Parity Nonconservation in Atoms: Status of Theory and Experiment

Abstract

This chapter reviews diverse experimental and theoretical programs engaged in the study of parity nonconservation in atoms. The existence of parity nonconservation in atoms is now reasonably well established by experiment. Four different laboratories have performed parity nonconservation (PNC)optical rotation experiments on bismuth. Although there is strong evidence for an effect of the sign and order of magnitude expected from the Weinberg–Salam theory, the various experiments are not consistent among themselves. The atomic calculations are judged to be reliable to about 30%. This chapter starts with a discussion on the neutral current interaction in atoms. In the absence of H PNC , the states of the atom have definite parity. Electric dipole (E1) transitions, which normally dominate atomic spectroscopy, are forbidden between states of like parity. However, H PNC mixes s and p states and causes, in some cases, small E1 transition amplitude to appear and to interfere with transitions (M1, E2) normally present but weak between states of like panty, giving rise to an observable PNC effect. For instance, when H PNC couples E1 amplitude into an M1 transition, the transition rate acquires a dependence on the sense of circular polarization of incident radiation. The optical rotation experiments utilize this effect. This chapter ends with a view of experiments on cesium and thallium, and atomic hydrogen.