Muonium-Antimuonium Conversion

The MACS experiment performed at PSI in the 1990s provided an yet unchallenged upper bound on probability for a spontaneous conversion of muonium atom, { M=}({\mu^+e^-}) M=(μ+e−) , into its antiatom, antimuonium {\overline{{M}} = }({\mu^-e^+}) display="inline">M¯=(μ−e+<mml:mo . It comprises culmination series measurements various accelerator laboratories worldwide. experimental limits process have input and steering further development variety theoretical models beyond standard theory, particular which address lepton number violating processes matter-antimatter oscillations. Several theory could be strongly disfavored. There is interest new measurement improved sensitivity reached by exploiting time evolution process, e.g., intense pulsed sources.