Search for tau-neutrino interactions in the BEBC beam dump experiment

Abstract A novel and efficient kinematic method is used to estimate the number of ν τ charged current interactions with E ν > 20 GeV in the BEBC beam dump experiment. The result, −14±12 ν τ events, is consistent with zero. The ratio of D s to D meson production in 400 GeV proton interactions in copper is estimated to be below 0.65 at 90% c.l. The oscillation probability P ( ν e → ν τ ) averaged over the electron-(anti)neutrino spectrum is found to be below 18%. The hypothesis that ν e and ν τ are identical is excluded by about 6 standard deviations. A remarkable event is described: it contains a muon, a high p T photon and a high p T hadron.