Chaoticity parameter $\lambda$ in two-pion interferometry in an expanding boson gas model

TL;DR

This paper models the chaoticity parameter in two-pion interferometry within an expanding boson gas, showing how Bose-Einstein condensation affects experimental measurements in heavy-ion collisions.

Contribution

It introduces a mean-field model with harmonic oscillator potential to analyze the impact of Bose-Einstein condensation on the chaoticity parameter in expanding pion gases.

Findings

Condensation can occur at hadronic phase temperatures.

Finite condensation reduces the chaoticity parameter at low momenta.

High momentum $\lambda$ values are only slightly affected.

Abstract

We investigate the chaoticity parameter $\lambda$ in two-pion interferometry in an expanding boson gas model. The degree of Bose-Einstein condensation of identical pions, density distributions, and Hanbury-Brown-Twiss (HBT) correlation functions are calculated for the expanding gas within the mean-field description with a harmonic oscillator potential. The results indicate that a sources with thousands of identical pions may exhibit a degree of Bose-Einstein condensation at the temperatures during the hadronic phase in relativistic heavy-ion collisions. This finite condensation may decrease the chaoticity parameter $\lambda$ in the two-pion interferometry measurements at low pion pair momenta, but influence only slightly the $\lambda$ value at high pion pair momentum.