Signatures of heavy-neutrino production at the CERN collider

We discuss the possibility of discovering at the CERN collider a new sequential neutrino or a mirror neutrino (which can mix with the light neutrinos). Three classes of event signatures are examined: purely leptonic decay channels, monojets with missing $p_T$, and monojets with isolated electrons and very little missing $p_T$. This last signal is studied in detail; a set of experimental cuts are suggested and a number of possible backgrounds are estimated. At least 1 ${\mathrm{pb}}^{\mathrm{-}1}$ of data is needed before nontrivial limits on heavy-neutrino parameters can be achieved.