$Λ_b \to p, Λ$ transition form factors from QCD light-cone sum rules

Abstract

Light-cone sum rules for the $Λ_b \to p, Λ$ transition form factors are derived from the correlation functions expanded by the twist of the distribution amplitudes of $Λ_b$ baryon. In terms of the $Λ_b$ three-quark distribution amplitudes models constrained by the QCD theory, we calculate the form factors at small momentum transfers and compare the results with that estimated in the conventional light-cone sum rules (LCSR) and perturbative QCD approaches. Our results indicate that the two different version of sum rules can lead to the consistent numbers of form factors responsible for $Λ_b \to p$ transition. The $Λ_b \to Λ$ transition form factors from LCSR with the asymptotic $Λ$ baryon distribution amplitudes are found to be almost one order larger than that obtained in the $Λ_b$-baryon LCSR, implying that the pre-asymptotic corrections to the baryonic distribution amplitudes are of great importance. Moreover, SU(3) symmetry breaking effect between the form factors $f_1^{Λ_b \to p}$ and $f_1^{Λ_b \to Λ}$ are computed as $28^{+14}_{-8} %$ in the framework of $Λ_b$-baryon LCSR.