Eur. Phys. J. C (2022) 82: 686
https://doi.org/10.1140/epjc/s10052-022-10642-0

Regular Article - Theoretical Physics

${\mathrm{\Lambda }}_b\to p$ transition form factors in perturbative QCD

¹ Department of Physics and Institute of Theoretical Physics, Nanjing Normal University, 210023, Nanjing, People’s Republic of China
² School of Nuclear Science and Technology, Frontiers Science Center for Rare Isotopes, Lanzhou University, 730000, Lanzhou, People’s Republic of China
³ Department of Physics, College of Sciences, Nanjing Agricultural University, 210095, Nanjing, People’s Republic of China
⁴ Institute of Physics, Academia Sinica, 115, Taipei, Taiwan ROC
⁵ College of Physics and Photoelectric Engineering, Ocean University of China, 266100, Qingdao, People’s Republic of China
⁶ Key Laboratory of Theoretical Physics of Gansu Province, Lanzhou Center for Theoretical Physics, Lanzhou University, 730000, Lanzhou, People’s Republic of China
⁷ Center for High Energy Physics, Peking University, 100871, Beijing, People’s Republic of China

^b liyakelly@163.com
^c hnli@phys.sinica.edu.tw
^d shenylmeteor@ouc.edu.cn
^e xiaozhenjun@njnu.edu.cn
^f yufsh@lzu.edu.cn

Received: 21 May 2022
Accepted: 26 July 2022
Published online: 6 August 2022

Abstract

We reanalyze the ${\mathrm{\Lambda }}_b\to p$ transition form factors in the perturbative QCD (PQCD) approach by including higher-twist light-cone distribution amplitudes (LCDAs) of a ${\mathrm{\Lambda }}_b$ baryon and a proton. The previous PQCD evaluation performed decades ago with only the leading-twist ${\mathrm{\Lambda }}_b$ 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 ${\mathrm{\Lambda }}_b$ 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 ${\mathrm{\Lambda }}_b\to p\ell {\overline{\nu }}_{\ell }$ and the hadronic decay ${\mathrm{\Lambda }}_b\to p\pi$ are also close to the data. It implies that the b quark mass is not really heavy enough, and higher-power contributions play 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.