The $$\Lambda _{b} \rightarrow \Lambda $$ transition form factors in perturbative QCD approach

Abstract We perform a systematic analysis of the $$\Lambda _b \rightarrow \Lambda $$ 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- $$q^2$$ q 2 region with lattice QCD predictions at high $$q^2,$$ 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 $$\Lambda _b \rightarrow \Lambda \mu ^+ \mu ^-,$$ Λ b → Λ μ + μ - , such as the differential branching fraction, the longitudinal polarization fraction of the dimuon system, and the forward–backward asymmetries.