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

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, JüBo, 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.

arXiv comment10 pages, 11 figures

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