First LHC results on coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions at sqrt{s_NN} = 2.76 TeV

TL;DR

This paper reports the first LHC measurements of coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions, providing insights into nuclear gluon shadowing effects at high energies.

Contribution

It presents the initial experimental results on exclusive J/psi production in ultra-peripheral heavy-ion collisions at the LHC, supporting models with nuclear gluon shadowing.

Findings

Measured coherent J/psi cross section: 1.00 +/- 0.18 (stat) +0.24 -0.26 (syst) mb

Results favor models with strong nuclear gluon shadowing

First LHC measurement of this kind in Pb-Pb collisions

Abstract

The first LHC measurement on ultra-peripheral heavy-ion collisions was carried out with the ALICE experiment. In this paper, ALICE results on exclusive J/psi studies in Pb-Pb collisions at sqrt(s_NN) = 2.76 TeV, in the rapidity region -3.6 < y < -2.6, are given. The coherent J/psi cross section was found to be dsigma/dy_coh_J/\psi = 1.00 +/- 0.18 (stat) +0.24 -0.26 (syst) mb. These studies favour theoretical models that include strong modifications to the nuclear gluon density, also known as nuclear gluon shadowing.