Average of R(D) and R(D*) for Winter 2016

This web page contains the averages of the ratios of Branching Fractions R(D*)=BF(B→D*τντ)/BF(B→D* l νl) and R(D)=BF(B→Dτντ)/BF(B→D l νl).
In the present average we consider the following measurements:

We use the BaBar and Belle results obtained imposing the isospin relations R(D0)=R(D+) and R(D*0)=R(D*+); LHCb instead measures only R(D*+).
LHCb uses τ→μνμντ 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 Phys.Rev.D 92, 072014 (2015) [arXiv:1507.03233 [hep-ex]]
BELLE 0.302 +/- 0.030 +/- 0.011 - - input Preliminary at Moriond EW 2016 [arXiv:1603.06711 [hep-ex]]
LHCb 0.336 +/- 0.027 +/- 0.030 - - input Phys.Rev.Lett.115,111803 (2015) [arXiv:1506.08614 [hep-ex]]
Average 0.316+/- 0.016 +/- 0.010 0.397+/- 0.040 +/- 0.028 -0.21 chi2/dof = 2.38/4 (CL = 0.67) pdf png

The SM predictions used here are:

R(D) and R(D*) exceed the SM predictions by 1.9σ and 3.3σ respectively. Considering the R(D)-R(D*) correlation of -0.21, the resulting combined χ2 is 19.73 for 2 degree of freedom, corresponding to a p-value of 5.2 x 10-5. The difference with the SM predictions reported above is at 4.0σ level.

Other calculations of R(D) are available and are consistent with the one reported above:

the difference with the SM is at 4.0σ level in both cases.