Measurement of the 6S-7S transition polarizablility in atomic cesium and an improved test of the standard model

The ratio of the off-diagonal hyperfine amplitude to the tensor transition polarizability (Mhf/beta) for the 6S-7S transition in cesium has been measured. The value of beta=27.024(43)(expt)(67)(theory)a_0^3 is then obtained using an accurate semi-empirical value of Mhf. 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=-72.06(28)(expt) (34)(theory) differs from the prediction of the standard model of elementary particle physics by 2.5 sigma.