Average of R(D) and R(D*) for EPS-HEP 2015

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 [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 χ2 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:

the difference with the SM stays at 3.9σ level in both cases.