New results on collectivity with CMS

TL;DR

This paper measures nonlinear flow response coefficients and elliptic flow skewness in PbPb collisions at 2.76 and 5.02 TeV, providing insights into the collective behavior of quark-gluon plasma and testing hydrodynamic models.

Contribution

It presents new measurements of nonlinear flow coefficients and flow skewness at different energies, comparing results with hydrodynamic models to improve understanding of collision dynamics.

Findings

Significant negative skewness observed in elliptic flow at 5.02 TeV.

Nonlinear response coefficients vary with transverse momentum and centrality.

Results favor hydrodynamic models with specific shear viscosity to entropy density ratios.

Abstract

Nonlinear response coefficients of higher-order anisotropy harmonics for charged particles are measured in PbPb collisions at 2.76 and 5.02 TeV as a function of transverse momentum and collision centrality. The nonlinear response coefficients are obtained from $v_{n}$ harmonics measured with respect to their own plane and the mixed harmonics. Additionally, at 5.02 TeV PbPb collisions, a significant negative skewness is observed by a fine splitting between $v_{2}\{4\}$ and $v_{2}\{6\}$ cumulants. The elliptic flow skewness is measured up to 60\% centrality. The results are compared with hydrodynamic models with different shear viscosity to entropy density ratios and initial conditions.