Experimental Restrictions on Ne'eman's Fifth Interaction

Recently, Ne'eman has proposed a "fifth interaction" between the strangeness current and a neutral vector meson $\chi$, for the purpose of breaking SU(3) symmetry. We show that a $\chi$ mass less than $2m_{\pi }$ would be inconsistent with a variety of experiments, including $K$-mesonic atoms, the long-range $\mathrm{pp}$ potential, $K_1$ regeneration from a $K_2$ beam, the Lamb shift, modern refinements of the Cavendish "ice-bucket" experiment, and the absence of ${\pi }^0\to \gamma +\chi$ and $\chi \to e^{+}+e^{-}$. The remaining possibility, that $m_{\chi }$ exceeds $2m_{\pi }$, is discussed briefly.