Average of R(D) and R(D*) for Moriod EW 2017

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:


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 Submitted to journal [arXiv:1612.00529 [hep-ex]]
Average 0.310 +/- 0.015 +/- 0.008 0.403 +/- 0.040 +/- 0.024 -0.23 chi2/dof = 3.167/5 (CL = 0.673) R(D)-R(D*).pdf  .png   .C 
(dashed curves correspond to 2-3-4 σ contours)
R(D) .pdf  .png   .C 
R(D*) .pdf  .png   .C 

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

The prediction obtained combining the two calculation above (FLAG Working Groups arXiv:1607.00299 [hep-lat] ) is R(D) =0.300 +- 0.008.

P. Gambino and D. Bigi in arXiv:1606.08030 [hep-ph] (to be published in PRD) combined the two lattice calculations, wih the experimental Form Factor of the B→ D l ν from BaBar (2010) and Belle (2016, obtaining R(D)=0.299+-0.003. The result is compatible with the results above, but more accurate.

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

R(D) and R(D*) exceed the SM predictions by 2.2σ and 3.4σ respectively (comparing with FLAG average). Considering the R(D)-R(D*) correlation of -0.23, the resulting combined χ2 is 18.62 for 2 degree of freedom, corresponding to a p-value of 8.8 x 10-5. The difference with the SM predictions reported above, is at about 3.9σ.