Rare decays B → (K, K∗) (ℓ+ℓ−, νν) in the quark model

Long-distance effects in exclusive rare semileptonic transitions B → (K, K∗) are analysed within a relativistic quark model. The meson transition form factors, describing the meson amplitudes of the effective weak Hamiltonian, are calculated within the dispersion formulation of the quark model as relativistic double spectral representations through the wave functions of the initial and final mesons. The dilepton spectra and lepton asymmetries are considered within the framework provided by the Standard Model. It is found that, while the non-resonant decay rates are very sensitive to quark model parameters, the model dependence of the predicted dilepton forward-backward and lepton polarization asymmetries is remarkably small, providing only an overall ∼ 10% uncertainty.