Measurement of electrons from beauty-hadron decays in p–Pb collisions at √sNN = 5.02 TeV and Pb–Pb collisions at √sNN = 2.76 TeV

The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1<pT<8 GeV/c in minimum-bias p-Pb collisions at sNN−−−√=5.02 TeV and in 1.3<pT<8 GeV/c in the 20% most central Pb-Pb collisions at sNN−−−√=2.76 TeV. The pp reference spectra at s√=5.02 TeV and s√=2.76 TeV, needed for the calculation of the nuclear modification factors RpPb and RPbPb, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at s√=7 TeV. In the pT interval 3<pT<8 GeV/c a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower pT, the RPbPb values increase with large systematic uncertainties. The RpPb is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured RpPb and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of RPbPb below unity at high pT may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions

Measurement of electrons from beauty-hadron decays in p-Pb collisions at sNN=5.02 \sqrt{s_{\mathrm{NN}}}=5.02 TeV and Pb-Pb collisions at sNN=2.76 \sqrt{s_{\mathrm{NN}}}=2.76 TeV

The production of beauty hadrons was measured via semi-leptonic decays at mid-rapidity with the ALICE detector at the LHC in the transverse momentum interval 1<p$_{T}$ < 8 GeV/c in minimum-bias p-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and in 1.3 < p$_{T}$ < 8 GeV/c in the 20% most central Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV. The pp reference spectra at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV and $\sqrt{s}=2.76$ TeV, needed for the calculation of the nuclear modification factors R$_{pPb}$ and R$_{PbPb}$, were obtained by a pQCD-driven scaling of the cross section of electrons from beauty-hadron decays measured at $\sqrt{s}=7$ TeV. In the p$_{T}$ interval 3 < p$_{T}$ < 8 GeV/c, a suppression of the yield of electrons from beauty-hadron decays is observed in Pb-Pb compared to pp collisions. Towards lower p$_{T}$, the R$_{PbPb}$ values increase with large systematic uncertainties. The R$_{pPb}$ is consistent with unity within systematic uncertainties and is well described by theoretical calculations that include cold nuclear matter effects in p-Pb collisions. The measured R$_{pPb}$ and these calculations indicate that cold nuclear matter effects are small at high transverse momentum also in Pb-Pb collisions. Therefore, the observed reduction of R$_{PbPb}$ below unity at high p$_{T}$ may be ascribed to an effect of the hot and dense medium formed in Pb-Pb collisions

J/ψ suppression at forward rapidity in Pb–Pb collisions at √sNN = 5.02 TeV

The inclusive J/ψ production has been studied in Pn-Pb and pp collisions at the centre-of-mass energy per nucleon pair sNN−−−√=5.02 TeV, using the ALICE detector at the CERN LHC. The J/ψ meson is reconstructed, in the centre-of-mass rapidity interval 2.5<y<4 and in the transverse-momentum range pT<12 GeV/c, via its decay to a muon pair. In this Letter, we present results on the inclusive J/ψ cross section in pp collisions at s√=5.02 TeV and on the nuclear modification factor RAA. The latter is presented as a function of the centrality of the collision and, for central collisions, as a function of the transverse momentum pT of the J/ψ. The measured RAA values indicate a suppression of the J/ψ in nuclear collisions and are then compared to our previous results obtained in Pb-Pb collisions at sNN−−−√=2.76 TeV. The ratio of the RAA values at the two energies is also computed and compared to calculations of statistical and dynamical models. The numerical value of the ratio for central events (0-10\% centrality) is 1.17±0.04(stat)±0.20(syst). In central events, as a function of pT, a slight increase of RAA with collision energy is visible in the region 2<pT<6 GeV/c. Theoretical calculations provide a good description of the measurements, within uncertainties