Characteristics of Neutrino-Produced Dimuon and Trimuon Events as Evidence for New Physics at the Lepton Vertex

The characteristics of six trimuon events observed in the new large-angle neutrino detector at Fermilab are described. The leptonic system appears to take an inordinate fraction of the incident neutrino energy if new hadrons are presumed to be the origin of these events. A similar effect seems to be present in the dimuon events previously observed. The events find a natural interpretation as the products of cascade decay of a new lepton (the M particle) through a lower-mass neutral lepton (the L^0 particle).