Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections

Abstract

The double polarization observable $E$ and the helicity dependent cross sections ${\sigma }_{1/2}$ and ${\sigma }_{3/2}$ were measured for $\eta$ photoproduction from quasi-free protons and neutrons. The circularly polarized tagged photon beam of the A2 experiment at the Mainz MAMI accelerator was used in combination with a longitudinally polarized deuterated butanol target. The almost $4\pi$ detector setup of the Crystal Ball and TAPS is ideally suited to detect the recoil nucleons and the decay photons from $\eta \to 2\gamma$ and $\eta \to 3{\pi }^0$. The results show that the narrow structure previously observed in $\eta$ photoproduction from the neutron is only apparent in ${\sigma }_{1/2}$ and hence, most likely related to a spin-1/2 amplitude. Nucleon resonances that contribute to this partial wave in $\eta$ production are only $N1/2^{-}$ ($S_{11}$) and $N1/2^{+}$ ($P_{11}$). Furthermore, the extracted Legendre coefficients of the angular distributions for ${\sigma }_{1/2}$ are in good agreement with recent reaction model predictions assuming a narrow resonance in the $P_{11}$ wave as the origin of this structure.

References in corpus (22)

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Cited by in corpus (22)

• Etaprime and Eta Mesons with Connection to Anomalous Glue
• Light Baryon Spectroscopy
• Photoproduction Reactions and Non-Strange Baryon Spectroscopy
• Eta and Etaprime Photoproduction on the Nucleon with the Isobar Model EtaMAID2018
• Helicity-dependent cross sections and double-polarization observable E in eta photoproduction from quasi-free protons and neutrons
• First measurement of the polarization observable $E$ and helicity-dependent cross sections in single ${\pi }^0$ photoproduction from quasi-free nucleons
• Study of the $\gamma p\to {\pi }^0\eta p$ reaction with the A2 setup at MAMI
• Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E
• Photo- and electro-production of narrow exotic states: from light quarks to charm and up to bottom
• $K^0\Lambda$ photoproduction off the neutron with nucleon resonances
• Is there a narrow $N(1685)$?
• Observation of Narrow $N^{+}(1685)$ and $N^0(1685)$ Resonances in $\gamma N\to \eta \pi N$ Reactions
• Photoproduction of {\boldmath{${\pi }^0$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region
• Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons
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• Effects of nucleon resonances on $\eta$ photoproduction off the neutron reexamined
• Feasibility study of the $K^{+}d\to K^{0}pp$ reaction for the "${\Theta }^{+}$" pentaquark
• New Narrow $N(1685)$ and $N(1726)$? Remarks on the Interpretation of the Neutron Anomaly as an Interference Phenomenon
• Compton scattering off proton in the third resonance region
• Helicity dependent cross sections for the photoproduction of ${\pi }^0{\pi }^{\pm }$ pairs from quasi-free nucleons
• Search for the $N$(1685) in $\eta \pi$-Photoproduction
• New narrow nucleon resonances $N^{\ast }(1685)$ and $N^{\ast }(1726)$ within the chiral quark-soliton model