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 calculated decay widths with those from other theoretical approaches when they are available.

We calculate the semileptonic and a subclass of sixteen nonleptonic two-body decays of the double charm baryon ground states Ξ þþ cc ; Ξ þ cc and Ω þ cc where we concentrate on the nonleptonic decay modes. We identify those nonleptonic decay channels in which the decay proceeds solely via the factorizing contribution precluding a contamination from W exchange. We use the covariant confined quark model previously developed by us to calculate the various helicity amplitudes which describe the dynamics of the 1=2 þ → 1=2 þ and 1=2 þ → 3=2 þ transitions induced by the Cabibbo-favored effective (c → s) and (d → u) currents. We then proceed to calculate the rates of the decays as well as polarization effects and angular decay distributions of the prominent decay chains resulting from the nonleptonic decays of the double heavy charm baryon parent states.

Here, we study the B s → D ( * ) s ℓν ℓ semileptonic decays within the Standard Model framework of covariant confined quark model. The necessary transition form factors are computed in the entire dynamical range of momentum transfer squared with built-in infrared confinement. Our computed ratios of the decay widths from tau mode to muon mode for D s and D * s mesons are found to be R(D s ) = 0.271 ± 0.069 and R(D * s ) = 0.240 ± 0.038. We further determine the ratio of the decay width from D s and D * s channel for muon mode Γ(B s → D s µ + ν µ )/Γ(B s → D * s µ + ν µ ) = 0.451±0.093. Our results are in excellent agreement with the data from recent LHCb experiments as well as lattice quantum chromodynamics simulations. We have also compared the shape of differential decay distribution for B s → D * s µ + ν µ with the recent LHCb data and our results are in very good agreement throughout all the individual bins. Some other physical observables such as forwardbackward asymmetry and longitudinal polarizations of leptons in the final state are also computed.