Heavy leptons

It is stated that Perl and his collaborators at SPEAR (Phys. Rev. Lett.; 35:1489 (1975)) have come upon a class of events of the sort e+ + e- → μ+- + e+ (also μ+-μ-+, e+-e-+) + missing mass where at most only a small fraction of these events are accompanied by π0s or K0s. An interpretation that suggests itself for these events is the production and decay of charged heavy leptons, that presumably can also decay semileptonically. This interpretation is here discussed, including implications for new kinds of physics and the involvement of charm production. A question raised is if heavy charged leptons exist, how do they fit into the scheme of things. This and other relevant questions are discussed, including experimental requirements. Much may be learned from studies of semileptonic decays. (author)