Description
Atomic parity nonconservation (PNC) provides a sensitive low-energy probe of electroweak interactions and a pathway to test physics beyond the Standard Model (SM). PNC amplitudes arise from neutral currents mediated by the SM $Z$ boson and may receive additional contributions from hypothetical gauge bosons such as a $Z'$ boson.
For a low-mass $Z'$ boson, its contribution does not scale as strongly with nuclear charge $Z$ as the SM contribution. Notably, the ratio of the $Z'$-induced amplitude to the SM $Z$ boson amplitude increases rapidly with decreasing $Z$, scaling faster than $1/Z^2$. This enhances the relative sensitivity of lighter atoms to new weak interactions, while also benefiting from improved theoretical accuracy compared to heavier systems.
We investigate PNC effects in light atomic systems, focusing on rubidium (Rb), strontium ion (Sr$^+$), and hydrogen. We evaluate the ratio of $Z'$ boson to SM $Z$ boson contributions for arbitrary $Z'$ mass, including both nuclear-spin-independent and nuclear-spin-dependent interactions. For Rb and Sr$^+$, we calculate parity nonconserving electric-dipole (E1) transition amplitudes for the $5s - 6s$ and $5s - 4d_{3/2}$ transitions, demonstrating enhanced sensitivity to $Z'$-induced effects relative to heavier atoms. In parallel, we analyse PNC in hydrogen, where the atomic structure is well understood and theoretical uncertainties are minimal. Although absolute PNC effects are smaller, the cleaner theoretical description enables more accurate interpretation of experimental results.
| I am the presenting author | Yes |
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