Rare decays of Λb→Λ+γ and Λb→Λ+l+l? in the light-cone sum rules

The weak decays of Λ _b →Λ+γ and Λ _b →Λ+l ⁺ l ⁻ are investigated in the standard model using the light-cone sum-rule approach. The higher-twist distribution amplitudes of the Λ baryon to the leading conformal spin are included in the sum rules for the transition form factors. Our results indicate that the higher-twist distribution amplitudes almost have no influence on the transition form factor f ₂(q ²) defined by the tensor current, while such corrections can have a significant impact on the form factors g ₂(q ²) defined by a vector current. Two phenomenological models (COZ and FZOZ) for the wave function of the Λ baryon are also employed in the sum rules for comparison, which can give rise to form factors approximately five times larger than that in terms of conformal expansion. Utilizing the form factors calculated in LCSR, the physical observables like the decay rate, the polarization asymmetry and forward–backward asymmetry are analyzed for the decays of Λ _b →Λ γ, Λ l ⁺ l ⁻.