Polarized ${\Lambda }_b\to {\Lambda }_{c}l\bar{\nu }$ decay in perturbative QCD

Abstract

We study the polarized ${\Lambda }_b$ baryon semileptonic decay ${\Lambda }_b\to {\Lambda }_{c}l\bar{\nu }$ 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 ${\Lambda }_b$ and ${\Lambda }_c$ baryon wave functions. With the heavy baryon wave functions determined in our previous work, we predict the asymmetry parameter $\alpha (\hat{e})\equiv (N_{+}-N_{-})/(N_{+}+N_{-})=-0.31\mathbf{P}\cdot \hat{e}$, where $\mathbf{P}$ is the ${\Lambda }_b$ baryon polarization, $\hat{e}$ a unit vector perpendicular to the ${\Lambda }_b$ 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 ${\Lambda }_b$ baryon from data of exclusive semileptonic decays.

9 pages in Latex file, some comments and one table added