Fluctuation and flow probes of early-time correlations in relativistic heavy ion collisions

TL;DR

This paper studies how early-time spatial correlations in heavy ion collisions influence various fluctuation observables, using a combined initial state and hydrodynamic model that matches experimental data.

Contribution

It introduces a unified approach to connect initial state correlations with final fluctuation observables, constraining early collision dynamics.

Findings

Correlation scale matches experimental data across systems.

Hydrodynamic flow modifies initial correlations.

Initial state fluctuations influence multiple observables.

Abstract

Fluctuation and correlation observables are often measured using multi-particle correlation methods and therefore mutually probe the origins of genuine correlations present in multi-particle distribution functions. We investigate the common influence of correlations arising from the spatially inhomogeneous initial state on multiplicity and momentum fluctuations as well as flow fluctuations. Although these observables reflect different aspects of the initial state, taken together, they can constrain a correlation scale set at the earliest moments of the collision. We calculate both the correlation scale in an initial stage Glasma flux tube picture and the modification to these correlations from later stage hydrodynamic flow and find quantitative agreement with experimental measurements over a range of collision systems and energies.