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Evidence for $ν_{μ} \to ν_{τ}$ appearance in the CNGS neutrino beam with the OPERA experiment

N. Agafonova¹, A. Aleksandrov², A. Anokhina³, S. Aoki⁴, A. Ariga⁵, T. Ariga⁵, T. Asada⁶, D. Autiero⁷, A. Ben Dhahbi⁵ et al. (OPERA Collaboration)

A. Ben Dhahbi⁵, A. Badertscher⁸, D. Bender⁹, A. Bertolin¹⁰, C. Bozza¹¹, R. Brugnera^12,10, F. Brunet¹³, G. Brunetti⁵, A. Buonaura^2,14, S. Buontempo², B. Büttner¹⁵, L. Chaussard⁷, M. Chernyavsky¹⁶, V. Chiarella¹⁷, A. Chukanov¹⁸, L. Consiglio², N. D’Ambrosio¹⁹, G. De Lellis^2,14, M. De Serio^20,21, P. Del Amo Sanchez¹³, A. Di Crescenzo^2,*, D. Di Ferdinando²², N. Di Marco¹⁹, S. Dmitrievski¹⁸, M. Dracos²³, D. Duchesneau¹³, S. Dusini¹⁰, T. Dzhatdoev³, J. Ebert¹⁵, A. Ereditato⁵, J. Favier¹³, T. Ferber^15,†, G. Ferone^2,14, R. A. Fini²⁰, T. Fukuda²⁴, G. Galati^20,21, A. Garfagnini^12,10, G. Giacomelli^25,22, C. Goellnitz¹⁵, J. Goldberg²⁶, Y. Gornushkin¹⁸, G. Grella¹¹, F. Grianti¹⁷, M. Guler⁹, C. Gustavino²⁷, C. Hagner¹⁵, K. Hakamata⁶, T. Hara⁴, T. Hayakawa⁶, M. Hierholzer^15,‡, A. Hollnagel¹⁵, B. Hosseini^2,14, H. Ishida²⁴, K. Ishiguro⁶, M. Ishikawa⁶, K. Jakovcic²⁸, C. Jollet²³, C. Kamiscioglu^9,29, M. Kamiscioglu⁹, T. Katsuragawa⁶, J. Kawada⁵, H. Kawahara⁶, J. H. Kim³⁰, S. H. Kim^30,§, M. Kimura⁵, N. Kitagawa⁶, B. Klicek²⁸, K. Kodama³¹, M. Komatsu⁶, U. Kose¹⁰, I. Kreslo⁵, A. Lauria^2,14, J. Lenkeit¹⁵, A. Ljubicic²⁸, A. Longhin^17,∥, P. Loverre^32,27, A. Malgin¹, G. Mandrioli²², J. Marteau⁷, T. Matsuo²⁴, V. Matveev¹, N. Mauri^25,22, E. Medinaceli^12,10, A. Meregaglia²³, P. Migliozzi², S. Mikado²⁴, M. Miyanishi⁶, E. Miyashita⁶, P. Monacelli³³, M. C. Montesi^2,14, K. Morishima⁶, M. T. Muciaccia^20,21, N. Naganawa⁶, T. Naka⁶, M. Nakamura⁶, T. Nakano⁶, Y. Nakatsuka⁶, K. Niwa⁶, S. Ogawa²⁴, N. Okateva¹⁶, A. Olshevsky¹⁸, T. Omura⁶, K. Ozaki⁴, A. Paoloni¹⁷, B. D. Park^30,¶, I. G. Park³⁰, A. Pastore²⁰, L. Patrizii²², E. Pennacchio⁷, H. Pessard¹³, C. Pistillo⁵, D. Podgrudkov³, N. Polukhina¹⁶, M. Pozzato^25,22, K. Pretzl⁵, F. Pupilli¹⁹, R. Rescigno¹¹, M. Roda^12,10, H. Rokujo⁶, T. Roganova³, G. Rosa^32,27, I. Rostovtseva³⁴, A. Rubbia⁸, O. Ryazhskaya¹, O. Sato⁶, Y. Sato³⁵, A. Schembri¹⁹, W. Schmidt-Parzefal¹⁵, I. Shakiryanova¹, T. Shchedrina², A. Sheshukov², H. Shibuya²⁴, T. Shiraishi⁶, G. Shoziyoev³, S. Simone^20,21, M. Sioli^25,22, C. Sirignano^12,10, G. Sirri²², M. Spinetti¹⁷, L. Stanco¹⁰, N. Starkov¹⁶, S. M. Stellacci¹¹, M. Stipcevic²⁸, T. Strauss⁵, P. Strolin^2,14, K. Suzuki⁶, S. Takahashi⁴, M. Tenti^25,22, F. Terranova^17,36, V. Tioukov², S. Tufanli⁵, P. Vilain³⁷, M. Vladimirov¹⁶, L. Votano¹⁷, J. L. Vuilleumier⁵, G. Wilquet³⁷, B. Wonsak¹⁵, C. S. Yoon³⁰, J. Yoshida⁶, M. Yoshimoto⁶, Y. Zaitsev³⁴, S. Zemskova¹⁸, and A. Zghiche¹³ (OPERA Collaboration)

