We investigate the semi-leptonic decays of $\bar B \to D^{(*)} \ell\barν$ in terms of the Heavy-Quark-Effective-Theory (HQET) parameterization for the form factors, which is described with the heavy quark expansion up to $\mathcal O(1/m_c^2)$ 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 to the decay distributions and rates. For this purpose, we perform Bayesian fit analyses by using Stan program, a state-of-the-art 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 $\text{SM} + \text{NP}$ scenarios, our fit analyses find that non-zero NP contribution is favored at the best fit point for both $\text{SM} + V_2$ and $\text{SM} + T$ depending on the HQET parameterization model. A key feature is then realized in the $\bar B \to D^{(*)} τ\barν$ observables. Our fit result of the HQET parameters in the $\text{SM} (+T)$ 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, $\text{SM}+V_2$ 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.
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.
Methods are described in the framework of light-cone expansion which allow one to determine the Cabibbo-Kobayashi-Maskawa matrix elements |V_ub| and |V_cb| from measurements of the differential decay rates as a function of the scaling variables in the inclusive semileptonic decays of B mesons. By these model-independent methods the dominant hadronic uncertainties can be avoided and the B -> X_u\ellνdecay can be very efficiently differentiated from the B -> X_c\ellνdecay, which may lead to precise determinations of |V_ub| and |V_cb|.
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…
We examine the possibility for precise determination of |V_{ts}| (and |V_{td}/V_{ts}|) from the exclusive decays, $B --> K \ell^+ \ell^-, B --> K^* \ell^+ \ell^-$ (and $B --> π\ell^+ \ell^-, B --> ρ\ell^+ \ell^-$). We show that the ratio |V_{ts}| can be extracted experimentally with a small theoretical uncertainty from hadronic form--factors, if we {\bf appropriately constrain} kinematical regions of $q^2$. We also give detailed analytical and numerical results on the differential decay width $dΓ(B --> K^* \ell^+ \ell^-)/dq^2$, and the ratios of integrated branching fractions, ${\cal B}(B --> …
We perform a combined analysis of $τ\to Kπν_τ$ decay and $πK$ scattering with constraints from $K_{\ell3}$ data using a $N/D$ approach that fulfills requirements from unitarity and analyticity. We obtain a good fit of the $I=1/2$ $πK$ amplitude in the $P$ wave using the LASS data above the elastic region while in this region data are generated via Monte Carlo using the FOCUS results based on $D_{\ell 4}$ decay. The spectrum and branching ratio of $τ\to Kπν_τ$ constrained by $K_{\ell3}$ decays are also well reproduced leading to $f_+(0) |V_{us}|= 0.2163 \pm 0.0014 $. Furthermore, we obtain the …
The precise determination of the CKM elements $V_{cb}$ and $V_{ub}$ is crucial for any new physics analysis in the flavour sector. Their values can be determined from several tree-level decays: $V_{cb}$ can be extracted from $B\to D\ellν$ and $B\to D^*\ellν$ while $V_{ub}$ can be obtained from $B\to π\ellν$, $B\to ρ\ellν$ and $B\toτν$. In addition, for both $V_{cb }$ and $V_{ub}$ an inclusive determination is available. There is a long lasting discrepancy between the inclusive and exclusive determinations which recently even increased for $V_{cb}$ above the $3\;σ$ level. In this article we stu…
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.
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…
We discuss the possibilities of assessing a non-zero $C_{7γ}^\prime$ from the direct and the indirect measurements of the photon polarization in the exclusive $b \to sγ^{(*)}$ decays. We focus on three methods and explore the following three decay modes: $B \to K^*(\to K_Sπ^0)γ$, $B \to K_1(\to Kππ)γ$, and $B \to K^*(\to Kπ)\ell^+\ell^-$. By studying different New Physics scenarios we show that the future measurement of conveniently defined observables in these decays could provide us with the full determination of $C_{7γ}$ and $C_{7γ}^\prime$.
