η−NInteraction andηProduction inπ−N (γ−N)Collisions

Abstract

Experimental data for the ${\pi }^{-}+p\to \eta +n$ reaction near threshold are analyzed by using the Breit-Wigner resonance formulas for $S_{\frac{1}{2}}$ and $D_{\frac{3}{2}}$ states. It is shown that the effects of $D_{\frac{3}{2}}$ are comparable to or larger than those of $S_{\frac{1}{2}}$ in the neighborhood of the observed peak of $\sigma ({\pi }^{-}+p\to \eta +n)$, and that from only the data for $\sigma ({\pi }^{-}+p\to \eta +n)$, the mass (${\omega }_r$) of the $S_{\frac{1}{2}}$ resonant state cannot be determined unambiguously without knowledge of its partial widths. In order to get some information concerning the partial widths ${\Gamma }_{\eta }$ and ${\Gamma }_{\pi }$ of the $S_{\frac{1}{2}}$ resonant state into the channels $\eta +N$ and $\pi +N$, the $\gamma +p\to \eta +p$ and $\gamma +N\to \pi +N$ reactions are studied. As one of the methods to determine value of the ${\omega }_r$, measurements of energy spectrum of ${\Sigma }^{-}$ in a reaction $K^{-}+d\to K^{-}+p+\eta$ are suggested.