Eur. Phys. J. C (2023) 83: 782
https://doi.org/10.1140/epjc/s10052-023-11819-x

Regular Article - Experimental Physics

Measurements of neutrino oscillation parameters from the T2K experiment using $3.6\times {10}^{21}$ protons on target

¹ Department of Theoretical Physics, University Autonoma Madrid, 28049, Madrid, Spain
² Laboratory for High Energy Physics (LHEP), Albert Einstein Center for Fundamental Physics, University of Bern, Bern, Switzerland
³ Department of Physics, Boston University, Boston, MA, USA
⁴ Department of Physics and Astronomy, University of California, Irvine, Irvine, CA, USA
⁵ IRFU, CEA, Université Paris-Saclay, 91191, Gif-sur-Yvette, France
⁶ Department of Physics, University of Colorado at Boulder, Boulder, CO, USA
⁷ Department of Physics, Colorado State University, Fort Collins, Colorado, USA
⁸ Department of Physics, Duke University, Durham, NC, USA
⁹ Department of Atomic Physics, Eötvös Loránd University, Budapest, Hungary
¹⁰ Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
¹¹ CERN European Organization for Nuclear Research, 1211, Geneva 23, Switzerland
¹² Section de Physique, DPNC, University of Geneva, Geneva, Switzerland
¹³ School of Physics and Astronomy, University of Glasgow, Glasgow, UK
¹⁴ H. Niewodniczanski Institute of Nuclear Physics PAN, Cracow, Poland
¹⁵ High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki, Japan
¹⁶ Department of Physics, University of Houston, Houston, TX, USA
¹⁷ Institut de Fisica d’Altes Energies (IFAE)-The Barcelona Institute of Science and Technology, Campus UAB, Bellaterra, Barcelona, Spain
¹⁸ Institut für Physik, Johannes Gutenberg-Universität Mainz, Staudingerweg 7, 55128, Mainz, Germany
¹⁹ IFIC (CSIC and University of Valencia), Valencia, Spain
²⁰ Institute For Interdisciplinary Research in Science and Education (IFIRSE), ICISE, Quy Nhon, Vietnam
²¹ Department of Physics, Imperial College London, London, UK
²² Dipartimento Interuniversitario di Fisica, INFN Sezione di Bari and Università e Politecnico di Bari, Bari, Italy
²³ Dipartimento di Fisica, INFN Sezione di Napoli and Università di Napoli, Naples, Italy
²⁴ Dipartimento di Fisica, INFN Sezione di Padova and Università di Padova, Padua, Italy
²⁵ INFN Sezione di Roma and Università di Roma “La Sapienza”, Rome, Italy
²⁶ Institute for Nuclear Research of the Russian Academy of Sciences, Moscow, Russia
²⁷ International Centre of Physics, Institute of Physics (IOP), Vietnam Academy of Science and Technology (VAST), 10 Dao Tan, Ba Dinh, Hanoi, Vietnam
²⁸ ILANCE, CNRS-University of Tokyo International Research Laboratory, 277-8582, Kashiwa, Chiba, Japan
²⁹ Kavli Institute for the Physics and Mathematics of the Universe (WPI), The University of Tokyo Institutes for Advanced Study, University of Tokyo, Kashiwa, Chiba, Japan
³⁰ Department of Physics, Keio University, Yokohama, Kanagawa, Japan
³¹ Department of Physics, King’s College London, Strand, WC2R 2LS, London, UK
³² Kobe University, Kobe, Japan
³³ Department of Physics, Kyoto University, Kyoto, Japan
³⁴ Physics Department, Lancaster University, Lancaster, UK
³⁵ Lawrence Berkeley National Laboratory, 94720, Berkeley, CA, USA
³⁶ Laboratoire Leprince-Ringuet, Ecole Polytechnique, IN2P3-CNRS, Palaiseau, France
³⁷ Department of Physics, University of Liverpool, Liverpool, UK
³⁸ Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA, USA
³⁹ Joint Institute for Nuclear Research, Dubna, Moscow Region, Russia
⁴⁰ Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
⁴¹ Department of Physics, Miyagi University of Education, Sendai, Japan
⁴² National Centre for Nuclear Research, Warsaw, Poland
⁴³ Department of Physics and Astronomy, State University of New York at Stony Brook, Stony Brook, NY, USA
⁴⁴ Department of Physics, Okayama University, Okayama, Japan
⁴⁵ Department of Physics, Osaka Metropolitan University, Osaka, Japan
⁴⁶ Department of Physics, Oxford University, Oxford, UK
⁴⁷ Department of Physics and Astronomy, University of Pennsylvania, 19104, Philadelphia, PA, USA
⁴⁸ Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, USA
⁴⁹ School of Physics and Astronomy, Queen Mary University of London, London, UK
⁵⁰ Department of Physics, University of Regina, Regina, Saskatchewan, Canada
⁵¹ Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA
⁵² Department of Physics, Royal Holloway University of London, Egham, Surrey, UK
⁵³ III. Physikalisches Institut, RWTH Aachen University, Aachen, Germany
⁵⁴ Departamento de Física Atómica, Molecular y Nuclear, Universidad de Sevilla, 41080, Sevilla, Spain
⁵⁵ Department of Physics and Astronomy, University of Sheffield, Sheffield, UK
⁵⁶ Institute of Physics, University of Silesia, Katowice, Poland
⁵⁷ Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Sorbonne Université, Université Paris Diderot, CNRS/IN2P3, Paris, France
⁵⁸ Rutherford Appleton Laboratory, STFC, Harwell, Oxford, UK
⁵⁹ Department of Physics, University of Tokyo, Tokyo, Japan
⁶⁰ Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo, Kamioka, Japan
⁶¹ Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Japan
⁶² Department of Physics, Tokyo Institute of Technology, Tokyo, Japan
⁶³ Department of Physics, Tokyo Metropolitan University, Tokyo, Japan
⁶⁴ Department of Physics, Faculty of Science and Technology, Tokyo University of Science, Noda, Chiba, Japan
⁶⁵ Department of Physics, University of Toronto, Toronto, ON, Canada
⁶⁶ TRIUMF, Vancouver, BC, Canada
⁶⁷ Faculty of Physics, University of Warsaw, Warsaw, Poland
⁶⁸ Institute of Radioelectronics and Multimedia Technology, Warsaw University of Technology, Warsaw, Poland
⁶⁹ Department of Physics, Faculty of Science, Tohoku University, Sendai, Miyagi, Japan
⁷⁰ Department of Physics, University of Warwick, Coventry, UK
⁷¹ Department of Physics, University of Winnipeg, Winnipeg, MB, Canada
⁷² Faculty of Physics and Astronomy, Wroclaw University, Wrocław, Poland
⁷³ Department of Physics, Yokohama National University, Yokohama, Japan
⁷⁴ Department of Physics and Astronomy, York University, Toronto, ON, Canada
⁷⁵ Université Paris-Saclay, Gif-sur-Yvette, France
⁷⁶ INFN-Laboratori Nazionali di Legnaro, Legnaro, Italy
⁷⁷ J-PARC, Tokai, Japan
⁷⁸ Kavli IPMU (WPI), The University of Tokyo, Tokyo, Japan
⁷⁹ Moscow Institute of Physics and Technology (MIPT), Moscow Region, Russia and National Research Nuclear University “MEPhI”, Moscow, Russia
⁸⁰ IPSA-DRII, Ivry-sur-Seine, France
⁸¹ The Graduate University of Science and Technology, Vietnam Academy of Science and Technology, Ho Chi Minh City, Vietnam
⁸² JINR, Dubna, Russia
⁸³ Nambu Yoichiro Institute of Theoretical and Experimental Physics (NITEP), Osaka, Japan
⁸⁴ Science Department, BMCC/CUNY, New York, NY, USA

