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Studies of azimuthal anisotropy harmonics in ultra-central PbPb collisions at sqrt(s[NN]) = 2.76 TeV

Abstract : Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at sqrt(s[NN]) = 2.76 TeV by the CMS collaboration, using data from the 2011 LHC heavy-ion run. The data set includes a sample of ultra-central (0-0.2% centrality) PbPb events collected using a trigger based on total transverse energy in the hadron forward calorimeters and the total multiplicity of pixel clusters in the silicon pixel tracker. A total of about 1.8 million ultra-central events were recorded, corresponding to an integrated luminosity of 120 inverse microbarns. The observed correlations in ultra-central PbPb events are expected to be particularly sensitive to initial-state fluctuations. The single-particle anisotropy Fourier harmonics, from v[2] to v[6], are extracted as a function of particle transverse momentum. At higher transverse momentum, the v[2] harmonic becomes significantly smaller than the higher-order v[n] (n greater than or equal to 3). The pt-averaged v[2] and v[3] are found to be equal within 2%, while higher-order v[n] decrease as n increases. The breakdown of factorization of dihadron correlations into single-particle azimuthal anisotropies is observed. This effect is found to be most prominent in the ultra-central PbPb collisions, where the initial-state fluctuations play a dominant role. A comparison of the factorization data to hydrodynamic predictions with event-by-event fluctuating initial conditions is also presented.
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Contributor : Sylvie Flores <>
Submitted on : Tuesday, December 10, 2013 - 7:26:05 AM
Last modification on : Wednesday, November 25, 2020 - 4:10:43 PM

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S. Chatrchyan, S. Baffioni, F. Beaudette, P. Busson, C. Charlot, et al.. Studies of azimuthal anisotropy harmonics in ultra-central PbPb collisions at sqrt(s[NN]) = 2.76 TeV. Journal of High Energy Physics, Springer, 2014, 02(2014), pp.088. ⟨10.1007/JHEP02(2014)088⟩. ⟨in2p3-00916273⟩



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