A search for decays of heavy neutrinos in the mass range 0.5–2.8 GeV

Abstract A search for decays of heavy neutrinos was conducted by the CHARM Collaboration in a prompt neutrino beam produced by dumping 400 GeV protons in a Cu target, and in the CERN wide-band neutrino beam produced by 400 GeV primary protons. No candidate event was found. In the beam-dump experiment heavy neutrinos have been assumed to be produced by mixing in charmed D meson decays. Neutrinos decaying into e + e − v e , μ + e − v μ , and μ + μ − v μ were searched for. Limits of | U ei | 2 , | U μi | 2 −7 were obtained for neutrino masses around 1.5 GeV. In the wide-band experiment heavy neutrinos were assumed to be produced by neutral-current neutrino interactions in the CHARM calorimeter. Here a search was made for neutrinos decaying into a μ and hadrons. This experiment is sensitive to decays of neutrinos with mass in the range 0.5–2.8 GeV with limits of | U μi | 2 −4 for masses around 2.5 GeV. These measurements extend our previous results in the mass range 10–400 MeV.