2-Photon laser spectroscopy of muonium: A tribute to Chebotayev inheritance

The method of Doppler-free two-photon laser spectroscopy is an ideal method for studying transitions between the 1S and 2S states in one-electron systems. An experiment at the Rutherford Appleton Laboratory has observed an unambiguous signal in the exotic muonium (mu+e-) atom. The transition frequency is DELTAnu1S-2S = 2455529002(33)(46) MHz, where the first error is of a statistical nature and the second one arises from systematic corrections, which mainly are related to the properties of the high-power pulsed laser system. There is agreement with a prior, less accurate, independent experiment at KEK and with QED theory within two standard deviations. The Lamb shift contributions are tested at the 8 x 10(-3) level. The muonium-hydrogen and muonium-deuterium isotope shifts of the 1S-2S transition have a high potential for a precise mass determination of the positive muon.