Cabibbo-suppressed charged-current semileptonic decays of ${\Xi }_b$ baryons

Abstract

We present the first perturbative QCD calculations of the ${\Xi }_b\to (\Lambda ,\Sigma )$ transition form factors at leading order in ${\alpha }_s$, which govern the Cabibbo-suppressed semileptonic decays ${\Xi }_b\to (\Lambda ,\Sigma )\ell {\nu }_{\ell }$ with $\ell =e,\mu ,\tau$. Using these form factors, we evaluate differential and integrated branching fractions and angular observables within the helicity formalism. The branching ratios are predicted to be of order $10^{-4}$ for $\Sigma$ final states and $10^{-5}$ for $\Lambda$ final states, making them accessible to ongoing experiments such as LHCb. Ratios of decay rates between $\tau$ and $e$ channels are also provided, offering new probes of lepton-flavor universality. Lepton-mass effects are found to significantly impact the integrated angular observables. Furthermore, a combined analysis of $b\to u$ and $b\to c$ transitions in ${\Xi }_b$ decays yields sub-percent precision for the ratios ${\mathcal{R}}_{\ell }(\Sigma /{\Xi }_c)$, enabling an independent determination of $|V_{ub}/V_{cb}|$ once the relevant decay-rate measurements become available.

Comments: 19 pages,5 figures