Discovery of τ Neutrino Appearance in the CNGS Neutrino Beam with the OPERA Experiment

Agafonova, N.; Aleksandrov, A.; Anokhina, A.; Aoki, S.; Ariga, A.; Ariga, T.; Bender, D.; Bertolin, A.; Bodnarchuk, I.; Bozza, Cristiano; Brugnera, R.; Buonaura, A.; Buontempo, S.; Büttner, B.; Chernyavsky, M.; Chukanov, A.; Consiglio, L.; D’Ambrosio, N.; De Lellis, G.; De Serio, M.; Del Amo Sanchez, P.; Di Crescenzo, A.; Di Ferdinando, D.; Di Marco, N.; Dmitrievski, S.; Dracos, M.; Duchesneau, D.; Dusini, S.; Dzhatdoev, T.; Ebert, J.; Ereditato, A.; Fini, R.  . A.; Fornari, F.; Fukuda, T.; Galati, G.; Garfagnini, A.; Goldberg, J.; Gornushkin, Y.; Grella, Giuseppe; Guler, A.  . M.; Gustavino, C.; Hagner, C.; Hara, T.; Hayakawa, H.; Hollnagel, A.; Hosseini, B.; Ishiguro, K.; Jakovcic, K.; Jollet, C.; Kamiscioglu, C.; Kamiscioglu, M.; Kim, J.  . H.; Kim, S.  . H.; Kitagawa, N.; Klicek, B.; Kodama, K.; Komatsu, M.; Kose, U.; Kreslo, I.; Laudisio, F.; Lauria, A.; Ljubicic, A.; Longhin, A.; Loverre, P.  . F.; Malgin, A.; Malenica, M.; Mandrioli, G.; Matsuo, T.; Matsushita, T.; Matveev, V.; Mauri, N.; Medinaceli, E.; Meregaglia, A.; Mikado, S.; Miyanishi, M.; Mizutani, F.; Monacelli, P.; Montesi, M.  . C.; Morishima, K.; Muciaccia, M.  . T.; Naganawa, N.; Naka, T.; Nakamura, M.; Nakano, T.; Nakatsuka, Y.; Niwa, K.; Ogawa, S.; Olchevsky, A.; Omura, T.; Ozaki, K.; Paoloni, A.; Paparella, L.; Park, B.  . D.; Park, I.  . G.; Pasqualini, L.; Pastore, A.; Patrizii, L.; Pessard, H.; Pistillo, C.; Podgrudkov, D.; Polukhina, N.; Pozzato, M.; Pupilli, F.; Roda, M.; Roganova, T.; Rokujo, H.; Rosa, G.; Ryazhskaya, O.; Sato, O.; Schembri, A.; Schmidt Parzefall, W.; Shakirianova, I.; Shchedrina, T.; Sheshukov, A.; Shibuya, H.; Shiraishi, T.; Shoziyoev, G.; Simone, S.; Sioli, M.; Sirignano, C.; Sirri, G.; Sotnikov, A.; Spinetti, M.; Stanco, L.; Starkov, N.; Stellacci, Simona Maria; Stipcevic, M.; Strolin, P.; Takahashi, S.; Tenti, M.; Terranova, F.; Tioukov, V.; Tufanli, S.; Vilain, P.; Vladymyrov, M.; Votano, L.; Vuilleumier, J.  . L.; Wilquet, G.; Wonsak, B.; Yoon, C.  . S.; Zemskova, S.

doi:10.1103/PhysRevLett.115.121802

The OPERA experiment was designed to search for ν μ → ν τ oscillations in appearance mode, i.e., by detecting the τ leptons produced in charged current ν τ interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of the ν μ → ν τ appearance, achieved with four candidate events in a subsample of the data, was previously reported. In this Letter, a fifth ν τ candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow us to assess the discovery of ν μ → ν τ oscillations in appearance mode with a significance larger than 5σ .