Impact of Atomic Parity Violation Measurements on Precision Electroweak Physics

The impact of atomic parity violation experiments on determination of the weak mixing parameter $\sin^2 \theta$ and the Peskin-Takeuchi parameters $S$ and $T$ is reassessed in the light of recent electroweak measurements at LEP, SLAC, and Fermilab. Since the weak charge $Q_W$ provides unique information on $S$, its determination with a factor of four better accuracy than present levels can have a noticeable effect on global fits. However, the measurement of $\Delta Q_W / Q_W$ for two different isotopes provides primarily information on $\sin^2 \theta$. To specify this quantity to an accuracy of $\pm 0.0004$, comparable to that now provided by other electroweak experiments, one would have to determine $\Delta Q_W/Q_W$ in cesium to about 0.1\% of its value, with comparable demands for other nuclei. The relative merits of absolute measurements of $Q_W$ and isotope ratios for discovering effects of new gauge bosons are noted briefly.