gamma suppression at forward rapidity in Pb-Pb collisions at root s(NN)=5.02 TeV

Inclusive gamma(1S) and gamma(2S) production have been measured in Pb-Pb collisions at the centre-of-mass energy per nucleon-nucleon pair root s(NN) = 5.02 TeV, using the ALICE detector at the CERN LHC. The gamma mesons are reconstructed in the centre-of-mass rapidity interval 2.5 < y < 4 and in the transverse momentum range p(T) < 15 GeV/c, via their decays to muon pairs. In this Letter, we present results on the inclusive gamma(1S) nuclear modification factor R-AA as a function of collision centrality, transverse momentum and rapidity. The gamma(1S) and gamma(2S) R-AA, integrated over the centrality range 0-90\%, are 0.37 +/- 0.02(stat) +/- 0.03(syst) and 0.10 +/- 0.04(stat) +/- 0.02(syst), respectively, leading to a ratio R-AA(gamma(2S))/R-AA(gamma(1S))of 0.28 +/- 0.12(stat) +/- 0.06(syst). The observed gamma(1S) suppression increases with the centrality of the collision and no significant variation is observed as a function of transverse momentum and rapidity. (C) 2018 Published by Elsevier B.V.