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Sökning: WFRF:(Manko V. I.)

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21.
  • Abelev, B., et al. (författare)
  • Elliptic flow of identified hadrons in Pb-Pb collisions at root(NN)-N-s=2.76 Tev
  • 2015
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :6
  • Tidskriftsartikel (refereegranskat)abstract
    • The elliptic flow coefficient (v(2)) of identified particles in Pb-Pb collisions at root s(NN) = 2.76 TeV was measured with the ALICE detector at the Large Hadron Collider (LHC). The results were obtained with the Scalar Product method, a two-particle correlation technique, using a pseudo-rapidity gap of |Delta eta| > 0.9 between the identified hadron under study and the reference particles. The v (2) is reported for pi(+/-), K-+/-, K-S(0), p+(p) over bar, phi, Lambda+(Lambda) over bar, Xi+(Xi) over bar (+) and Omega(-)+(Omega) over bar (+) in several collision centralities. In the low transverse momentum (p(T)) region, p(T) < 3 GeV/c, v(2)(p(T)) exhibits a particle mass dependence consistent with elliptic flow accompanied by the transverse radial expansion of the system with a common velocity field. The experimental data for pi (+/-) and the combined K-+/- and K-S(0) results, are described fairly well by hydrodynamic calculations coupled to a hadronic cascade model (VISHNU) for central collisions. However, the same calculations fail to reproduce the v(2)(p(T)) for p+(p) over bar, phi, Lambda+(Lambda) over bar, Xi+(Xi) over bar (+). For transverse momentum values larger than about 3 GeV/c, particles tend to group according to their type, i.e. mesons and baryons. The present measurements exhibit deviations from the number of constituent quark (NCQ) scaling at the level of +/- 20% for p(T) > 3 GeV/c.
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22.
  • Abelev, B., et al. (författare)
  • Event-by-event mean p(T) fluctuations in pp and Pb-Pb collisions at the LHC
  • 2014
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 74:10
  • Tidskriftsartikel (refereegranskat)abstract
    • Event-by-event fluctuations of the mean transverse momentum of charged particles produced in pp collisions at root s = 0.9, 2.76 and 7 TeV, and Pb-Pb collisions at root S-NN = 2.76 TeV are studied as a function of the charged-particle multiplicity using the ALICE detector at the LHC. Dynamical fluctuations indicative of correlated particle emission are observed in all systems. The results in pp collisions show little dependence on collision energy. The Monte Carlo event generators PYTHIA and PHOJET are in qualitative agreement with the data. Peripheral Pb-Pb data exhibit a similar-multiplicity dependence as that observed in pp. In central Pb-Pb, the results deviate from this trend, featuring a significant reduction of the fluctuation strength. The results in Pb-Pb are in qualitative agreement with previous measurements in Au-Au at lower collision energies and with expectations from models that incorporate collective phenomena.
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24.
  • Abelev, B., et al. (författare)
  • Freeze-out radii extracted from three-pion cumulants in pp, p-Pb and Pb-Pb collisions at the LHC
  • 2014
  • Ingår i: Physics Letters. Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 739, s. 139-151
  • Tidskriftsartikel (refereegranskat)abstract
    • In high-energy collisions, the spatio-temporal size of the particle production region can be measured using the Bose-Einstein correlations of identical bosons at low relative momentum. The source radii are typically extracted using two-pion correlations, and characterize the system at the last stage of interaction, called kinetic freeze-out. In low-multiplicity collisions, unlike in high-multiplicity collisions, two-pion correlations are substantially altered by background correlations, e. g. mini-jets. Such correlations can be suppressed using three-pion cumulant correlations. We present the first measurements of the size of the system at freeze-out extracted from three-pion cumulant correlations in pp, p-Pb and Pb-Pb collisions at the LHC with ALICE. At similar multiplicity, the invariant radii extracted in p-Pb collisions are found to be 5-15% larger than those in pp, while those in Pb-Pb are 35-55% larger than those in p-Pb. Our measurements disfavor models which incorporate substantially stronger collective expansion in p-Pb as compared to pp collisions at similar multiplicity. (C) 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license
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25.
  • Abelev, B., et al. (författare)
  • Inclusive photon production at forward rapidities in proton-proton collisions at root s=0.9, 2.76 and 7 TeV
  • 2015
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 75:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The multiplicity and pseudorapidity distributions of inclusive photons have been measured at forward rapidities (2.3 < eta < 3.9) in proton-proton collisions at three center-of-mass energies, root s = 0.9, 2.76 and 7 TeV using the ALICE detector. It is observed that the increase in the average photon multiplicity as a function of beam energy is compatible with both a logarithmic and a power-law dependence. The relative increase in average photon multiplicity produced in inelastic pp collisions at 2.76 and 7 TeV center-of-mass energies with respect to 0.9 TeV are 37.2 +/- 0.3% (stat) +/- 8.8% (sys) and 61.2 +/- 0.3% (stat) +/- 7.6% (sys), respectively. The photon multiplicity distributions for all center-of-mass energies are well described by negative binomial distributions. The multiplicity distributions are also presented in terms of KNO variables. The results are compared to model predictions, which are found in general to underestimate the data at large photon multiplicities, in particular at the highest center-of-mass energy. Limiting fragmentation behavior of photons has been explored with the data, but is not observed in the measured pseudorapidity range.
