Charmonium photoproduction in ultra-peripheral p-Pb and Pb-Pb collisions at the LHC with the ALICE experiment

TL;DR

This paper reports the first measurements of charmonium photoproduction cross sections in ultra-peripheral p-Pb and Pb-Pb collisions at the LHC, providing insights into nuclear gluon shadowing and gluon structure functions.

Contribution

It presents the first experimental measurements of coherent J/ψ and ψ(2S) photoproduction in Pb-Pb and p-Pb ultra-peripheral collisions at the LHC, comparing results with theoretical models.

Findings

First measurement of coherent J/ψ and ψ(2S) photoproduction in Pb-Pb collisions.

First measurement of exclusive J/ψ photoproduction off protons in p-Pb collisions.

Results compared to STARLIGHT and QCD models.

Abstract

Vector mesons are copiously produced in ultra-peripheral collisions. In these collisions, the impact parameter is larger than the sum of the radii of two projectiles, implying that electromagnetic processes become dominant. The cross section for this process is sensitive to the gluon distribution and can therefore probe nuclear gluon shadowing (Pb-Pb) and the gluon structure function in the nucleon (p-Pb). The ALICE Collaboration has performed the first measurement of the coherent J/$\psi$ and $\psi$(2S) photoproduction cross section in Pb-Pb collisions and that for exclusive J/$\psi$ photoproduction off protons in ultra-peripheral proton-lead collisions at the LHC. The results are compared to STARLIGHT and to QCD based models.