We carry out an analysis of the full set of ten $\bar{B}\to D^{(*)}$ form factors within the framework of the Heavy-Quark Expansion (HQE) to order $\mathcal{O}(α_s,\,1/m_b,\,1/m_c^2)$, 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 $\bar{B}\to D^{(*)}\lbrace e^-,μ^-\rbrace\barν$ 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 $τ$ polarization observables $P_τ^{D^{(*)}}$, 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.
We discuss the renormalization of the electroweak Standard Model at 1-loop using the leptonic effective weak mixing angle as one of the input parameters. We evaluate the impact of this choice in the prediction of the forward-backward asymmetry for the neutral current Drell-Yan process. The proposed input scheme is suitable for a direct determination of the effective leptonic weak mixing angle from the experimental data.
We reassess the $B\toπ\ellν_{\ell}$ differential branching ratio distribution experimental data released by the BaBar and Belle Collaborations supplemented with all lattice calculations of the $B\toπ$ form factor shape available up to date obtained by the HPQCD, FNAL/MILC and RBC/UKQCD Collaborations. Our study is based on the method of Padé approximants, and includes a detailed scrutiny of each individual data set that allow us to obtain $|V_{ub}|=3.53(8)_{\rm{stat}}(6)_{\rm{syst}}\times10^{-3}$. The semileptonic $B^{+}\toη^{(\prime)}\ell^{+}ν_{\ell}$ decays are also addressed and the $η$-$η^…
We derive model-independent bounds on the form factors for the decay $B_c^+ \to η_c\, \ell^+\, ν$ including full mass effects, i.e. $\ell = e,\, μ, \text{ and } τ$. The bounds are obtained by using the BGL parameterization for the form factors, and fitting to the preliminary lattice data of the HPQCD Collaboration. Our main result after bounding the form factors is the Standard Model (SM) prediction for the ratio of branching fractions $R(η_c) = \mathcal{B}(B_c^+ \to η_c\, τ^+\, ν_τ) / \mathcal{B}(B_c^+ \to η_c\, μ^+\, ν_μ)$. We find $R(η_c)|_{\text{SM}} = 0.31^{+0.04}_{-0.02}$, and argue that…
In light of the first observation of the semileptonic decay $B^{0}_{s}\to K^{-}μ^{+}ν_μ$ by the LHCb collaboration, we revisit the determination of the CKM parameter $|V_{ub}|$ from exclusive semileptonic $B$-meson decays. A controlled theoretical input on the Standard Model $B\toπ$ and $B_{s}\to K$ vector and scalar form factors from Lattice QCD in the large $q^{2}$ region, in combination with experimental measurements of the differential $B\toπ\ellν_{\ell}$ and $B^{0}_{s}\to K^{-}μ^{+}ν_μ$ branching ratio distributions, has allowed us determine $|V_{ub}|=3.86(11)\times10^{-3}$ and $|V_{ub}|=…
We reconsider the possibility that the tension in the $|V_{cb}|$ determinations from inclusive and exclusive $B$ decay modes is due to a new physics effect. We modify the Standard Model effective Hamiltonian for semileptonic $b \to c$ transitions including a tensor operator with a lepton flavour dependent coupling $ε_T^\ell$, and investigate separately the muon and electron modes. The interference term between SM and NP, proportional to the lepton mass, has different impact in the inclusive and exclusive $B$ modes to muon. Moreover, even when the lepton mass is small as for the electron, the N…
We extract the Cabibbo-Kobayashi-Maskawa matrix element $V_{cb}$ from the exclusive decays of $Λ_b\to Λ_c\ell\bar ν_\ell$ and $Λ_b\to Λ_c M_{(c)}$ with $M=(π^-,K^-)$ and $M_c=(D^-,D^-_s)$, where the branching ratios of $Λ_b\to ΛM_{(c)}$ measured with high precisions have not been used in the previous studies. Explicitly, we find $|V_{cb}|=(44.0\pm 3.5)\times 10^{-3}$, which agrees with the value of $(42.11\pm 0.74)\times 10^{-3}$ from the inclusive $B\to X_c\ell\bar ν_\ell$ decays. Furthermore, based on the most recent ratio of $|V_{ub}|/|V_{cb}|$ from the exclusive $Λ_b$ decays, we obtain $|V…
