Observation of nu_tau appearance in the CNGS beam with the OPERA   experiment
  The OPERA experiment is searching for nu_mu -> nu_tau oscillations in appearance mode i.e. via the direct detection of tau leptons in nu_tau charged current interactions. The evidence of nu_mu -> nu_tau appearance has been previously reported with three nu_tau candidate events using a sub-sample of data from the 2008-2012 runs. We report here a fourth nu_tau candidate event, with the tau decaying into a hadron, found after adding the 2012 run events without any muon in the final state to the data sample. Given the number of analysed events and the low background, nu_mu -> nu_tau oscillations are established with a significance of 4.2sigma. 
OPERA Collaboration: N. Agafonova, A. Aleksandrov, A. Anokhina, S.   Aoki, A. Ariga, T. Ariga, T. Asada, D. Bender, A. Berto...
hep-ex