Λb → p transition form factors in perturbative QCD

We reanalyze the Lambda(b) -> p transition form factors in the perturbative QCD (PQCD) approach by including higher-twist light-cone distribution amplitudes (LCDAs) of a Lambda(b) baryon and a proton. The previous PQCD evaluation performed decades ago with only the leading-twist Lambda(b) baryon and proton LCDAs gave the form factors, which are two orders of magnitude smaller than indicated by experimental data. We find that the twist-4 Lambda(b) baryon LCDAs and the twist-4 and -5 proton LCDAs contribute dominantly, and the enhanced form factors become consistent with those from lattice QCD and other nonperturbative methods. The estimated branching ratios of the semileptonic decays Lambda(b) -> pl (v) over bar (l) and the hadronic decay Lambda(b) -> 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 a crucial role, similar to the observation made in analyses of B meson transition form factors. With the formalism established in this work, we are ready to study various exclusive heavy baryon decays systematically in the PQCD approach.

Automated summary

In this study, we reanalyzed the Lambda(b) -> p transition form factors using the PQCD approach and found that including higher-twist LCDAs significantly improved the agreement with experimental data. The study also highlighted the importance of higher-power contributions in heavy baryon decays.