Observation of New-Particle Production by High-Energy Neutrinos and Antineutrinos

We have observed fourteen events in which two muons are produced by high-energy neutrino and antineutrino interactions. The absence of trimuon events and the observed characteristics of the dimuon events require the existence of one or more new massive particles that decay through the weak interaction. The new particle mass is estimated to lie between 2 and 4 GeV.