Observation of the γ(3S) Meson and Suppression of γ States in Pb-Pb Collisions at √sNN=5.02 TeV

Abstract

The production of gamma(2S) and gamma(3S) mesons in lead-lead (Pb-Pb) and proton-proton (pp) collisions is studied in their dimuon decay channel using the CMS detector at the LHC. The gamma(3S) meson is observed for the first time in Pb-Pb collisions, with a significance above 5 standard deviations. The ratios of yields measured in Pb-Pb and pp collisions are reported for both the gamma(2S) and gamma(3S) mesons, as functions of transverse momentum and Pb-Pb collision centrality. These ratios, when appropriately scaled, are significantly less than unity, indicating a suppression of gamma yields in Pb-Pb collisions. This suppression increases from peripheral to central Pb-Pb collisions. Furthermore, the suppression is stronger for gamma(3S) mesons compared to gamma(2S) mesons, extending the pattern of sequential suppression of quarkonium states in nuclear collisions previously seen for the J/psi, psi(2S), gamma(1S), and gamma(2S) mesons.