We study the semileptonic $B_s$ and $B$ decays into the $D_{s 0}^{\ast} (2317)$ and $D_{0}^{\ast} (2400)$ resonances, respectively. With the help of a chiral unitarity model in coupled channels we compute the ratio of the decay widths of both processes. Using current values of the width for the $\bar{B}^{0} \to D_{0}^{\ast} (2400)^{+} \barν_{l} l^{-}$ decay we make predictions for the rate of the $\bar{B}_{s}^{0} \to D_{s0}^{\ast} (2317)^{+} \barν_{l} l^{-}$ decay.
We briefly summarize up-to-date results on the determination of the parameters of the Cabibbo-Kobayashi-Maskawa matrix $|V_{cb}|$ and $|V_{ub}|$, which play an important role in the unitarity triangle and in testing the Standard Model, and recent results on semileptonic $B$ meson decays involving a $τ$ lepton.
Latest measurement of the ratio of branching ratios $R_D = \mathcal B(B \to D\,τ\,ν)/\mathcal B(B \to D\,l\,ν)$ and $R_{D^{\ast}} = \mathcal B(B \to D^{\ast}\,τ\,ν)/\mathcal B(B \to D^{\ast}\,l\,ν)$, where $l$ is either an electron or muon, differs from the standard model expectation by $1.9σ$ and $3.3σ$, respectively. Similar tension has been observed in purely leptonic $B \to τν$ decays as well. In this context, we consider the most general effective Lagrangian in the presence of new physics and perform a model independent analysis to explore various new physics couplings. Motivated by the r…
In this work we study the semileptonic decays of $B_c$ meson. We evaluated $B_{c}\rightarrow D(D^{\ast})$, $B_{c}\rightarrow D_s(D_s^{\ast})$ and $B_{c}\rightarrow η_{c}(J/ψ)$ transitions form factors in the full kinematical region within the covariant quark model. The calculated form factors are used to evaluate the semileptonic decays of $B_c$ meson and it was defined ratios ($R_{η_{c}}$, $R_{J/ψ}$, $R_{ D}$ ,$R_{ D^{\ast}}$) of the branching ratios, which will be hopefully tested on LHC experiments.We compare the obtained results with the results from other theoretical approaches.
I review the recent theoretical progress on the study of tree-level semileptonic $b\to c$ decays. After briefly reviewing the latest developments on the exclusive determinations of $|V_{cb}|$, I discuss the hints on lepton flavor universality violation in $B\to D^{(\ast)}\ell \barν$ decays. Particular emphasis is given to the implications of these anomalies and to the possibilities to experimentally test the proposed New Physics explanations.
Lepton Flavour Universality tests with semileptonic $Λ_b\toΛ_c^*$ decays are important to corroborate the present anomalies in the similar ratios $R_{D^{(*)}}$, and can provide complementary constraints on possible origins of these anomalies beyond the Standard Model. In this paper we provide - for the first time - all the necessary theoretical ingredients to perform and interpret measurements of $R_{Λ_c^*}$ at the LHCb experiment. For this, we revisit the heavy-quark expansion of the relevant hadronic matrix elements, and provide their expressions to order $α_s$ and $1/m$ accuracy. Moreover, …
Search for New Physics through the Observables of Semileptonic $B_{c}^+\to D^{\ast+}\ell^{+}\ell^{-}$ Decay
National University of Sciences and Technology (NUST)（国立科学技术大学）；Lahore University of Management Sciences (LUMS)（拉合尔管理科学大学）；National Centre for Physics（国家物理中心）
We present recent progress in calculating the semileptonic form factors $h_{A_1}(w)$ for the $\bar{B} \to D^{\ast} \ell \barν$ decays. We use the Oktay-Kronfeld (OK) action for the charm and bottom valence quarks and the HISQ action for light quarks. We adopt the Newton method combined with the scanning method to find a good initial guess for the $χ^2$ minimizer in the fitting of the 2pt correlation functions. The main advantage is that the Newton method lets us to consume all the time slices allowed by the physical positivity. We report the first, reliable, but preliminary results for $h_{A_1…
In this paper we study the semileptonic decays of $B^\ast$, $B_s^\ast$, and $B_c^\ast$ by using the Bethe-Salpeter method with instantaneous approximation. Both the $V\to Pl^-\barν_l$ and $V\to Vl^-\barν_l$ cases are considered. The largest partial width of these channels is of the order of $10^{-14}$ GeV. The branching ratios of these semileptonic decays are also estimated by using the partial width of the one photon decay channel to approximate the total width. For $B^{\ast-}\to D^{(\ast)0}e^-\barν_e$ and $B_s^{\ast0}\to D_s^{(\ast)+}e^-\barν_e$, the branching ratios are of the order of $10^…
