Lifetime of the23S1state of heliumlikeBr33+79

We report a measurement of the lifetime of the $2^3$ ${\mathit{S}}_1$ level in heliumlike ${}_{}{}^{79}{}_{}{}^{}\mathrm{Br}_{}^{33+}{}_{}{}^{}$. Our result is ${\mathrm{\tau }}^{\exp }$(2 ${}_{}{}^3{}_{}{}^{}$ ${\mathit{S}}_1$)=224.1(7.1) ps. This agrees with the theoretical calculation of 230(2) ps and provides a test of O(${\mathit{Z}}^2$ ${\mathrm{\alpha }}^2$) corrections to the lifetime. The experimental error is dominated by uncertainties in the correction required to account for long-lived cascades from highly excited states.