Muonic atoms and the nuclear structure

TL;DR

This paper reviews how muonic atoms, especially muonic hydrogen, are used to precisely measure nuclear properties like charge and magnetic radii, highlighting their role in addressing the proton radius puzzle and advancing nuclear physics.

Contribution

It summarizes the current status of muonic atom research, discusses the proton radius puzzle, and explores methods to extract magnetic nuclear radii, bridging atomic and nuclear physics.

Findings

Muon spectroscopy yields highly precise nuclear charge radii.

The proton radius puzzle remains unresolved with a 7-sigma discrepancy.

Muonic atoms can also be used to infer magnetic nuclear radii.

Abstract

High-precision laser spectroscopy of atomic energy levels enables the measurement of nuclear properties. Sensitivity to these properties is particularly enhanced in muonic atoms which are bound systems of a muon and a nucleus. Exemplary is the measurement of the proton charge radius from muonic hydrogen performed by the CREMA collaboration which resulted in an order of magnitude more precise charge radius as extracted from other methods but at a variance of 7 standard deviations. Here, we summarize the role of muonic atoms for the extraction of nuclear charge radii, we present the status of the so called "proton charge radius puzzle", and we sketch how muonic atoms can be used to infer also the magnetic nuclear radii, demonstrating again an interesting interplay between atomic and particle/nuclear physics.