Lifetime of the $2^3$${\mathit{S}}_1$ state of heliumlike ${}_{}{}^{79}{}_{}{}^{}\mathrm{Br}_{}^{33+}{}_{}{}^{}$

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.