New data on $\vec{\gamma} \vec{p}\rightarrow \eta p$ with polarized photons and protons and their implications for $N^* \to N\eta$ decays

TL;DR

This paper reports new measurements of polarization observables in eta meson photoproduction off protons, compares them with theoretical models, and refines nucleon resonance decay branching ratios, especially for N(1650)1/2^-.

Contribution

It provides the first comprehensive polarization data for eta photoproduction and refines resonance decay parameters through a combined experimental and theoretical analysis.

Findings

Measured polarization observables T, E, P, H, G across wide energy range.

Compared data with multiple partial-wave analysis predictions.

Refined the N(1650)1/2^- to Nη branching ratio to 0.33±0.04.

Abstract

The polarization observables $T, E, P, H$, and $G$ in photoproduction of $\eta$ mesons off protons are measured for photon energies from threshold to $W=2400\,$MeV ($T$), 2280 MeV ($E$), 1620 MeV ($P, H$), or 1820 MeV ($G$), covering nearly the full solid angle. The data are compared to predictions from the SAID, MAID, J\"uBo, and BnGa partial-wave analyses. A refit within the BnGa approach including further data yields precise branching ratios for the $N\eta$ decay of nucleon resonances. A $N\eta$-branching ratio of $0.33\pm 0.04$ for $N(1650)1/2^-$ is found, which reduces the large and controversially discussed $N\eta$-branching ratio difference of the two lowest mass $J^P=1/2^-$-resonances significantly.