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Type: Journal article
Title: Measurement of the azimuthal anisotropy for charged particle production in √sNN = 2.76 TeV lead-lead collisions with the ATLAS detector
Other Titles: Measurement of the azimuthal anisotropy for charged particle production in root sNN = 2.76 TeV lead-lead collisions with the ATLAS detector
Author: Aad, G.
ATLAS Collaboration
Citation: Physical Review C, 2012; 86(1):014907-1-014907-41
Publisher: American Physical Society
Issue Date: 2012
ISSN: 0556-2813
Statement of
G. Aad ... P. Jackson ... L. Lee ... A. Petridis ... N. Soni ... M.J. White ... et al. (ATLAS Collaboration)
Abstract: Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at √sNN = 2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 μb⁻¹. This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle relative to the reaction plane, with the coefficients vn denoting the magnitude of the anisotropy. Significant v₂–v₆ values are obtained as a function of transverse momentum (0.5 < pτ < 20 GeV), pseudorapidity (|η| <2.5), and centrality using an event plane method. The vn values for n≥3 are found to vary weakly with both η and centrality, and their pτ dependencies are found to follow an approximate scaling relation, v1/nn(pτ)∝v1/22(pτ), except in the top 5% most central collisions. A Fourier analysis of the charged particle pair distribution in relative azimuthal angle (Δφ=φa−φb) is performed to extract the coefficients vn,n=⟨cosnΔφ⟩. For pairs of charged particles with a large pseudorapidity gap (|Δη=ηa−ηb|>2) and one particle with pT<3 GeV, the v2,2–v6,6 values are found to factorize as vn,n(paT,pbT)≈vn(paT)vn(pbT) in central and midcentral events. Such factorization suggests that these values of v₂,₂–v₆,₆ are primarily attributable to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the v₁,₁(paτ,pbτ) data are consistent with the combined contributions from a rapidity-even v₁ and global momentum conservation. A two-component fit is used to extract the v₁ contribution. The extracted v₁ is observed to cross zero at pT≈1.0 GeV, reaches a maximum at 4–5 GeV with a value comparable to that for v₃, and decreases at higher pτ.
Rights: ©2012 CERN, for the ATLAS Collaboration. Published by the American Physical Society under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
RMID: 0020132685
DOI: 10.1103/PhysRevC.86.014907
Appears in Collections:Physics publications

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