text: The muon decays as  and . Decays without neutrino emission, such as , ,  and  are so unlikely that they are considered prohibited and their observation would be considered evidence of new physics. A number of experiments are pursuing this path such as Mu to E Gamma, Comet, and Mu2e for  and Mu3e for .
  Neutrinoless tau conversion in the form  has been searched for by the CMS experiment.