Transverse hydrodynamics with sudden isotropization and freeze-out

TL;DR

This paper proposes a transverse hydrodynamics model with sudden isotropization and freeze-out to describe relativistic heavy-ion collisions, successfully reproducing key experimental observables without requiring full early thermalization.

Contribution

It introduces a novel scenario where only transverse degrees are thermalized initially, with a sudden isotropization and freeze-out, providing a new approach to modeling heavy-ion collision dynamics.

Findings

Reproduces transverse-momentum spectra and elliptic flow v2 at RHIC

Successfully models HBT radii of pions and kaons

Suggests early thermalization is not necessary for observed phenomena

Abstract

We assume that the early evolution of matter produced in relativistic heavy-ion collisions is described by the transverse hydrodynamics. In this approach only transverse degrees of freedom are thermalized, while the longitudinal motion is described by free streaming. When the energy density of the system drops to a certain value, the system becomes isotropic (locally, in the momentum space) and freezes out. The sudden isotropization transition is described with the help of the Landau matching conditions, and the freeze-out is modeled with THERMINATOR. Within this scenario one is able to reproduce in the quite satisfactory way the transverse-momentum spectra, the elliptic flow coefficient v2, and the HBT radii of pions and kaons studied at RHIC (Au+Au collisions at the top beam energy). The obtained results indicate that the system produced at RHIC does not have to be fully thermalized in the early stage. On the other hand, the final three-dimensional thermalization is necessary to reproduce the HBT radius Rlong.