Applicability of perturbative QCD to ${\Lambda }_b\to {\Lambda }_c$ decays

Abstract

We develop perturbative QCD factorization theorem for the semileptonic heavy baryon decay ${\Lambda }_b\to {\Lambda }_{c}l\bar{\nu }$, whose form factors are expressed as the convolutions of hard $b$ quark decay amplitudes with universal ${\Lambda }_b$ and ${\Lambda }_c$ baryon wave functions. Large logarithmic corrections are organized to all orders by the Sudakov resummation, which renders perturbative expansions more reliable. It is observed that perturbative QCD is applicable to ${\Lambda }_b\to {\Lambda }_c$ decays for velocity transfer greater than 1.2. Under requirement of heavy quark symmetry, we predict the branching ratio $B({\Lambda }_b\to {\Lambda }_{c}l\bar{\nu })\sim 2$, and determine the ${\Lambda }_b$ and ${\Lambda }_c$ baryon wave functions.

Comments: 12 pages in Latex file, 3 figures in postscript files, some results are changed, but the conclusion is the same