Ultraslow Muonium for a Muon beam of ultra high quality

E_cient conversion of a standard muon beam into a high quality slow muon beam by using the muonium ionization method is shown to be achievable with a new kind of converter. It consists of a superfluid helium layer from which muonium atoms escape because of their negative a_nity. Application to pulsed muon beams in an optimized target configuration leads to a reduction of the necessary VUV laser energy by a factor of 100. The resulting muon beam has more than 4 orders of magnitude better phase space quality than what is obtained today with the silica powder converter. When using the superfluid helium converter in association with high quality DC muon beams in development at the Paul Scherrer Institute, it should be possible to use intense continuous lasers for ionization and obtain ultra-high quality continuous muon beams with precise timing of the muon arrival.