Study of Coherent $J/\psi $ Production in Lead-Lead Collisions at $\sqrt {s_{NN}}=5$ TeV with the LHCb Experiment

Coherent production of $J\psi$ mesons is studied in lead–lead collision data at a nucleon–nucleon centre-of-mass energy of 5 TeV collected by the LHCb experiment. The data set corresponds to an integrated luminosity of about 10 $\mu b^{-1}$. The $J\psi$ mesons are reconstructed in the dimuon final state, where the muons are detected within the pseudorapidity region 2:0 < $\eta$ < 4:5. The $J\psi$ mesons are required to have transverse momentum $p_T$ < 1 GeV and rapidity 2:0 < $y$ < 4.5. The cross section within this fiducial region is measured to be $\sigma$ = 5.3 $\pm$ 0.2 (stat.) $\pm$ 0.5 (syst.) $\pm$ 0.7 (lumi.) mb. The differential cross section is also measured in five bins of $J\psi$ rapidity. The results are compared to predictions from phenomenological models.