Investigation of $\Lambda_{b}\to \Lambda_{c} \ell^-\overline\nu_\ell$ Decays in Perturbative QCD Approach

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, $\mathcal{R}_{\Lambda_c} = 0.29^{+0.12}_{-0.11}$, 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.