Motivated by recent $R_D$, $R_{D^*}$ and $R_{J/ψ}$ anomalies in $B\to D\ell^- \barν_{\ell}$, $B\to D^*\ell^- \barν_{\ell}$ and $B_c\to J/ψ\ell^- \barν_{\ell}$ decays, respectively, we study possible R-parity violating supersymmetric effects in $B_c\to J/ψ\ell^- \barν_{\ell},η_c\ell^- \barν_{\ell}$ and $Λ_b \to Λ_c \ell^- \barν_{\ell}$ decays, which are also induced by $b\to c \ell^- \barν_{\ell}$ at quark level. We find that (I) the constrained slepton exchange couplings $λ_{i33}\tildeλ'^*_{i23}$ involving in $b\to c τ^- \barν_τ$ transition from relevant latest experimental data still have qui…
We use the exclusive baryonic $B$ decays to determine the Cabibbo-Kobayashi-Maskawa (CKM) matrix element $V_{ub}$. From the relation $|V_{ub}|^2/|V_{cb}|^2=({\cal B}_π/{\cal B}_D){\cal R}_{ff}$ based on $B^-\to p\bar p π^-$ and $\bar B^0\to p\bar p D^0$ decays, where $|V_{cb}|$ and ${\cal B}_π/{\cal B}_D\equiv{\cal B}(B^-\to p\bar p π^-)/{\cal B}(\bar B^0\to p\bar p D^0)$ are the data input parameters, while ${\cal R}_{ff}$ is the one fixed by the $B\to p\bar p$ transition matrix elements, we find $|V_{ub}|=(3.48^{+0.87}_{-0.63}\pm 0.40\pm 0.07)\times 10^{-3}$ with the errors corresponding to …
At present, there are discrepancies with the predictions of the standard model in ${\bar B}^0 \to D^{*+} \ell^- {\barν}_\ell$ decays, hinting at the presence of new physics (NP) in $b \to c τ^- {\barν}$. Various NP models have been proposed to explain the data. In this talk, I discuss how the measurement of CP-violating observables in ${\bar B}^0 \to D^{*+} \ell^- {\barν}_\ell$ can be used to differentiate the NP scenarios.
Using a fully relativistic lattice fermion action, we compute the form factors of the semileptonic decay $B\toπ\ellν$, which is required for the determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$. We employ the Möbius domain-wall fermion formalism for the generation of lattice ensembles with 2+1 sea quark flavours as well as for the valence heavy and light quarks. We compute the form factors at various values of the lattice spacing and multiple light and heavy quark masses, and extrapolate the results to the physical point. We combine our lattice results with the availabl…
Exclusive semileptonic decays based on $b\to s$ transitions have been attracting a lot of attention as some angular observables deviate significantly from the Standard Model (SM) predictions in specific $q^2$ bins. B meson decays induced by other Flavor Changing Neutral Current (FCNC), $b\to d$, can also offer a probe to new physics with an additional sensitivity to the weak phase in Cabibbo-Kobayashi-Masakawa (CKM) matrix. We provide predictions for angular observables for $b\to d$ semileptonic transitions, namely $\bar{B}_s\to K^{\ast}\ell^+\ell^-$, $\bar{B}^0\toρ^0 \ell^+\ell^-$, and their …
We systematically revisit the baryonic four-body semileptonic decays of $B^- \to {\bf B}\bar{\bf B}'\ell^- \barν_{\ell}$ by the perturbative QCD counting rules with ${\bf B}$ representing octet baryons and $\ell=e,μ$. We study the transition form factors of $B^- \to {\bf B} \bar{\bf B}'$ in the limit of $(p_{\bf B}+p_{\bar{\bf B}'})^2 \to \infty $ with the three-body $\bar{B}\to {\bf B}\bar{\bf B}' M$ and $B^- \to p\bar{p} μ^- \barν_μ$ data along with $SU(3)_f$ flavor symmetry. We calculate the decay branching ratios and angular asymmetries as well as the differential decay branching fractions…
In this paper, we investigate the tree-dominated $\bar{B}^*_{u,d,s,c} \to V \ell^- \barν_\ell$ ($V=D^*_{u,d}\,,D^*_s\,,J/ψ$ and $\ell=e\,,μ\,,τ$) decays in the Standard Model with the relevant form factors obtained in the light-front quark model. These decays involve much more helicity states relative to the corresponding $\bar{B}^* \to P \ell^- \barν_\ell$ and $\bar{B} \to V \ell^- \barν_\ell$ decays, and moreover, the contribution of longitudinal polarization mode ($V$ meson) is relatively small, $\sim 30\%$, compared with the corresponding $B$ meson decays. We have also computed the branchi…
