Consistent analysis of the reactionsγp→pη′andpp→ppη′

Abstract

The production of ${\ensuremath{\eta}}^{\ensuremath{'}}$ mesons in the reactions $\ensuremath{\gamma}p\ensuremath{\rightarrow}p{\ensuremath{\eta}}^{\ensuremath{'}}$ and $pp\ensuremath{\rightarrow}pp{\ensuremath{\eta}}^{\ensuremath{'}}$ is described consistently within a relativistic meson exchange model of hadronic interactions. The photoproduction can be described quite well over the entire energy range of available data by considering an ${S}_{11}$ and a ${P}_{11}$ resonance, in addition to the $t$-channel mesonic current. The observed angular distribution is due to the interference between the $t$-channel and the nucleon resonance $s$- and $u$-channel contributions. Our analysis yields positions close to $1650\phantom{\rule{0.3em}{0ex}}\text{MeV}$ and $1870\phantom{\rule{0.3em}{0ex}}\text{MeV}$ for the ${S}_{11}$ and ${P}_{11}$ resonances, respectively. We argue that, at present, identifying these states with the known ${S}_{11}(1650)$ resonance and the missing ${P}_{11}$ resonance predicted at $1880\phantom{\rule{0.3em}{0ex}}\text{MeV}$, respectively, would be premature. It is found that the nucleonic current is relatively small and that the $NN{\ensuremath{\eta}}^{\ensuremath{'}}$ coupling constant cannot be much larger than ${g}_{NN{\ensuremath{\eta}}^{\ensuremath{'}}}=3$. As for the $pp\ensuremath{\rightarrow}pp{\ensuremath{\eta}}^{\ensuremath{'}}$ reaction, different current contributions are constrained by a combined analysis of this and the photoproduction reaction. Difficulties to simultaneously account for the $47\phantom{\rule{0.3em}{0ex}}\text{MeV}$ and $144\phantom{\rule{0.3em}{0ex}}\text{MeV}$ angular distributions measured by the COSY-11 and DISTO collaborations, respectively, are addressed.