QED $m\alpha^7$ effects for triplet states of helium-like ions

TL;DR

This paper calculates high-order quantum electrodynamics (QED) effects for helium-like ions, significantly improving theoretical accuracy and comparing results with experiments, revealing some discrepancies in ionization energies.

Contribution

The study provides ab initio calculations of $m\alpha^7$ QED effects for helium-like ions, enhancing the precision of theoretical energy predictions.

Findings

Good agreement with experimental transition energies.

Discrepancies observed in ionization energy calculations.

Improved theoretical accuracy by an order of magnitude.

Abstract

We perform ab initio calculations of the QED effects of order $m\alpha^7$ for the $2^3S$ and $2^3P$ states of He-like ions. The computed effects are combined with previously calculated energies from [V. A. Yerokhin and K. Pachucki, Phys. Rev. A 81, 022507 (2010)], thus improving the theoretical accuracy by an order of magnitude. The obtained theoretical values for the $2^3S$-$2^3P_{0,2}$ transition energies are in good agreement with available experimental results and with previous calculations performed to all orders in the nuclear binding strength parameter $Z\alpha$. For the ionization energies, however, we find some inconsistency between the $Z\alpha$-expansion and all-order calculations, which might be related to a similar discrepancy between the theoretical and experimental results for the ionization energies of helium [V. Patk\'o\v{s} et al., Phys. Rev. A 103, 042809 (2021)].