Measurement of the Width and Skewness of Elliptic Flow Fluctuations in PbPb Collisions at 5.02 TeV with CMS

摘要

Flow harmonic fluctuations are studied for PbPb collisions at root S-NN = 5.02 TeV using the CMS detector at the LHC. Flow harmonic probability distributions p (v(2)) are obtained by unfolding smearing effects from observed azimuthal anisotropy distributions using particles of 0.3 < p(T) < 3.0 GeV/c and vertical bar eta vertical bar < 1.0. Cumulant flow harmonics are determined from the moments of p (v(2)) and used to estimate the standardized elliptic flow skewness. Hydrodynamic models predict this skewness to be negative with respect to the reaction plane. A statistically significant negative skewness is observed for all centrality bins as evidenced by a splitting between v(2) {4), v(2) {6), and v(2) {8} cumulants. Elliptic power law distribution fits are made to p (v(2)) distributions to infer information on the nature of initial-state eccentricity distributions and found to provide a more accurate description of the fluctuations than a Bessel-Gaussian parametrization.