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Register a new userRare $b to d$ decays in covariant confined quark model
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In this article, we study the rare decays corresponding to $b to d$ transition in the framework of covariant confined quark model. The transition form factors for the channels $B^{+(0)} to (pi^{+(0)}, rho^{+(0)},omega)$ 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 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.
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Recently, the BESIII collaboration has reported numerous measurements of various $D_{(s)}$ meson semileptonic decays with significantly improved precision. Together with similar studies carried out at BABAR, Belle, and CLEO, new windows to a better understanding of weak and strong interactions in the charm sector have been opened. In light of new experimental data, we review the theoretical description and predictions for the semileptonic decays of $D_{(s)}$ to a pseudoscalar or a vector meson. This review is essentially an extended discussion of our recently published results obtained in the framework of the covariant confining quark model.
We have studied the dominant radiative transitions of the charmonium $S$- and $P$-wave states within the CCQM. 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 the global infrared cutoff $lambda=0.181$ GeV. We additionally introduce only one adjustable parameter $varrho>0$ common for the the charmonium states $eta_c({}^1!S_0)$, $J/psi({}^3!S_1)$, $chi_{c0}({^{3}}!P_{0})$, $chi_{c1}({^{3}}!P_{1})$, $h_c({^{1}}!P_{1})$, and $chi_{c2}({^{3}}!P_{2})$ to describe the quark distribution inside the hadron. This parameter describes the ratio between the charmonium size and its physical mass. The optimal value $varrho=0.485$ has been fixed by fitting the latest data for the partial widths of the one-photon radiative decays of the triplet $chi_{cJ}({^{3}}!P_{J}),~J={0,1,2}$. Then, we calculate corresponding fractional widths for states $J/psi({}^3!S_1)$ and $h_c({^{1}}!P_{1})$. Estimated results are in good agreement with the latest data. By using the fraction data from PDG2020 and our estimated partial decay width for $h_c({^{1}}!P_{1})$ we recalculate the theoretical full width $Gamma^{rm theor}_{h_c} simeq ( 0.57 pm 0.12 )$ MeV in comparison with latest data $Gamma^{rm exp}_{h_c} simeq (0.7pm 0.4)$ MeV. We also repeated our calculations by gradually decreasing the global cutoff parameter and revealed that the results do not change for any $lambda<0.181$ GeV up to the deconfinement limit.
We calculate the contributions to the rare decays $B to X_{s,d} u bar u$ and $B_{s,d} to l^+l^-$ from one-loop $Z^0$-penguin diagrams in the framework of Topcolor-assisted Technicolor Model. Within the parameter space, we find that: (a) the new contribution from technipions is less than 2% of the standard model prediction; (b) the top-pions can provide a factor of 10 to 30 enhancement to the ratios in question; (c) the topcolor-assisted technicolor model is consistent with the current experimental data.
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 $Omega_{b}^{-}toOmega_{c}^{(*)0}rho^{-}(pi^{-}),, Omega_{b}^{-}toOmega^{-}J/psi(eta_{c}),, Xi_{b}^{0,-}toXi^{0,-}J/psi(eta_{c}),, Lambda_{b}to Lambda J/psi(eta_{c}),, Lambda_{b}to Lambda_{c} D_{s}^{(ast)},, Omega_{c}^{0}toOmega^{-}rho^{+}(pi^{+})$, and $Lambda_c to p phi$. We make use of the covariant confined quark model previously developed by us to calculate the tree graph contributions to these decays. We calculate rates, branching fractions and, for some of these decays, decay asymmetry parameters. We compare our results to experimental findings and the results of other theoretical approaches when they are available. Our main focus is on decays to final states with a lepton pair because of their clean experimental signature. For these decays we discuss two-fold polar angle decay distributions such as in the cascade decay $Omega_{b}^{-}toOmega^{-}(to Xipi,Lambda K^{-})+J/psi(to ell^{+}ell^{-})$. Lepton mass effects are always included in our analysis.
We calculate the contributions to the rare B-decays, $B to X_{s,d} u bar u$, $B_{s,d} to l^+l^- $ from the unit-charged technipions. Within the considered parameter space we find that: (a) the enhancements to the branching ratios in question can be as large as three orders of magnitude; (b) the ALEPH data of $B to X_s u bar u$ lead to strong mass bounds on $m_{p1}$ and $m_{p8}$: $m_{p8} geq 620, 475 GeV$ for $F_Q=40GeV$ and $m_{p1}=100, 400 GeV$ respectively. (c) the CDF data of $B_s to mu bar mu$ lead to a relatively weak limit: $m_{p8} geq 320 GeV$ for $F_Q=40GeV$ and $m_{p1}=200 GeV$.
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