Spheroidal expansion and freeze-out geometry of heavy-ion collisions in the few-GeV energy regime

TL;DR

This paper introduces a spheroidal expansion model for heavy-ion collisions at a few-GeV energies, improving the description of particle distributions and correlations compared to previous spherical models.

Contribution

It extends the Siemens-Rasmussen blast-wave model to spheroidal symmetry, providing a better fit to experimental data in the few-GeV energy regime.

Findings

Enhanced fit to transverse-mass and rapidity distributions

Qualitative agreement with pion HBT correlation radii

Supports spheroidal symmetry in hadronic systems

Abstract

A spheroidal model of the expansion of hadronic matter produced in heavy-ion collisions in the few-GeV energy regime is proposed. It constitutes an extension of the spherically symmetric Siemens-Rasmussen blast-wave model used in our previous works. The spheroidal form of the expansion, combined with a single-freeze-out scenario, allows for a significantly improved description of both the transverse-mass and the rapidity distributions of the produced particles. With the model parameters determined by the hadronic abundances and spectra, we make further predictions of the pion HBT correlation radii that turn out to be in a qualitative agreement with the measured ones. The overall successful description of the data supports the concept of spheroidal symmetry of the produced hadronic systems in this energy range.