Bayesian fit analysis to full distribution data of $$ \overline{\mathrm{B}}\to {\mathrm{D}}^{\left(\ast \right)}\mathrm{\ell}\overline{\nu }:\left|{\mathrm{V}}_{\mathrm{cb}}\right| $$ determination and new physics constraints

Abstract

We investigate the semi-leptonic decays ofB → D (*) ν in terms of the Heavy-Quark-Effective-Theory (HQET) parameterization for the form factors, which is described with the heavy quark expansion up to O(1/m 2 c) beyond the simple approximation considered in the original CLN parameterization. An analysis with this setup was first given in the literature, and then we extend it to the comprehensive analyses including (i) simultaneous fit of |V cb | and the HQET parameters to available experimental full distribution data and theory constraints, and (ii) New Physics (NP) contributions of the V 2 and T types, such as (cγ µ P R b)(γ µ P L ν) and (cσ µν P L b)(σ µν P L ν), to the decay distributions and rates. For this purpose, we perform Bayesian fit analyses by using Stan program, a state-of-theart public platform for statistical computation. Then, we show that our |V cb | fit results for the SM scenarios are close to the PDG combined average from the exclusive mode, and indicate significance of the angular distribution data. In turn, for the SM + NP scenarios, our fit analyses find that non-zero NP contribution is favored at the best fit point for both SM + V 2 and SM + T depending on the HQET parameterization model. A key feature is then realized in theB → D (*) τν observables. Our fit result of the HQET parameters in the SM(+T) produces a consistent value for R D while smaller for R D * , compared with the previous SM prediction in the HFLAV report. On the other hand, SM + V 2 points to smaller and larger values for R D and R D * than the SM predictions. In particular, the R D * deviation from the experimental measurement becomes smaller, which could be interesting for future improvement on measurements at the Belle II experiment.

Implications for new physics from a novel puzzle in B¯(s)0→Iguro1, Kitahara2 2020Phys. Rev. DSelf Cite311240View full textAdd to dashboardCite

“…These SM predictions are obtained by the QCD factorization (QCDF) [3][4][5] at leading power in Λ QCD =m b , where the Wilson coefficients at next-to-nextto-leading logarithmic accuracy are used [6]. Compared to the previous estimations [7], the theoretical uncertainties are significantly reduced thanks to recent developments in theB ðsÞ → D ðÃÞ ðsÞ form factors including order Oð1=m 2 c Þ corrections within the framework of the heavy-quark expansion [8][9][10][11].…”

“…Note that the exclusive jV cb j, however, produces an additional 4.2σ level tension in ε K [13]. See also [11] for a more recent determination of the exclusive jV cb j using the full angular distribution data.…”

Relations between b → cτν decay modes in scalar models

“…∀ B q → P τ ν : 18) and again analogous equations for the decay rates with fixed D * -or τ -polarization. If the above equations are applied to multiple bins of one or several decay modes, it can be directly solved for the NP parameters.…”

“…[16] R(D * ) SM = 0.254 +0.007 −0.006 , (1.6) see also refs. [17,18]. There are further hadronic decays with the same underlying quark level transition like B s → D…”

“…For progress, form factor results from lattice QCD [30,[70][71][72][73][74][75][76][77][78][79][80][81][82][83][84] and also LCSRs [85][86][87][88] are very important. A lot of progress has been made in the research of the ability of new physics (NP) models, including from the beginning scalar models, to explain the data [12,17,18,36,48,50,[89][90][91]. An important way to probe for NP are relations between different decay modes.…”