Parity violation in hydrogen revisited

Abstract

We reconsider parity violation experiments in atomic hydrogen and deuterium in the light of existing tests of the Electroweak interactions, and assess whether new experiments, using improved experimental techniques, could make useful contributions to testing the Standard Model (SM). We find that, if parity experiments in hydrogen can be done, they remain highly desirable because there is negligible atomic-physics uncertainty and low energy tests of weak neutral current interactions are needed to probe for new physics beyond the SM. Of particular interest would be a measurement of the nuclear spin independent coupling C_{1D} for the deuteron at a combined error (theory + experiment) of 0.3%. This would provide a factor of three improvement to the precision on sin^2 theta_W at very low momentum transfer provided by heavy atom Atomic Parity Violation (APV) experiments. Also, experiments in H and D could provide precise measurements of three other electron-nucleon, weak-neutral-current coupling constants: C_{1p}, C_{2p},and C_{2D}, which have not been accurately determined to date. Analysis of a generic APV experiment in deuterium indicates that a 0.3% measurement of C_{1D} requires development of a slow (77K) metastable beam of ~ 5x10^14 D(2S) s^-1 per hyperfine component. The advent of UV radiation from free electron laser (FEL) technology could allow production of such a beam.