High-precision measurement of parity nonconserving optical rotation in atomic lead

A new measurement of parity nonconserving (PNC) optical rotation near the 1.279 mu m magnetic dipole absorption line in lead was completed. The ratio of the PNC E1 amplitude to the M1 amplitude was found to be R = (--9.86 plus/minus 0.12) x 10 exp --8 , consistent with theoretical predictions. Difficulties in the atomic theory of lead presently limit the extent to which the result tests the standard model of electroweak interactions. The amplitude of the nuclear spin-dependent PNC rotation is found to be < 2 x 10 exp --2 of the nuclear spin-independent rotation.