Precision measurement of parity nonconservation in atomic cesium.

Abstract

We have performed a precise measurement of the strength of the parity non-conserving transition amplitude in atomic cesium arising from the weak neutral current interaction. We observe the interference of this amplitude with a larger Stark-induced amplitude on the 6S $\to$ 7S transition in cesium. Our results allow us to place new lower limits on the masses of extra neutral bosons predicted in many grand unified theories. We use a high finesse Fabry-Perot interferometer to increase the laser fields, which increases our PNC signal to noise ratio. The high laser fields also give rise to an unusual asymmetry in our line shape. (The use of a standing wave was originally expected to prevent a line asymmetry). We show that this asymmetry is explained by spatial variations in the ac Stark shifts of the atomic levels, combined with identical spatial variations in the excitation rate.