Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at sNN=5.02 TeV

Abstract The differential invariant yield as a function of transverse momentum ( p T ) of electrons from semileptonic heavy-flavour hadron decays was measured at midrapidity in central (0–10%), semi-central (30–50%) and peripheral (60–80%) lead–lead (Pb–Pb) collisions at s NN = 5.02  TeV in the p T intervals 0.5–26 GeV/c (0–10% and 30–50%) and 0.5–10 GeV/c (60–80%). The production cross section in proton–proton (pp) collisions at s = 5.02 TeV was measured as well in 0.5 p T 10 GeV/c and it lies close to the upper band of perturbative QCD calculation uncertainties up to p T = 5 GeV/c and close to the mean value for larger p T . The modification of the electron yield with respect to what is expected for an incoherent superposition of nucleon–nucleon collisions is evaluated by measuring the nuclear modification factor R AA . The measurement of the R AA in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The R AA shows a suppression with respect to unity at intermediate p T , which increases while moving towards more central collisions. Moreover, the measured R AA is sensitive to the modification of the parton distribution functions (PDF) in nuclei, like nuclear shadowing, which causes a suppression of the heavy-quark production at low p T in heavy-ion collisions at LHC.