The Λ b → Λ transition form factors in perturbative QCD approach

We perform a systematic analysis of the Λ b → Λ Λ b → Λ transition form factors using the perturbative QCD (PQCD) approach, taking into account contributions from higher-twist light-cone distribution amplitudes (LCDAs). Using inputs from lattice QCD, we show that the baryon higher-twist LCDAs give numerically dominant contributions to the form factors. By combining our PQCD results at low- q² q 2 region with lattice QCD predictions at high q², q 2 , we carry out z -series expansion fits to obtain a unified description of the form factors over the full physical kinematic range. We also provide predictions for physical observables in the rare decay Λ b → Λ μ ⁺ μ ⁻, Λ b → Λ μ + μ - , such as the differential branching fraction, the longitudinal polarization fraction of the dimuon system, and the forward–backward asymmetries.