Search for Neutral Heavy Leptons in the NuTeV Experiment at Fermilab
  Preliminary results from a search for neutral heavy leptons in the NuTeV experiment at Fermilab. The upgraded NuTeV neutrino detector for the 1996-1997 run included an instrumented decay region for the NHL search which, combined with the NuTeV calorimeter, allows detection in several decay modes (mu-mu-nu, mu-e-nu, mu-pi, e-pi, and e-e-nu). We see no evidence for neutral heavy leptons in our current search in the mass range from 0.3 GeV to 2.0 GeV decaying into final states containing a muon. 
NuTeV Collaboration, R. B. Drucker, et al