Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb-Pb collisions at root s(NN)=5.02 TeV

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 root s(NN) = 5.02 TeV in the p(T) intervals 0.5-26GeV/c( 0-10% and 30-50%) and 0.5-10 GeV/c (60-80%). The production cross section in proton-proton (pp) collisions at root s = 5.02 TeV was measured as well in 0.5 < pT< 10GeV/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. (c) 2020 Conseil Europeen pour la Recherche Nucleaire.