3,918 research outputs found
W and Z boson production in p-Pb collisions at √sNN=5.02 TeV
No full textThe 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-pTelectrons from heavy-flavour hadron decays in Pb-Pb collisions at sNN=2.76 ATeV
No full textElectrons 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
Centrality dependence of the pseudorapidity density distribution for charged particles in Pb-Pb collisions at sNN=5.02A TeV
No full textWe present the charged-particle pseudorapidity density in Pb-Pb collisions at root s(NN) = 5.02 TeV in centrality classes measured by ALICE. The measurement covers a wide pseudorapidity range from -3.5 to 5, which is sufficient for reliable estimates of the total number of charged particles produced in the collisions. For the most central (0-5%) collisions we find 21 400 +/- 1 300, while for the most peripheral (80-90%) we find 230 +/- 38. This corresponds to an increase of (27 +/- 4)% over the results at root s(NN) = 2.76 TeV previously reported by ALICE. The energy dependence of the total number of charged particles produced in heavy-ion collisions is found to obey a modified power-law like behaviour. The charged-particle pseudorapidity density of the most central collisions is compared to model calculations-none of which fully describes the measured distribution. We also present an estimate of the rapidity density of charged particles. The width of that distribution is found to exhibit a remarkable proportionality to the beam rapidity, independent of the collision energy from the top SPS to LHC energies. (C) 2017 The Author(s). Published by Elsevier B.V
J/psi production as a function of charged-particle pseudorapidity density in p-Pb collisions at sNN=5.02TeV
No full textWe report measurements of the inclusive J/ ψ yield and average transverse momentum as a function of charged-particle pseudorapidity density d N ch / d η in p–Pb collisions at √ s NN = 5 . 02 TeV with ALICE at the LHC. The observables are normalised to their corresponding averages in non-single diffractive events. An increase of the normalised J/ ψ yield with normalised d N ch / d η , measured at mid-rapidity, is observed at mid-rapidity and backward rapidity. At forward rapidity, a saturation of the relative yield is observed for high charged-particle multiplicities. The normalised average transverse momentum at forward and backward rapidities increases with multiplicity at low multiplicities and saturates beyond moderate multiplicities. In addition, the forward-to-backward nuclear modification factor ratio is also reported, showing an increasing suppression of J/ ψ production at forward rapidity with respect to backward rapidity for increasing charged-particle multiplicity
Azimuthal anisotropy of D-meson production in Pb-Pb collisions at root s(NN)=2.76 TeV
No full textThe production of the prompt charmed mesonsD(0), D+, andD(*+) relative to the reaction plane was measured in Pb-Pb collisions at a center-of-mass energy per nucleon-nucleon collision of root s(NN) = 2.76 TeV with the ALICE detector at the CERN Large Hadron Collider. D mesons were reconstructed via their hadronic decays at central rapidity in the transverse-momentum (pT) interval 2-16 GeV/c. The azimuthal anisotropy is quantified in terms of the second coefficient v(2) in a Fourier expansion of the D-meson azimuthal distribution and in terms of the nuclear modification factor R-AA, measured in the direction of the reaction plane and orthogonal to it. The v(2) coefficient was measured with three different methods and in three centrality classes in the interval 0%-50%. A positive v(2) is observed in midcentral collisions (30%-50% centrality class), with a mean value of 0.204(-0.036)(+0.099) (tot.unc.) in the interval 2 < pT < 6 GeV/c, which decreases towards more central collisions (10%-30% and 0%-10% classes). The positive v(2) is also reflected in the nuclear modification factor, which shows a stronger suppression in the direction orthogonal to the reaction plane formidcentral collisions. The measurements are compared to theoretical calculations of charm-quark transport and energy loss in high-density strongly interacting matter at high temperature. The models that include substantial elastic interactions with an expanding medium provide a good description of the observed anisotropy. However, they are challenged to simultaneously describe the strong suppression of high-pT yield of D mesons in central collisions and their azimuthal anisotropy in noncentral collision
