Laser Spectroscopy of Muonic Atoms and Ions

TL;DR

This paper discusses laser spectroscopy measurements of muonic atoms that significantly improve the accuracy of nuclear charge radii, revealing discrepancies with previous data and promising future insights into nuclear structure.

Contribution

It reports highly precise measurements of nuclear charge radii using muonic atom spectroscopy, and outlines future plans to determine magnetic and hyperfine properties.

Findings

Proton and deuteron radii are 10 and 3 times more accurate than CODATA.

Measured radii are 7 standard deviations smaller than previous values.

Ongoing analysis of muonic helium ions will provide new nuclear insights.

Abstract

Laser spectroscopy of the Lamb shift (2S-2P energy difference) in light muonic atoms or ions, in which one negative muon $\mu^-$ is bound to a nucleus, has been performed. The measurements yield significantly improved values of the root-mean-square charge radii of the nuclei, owing to the large muon mass, which results in a vastly increased muon wave function overlap with the nucleus. The values of the proton and deuteron radii are 10 and 3 times more accurate than the respective CODATA values, but 7 standard deviations smaller. Data on muonic helium-3 and -4 ions is being analyzed and will give new insights. In future, the (magnetic) Zemach radii of the proton and the helium-3 nuclei will be determined from laser spectroscopy of the 1S hyperfine splittings, and the Lamb shifts of muonic Li, Be and B can be used to improve the respective charge radii.