Evidence for an Excess ofB¯→D(*)τ−ν¯τ

Abstract

Based on the full BABAR data sample, we report improved measurements of the ratios R(D(*))=B(B[over ¯]→D(*)τ(-)ν[over ¯](τ))/B(B[over ¯]→D(*)ℓ(ℓ)(-)ν[over ¯](ℓ)), where ℓ is either e or μ. These ratios are sensitive to new physics contributions in the form of a charged Higgs boson. We measure R(D)=0.440±0.058±0.042 and R(D(*))=0.332±0.024±0.018, which exceed the standard model expectations by 2.0σ and 2.7σ, respectively. Taken together, our results disagree with these expectations at the 3.4σ level. This excess cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model.

Y and ψ leptonic decays as probes of solutions to the R(D (*)) puzzle

“…This choice is taken to avoid large production rate at the LHC and dangerous FCNC transitions in the first and second generation. 1 To determine uniquely the flavor structure of the NP couplings one should further specify the mass basis alignment of the UV operators. In what follows, we always consider alignment to the down mass basis, with…”

“…The combined results of BaBar [1,2], Belle [3][4][5][6] and LHCb [7] read [8] R(D) = 0.403 ± 0.047, R(D * ) = 0.310 ± 0.017, ρ = −0.23,…”

Status of B to D(*) τ ν decays in two-Higgs-doublet models

“…The latest BaBar measurements of R(D) and R(D * ) exclude the type-II 2HDM at 99.8% CL for any value of tan β /M H ± as long as M H ± > 10 GeV [2]. The remaining region of the parameter space, namely M H ± ≤ 10 GeV, is excluded in Ref.…”

“…The remaining region of the parameter space, namely M H ± ≤ 10 GeV, is excluded in Ref. [2] by considering the loop-induced processB → X s γ, which sets the tan β -independent bound M H ± > 380 GeV at 95% CL in this model [11]. While this argument is perfectly correct, it relies on a comparison of limits obtained from tree-level and loop-induced processes.…”

“…A recent measurement of the exclusive semileptonicB → D ( * ) τ −ν τ decay rates performed by the BaBar collaboration, suggesting a significant violation of lepton flavour universality (LFU), has raised interest as a possible new physics signature. The BaBar collaboration measured the ratios [2] R(D ( * ) ) = Γ(B → D ( * ) τ −ν τ ) Γ(B → D ( * ) −ν ) , (1.1) where is either e or µ, finding R(D) = 0.440 ± 0.058 ± 0.042 and R(D * ) = 0.332 ± 0.024 ± 0.018. These results show a 2.0σ and 2.7σ excess with respect to the standard model (SM) predictions respectively [3,4].…”