The ALICE Transition Radiation Detector: Construction, operation, and performance
No full textThe Transition Radiation Detector (TRD) was designed and built to enhance the capabilities of the ALICE detector at the Large Hadron Collider (LHC). While aimed at providing electron identification and triggering, the TRD also contributes significantly to the track reconstruction and calibration in the central barrel of ALICE. In this paper the design, construction, operation, and performance of this detector are discussed. A pion rejection factor of up to 410 is achieved at a momentum of 1 GeV/ c in p–Pb collisions and the resolution at high transverse momentum improves by about 40% when including the TRD information in track reconstruction. The triggering capability is demonstrated both for jet, light nuclei, and electron selectio
Centrality dependence of high-p(T) D meson suppression in Pb-Pb collisions at root s(NN)=2.76 TeV
No full textThe nuclear modification factor, R-AA, of the prompt charmed mesons D-0, D+ and D*+, and their antiparticles, was measured with the ALICE detector in Pb-Pb collisions at a centre-of-mass energy root s(NN) = 2 : 76 TeV in two transverse momentum intervals, 5 < p(T) < 8 GeV/c and 8 < p(T) < 16 GeV/c, and in six collision centrality classes. The R-AA shows a maximum suppression of a factor of 5{6 in the 10% most central collisions. The suppression and its centrality dependence are compatible within uncertainties with those of charged pions. A comparison with the R-AA of non-prompt J/psi from B meson decays, measured by the CMS Collaboration, hints at a larger suppression of D mesons in the most central collisions
Suppression of psi(2S) production in p-Pb collisions at root sNN = 5.02 TeV
No full textThe ALICE Collaboration has studied the inclusive production of the charmonium state psi(2S) in proton-lead (p-Pb) collisions at the nucleon-nucleon centre of mass energy root sNN=5.02TeV at the CERN LHC. The measurement was performed at forward(2.03 cms cms psi(2S), both integrated and as a function of the transverse momentum pT, for the two ycms domains. The results are compared to those obtained for the 1S vector state (J/psi), by showing the ratios between the production cross sections, as well as the double ratios [sigmapsi(2S)/sigmaJ/psi]pPb/[sigma&(2S)/sigma J/&PSI]pp between p-Pb and proton-proton collisions. Finally, the nuclear modification factor for inclusive psi(2S) is evaluated and compared to the measurement of the same quantity for J/psi and to theoretical models including parton shadowing and coherent energy loss mechanisms. The results show a significantly larger suppression of the psi(2S) compared to that measured for J/psi and to models. These observations represent a clear indication for sizeable final state effects on psi(2S) production
Transverse momentum dependence of inclusive primary charged-particle production in p-Pb collisions at root S-NN=5.02 TeV
No full textThe 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 Te
First measurement of jet mass in Pb-Pb and p-Pb collisions at the LHC
No full textThis letter presents the first measurement of jet mass in Pb–Pb and p–Pb collisions at sqrt(sNN) = 2.76 TeV and 5.02 TeV, respectively. Both the jet energy and the jet mass are expected to be sensitive to jet quenching in the hot Quantum Chromodynamics (QCD) matter created in nuclear collisions at collider energies. Jets are reconstructed from charged particles using the anti- jet algorithm and resolution parameter R=0.4. The jets are measured in the pseudorapidity range |y|<0.5 and in three intervals of transverse momentum between 60 GeV/c and 120 GeV/c. The measurement of the jet mass in central Pb–Pb collisions is compared to the jet mass as measured in p–Pb reference collisions, to vacuum event generators, and to models including jet quenching. It is observed that the jet mass in central Pb–Pb collisions is consistent within uncertainties with p–Pb reference measurements. Furthermore, the measured jet mass in Pb–Pb collisions is not reproduced by the quenching models considered in this letter and is found to be consistent with PYTHIA expectations within systematic uncertainties
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