Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations

The T2K Collaboration

doi:10.1038/s41586-020-2177-0

Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations

The T2K Collaboration

Institute for Cosmic Ray Research
University of Tokyo
Kyoto University
ETH Zurich
CCLRC Rutherford Appleton Laboratory
University of Liverpool
University of Sheffield
Kobe University
University of Bern
Tokyo Metropolitan University
Yokohama National University
Imperial College London
University of Regina
University of Warwick
University of Oxford
Institute for Nuclear Physics
Institute for Nuclear Research of the Russian Academy of Sciences
Politecnico di Bari
University of British Columbia
TRIUMF
Tokyo Institute of Technology
York University
Sorbonne Université
University of Geneva
Universite Paris-Saclay
The Barcelona Institute of Science and Technology
Lancaster University
Universidad Autónoma de Madrid
University of Silesia
Michigan State University
University of Colorado Boulder
High Energy Accelerator Research Organization (KEK)
The University of Sheffield
INFN
University of Houston
European Organization for Nuclear Research
INFN Sezione di Napoli
King's College London
Stony Brook University
University of Glasgow
Okayama University
Tokyo University of Science
Miyagi University of Education
Wroclaw University
RWTH Aachen University
Colorado State University
ICISE
Vietnam Academy of Science and Technology
University of Winnipeg
Royal Holloway University of London
University of Victoria
Louisiana State University
Boston University
Osaka City University
National Centre for Nuclear Research (NCBJ)
National Research Nuclear University MEPhI
Warsaw University of Technology
University of Rome
University of Rochester
University of Toronto
Long Beach VA and University of California
Keio University
Queen Mary University of London
University of Pittsburgh
University of Warsaw
Duke University
Stanford Linear Accelerator Center

Research output: Contribution to journal › Article › peer-review

448 Citations (Scopus)

Abstract

The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 1964¹, and CP violation in the weak interactions of quarks was soon established². Sakharov proposed³ that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis⁴. Leptonic mixing, which appears in the standard model’s charged current interactions^5,6, provides a potential source of CP violation through a complex phase δ_CP, which is required by some theoretical models of leptogenesis^7–9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments^10,11. Until now, the value of δ_CP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δ_CP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δ_CP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.

Original language	English
Pages (from-to)	339-344
Number of pages	6
Journal	Nature
Volume	580
Issue number	7803
DOIs	https://doi.org/10.1038/s41586-020-2177-0
Publication status	Published - 16 Apr 2020

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@article{b98a01a7cfb547f6ba4ef55d44ffcdbc,

title = "Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations",

abstract = "The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard model{\textquoteright}s charged current interactions5,6, provides a potential source of CP violation through a complex phase δCP, which is required by some theoretical models of leptogenesis7–9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.",

author = "\{The T2K Collaboration\} and K. Abe and R. Akutsu and A. Ali and C. Alt and C. Andreopoulos and L. Anthony and M. Antonova and S. Aoki and A. Ariga and T. Arihara and Y. Asada and Y. Ashida and Atkin, \{E. T.\} and Y. Awataguchi and S. Ban and M. Barbi and Barker, \{G. J.\} and G. Barr and D. Barrow and C. Barry and M. Batkiewicz-Kwasniak and A. Beloshapkin and F. Bench and V. Berardi and S. Berkman and L. Berns and S. Bhadra and S. Bienstock and A. Blondel and S. Bolognesi and B. Bourguille and Boyd, \{S. B.\} and D. Brailsford and A. Bravar and Bergu{\~n}o, \{D. Bravo\} and C. Bronner and A. Bubak and Avanzini, \{M. Buizza\} and J. Calcutt and T. Campbell and S. Cao and Cartwright, \{S. L.\} and Catanesi, \{M. G.\} and A. Cervera and A. Chappell and C. Checchia and D. Cherdack and O. Drapier and M. Gonin and B. Quilain",

note = "Publisher Copyright: {\textcopyright} 2020, The Author(s), under exclusive licence to Springer Nature Limited.",

year = "2020",

month = apr,

day = "16",

doi = "10.1038/s41586-020-2177-0",

language = "English",

volume = "580",

pages = "339--344",

journal = "Nature",

issn = "0028-0836",

publisher = "Nature Research",

number = "7803",

}

TY - JOUR

T1 - Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations

AU - The T2K Collaboration

AU - Abe, K.

AU - Akutsu, R.

AU - Ali, A.

AU - Alt, C.

AU - Andreopoulos, C.

AU - Anthony, L.

AU - Antonova, M.

AU - Aoki, S.

AU - Ariga, A.

AU - Arihara, T.

AU - Asada, Y.

AU - Ashida, Y.

AU - Atkin, E. T.

AU - Awataguchi, Y.

AU - Ban, S.

AU - Barbi, M.

AU - Barker, G. J.

AU - Barr, G.

AU - Barrow, D.

AU - Barry, C.

AU - Batkiewicz-Kwasniak, M.

AU - Beloshapkin, A.

AU - Bench, F.

AU - Berardi, V.

AU - Berkman, S.

AU - Berns, L.

AU - Bhadra, S.

AU - Bienstock, S.

AU - Blondel, A.

AU - Bolognesi, S.

AU - Bourguille, B.

AU - Boyd, S. B.

AU - Brailsford, D.

AU - Bravar, A.

AU - Berguño, D. Bravo

AU - Bronner, C.

AU - Bubak, A.

AU - Avanzini, M. Buizza

AU - Calcutt, J.

AU - Campbell, T.

AU - Cao, S.

AU - Cartwright, S. L.

AU - Catanesi, M. G.

AU - Cervera, A.

AU - Chappell, A.

AU - Checchia, C.

AU - Cherdack, D.

AU - Drapier, O.

AU - Gonin, M.

AU - Quilain, B.

PY - 2020/4/16

Y1 - 2020/4/16

N2 - The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard model’s charged current interactions5,6, provides a potential source of CP violation through a complex phase δCP, which is required by some theoretical models of leptogenesis7–9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.

AB - The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 19641, and CP violation in the weak interactions of quarks was soon established2. Sakharov proposed3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis4. Leptonic mixing, which appears in the standard model’s charged current interactions5,6, provides a potential source of CP violation through a complex phase δCP, which is required by some theoretical models of leptogenesis7–9. This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments10,11. Until now, the value of δCP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δCP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3σ). The 3σ confidence interval for δCP, which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks.

U2 - 10.1038/s41586-020-2177-0

DO - 10.1038/s41586-020-2177-0

M3 - Article

C2 - 32296192

AN - SCOPUS:85083443655

SN - 0028-0836

VL - 580

SP - 339

EP - 344

JO - Nature

JF - Nature

IS - 7803

ER -

Constraint on the matter–antimatter symmetry-violating phase in neutrino oscillations

Abstract

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