Abstract
We carry out an analysis of the full set of ten bar{B}rightarrow 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^2right) , 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 } measurements. The coefficients entering at the 1/m_c^2 level are found to be of mathcal {O}(1), indicating convergence of the HQE. The phenomenological implications of our study include an updated exclusive determination of |V_{cb}| 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^{(*)}}, the tau polarization observables P_tau ^{D^{(*)}}, and the longitudinal polarization fraction F_L. Posterior samples for the HQE parameters are provided as ancillary files, allowing for their use in subsequent studies.
Highlights
The inference of phenomenological parameters such as |Vcb| or the e-mail: danny.van.dyk@gmail.com tive Field Theory (EFT) Wilson coefficients from experimental measurements of branching ratios and kinematical distributions in B → D(∗) −νdecays requires knowledge of the relevant hadronic matrix elements
A recent light-cone sum rule (LCSR) calculation [9] provides for the first time information on all form factors parametrizing matrix elements of the basis of dimensionsix operators, including those appearing only in connection with New Physics (NP) effects
We analyze various scenarios with different classes of inputs in order to probe their mutual compatibility; we provide the fit results for form factors and quantities of interest like R(D(∗)) in the viable scenarios
Summary
The inference of phenomenological parameters such as |Vcb| or the EFT Wilson coefficients from experimental measurements of branching ratios and kinematical distributions in B → D(∗) −νdecays requires knowledge of the relevant hadronic matrix elements The latter are commonly described by a set of ten independent hadronic form factors, which parametrize the strong-interaction dynamics in these modes as functions of the four-momentum transfer q2. The available theoretical calculations were insufficient to fully determine these form factors independently of experimental data; instead, the form factor shapes and |Vcb| were fitted together to the light-lepton modes This approach requires the assumption of absence of NP in these modes; this does not seem appropriate, given the anomalies in b → cτ ν data, and in b → sμ+μ− modes, since models accommodating both anomalies commonly modify the couplings to light leptons in chargedcurrent transitions. The determination of B → D(∗) form factors has advanced, due to both experimental and theoretical improvements: on the experimental
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