We investigate the experimentally-accessible kinematic distributions of the $\bar B\to D^{(*)}τ^-(\to\ell^-\barν_\ellν_τ)\barν_τ$ decays. Specifically, we study the decay rates as functions of the $B\to D^{(*)}$ transferred squared momentum, the energy of the final charged lepton and the angle of its 3-momentum relative to the 3-momentum of the recoiling $D^{(*)}$. The angular distribution allows to introduce new observables, like a forward-backward asymmetry, which are complementary to the total rates. We present analytic formulas for the observable 3-fold 5-body differential decay rates, stu…
We present a detailed analysis of QED corrections to $\bar{B} \to \bar{K} \ell^+ \ell^-$ decays at the double-differential level. Cancellations of soft and collinear divergences are demonstrated analytically using the phase space slicing method. Whereas soft divergences are found to cancel at the differential level, the cancellation of the hard-collinear logs $\ln m_\ell$ require, besides photon-inclusiveness, a specific choice of kinematic variables. In particular, hard-collinear logs in the lepton-pair invariant mass distribution ($q^2$), are sizeable and need to be treated with care when co…
We analyze the factorization to subleading power in the flavor changing neutral current process $\bar B\to X_s \ell^+ \ell^-$. In particular, we compute the so-called resolved contributions and explore the numerical impact on observables. In these contributions the virtual photon couples to light partons instead of connecting directly to the effective weak-interaction vertex. They represent an irreducible uncertainty in the inclusive $\bar B \to X_s \ell^+ \ell^-$ decay which cannot be removed by relaxing the experimentally necessary cuts in the hadronic mass spectrum.
In the framework of a baryon-number-violating effective Lagrangian, we calculate improved lower bounds on partial lifetimes for proton and bound neutron decays, including $p \to \ell^+ \ell'^+ \ell'^-$, $n \to \barν\ell^+ \ell'^-$, $p \to \ell^+ ν\barν$, and $n \to \barν\barνν$, where $\ell$ and $\ell'$ denote $e$ or $μ$, with both $\ell = \ell'$ and $\ell \ne \ell'$ cases. Our lower bounds are substantially stronger than the corresponding lower bounds from direct experimental searches. We also present lower bounds on $(τ/B)_{p \to \ell^+γ}$, $(τ/B)_{n \to \barνγ}$, $(τ/B)_{p \to \ell^+ γγ}$, …
The $B$ meson semileptonic modes to $ρ(770)$ and $a_1 (1260)$ are useful to pin down possible non Standard Model effects. The 4d differential $\bar B \to ρ(ππ) \ell^- \bar ν_\ell$ and $ \bar B \to a_1 (ρπ) \ell^- \bar ν_\ell$ decay distributions are computed in SM and in extensions involving new Lepton Flavour Universality violating semileptonic $b \to u$ operators. The Large Energy limit for the light meson is also considered for both modes. The new effective couplings are constrained using the available data, and several observables in $\bar B \to ρ(ππ) \ell^- \bar ν_\ell$ in which NP effect…
BELLE has recently reported the measurement of the branching fraction of the semileptonic $B^{-}\toπ^{+}π^{-}\ell^{-}\barν_\ell$ decay, where $\ell$ represents an electron or a muon. With the new information on the $ππ$ invariant mass spectrum, we extract $|V_{ub}|=(3.31\pm 0.61)\times 10^{-3}$ in agreement with those from the other exclusive $B$ decays. In particular, we determine the non-resonant $B\toππ$ transition form factors, and predict the non-resonant branching fraction ${\cal B}(B^{-}\toπ^{+}π^{-}\ell^{-}\barν_\ell)=(3.5\pm 1.4^{+4.3}_{-2.4})\times 10^{-5}$, which is accessible to th…
A novel approach to reconstruct inclusive $\bar{B} \to X_{s} \ell^{+}\ell^{-}$ decays is presented. The method relies on isopsin symmetry to extrapolate the semi-inclusive signature $X_{b}\to K^{+} \ell^{+}\ell^{-} X$ to the fully inclusive rate in $B^{+}$ and $B^{0}$ decays. We investigate the possibility to measure branching fractions and other observables such as lepton universality ratios and $CP$ asymmetries. As a proof of concept, fast simulation is used to compare the $X_{b}\to K^{+} \ell^{+}\ell^{-} X$ signature with a fully inclusive approach. Several experimental advantages are seen …
