Investigation of ${\Lambda }_b\to {\Lambda }_c{\ell }^{-}{\overline{\nu }}_{\ell }$ Decays in Perturbative QCD Approach

Abstract

We investigate the semileptonic decays ${\Lambda }_b\to {\Lambda }_c{\ell }^{-}{\bar{\nu }}_{\ell }$ (with $\ell =e,\mu ,\tau$) within the framework of perturbative QCD (pQCD). The six independent ${\Lambda }_b\to {\Lambda }_c$ transition form factors are first calculated in the low-$q^2$ region using the $k_T$ factorization approach. These are then extrapolated to the full physical $q^2$ range via the model-independent $z$-expansion, incorporating recent lattice QCD results at high $q^2$. Based on the obtained form factors, we compute the branching fractions of ${\Lambda }_b\to {\Lambda }_c{\ell }^{-}{\bar{\nu }}_{\ell }$ decays. Our prediction for the lepton flavor universality ratio, ${\mathcal{R}}_{{\Lambda }_c}=0.29_{-0.11}^{+0.12}$, is slightly larger than the latest experimental measurement. In addition, we analyze several angular observables, including forward-backward asymmetries, lepton-side convexity parameters, and polarization asymmetries. These results offer valuable theoretical input for current and future experimental investigations of semileptonic heavy-to-heavy baryon transitions.

Comments: 16 pages, 7 figures