Observable consequences of event-by-event fluctuations of HBT radii

TL;DR

This paper investigates how event-by-event fluctuations of HBT radii in heavy-ion collisions can be experimentally observed and related to the properties of quark-gluon plasma, especially its shear viscosity, using hydrodynamic simulations.

Contribution

It introduces a method to measure the mean and variance of HBT radii fluctuations and studies their sensitivity to the temperature-dependent shear viscosity of QGP.

Findings

Mean and variance of HBT radii are sensitive to shear viscosity.

Proposed method can experimentally determine fluctuation characteristics.

Sensitivity levels comparable to flow measurements (10-20%).

Abstract

We explore the effects of event-by-event fluctuations of Hanbury Brown-Twiss (HBT) radii and show how they can be observed experimentally. The relation of measured HBT radii extracted from ensemble-averaged correlation functions to the mean of their event-by-event probability distribution is clarified. We propose a method to experimentally determine the mean and variance of this distribution and test it on an ensemble of fluctuating events generated with the viscous hydrodynamic code VISH2+1. Using the same code, the sensitivity of the mean and variance of the HBT radii to the specific QGP shear viscosity $\eta/s$ is studied. We report sensitivity of the mean pion HBT radii and their variances to the temperature dependence of $\eta/s$ near the quark-hadron transition at a level similar (10-20%) to that which was previously observed for elliptic and quadrangular flow of charged hadrons [1].