New Bounds from a Search for Muonium to Antimuonium Conversion

A new upper limit for the probability of spontaneous muonium to antimuonium conversion was established at P_MM¯<=8.3×10^-11 ( 90% C.L.) in 0.1 T magnetic field, which implies consequences for speculative extensions to the standard model. Coupling parameters in R-parity-violating supersymmetry and the mass of a flavor diagonal bileptonic gauge boson can be significantly restricted. A Z₈ model with radiative mass generation through heavy lepton seed and the minimal version of 331 models are disfavored.