Geometry of particle emission in UrQMD Ar+Sc collisions at SPS energies

TL;DR

This study analyzes the geometry of particle emission in Ar+Sc collisions at SPS energies using UrQMD simulations, revealing that the two-pion source can be described by Lévy-stable distributions, providing a baseline for future experiments.

Contribution

First application of Lévy-stable source modeling to intermediate Ar+Sc collisions at SPS energies using UrQMD simulations.

Findings

The two-pion source is well described by Lévy-stable distributions.

Extracted Lévy parameters relate to source size, shape, and strength.

Provides a baseline for future experimental measurements in intermediate systems.

Abstract

Over the past few decades, progress in femtoscopy has been driven by the interplay between experimental measurements and theoretical calculations. Measurements provide data to support the theory, while theoretical predictions guide new measurements. In the recent decade, several experiments have confirmed that the two-particle pion-emitting source is well described by L\'evy alpha-stable distributions. To enable theoretical interpretation, phenomenological simulations have been done at RHIC and LHC energies, in large systems such as Au+Au or Pb+Pb, using various available heavy-ion collision models. However, such simulations have not been done in intermediate systems. In this paper, we investigate three-dimensional two-pion pair source distributions from $^{40}$Ar+$^{45}$Sc central collisions at SPS energies, generated with the Ultra-Relativistic Quantum Molecular Dynamics Monte-Carlo event generator. Supplemented by a validation of the simulated hadronic spectra, we find that the pair source can be described with L\'evy-stable distributions. We subsequently interpret the physical meaning of the extracted L\'evy parameters corresponding to the spatial scale, shape, and strength of the source. Our results form a baseline for future experimental measurements in intermediate systems.