Eta photoproduction in a combined analysis of pion- and photon-induced reactions

TL;DR

This paper performs a comprehensive combined analysis of eta photoproduction and related reactions using a coupled-channel framework to better understand the spectrum of excited nucleons and the influence of recent polarization data.

Contribution

It introduces a combined analysis approach using the Jülich coupled-channel framework to extract nucleon resonance properties from eta and pion photoproduction data.

Findings

Resonance spectrum and properties are determined.

Influence of recent MAMI polarization data is analyzed.

Enhanced understanding of excited nucleon states.

Abstract

The $\eta N$ final state is isospin-selective and thus provides access to the spectrum of excited nucleons without being affected by excited $\Delta$ states. To this end, the world database on eta photoproduction off the proton up to a center-of-mass energy of $E\sim 2.3$ GeV is analyzed, including data on differential cross sections, and single and double polarization observables. The resonance spectrum and its properties are determined in a combined analysis of eta and pion photoproduction off the proton together with the reactions $\pi N\to \pi N$, $\eta N$, $K\Lambda$ and $K\Sigma$. For the analysis, the so-called J\"ulich coupled-channel framework is used, incorporating unitarity, analyticity, and effective three-body channels. Parameters tied to photoproduction and hadronic interactions are varied simultaneously. The influence of recent MAMI $T$ and $F$ asymmetry data on the eta photoproduction amplitude is discussed in detail.