Evidence against nuclear polarization as source of fine-structure anomalies in muonic atoms

TL;DR

This study investigates fine-structure anomalies in muonic atoms, finding that nuclear polarization effects are unlikely to be the cause, and suggesting that refined QED corrections or other factors may explain the discrepancies.

Contribution

The paper provides the most comprehensive calculations to date of nuclear-polarization energy shifts in muonic atoms, challenging the nuclear polarization hypothesis for the anomalies.

Findings

Nuclear polarization effects are insufficient to explain the anomalies.

Uncertainties in calculations are smaller than observed discrepancies.

Refined QED corrections may be needed to resolve the anomalies.

Abstract

A long-standing problem of fine-structure anomalies in muonic atoms is revisited by considering the $\Delta 2p$ splitting in muonic $^{90}\mathrm{Zr}$, $^{120}\mathrm{Sn}$ and $^{208}\mathrm{Pb}$ and the $\Delta 3p$ splitting in muonic $^{208}\mathrm{Pb}$. State-of-the-art techniques from both nuclear and atomic physics are brought together in order to perform the most comprehensive to date calculations of nuclear-polarization energy shifts. Barring the more subtle case of muonic $^{208}\mathrm{Pb}$, the results suggest that the dominant calculation uncertainty is much smaller than the persisting discrepancies between theory and experiment. We conclude that the resolution to the anomalies is likely to be rooted in refined QED corrections or even some other previously unaccounted-for contributions.