Studies of azimuthal dihadron correlations in ultra-central PbPb collisions at √s[subscript NN] =2.76 TeV
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Chatrchyan-2014-Studies of azimuthal.pdf
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Author(s)
Apyan, Aram
Busza, Wit
Cali, Ivan Amos
Chan, M.
Di Matteo, Leonardo
Gomez-Ceballos, Guillelmo
Goncharov, Maxim
Gulhan, Doga Can
Klute, Markus
Lai, Yue Shi
Date Issued
February 2014
Journal
Journal of High Energy Physics
Publisher
Springer-Verlag
Citation
Chatrchyan, S., V. Khachatryan, A. M. Sirunyan, A. Tumasyan, W. Adam, T. Bergauer, M. Dragicevic, et al. “Studies of Azimuthal Dihadron Correlations in Ultra-Central PbPb Collisions at √s[subscript NN] =2.76 TeV.” J. High Energ. Phys. 2014, no. 2 (February 2014). © CERN, for the benefit of the CMS Collaboration
Version
Final published version
Abstract
Azimuthal dihadron correlations of charged particles have been measured in PbPb collisions at √s[subscript NN] = 2.76TeV 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 μb − 1. 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 [subscript 2] to v [subscript 6], are extracted as a function of particle transverse momentum. At higher transverse momentum, the v [subscript 2] harmonic becomes significantly smaller than the higher-order v [subscript n] (n ≥ 3). The p [subscript T]-averaged [subscript v] 2 and [subscript v] 3 are found to be equal within 2%, while higher-order v [subscript 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.
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Laboratory for Nuclear Science
Massachusetts Institute of Technology. School of Science
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DOI of Published Version
https://doi.org/10.1007/jhep02(2014)088
