A model-independent determination of the CKM matrix element V_{ us} from five measured strangeness-changing hyperon semileptonic decays is performed. Flavor SU(3) symmetry breaking effects in the leading vector and axial-vector form factors are analyzed in the framework of the 1/N_c expansion of QCD. A fit to experimental data allows one to extract the value V_{ us}=0.2199\pm 0.0026, which is comparable to the one from K_{ e3} decays. This reconciliation is achieved through second-order symmetry breaking effects of a few percent in the form factors f_1, which increase their magnitudes over their SU(3) predictions.
Categories: hep-ph