Positron scattering and annihilation on noble gas atoms

TL;DR

This paper uses many-body theory to accurately study positron scattering and annihilation on noble gases below the positronium formation threshold, revealing the importance of correlations and matching experimental data.

Contribution

It provides a comprehensive ab initio analysis of positron interactions with noble gases, including correlation effects and accurate predictions of scattering and annihilation rates.

Findings

Computed elastic scattering cross sections agree with experiments.

Annihilation rate parameter $Z_{eff}$ increases across noble gases, matching experimental trends.

Correlations significantly enhance annihilation rates compared to mean-field models.

Abstract

Positron scattering and annihilation on noble gas atoms below the positronium formation threshold is studied ab initio using many-body theory methods. The many-body theory provides a near-complete understanding of the positron-noble-gas-atom system at these energies and yields accurate numerical results. It accounts for positron-atom and electron-positron correlations, e.g., polarization of the atom by the incident positron and the non-perturbative process of virtual positronium formation. These correlations have a large effect on the scattering dynamics and result in a strong enhancement of the annihilation rates compared to the independent-particle mean-field description. Computed elastic scattering cross sections are found to be in good agreement with recent experimental results and Kohn variational and convergent close-coupling calculations. The calculated values of the annihilation rate parameter $Z_{\rm eff}$ (effective number of electrons participating in annihilation) rise steeply along the sequence of noble gas atoms due to the increasing strength of the correlation effects, and agree well with experimental data.