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*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]
• Belle Collaboration: Phys.Rev. D92, 072014 (2015) [arXiv:1507.03233] and arXiv:1603.06711 (Moriond EW 2016 preliminary)
• LHCb Collaboration: Phys.Rev.Lett. 115, 111803 (2015), Addendum: Phys.Rev.Lett. 115, 159901 (2015) [arXiv:1506.08614]

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→μν_μν_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.

The SM predictions used here are:

• R(D) =0.300 +- 0.008, H. Na et al., Phys.Rev.D 92, 054410 (2015) arXiv:1505.03925 [hep-lat]
• 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 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:

• R(D) =0.297 +- 0.017, J.F.Kamenik, and F.Mescia, Phys.Rev.D 78, 014003 (2008)arXiv:0802.3790 [hep-ph]
• 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]