Measurement of the Lamb shift in the n = 2 state of muonium

We report the results of a measurement of the Lamb shift in the n=2 state of muonium. Muonium atoms in the metastable 2S state were produced by the beam-foil method and the formation rate was determined by observation of the Ly-α photons emitted when the metastable atoms were quenched in a static electric field. The Lamb shift (${\mathrm{scrS}}_{\mathrm{Mu}}$) was measured through observation of the microwave-induced 2 ${}_{}{}^2{}_{}{}^{}\mathrm{S}_{1/2}^{}{}_{}{}^{}$–2 ${}_{}{}^2{}_{}{}^{}P_{1/2}^{}{}_{}{}^{}$ transition with the result ${\mathrm{scrS}}_{\mathrm{Mu}{=1042\mathrm{}}_{\mathrm{-}23}^{+21\mathrm{}}}$ MHz. This result is in agreement with the current theoretical value.