Deviations from the standard model prediction have been observed not only in $b \to c$ charged current interactions but also in $b \to s$ flavor changing neutral current interactions. In particular, the deviation observed in the measured ratio of branching fractions $R_D = \mathcal B(B \to Dτν)/\mathcal B(B \to D\,l\,ν)$ and $R_{D^{\ast}} =\mathcal B(B \to D^{\ast}τν)/\mathcal B(B \to D^{\ast}\,l\,ν)$, where $l = (e,\,μ)$, is more pronounced and the combined excess currently stands at $3.9σ$ level. If it persists and confirmed by future experiments, it would be a definite hint of new physics. …
The semileptonic decays and two-body nonleptonic decays of light baryon octet ($T_8$) and decuplet ($T_{10}$) consisting of light $u,d,s$ quarks are studied with the SU(3) flavor symmetry in this work. We obtain the amplitude relations between different decay modes by the SU(3) irreducible representation approach, and then predict relevant branching ratios by present experimental data within $1 σ$ error. We find that the predictions for all branching ratios except $\mathcal{B}(Ξ\rightarrow Λ^0π)$ and $\mathcal{B}(Ξ^*\rightarrow Ξπ)$ are in good agreement with present experimental data, that im…
Deviation from the standard model prediction is observed in many semileptonic $B$ decays mediated via $b \to c$ charged current interactions. In particular, current experimental measurements of the ratio of branching ratio $R_D$ and $R_{D^{\ast}}$ in $B \rightarrow D^{(*)}l ν$ decays disagree with standard model expectations at the level of about $4.1σ$. Moreover, recent measurement of the ratio of branching ratio $R_{J/Ψ}$ by LHCb, where $R_{J/Ψ} = \mathcal B(B_c \to J/Ψ\,τν)/\mathcal B(B_c \to J/Ψ\,μν)$, is more than $2σ$ away from the standard model prediction. In this context, we consider …
In light of prospects for measurements of $B_c \rightarrow D^{(\ast)} l ν$ decays in the upcoming Upgrade II of the LHC, we show that by using calculated $B_c \rightarrow D^{(\ast)}$ form factors competitive extraction of the $|V_{ub}|$ CKM matrix element from the $B_c \to D μ\barν_μ$ decay might be possible. To minimize experimental and theoretical uncertainties we provide the ratio $|V_{ub}|/|V_{cb}|$ by normalizing the $B_c \rightarrow D^{(\ast)} μ\barν_μ$ to $B_c \to J/ψμ\barν_μ$ decay. We also briefly examine the suggestion to extract $|V_{ub}|/|V_{cs}|$ from the theoretically interesting…
Deviation from the standard model prediction is observed in many semileptonic $B$ decays mediated via $b \to c$ charged current interactions. In particular, current experimental measurements of the ratio of branching ratio $R_D$ and $R_{D^{\ast}}$ in $B \rightarrow D^{(*)}l ν$ decays disagree with standard model expectations at the level of about $4.1σ$. Moreover, recent measurement of the ratio of branching ratio $R_{J/Ψ}$ by LHCb, where $R_{J/Ψ} = \mathcal B(B_c \to J/Ψ\,τν)/\mathcal B(B_c \to J/Ψ\,μν)$, is more than $2σ$ away from the standard model prediction. In this context, we consider …
We study the exclusive semileptonic rare $B_c^+ \to D^+ ν\barν$ decay in the framework of light-cone quark model. The transition form factors $f_{+}(q^2)$ and $f_{T}(q^2)$ are evaluated in the time-like region using the analytic continuation method in $q^{+} = 0$ frame. The analytic solutions of these form factors are compared with the results obtained from the double pole parametric form. The branching ratio for $B_c^+ \to D^+ ν\barν$ decay is calculated and compared with the other theoretical model predictions. The predicted results in this model can be tested at the LHCb experiments in near…
We compute the decays ${B\to D^\ast_0}$ and ${B\to D^\ast_2}$ with finite masses for the $b$ and $c$ quarks. We first discuss the spectral properties of both the $B$ meson as a function of its momentum and of the $D^\ast_0$ and $D^\ast_2$ at rest. We compute the theoretical formulae leading to the decay amplitudes from the three-point and two-point correlators. We then compute the amplitudes at zero recoil of ${B\to D^\ast_0}$ which turns out not to be vanishing contrary to what happens in the heavy quark limit. This opens a possibility to get a better agreement with experiment. To improve the…
In anticipation of abundant $B^*$ data samples at high-luminosity heavy-flavor experiments in the future, the tree-dominated semileptonic $\bar{B}^*_{u,d,s} \to P \ell^- \barν_\ell$ $(P=D\,,D_s\,,π\,,K)$ decays are studied within the Standard Model. After a detailed calculation of the helicity amplitudes, the theoretical predictions for branching fraction~(decay rate), lepton spin asymmetry, forward-backward asymmetry and ratio $R_D^{\ast(L)}$ are firstly presented. It is found that the CKM-favored $\bar{B}^* \to D \ell^- \barν_\ell$ decays have relatively large branching fractions of ${\cal O…
