Non-factorisable contributions of strong-penguin operators in Λb → Λℓ+ℓ− decays

A bstract We investigate for the first time a certain class of non-factorisable contributions of the four-quark operators O O 3 − 6 in the weak effective Hamiltonian to the Λ b → Λ ℓ + ℓ − decay amplitude. We focus on the case where a virtual photon is radiated from one of the light constituents of the Λ b baryon, in the kinematic situation of large hadronic recoil with an energetic Λ baryon in the final state. The effect on the suitably defined “non-local form factors” is calculated using the light-cone sum rule approach for a correlator with an interpolating current for the light Λ baryon. We find that this approach requires the introduction of new soft functions that generalise the standard light-cone distribution amplitudes (LCDAs) for the heavy Λ b baryon. We give a heuristic discussion of their properties and a model that relates them to the standard LCDAs. Within this framework, we provide numerical results for the size of the non-local form factors considered.