Precision measurement of relativistic and QED effects in heliumlike beryllium

Abstract

We have used fast-ion-beam laser spectroscopy to measure the 1s2${\mathit{s}}^{3}$s-1s2${\mathit{p}}^{3}$${\mathit{P}}^{\mathit{o}}$ intervals in Be iii to an absolute accuracy of 1 part in ${10}^{8}$. Our results are (in ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$): \ensuremath{\sigma}(1s2${\mathit{s}}^{3}$${\mathit{S}}_{1}$-1s2${\mathit{p}}^{3}$${\mathit{P}}_{0}^{\mathit{o}}$=28 864.6120(4), \ensuremath{\sigma}(1s2${\mathit{s}}^{3}$${\mathit{S}}_{1\mathrm{\ensuremath{-}}}$1s2${\mathit{p}}^{3}$${\mathit{P}}_{1}^{\mathit{o}}$=26 853.0534(3), \ensuremath{\sigma}(1s2${\mathit{s}}^{3}$${\mathit{S}}_{1\mathrm{\ensuremath{-}}}$1s2${\mathit{p}}^{3}$${\mathit{P}}_{2}^{\mathit{o}}$) =26 867.9484(3). These results are an improvement over previous measurements by nearly 3 orders of magnitude and show evidence of uncalculated O(${\mathrm{\ensuremath{\alpha}}}^{4}$${\mathit{Z}}^{4}$) relativistic corrections. Once those terms are computed, our measurement will allow QED calculations in two-electron atoms to be tested at the 100 ppm level.