Abstract: Muonium is the bound state of a positive muon and an electron. This characteristic enables a precise QED calculation of its physical properties, and the measurement can be performed with high precision because of its relatively long lifetime and the parity violation when the muon decays.

The MuSEUM (Muonium Spectroscopy Experiment Using Microwave) collaboration aims to measure the muonium hyperfine structure by using the muon beam line at the J-PARC MLF (Materials and Life science Facility). This precise measurement will be a stringent test of the bound-state QED.  By using muonium hyperfine spectroscopy with a high magnetic field, the muon-proton magnetic moment ratio and the muon-electron mass ratio can be extracted as by-products, in which the precision is significant compared with other muon physical properties. The muon-proton magnetic moment ratio is the parameter that determines the muon anomalous magnetic moment. There is a 3.7 standard deviation discrepancy between the theoretical precision and the experimental result. The precision of the muon-electron mass ratio is the dominant uncertainty in the muonium hyperfine structure in theoretical calculation. The MuSEUM collaboration succeeded in measuring the muonium hyperfine structure with an extremely low magnetic field. We are continuing and planning a new measurement with the high magnetic field.

In this presentation, I will present an overview of the measurement status and the research and development for future high-field measurement.