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

• Received 7 November 1977

DOI:https://doi.org/10.1103/PhysRevLett.40.144