Skewness of elliptic flow fluctuations

Abstract

Using event-by-event hydrodynamic calculations, we find that the fluctuations of the elliptic flow ($v_2$) in the reaction plane have a negative skew. We compare the skewness of $v_2$ fluctuations to that of initial eccentricity fluctuations. We show that skewness is the main effect lifting the degeneracy between higher-order cumulants, with negative skew corresponding to the hierarchy $v_2\{4\}>v_2\{6\}$ observed in Pb+Pb collisions at the LHC. We describe how the skewness can be measured experimentally and show that hydrodynamics naturally reproduces its magnitude and centrality dependence.

Comments: 7 pages, 6 figures. v2: We now use data from Fig.9b of arXiv:1408.4342 instead of using data from Fig.9a. v3: Published version. Overall revision of the text. Added discussion after Figure 6. Statistics of events is increased in central collisions