Intensity interferometry for a chaotic source with a collective flow and multiple scattering

Abstract

We study the effects of a collective flow and multiple scattering on two-particle correlation measurements in Hanbury-Brown–Twiss (HBT) intensity interferometry. While the derivation in this paper is not rigorous, we propose a semi-quantitative derivation to shed further light on the interesting RHIC HBT puzzle. We find that under a collective flow the effective source distribution in a two-particle correlation measurement depends on the initial source distribution. In addition, it depends on a collective flow phase function which consists of terms that tend to cancel each other. As the detected particles traverse from the source point to the freeze-out point, they are subject to multiple scattering with medium particles. We examine the effects of multiple scattering on HBT correlations. Applying the Glauber theory to multiple scattering at high energies and the optical model at intermediate energies, we find that multiple scattering leads to an absorption and an effective density distribution that depends on the initial source distribution.