This web page contains the averages of the ratios of Branching Fractions
R(D*)=BF(B→D*τν_{τ})/BF(B→D* l ν_{l})
and R(D)=BF(B→Dτν_{τ})/BF(B→D l ν_{l}).

In the present average we consider the following measurements:

- BaBar Collaboration: Phys.Rev.Lett 109, 101802 (2012) [arXiv:1205.5442] and
Phys.Rev.D 88, 072012 (2013) [arXiv:1303.0571]

Combined measurement of R(D) and R(D*) based on the hadronic tagging sample and it is a combined. We use the results obtained imposing the isospin relations R(D^{0})=R(D^{+}) and R(D^{*0})=R(D^{*+}). - Belle Collaboration: Phys.Rev. D92, 072014 (2015) [arXiv:1507.03233]

Similar to the BaBar analysis: combined measurement of R(D) and R(D*), based on the hadronic tagging sample. - LHCb Collaboration: Phys.Rev.Lett. 115, 111803 (2015), Addendum: Phys.Rev.Lett. 115, 159901 (2015) [arXiv:1506.08614]

Measurement of R(D^{*+}). Only the τ→μν_{μ}ν_{τ}decay mode is used. - Belle Collaboration: Phys.Rev. D94, 072007 (2016):arXiv:1607.07923

Measurement of R(D^{*+}) based on a semileptonic tagging method. - Belle Collaboration: Phys.Rev.Lett. 118, 211801 (2017)arXiv:1612.00529

Measurement of R(D*) based on an hadronic tagging sample. The τ is reconstructed in the hadronic decay channels τ→πν and τ→ρν. This is a simultaneous measurement of R(D*) and the τ polarization. - LHCb Collaboration: presented at FPCP 2017 Slides

Measurement of R(D*) where τ is reconstructed in the hadronic decay channels τ→3πν.

In the average we assume 100% correlation for the systematic uncertainties associated with the D(*) form factors, the D** composition and shapes and the τ branching fractions. The other uncertainties are considered uncorrelated between the various experiments.

Experiment | R(D*) | R(D) | Rescaled Correlation (stat/syst/total) | Parameters | Remarks |
---|---|---|---|---|---|

BaBar | 0.332 +/- 0.024+/- 0.018 | 0.440 +/- 0.058 +/- 0.042 | -0.45/-0.07/-0.27 | input | Phys.Rev.Lett. 109,101802 (2012) [arXiv:1205.5442 [hep-ex]] Phys.Rev.D 88, 072012 (2013) [arXiv:1303.0571] |

BELLE | 0.293 +/- 0.038 +/- 0.015 | 0.375 +/- 0.064 +/- 0.026 | -0.56/-0.11/-0.49 | input | Phys.Rev.D 92, 072014 (2015) [arXiv:1507.03233 [hep-ex]] |

BELLE | 0.302 +/- 0.030 +/- 0.011 | - | - | input | Phys.Rev. D94,072007 (2016) [arXiv:1607.07923 [hep-ex]] |

LHCb | 0.336 +/- 0.027 +/- 0.030 | - | - | input | Phys.Rev.Lett.115,111803 (2015) [arXiv:1506.08614 [hep-ex]] |

BELLE | 0.270 +/- 0.035 ^{+ 0.028}_{-0.025} |
- | - | input | Phys.Rev.Lett.118,211801 (2017) [arXiv:1612.00529 [hep-ex]] |

LHCb | 0.285 +/- 0.019 +/- 0.029 | - | - | input | Presented at FPCP2017 [Slides] |

Average |
0.304 +/- 0.013 +/- 0.007 |
0.407 +/- 0.039 +/- 0.024 |
-0.20 |
chi2/dof = 3.71/6 (CL = 0.716) |
R(D)-R(D*).pdf
.png
.C (dashed curves correspond to 2 and 4 σ contours) R(D) .pdf .png .C R(D*) .pdf .png .C |

SM predictions for R(D) based on recent Lattice calculations:

- R(D) =0.299 +- 0.011, J.A.Bailey et al. [FNAL/MILC Collaboration], Phys.Rev.D 92, 034506 (2015)arXiv:1503.07237 [hep-lat]
- R(D) =0.300 +- 0.008, H. Na et al., Phys.Rev.D 92, 054410 (2015) arXiv:1505.03925 [hep-lat]

The most recent SM prediction for R(D*):

- R(D*)=0.252 +- 0.003, S.Fajfer, J.F.Kamenik, and I.Nisandzic, Phys.Rev.D85(2012) 094025 arXiv:1203.2654 [hep-ex]

R(D) and R(D*) exceed the SM predictions by 2.3σ and 3.4σ respectively (comparing R(D) with FLAG average).
Considering the R(D)-R(D*) correlation of -0.20, the resulting combined χ^{2} is 20.60 for 2 degree of freedom,
corresponding to a p-value of 4.13 x 10^{-5}. The difference with the SM predictions reported above,
corresponds to about 4.1σ.