Upper Limits toνμ−ντOscillation andνμ−τCoupling

A search for $\tau$ lepton production in a sample of 1241 neutrino interactions with use of a hybrid emulsion spectrometer in the Fermilab wide-band neutrino beam is reported. No such events are seen and an upper limit to the ${\nu }_{\mu }-\tau$ coupling of 0.63% (90% C.L.) is set. For ${\nu }_{\mu }-{\nu }_{\tau }$ oscillations this sets a limit of $|{m_{{\nu }_{\mu }}}^2-{m_{{\nu }_{\tau }}}^2|<\mathrm{}3.0\mathrm{}$ ${\mathrm{eV}}^2$ (90% C.L.) for maximum mixing.