Particle interferometry for relativistic heavy-ion collisions

Abstract

In this report we give a detailed account on Hanbury Brown/Twiss (HBT) particle interferometric methods for relativistic heavy-ion collisions. These exploit identical two-particle correlations to gain access to the space-time geometry and dynamics of the final freeze-out stage. The connection between the measured correlations in momentum space and the phase-space structure of the particle emitter is established, both with and without final state interactions. Suitable Gaussian parametrizations for the two-particle correlation function are derived and the physical interpretation of their parameters is explained. After reviewing various model studies, we show how a combined analysis of single-and two-particle spectra allows to reconstruct the final state of relativistic heavy-ion collisions.

Fitted HBT radii versus space-time variances in flow-dominated models

“…7 the range of this variation, indicated by vertical lines, is plotted as a function of K T . Consistent with the theorem [8] that the spatial RMS variances (6) of the source control the curvature of the correlator C(q q q) at q q q = 0, the blue stars in Fig. 7 coincide with the q max → 0 limit of the fitted 1D radii.…”

“…If the homogeneity region is indeed Gaussian in profile, then the HBT radii agree exactly with appropriate combinations of the root-mean-squared (RMS) variances of its spatial distribution [8]. Given a theoretical model for the freezeout configuration, calculating these space-time variances is much easier than computing and fitting the correlation function.…”

“…Here q o , q s , q l are the relative momentum components in the Bertsch-Pratt ("out-side-long") coordinate system [1,8].…”

Kaon phase space density in heavy-ion collisions

“…Dividing d 3 N k /dp 3 by the Lorentz invariant volume, [1,6] gives the spatially averaged phase space density.…”

Does HBT measure the freeze-out source distribution?

“…The difficulties of explaining these HBT measurements with theoretical models, known as the "HBT puzzles", have been discussed by many authors [2,3]. In these comparisons with theoretical models, it is generally assumed that as a result of multiple scattering, the source distribution measured in an HBT measurement corresponds to a chaotic source at freeze-out, in which a detected hadron suffers its last hadron-hadron scattering.…”