$\Lambda_b \to p, \Lambda$ transition form factors from QCD light-cone sum rules

Abstract

Light-cone sum rules for the $\Lambda_b \to p, \Lambda$ transition form factors are derived from the correlation functions expanded by the twist of the distribution amplitudes of $\Lambda_b$ baryon. In terms of the $\Lambda_b$ 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 $\Lambda_b \to p$ transition. The $\Lambda_b \to \Lambda$ transition form factors from LCSR with the asymptotic $\Lambda$ baryon distribution amplitudes are found to be almost one order larger than that obtained in the $\Lambda_b$-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 $f_1^{\Lambda_b \to p}$ and $f_1^{\Lambda_b \to \Lambda}$ are computed as $28^{+14}_{-8} %$ in the framework of $\Lambda_b$-baryon LCSR.