QED <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>m</mml:mi><mml:msup><mml:mi>α</mml:mi><mml:mn>7</mml:mn></mml:msup></mml:mrow></mml:math> effects for triplet states of heliumlike ions
V. A. Yerokhin, Vojtěch Patkóš, Krzysztof Pachucki
Abstract
We perform ab initio calculations of the QED effects of order $m{\ensuremath{\alpha}}^{7}$ for the $2^{3}S$ and $2^{3}P$ states of He-like ions. The computed effects are combined with previously calculated energies [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 $2\phantom{\rule{0.16em}{0ex}}^{3}S\ensuremath{-}2\phantom{\rule{0.16em}{0ex}}^{3}P_{0,2}$ transition energies are in good agreement with available experimental results and with previous calculations performed to all orders in the nuclear binding strength parameter $Z\ensuremath{\alpha}$. For the ionization energies, however, we find some inconsistency between the $Z\ensuremath{\alpha}$-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\ifmmode \check{s}\else \v{s}\fi{} et al., Phys. Rev. A 103, 042809 (2021)].