Higher-order recoil corrections for triplet states of the helium atom

TL;DR

This paper calculates higher-order nuclear recoil corrections for helium triplet states, refining isotope shift predictions and aiding in determining helium nuclear charge radii from spectroscopy.

Contribution

It introduces a new calculation of recoil corrections of order α^6 m^2/M for helium triplet states, advancing theoretical accuracy.

Findings

Improved prediction of isotope shift for 2^3S-2^3P transition

Enhanced understanding of helium nuclear charge radii difference

Progress towards direct helium nucleus charge radius measurement

Abstract

Nuclear recoil corrections of order $\alpha^6\,m^2/M$ are calculated for the lowest-lying triplet states of the helium atom. It improves the theoretical prediction for the isotope shift of the $2^3S-2^3P$ transition energy and influences the determination of the ${}^3\textrm{He}-{}^4\textrm{He}$ nuclear charge radii difference. This calculation is a step forward on the way towards the direct determination of the charge radius of the helium nucleus from spectroscopic measurements.