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

Abstract The ALICE collaboration performed the first rapidity-differential measurement of coherent J / ψ photoproduction in ultra-peripheral Pb–Pb collisions at a center-of-mass energy s NN = 5.02 TeV. The J / ψ 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 μb−1. The cross section for coherent J / ψ production is presented in six rapidity bins. The results are compared with theoretical models for coherent J / ψ photoproduction. These comparisons indicate that gluon shadowing effects play a role in the photoproduction process. The ratio of ψ ′ to J / ψ coherent photoproduction cross sections was measured and found to be consistent with that measured for photoproduction off protons.