22 research outputs found

    Production of charged pions, kaons and protons at large transverse momenta in pp and Pb-Pb collisions at √sNN=2.76 TeV

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    Transverse momentum spectra of π ±, K ± and p(p-) up to pT = 20 GeV/c at mid-rapidity in pp, peripheral (60-80%) and central (0-5%) Pb-Pb collisions at √sNN=2.76 TeV have been measured using the ALICE detector at the Large Hadron Collider. The proton-to-pion and the kaon-to-pion ratios both show a distinct peak at pT ≈ 3 GeV/c in central Pb-Pb collisions. Below the peak, pT < 3 GeV/c, both ratios are in good agreement with hydrodynamical calculations, suggesting that the peak itself is dominantly the result of radial flow rather than anomalous hadronization processes. For pT > 10 GeV/c particle ratios in pp and Pb-Pb collisions are in agreement and the nuclear modification factors for π ±, K ± and p(p-) indicate that, within the systematic and statistical uncertainties, the suppression is the same. This suggests that the chemical composition of leading particles from jets in the medium is similar to that of vacuum jets. © 2014 The Authors

    ALICE Collaboration

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    Centrality, rapidity and transverse momentum dependence of J/ψ suppression in Pb-Pb collisions at √sNN= 2.76TeV

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    The inclusive J/ψ nuclear modification factor (RAA) in Pb-Pb collisions at √sNN=2.76TeV 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. © 2014 The Authors

    Multi-strange baryon production at mid-rapidity in Pb-Pb collisions at √sNN=2.76 TeV

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    The production of Ξ- and ω- baryons and their anti-particles in Pb-Pb collisions at √sNN = 2.76 TeV has been measured using the ALICE detector. The transverse momentum spectra at mid-rapidity (|y| < 0.5) for charged Ξ and ω hyperons have been studied in the range 0.6 < PT < 8.0 GeV/c and 1.2 < PT < 7.0 GeV/c, respectively, and in several centrality intervals (from the most central 0-10% to the most peripheral 60-80% collisions). These spectra have been compared with the predictions of recent hydrodynamic models. In particular, the Kraków and EPOS models give a satisfactory description of the data, with the latter covering a wider PT range. Mid-rapidity yields, integrated over PT, have been determined. The hyperon-to-pion ratios are similar to those at RHIC: they rise smoothly with centrality up to (Npart) ~ 150 and saturate thereafter. The enhancements (yields per participant nucleon relative to those in pp collisions) increase both with the strangeness content of the baryon and with centrality, but are less pronounced than at lower energies. © 2013 The Authors. Published by Elsevier B.V

    Multiplicity dependence of pion, kaon, proton and lambda production in p-Pb collisions at √SNN = 5.02 TeV

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    In this Letter, comprehensive results on π±, K±, KoS, p(p) and A(A) production at mid-rapidity (0 < yCMS < 0.5) in p-Pb collisions at √SNN = 5.02 TeV, measured by the ALICE detector at the LHC, are reported. The transverse momentum distributions exhibit a hardening as a function of event multiplicity, which is stronger for heavier particles. This behavior is similar to what has been observed in pp and Pb-Pb collisions at the LHC. The measured pT distributions are compared to d-Au, Au-Au and Pb-Pb results at lower energy and with predictions based on QCD-inspired and hydrodynamic models. © 2013 The Authors. Published by Elsevier B.V

    Long-range angular correlations of π, K and p in p-Pb collisions at sNN=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<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. © 2013 CERN
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