Search for τ− → μ−μ+μ− decays at the LHCb experiment with Run 2 data

Journal of High Energy Physics, vol. 2026

Abstract

A bstract A search for the lepton-flavour-violating decay τ − → μ − μ + μ − is carried out using data collected by the LHCb experiment between 2016 and 2018 in proton-proton collisions at the LHC at a centre-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb − 1 . An upper limit of 1 . 9 (2 . 3) × 10 − 8 is set at the 90% (95%) confidence level on the branching fraction of the decay.

Authors 99

1. R. Aaij

   National Institute for Subatomic Physics

   Affiliation as printed

   Nikhef National Institute for Subatomic Physics

2. A. S. W. Abdelmotteleb

   University of Warwick

   Affiliation as printed

   University of Warwick

3. Carlos Abellán Beteta

   University of Zurich

   Affiliation as printed

   Universität Zürich

4. C. Abellán Beteta

   University of Warwick

   Affiliation as printed

   University of Warwick

5. T. Ackernley

   University of Liverpool

   Affiliation as printed

   University of Liverpool

6. A. A. Adefisoye

   Syracuse University

   Affiliation as printed

   Syracuse University

7. B. Adeva

   Universidade de Santiago de Compostela

   Affiliation as printed

   Universidade de Santiago de Compostela

8. M. Adinolfi

   University of Bristol

   Affiliation as printed

   University of Bristol

9. P. Adlarson

   Uppsala University

   Affiliation as printed

   Uppsala University

10. C. Agapopoulou

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut National de Physique Nucléaire et de Physique des Particules · Laboratoire de Physique des 2 Infinis Irène Joliot-Curie

    Affiliation as printed

    Université Paris-Saclay, CNRS/IN2P3, IJCLab

11. C. Aidala

    University of Michigan

    Affiliation as printed

    University of Michigan

12. Z. Ajaltouni

    Centre National de la Recherche Scientifique · Université Clermont Auvergne · Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Université Clermont Auvergne, CNRS/IN2P3, LPC

13. S. Akar

    Centre National de la Recherche Scientifique · Université Clermont Auvergne · Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Université Clermont Auvergne, CNRS/IN2P3, LPC

14. K. Carvalho Akiba

    National Institute for Subatomic Physics

    Affiliation as printed

    Nikhef National Institute for Subatomic Physics

15. Muzammil Akthar

    AGH University of Krakow

    Affiliation as printed

    AGH – University of Krakow, Faculty of Physics and Applied Computer Science

16. P. Albicocco

    Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati

    Affiliation as printed

    INFN Laboratori Nazionali di Frascati

17. J. Albrecht

    TU Dortmund University

    Affiliation as printed

    Technische Universität Dortmund

18. R. Aleksiejūnas

    Vilnius University

    Affiliation as printed

    Vilnius University

19. F. Alessio

    European Organization for Nuclear Research

    Affiliation as printed

    European Organization for Nuclear Research (CERN)

20. P. Álvarez Cartelle

    Universidade de Santiago de Compostela · University of Cambridge

    Affiliation as printed

    Universidade de Santiago de Compostela

    University of Cambridge

21. R. Amalric

    Centre National de la Recherche Scientifique · Sorbonne Université · Laboratoire de Physique Nucléaire et de Hautes Énergies · Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Sorbonne Université, CNRS/IN2P3

22. S. Amato

    Universidade Federal do Rio de Janeiro

    Affiliation as printed

    Universidade Federal do Rio de Janeiro (UFRJ)

23. Y. Amhis

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut National de Physique Nucléaire et de Physique des Particules · Laboratoire de Physique des 2 Infinis Irène Joliot-Curie

    Affiliation as printed

    Université Paris-Saclay, CNRS/IN2P3, IJCLab

24. Liupan An

    Peking University

    Affiliation as printed

    Peking University

25. L An

    Istituto Nazionale di Fisica Nucleare, Sezione di Firenze

    Affiliation as printed

    INFN Sezione di Firenze

26. M. Andersson

    University of Zurich

    Affiliation as printed

    Universität Zürich

27. P. Andreola

    University of Zurich

    Affiliation as printed

    Universität Zürich

28. M. Andreotti

    Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara

    Affiliation as printed

    INFN Sezione di Ferrara

29. Sergio Andres Estrada

    Universidade da Coruña

    Affiliation as printed

    Universidade da Coruña

30. Alessia Anelli

    Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca

    Affiliation as printed

    INFN Sezione di Milano-Bicocca

31. D. Ao

    University of Chinese Academy of Sciences

    Affiliation as printed

    University of Chinese Academy of Sciences

32. C. Arata

    Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · CEA Paris-Saclay - Etablissement de Saclay · Institut de Recherche sur les Lois Fondamentales de l'Univers

