#### Abstract

The ratio of the off-diagonal hyperfine amplitude to the tensor transition polarizability $\left({M}_{\mathrm{hf}}/\beta \right)$ for the $6S\to 7S$ transition in cesium has been measured. The value of $\beta \phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}27.024\mathrm{}\left(43{)}_{\mathrm{expt}}\right(67{)}_{\mathrm{theor}}{a}_{0}^{3}$ is then obtained using an accurate semiempirical value of ${M}_{\mathrm{hf}}$. This is combined with a previous measurement of parity nonconservation in atomic cesium and previous atomic structure calculations to determine the value of the weak charge. The uncertainties in the atomic structure calculations are updated (and reduced) in light of new experimental tests. The result ${Q}_{W}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}-72.06\mathrm{}\left(28{)}_{\mathrm{expt}}\right(34{)}_{\mathrm{theor}}$ differs from the prediction of the standard model of elementary particle physics by 2.5 $\sigma $.

- Received 20 October 1998

DOI:https://doi.org/10.1103/PhysRevLett.82.2484

©1999 American Physical Society