Calculations of positronium-atom scattering using a spherical cavity

TL;DR

This study models positronium scattering by noble gases using a spherical cavity approach, calculating phase shifts and cross sections, and finds van der Waals forces do not account for recent experimental results.

Contribution

It introduces a spherical cavity method for positronium-atom scattering and compares the effects of van der Waals interactions with experimental data.

Findings

Van der Waals interaction does not explain recent experimental data.

Calculated scattering phase shifts agree with some existing data.

Method provides a new way to analyze positronium scattering phenomena.

Abstract

Positronium (Ps) scattering by noble-gas atoms (He, Ne, Ar, Kr, and Xe) is studied in the frozen-target approximation and with inclusion of the van der Waals interaction. Single-particle electron and positron states in the field of the target atom are calculated, with the system enclosed by a hard spherical wall. The two-particle Ps wave function is expanded in these states, and the Hamiltonian matrix is diagonalized, giving the Ps energy levels in the cavity. Scattering phase shifts, scattering lengths, and cross sections are extracted from these energies and compared with existing calculations and experimental data. Analysis of the effect of the van der Waals interaction shows that it cannot explain the recent experimental data of Brawley et al. for Ar and Xe [Phys. Rev. Lett. 115, 223201 (2015)].