Abstract
Event-by-event fluctuations in the elliptic-flow coefficient v2 are studied in PbPb collisions at sNN=5.02 TeV using the CMS detector at the CERN LHC. Elliptic-flow probability distributions p(v2) for charged particles with transverse momentum 0.3<pT<3.0GeV/c and pseudorapidity |η|<1.0 are determined for different collision centrality classes. The moments of the p(v2) distributions are used to calculate the v2 coefficients based on cumulant orders 2, 4, 6, and 8. A rank ordering of the higher-order cumulant results and nonzero standardized skewness values obtained for the p(v2) distributions indicate non-Gaussian initial-state fluctuations. Bessel–Gaussian and elliptic power fits to the flow distributions are studied to characterize the initial-state spatial anisotropy.
Highlights
Ultrarelativistic heavy ion collisions at both the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC) create a hot and dense state of matter that consists of strongly interacting quarks and gluons, the “quark–gluon plasma” (QGP) [1,2,3,4,5,6,7]
A non-Gaussian behavior is observed in the eventby-event collisions fluctuations recorded by of the elliptic flow v the CMS detector at 2√csoNeNffi=ci5e.n0t2s in PbPb TeV
60% centrality are found by unfolding statistical resolution effects from measured flow distributions
Summary
Ultrarelativistic heavy ion collisions at both the BNL Relativistic Heavy Ion Collider (RHIC) and the CERN Large Hadron Collider (LHC) create a hot and dense state of matter that consists of strongly interacting quarks and gluons, the “quark–gluon plasma” (QGP) [1,2,3,4,5,6,7]. The standardized skewness estimate vanishes for fluctuations that arise from an isotropic Gaussian transverse initial-state energy density profile In this case, the p(v2) distribution is found by taking an integral over the azimuthal dependence of the two-dimensional Gaussian function [31,34]. Non-Gaussian fluctuations are expected in the initial-state energy density [33], which should lead to differences in the higher order cumulant coefficients. Such differences have been reported by the ATLAS Collaboration [16] in a similar measurement of peripheral PbPb collisions to that reported here. Gaussian fits to the flow distributions are presented to gain further insight into the initial-state and its fluctuations
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