Semileptonic baryon decays $Ξ_b\rightarrow Ξ_c \ell^- \barν_\ell $ in perturbative QCD

Abstract

We perform a detailed analysis of the semileptonic $Ξ_b\rightarrow Ξ_c \ell^- \barν_\ell$ decays within the perturbative QCD framework. In our study, the $Ξ_b\rightarrow Ξ_c$ transition form factors are calculated using several popular models for baryonic light-cone distribution amplitudes. These form factors are then employed to analyze a range of observable quantities for the semileptonic processes via the helicity formalism. Our work presents predictions for the branching fractions of these decays for both the $τ$ and $e$ channels. Notably, the obtained lepton flavor universality ratio, $\mathcal{R}_{Ξ_c}\approx 0.3$, may offer new insights into the $\mathcal{R}^{(*)}$ puzzle. Furthermore, we investigate various angular observables, such as forward-backward asymmetries, lepton-side convexity parameters, and polarization asymmetries, which provide complementary information regarding potential new physics in $b$-baryonic semileptonic transitions. The numerical results for these angular observables are presented as both functions of $q^2$ and as averaged values. We observe that the lepton mass plays a significant role in shaping the angular distributions, affecting most of the observables under consideration. These results are expected to be valuable for both current and future experimental investigations of semileptonic heavy-to-heavy baryon decays.