Non-Gaussian elliptic-flow fluctuations in PbPb collisions at √s_NN = 5.02 TeV

Abstract

Event-by-event fluctuations in the elliptic-flow coefficient \({v}_{2}\) are studied in PbPb collisions at \(\sqrt{{s}_{\text{NN}}}=5.02\) TeV using the CMS detector at the CERN LHC. Elliptic-flow probability distributions \(p\left({v}_{2}\right)\) for charged particles with transverse momentum \(0.3<{p}_{T}<3.0\)\(\phantom{\rule{0.2em}{0ex}}\text{GeV}/c\) and pseudorapidity \(|\eta |<1.0\) are determined for different collision centrality classes. The moments of the \(p\left({v}_{2}\right)\) distributions are used to calculate the \({v}_{2}\) 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 \(p\left({v}_{2}\right)\) 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.