New physics and the tau polarization vector in b → cτ −ν¯τ decays


  • Neus Penalva IFIC (CSIC-UV)
  • Juan Nieves IFIC (CSIC-UV)
  • Eliecer Hernández U.Salamanca



Beyond the Standard Model, CP violation, Lepton Flavour Universality


For a general H_b→H_c τ ν_τ decay, we analyze the role of theτpolarization vector P^μ in the context of lepton flavor universality violation studies. We use a general phenomenological approach that includes several new physics terms and we make specific evaluations of P^μ fordifferent decays. We show that a P^μ component orthogonal to the plane determined by the final hadron and τ three-momenta is only possiblefor complex Wilson coefficients and it would be associated to a violation of the CP symmetry.


- Yasmine Sara Amhis et al. Averages of b-hadron, c-hadron,andτ-lepton properties as of 2018.Eur. Phys. J. C, 81(3):226,2021.

- J. P. Lees et al. Evidence for an excess of ̄B→D(∗)τ− ̄ντdecays.Phys. Rev. Lett., 109:101802, 2012.

J. P. Lees et al. Measurement of an Excess of ̄B→D(∗)τ− ̄ντDecays and Implications for Charged Higgs Bosons.Phys.Rev., D88(7):072012, 2013

M. Huschle et al.Measurement of the branching ratio of ̄B→D(∗)τ− ̄ντrelative to ̄B→D(∗)ℓ− ̄νℓdecays withhadronic tagging at Belle.Phys. Rev., D92(7):072014, 2015.

Y. Sato et al. Measurement of the branching ratio of ̄B0→D∗+τ− ̄ντrelative to ̄B0→D∗+ℓ− ̄νℓdecays with a semilep-tonic tagging method.Phys. Rev., D94(7):072007, 2016

S. Hirose et al. Measurement of theτlepton polarizationand R(D∗) in the decay ̄B→D∗τ− ̄ντ. Phys. Rev. Lett.,118(21):211801, 2017

G. Caria et al. Measurement of R(D) and R(D∗) with asemileptonic tagging method. Phys. Rev. Lett., 124(16):161803,2020.

Roel Aaij et al. Measurement of the ratio of branching fractions B( ̄B0→D∗+τ− ̄ντ)/B( ̄B0→D∗+μ− ̄νμ). Phys.Rev. Lett., 115(11):111803, 2015.[Erratum: Phys. Rev.Lett.115,no.15,159901(2015)]

R. Aaij et al. Measurement of the ratio of the B0→D∗−τ+ντ and B0→D∗−μ+νμ branching fractions using three-prong τ-lepton decays. Phys. Rev. Lett., 120(17):171802, 2018

Clara Murgui, Ana Pen ̃uelas, Martin Jung, and Antonio Pich.Global fit tob→cτνtransitions.JHEP, 09:103, 2019

Neus Penalva, Eliecer Hern ́andez, and Juan Nieves.Newphysics and the tau polarization vector inb→cτ ̄ντdecays.JHEP, 06:118, 2021.

Neus Penalva, Eliecer Hern ́andez, and Juan Nieves. ̄Bc→ηc, ̄Bc→J/ψand ̄B→D(∗)semileptonic decays including newphysics.Phys. Rev. D, 102(9):096016, 2020.

N. Penalva, E. Hern ́andez, and J. Nieves. Hadron and leptontensors in semileptonic decays including new physics.Phys.Rev. D, 101(11):113004, 2020.

Mikhail A. Ivanov, J ̈urgen G. K ̈orner, and Chien-Thang Tran.Probing new physics in ̄B0→D(∗)τ− ̄ντusing the longitudi-nal, transverse, and normal polarization components of the taulepton.Phys. Rev. D, 95(3):036021, 2017.

Rui-Xiang Shi, Li-Sheng Geng, Benjamín Grinstein, Sebastian Jäger, and Jorge Martin Camalich. Revisiting the new-physics interpretation of theb→cτνdata.JHEP, 12:065,2019

Neus Penalva, Eliecer Hernández, and Juan Nieves. The role ofright-handed neutrinos in b→ct(π νt,ρ νt,μ νμ νt)νt from visible final-state kinematics.JHEP, 10:122, 2021.

Pouya Asadi, Anna Hallin, Jorge Martin Camalich, David Shih,and Susanne Westhoff. Complete framework for tau polarimetry in B→D(∗)τν decays. Phys. Rev. D, 102(9):095028,2020




How to Cite

Penalva N, Nieves J, Hernández E. New physics and the tau polarization vector in b → cτ −ν¯τ decays. Supl. Rev. Mex. Fis. [Internet]. 2022 Jun. 13 [cited 2024 May 29];3(3):0308058 1-5. Available from: