Eur. Phys. J. C (2020) 80: 699
https://doi.org/10.1140/epjc/s10052-020-8160-y

Regular Article - Experimental Physics

First observation of a tau neutrino charged current interaction with charm production in the OPERA experiment

OPERA Collaboration

¹ INR - Institute for Nuclear Research of the Russian Academy of Sciences, 117312, Moscow, Russia
² SINP MSU - Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119991, Moscow, Russia
³ INFN Sezione di Napoli, 80125, Naples, Italy
⁴ Kobe University, 657-8501, Kobe, Japan
⁵ Albert Einstein Center for Fundamental Physics, Laboratory for High Energy Physics (LHEP), University of Bern, 3012, Bern, Switzerland
⁶ Faculty of Arts and Science, Kyushu University, Fukuoka, Japan
⁷ INFN Sezione di Padova, 35131, Padova, Italy
⁸ Dipartimento di Matematica dell’Università di Salerno and “Gruppo Collegato” INFN, 84084, Fisciano, Salerno, Italy
⁹ Dipartimento di Fisica e Astronomia dell’Università di Padova, 35131, Padua, Italy
¹⁰ Dipartimento di Fisica dell’Università Federico II di Napoli, 80125, Naples, Italy
¹¹ LPI - Lebedev Physical Institute of the Russian Academy of Sciences, 119991, Moscow, Russia
¹² JINR - Joint Institute for Nuclear Research, 141980, Dubna, Russia
¹³ INFN-Laboratori Nazionali del Gran Sasso, 67010, Assergi, L’Aquila, Italy
¹⁴ CERN, Geneva, Switzerland
¹⁵ Dipartimento di Fisica dell’Università di Bari, 70126, Bari, Italy
¹⁶ INFN Sezione di Bari, 70126, Bari, Italy
¹⁷ LAPP, Université Savoie Mont Blanc, CNRS/IN2P3, 74941, Annecy-le-Vieux, France
¹⁸ INFN Sezione di Bologna, 40127, Bologna, Italy
¹⁹ IPHC, Université de Strasbourg, CNRS/IN2P3, 67037, Strasbourg, France
²⁰ Hamburg University, 22761, Hamburg, Germany
²¹ Dipartimento di Fisica e Astronomia dell’Università di Bologna, 40127, Bologna, Italy
²² Nagoya University, Nagoya, 464-8602, Japan
²³ National University of Science and Technology, MISiS, Moscow, Russia
²⁴ Department of Physics, Technion, 32000, Haifa, Israel
²⁵ Dipartimento di Fisica dell’Università di Salerno and “Gruppo Collegato” INFN, 84084, Fisciano, Salerno, Italy
²⁶ METU - Middle East Technical University, 06800, Ankara, Turkey
²⁷ INFN Sezione di Roma, 00185, Rome, Italy
²⁸ Rudjer Boskovic Institute, 10002, Zagreb, Croatia
²⁹ Ankara University, 06560, Ankara, Turkey
³⁰ Gyeongsang National University, 900 Gazwa-dong, Jinju, 660-701, Korea
³¹ Center of Excellence for Advanced Materials and Sensing Devices, Ruder Bošković Institute, 10002, Zagreb, Croatia
³² Aichi University of Education, Kariya, Aichi-Ken, 448-8542, Japan
³³ Toho University, Funabashi, 274-8510, Japan
³⁴ Nihon University, Narashino, Chiba, 275-8576, Japan
³⁵ INFN - Laboratori Nazionali di Frascati dell’INFN, 00044, Frascati, Rome, Italy
³⁶ Moscow Engineering Physical Institute Moscow, Moscow, Russia
³⁷ Dipartimento di Fisica dell’Università di Milano-Bicocca, 20126, Milan, Italy
³⁸ IIHE, Université Libre de Bruxelles, 1050, Brussels, Belgium

^* e-mail: chiara.sirignano@unipd.it

Received: 20 March 2020
Accepted: 16 June 2020
Published online: 4 August 2020

Abstract

An event topology with two secondary vertices compatible with the decay of short-lived particles was found in the analysis of neutrino interactions in the OPERA target. The observed topology is compatible with tau neutrino charged current (CC) interactions with charm production and neutrino neutral current (NC) interactions with pair production. However, other processes can mimic this topology. A dedicated analysis was implemented to identify the underlying process. A Monte Carlo simulation was developed and complementary procedures were introduced in the kinematic reconstruction. A multivariate analysis technique was used to achieve an optimal separation of signal from background. Most likely, this event is a CC interaction with charm production, the tau and charm particle decaying into 1 prong and 2 prongs, respectively. The significance of this observation is evaluated.