Form factors for semileptonic, nonleptonic and rare \(B\, (B_s)\) meson decays

We provide new values for the model parameters of the covariant constituent quark model (with built--in infrared confinement) in the meson sector by a fit to the leptonic decay constants and a number of electromagnetic decays. We then evaluate, in a parameter free way, the form factors of the \(B(B_s)\to P(V)\)-transitions in the full kinematical region of momentum transfer. As an application of our results we calculate the widths of the nonleptonic \(B_s\)-decays into \(D_s^- D_s^+,\) \(D_s^{\ast\,-} D_s^{+}+D_s^- D_s^{\ast\,+}\) and \(D_s^{\ast\,-} D_s^{\ast\,+}\). These modes give the largest contribution to \(\Delta\Gamma\) for the \(B_s-\bar B_s\) system. We also treat the nonleptonic decay \(B_{s}\to\Jpsi\phi\). Although this mode is color suppressed this decay has important implications for the search of possible CP-violating New Physics effects in \(B_s-\bar B_s\) mixing.