    Affiliation as printed

    Université Paris-Saclay, Centre d’Etudes de Saclay (CEA), IRFU

33. F. Archilli

    Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata

    Affiliation as printed

    INFN Sezione di Roma Tor Vergata

34. Zaratsyan Areg

    Syracuse University

    Affiliation as printed

    Syracuse University

35. Marco Argenton

    Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara

    Affiliation as printed

    INFN Sezione di Ferrara

36. S. Arguedas Cuendis

    Consejo Nacional de Rectores · European Organization for Nuclear Research

    Affiliation as printed

    Consejo Nacional de Rectores (CONARE)

    European Organization for Nuclear Research (CERN)

37. Lisa Arnone

    Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca

    Affiliation as printed

    INFN Sezione di Milano-Bicocca

38. A. Artamonov
39. M. Artuso

    Syracuse University

    Affiliation as printed

    Syracuse University

40. E. Aslanides

    Centre National de la Recherche Scientifique · Aix-Marseille Université · Centre de physique des particules de Marseille · Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Aix Marseille Univ, CNRS/IN2P3, CPPM

41. R. Ataíde Da Silva

    École Polytechnique Fédérale de Lausanne

    Affiliation as printed

    Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)

42. M. Atzeni

    Massachusetts Institute of Technology

    Affiliation as printed

    Massachusetts Institute of Technology

43. B. Audurier

    Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · CEA Paris-Saclay - Etablissement de Saclay · Institut de Recherche sur les Lois Fondamentales de l'Univers

    Affiliation as printed

    Université Paris-Saclay, Centre d’Etudes de Saclay (CEA), IRFU

44. Juliette Authier

    Centre National de la Recherche Scientifique · École Polytechnique · Institut National de Physique Nucléaire et de Physique des Particules · Institut Polytechnique de Paris · Laboratoire Leprince-Ringuet

    Affiliation as printed

    Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, Institut Polytechnique de Paris

45. D. Bacher

    University of Oxford

    Affiliation as printed

    University of Oxford

46. I. Bachiller

    École Polytechnique Fédérale de Lausanne

    Affiliation as printed

    Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)

47. S. Bachmann

    Heidelberg University

    Affiliation as printed

    Ruprecht-Karls-Universität Heidelberg

48. Marie Bachmayer

    École Polytechnique Fédérale de Lausanne

    Affiliation as printed

    Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)

49. John J Back

    University of Warwick

    Affiliation as printed

    University of Warwick

50. P. Baladrón Rodríguez

    Universidade de Santiago de Compostela

    Affiliation as printed

    Universidade de Santiago de Compostela

51. V. Balagura

    Centre National de la Recherche Scientifique · École Polytechnique · Institut National de Physique Nucléaire et de Physique des Particules · Institut Polytechnique de Paris · Laboratoire Leprince-Ringuet

    Affiliation as printed

    Laboratoire Leprince-Ringuet, CNRS/IN2P3, Ecole Polytechnique, Institut Polytechnique de Paris

52. Alessandro Balboni

    Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara

    Affiliation as printed

    INFN Sezione di Ferrara

53. W. Baldini

    Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara

    Affiliation as printed

    INFN Sezione di Ferrara

54. Zachary Baldwin

    Ruhr University Bochum

    Affiliation as printed

    Ruhr Universitaet Bochum, Fakultaet f. Physik und Astronomie

55. Luca Balzani

    TU Dortmund University

    Affiliation as printed

    Technische Universität Dortmund

56. H. -R. Bao

    University of Chinese Academy of Sciences

    Affiliation as printed

    University of Chinese Academy of Sciences

57. J. Baptista de Souza Leite

    Centro Brasileiro de Pesquisas Físicas

    Affiliation as printed

    Centro Brasileiro de Pesquisas Físicas (CBPF)

58. C. Barbero Pretel

    Universidade de Santiago de Compostela · Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · CEA Paris-Saclay - Etablissement de Saclay · Institut de Recherche sur les Lois Fondamentales de l'Univers

    Affiliation as printed

    Universidade de Santiago de Compostela

    Université Paris-Saclay, Centre d’Etudes de Saclay (CEA), IRFU

59. M. Barbetti

    Istituto Nazionale di Fisica Nucleare, Sezione di Firenze

    Affiliation as printed

    INFN Sezione di Firenze

60. I. R. Barbosa

    Pontifícia Universidade Católica do Rio de Janeiro

    Affiliation as printed

    Pontifícia Universidade Católica do Rio de Janeiro (PUC-Rio)

61. Roger John Barlow

    University of Manchester

    Affiliation as printed

    University of Manchester

62. Mikhail Barnyakov

    Istituto Nazionale di Fisica Nucleare, Sezione di Bologna

    Affiliation as printed

    INFN Sezione di Bologna

63. S. Barsuk

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut National de Physique Nucléaire et de Physique des Particules · Laboratoire de Physique des 2 Infinis Irène Joliot-Curie

