Skewness of elliptic flow fluctuations

TL;DR

This paper investigates the negative skewness in elliptic flow fluctuations using hydrodynamic models, revealing its role in understanding flow cumulants and matching experimental observations.

Contribution

It demonstrates that skewness explains the hierarchy of flow cumulants and shows hydrodynamics reproduces the observed skewness magnitude and centrality dependence.

Findings

Negative skewness in $v_2$ fluctuations identified

Skewness explains the hierarchy of flow cumulants

Hydrodynamics reproduces skewness magnitude and dependence

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.