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.