S-wave elastic scattering of ${\it o}$-Ps from $\text{H}_2$ at low energy

TL;DR

This study uses advanced quantum mechanical methods to accurately calculate low-energy elastic scattering parameters of ortho-positronium from hydrogen molecules, aligning well with experimental data.

Contribution

First-principles quantum calculations of S-wave phase shifts and annihilation parameters for o-Ps scattering from H₂ at low energies.

Findings

Determined S-wave scattering length A_s=2.06a_0.

Calculated zero-energy pick-off annihilation parameter ^1Z_eff=0.1858.

Results agree with experimental measurements.

Abstract

The confined variational method is applied to investigate the low-energy elastic scattering of ortho-positronium from $\text{H}_2$ by first-principles quantum mechanics. Describing the correlation effect with explicitly correlated Gaussians, we obtain accurate $S$-wave phase shifts and pick-off annihilation parameters for different incident momenta. By a least-squares fit of the data to the effective-range theory, we determine the $S$-wave scattering length, $A_s=2.06a_0$, and the zero-energy value of the pick-off annihilation parameter, $^1\!\text{Z}_\text{eff}=0.1858$. The obtained $^1\!\text{Z}_\text{eff}$ agrees well with the precise experimental value of $0.186(1)$ (J.\ Phys.\ B \textbf{16}, 4065 (1983)) and the obtained $A_s$ agrees well with the value of $2.1(2)a_0$ estimated from the average experimental momentum-transfer cross section for Ps energy below 0.3 eV (J.\ Phys.\ B \textbf{36}, 4191 (2003)).