Highly-anisotropic hydrodynamics in 3+1 space-time dimensions

TL;DR

This paper demonstrates that initial pressure anisotropy in ultra-relativistic heavy-ion collisions can be effectively masked by adjusting initial conditions, challenging the necessity of early thermalization to explain observed hadronic data.

Contribution

It introduces a 3+1D highly-anisotropic hydrodynamics model showing that early pressure anisotropy effects can be compensated, reducing the need for early thermalization assumptions.

Findings

Final hadronic observables are insensitive to initial pressure anisotropy.

Early thermalization is not required to reproduce elliptic flow v_2.

Complete thermalization likely occurs around 1-2 fm/c, consistent with microscopic models.

Abstract

Recently formulated model of highly-anisotropic and strongly dissipative hydrodynamics is used in 3+1 dimensions to study behavior of matter produced in ultra-relativistic heavy-ion collisions. We search for possible effects of the initial high anisotropy of pressure on the final soft-hadronic observables. We find that by appropriate adjustment of the initial energy density and/or the initial pseudorapidity distributions, the effects of the initial anisotropy of pressure may be easily compensated and the final hadronic observables become insensitive to early dynamics. Our results indicate that the early thermalization assumption is not necessary to describe hadronic data, in particular, to reproduce the measured elliptic flow v_2. The complete thermalization of matter (local equilibration) may take place only at the times of about 1-2 fm/c, in agreement with the results of microscopic models.