Possibility of a ninthJP=12+baryon

Abstract

It is shown that (i) the small but definite discrepancy between the mass-squared Gell-Mann-Okubo mass formula of the ${\frac{1}{2}}^{+}$ baryons and experiment, (ii) the trouble of the $\ensuremath{\Sigma}\ensuremath{-}\ensuremath{\Lambda}$ degeneracy, and (iii) the deviation of the $\frac{D}{F}$ ratio of the axial-vector semileptonic couplings from the SU(6) value as indicated by the value $|\frac{{G}_{A}}{{G}_{V}}|=0.435\ifmmode\pm\else\textpm\fi{}0.035$ of the latest high-statistics experiment on the ${\ensuremath{\Sigma}}^{\ensuremath{-}}\ensuremath{\rightarrow}n+{e}^{\ensuremath{-}}+\overline{\ensuremath{\nu}}$ decay as compared with the SU(6) value \ensuremath{\simeq} 0.25, can be explained simultaneously if a ninth $I=0,{\frac{1}{2}}^{+}$ baryon ${\ensuremath{\Lambda}}^{\ensuremath{'}}$ exists around 1700 MeV with a broad width of about 1 GeV. The hyperon semileptonic decays in the presence of the ${\ensuremath{\Lambda}}^{\ensuremath{'}}$ are analyzed in detail. The Cabibbo angles are determined to be $sin{\ensuremath{\theta}}_{V}=0.227\ifmmode\pm\else\textpm\fi{}0.008$ and $sin{\ensuremath{\theta}}_{A}=0.220\ifmmode\pm\else\textpm\fi{}0.020$. The theoretical frameworks used are asymptotic SU(3), chiral $\mathrm{SU}(3)\ensuremath{\bigotimes}\mathrm{SU}(3)$ charge algebra, and the simple mechanism of symmetry breaking.