Recent results for forward J/$\boldsymbol{\psi}$ production in Pb--Pb Ultra-Peripheral Collisions at $\mathbf{ \sqrt{s_{\mathbf N\mathbf N}} = 5.02 }$ TeV with the ALICE detector

TL;DR

This paper presents recent experimental results on forward J/ψ meson production in ultra-peripheral Pb--Pb collisions at the LHC, demonstrating the collider's capability as a high-energy photon source for studying photon-induced interactions.

Contribution

It reports new measurements of J/ψ production in ultra-peripheral heavy-ion collisions at 5.02 TeV, highlighting the role of electromagnetic interactions at the LHC.

Findings

Enhanced photon-induced J/ψ production observed.

Results support photonuclear interaction models.

LHC as a high-energy photon source confirmed.

Abstract

The LHC is not only the highest energy collider for protons and heavy ions, but also for photon photon and photon hadron ($\gamma$p and $\gamma$Pb) interactions. This is because the protons and ions accelerated in the LHC carry an electromagnetic field, which can be viewed as a source of photons, and such photons can interact with either other photons or with hadrons. Ultra Peripheral Collisions (UPC) occur when the incoming ions pass beyond the range of the strong force, with impact parameters larger than the sum of the radii of the incoming projectiles, and are mediated by the exchange of virtual photons between the nuclei. The number of photons scales with the square of the nuclear electric charge, and the photon energies increase rapidly with beam energy. The beam energies at the LHC make the LHC the most energetic photon source ever built. In particular, the photoproduction of heavy vector mesons is favoured because such mesons couple to the photon. Recent results for forward J/$\psi$ production in Pb--Pb UPCs at $\sqrt{s_{\rm NN}} = 5.02$ TeV with the ALICE detector are presented here.