Relating Measurable Correlations in Heavy Ion Collisions to Bulk Properties of Equilibrated QCD Matter

TL;DR

This paper explores how measurable correlations in heavy ion collisions relate to the bulk properties of equilibrated QCD matter, extending previous work on conserved charge fluctuations to include momentum and energy correlations.

Contribution

It introduces a framework to connect fluctuations of momentum and energy in heavy ion collisions to the bulk properties of QCD matter, considering finite transport times and simple models.

Findings

Correlations in relative spatial rapidity are sensitive to the equation of state.

The approach links experimental energy correlations to theoretical susceptibilities.

Extensions to realistic models and experimental comparisons are discussed.

Abstract

In order to compare theoretical calculations of thermal fluctuations of conserved quantities, such as charge susceptibilities or the specific heat, to experimentally measured correlations and fluctuations in heavy ion collisions, one must confront the reality of changing conditions within the collision environment, and transport of conserved quantities within the finite duration of the expansion and dissolution of the reaction. In previous work, fluctuations of conserved charges from lattice calculations, where charge is allowed to fluctuate within the designated volume consistent with the grand canonical ensemble, was linked to correlations in heavy-ion collisions, which accounted for the finite time with which to transport absolutely conserved quanatities. In this case details of the correlations were related to the evolution of the susceptibility. In this work, this paradigm is extended to compare fluctuations of momentum or energy to transverse energy correlations that can be measured in heavy-ion collisions. The sensitivity of these correlations to the equation of state, viscosity and diffusion is illustrated by considering simple models without transverse expansion. Only correlations in relative spatial rapidity are discussed here, but the prospects for extending these ideas to realistic calculations and for making realistic connections with experiment are discussed.