Search for Heavy Neutrino Decays in the {BEBC} Beam Dump Experiment

Abstract New limits on lepton mixing parameters are derived from a search for decays of heavy neutrinos in a proton beam dump experiment. The limits | U oi | 2 , | U e i | 2 −6 −10 −7 are obtained for neutrino mass eigenstates v i of mass between 0.5 and 1.75 GeV, which can be produced through mixing in charmed D meson decays. This is the first such limit on | U o i | 2 for neutrino masses greater than 0.5 GeV. For the mass eigenstate v 3 in particular, we obtain the limits | U o 3 | 2 −7 −10 −8 , | U e 3 | 2 −9 −10 −10 for the mass range 150–190 MeV, assuming the v 3 to be produced directly in charmed F meson decays.