Muonium Lamb shift: theory update and experimental prospects

TL;DR

This paper reviews the theoretical calculations of the muonium Lamb shift, updates its numerical value, and discusses experimental prospects for measuring it more precisely to explore potential new physics in the muonic sector.

Contribution

It provides an updated theoretical value for the muonium Lamb shift and discusses experimental upgrades that could test higher-order recoil and self-energy effects.

Findings

Enhanced recoil and self-energy contributions in muonium compared to hydrogen.

Potential to improve measurement sensitivity with upgraded Mu-MASS setup.

Prospects for probing new physics in the muonic sector.

Abstract

We review the theory of the Lamb shift for muonium, provide an updated numerical value and present the prospects of the Mu-MASS collaboration at PSI to improve upon their recent measurement. Due to its smaller nuclear mass, the contributions of the higher-order recoil corrections (160kHz level) and nucleus self-energy 40kHz level) are enhanced for muonium compared to hydrogen where those are below the level of the latest measurement performed by Hessels et al. and thus could not be tested yet. The ongoing upgrades to the Mu-MASS setup will open up the possibility to probe these contributions and improve the sensitivity of this measurement to searches for new physics in the muonic sector.