^sg clarence.wret@physics.ox.ac.uk

Received: 7 March 2023
Accepted: 10 July 2023
Published online: 5 September 2023

Abstract

The T2K experiment presents new measurements of neutrino oscillation parameters using $19.7(16.3)\times {10}^{20}$ protons on target (POT) in (anti-)neutrino mode at the far detector (FD). Compared to the previous analysis, an additional $4.7\times {10}^{20}$ POT neutrino data was collected at the FD. Significant improvements were made to the analysis methodology, with the near-detector analysis introducing new selections and using more than double the data. Additionally, this is the first T2K oscillation analysis to use NA61/SHINE data on a replica of the T2K target to tune the neutrino flux model, and the neutrino interaction model was improved to include new nuclear effects and calculations. Frequentist and Bayesian analyses are presented, including results on ${sin}^2{\theta }_{13}$ and the impact of priors on the ${\delta }_{\text{CP}}$ measurement. Both analyses prefer the normal mass ordering and upper octant of ${sin}^2{\theta }_{23}$ with a nearly maximally CP-violating phase. Assuming the normal ordering and using the constraint on ${sin}^2{\theta }_{13}$ from reactors, ${sin}^2{\theta }_{23}=0.{561}_{-0.032}^{+0.021}$ using Feldman–Cousins corrected intervals, and $\Delta m_{32}^2=2.{494}_{-0.058}^{+0.041}\times {10}^{-3}{\text{eV}}^2$ using constant $\Delta {\chi }^2$ intervals. The CP-violating phase is constrained to ${\delta }_{\text{CP}}=-1.{97}_{-0.70}^{+0.97}$ using Feldman–Cousins corrected intervals, and ${\delta }_{\text{CP}}=0,\pi$ is excluded at more than 90% confidence level. A Jarlskog invariant of zero is excluded at more than $2\sigma$ credible level using a flat prior in ${\delta }_{\text{CP}},$ and just below $2\sigma$ using a flat prior in $sin{\delta }_{\text{CP}}.$ When the external constraint on ${sin}^2{\theta }_{13}$ is removed, ${sin}^2{\theta }_{13}=28.0_{-6.5}^{+2.8}\times {10}^{-3},$ in agreement with measurements from reactor experiments. These results are consistent with previous T2K analyses.