Gauge-Theory Heavy Muons: An Experimental Search

We have observed 1522 neutrino events with a ${\ensuremath{\mu}}^{\ensuremath{-}}$ secondary and 8 events with a ${\ensuremath{\mu}}^{+}$ secondary from a beam consisting mostly of neutrinos. The ${\ensuremath{\mu}}^{+}$ events are consistent in number and kinematic properties with beam contamination by ${\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}}$. This experiment sees no evidence for production of heavy positively charged leptons. Assuming a coupling constant equal to the universal Fermi constant and a branching ratio to muons $B=0.3$, our 90% confidence lower limit corresponds to ${M}_{{Y}^{+}}\ensuremath{\gtrsim}8.4$ ${\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c}}^{2}$.