Result from Donut First Direct Evidence for Tau Neutrino

At FNAL beam dump experiment DONUT, tau neutrino interactions are confirmed by the use of a modern emulsion technique. This is first direct evidence for tau neutrino in the history. Within secondary tracks of neutrino CC interactions, tau lepton is confirmed by the event analysis having a short decay track. Four clear events and one candidate are found in 203 prompt neutrino interactions. For four events a total of 0.4 background events is estimated both from charged charm decay and secondary interactions. These events are the evidence of tau neutrino.