Imaging of granular sources in high energy heavy ion collisions

TL;DR

This paper explores the imaging of granular sources in high energy heavy ion collisions, demonstrating the technique's effectiveness at RHIC energies and its ability to distinguish granular structures from simpler models.

Contribution

It introduces a method to identify granular structures in pion-emitting sources using two-pion source functions and imaging techniques, with application to AGS and RHIC collision data.

Findings

Granular sources show a two-tiered structure in source functions.

Imaging technique effectively probes granular structures.

Data at RHIC energies favor granular source models over Gaussian.

Abstract

We investigate the source imaging for a granular pion-emitting source model in high energy heavy ion collisions. The two-pion source functions of the granular sources exhibit a two-tiered structure. Using a parametrized formula of granular two-pion source function, we examine the two-tiered structure of the source functions for the imaging data of Au+Au collisions at Alternating Gradient Synchrotron (AGS) and Relativistic Heavy Ion Collider (RHIC). We find that the imaging technique introduced by Brown and Danielewicz is suitable for probing the granular structure of the sources. Our data-fitting results indicate that there is not visible granularity for the sources at AGS energies. However, the data for the RHIC collisions with the selections of $40 < {\rm centrality} < 90%$ and $0.20<k_{\rm T}<0.36$ GeV/c are better described by the model with granular emission than that of one Gaussian. The model with granular source has more parameters than the simple Gaussian, hence can describe more complicated shapes.