Effects of a phase transition on HBT correlations in an integrated Boltzmann+Hydrodynamics approach

TL;DR

This study investigates how phase transitions influence HBT radii in heavy ion collisions using a hybrid Boltzmann+hydrodynamics model, revealing sensitivities to the equation of state but no support for a QGP phase transition based on current data.

Contribution

It introduces a hybrid (3+1)d Boltzmann+hydrodynamics approach to analyze HBT correlations, comparing different equations of state and freeze-out procedures in heavy ion collisions.

Findings

HBT radii are insensitive to freeze-out details when final hadronic interactions are included.

HBT radii are sensitive to the equation of state during hydrodynamic evolution.

Data does not support increased lifetime due to a QGP phase transition with a Bag Model EoS.

Abstract

A systematic study of HBT radii of pions, produced in heavy ion collisions in the intermediate energy regime (SPS), from an integrated (3+1)d Boltzmann+hydrodynamics approach is presented. The calculations in this hybrid approach, incorporating an hydrodynamic stage into the Ultra-relativistic Quantum Molecular Dynamics transport model, allow for a comparison of different equations of state retaining the same initial conditions and final freeze-out. The results are also compared to the pure cascade transport model calculations in the context of the available data. Furthermore, the effect of different treatments of the hydrodynamic freeze-out procedure on the HBT radii are investigated. It is found that the HBT radii are essentially insensitive to the details of the freeze-out prescription as long as the final hadronic interactions in the cascade are taken into account. The HBT radii $R_L$ and $R_O$ and the $R_O/R_S$ ratio are sensitive to the EoS that is employed during the hydrodynamic evolution. We conclude that the increased lifetime in case of a phase transition to a QGP (via a Bag Model equation of state) is not supported by the available data.