Resolving the HBT Puzzle in Relativistic Heavy Ion Collision

TL;DR

This paper investigates the HBT puzzle in relativistic heavy ion collisions, revealing it results from multiple factors like pre-thermal acceleration, stiffer equations of state, and viscous effects, rather than a single hydrodynamic failure.

Contribution

It demonstrates that resolving the HBT puzzle requires considering multiple effects in hydrodynamic models, not just a single modification.

Findings

HBT puzzle arises from combined effects in hydrodynamics

Pre-thermalized acceleration impacts femtoscopic measurements

Viscous corrections and stiffer EoS are crucial for accurate modeling

Abstract

Two particle correlation data from the Relativistic Heavy Ion Collider have provided detailed femtoscopic information describing the space-time structure of the emission of pions. This data had avoided description with hydrodynamic-based approaches, in contrast to the success of hydrodynamics in reproducing other classes of observables. This failure has inspired the term ``HBT puzzle'', where HBT refers to femtoscopic studies which were originally based on Hanbury-Brown Twiss interferometry. Here, the puzzle is shown to originate not from a single shortcoming of hydrodynamic models, but the combination of several effects: mainly including pre-thermalized acceleration, using a stiffer equation of state, and adding viscous corrections.