The Long Slow Death of the HBT Puzzle

TL;DR

This paper addresses the HBT puzzle in heavy-ion collisions by using a hybrid model with viscous hydrodynamics and hadronic cascade, incorporating early acceleration, viscosity, and a stiffer equation of state to better match experimental data.

Contribution

It demonstrates that including viscosity, early acceleration, and a stiffer equation of state in hybrid models significantly improves agreement with femtoscopic measurements.

Findings

Source sizes align more closely with experimental data

Inclusion of viscosity reduces discrepancies

Early acceleration impacts femtoscopic observables

Abstract

Femtoscopic measurements at RHIC have been hailed as a source of insight into the bulk properties of QCD matter. However, hydrodynamic models, which have been successful in reproducing other observables have failed to satisfactorily explain femtoscopic two-particle correlation measurements. This failure has been labeled the "HBT puzzle". In this talk, I present correlations using a hybrid model composed of a viscous hydrodynamic module and a hadronic cascade. After incorporating early acceleration, viscosity and a stiffer equation of state, the extracted source sizes come much closer to experiment.