Consistent analysis of the reaction $\gamma p \to p \eta^\prime$ and $pp \to pp\eta^\prime$

Abstract

The production of $\eta'$ mesons in the reactions $\gamma p\to p\eta'$ and $pp\to pp\eta'$ 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 MeV and 1870 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 MeV, respectively, would be premature. It is found that the nucleonic current is relatively small and that the $NN\eta^\prime$ coupling constant cannot be much larger than $g_{NN\eta^\prime}=3$. As for the $p p \to p p \eta^\prime$ reaction, different current contributions are constrained by a combined analysis of this and the photoproduction reaction. Difficulties to simultaneously account for the 47-MeV and 144-MeV angular distributions measured by the COSY-11 and DISTO collaborations, respectively, are addressed.