2025/07/14 by Bacchio, Simone, Konstantinou, Andreas
#FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2507.09970
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 CKM matrix element |Vus| 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 non-standard scalar and tensor interactions. We compare our non-perturbative results with next-to-next-to-leading order expansions in the small parameter δ= (mΛ- mN)/mΛ≈ 0.16. We find that the common phenomenological approximation of neglecting the q2-dependence of the form factors leads to a ∼ 4% deviation in the decay rate. This underscores the critical importance of precise, fully non-perturbative form factor inputs for achieving the sub-percent precision targets of upcoming experimental programs.