Search for heavy isosinglet neutrino in $e^+ e^-$ annihilation at LEP

We report on a search for the first generation heavy neutrino that is an isosinglet under the standard $SU(2)_L$ gauge group. The data collected with the L3 detector at center-of-mass energies between 130~\hbox{\rm\ Ge\kern -0.1em V} and 208~\hbox{\rm\ Ge\kern -0.1em V} are used. The decay channel $\mathrm{N}_\mathrm{e} \rightarrow \mathrm{e} \mathrm{W}$ is investigated and no evidence is found for a heavy neutrino, $\mathrm{N}_\mathrm{e}$, in a mass range between 80~\hbox{\rm\ Ge\kern -0.1em V} and 205~\hbox{\rm\ Ge\kern -0.1em V}. Upper limits on the mixing parameter between the heavy and light neutrino are derived.