A transverse momentum differential global analysis of Heavy Ion Collisions

TL;DR

This paper performs a comprehensive global analysis of heavy ion collision data, focusing on transverse momentum distributions and flow coefficients, to better understand quark-gluon plasma formation using an extended hydrodynamic model.

Contribution

It introduces a global model fit including a free streaming prehydrodynamic phase with variable velocity, expanding the scope of initial conditions considered in heavy ion collision analysis.

Findings

Free streaming velocity prefers values below the speed of light.

Bulk viscosity is found to be small or consistent with zero.

The model successfully describes transverse momentum dependence of yields and flow coefficients.

Abstract

The understanding of heavy ion collisions and its quark-gluon plasma formation requires a complicated interplay of rich physics in a wealth of experimental data. In this work we compare for identified particles the transverse momentum dependence of both the yields and the anisotropic flow coefficients for both PbPb and $p$Pb collisions. We do this in a global model fit including a free streaming prehydrodynamic phase with variable velocity $v_\text{fs}$, thereby widening the scope of initial conditions. During the hydrodynamic phase we vary three second order transport coefficients. The free streaming velocity has a preference slightly below the speed of light. In this extended model the bulk viscosity is small and even consistent with zero.