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26.
  • Abelev, B., et al. (författare)
  • J/psi production and nuclear effects in p-Pb collisions at=5.02 TeV
  • 2014
  • Ingår i: Journal of High Energy Physics. - 1029-8479. ; :2
  • Tidskriftsartikel (refereegranskat)abstract
    • Inclusive J/psi production has been studied with the ALICE detector in p-Pb collisions at the nucleon-nucleon center of mass energy = 5.02 TeV at the CERN LHC. The measurement is performed in the center of mass rapidity domains 2.03 < y (cms) < 3.53 and -4.46 < y (cms) < -2.96, down to zero transverse momentum, studying the mu (+) mu (-) decay mode. In this paper, the J/psi production cross section and the nuclear modification factor R (pPb) for the rapidities under study are presented. While at forward rapidity, corresponding to the proton direction, a suppression of the J/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.
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27.
  • Abelev, B, et al. (författare)
  • K_{S}^{0} and Λ Production in Pb-Pb Collisions at sqrt[s_{NN}]=2.76 TeV.
  • 2013
  • Ingår i: Physical Review Letters. - 1079-7114. ; 111:22
  • Tidskriftsartikel (refereegranskat)abstract
    • The ALICE measurement of K_{S}^{0} and Λ production at midrapidity in Pb-Pb collisions at sqrt[s_{NN}]=2.76 TeV is presented. The transverse momentum (p_{T}) spectra are shown for several collision centrality intervals and in the p_{T} range from 0.4 GeV/c (0.6 GeV/c for Λ) to 12 GeV/c. The p_{T} dependence of the Λ/K_{S}^{0} ratios exhibits maxima in the vicinity of 3 GeV/c, and the positions of the maxima shift towards higher p_{T} with increasing collision centrality. The magnitude of these maxima increases by almost a factor of three between most peripheral and most central Pb-Pb collisions. This baryon excess at intermediate p_{T} is not observed in pp interactions at sqrt[s]=0.9 TeV and at sqrt[s]=7 TeV. Qualitatively, the baryon enhancement in heavy-ion collisions is expected from radial flow. However, the measured p_{T} spectra above 2 GeV/c progressively decouple from hydrodynamical-model calculations. For higher values of p_{T}, models that incorporate the influence of the medium on the fragmentation and hadronization processes describe qualitatively the p_{T} dependence of the Λ/K_{S}^{0} ratio.
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28.
  • Abelev, B., et al. (författare)
  • Measurement of electrons from semileptonic heavy-flavor hadron decays in pp collisions at root s=2.76 TeV
  • 2015
  • Ingår i: Physical Review D (Particles, Fields, Gravitation and Cosmology). - 1550-2368. ; 91:1
  • Tidskriftsartikel (refereegranskat)abstract
    • The p(T)-differential production cross section of electrons from semileptonic decays of heavy-flavor hadrons has been measured at midrapidity in proton-proton collisions at root s = 2.76 TeV in the transverse momentum range 0.5 < p(T) < 12 GeV/c with the ALICE detector at the LHC. The analysis was performed using minimum bias events and events triggered by the electromagnetic calorimeter. Predictions from perturbative QCD calculations agree with the data within the theoretical and experimental uncertainties.
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29.
  • Abelev, B., et al. (författare)
  • Measurement of inelastic, single- and double-diffraction cross sections in proton-proton collisions at the LHC with ALICE
  • 2013
  • Ingår i: European Physical Journal C. Particles and Fields. - : Springer Science and Business Media LLC. - 1434-6044. ; 73:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Measurements of cross sections of inelastic and diffractive processes in proton-proton collisions at LHC energies were carried out with the ALICE detector. The fractions of diffractive processes in inelastic collisions were determined from a study of gaps in charged particle pseudorapidity distributions: for single diffraction (diffractive mass M-X < 200 GeV/c(2)) sigma(SD)/sigma(INEL) = 0.21 +/- 0.03, 0.20(-0.08)(+0.07,) and 0.20(-0.07)(+0.04), respectively at centre-of-mass energies root s = 0.9, 2.76, and 7 TeV; for double diffraction (for a pseudorapidity gap Delta eta > 3) sigma(DD)/sigma(INEL) = 0.11 +/- 0.03, 0.12 +/- 0.05, and 0.12(-0.04)(+0.05), respectively at root s = 0.9, 2.76, and 7 TeV. To measure the inelastic cross section, beam properties were determined with van der Meer scans, and, using a simulation of diffraction adjusted to data, the following values were obtained: sigma(INEL) = 62.8(-4.0)(+2.4)(model) +/- 1.2(lumi) mb at root s = 2.76 TeV and 73.2(-4.6)(+2.0)(model) +/- 2.6(lumi) mb at root s = 7 TeV. The single- and double-diffractive cross sections were calculated combining relative rates of diffraction with inelastic cross sections. The results are compared to previous measurements at proton-antiproton and proton-proton colliders at lower energies, to measurements by other experiments at the LHC, and to theoretical models.
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  • Resultat 21-30 av 260

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