CERN Accelerating science

Tau decays


Tau branching fractions

  • global constrained fit of tau branching fractions
  • test lepton universality, compute Vus

Tau lepton flavour violation

  • report all the best experimental upper limits
  • compute combinations of experimental upper limits


  • Swagato Banerjee, convener (University of Louisville, Belle II)
  • Marcin Chrząszcz (University of Zürich & Kraków, LHCb)
  • Kiyoshi Hayasaka (Niigata University, Belle)
  • Alberto Lusiani, convener (Scuola Normale Superiore and INFN Pisa, BaBar)
  • Mike Roney (University of Victoria, BaBar)

Past members

  • Hisaki Hayashii (Nara Woman's University, Belle)
  • Boris Shwartz (BINP, Belle)

Current HFLAV Tau Web Report

  • HFLAV Tau Winter 2022 web report (15 June 2022)
    • new radiative corrections published in 2021 for tau hadronic decays have been used
    • the LFV upper limits combinations have not been updated in this edition

Current HFLAV Report

Latest contribution to the PDG

  • The PDG 2020 includes a tau branching fractions fit and a tau branching fraction review based on the same published experimental inputs that are used by the HFLAV End 2018 fit, but without inclusion of the preliminary results. Furthermore, the PDG fit uses the customary PDG unitarity constraint, while the HFLAV fit does not.

Past reports

  • End 2018 HFLAV report (September 2019)
    • Averages of b-hadron, c-hadron, and tau-lepton properties as of summer 2018arXiv:1909.12524Eur. Phys. J. C (2021) 81: 226
    • HFLAV Tau End 2018 web report (27 September 2019)
    • with respect to the previous [Spring 2017] report, some new published and preliminary BaBar tau branching fractions measurements have been included and the Vus calculations have been revised and updated
  • Spring 2017 HFLAV report (December 2017)
  • Summer 2016 HFLAV report (October 2016)
    • arXiv:1612.07233 [hep-ex], Y. Amhis et al., "Averages of b-hadron, c-hadron, and tau-lepton properties as of Summer 2016"
    • HFLAV Tau Summer 2016 web report, published on 7 October 2016
    • no significant updates since 2014, but several minor improvement and fixes
  • Summer 2014 HFLAV report
    • arXiv:1412.7515 [hep-ex], Y. Amhis et al., "Averages of b-hadron, c-hadron, and tau-lepton properties as of Summer 2014"
    • HFLAV Tau Summer 2014 web report
    • includes combinations on limits on searches for Lepton flavor Violation in tau decays
  • Early 2012 HFLAV report
  • HFLAV Tau Summer 2011 web report
    • since March 2011 includes some additional new and old measurements
  • Summer 2010 HFLAV report
    • arXiv:1010.1589v3 [hep-ex], D. Asner et al., "Averages of b-hadron, c-hadron, and tau-lepton Properties"
      • (this HFLAV report includes for the first time a Tau section)

Past contributions to the PDG

  • PDG 2016, 2017 and 2018 include a tau branching fractions fit and a tau branching fraction review (not yet published as of 18 October 2019) based on the same experimental inputs of the HFLAV Spring 2017 fit, but treated with the customary PDG unitarity constraint

Additional useful references, which are not official HFLAV Tau reports

  • Tau 2010 proceedings contribution on HFLAV Tau on-going work

    • S. Banerjee et al., Status Report from Tau subgroup of the HFLAV,
      Proceedings of the 11th International Workshop on Tau Lepton Physics, Manchester, UK, 13-17 September 2010,
      arXiv:1101.5138 [hep-ex]