[Paper Review] Fine tuning two particle interferometry. 2. Opacity effects

Boris Tomášik, Ulrich Heinz|arXiv (Cornell University)|May 7, 1998

High-Energy Particle Collisions Research3 citations

TL;DR

This paper investigates opacity effects in two-particle interferometry using a model of pion sources in heavy-ion collisions. It demonstrates that the temporal radius parameter R₀² is highly sensitive to source opacity, and analysis of CERN Pb+Pb data at 158 A GeV/c indicates a non-opaque source. A modified YKP parametrization is proposed to address inapplicability in opaque systems, preserving physical interpretability of parameters.

ABSTRACT

We present a model study of single-particle spectra and two-particle Bose-Einstein correlations for opaque sources. We study the transverse mass dependence of the correlation radii R_\\perp, R_\\parallel and R_0 in the YKP parametrization and find a strong sensitivity of the temporal radius parameter R_0^2 to the source opacity. A simple comparison with the published data from 158 A GeV/c Pb+Pb collisions at CERN indicates that the pion source created in these collisions emits particles from the whole reaction volume and is not opaque. For opaque sources we find certain regions of inapplicability of the YKP parametrization which can be avoided by a slightly different parametrization for the correlator. The physical meaning of the modified parameters is briefly discussed.

Motivation & Objective

• To investigate the impact of source opacity on two-particle Bose-Einstein correlations in heavy-ion collisions.
• To assess the validity of the YKP parametrization for opaque sources in interferometric analyses.
• To determine whether experimental data from 158 A GeV/c Pb+Pb collisions indicate an opaque or non-opaque pion source.
• To propose a modified parametrization of the correlation function that remains applicable in opaque source scenarios.
• To clarify the physical meaning of the modified parameters in opaque systems.

Proposed method

• A model study of single-particle spectra and two-particle correlations is conducted for opaque sources.
• The YKP parametrization is applied to extract correlation radii R⊥, R∥, and R₀ from simulated data.
• The transverse mass dependence of R⊥, R∥, and R₀² is analyzed to probe opacity effects.
• The temporal radius R₀² is used as a key diagnostic for source opacity.
• A modified parametrization of the correlation function is derived to maintain applicability in opaque regimes.
• The modified parameters are interpreted in terms of physical source properties such as emission duration and spatial extent.

Experimental results

Research questions

• RQ1 How does source opacity affect the extracted values of correlation radii R⊥, R∥, and R₀ in the YKP parametrization?
• RQ2 To what extent is the YKP parametrization invalid for opaque sources, and where do its limitations arise?
• RQ3 What is the opacity status of the pion source produced in 158 A GeV/c Pb+Pb collisions based on R₀² sensitivity?
• RQ4 Can a modified parametrization restore the applicability of interferometric analysis in opaque systems?
• RQ5 What is the physical interpretation of the parameters in the modified correlation function?

Key findings

• The temporal radius parameter R₀² shows strong sensitivity to source opacity, making it a key diagnostic for opacity.
• Analysis of CERN Pb+Pb data at 158 A GeV/c indicates that the pion source is not opaque, as R₀² values are consistent with emission from the full reaction volume.
• The standard YKP parametrization becomes inapplicable in certain regions for opaque sources due to unphysical parameter behavior.
• A slightly modified parametrization of the correlation function is proposed to maintain validity across all opacity regimes.
• The modified parameters retain physical meaning, allowing consistent interpretation of emission duration and spatial extent in opaque systems.
• The study establishes that opacity effects must be accounted for in interferometric analyses to avoid misinterpretation of source geometry and dynamics.