Measurement of the Skewness of Elliptic Flow Fluctuations in PbPb Collisions at $\sqrt{s_{NN}} = 5.02~\mathrm{TeV}$

Event-by-event flow harmonics are studied for PbPb collisions at $\sqrt{s_{NN}} = 5.02~\mathrm{TeV}$ using the CMS detector at the LHC. Flow harmonic probability distributions $p\left(v_2\right)$ are obtained using particles of $0.3 \leq p_{T} \leq 3.0~\mathrm{GeV}/c$ and $\left|\eta\right| \leq 1.0$ and are unfolded to remove smearing effects from observed azimuthal particle distributions. Cumulant flow harmonics are determined from the moments of $p\left(v_2\right)$ and used to estimate the standardized elliptic flow skewness in $5\%$ wide centrality bins up to $60\%$. Hydrodynamic models predict that flow fluctuations will lead to a non-Gaussian component in the flow distributions with a negative skew with respect to the reaction plane. A significant negative skewness is observed for all centrality bins as evidenced by a splitting between $v_2\left\{4\right\}$ and $v_2\left\{6\right\}$ cumulants. In addition, elliptic power law distribution fits are made to the $p\left(v_2\right)$ distributions to infer information on the nature of initial-state eccentricity distributions. The elliptic power law parametrization is found to provide a more accurate description of the fluctuations than the Bessel-Gaussian parametrization.