Recent results on the $\Lambda \rightarrow p\ell \bar{\nu}_\ell$ semileptonic decay

TL;DR

This paper presents a lattice-QCD calculation of the $ ext{Lambda} o p$ semileptonic decay form factors, enabling precise decay rate predictions and tests of lepton-flavor universality, with implications for determining the CKM matrix element $|V_{us}|$.

Contribution

It provides the first complete lattice-QCD determination of all relevant form factors for $ ext{Lambda} o p$ decay, including second-class contributions, on a physical quark mass ensemble.

Findings

Precise form factors for $ ext{Lambda} o p$ decay obtained.

Decay rates for electronic and muonic channels computed.

Estimate of $|V_{us}|$ from baryon decay data provided.

Abstract

We present a lattice-QCD determination of the $\Lambda \to p$ vector and axial-vector form factors, providing theoretical input for studies of the semileptonic decay $\Lambda \to p\ell\bar{\nu}_\ell$. The calculation is carried out on a single gauge ensemble with physical light, strange, and charm quark masses and delivers a precise determination of the complete set of transition form factors, including second-class contributions. Using these form factors, we compute decay rates for both the electronic and muonic channels, as well as their ratio, which offers a sensitive test of lepton-flavor universality and possible non-standard scalar or tensor interactions. This decay mode provides a theoretically well-controlled avenue for extracting the CKM matrix element $|V_{us}|$ from the baryon sector. Our estimate of $|V_{us}|$ is obtained by combining our recent lattice-QCD results with recent measurements of the relevant branching fraction reported by BESIII and LHCb.