Counting hot/cold spots in quark-gluon plasma

TL;DR

This paper investigates how initial density fluctuations, especially hot and cold spots, in quark-gluon plasma affect harmonic moment correlations, providing a method to quantify initial inhomogeneities through final state measurements.

Contribution

It introduces a novel approach to quantify initial density inhomogeneities in quark-gluon plasma via correlations of harmonic moments in final state distributions.

Findings

Correlations between harmonic moments are sensitive to hot and cold spot counts.

Hydrodynamic evolution maps initial fluctuations to measurable final state anisotropies.

Measurement of these correlations can quantify initial state inhomogeneity.

Abstract

We study how local fluctuations in the initial states of relativistic heavy-ion collisions manifest themselves in the correlations between different orders of harmonic moments of the density profiles, particularly those involving only odd harmonics which purely arise from initial state fluctuations. We find the strengths of those correlations are sensitive to the number of hot and cold spots in the initial states. Hydrodynamic evolution of the fireball translates initial state geometric anisotropies as well as their correlations into final state momentum anisotropies and correlations. We conclude that the measurement of the correlations between different harmonic moments of final state azimuthal distribution can be employed to quantify the inhomogeneity of the initial density profiles such as the population of hot and cold spots that are produced in high energy nuclear collisions.