HIGH-PRECISION MEASUREMENT OF PARITY NONCONSERVING OPTICAL-ROTATION IN ATOMIC LEAD

We have completed a new measurement of parity nonconserving (PNC) opti cal rotation near the 1.279 mum magnetic dipole absorption line in lea d, improving earlier results on this line by a factor of 20. We find t he ratio of the PNC E1 amplitude to the Ml amplitude to be R = (-9.86/-0.12) x 10(-8), consistent with theoretical predictions. Difficultie s in the atomic theory of lead presently limit the extent to which our result tests the standard model of electroweak interactions. The ampl itude of the nuclear spin-dependent PNC rotation is found to be less t han 2 x 10(-2) of the nuclear spin-independent rotation.