560 research outputs found

    Measurement of Prompt D-Meson Production in p-Pb Collisions at root s(NN)=5.02 TeV

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    The p(T)-differential production cross sections of the prompt charmed mesons D-0, D+, D*(-), and D-s(+) and their charge conjugate in the rapidity interval -0.96 < y(cms) < 0.04 were measured in p-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The nuclear modification factor R-pPb, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%-20% uncertainties with unity in the transverse momentum interval 1 < p(T) < 24 GeV/c. No significant difference among the R-pPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter

    W and Z boson production in p-Pb collisions at TeV root s(NN)=5.02 TeV

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    The W and Z boson production was measured via the muonic decay channel in proton-lead collisions at root s(NN) = 5.02 TeV at the Large Hadron Collider with the ALICE detector. The measurement covers backward (4.46 < y(cms) < 2.96) and forward (2.03 < y(cms) < 3.53) rapidity regions, corresponding to Pb-going and p-going directions, respectively. The Z-boson production cross section, with dimuon invariant mass of 60 < m(mu mu) < 120 GeV/c(2) and muon transverse momentum (p(T)(mu)) larger than 20 GeV/c, is measured. The production cross section and charge asymmetry of muons from W-boson decays with p(T)(mu) > 10 GeV/c are determined. The results are compared to theoretical calculations both with and without including the nuclear modification of the parton distribution functions. The W-boson production is also studied as a function of the collision centrality: the cross section of muons from W-boson decays is found to scale with the average number of binary nucleon-nucleon collisions within uncertainties

    Measurement of the production of high-p(T) electrons from heavy-flavour hadron decays in Pb-Pb collisions at root s(NN)=2.76 TeV

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    Electrons from heavy-flavour hadron decays (charm and beauty) were measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass of energy root s(NN) = 2.76 TeV. The transverse momentum (pT) differential production yields at mid-rapidity were used to calculate the nuclear modification factor R-AA in the interval 3 < p(T) < 18 GeV/c. The R-AA shows a strong suppression compared to binary scaling of pp collisions at the same energy (up to a factor of 4) in the 10% most central Pb-Pb collisions. There is a centrality trend of suppression, and a weaker suppression (down to a factor of 2) in semi-peripheral (50-80%) collisions is observed. The suppression of electrons in this broad p(T) interval indicates that both charm and beauty quarks lose energy when they traverse the hot medium formed in Pb-Pb collisions at LHC. (C) 2017 The Author. Published by Elsevier B.V

    Two-pion femtoscopy in p-Pb collisions at root(NN)-N-S=5.02 TeV

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    We report the results of the femtoscopic analysis of pairs of identical pions measured in p-Pb collisions at root(NN)-N-S = 5.02 TeV. Femtoscopic radii are determined as a function of event multiplicity and pair momentum in three spatial dimensions. As in the pp collision system, the analysis is complicated by the presence of sizable background correlation structures in addition to the femtoscopic signal. The radii increase with event multiplicity and decrease with pair transverse momentum. When taken at comparable multiplicity, the radii measured in p-Pb collisions, at high multiplicity and low pair transverse momentum, are 10%-20% higher than those observed in pp collisions but below those observed in A-A collisions. The results are compared to hydrodynamic predictions at large event multiplicity as well as discussed in the context of calculations based on gluon saturation

    Transverse momentum dependence of inclusive primary charged-particle production in p-Pb collisions at root S-NN=5.02 TeV

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    The transverse momentum (pT) distribution of primary charged particles is measured at midrapidity in minimum-bias p-Pb collisions at root S-NN = 5.02 TeV with the ALICE detector at the LHC in the range 0.15 < pT < 50 GeV/c. The spectra are compared to the expectation based on binary collision scaling of particle production in pp collisions, leading to a nuclear modification factor consistent with unity for pT larger than 2 GeV/c, with a weak indication of a Cronin-like enhancement for pT around 4 GeV/c. The measurement is compared to theoretical calculations and to data in Pb-Pb collisions at root S-NN = 2.76 TeV

    Measurement of D-0, D+, D+* and D-s(+) production in pp collisions at root s=5.02 TeV with ALICE

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    The measurements of the production of prompt D0 , D+ , D∗+ , and D+s mesons in proton–proton (pp) col- lisions at √s = 5.02 TeV with the ALICE detector at the Large Hadron Collider (LHC) are reported. D mesons were reconstructed at mid-rapidity (|y| < 0.5) via their hadronic decay channels D0 → K−π+, D+ → K−π+π+, D∗+ → D0π+ → K−π+π+, D+s → φπ+ → K+K−π+, and their charge conjugates. The production cross sections were measured in the transverse momentum interval 0 < pT < 36GeV/cforD0,1 < pT < 36GeV/cforD+ and D∗+, and in 2 < pT < 24 GeV/c for D+s mesons. Thanks to the higher integrated luminosity, an analysis in finer pT bins with respect to the previous measurements at √s = 7 TeV was performed, allowing for a more detailed description of the cross-section pT shape. The measured pT- differential production cross sections are compared to the results at √s = 7 TeV and to four different perturbative QCD calculations. Its rapidity dependence is also tested combin- ing the ALICE and LHCb measurements in pp collisions at √s = 5.02 TeV. This measurement will allow for a more accurate determination of the nuclear modification factor in p–Pb and Pb–Pb collisions performed at the same nucleon– nucleon centre-of-mass energy

