PHENIX measurements of 3D emission source functions in Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV

TL;DR

This paper employs advanced 3D source imaging to analyze pion emission in gold-gold collisions at high energy, revealing non-Gaussian features and providing insights into the phase transition nature of the quark-gluon plasma.

Contribution

It introduces a novel 3D source imaging technique to extract detailed emission source functions in heavy-ion collisions, challenging previous phase transition predictions.

Findings

Identification of a non-Gaussian tail in the source function

Estimates of emission source size, breakup time, and duration

Results suggest a crossover, not first-order, phase transition

Abstract

A state-of-the-art 3D source imaging technique is used to extract the 3D two-pion source function in central and mid-central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. The source function indicates a previously unresolved non-Gaussian tail in the directions of the pion pair transverse momentum (out) and along the beam (long). Model comparisons give robust estimates for several characteristics of the emission source, including its transverse size, its mean proper breakup time $\tau$ and its emission duration $\Delta\tau$. These estimates are incompatible with the predictions for a first order phase transition. However, they point to significant relative emission times which could result from a crossover phase transition.