In this article, we study the rare decays corresponding to $b \to d$ transition in the framework of the covariant confined quark model. The transition form factors for the channels $B^{+(0)} \to (π^{+(0)}, ρ^{+(0)},ω)$ and $B_s^0 \to K^{(*)0}$ are computed in the entire dynamical range of momentum transfer squared. Using the form factors, we compute the branching fractions of the rare decays and our results are found to be matching well with the experimental data. We also compute the ratios of the branching fractions of the $b \to s$ to $b \to d$ rare decays using the inputs from previous papers on $b \to s \ell^+\ell^-$ using this model. Further, using the form factors, model dependent and independent parameters, we also compute different other physical observables such as forward backward asymmetry, longitudinal polarization and angular observables in the entire $q^2$ range as well as in $q^2$ bins [0.1 -- 0.98] GeV$^2$ and [1.1 -- 6] GeV$^2$. We also compare our findings with different theoretical predictions.
We evaluate $B \rightarrow ρ$ transition form factors in the full kinematical region within the covariant confined quark model. We compare the obtained results with the results from light-cone sum rules. The calculated form factors can be used to calculate the $B^+ \rightarrow ρ^+ μ^+ μ^-$ rare decay branching ratio.
Decay processes $B\rightarrow D_{\left(s\right)}^{\left(*\right)}h$ ($h=π,ρ$) are studied in the framework of the confined covariant quark model using the naïve factorization assumption. We observe that the theoretical results on branching fractions have tendency to systematically exceed the experimental numbers. Such a behavior has already been seen for similar processes by other authors.
In the wake of the recent measurements of the decays $B_c\to J/ψ\,π(K)$ and $B_c\to J/ψ\,\ellν_\ell$ reported by the LHCb Collaboration we calculate the form factors for the $B_c\to J/ψ$ and $B_c\to η_{c}$ transitions in full kinematical region within covariant confined quark model. Then we use the calculated form factors to evaluate the partial decay widths of the above-mentioned semileptonic and nonleptonic decays of the $B_{c}$ meson. We find that the theoretical predictions on the ratios of $\mathcal{R}_{K^{+}/ π^{+}}$ and $\mathcal{R_{π^{+}/ μ^{+} ν}}$ are in good agreement with last LHCb…
We evaluate $B_{s}\rightarrow K^{\ast 0}$ transition form factors in the full kinematical region within the covariant confined quark model. The calculated form factors can be used to calculate the $B_{s}\rightarrow K^{\ast 0}μ^+ μ^-$ rare decay branching ratio, which was recently measured by LHCb collaboration.
We have made a survey of heavy-to-heavy and heavy-to-light nonleptonic heavy baryon two-body decays and have identified those decays that proceed solely via $W$-boson emission, i.e. via the tree graph contribution. Some sample decays are $Ω_{b}^{-}\toΩ_{c}^{(*)0}ρ^{-}(π^{-}),\, Ω_{b}^{-}\toΩ^{-}J/ψ(η_{c}),\, Ξ_{b}^{0,-}\toΞ^{0,-}J/ψ(η_{c}),\, Λ_{b}\to ΛJ/ψ(η_{c}),\, Λ_{b}\to Λ_{c} D_{s}^{(\ast)},\, Ω_{c}^{0}\toΩ^{-}ρ^{+}(π^{+})$, and $Λ_c \to p ϕ$. We make use of the covariant confined quark model previously developed by us to calculate the tree graph contributions to these decays. We calculat…
We have studied the dominant radiative transitions of the charmonium $S$-and $P$-wave states within the covariant confined quark model. The gauge invariant leading-order transition amplitudes have been expressed by using either the conventional Lorentz structures, or the helicity amplitudes, where it was effective. The renormalization couplings of the charmonium states have been strictly fixed by the compositeness conditions that excludes the constituent degrees of freedom from the space of physical states. We use the basic model parameters for the constituent c-quark mass $m_c=1.80$ GeV and t…
We study the rare radiative leptonic decays $B_s\to\ell^+\ell^-γ$ ($\ell=e,μ,τ$) within the Standard Model, considering both the structure-dependent amplitude and bremsstrahlung. In the framework of the covariant confined quark model developed by us, we calculate the form factors characterizing the $B_s\toγ$ transition in the full kinematical region of the dilepton momentum squared and discuss their behavior. We provide the analytic formula for the differential decay distribution and give predictions for the branching fractions in both cases: with and without long-distance contributions. Final…
Semileptonic decays $Λ_c^+ \to Λ\ell^+ ν_\ell\,\,(\ell=e,μ)$ in the covariant quark model and comparison with the new absolute branching fraction measurements of Belle and BESIII
Our article is devoted to the study of the rare $B_s\to ϕ\ell^+\ell^-$ decay where $\ell=μ,τ$. We compute the relevant form factors in the framework of the covariant quark model with infrared confinement in the full kinematical momentum transfer region. The calculated form factors are used to evaluate branching fractions and polarization observables in the cascade decay $B\to ϕ(\to K^+K^-)\ell^+\ell^-$. We compare the obtained results with available experimental data and the results from other theoretical approaches.
