Two-pion interferometry for viscous hydrodynamic sources

TL;DR

This study uses viscous hydrodynamics to analyze two-pion interferometry in heavy ion collisions, revealing that bulk viscosity significantly affects the spatial extent of particle-emitting sources, aligning results with experimental data.

Contribution

It introduces a numerical analysis of viscous effects, including bulk viscosity, on two-pion HBT interferometry in (1+1)-D hydrodynamic models of heavy ion collisions.

Findings

Bulk viscosity increases transverse HBT radii.

Shear viscosity has a minimal effect on HBT results.

Longitudinal HBT radius matches experimental data.

Abstract

The space-time evolution of the (1+1)-dimensional viscous hydrodynamics with an initial quark-gluon plasma (QGP) produced in ultrarelativistic heavy ion collisions is studied numerically. The particle-emitting sources undergo a crossover transition from the QGP to hadronic gas. We take into account a usual shear viscosity for the strongly coupled QGP as well as the bulk viscosity which increases significantly in the crossover region. The two-pion Hanbury-Brown-Twiss (HBT) interferometry for the viscous hydrodynamic sources is performed. The HBT analyses indicate that the viscosity effect on the two-pion HBT results is small if only the shear viscosity is taken into consideration in the calculations. The bulk viscosity leads to a larger transverse freeze-out configuration of the pion-emitting sources, and thus increases the transverse HBT radii. The results of the longitudinal HBT radius for the source with Bjorken longitudinal scaling are consistent with the experimental data.