Speaker
Description
Semileptonic hyperon decays provide a powerful and largely unexplored laboratory to test the Standard Model in the strange sector. In particular, they offer complementary sensitivity to lepton flavour universality (LFU) and to the CKM matrix element |$V_{us}$|, with different hadronic and operator sensitivities from the kaon sector. While the electron modes are known with relatively good precision, the corresponding muonic branching fractions are still poorly measured in several channels, leaving LFU tests in strange baryons essentially open.
In this talk, I will present the LHCb programme on hyperon semileptonic decays, focusing on the channels $\Lambda \to p \ell^- \bar{\nu}_\ell$ and $\Xi^- \to \Lambda \ell^- \bar{\nu}_\ell$. I will discuss the experimental strategy developed at LHCb to reconstruct decays with a neutrino in the final state, including kinematics-driven selections, background suppression, and multidimensional fit techniques. I will also highlight recent progress from Run 2 and the prospects for Run 3, where the all-software trigger and larger strange-hadron samples enable a significant improvement in precision.
These measurements open the way to the first single-experiment LFU tests in hyperon decays, to studies of semileptonic form factors, and to an independent baryon-based determination of |$V_{us}$|, with direct implications for the Cabibbo-angle anomaly and first-row CKM unitarity tests.