Eta-meson production in the resonance energy region

TL;DR

This paper updates the analysis of eta-meson production near resonance energies, explaining observed cross-section features through interference of specific nucleon resonances and providing insights into reaction mechanisms and scattering parameters.

Contribution

It introduces a coupled-channel analysis incorporating recent data, clarifies the roles of specific resonances, and refutes the existence of a narrow resonance at 1680 MeV.

Findings

Interference between $S_{11}(1535)$ and $S_{11}(1560)$ explains the dip at 1.68 GeV.

Small but significant contribution from $P_{11}(1710)$ to differential cross sections.

No evidence found for a narrow 15 MeV wide state at 1680 MeV.

Abstract

We perform an updated coupled-channel analysis of eta-meson production including all recent photoproduction data on the proton. The dip observed in the differential cross sections at c.m. energies W=1.68 GeV is explained by destructive interference between the $S_{11}(1535)$ and $S_{11}(1560)$ states. The effect from $P_{11}(1710)$ is found to be small but still important to reproduce the correct shape of the differential cross section. For the $\pi^- N \to \eta N$ scattering we suggest a reaction mechanism in terms of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ states. Our conclusion on the importance of the $S_{11}(1535)$, $S_{11}(1560)$, and $P_{11}(1710)$ resonances in the eta-production reactions is in line with our previous results. No strong indication for a narrow state with a width of 15 MeV and the mass of 1680 MeV is found in the analysis. $\eta N$ scattering length is extracted and discussed.