Muonium excited state

Metastable muonium atoms in the 2s state have been produced with a beam foil technique at LAMPF and at the Tri University Meson Physics Facility (TRI-UMF) at Vancouver, Canada. Only moderate numbers of atoms could be obtained. The velocity resonance nature of the electron transfer reaction results in a muonium beam at keV energies. Very difficult and challenging experiments using electromagnetic transitions in excited states, particularly the 2 Si/2 2 Pi/2 classical Lamb shift and 2 Si/2-2 P3/2 splitting could be induced with microwaves. However, the achieved experimental accuracy at the 1.5 % level [18,19,20], does not represent a severe test of theory yet. 

The fact that y e can now be studied in vacuum is very important for a number of fundamental experiments. One is the measurement of the Lamb shift in the first excited state of muonium (Fig.5). The beam-foil method produces not only the n=l state but excited states as well l with a probability roughly as l/n. We expect that 15% of the muonium formed is in the 2S state. 

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