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…
We study the four-body exclusive semileptonic baryonic $\bar B$ decays of $B^-\to p\bar p \ell^- \barν_{\ell}$ ($\ell=e,μ,τ$) in the standard model. We find that their decay branching ratios are about $(1.0, 1.0,0.5)\times 10^{-4}$, respectively. In particular, the electron mode is close to the corresponding CLEO's upper limit of $5.2\times 10^{-3}$, while all results are about one or two orders of magnitude larger than the previous estimated values for the inclusive modes of $\bar B\to {\bf B\bar B'}\ell \bar ν$. Clearly, both B-factories of Belle and BaBar should be able to observe these exc…
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 study the charged Higgs effects on the decays of $B^{-} \to τ\barν_τ$ and $\bar B\to P(V) \ell \barν_{\ell}$ with $P=π^{+},D^{+}$ and $V=ρ^{+},D^{*+}$. We concentrate on the minimal supersymmetric standard model with nonholomorphic terms at a large $\tanβ$. To extract new physics contributions, we define several physical quantities related to the decay rate and angular distributions to reduce uncertainties from the QCD as well as the CKM elements. With the constraints from the recent measurement on the decay branching ratio of $B^{-} \to τ\barν_τ$, we find that the charged Higgs effects cou…
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…
The rare multi-body decays B->K pi ll and B_s->K K ll are both important as backgrounds to precision analyses in the benchmark modes B->K* ll and B_s->phi ll as well as sensitive probes of flavor physics in and beyond the standard model. We work out non-resonant contributions to B->K pi ll and B_s->K K ll amplitudes, where l=e,mu, at low hadronic recoil in a model-independent way. Using the operator product expansion in 1/m_b, we present expressions for the full angular distribution. The latter allows to probe new combinations of |Delta B|=|Delta S|=1 couplings and gives access to strong phase…
We study the effect of a right-handed coupling of quarks to the W-boson on the measurements of |V_ub| and |V_cb|. It is shown that such a coupling can remove the discrepancies between the determinations of |V_ub| from B\toπ\ellν, B^+\toτ^+ νand B\to X_u\ellν. Further the measurements of |V_cb| from B\to D^*\ellν, B\to D\ellνand inclusive B\to X_c\ellνdecays can be brought into better agreement. We demonstrate that a right-handed coupling can be generated within the MSSM by a finite gluino-squark loop. The effect involves the parameters δ^{u RL}_{23} and δ^{u RL}_{13} of the squark mass matrice…
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…
The interpretation of Drell-Yan production in terms of the antiquark densities depends on NLO corrections. Besides the NLO corrections to the familiar annihilation $q\bar{q}\to γ^* \to l^+ l^-$, there is a substantial contribution from the QCD Compton subprocesses $gq \to qγ^* \to q l^+ l^-$ and $g\bar{q} \to qγ^* \to q l^+ l^-$. The beam and target dependence of the two classes of corrections is different. We discuss the impact of this difference on the determination of the $\bar{d}-\bar{u}$ asymmetry in the proton from the comparison of the $pp$ and $pn$ Drell-Yan production.
We investigate the future determination of the CKM matrix using theoretically clean quantities, like $B(K^+\toπ^+ν\barν)$, $B(K_L\toπ^0ν\barν)$ or $\sin 2β$, $\sin 2α$ as extracted from CP violation studies in $B$ physics. The theoretical status of $K\toπν\barν$ is briefly reviewed and their phenomenological potential is compared with that of CP asymmetries in $B$ decays. We stress the unique opportunities provided by measuring the CP violating rare decay $K_L\toπ^0ν\barν$. It is pointed out that this mode is likely to offer the most precise determination of ${\rm Im}V^*_{ts}V_{td}$ and the Ja…
A new global QCD analysis of DIS data is presented. The νFe and \barνFe differential cross-section data are included to constrain the strange component of the nucleon sea. As a result we found a hard strangeness at high-x and some evidence for an asymmetry between xs(x) and x\bar{s}(x).
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).
It is the first time that the study of three-body baryonic B decays offers an independent determination of the nucleon form factors for the time-like four momentum transfer $(t>0)$ region, such as $G^{p,n}_M(t)$ of vector currents and those of axial ones. Explicitly, from the data of $\bar B^0\to n\bar p D^{*+}$ and $Λ\bar pπ^+$ we find a constant ratio of $G^n_M(t)/G^p_M(t)=-1.3\pm0.4$, which supports the FENICE experimental result. The vector and axial-vector form factors of $p\bar n$, $p\bar p$ and $n\bar n$ pairs due to weak currents are also presented, which can be tested in future experi…
We compute the rate of the decay $B^- \to μ^- {\bar ν}_μγ$ by a QCD relativistic potential model, with the result: ${\cal B}(B^- \to μ^- {\bar ν}_μγ)=0.9 \cdot 10^{-6}$. We also discuss how this decay mode can be used to access $f_B$.
We present a summary of the results of two recent precise calculations of the muon anomalous magnetic moment ($g_μ-2$) and the electromagnetic coupling on the $Z$ ($\barα_{\rm Q.E.D.}(M^2_{Z})$). The main sources of uncertainty are underlined.
We present a theoretical reappraisal of the branching ratios and CP asymmetries for the decays $ B \to X_q \ell^+ \ell^-$, with $q=d,s$, taking into account current theoretical uncertainties in the description of the inclusive decay amplitudes from the long-distance contributions, an improved treatment of the renormalization scale dependence, and other parametric dependencies. Concentrating on the partial branching ratios $Δ{\cal B}(B \to X_q \ell^+ \ell^-)$, integrated over the invariant dilepton mass region $1 {GeV}^2 \leq s \leq 6 {GeV}^2$, we calculate theoretical precision on the charge-c…
Due a mistake in identifying the operators $O_9$ and $O_{10}$ which leads to errorous expressions in eq. 9. With the correct expressions (exchange c_9 and c_{10} in eq. 9), the analysis followed are invalide.