New physics searches via angular distributions of $ \bar{B} \to D^* (\to D π) τ(\to \ell ν_τ\barν_\ell) \barν_τ$ decays
Lawrence Technological University（劳伦斯理工大学）；University of Hawaii（夏威夷大学）；University of Mississippi（密西西比大学）；Université Paris-Saclay（巴黎萨克雷大学）；Nankai University（南开大学）
We consider the exclusive $P_{\ell 4}$ decays, $P\to (P_1P_2)_V\ell ν_{\ell}$, where the subindex $V$ means that the invariant mass of the pseudoscalar pair is taken within a small window around the mass of the vector meson $V$. Pole contributions beyond the dominant $P\to V(\to P_1P_2)\ellν_{\ell}$ amplitude of $P_{\ell 4}$ decays are identified, which, in turn, affects the determination of the CKM matrix elements $|V_{qq'}|$. We evaluate the effects of those contributions in the extraction of bottom and charm quark mixings. An application to $B\to (ππ)_ρ\ell ν_{\ell}$ data from Belle collabo…
We determine $|V_{cb}|$ using the third-order perturbative series for the inclusive semileptonic $B$ decay width and for the masses of the bottomonium 1S states. We use the masses of $η_b(1S)$ and $Υ(1S)$ as short-distance masses and point out that there is a sizable difference of $|V_{cb}|$ between the two 1S mass schemes. This is the dominant error of our determination and stems from insufficiency to describe theoretically the observed mass splitting of the bottomonium 1S states. We also study the significance of the $\mathcal{O}(Λ_{\overline{\rm MS}}^2)$ non-perturbative effects in HQET wit…
Bardeen-Buras-Gérard have proposed a large N$_c$ method to evaluate hadronic weak matrix elements to attack for instance the determination of the $ΔI= \frac{1}{2}$-rule and $\mathrm{Re}(\frac{ε'}ε)$. Here we test this method to the determination of the form factor parameters $a_+$ and $b_+$ in the decays $K^+ \rightarrow π^+ \ell^+ \ell^- $ and $K_S \rightarrow π^0 \ell^+ \ell^-$. The results are encouraging: in particular after a complete treatment of Vector Meson Dominance (VMD).
The strong coupling constant of doubly heavy baryons with light pseudoscalar mesons $ π$ and $ K $ are computed within the light cone sum rules. We take into account two-particle and three-particle distribution amplitudes of the said pseudoscalar mesons. We compare our result with the one existing in the literature.
We derive the expressions for the full angular distributions of $\bar B\to D\ell\bar ν_\ell$ and $\bar B\to D^{\ast }\ell\bar ν_\ell$ decays and discuss the spectra on each angle separately. The coefficient functions, depending on helicity amplitudes, can then be combined in an ensemble of observables which can then be used to check for the presence of New Physics. We examine the sensitivity of each of these observables on the presence of non-Standard Model interaction terms at low energies. The expressions presented here are general and can be used for studying any other semileptonic pseudosc…
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 $τ$ vs $μ, e$. However, the question has been raised about the role of the parametrization of t…
A new model-independent parametrization is proposed for the hadronic form factors in the semileptonic $\bar{B}\to D\ell\barν_\ell$ decay. By a combined consideration of the recent experimental and lattice QCD data, we determine precisely the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|=41.01(75)\times 10^{-3}$ and the ratio $\mathcal{R}_D=\frac{\mathcal{BR}(\bar{B}\to D τ\barν_τ)}{\mathcal{BR}(\bar{B}\to D \ell \barν_\ell)}=0.301(5)$. The coefficients in this parametrization, related to phase shifts by sumrulelike dispersion relations and hence called phase moments, encode important scat…
Comment on ``Next-to-next-to-leading order vacuum polarization function of heavy quark near threshold and sum rules for $b \bar b$ system'' and ``Next-to-next-to-leading order relation between $R(e^+e^-\to b\bar b)$ and $Γ_{\rm sl}(b\to clν_l)$ and precise determination of $|V_{cb}|$''
