Azimuthal anisotropy of charged particles at high transverse momenta in PbPb collisions at sqrt(s_NN) = 2.76 TeV

Abstract

The azimuthal anisotropy of charged hadrons is determined over an extended transverse momentum (pT) range, 1 < pT < 60 GeV/c, in PbPb collisions at sqrt(s_NN) = 2.76 TeV. The data were collected with the CMS detector at the LHC. The anisotropy parameter (v_2) of the high-pT particles is extracted by correlating charged tracks with respect to the event plane reconstructed using the energy deposited in forward-angle calorimeters. The observed v_2(pT) values for six equal centrality bins spanning the range of 0-60% most-central events reach a maximum around pT = 3 GeV/c, then very gradually decrease, persisting up to at least pT = 40 GeV/c over the full centrality range measured. A long-range dihadron correlation in pseudorapidity (over at least 3.5 units) is also observed between very high-pT (>20 GeV/c) and low-pT (1--2 GeV/c) particles with similar azimuthal angles, suggesting a possible relationship with the single-particle azimuthal anisotropy driven by the initial collision geometry.

Approved Plots ( click on plot to get .pdf )

Figure Abbreviated Caption
click on it to get it The anisotropy harmonics, v_2, as a function of pT from 1.0 to 60.0 GeV/c with abs(eta)<1 for six centrality ranges in PbPb collisions at sqrt(s_NN) = 2.76 TeV, measured by the CMS experiment (solid markers). Error bars denote the statistical uncertainties, while the grey bands correspond to the systematic uncertainties. Comparison to results from the ATLAS (open squares) and CMS (open circles) experiments using data collected in 2010 is also shown.
click on it to get it The anisotropy harmonics, v_2, as a function of pT with 1<abs(eta)<2 under the same conditions as in Fig. 1.
click on it to get it The single-particle azimuthal anisotropy harmonics, v_2, as a function of N_part with abs(eta)<1 (solid circles) and 1<abs(eta)<2 (open squares) for six pT ranges in PbPb collisions at sqrt(s_NN) = 2.76 TeV, measured by the CMS experiment. Error bars denote the statistical uncertainties, while the grey bands correspond to the systematic uncertainties.
click on it to get it (a) The 2D associated yield distribution of charged hadrons as a function of abs(Delta-eta) and abs(Delta-phi) for pT_trig > 20 GeV/c and 1 < pT_assoc < 2 GeV/c from 0--30% central PbPb collisions; (b) The 1D projection of (a) as a function of abs(Delta-phi) at the long-range region (2 < abs(Delta-eta) < 3.5).
click on it to get it Technical plot: Single-track high-level trigger efficiency as a function of leading track pT for abs(eta)<1 in 0-40% centrality PbPb collisions at sqrt(s_NN) = 2.76 TeV. Three different trigger pT thresholds are shown: 12, 14 and 20 GeV/c.
click on it to get it Technical plot: Single-track high-level trigger efficiency as a function of leading track pT for abs(eta)<1 in 40-100% centrality PbPb collisions at sqrt(s_NN) = 2.76 TeV. Three different trigger pT thresholds are shown: 12, 14 and 20 GeV/c.
click on it to get it Technical plot: Systematic studies of v_2 as a function of pseudorapidity gap between tracks and event plane angle for five selected pT ranges, six centrality ranges in PbPb collisions at sqrt(s_NN) = 2.76 TeV.
click on it to get it The anisotropy harmonics, v_2, as a function of pT from 1.0 to 60.0 GeV/c with abs(eta)<1 for six centrality ranges in PbPb collisions at sqrt(s_NN) = 2.76 TeV, measured by the CMS experiment (solid markers). Error bars denote the statistical uncertainties, while the grey bands correspond to the systematic uncertainties. Comparison to results from the ATLAS (open squares), ALICE (solid stars) and CMS (open circles) experiments using data collected in 2010 is also shown.

-- WeiLi - 17-Feb-2012

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Topic revision: r13 - 2012-12-06 - GaborIVeres
 
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