A model-independent determination of the Cabibbo-Kobayashi-Maskawa quark-mixing matrix (CKM) element $V_{us}$ from five measured strangeness-changing hyperon semileptonic decays is performed. Flavor $\mathrm{S}\mathrm{U}(3)$ 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 $\mathrm{S}\mathrm{U}(3)$ predictions.

• Received 12 October 2004

DOI:https://doi.org/10.1103/PhysRevD.70.114036