g J Factor of an Ion: Determination of g J ( He + 4 , 1 S 1 2 2 ) g J ( He 4 , 2 S 1 3 )

Abstract

A measurement of the ${g}_{J}$ factor of the hydrogenlike ion $^{4}\mathrm{He}^{+}$ in its $1^{2}S_{\frac{1}{2}}$ ground state has been made using an optical pumping technique. This represents the first precision measurement of the ${g}_{J}$ factor of a simple atomic ion. The result is $\frac{{g}_{J}(^{4}\mathrm{He}^{+},1^{2}S_{\frac{1}{2}})}{g({e}^{\ensuremath{-}})}=1\ensuremath{-}70.87(30)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$. This value agrees with theory and provides confirmation of the Breit term $\frac{1}{3}{(Z\ensuremath{\alpha})}^{2}$ to within 0.5%.