Abstract
Motivated by the persistent anomalies reported in the bto ctau overline{v} data, we perform a general model-independent analysis of these transitions, in the presence of light right-handed neutrinos. We adopt an effective field theory approach and write a low-energy effective Hamiltonian, including all possible dimension-six operators. The corresponding Wilson coefficients are determined through a numerical fit to all available experimental data. In order to work with a manageable set of free parameters, we define eleven well- motivated scenarios, characterized by the different types of new physics that could mediate these transitions, and analyse which options seem to be preferred by the current measurements. The data exhibit a clear preference for new-physics contributions, and good fits to the data are obtained in several cases. However, the current measurement of the longitudinal D∗ polarization in Bto {D}^{ast}tau overline{v} cannot be easily accommodated within its experimental 1σ range. A general analysis of the three-body Bto Dtau overline{v} and four-body Bto {D}^{ast}left(to Dpi right)tau overline{v} angular distributions is also presented. The accessible angular observables are studied in order to assess their sensitivity to the different new physics scenarios. Experimental information on these distributions would help to disentangle the dynamical origin of the current anomalies.
Highlights
Intriguing hints of discrepancies between the measured data and the Standard Model (SM) predictions have been observed in B decays by several experimental collaborations [1, 2]
In order to work with a manageable set of free parameters, we define eleven wellmotivated scenarios, characterized by the different types of new physics that could mediate these transitions, and analyse which options seem to be preferred by the current measurements
We show from a theoretical perspective the implications of new physics in the observables involving b → c transitions and discuss the possible ultraviolet (UV) scenarios that could give rise to such anomalies in the context of b → c processes involving both left- and right-handed neutrinos
Summary
Intriguing hints of discrepancies between the measured data and the Standard Model (SM) predictions have been observed in B decays by several experimental collaborations [1, 2]. All phenomenological analyses need to rely on the underlying assumption that the differential decay distributions, and the experimental acceptances, are not significantly modified by the NP contributions While this assumption is unavoidable, in the absence of direct access to the data, none of the previous studies have included the measured q2 distributions in their fits. [31] to a basis of dimension-six operators that includes light RHNs. In our fit procedure, we consider all observables measured for B → D(∗)τ νdecays until date; including the data for binned differential distributions with respect to the lepton-neutrino invariant-mass squared, the D∗ longitudinal polarization fraction FLD∗, the lepton polarization asymmetry PτD∗ and the experimental results for RD(∗). Many technical details, such as hadronic matrix elements, FFs, and the full set of relevant helicity amplitudes, are compiled in several appendices
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