Heavy ion physics at LHCb

Proton-ion collisions are probed in the forward acceptance by the LHCb detector in a unique kinematic range, complementary to the other LHC experiments. The production of J/ψ and decaying into two muons is studied in proton-lead collisions at a proton-nucleon centre-of-mass energy . The results are based on a data sample corresponding to an integrated luminosity of 1.6 nb(-1). The nuclear modification factor and the forward-backward production ratio are determined for J/ψ and (1S) mesons. Significant suppression of prompt J/ψ production is observed with respect to the production in pp collisions at large rapidity, while the suppression of J/ψ from b-hadron decays is less pronounced. The nuclear modification factor for (1S) mesons in the forward region is found to be similar to those for J/ψ from b-hadron decays. First observation of Z bosons in proton-lead collisions at a proton-nucleon centre-of-mass energy is also reported.