¹INR Institute for Nuclear Research, Russian Academy of Sciences RUS-117312 Moscow, Russia
²INFN Sezione di Napoli, I-80125 Napoli, Italy
³SINP MSU-Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, RUS-119992 Moscow, Russia
⁴Kobe University, J-657-8501 Kobe, Japan
⁵Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics (LHEP), University of Bern, CH-3012 Bern, Switzerland
⁶Nagoya University, J-464-8602 Nagoya, Japan
⁷IPNL, Université Claude Bernard Lyon 1, CNRS/IN2P3, F-69622 Villeurbanne, France
⁸Institute for Particle Physics, ETH Zurich, CH-8093 Zurich, Switzerland
⁹METU Middle East Technical University, TR-06531 Ankara, Turkey
¹⁰INFN Sezione di Padova, I-35131 Padova, Italy
¹¹Dipartimento di Fisica dell’Uni. di Salerno and “Gruppo Collegato” INFN, I-84084 Fisciano (SA), Italy
¹²Dipartimento di Fisica dell’Università di Padova, I-35131 Padova, Italy
¹³LAPP, Université de Savoie, CNRS IN2P3, F-74941 Annecy-le-Vieux, France
¹⁴Dipartimento di Scienze Fisiche dell’Università Federico II di Napoli, I-80125 Napoli, Italy
¹⁵Hamburg University, D-22761 Hamburg, Germany
¹⁶LPI-Lebedev Physical Institute of the Russian Academy of Sciences, 119991 Moscow, Russia
¹⁷INFN-Laboratori Nazionali di Frascati dell’INFN, I-00044 Frascati (Roma), Italy
¹⁸JINR-Joint Institute for Nuclear Research, RUS-141980 Dubna, Russia
¹⁹INFN-Laboratori Nazionali del Gran Sasso, I-67010 Assergi (L’Aquila), Italy
²⁰INFN Sezione di Bari, I-70126 Bari, Italy
²¹Dipartimento di Fisica dell’Università di Bari, I-70126 Bari, Italy
²²INFN Sezione di Bologna, I-40127 Bologna, Italy
²³IPHC, Université de Strasbourg, CNRS/IN2P3, F-67037 Strasbourg, France
²⁴Toho University, J-274-8510 Funabashi, Japan
²⁵Dipartimento di Fisica dell’Università di Bologna, I-40127 Bologna, Italy
²⁶Department of Physics, Technion, IL-32000 Haifa, Israel
²⁷INFN Sezione di Roma, I-00185 Roma, Italy
²⁸IRB-Rudjer Boskovic Institute, HR-10002 Zagreb, Croatia
²⁹Ankara University, TR-06100 Ankara, Turkey
³⁰Gyeongsang National University, ROK-900 Gazwa-dong, Jinju 660-701, Korea
³¹Aichi University of Education, J-448-8542 Kariya (Aichi-Ken), Japan
³²Dipartimento di Fisica dell’Università di Roma ‘La Sapienza’ and INFN, I-00185 Roma, Italy
³³Dipartimento di Fisica dell’Università dell’Aquila and INFN, I-67100L’Aquila, Italy
³⁴ITEP-Institute for Theoretical and Experimental Physics, RUS-317259 Moscow, Russia
³⁵Utsunomiya University, J-321-8505 Tochigi-Ken, Utsunomiya, Japan
³⁶Dipartimento di Fisica dell’Università di Milano-Bicocca, I-20126 Milano, Italy
³⁷IIHE, Université Libre de Bruxelles, B-1050 Brussels, Belgium

^*Corresponding author. dicrescenzo@na.infn.it
^†Present address: Deutsches Elektronen Synchrotron (DESY), 22607 Hamburg, Germany.
^‡Present address: LHEP, University of Bern, CH-3012 Bern, Switzerland.
^§Present address: Kyungpook National University, Daegu, Korea.
^∥Corresponding author. longhin@lnf.infn.it
^¶Present address: Samsung Changwon Hospital, SKKU, Changwon, Korea.

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Phys. Rev. D 89, 051102(R) – Published 5 March, 2014

DOI: https://doi.org/10.1103/PhysRevD.89.051102

Abstract

The OPERA experiment is designed to search for $ν_{μ} \to ν_{τ}$ oscillations in appearance mode, i.e., through the direct observation of the $τ$ lepton in $ν_{τ}$ -charged current interactions. The experiment has taken data for five years, since 2008, with the CERN Neutrino to Gran Sasso beam. Previously, two $ν_{τ}$ candidates with a $τ$ decaying into hadrons were observed in a subsample of data of the 2008–2011 runs. Here we report the observation of a third $ν_{τ}$ candidate in the $τ^{-} \to μ^{-}$ decay channel coming from the analysis of a subsample of the 2012 run. Taking into account the estimated background, the absence of $ν_{μ} \to ν_{τ}$ oscillations is excluded at the $3.4 σ$ level.