We investigate the exclusive semileptonic and rare $D\to π(K)$ decays within the standard model together with the light-front quark model (LFQM) constrained by the variational principle for the QCD-motivated effective Hamiltonian. The form factors are obtained in the $q^+=0$ frame and then analytically continue to the physical timelike region. Together with our recent analysis of the current-component independent form factors $f_\pm(q^2)$ for the semileptonic decays, we present the current-component independent tensor form factor $f_T(q^2)$ for the rare decays to make the complete set of hadro…
We have made an ab initio three-loop quark model calculation of the $W$-exchange contribution to the nonleptonic two-body decays of the doubly charmed baryons $Ξ_{cc}^{++}$ and $Ω_{cc}^{+}$. The $W$-exchange contributions appear in addition to the factorizable tree graph contributions and are not suppressed in general. We make use of the covariant confined quark model previously developed by us to calculate the tree graph as well as the $W$-exchange contribution. We calculate helicity amplitudes and quantitatively compare the tree graph and $W$-exchange contributions. Finally, we compare the c…
Within the framework of covariant confined quark model, we compute the transition form factors of $D$ and $D_s$ mesons decaying to light scalar mesons $f_0(980)$ and $a_0(980)$. The transition form factors are then utilized to compute the semileptonic branching fractions. We study the channels namely, $D_{(s)}^+ \to f_0(980) \ell^+ ν_\ell$ and $D \to a_0(980) \ell^+ ν_\ell$ for $\ell = e$ and $μ$. For computation of semileptonic branching fractions, we consider the $a_0(980)$ meson to be the conventional quark-antiquark structure and the $f_0(980)$ meson as the admixture of $s\bar{s}$ and ligh…
We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to cτν$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding…
We study the radiative and weak nonleptonic decays of vector B-mesons within the covariant confined quark model (CCQM) developed in our previous papers. First, we calculate the matrix elements and decays widths of the radiative decays $B^\ast\to Bγ$. The obtained results are compared with those obtained in other approaches. Then we consider the nonleptonic decays $B^\ast\to D^\ast V$ which proceed via tree-level quark diagrams. It is shown that the analytical expressions for the amplitudes correspond to the factorization approach. In the framework of our model we calculate the leptonic decay c…
Strong decays of the charmonium-like state $Y(4320)$ have been studied in the framework of the covariant confined quark model. The resonance $Y$ has been interpreted as a four-quark state of the molecular type. We evaluate the hidden-charm decay width of $Y$ to a vector and a scalar, with the latter decaying subsequently to a pair of charged pseudoscalar states. The strong decay modes $Y \!\to\! π^{+}π^{-}J/Ψ$ and $Y \!\to\! K^{+}K^{-} J/Ψ$ have been studied by involving the scalar resonance state $f_0(980)$. We have calculated the fractal widths of the related strong decays and the branching …
We present results for the invariant and helicity amplitudes in the transitions $Λ_b\toΛ^{(\ast)}(J^P)+J/ψ$ where the $Λ^{(\ast)}(J^P)$ are $Λ(sud)$-type ground and excited states with $J^P$ quantum numbers $J^P=\frac12^{\pm},\frac32^{\pm}$. The calculations are performed in the framework of a covariant confined quark model. This analysis is important for the identification of the hidden charm pentaquark states $P_c^+(4380)$ and $P_c^+(4450)$ which were discovered by the LHCb Coll. We also discuss the possible New Physics effects in the exclusive decays $\bar{B}^0 \to D^{(\ast)} τ^- \barν_τ$. …
In a covariant quark-diquark model, we investigate the rare decay of $Λ_b \rightarrow n l^+ l^-$ and $Λ_b \rightarrow n γ$ in the Bethe-Salpeter equation approach. In this model the baryons are treated as bound states of a constituent quark and a diquark interacting via a gluon exchange and the linear confinement. We find that the ratio of form factors $R$ is varies from $-0.90$ to $-0.25$ and the branching ratios $Br(Λ_b \rightarrow n l^+ l^-)\times 10^{8}$ are $6.79(l=e),~4.08 ~ (l=μ),~2.9 ~(l=τ) $ and the branching ratio $Br(Λ_b \rightarrow γ)\times 10^{7} )=3.69$ in central values of param…
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…
Angular observables and branching ratio for $B_s\to ϕ\ell^+ \ell^-$ decay
The Institute of Nuclear Physics, Agency of the Republic of Kazakhstan for Atomic Energy（哈萨克斯坦原子能机构核物理研究所）；Joint Institute for Nuclear Research（俄罗斯杜布纳联合核研究所）
