Poles and Resonances inηPhotoproduction

Abstract

Various combinations of poles and resonances have been tried to determine just which combinations yield reasonable fits to the total and differential cross-section data for the process $\gamma +p\to \eta +p$. In each case the best values of the parameters have been obtained by minimizing ${\chi }^2$. Excellent fits ($\frac{{\chi }^2}{N}\approx 0.8$) are obtained for certain combinations of poles and resonances. All solutions with the $S_{11}\mathrm{}\left(1570\right)\mathrm{}$ resonance omitted have rather poor values of ${\chi }^2$, and the $P_{11}\mathrm{}\left(1400\right)\mathrm{}$ resonance cannot be used in lieu of the $S_{11}\mathrm{}\left(1570\right)\mathrm{}$ in this process. Evidence is obtained for classifying the $F_{15}\mathrm{}\left(1688\right)\mathrm{}$ as a member of an octet rather than a 27-plet. For all the models considered here, the value of the $\eta$-nucleon coupling constant ($\frac{{g_{\eta }}^2}{4\pi }$) is less than 2, indicating a $\frac{D}{F}$ ratio larger than $\frac{3}{2}$.