Parity Nonconservation in Hydrogen Induced by Low-Mass Vector-Boson Exchange

TL;DR

This paper explores how hypothetical low-mass Z' bosons could induce parity nonconservation effects in hydrogen and deuterium, offering a cleaner experimental setting to detect new physics beyond the Standard Model.

Contribution

It calculates the ratio of Z' to Z-boson contributions to parity violation in hydrogen and deuterium for arbitrary Z' masses, including NSI and NSD interactions.

Findings

The Z' contribution ratio increases rapidly with decreasing Z.

Hydrogen's theoretical simplicity allows for more precise interpretation of PNC experiments.

Hydrogen and deuterium experiments can better distinguish Z' effects from Standard Model background.

Abstract

Parity-nonconserving (PNC) effects in atoms produced by $Z$-boson exchange between the electron and the nucleus grow rapidly with the nuclear charge $Z$. If a hypothetical additional $Z'$ boson is light, however, its contribution does not exhibit the same strong enhancement with $Z$. As a result, the ratio of the low-mass $Z'$ contribution to the Standard Model $Z$-boson contribution increases rapidly with decreasing $Z$, in fact faster than $1/Z^2$. Hydrogen has a further important advantage: its theoretical description is substantially cleaner than that of heavy atoms, allowing a more accurate interpretation of experimental results. For these two reasons, hydrogen and deuterium PNC experiments may provide an especially favorable setting in which to disentangle a possible $Z'$ contribution from the Standard Model background. In this paper we calculate the ratio of the $Z'$-boson contribution, for arbitrary $Z'$ mass, to the Standard Model $Z$-boson contribution to parity violation in hydrogen and deuterium, including both nuclear-spin-independent (NSI) and nuclear-spin-dependent (NSD) interactions.