Measurement of electrons from semileptonic heavy-flavour hadron decays at midrapidity in pp and Pb–Pb collisions at 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 $\sqrt{{s}_{\mathrm{NN}}}=5.02\text{TeV}$ 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 $\sqrt{s}=5.02$ 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 ${R}_{\mathrm{AA}}$. The measurement of the ${R}_{\mathrm{AA}}$ in different centrality classes allows in-medium energy loss of charm and beauty quarks to be investigated. The ${R}_{\mathrm{AA}}$ shows a suppression with respect to unity at intermediate ${p}_{T}$, which increases while moving towards more central collisions. Moreover, the measured ${R}_{\mathrm{AA}}$ 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.