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Register a new userUn-binned Angular Analysis of $Bto D^*ell u_ell$ and the Right-handed Current
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In this article, we perform a sensitivity study of an un-binned angular analysis of the $Bto D^*ell u_ell$ decay, including the contributions from the right-handed current. We show that the angular observable can constrain very strongly the right-handed current without the intervention of the yet unsolved $V_{cb}$ puzzle.
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After improving the knowledge about residua of the semileptonic form factor at its first two poles we show that $f_+^{Dpi}(q^2)$ is not saturated when compared with the experimental data. To fill the difference we approximate the rest of discontinuity by an effective pole and show that the data can be described very well with the position of the effective pole larger than the next excitation in the spectrum of $D^ast$ state. The results of fits with experimental data also suggest the validity of superconvergence which in the pole models translates to a vanishing of the sum of residua of the form factor at all poles. A similar discussion in the case of $Bto pi ell u_ell$ leads to the possibility of extracting $vert V_{ub}vert$, the error of which appears to be dominated by $g_{B^ast Bpi}$, which can be nowadays computed on the lattice. In evaluating the residua of the form factors at their nearest pole we needed the vector meson decay constants $f_{D^ast}$ and $f_{B^ast}$, which we computed by using the numerical simulations of QCD on the lattice with $N_{rm f}=2$ dynamical quarks. We obtain, $f_{D^ast}/f_D=1.208(27)$ and $f_{B^ast}/f_B=1.051(17)$.
We extract $|V_{cb}|$ from the available data in the decay $B to D^{(*)}ell u_{ell}$. Our analysis uses the $q^2(w)$ binned differential decay rates in different subsamples of $Bto Dell u_ell$ ($ell = e, mu$), while for the decay $Bto D^*ell u_ell$, the unfolded binned differential decay rates of four kinematic variables including the $q^2$ bins have been used. In the CLN and BGL parameterizations of the form factors, the combined fit to all the available data along with their correlations yields $|V_{cb}| = (39.77 pm 0.89)times 10^{-3}$ and $(40.90 pm 0.94)times 10^{-3}$ respectively. In these fits, we have used the inputs from lattice and light cone sum rule (LCSR) along with the data. Using our fit results and the HQET relations (with the known corrections included) amongst the form factors, and parameterizing the unknown higher order corrections (in the ratios of HQET form factors) with a conservative estimate of the normalizing parameters, we obtain $R(D^{*}) = 0.259 pm 0.006$ (CLN) and $R(D^*) = 0.257 pm 0.005$ (BGL).
We update the standard model (SM) predictions of $R(D^*)$ using the latest results on the decay distributions in $B to D^* ell u_{ell}$ ($ell = mu, e$) by Belle collaboration, while extracting $|V_{cb}|$ at the same time. Depending on the inputs used in the analysis, we define various fit scenarios. Although the central values of the predicted $R(D^*)$ in all the scenarios have reduced from its earlier predictions in 2017, the results are consistent with each other within the uncertainties. In this analysis, our prediction of $R(D^*)$ is consistent with the respective world average at $sim 3sigma$. We have also predicted several angular observables associated with $B to D^* tau u_{tau}$ decays. We note that the predicted $F_L(D^*)$ is consistent with the corresponding measurement at 2$sigma$. Utilizing these new results, we fit the Wilson coefficients appearing beyond the standard model of particle physics (BSM). To see the trend of SM predictions, we have utilized the recently published preliminary results on the form-factors at non-zero recoil by the lattice groups like Fermilab-MILC and JLQCD and predicted the observables in $B to D^* ell u_{ell}$, and $B to D^* tau u_{tau}$ decays.
Besides being important to determine Standard Model parameters such as the CKM matrix elements $|V_{cb}|$ and $|V_{ub}|$, semileptonic $B$ decays seem also promising to reveal new physics (NP) phenomena, in particular in connection with the possibility of uncovering lepton flavour universality (LFU) violating effects. In this view, it could be natural to connect the tensions in the inclusive versus exclusive determinations of $|V_{cb}|$ to the anomalies in the ratios $R(D^{(*)})$ of decay rates into $tau$ vs $mu, e$. However, the question has been raised about the role of the parametrization of the hadronic $B to D^{(*)}$ form factors in exclusive $B$ decay modes. We focus on the fully differential angular distributions of $bar B to D^* ell^-{bar u}_ell$ with $D^* to D pi$ or $D^* to D gamma$, the latter mode being important in the case of $B_s to D_s^*$ decays. We show that the angular coefficients in the distributions can be used to scrutinize the role of the form factor parametrization and to pin down deviations from SM. As an example of a NP scenario, we include a tensor operator in the $b to c$ semileptonic effective Hamiltonian, and discuss how the angular coefficients allow to construct observables sensitive to this structure, also defining ratios useful to test LFU.
We present a measurement of angular observables and a test of lepton flavor universality in the $Bto K^ast ell^+ell^-$ decay, where $ell$ is either $e$ or $mu$. The analysis is performed on a data sample corresponding to an integrated luminosity of $711~mathrm{fb}^{-1}$ containing $772times 10^{6}$ $Bbar B$ pairs, collected at the $Upsilon(4S)$ resonance with the Belle detector at the asymmetric-energy $e^+e^-$ collider KEKB. The result is consistent with Standard Model (SM) expectations, where the largest discrepancy from a SM prediction is observed in the muon modes with a local significance of $2.6sigma$.
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