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:
We use the BaBar and Belle results obtained imposing the isospin relations R(D^{0})=R(D^{+}) and
R(D^{*0})=R(D^{*+}); LHCb instead measures only R(D*^{+}).
LHCb uses τ→μν_{μ}ν_{τ} decay mode, BaBar and Belle use both τ→e and
τ→μ leptonic tau decays.
In the average we assume 100% correlation for the systematic uncertainties
associated with the D(*) form factors and with the D** composition and shapes.
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 | [arXiv:1507.03233 [hep-ex]] |
LHCb | 0.336 +/- 0.027 +/- 0.030 | - | - | input | [arXiv:1506.08614 [hep-ex]] |
Average | 0.322+/- 0.018 +/- 0.012 | 0.391+/- 0.041 +/- 0.028 | -0.41/-0.10/-0.29 | chi2/dof = 2.1/3 (CL = 0.55) | png pdf ( rd.png rd.pdf rds.png rds.pdf ) |
The SM predictions used here are:
R(D) and R(D*) exceed the SM predictions by 1.7σ and 3.0σ respectively.
Considering the R(D)-R(D*) correlation of -0.29, the resulting combined χ^{2} is 18.2 for 2 degree of freedom,
corresponding to a p-value of 1.1 x 10^{-4}. The difference with the SM predictions reported above is at 3.9σ level.
Some more recent lattice calculations of R(D) are available and are consistent with and more precise than the R(D) reported above: