J/$\psi$ suppression at forward rapidity in Pb–Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

The inclusive J/$\psi$ production has been studied in Pb-Pb and pp interactions at the centre-of-mass energy per nucleon-nucleon collision $\sqrt{s_{\rm NN}} = 5.02$ TeV, using the ALICE detector at the CERN LHC. The J/$\psi$ meson is detected, in the centre-of-mass rapidity interval $2.5<y<4$ and in the transverse momentum range $p_{\rm T}<12$ GeV/$c$, via its decay to a muon pair. In this Letter, we present results on the inclusive J/$\psi$ cross section in pp collisions at $\sqrt{s}=5.02$ TeV and on the nuclear modification factor $R_{\rm AA}$. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum $p_{\rm T}$ of the J/$\psi$. The measured $R_{\rm AA}$ values are compared to previous results obtained by ALICE in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV. The ratio of the $R_{\rm AA}$ values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0-10% centrality) is 1.20 $\pm$ 0.04 (stat.) $\pm$ 0.21 (syst.). In central events, as a function of $p_{\rm T}$, a slight increase of $R_{\rm AA}$ with $\sqrt{s_{\rm NN}}$ is visible in the region $2<p_{\rm T}<6 GeV/$c$. Theoretical calculations provide a good description of the measurements, within uncertainties.