Photoproduction of $J/\psi$ mesons in peripheral and semi-central heavy ion collisions

Abstract

We calculate total and differential cross sections for $J/\psi$ photoproduction in ultrarelativistic lead-lead collisions at the LHC energy $\sqrt{s_{NN}}=2.76$ TeV. In the present approach we use a simple model based on vector dominance picture and multiple scattering of the hadronic ($c \bar c$) state in a cold nucleus as an example. In our analysis we use both the classical mechanics and quantum (Glauber) formulae for calculating $\sigma_{tot}(J/\psi Pb)$ which is a building block of our model. We compare our UPC results with ALICE and CMS data. For semi-central collisions ($b<R_A+R_B$) a modification of the photon flux seems necessary. We discuss different physics motivated approximations. We try to estimate the cross sections for different centrality bins and for $J/\psi$ mesons emitted in forward rapidity range ($2.5<y<4$) corresponding to recent ALICE experimental results. Reasonable results are obtained but open questions are discussed.