Partial-wave analyses of $\gamma p \rightarrow \eta p$ \ and $\gamma n \rightarrow \eta n$ using a multichannel framework

TL;DR

This study performs partial-wave analyses of eta photoproduction on protons and neutrons, revealing dominant and higher-order partial waves, with implications for understanding nucleon resonance contributions at energies up to 1900 MeV.

Contribution

It introduces a multichannel framework for analyzing eta photoproduction data, identifying significant higher-order partial waves above 1600 MeV, and providing detailed resonance contributions.

Findings

Dominant $S_{11}$ amplitude from threshold to 1900 MeV.

Higher-order partial waves like $P_{11}$, $P_{13}$, and $F_{15}$ become significant above 1600 MeV.

Data suggest $F_{17}$ is needed for double-polarization observables above 1900 MeV.

Abstract

This paper presents results from partial-wave analyses of the photoproduction reactions $\gamma p \rightarrow \eta p$ and $\gamma n \rightarrow \eta n$. World data for the observables \DSG, $\Sigma$, $T$, $P$, $F$, and $E$ were analyzed as part of this work. The dominant amplitude in the fitting range from threshold to a c.m.\ energy of 1900 MeV was found to be $S_{11}$ in both reactions, consistent with results of other groups. At c.m.\ energies above 1600 MeV, our solution deviates from published results, with this work finding higher-order partial waves becoming significant. Data off the proton suggest that the higher-order terms contributing to the reaction include $P_{11}$, $P_{13}$, and $F_{15}$. The final results also hint that $F_{17}$ is needed to fit double-polarization observables above 1900 MeV. Data off the neutron show a contribution from $P_{13}$, as well as strong contributions from $D_{13}$ and $D_{15}$.