Study of coherent $J/\psi$ production in lead-lead collisions at $\sqrt{s_{\rm NN}} =5\ \rm{TeV}$ 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 $5 \ \rm{TeV}$ 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 ${p_{\mathrm{ T}}}<1 {\mathrm{\,Ge\kern -0.1em V}}$ and rapidity $2.0 < y < 4.5$. The cross-section times branching fraction within this fiducial region is measured to be $\sigma={5.3 \pm {0.2} \mbox{ (stat)} \pm {0.5} \mbox{ (syst)} \pm {0.7} \mbox{ (lumi)}} {\mathrm{ \,mb}}$. The cross-section is also measured in five bins of $J\psi$ rapidity. The results are compared to predictions from phenomenological models.