Non-Gaussian elliptic-flow fluctuations in PbPb collisions at $\sqrt{\smash[b]{s_{_\text{NN}}}} =$ 5.02 TeV

TL;DR

This study investigates non-Gaussian fluctuations in elliptic flow in PbPb collisions at 5.02 TeV, revealing complex initial-state fluctuation behavior through detailed statistical analysis of flow distributions.

Contribution

It provides the first detailed measurement of non-Gaussian elliptic-flow fluctuations and compares different models to characterize initial-state spatial anisotropy.

Findings

Non-Gaussian features observed in flow fluctuations.

Higher-order cumulants show rank ordering consistent with non-Gaussian behavior.

Flow distribution fits suggest complex initial-state spatial anisotropy.

Abstract

Event-by-event fluctuations in the elliptic-flow coefficient $v_2$ are studied in PbPb collisions at $\sqrt{s_{_\text{NN}}} =$ 5.02 TeV using the CMS detector at the CERN LHC. Elliptic-flow probability distributions ${p}(v_2)$ for charged particles with transverse momentum 0.3 $< p_\mathrm{T} <$ 3.0 GeV and pseudorapidity $| \eta | <$ 1.0 are determined for different collision centrality classes. The moments of the ${p}(v_2)$ distributions are used to calculate the $v_{2}$ coefficients based on cumulant orders 2, 4, 6, and 8. A rank ordering of the higher-order cumulant results and nonzero standardized skewness values obtained for the ${p}(v_2)$ distributions indicate non-Gaussian initial-state fluctuation behavior. Bessel-Gaussian and elliptic power fits to the flow distributions are studied to characterize the initial-state spatial anisotropy.