Higher order cumulants of transverse momentum and harmonic flow in relativistic heavy ion collisions

TL;DR

This paper investigates higher order symmetric cumulants of collective observables in heavy ion collisions, using hydrodynamic models and initial state correlations to understand the underlying physics.

Contribution

It introduces a method to calculate third and fourth order cumulants of key observables and uses a linear predictor to connect initial state moments with final state correlations.

Findings

Third and fourth order cumulants are computed in hydrodynamic models.

Symmetric cumulants normalized by averages or standard deviations reveal initial state correlations.

The approach provides a fine tool for studying initial state effects in heavy ion collisions.

Abstract

Higher order symmetric cumulants of global collective observables in heavy ion collisions are studied. The symmetric cumulants can be straightforwardly constructed for scalar observables: the average transverse momentum, the multiplicity, and the squares of harmonic flow vectors. Third and fourth order cumulants are calculated in the hydrodynamic model. A linear predictor of the average transverse momentum and harmonic flow coefficients in a collision is used to predict the value of the cumulants from the moments of the initial distribution. The symmetric cumulants divided by the averages (or the standard deviations) of the considered observables can be used as a fine tool to study correlations present in the initial state of the collision.