Determining initial-state fluctuations from flow measurements in heavy-ion collisions

TL;DR

This paper introduces new flow observables from multiparticle azimuthal correlations in heavy-ion collisions, enabling more precise characterization of initial-state fluctuations and medium properties, with predictions from Monte Carlo models compared to data.

Contribution

It proposes novel joint correlation observables between flow coefficients to better constrain initial-state fluctuations in heavy-ion collisions.

Findings

New flow observables are proposed and measured.

Ratios of observables reduce sensitivity to hydrodynamic response.

Model predictions are compared with experimental data.

Abstract

We present a number of independent flow observables that can be measured using multiparticle azimuthal correlations in heavy-ion collisions. Some of these observables are already well known, such as v2{2} and v2{4}, but most are new--in particular, joint correlations between v1, v2 and v3. Taken together, these measurements will allow for a more precise determination of the medium properties than is currently possible. In particular, by taking ratios of these observables, we construct quantities which are less sensitive to the hydrodynamic response of the medium, and thus more directly characterize the initial-state fluctuations of the event shape, which may constrain models for early-time, non-equilibrium QCD dynamics. We present predictions for these ratios using two Monte-Carlo models, and compare to available data.