We study the semileptonic decays of $D_{s}^{+}$, $D^{+}$, and $D^{0}$ mesons into the light scalar mesons [$f_{0} (500)$, $K_{0}^{\ast} (800)$, $f_{0} (980)$, and $a_{0}(980)$] and the light vector mesons [$ρ(770)$, $ω(782)$, $K^{\ast} (892)$, and $ϕ(1020)$]. With the help of a chiral unitarity approach in coupled channels, we compute the branching fractions for scalar meson processes of the semileptonic $D$ decays in a simple way. Using current known values of the branching fractions, we make predictions for the branching fractions of the semileptonic decay modes with other scalar and vector …
Inspired by recent improved measurements of charm semileptonic decays at BESIII, we study a large set of $D(D_s)$-meson semileptonic decays where the hadron in the final state is one of $D^0$, $ρ$, $ω$, $η^{(\prime)}$ in the case of $D^+$ decays, and $D^0$, $ϕ$, $K^0$, $K^\ast(892)^0$, $η^{(\prime)}$ in the case of $D^+_s$ decays. The required hadronic form factors are computed in the full kinematical range of momentum transfer by employing the covariant confined quark model developed by us. A detailed comparison of the form factors with those from other approaches is provided. We calculate th…
Using a symmetry-preserving regularisation of a vector$\times$vector contact interaction (SCI), we complete a systematic treatment of twelve semileptonic transitions with vector meson final states: $D\to ρ$, $D_{(s)}\to K^\ast$, $D_s\to ϕ$, $B\to ρ$, $B_s\to K^\ast$, $B_{(s)}\to D_{(s)}^\ast$, $B_c \to B_{(s)}^\ast, J/ψ, D^\ast$; and thereby finalise a unified analysis of semileptonic decays of heavy+heavy and heavy+light pseudoscalar mesons to both pseudoscalar and vector meson final states. The analysis is marked by algebraic simplicity, few parameters, and the ability to consistently descri…
We discuss $B_c \to η_c$ and $B_c \to J/ψ$ semileptonic decays within the Standard Model (SM) and beyond. The relevant transition form factors, being the main source of theoretical uncertainties, are calculated in the sum rule approach and are provided in a full $q^2$ range. We calculate the semileptonic branching fractions and find for the ratios, $R_{η_c}|_{\rm SM}= 0.32 \pm 0.02$, $R_{J/ψ}|_{\rm SM} = 0.23 \pm 0.01$. Both predictions are in agreement with other existing calculations and support the current tension in $R_{J/ψ}$ at 2$σ$ level with the experiment. To extend the potential of te…
Semileptonic $B_{(s)}$ meson decays to $D_{0}^{\ast}(2300) ,D_{s0}^{\ast}(2317) , D_{s1}(2460), D_{s1}(2536), D_{1}(2420)$ and $D_{1}(2430)$ within the covariant light-front approach
Experimental measurements of $R_{D}$, $R_{D^*}$ and $R_{J/Ψ}$ in $B \to (D,\,D^{\ast})lν$ and $B_c \to J/Ψl ν$ decays mediated via $b \to c\,l\,ν$ charged current interactions deviate from standard model prediction by $2.3σ$, $3.4σ$ and $2σ$, respectively. In addition, a deviation of $1.5σ$ from the standard model prediction has been witnessed in $\mathcal B(B \to τν)$ mediated via $b \to u\,l\,ν$ charged current interactions as well. Motivated by the anomalies present in $B$ and $B_c$ meson decays, we analyze the corresponding $B_s \to (K,\,K^{\ast})\,τ\,ν$ and $B \to πτν$ semileptonic decays…
Investigating New Physics through the Observables of Semileptonic $B_{s}\to K^{\ast}(\to K π)μ^{+}μ^{-}$ Decay
National University of Sciences and Technology（国立科学与技术大学）；Lahore University of Management Sciences (LUMS)（拉合尔管理科学大学）；National Centre for Physics（国家物理中心）
本文基于 $B_s \to K^{\ast}(\to K π)μ^{+}μ^{-}$ 衰变，利用弱有效场论框架，计算了多个关键物理可观测量，并探讨了新物理对这些可观测量的影响，揭示了与标准模型预测的显著差异。
We study $B_c \to (D,\,D^{\ast})\,l\,ν$ semileptonic decays mediated via $b \to u\,l\,ν$ charged current interactions using the $B_c \to (D,\,D^{\ast})$ transition form factors obtained in the covariant light front quark model. We give predictions on the branching ratios, ratio of branching ratios, and various asymmetries pertaining to these decay modes within the standard model. These results can be tested in the ongoing or in the future experiments and can provide complimentary information regarding the observed anomalies in $B \to (D,\,D^{\ast})τν$ and $B_c \to J/Ψτν$ decays.
The form factors of the $Λ_{b} \to N^\ast \ell^+ \ell^-$ decay are calculated in the framework of the light cone QCD sum rules. In the calculations the contribution of the negative parity $Λ_b^\ast$ baryon is eliminated by constructing the sum rules for different Lorentz structures. Furthermore the branching ratio of the semileptonic $Λ_b \to N^\ast \ell^+ \ell^-$ decay is calculated. The numerical study for the branching ratio of the $Λ_{b} \to N^\ast \ell^+ \ell^-$ decay indicates that it is quite large and could be measurable at future planned experiments to be conducted at LHCb.
