Spectroscopy of the 1s-2s splitting in muonium

A measurement of the 1S-2S energy splitting by Doppler-free two-photon spectroscopy yields a value of 2 455 529 002 (33)(46) MHz, which agrees with QED theory within two standard deviations. The mass of the positive muon is derived as 105.658 80 (29) (43) MeV/c/sup 2/ from the isotope shifts in this transition to hydrogen and deuterium.<
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