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Abstract We analyze in detail the angular distributions in $${\bar{B}}\rightarrow D^*\ell {{\bar{\nu }}}$$ B ¯ → D ∗ ℓ ν ¯ decays, with a focus on lepton-flavour non-universality. We investigate the minimal number of angular observables that fully describes current and upcoming datasets, and explore their sensitivity to physics beyond the Standard Model (BSM) in the most general weak effective theory. We apply our findings to the current datasets, extract the non-redundant set of angular observables from the data, and compare to precise SM predictions that include lepton-flavour universality violating mass effects. Our analysis shows that the number of independent angular observables that can be inferred from current experimental data is limited to only four. These are insufficient to extract the full set of relevant BSM parameters. We uncover a $$\sim 4\sigma $$ ∼ 4 σ tension between data and predictions that is hidden in the redundant presentation of the Belle 2018 data on $${\bar{B}}\rightarrow D^*\ell {{\bar{\nu }}}$$ B ¯ → D ∗ ℓ ν ¯ decays. This tension specifically involves observables that probe $$e-\mu $$ e - μ lepton-flavour universality. However, we find inconsistencies in these data, which renders results based on it suspicious. Nevertheless, we discuss which generic BSM scenarios could explain the tension, in the case that the inconsistencies do not affect the data materially. Our findings highlight that $$e-\mu $$ e - μ non-universality in the SM, introduced by the finite muon mass, is already significant in a subset of angular observables with respect to the experimental precision.

Abstract We provide updated predictions for the hadronic decays $$\bar{B}_s^0\rightarrow D_s^{(*)+} \pi ^-$$ B ¯ s 0 → D s ( ∗ ) + π - and $$\bar{B}^0\rightarrow D^{(*)+} K^-$$ B ¯ 0 → D ( ∗ ) + K - . They are based on $${\mathcal {O}}(\alpha _s^2)$$ O ( α s 2 ) results for the QCD factorization amplitudes at leading power and on recent results for the $$\bar{B}_{(s)} \rightarrow D_{(s)}^{(*)}$$ B ¯ ( s ) → D ( s ) ( ∗ ) form factors up to order $$\mathcal{O}(\Lambda _\mathrm{QCD}^2/m_c^2)$$ O ( Λ QCD 2 / m c 2 ) in the heavy-quark expansion. We give quantitative estimates of the matrix elements entering the hadronic decay amplitudes at order $$\mathcal{O}(\Lambda _\mathrm{QCD}/m_b)$$ O ( Λ QCD / m b ) for the first time. Our results are very precise, and uncover a substantial discrepancy between the theory predictions and the experimental measurements. We explore two possibilities for this discrepancy: non-factorizable contributions larger than predicted by the QCD factorization power counting, and contributions beyond the Standard Model. We determine the $$f_s/f_d$$ f s / f d fragmentation fraction for the CDF, D0 and LHCb experiments for both scenarios.

Abstract We carry out a comprehensive analysis of the full set of $${\bar{B}}_q \rightarrow D_q^{(*)}$$ B¯q→Dq(∗) form factors for spectator quarks $$q=u,d,s$$ q=u,d,s within the framework of the Heavy-Quark expansion (HQE) to order $${\mathcal {O}}\left( \alpha _s, 1/m_b, 1/m_c^2\right) $$ Oαs,1/mb,1/mc2 . In addition to the available lattice QCD calculations we make use of two new sets of theoretical constraints: we produce for the first time numerical predictions for the full set of $${\bar{B}}_s \rightarrow D_s^{(*)}$$ B¯s→Ds(∗) form factors using Light-Cone sum rules with $$B_s$$ Bs -meson distribution amplitudes. Furthermore, we reassess the QCD three-point sum rule results for the Isgur-Wise functions entering all our form factors for both $$q=u,d$$ q=u,d and $$q=s$$ q=s spectator quarks. These additional constraints allow us to go beyond the commonly used assumption of $$SU(3)_F$$ SU(3)F symmetry for the $${{\bar{B}}}_s\rightarrow D_s^{(*)}$$ B¯s→Ds(∗) form factors, especially in the unitarity constraints which we impose throughout our analysis. We find the coefficients of the IW functions emerging at $${\mathcal {O}}\left( 1/m_c^2\right) $$ O1/mc2 to be consistent with the naive $${\mathcal {O}}\left( 1\right) $$ O1 expectation, indicating a good convergence of the HQE. While we do not find significant SU(3) breaking, the explicit treatment of $$q=s$$ q=s as compared to a simple symmetry assumption renders the unitarity constraints more effective. We find that the (pseudo)scalar bounds are saturated to a large degree, which affects our theory predictions. We analyze the phenomenological consequences of our improved form factors by extracting $$|V_{cb}|$$ |Vcb| from $${\bar{B}}\rightarrow D^{(*)}\ell \nu $$ B¯→D(∗)ℓν decays and producing theoretical predictions for the lepton-flavour universality ratios R(D), $$R(D^*)$$ R(D∗) , $$R(D_s)$$ R(Ds) and $$R(D_s^*)$$ R(Ds∗) , as well as the $$\tau $$ τ - and $$D_q^*$$ Dq∗ polarization fractions for the $${\bar{B}}_q\rightarrow D_q^{(*)}\tau \nu $$ B¯q→Dq(∗)τν modes.

Abstract We carry out an analysis of the full set of ten $$\bar{B}\rightarrow D^{(*)}$$ B¯→D(∗) form factors within the framework of the Heavy-Quark Expansion (HQE) to order $$\mathcal {O}\left( \alpha _s,\,1/m_b,\,1/m_c^2\right) $$ Oαs,1/mb,1/mc2 , both with and without the use of experimental data. This becomes possible due to a recent calculation of these form factors at and beyond the maximal physical recoil using QCD light-cone sum rules, in combination with constraints from lattice QCD, QCD three-point sum rules and unitarity. We find good agreement amongst the various theoretical results, as well as between the theoretical results and the kinematical distributions in $$\bar{B}\rightarrow D^{(*)}\lbrace e^-,\mu ^-\rbrace \bar{\nu }$$ B¯→D(∗){e-,μ-}ν¯ measurements. The coefficients entering at the $$1/m_c^2$$ 1/mc2 level are found to be of $$\mathcal {O}(1)$$ O(1) , indicating convergence of the HQE. The phenomenological implications of our study include an updated exclusive determination of $$|V_{cb}|$$ |Vcb| in the HQE, which is compatible with both the exclusive determination using the BGL parametrization and with the inclusive determination. We also revisit predictions for the lepton-flavour universality ratios $$R_{D^{(*)}}$$ RD(∗) , the $$\tau $$ τ polarization observables $$P_\tau ^{D^{(*)}}$$ PτD(∗) , and the longitudinal polarization fraction $$F_L$$ FL . Posterior samples for the HQE parameters are provided as ancillary files, allowing for their use in subsequent studies.