عنوان

Measurement of the azimuthal anisotropy for charged particle production in √SNN = 2.76 TeV lead-lead collisions with the ATLAS detector

LA4kk2r8hc

Measurement of the azimuthal anisotropy for charged particle production in √SNN = 2.76 TeV lead-lead collisions with the ATLAS detector

[Article]

Aad, G; Abbott, B; Abdallah, J; Abdel Khalek, S; Abdelalim, AA; Abdesselam, A; Abdinov, O; Abi, B; Abolins, M; Abou Zeid, OS; Abramowicz, H; Abreu, H; Acerbi, E; Acharya, BS; Adamczyk, L; Adams, DL; Addy, TN; Adelman, J; Aderholz, M; Adomeit, S; Adragna, P; Adye, T; Aefsky, S; Aguilar-Saavedra, JA; et al.

© 2012 CERN, for the ATLAS Collaboration. 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 < pT < 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 pT dependencies are found to follow an approximate scaling relation, v1/nn (pT) ∝ v1/22 (pT), 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 = (cos nΔϕ). 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(paT, pbT) 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 isobserved 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 pT.

2012

UC Santa Cruz

[Article]

275578

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