Update of Muonium 1S-2S transition frequency

TL;DR

This paper updates the measurement of the Muonium 1S-2S transition frequency, discusses the theoretical contributions and uncertainties, and reports on the progress of the Mu-MASS experiment aiming for high-precision results.

Contribution

It provides an updated value of the Muonium 1S-2S transition frequency and details the experimental efforts to improve measurement precision.

Findings

Current uncertainty dominated by electron-to-muon mass ratio

Progress in Mu-MASS experiment toward 10 kHz measurement precision

Potential to refine fundamental constants with improved measurements

Abstract

We present an updated value of the Muonium 1S-2S transition frequency, highlighting contributions from different QED corrections as well as the large uncertainty in the Dirac contribution, stemming from the uncertainty of the electron-to-muon mass ratio. Improving the measurement of this spectral line would allow to extract a more accurate determination of fundamental constants, such as the electron-to-muon mass ratio or, combined with the Muonium hyperfine splitting, an independent value of the Rydberg constant. Furthermore we report on the current status of the Mu-MASS experiment, which aims at measuring the Muonium 1S-2S transition frequency at a 10 kHz uncertainty level.