Fitted Hanbury-Brown–Twiss radii versus space-time variances in flow-dominated models

Abstract

The inability of otherwise successful dynamical models to reproduce the Hanbury-Brown-Twiss (HBT) radii extracted from two-particle correlations measured at the Relativistic Heavy Ion Collider (RHIC) is known as the RHIC HBT Puzzle. Most comparisons between models and experiment exploit the fact that for Gaussian sources the HBT radii agree with certain combinations of the space-time widths of the source that can be directly computed from the emission function without having to evaluate, at significant expense, the two-particle correlation function. We here study the validity of this approach for realistic emission function models, some of which exhibit significant deviations from simple Gaussian behavior. By Fourier transforming the emission function, we compute the two-particle correlation function, and fit it with a Gaussian to partially mimic the procedure used for measured correlation functions. We describe a novel algorithm to perform this Gaussian fit analytically. We find that for realistic hydrodynamic models the HBT radii extracted from this procedure agree better with the data than the values previously extracted from the space-time widths of the emission function. Although serious discrepancies between the calculated and the measured HBT radii remain, we show that a more apples-to-apples comparison of models with data can play an important role in any eventually successful theoretical description of RHIC HBT data.

Determining fundamental properties of matter created in ultrarelativistic heavy-ion collisions

“…Finally, the procedure of extracting Gaussian radii from correlation functions can affect the answer. Since the actual correlations are not Gaussian, the fitted radii can depend on how various parts of the correlation function are weighted in the fit [65]. The calculations could be improved by using the same binnings and cuts as was used for the data, e.g., correlations at very small momenta are cut off experimentally due to two-track resolution issues.…”

Analysis of pion elliptic flow and Hanbury-Brown–Twiss interferometry in a granular quark-gluon plasma droplet model

“…The HBT puzzle is contrary to many earlier theoretical expectations [16,17,18,19,20,21]. Various models have been put forth to explain the HBT puzzle [22,23,24,25,26,27,28,29,30,31,32,33,34]. There have also been many attempts to provide a consistent explanation for both the elliptic flow and HBT measurements at RHIC [35,36,37,38,39,40,41].…”

Interferometric signatures of the temperature dependence of the specific shear viscosity in heavy-ion collisions

“…This approximation, which holds exactly only for Gaussian sources [12], is known to be sufficient to discern qualitative features of the HBT radii and their K T dependences, although it is not accurate enough for quantitative comparisons with experimental data [17].…”