Spectroscopy of the 1S-2S energy splitting in muonium

A new measurement of the 1/sup 2/S/sub 1/2/-2/sup 2/5/sub 1/2/ energy splitting in muonium (/spl mu//sup +/e/sup -/) by Doppler-free two-photon laser spectroscopy yields a value of 2 455 529 002 (33) (46) MHz, where the 33 MHz error arises from statistics and the 46 MHz uncertainty is due to systematic line shifts. The experiment agrees with quantum electrodynamics theory within two standard deviations. The mass of the positive muon can be derived as 105.65880 (29) (43) MeV/c/sup 2/ from the measured muonium-hydrogen and muonium-deuterium 1S-2S isotope shifts. The measurement may alternatively be interpreted as a test of the equality of the electric charges of muon and electron with a precision of 1.4 (1.2) l0{-8}. >