Coherent J/ψ photoproduction at forward rapidity in ultra-peripheral Pb–Pb collisions at sNN=5.02 TeV

The ALICE collaboration performed the first rapidity-differential measurement of coherent J/psi photoproduction in ultra-peripheral Pb-Pbcollisions at a center-of-mass energy root s(NN) = 5.02TeV. 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. (C) 2019 The Author. Published by Elsevier B.V.