QM2011 Elliptic Flow Results

The following plots from the anaysis of pseudorapidity and transverse momentum dependence of elliptic flow for charged particles in Pb+Pb collisions at sqrt(s_NN)=2.76 TeV are approved to be shown in conferences.

Centrality bins In Pb+Pb Collisions Centrality bins defined by cuts on the total transverse energy (ΣET) deposited in forward calorimeters. Bins are expressed in percentiles of the total inelastic non-Coulombic Pb+Pb cross section (0-10%, 10-20%, ..., 70-80%) with the most central bin (0-10%) corresponding to the 10% most central collisions. The measured ΣET distribution for a subset of the data (Lint approximately 200mb-1) divided into 10% centrality bins is shown in the figure (black histogram). Grey histogram represents 2.76TeV proton-proton data convolved with a Glauber Monte Carlo calculation, assuming the number of effective p+p collisions per Pb+Pb event, N=(1-x)Npart/2+xNcoll, where Npart denotes the number of participants and Ncoll denotes the number of binary collisions. The only free parameter, x, is found to best describe the data when x=0.088.

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Azimuthal distributions Distribution of the azimuthal angle of individual tracks relative to the measured event plane, Ψ2, in eight centrality bins. These distributions are meant to illustrate the observed correlation relative to the event plane, and are not used in the quantitative estimates of v2. The red curve is a fit to 1+Σn2vncos(n[φ-Ψ2]) up to n=6.

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Event plane correlations Distribution of the difference between the event planes at positive and negative η obtained using Layer1 FCal towers, both with full and half acceptance. The plot is shown for a single run (∼1.75×106 events, Lint∼280mb-1).

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Event plane resolution correction Dependence of the resolution correction, R, on ΣET for event planes from Layer1 FCal towers in full acceptance (full symbols) and half acceptance (open symbols). The plot is shown for a single run (∼1.75×106 events, Lint∼280mb-1).

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pT-dependence of elliptic flow (|η|<1) Differential elliptic flow v2(pT) for eight 10% centrality bins, for pT from 0.5 to 20GeV, and for pseudorapidity range, |η|<1. Error bars show statistical and systematic uncertainties added in quadrature. An overall scale uncertainty due to centrality uncertainties, ranging from 2% for central collisions up to 4% for peripheral events, is not shown.

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pT-dependence of elliptic flow (1<|η|<2) Differential elliptic flow v2(pT) for eight 10% centrality bins, for pT from 0.5 to 20GeV, and for pseudorapidity range, 1<|η|<2. Error bars show statistical and systematic uncertainties added in quadrature. An overall scale uncertainty due to centrality uncertainties, ranging from 2% for central collisions up to 4% for peripheral events, is not shown.

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pT-dependence of elliptic flow (2<|η|<2.5) Differential elliptic flow v2(pT) for eight 10% centrality bins, for pT from 0.5 to 20GeV, and for pseudorapidity range, 2<|η|<2.5. Error bars show statistical and systematic uncertainties added in quadrature. An overall scale uncertainty due to centrality uncertainties, ranging from 2% for central collisions up to 4% for peripheral events, is not shown.

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η-dependence of elliptic flow Pseudorapidity dependence of v2(pT, η) for 0.5 < pT < 20 GeV in five pT bins and eight 10% bins in centrality. Error bars show statistical and systematic uncertainties added in quadrature. An overall scale uncertainty due to centrality uncertainties, ranging from 2% for central collisions up to 4% for peripheral events, is not shown.

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Comparison to previous experimental data v2 vs. pT at |η|<1 in the 40-50% centrality bin, compared to previous experimental data: ALICE v2 {2} [Phys.Rev.Lett.105(2010)252302] for inclusive charged particles, PHENIX [Phys.Rev.Lett.105(2010)142301] v2 for identified π0, and STAR data on v2{2} [Phys.Rev.C72(2005)051901] for inclusive charged particles for the 40-60% bin.

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Responsible: Main.AdamTrzupek
Subject: public