71 research outputs found

    Long-range angular correlations on the near and away side in p–Pb collisions at

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    Underlying Event measurements in pp collisions at s=0.9 \sqrt {s} = 0.9 and 7 TeV with the ALICE experiment at the LHC

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    Where Brain, Body and World Collide

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    The production cross section of electrons from semileptonic decays of beauty hadrons was measured at mid-rapidity (|y| < 0.8) in the transverse momentum range 1 < pt < 8 Gev/c with the ALICE experiment at the CERN LHC in pp collisions at a center of mass energy sqrt{s} = 7 TeV using an integrated luminosity of 2.2 nb^{-1}. Electrons from beauty hadron decays were selected based on the displacement of the decay vertex from the collision vertex. A perturbative QCD calculation agrees with the measurement within uncertainties. The data were extrapolated to the full phase space to determine the total cross section for the production of beauty quark-antiquark pairs

    Long-range angular correlations of π, K and p in p–Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV

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    Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon--nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3 < pTp_T < 4 GeV/c. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |ηlab\eta_{lab}| < 0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of pTp_T and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, v2pv_2^p, is observed to be smaller than that for pions, v2πv_2^\pi, up to about pTp_T = 2 GeV/c. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The v2pv_2^p is found to be smaller at low pTp_T and larger at higher pTp_T than v2πv_2^\pi, with a crossing occurring at about 2 GeV. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system.Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p-Pb collisions at a nucleon-nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3<pT<40.3 < p_{\rm T} < 4 GeV/cc. The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range ηlab<0.8|\eta_{\rm lab}|<0.8. Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of pTp_{\rm T} and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, v2pv_2^p, is observed to be smaller than that for pions, v2πv_2^\pi, up to about pT=2p_{\rm T} = 2 GeV/cc. To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The v2pv_2^p is found to be smaller at low pTp_{\rm T} and larger at higher pTp_{\rm T} than v2piv_2^pi, with a crossing occurring at about 2 GeV. This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system.Angular correlations between unidentified charged trigger particles and various species of charged associated particles (unidentified particles, pions, kaons, protons and antiprotons) are measured by the ALICE detector in p–Pb collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV in the transverse-momentum range 0.3<pT<4 GeV/c . The correlations expressed as associated yield per trigger particle are obtained in the pseudorapidity range |ηlab|<0.8 . Fourier coefficients are extracted from the long-range correlations projected onto the azimuthal angle difference and studied as a function of pT and in intervals of event multiplicity. In high-multiplicity events, the second-order coefficient for protons, v2p , is observed to be smaller than that for pions, v2π , up to about pT=2 GeV/c . To reduce correlations due to jets, the per-trigger yield measured in low-multiplicity events is subtracted from that in high-multiplicity events. A two-ridge structure is obtained for all particle species. The Fourier decomposition of this structure shows that the second-order coefficients for pions and kaons are similar. The v2p is found to be smaller at low pT and larger at higher pT than v2π , with a crossing occurring at about 2 GeV/c . This is qualitatively similar to the elliptic-flow pattern observed in heavy-ion collisions. A mass ordering effect at low transverse momenta is consistent with expectations from hydrodynamic model calculations assuming a collectively expanding system

    J/ψJ/\psi production and nuclear effects in p-Pb collisions at SNN\sqrt{S_{NN}} = 5.02 TeV

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    Inclusive J/ψ\psi production has been studied with the ALICE detector in p-Pb collisions at sNN\sqrt{s_{NN}} = 5.02 TeV at the CERN LHC, in the rapidity domains 2.03 < ycms_{cms} < 3.53 and −4.46 < ycms_{cms} < −2.96, down to zero transverse momentum. The J/ψ\psi measurement is performed in the Muon Spectrometer through the μ+μ\mu^+\mu^− decay mode. In this Letter, the J/ψ\psi production cross section and the nuclear modification factor RpPb_{pPb} for the rapidities under study are presented. While at forward rapidity a suppression of the J/ψ\psi yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also shown differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results.Inclusive J/ψ\psi production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy sNN\sqrt{s_{\rm NN}} = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03<ycms<3.532.03<y_{\rm cms}<3.53 and 4.46<ycms<2.96-4.46<y_{\rm cms}<-2.96, down to zero transverse momentum, studying the μ+μ\mu^+\mu^- decay mode. In this paper, the J/ψ\psi production cross section and the nuclear modification factor RpPbR_{\rm pPb} for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/ψ\psi yield with respect to binary-scaled pp collisions is observed, in the backward region no suppression is present. The ratio of the forward and backward yields is also measured differentially in rapidity and transverse momentum. Theoretical predictions based on nuclear shadowing, as well as on models including, in addition, a contribution from partonic energy loss, are in fair agreement with the experimental results

