Light-front quark model analysis of rare B→ Kℓ+ℓ- decays

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Using the light-front quark model, we calculate the transition form factors, decay rates, and longitudinal lepton polarization asymmetries for the exclusive rare B→ Kℓ+ℓ-(ℓ=e,μ,τ) decays within the standard model. Evaluating the timelike form factors, we use the analytic continuation method in q+=0 frame to obtain the form factors F+ and Fₜ, which are free from zero-mode. The form factor F- which is not free from zero-mode in q+ = 0 frame and contaminated by the higher(or nonvalence) Fock states in q+ ≠ 0 frame is obtained from an effective treatment for handling the nonvalence contribution based on the Bethe-Salpeter formalism. The covariance(i.e. frame-independence) of our model calculation is discussed. We obtain the branching ratios for BR(B→ Kℓ+ℓ-) as 4.96×10⁻⁷|Vts/Vcb|² for ℓ=e,μ and 1.27× 10⁻⁷|Vts/Vcb|² for ℓ=τ.