Azimuthal-sensitive three-dimensional HBT radius in Au-Au collisions at $E_{beam} = 1.23$$A$ GeV by the IQMD model

TL;DR

This study uses the IQMD model to simulate Au-Au collisions at 1.23A GeV, analyzing pion emission patterns and HBT radii to understand the collision dynamics and spatial asymmetries.

Contribution

It provides a detailed analysis of azimuthal-sensitive 3D HBT radii and emission eccentricities in heavy-ion collisions at intermediate energies, aligning with experimental data.

Findings

The model reproduces pion spectra and apparent temperatures consistent with HADES data.

The azimuthal dependence of HBT radii reveals emission asymmetries.

Eccentricity analysis shows increased xy-plane asymmetry with higher transverse momentum and centrality.

Abstract

We used an Isospin dependent Quantum Molecular Dynamics (IQMD) model to simulate Au + Au collisions at beam energy $E_{beam}$ = 1.23$A$ GeV, which corresponds to center of mass energy $\sqrt{s_{NN}} = 2.4$ GeV. Firstly, we obtained reasonable rapidity and transverse mass spectra of $\pi^-$ and $\pi^+$ as well as "apparent" temperature parameters in comparison with the HADES data. Then by calculating three-dimensional Hanbury Brown and Twiss (HBT) radius of same charged pion-pairs, we obtained the square difference of outward radius and sideward radius, i.e. $R_{out}^{2}-R_{side}^{2}$, as well as the freeze-out volume ($V_{fo}$), which were basically consistent with the trend of HADES experimental results. The azimuthal dependence of the HBT radii was also calculated by a matrix method, and corrected by the rotation matrix. In addition, the eccentricities of the $xy$- and $zy$- planes of pion-pair emissions were also extracted for different pair transverse momentum and collision centrality, which show that the $xy$-eccentricity increases with pair transverse momentum as well as centrality but not for $zy$-eccentricity, indicating a more asymmetric transverse emission of particle-pairs with higher transverse momentum in off-central collisions.