Experimental Limits on Heavy Lepton Production by Neutrinos

We present upper limits on the production of heavy leptons (${L}^{\ifmmode\pm\else\textpm\fi{}}$) by neutrinos via the process ${\ensuremath{\nu}}_{\ensuremath{\mu}}+\mathrm{Ne}\ensuremath{\rightarrow}{L}^{\ifmmode\pm\else\textpm\fi{}}+\ensuremath{\cdots}$, ${L}^{\ifmmode\pm\else\textpm\fi{}}\ensuremath{\rightarrow}{e}^{\ifmmode\pm\else\textpm\fi{}}+\ensuremath{\nu}+\overline{\ensuremath{\nu}}$. These limits imply that the ${L}^{\ensuremath{-}}$ and ${L}^{+}$, if they couple in full strength to ${\ensuremath{\nu}}_{\ensuremath{\mu}}$, are heavier than 7.5 and 9 GeV, respectively. They also imply that the coupling strength ${\ensuremath{\nu}}_{\ensuremath{\mu}}$ to the recently discovered 1.9-GeV heavy lepton $\ensuremath{\tau}$ is less than 0.025 of the normal ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{-}\ensuremath{\mu}$ coupling.