J/ψ suppression at forward rapidity in Pb-Pb collisions at √sNN = 5.02 TeV

Abstract

The inclusive J/ψproduction has been studied in Pb–Pb and pp collisions at the centre-of-mass energy per nucleon pair √sNN=5.02TeV, using the ALICE detector at the CERN LHC. The J/ψmeson is reconstructed, in the centre-of-mass rapidity interval 2.5 < y < 4and in the transverse-momentum range pT < 12GeV/c, via its decay to a muon pair. In this Letter, we present results on the inclusive J/ψcross section in pp collisions at √s=5.02TeVand on the nuclear modification factor RAA. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum pTof the J/ψ. The measured RAAvalues indicate a suppression of the J/ψin nuclear collisions and are then compared to our previous results obtained in Pb–Pb collisions at √sNN = 2.76TeV. The ratio of the RAAvalues at the two energies is also computed and compared to calculations of tatistical and dynamical models. The numerical value of the ratio for central events (0–10% centrality) is 1.17 ±0.04(stat)±0.20(syst). In central events, as a function of pT, a slight increase of AAwith collision energy is visible in the region 2 < pT < 6GeV/c. Theoretical calculations qualitatively describe the measurements, within uncertainties.