    Affiliation as printed

    Université Paris-Saclay, CNRS/IN2P3, IJCLab

64. W. Barter

    University of Edinburgh

    Affiliation as printed

    University of Edinburgh

65. W. Barter

    Syracuse University

    Affiliation as printed

    Syracuse University

66. Saliha Bashir

    AGH University of Krakow

    Affiliation as printed

    AGH – University of Krakow, Faculty of Physics and Applied Computer Science

67. B. Batsukh

    Institute for High Energy Physics · Institute of High Energy Physics

    Affiliation as printed

    Institute Of High Energy Physics (IHEP)

68. Piera Battista

    Centre National de la Recherche Scientifique · Université Paris-Saclay · Institut National de Physique Nucléaire et de Physique des Particules · Laboratoire de Physique des 2 Infinis Irène Joliot-Curie

    Affiliation as printed

    Université Paris-Saclay, CNRS/IN2P3, IJCLab

69. Ali Bavarchee

    Eötvös Loránd University

    Affiliation as printed

    Eotvos Lorand University

70. A. Bay

    École Polytechnique Fédérale de Lausanne

    Affiliation as printed

    Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL)

71. A. Beck

    Massachusetts Institute of Technology

    Affiliation as printed

    Massachusetts Institute of Technology

72. A. Beck

    TU Dortmund University

    Affiliation as printed

    Technische Universität Dortmund

73. F. Bedeschi

    Istituto Nazionale di Fisica Nucleare, Sezione di Pisa

    Affiliation as printed

    INFN Sezione di Pisa

74. I. Bediaga

    Centro Brasileiro de Pesquisas Físicas

    Affiliation as printed

    Centro Brasileiro de Pesquisas Físicas (CBPF)

75. Noah Albin Behling

    TU Dortmund University

    Affiliation as printed

    Technische Universität Dortmund

76. S. Belin

    Universidade de Santiago de Compostela

    Affiliation as printed

    Universidade de Santiago de Compostela

77. Alberto Bellavista

    Istituto Nazionale di Fisica Nucleare, Sezione di Bologna

    Affiliation as printed

    INFN Sezione di Bologna

78. K. Belous
79. I. Belov

    Istituto Nazionale di Fisica Nucleare, Sezione di Genova

    Affiliation as printed

    INFN Sezione di Genova

80. I. Belyaev

    Istituto Nazionale di Fisica Nucleare, Sezione di Roma I

    Affiliation as printed

    INFN Sezione di Roma La Sapienza

81. E. Ben-Haim

    Centre National de la Recherche Scientifique · Sorbonne Université · Laboratoire de Physique Nucléaire et de Hautes Énergies · Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE), Sorbonne Université, CNRS/IN2P3

82. G Benane

    Centre National de la Recherche Scientifique · Aix-Marseille Université · Centre de physique des particules de Marseille · Institut National de Physique Nucléaire et de Physique des Particules

    Affiliation as printed

    Aix Marseille Univ, CNRS/IN2P3, CPPM

83. G Bencivenni

    Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati

    Affiliation as printed

    INFN Laboratori Nazionali di Frascati

84. Alexander Berezhnoy
85. R. Bernet

    University of Zurich

    Affiliation as printed

    Universität Zürich

86. R. Bernet

    Universitat Ramon Llull

    Affiliation as printed

    La Salle, Universitat Ramon Llull

87. A. Bertolin

    Istituto Nazionale di Fisica Nucleare, Sezione di Padova

    Affiliation as printed

    INFN Sezione di Padova

88. F. Betti

    University of Edinburgh

    Affiliation as printed

    University of Edinburgh

89. J. Bex

    University of Cambridge

    Affiliation as printed

    University of Cambridge

90. Oleg Bezshyyko

    Taras Shevchenko National University of Kyiv

    Affiliation as printed

    Taras Schevchenko University of Kyiv, Faculty of Physics

91. Senjuti Bhattacharya

    Eötvös Loránd University

    Affiliation as printed

    Eotvos Lorand University

92. M. S. Bieker

    University of Bonn

    Affiliation as printed

    Universität Bonn – Helmholtz-Institut für Strahlen und Kernphysik

93. N. V. Biesuz

    Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara

    Affiliation as printed

    INFN Sezione di Ferrara

94. Alice Biolchini

    National Institute for Subatomic Physics

    Affiliation as printed

    Nikhef National Institute for Subatomic Physics

95. M. Birch

    Imperial College London

    Affiliation as printed

    Imperial College London

96. F. C. R. Bishop

    Centre National de la Recherche Scientifique · Laboratoire d’Annecy de Physique des Particules · Institut National de Physique Nucléaire et de Physique des Particules · Université Savoie Mont Blanc

    Affiliation as printed

    Université Savoie Mont Blanc, CNRS, IN2P3-LAPP

97. A. Bitadze

    University of Manchester

    Affiliation as printed

    University of Manchester

98. A. Bizzeti

    Istituto Nazionale di Fisica Nucleare, Sezione di Firenze

    Affiliation as printed

    INFN Sezione di Firenze

99. T. Blake

    University of Warwick

    Affiliation as printed

    University of Warwick