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…
We study the exclusive leptonic and semileptonic $B$ decays $B \to \ell^- \barν$ and $B \to D^{(\ast)} \ell^-\barν$ in the framework of the covariant quark model with built-in infrared confinement. We compute the relevant form factors in the full kinematical momentum transfer region. The calculated form factors are used to evaluate branching fractions and polarization observables of the above transitions. We compare our results with experimental data and results from other theoretical studies.
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…
The most recent recalculation of the two-loop correction to the static quark-antiquark potential gave the numerical value different from the previously known one. We comment on the effect this change produces on the numerical estimates of the bottom quark pole mass $m_b$, the strong coupling constant $\al_s$ and the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ obtained in our papers [1,2].
A precise comparison is made between the Dalitz decay $H\to\ell\bar{\ell}γ$ and the two body decay $H\toγZ,Z\to\ell\bar{\ell}$ for electrons and for muons including experimental cuts appropriate for the ATLAS detector. The widths for these two processes differ by 8% for electrons and 3% for muons. Given that there remain QCD radiative corrections of this order that are not included, this suggests that the isolation of the Dalitz decay will be challenging.
We present an analysis of the decay process ${\bar B} \to {\bar K}_2(1430) \ell^+ \ell^-$, where this process has all the features of the related and well investigated process ${\bar B} \to {\bar K}^*(890) \ell^+ \ell^-$, with theoretically comparable branching ratios. The differential decay rate as well as the forward-backward asymmetry are worked out, where the sensitivity of these to possible right-handed couplings for the related $b \to s$ radiative decay are also investigated.
Using recently evaluated contributions (including a novel one calculated here), we present updated values for the pole mass and $\bar{MS}$ mass of the $b$ quark: $m_b=5022\pm58$ MeV, for the pole mass, and $\bar{m}_b(\bar{m}_b)=4286\pm36$ MeV for the $\bar{MS}$ one. These values are accurate including, respectively, $O(α_s^5\logα_s)$ and $O(α_s^3)$ corrections and, in both cases, leading orders in the ratio $m_c^2/m_b^2$.
Measurements of the $Λ_b \to p \ell^- \barν_\ell$ and $Λ_b \to Λ_c \ell^- \barν_\ell$ decay rates can be used to determine the magnitudes of the CKM matrix elements $V_{ub}$ and $V_{cb}$, provided that the relevant hadronic form factors are known. Here we present a precise calculation of these form factors using lattice QCD with 2+1 flavors of dynamical domain-wall fermions. The $b$ and $c$ quarks are implemented with relativistic heavy-quark actions, allowing us to work directly at the physical heavy-quark masses. The lattice computation is performed for six different pion masses and two diff…
In this work we will study the longitudinal polarisations of both leptons in the decay process ${\bar B} \to {\bar K}_2(1430)\, \ell^+ \, \ell^-$. This process has all the features of the related and well investigated process ${\bar B} \to {\bar K}^*(890) \, \ell^+ \, \ell^-$, with theoretically comparable branching ratios. The polarised differential decay rates as well as the single and double polarisation asymmetries are worked out, where the sensitivity of these to possible right-handed couplings for the related $b \to s$ radiative decay (and other generic BSM parameters) are also investiga…
We study the hadronic matrix elements describing the $B_s \to D_s\ell \barν_\ell$ decay in and beyond the Standard Model. By using the twisted mass QCD on the lattice with $N_f=2$ dynamical flavors we compute the normalization $\mathscr G_s(1)$ of the form factor dominating $B_s\to D_s \ell \barν_\ell$ in the SM. We also make the first lattice determination of $F_0(q^2)/F_+(q^2)$ and $F_T(q^2)/F_+(q^2)$ near zero recoil (near $q^2_{\rm max}$). We briefly discuss the non-strange case $B \to D\ell \barν_\ell$ as well.
We compute a formula including OPE power corrections to describe the running of a QCD coupling non-perturbatively defined through the ghost and gluon dressing functions. This turns out to be rather accurate. We propose the ``{\it plateau}''-procedure to compute $Λ_{\bar{\rm MS}}$ from the lattice computation of the running coupling constant. We show a good agreement between the different methods which have been used to estimate $Λ_{\bar{\rm MS}}^{N_f=0}$. We argue that $Λ_{\bar{\rm MS}}$ or the strong coupling constant computed with different lattice spacings may be used to estimate the lattic…
We explored various cases for the branching ratios (BRs) of $B_s\to K^+K^-$, $B_s\to K^0\bar{K}^0$ and $B_d\to π^+ π^-$ decays. We study the possibility of determining $γ$ by using the following the measurements: (a) BRs of $B_s\to K^+K^-$, and $B_s\to K^0\bar{K}^0$; (b) the ratio of direct CP asymmetries in $B_d\to π^+ π^-$ and $B_s\to K^+K^-$; (c) the mix-induced CP asymmetry in $B_d\to π^+ π^-$; and (d) the angle of $β$.