    Two-pion femtoscopy in p -Pb collisions at s N N = 5.02 TeV

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    We report the results of the femtoscopic analysis of pairs of identical pions measured in p-Pb collisions at root(NN)-N-S = 5.02 TeV. Femtoscopic radii are determined as a function of event multiplicity and pair momentum in three spatial dimensions. As in the pp collision system, the analysis is complicated by the presence of sizable background correlation structures in addition to the femtoscopic signal. The radii increase with event multiplicity and decrease with pair transverse momentum. When taken at comparable multiplicity, the radii measured in p-Pb collisions, at high multiplicity and low pair transverse momentum, are 10%-20% higher than those observed in pp collisions but below those observed in A-A collisions. The results are compared to hydrodynamic predictions at large event multiplicity as well as discussed in the context of calculations based on gluon saturation

    Rapidity and transverse-momentum dependence of the inclusive J/ψ nuclear modification factor in p-Pb collisions at sNN \sqrt{s_{\rm NN}} = 5.02 TeV

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    We have studied the transverse-momentum (p(T)) dependence of the inclusive J/psi production in p-Pb collisions at root s(NN) = 5.02 TeV, in three center-of-mass rapidity (y(cms)) regions, down to zero p(T). Results in the forward and backward rapidity ranges (2.03 < y(cms) < 3.53 and -4.46 < y(cms) < -2.96) are obtained by studying the J/psi decay to mu(+)mu(-), while the mid-rapidity region (-1.37 < y(cms) < 0.43) is investigated by measuring the e(+)e(-) decay channel. The p(T) dependence of the J/psi production cross section and nuclear modification factor are presented for each of the rapidity intervals, as well as the J/psi mean p(T) values. Forward and mid-rapidity results show a suppression of the J/psi yield, with respect to pp collisions, which decreases with increasing p(T). At backward rapidity no significant J/psi suppression is observed. Theoretical models including a combination of cold nuclear matter effects such as shadowing and partonic energy loss, are in fair agreement with the data, except at forward rapidity and low transverse momentum. The implications of the p-Pb results for the evaluation of cold nuclear matter effects on J/psi production in Pb-Pb collisions are also discussed

    Measurement of prompt D -meson production in p-Pb collisions at sNN =5.02TeV

    No full text
    The p(T)-differential production cross sections of the prompt charmed mesons D-0, D+, D*(-), and D-s(+) and their charge conjugate in the rapidity interval -0.96 < y(cms) < 0.04 were measured in p-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV with the ALICE detector at the LHC. The nuclear modification factor R-pPb, quantifying the D-meson yield in p-Pb collisions relative to the yield in pp collisions scaled by the number of binary nucleon-nucleon collisions, is compatible within the 15%-20% uncertainties with unity in the transverse momentum interval 1 < p(T) < 24 GeV/c. No significant difference among the R-pPb of the four D-meson species is observed. The results are described within uncertainties by theoretical calculations that include initial-state effects. The measurement adds experimental evidence that the modification of the momentum spectrum of D mesons observed in Pb-Pb collisions with respect to pp collisions is due to strong final-state effects induced by hot partonic matter

    Centrality dependence of particle production in p − Pb collisions at s NN = 5.02 TeV

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    We report measurements of the primary charged-particle pseudorapidity density and transverse momentum distributions in p-Pb collisions at root s(NN) = 5.02 TeV and investigate their correlation with experimental observables sensitive to the centrality of the collision. Centrality classes are defined by using different event-activity estimators, i.e., charged-particle multiplicities measured in three different pseudorapidity regions as well as the energy measured at beam rapidity (zero degree). The procedures to determine the centrality, quantified by the number of participants (N-part) or the number of nucleon-nucleon binary collisions (N-coll) are described. We show that, in contrast to Pb-Pb collisions, in p-Pb collisions large multiplicity fluctuations together with the small range of participants available generate a dynamical bias in centrality classes based on particle multiplicity. We propose to use the zero-degree energy, which we expect not to introduce a dynamical bias, as an alternative event-centrality estimator. Based on zero-degree energy-centrality classes, the N-part dependence of particle production is studied. Under the assumption that the multiplicity measured in the Pb-going rapidity region scales with the number of Pb participants, an approximate independence of the multiplicity per participating nucleon measured at mid-rapidity of the number of participating nucleons is observed. Furthermore, at high-pT the p-Pb spectra are found to be consistent with the pp spectra scaled by N-coll for all centrality classes. Our results represent valuable input for the study of the event-activity dependence of hard probes in p-Pb collisions and, hence, help to establish baselines for the interpretation of the Pb-Pb data
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