Polarized $Λ_b\to Λ_c l \barν$ decay in perturbative QCD

Abstract

We study the polarized $Λ_b$ baryon semileptonic decay $Λ_b \to Λ_cl{\barν}$ using perturbative QCD factorization theorem. In this approach heavy baryon transition form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal $Λ_b$ and $Λ_c$ baryon wave functions. With the heavy baryon wave functions determined in our previous work, we predict the asymmetry parameter $α({\hat e})\equiv (N_+-N_-)/(N_++N_-)=-0.31 {\bf P}\cdot{\hat e}$, where ${\bf P}$ is the $Λ_b$ baryon polarization, ${\hat e}$ a unit vector perpendicular to the $Λ_b$ baryon momentum, $N_+$ ($N_-$) the number of leptons whose momenta possess positive (negative) components along ${\hat e}$. This result is useful for extracting the transverse polarization of a $Λ_b$ baryon from data of exclusive semileptonic decays.