SU(3) breaking effects in hyperon beta decay from lattice QCD

We present results of an exploratory study of flavor SU(3) breaking effects in hyperon beta decays using domain wall fermions. From phenomenological point of view, the significance of this subject is twofold: (1) to extract the element V_us of the Cabibbo-Kabayashi-Maskawa mixing matrix from the ΔS = 1 decay process, and (2) to provide vital information to analysis of the strange quark fraction of the proton spin with the polarized deep inelastic scattering data. In this study, we explore the Ξ⁰ → Σ⁺ beta decay, which is highly sensitive to the SU(3) breaking since this decay corresponds to the direct analogue of neutron beta decay under an exchange between the down quark and the strange quark. We expose the SU(3) breaking effect on g_A/g_V = g₁(0)/f₁(0) up to the first order in breaking. The second-class form factors g₂ and f₃, of which non-zero values are the direct signals of the SU(3) breaking effect, are also measured. Finally, we estimate f₁(0) up to the second-order correction and then evaluate |V_us| combined with the KTeV experiment.