Measurement of the 2S1/2,F=0 → 2P1/2,F=1 transition in Muonium

Abstract Here we present the results of the first measurement of the 2S1/2, F=0 -> 2P1/2, F=1 transition in Muonium, the hydrogen-like bound state of a positive muon and an electron. The measured value of 580.6+-6.8 MHz is in agreement with the theoretical calculations. From this measurement a value of the Lamb shift of 1045.5+-6.8 MHz is extracted, compatible with previous experiments. We also determine for the first time the 2S hyperfine splitting in Muonium to be 559.6+-7.2 MHz. The measured transition being isolated from the other hyperfine levels holds the promise to provide an improved determination of the Muonium Lamb shift at a level where bound state QED recoil corrections not accessible in hydrogen could be tested. Such a measurement will also be sensitive to new physics in the muonic sector, e.g. to new bosons which might provide an explanation of the g-2 muon anomaly or Lorentz and CPT violation. We also present the first observation of Muonium in the n = 3 excited state opening up the possibility of new precise microwave measurements as realized in hydrogen.