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We reanalyze the $\Lambda_b\to p$ transition form factors in the perturbativeQCD (PQCD) approach by including higher-twist light-cone distributionamplitudes (LCDAs) of a $\Lambda_b$ baryon and a proton. The previous PQCDevaluation performed decades ago with only the leading-twist $\Lambda_b$ baryonand proton LCDAs gave the form factors, which are two orders of magnitudesmaller than indicated by experimental data. We find that the twist-4$\Lambda_b$ baryon LCDAs and the twist-4 and -5 proton LCDAs contributedominantly, and the enhanced form factors become consistent with those fromlattice QCD and other nonperturbative methods. The estimated branching ratiosof the semileptonic decays $\Lambda_b\to p\ell\bar{\nu}_\ell$ and the hadronicdecay $\Lambda_b\to p\pi$ are also close to the data. It implies that the $b$quark mass is not really heavy enough, and higher-power contributions play acrucial role, similar to the observation made in analyses of $B$ mesontransition form factors. With the formalism established in this work, we areready to study various exclusive heavy baryon decays systematically in the PQCDapproach.

$\Lambda_b\to p$ transition form factors in perturbative QCD