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arXiv · 2606.29253

Low-energy positron scattering from metastable helium

Ning-Ning Gao·Hui-Li Han·Ting-Yun Shi·Li-Yan Tang
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Abstract

Low-energy positron scattering from singlet and triplet metastable He($1s2s$) is investigated using the $R$-matrix propagation method in hyperspherical coordinates. Elastic and positronium-formation cross sections are reported, and near-threshold resonance structures are analyzed in terms of eigenphase sums and the time-delay matrix. For the triplet target, the calculated cross sections are in agreement with available convergent-close-coupling results and display the expected threshold behavior. Beyond the known $S$-wave features, Feshbach resonance series in higher partial waves extending up to highly excited atomic thresholds are systematically identified. The time-delay matrix further uncovers hidden resonances that produce obvious structures in the positronium-formation cross sections.

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Ning-Ning Gao, Hui-Li Han, Ting-Yun Shi, Li-Yan Tang. 2026-06-28. Low-energy positron scattering from metastable helium. https://arxiv.org/abs/2606.29253

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