Low mass dilepton production in pp, p–Pb and Pb–Pb collisions with ALICE

Abstract

Low mass vector meson (ρ, ω, ϕ) production provides key information on the hot and dense state of strongly interacting matter produced in high-energy heavy-ion collisions (called Quark-Gluon Plasma, QGP). Strangeness enhancement is one of the possible signatures of the Quark-Gluon Plasma formation and can be accessed through the measurement of ϕ meson production with respect to ρ and ω mesons. The production dynamics and hadronization process in relativistic heavy-ion collisions can be probed through the measurement of the ϕ nuclear modification factor. We present results on the low mass dimuon analysis in pp, p–Pb and Pb–Pb collisions. In pp collisions at √s = 2.76 TeV the ϕ differential cross section as a function of the transverse momentum has been measured, serving as a baseline for Pb–Pb data. The ϕ yield and the nuclear modification factor RpPb at forward and backward rapidity have been measured for p–Pb collisions at √s = 5.02 TeV. At forward rapidity, RpPb increases as a function of pT, saturating for pT > 3 GeV/c at RpPb ~ 1. At backward rapidity, RpPb shows an increase as a function of the transverse momentum up to a factor of 1.6 for pT ~ 3-4 GeV/c, followed by a decrease at higher pT. The ϕ yield and nuclear modification factor RAA have been measured for Pb–Pb collisions at √sNN = 2.76 TeV in the intermediate pT region 2 < pT < 5 GeV/c, as a function of the number of participating nucleons. Remarkable differences are observed in the comparison between the results at forward rapidity in the dimuon channel and the ones measured in the same pT range at midrapidity in the hadronic channel ϕ → KK. In the dielectron channel at midrapidity, the invariant mass distributions in the range 0 < mee < 3 GeV/c2 are compared with the expected hadronic sources for pp collisions at √s = 7 TeV, and for p–Pb collisions at √sNN = 5.02 TeV. Latest results of the analysis of Pb–Pb collisions at √sNN = 2.76 TeV are presented.