Formation Of Muonium In The 2s State And Observation Of The Lamb Shift Transition

Muonium in the $2S$ state has been produced by the beam-foil method with a ${\ensuremath{\mu}}^{+}$ beam of 10 MeV/c. The metastable $2S$ state of muonium has been detected by a static electric field quenching method, and the transition $2{S}_{\frac{1}{2}}$, $F=1\ensuremath{\rightarrow}2{P}_{\frac{1}{2}}$, $F=1$ induced by a radio-frequency electric field has been observed with an event rate of about 4/h.