shadowing corrections, corresponding to triple-Pomeron terms or shadowing from large mass diffraction.