Parity violation in hydrogen revisited

TL;DR

Reevaluating parity violation experiments in hydrogen and deuterium shows they are highly valuable for testing the Standard Model with minimal atomic physics uncertainties, especially for measuring weak interaction constants.

Contribution

The paper assesses the potential of new parity violation experiments in hydrogen and deuterium to improve measurements of weak neutral current couplings, with specific focus on experimental feasibility and precision gains.

Findings

Hydrogen experiments can significantly improve tests of the Standard Model.

A 0.3% measurement of C_{1D} is feasible with advanced metastable beam technology.

Experiments could precisely determine three weak-neutral-current coupling constants.

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.