Study of the Λ → p ℓ ν ¯ ℓ Semileptonic Decay in Lattice QCD

We present the first lattice QCD determination of the Λ → N vector and axial-vector form factors, which are essential inputs for studying the semileptonic decay Λ → p ℓ ν ¯ ℓ . This channel provides a clean, theoretically controlled avenue for extracting the Cabibbo-Kobayashi-Maskawa matrix element | V u s | from the baryon sector. Our analysis uses a gauge ensemble with physical light, strange, and charm quark masses and yields the most precise determination to date of the full set of transition form factors—including second-class contributions—as well as the associated couplings, radii, and the ratio of muon-to-electron decay rates, an observable sensitive to possible nonstandard scalar and tensor interactions. We compare our nonperturbative results with next-to-next-to-leading order expansions in the small parameter δ = ( m Λ − m N ) / m Λ ≈ 0.16 . We find that the common phenomenological approximation of neglecting the q 2 dependence of the form factors leads to a ∼ 4 % deviation in the decay rate. This underscores the critical importance of precise, fully nonperturbative form factor inputs for achieving the subpercent precision targets of upcoming experimental programs.