Impact of atomic parity violation measurements on precision electroweak physics

The impact of atomic parity violation experiments on the 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 CERN LEP, SLAC, and Fermilab. Since the weak charge $Q_W$ provides unique information on $S$, its determination with a factor of 4 better accuracy than present levels can have a noticeable effect on global fits. However, the measurement of $\frac{\Delta Q_W}{Q_W}$ for two different isotopes provides primarily information on ${sin}^2\theta$. To specify this quantity to an accuracy of ±0.0004, comparable to that now provided by other electroweak experiments, one would have to determine $\frac{\Delta Q_W}{Q_W}$ 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.