Mass Limit on a Positively Charged Heavy Muon

We report a preliminary search for a positively charged lepton ($Y^{+}$) coupled directly to the ${\mu }^{-}$ and ${\nu }_{\mu }$ (i.e., muon number = + 1). Using the production process ${\nu }_{\mu }+N\to Y^{+}+\mathrm{anything}$, we have looked for the ${\mu }^{+}$ from the decay $Y^{+}\to {\mu }^{+}+{\nu }_{\mu }+{\nu }_{\mu }$. The expected number of ${\mu }^{+}$ events is given as a function of the heavy-lepton mass, the branching fraction to muons, and the heavy-lepton coupling. For typical gauge-theory predictions, we obtain the 90% confidence limit $M_Y>2\mathrm{}$ GeV/${\mathit{c}}^2$.