    Energy Dependence of the Transverse Momentum Distributions of Charged Particles in pp Collisions Measured by ALICE

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    Differential cross sections of charged particles in inelastic pp collisions as a function of p_T have been measured at s\sqrt{s} = 0.9, 2.76 and 7 TeV at the LHC. The pTp_T spectra are compared to NLO-pQCD calculations. Though the differential cross section for an individual s\sqrt{s} cannot be described by NLO-pQCD, the relative increase of cross section with sqrt(s) is in agreement with NLO-pQCD. Based on these measurements and observations, procedures are discussed to construct pp reference spectra at s\sqrt{s} = 2.76 and 5.02 TeV up to pTp_T = 50 GeV/c as required for the calculation of the nuclear modification factor in nucleus-nucleus and proton-nucleus collisions

    Corrigendum to 'Multi-strange baryon production at mid-rapidity in Pb-Pb collisions at sNN\sqrt{s_{NN}} = 2.76 TeV' [Phys. Lett. B 728 (2014) 216-227]

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    Centrality, rapidity and transverse momentum dependence of J/ψJ/\psi suppression in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}}=2.76 TeV

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    The inclusive J/ψ\psi nuclear modification factor (RAAR_{AA}) in Pb-Pb collisions at sNN\sqrt{s_{NN}}=2.76TeV has been measured by ALICE as a function of centrality in the e+ee^+e^- decay channel at mid-rapidity |y| < 0.8 and as a function of centrality, transverse momentum and rapidity in the μ+μ\mu^+\mu^- decay channel at forward-rapidity 2.5 < y < 4.The J/ψ\psi yields measured in Pb-Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions.The RAAR_{AA} integrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is 0.72 +- 0.06 (stat.) +- 0.10 (syst.) at mid-rapidity and 0.57 +- 0.01 (stat.) +- 0.09 (syst.) at forward-rapidity. At low transverse momentum, significantly larger values of RAAR_{AA} are measured at forward-rapidity compared to measurements at lower energy.These features suggest that a contribution to the J/ψ\psi yield originates from charm quarks (re)combination in the deconfined partonic medium.The inclusive J/ψ nuclear modification factor ( RAA ) in Pb–Pb collisions at sNN=2.76 TeV has been measured by ALICE as a function of centrality in the e+e− decay channel at mid-rapidity ( |y|<0.8 ) and as a function of centrality, transverse momentum and rapidity in the μ+μ− decay channel at forward-rapidity ( 2.5<y<4 ). The J/ψ yields measured in Pb–Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions. The RAA integrated over a centrality range corresponding to 90% of the inelastic Pb–Pb cross section is 0.72±0.06(stat.)±0.10(syst.) at mid-rapidity and 0.58±0.01(stat.)±0.09(syst.) at forward-rapidity. At low transverse momentum, significantly larger values of RAA are measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the J/ψ yield originates from charm quark (re)combination in the deconfined partonic medium.The inclusive J/ψJ/\psi nuclear modification factor RAAR_{\rm AA} in Pb-Pb collisions at sNN\sqrt{s_{\rm NN}}=2.76 TeV has been measured by ALICE as a function of centrality in the e+^+e^- decay channel at mid-rapidity y<0.8|y|<0.8 and as a function of centrality, transverse momentum and rapidity in the μ+μ\mu^{+}\mu^{-} decay channel at forward-rapidity 2.5<y<42.5<y<4.The J/ψJ/\psi yields measured in Pb-Pb are suppressed compared to those in pp collisions scaled by the number of binary collisions. The RAAR_{\rm AA} integrated over a centrality range corresponding to 90% of the inelastic Pb-Pb cross section is 0.72±0.060.72\pm0.06 (stat.) ±0.10\pm0.10 (syst.) at mid-rapidity and 0.57±0.010.57 \pm 0.01 (stat.) ±0.09\pm0.09 (syst.) at forward-rapidity. At low transverse momentum, significantly larger values of RAAR_{\rm AA} are measured at forward-rapidity compared to measurements at lower energy. These features suggest that a contribution to the J/ψJ/\psi yield originates from charm quarks (re)combination in the deconfined partonic medium
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