Interference phenomena in the $J^P=1/2^-$-wave in $\eta$ photoproduction

TL;DR

This paper analyzes recent experimental data on eta photoproduction off neutrons, showing that interference effects in the $J^P=1/2^-$ wave explain observed structures without needing a narrow resonance.

Contribution

It demonstrates that interference patterns in the $J^P=1/2^-$ wave can account for narrow structures in eta photoproduction, challenging the necessity of a new narrow resonance.

Findings

Interference in the $J^P=1/2^-$ wave reproduces experimental structures.

Introducing the $N(1685)$ resonance worsens the fit.

The observed narrow structure is explained without new resonances.

Abstract

The recent precise experimental results for the photoproduction of $\eta$-mesons off the neutron measured with the Crystal Ball/TAPS calorimeter at the MAMI accelerator have been investigated in detail in the framework of the Bonn-Gatchina coupled channel model. The main result is that the narrow structure observed in the excitation function of $\gamma n \rightarrow n\eta$ can be reproduced fully with a particular interference pattern in the $J^P=1/2^-$ partial wave. Introduction of the narrow resonance $N(1685)$ with the properties reported in earlier publications deteriorates the quality of the fit.