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

TL;DR

This paper investigates SU(3) symmetry breaking effects in hyperon beta decays using lattice QCD, providing insights into the CKM matrix element V_{us} and the strange quark contribution to proton spin.

Contribution

It presents the first lattice QCD calculation of SU(3) breaking effects in hyperon beta decay, including form factors and their impact on V_{us} extraction.

Findings

SU(3) breaking effects on g_A/g_V are quantified.

Second-class form factors g_2 and f_3 are measured, indicating SU(3) breaking.

Estimated V_{us} value aligns with experimental data.

Abstract

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 $\Delta S=1$ 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 $\Xi^0 \to \Sigma^+$ 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 $g_A/g_V=g_1(0)/f_1(0)$ up to the first order in breaking. The second-class form factors $g_2$ and $f_3$, of which non-zero values are the direct signals of the SU(3) breaking effect, are also measured. Finally, we estimate $f_1(0)$ up to the second-order correction and then evaluate $|V_{us}|$ combined with the KTeV experiment.