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 (9)

• Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
• Study of the gp-->etap reaction with the Crystal Ball detector at the Mainz Microtron(MAMI-C)
• Evidence for a narrow structure at W~1.68 GeV in eta photoproduction on the neutron
• Quasi-free photoproduction of eta-mesons of the neutron
• eta-photoproduction in the resonance energy region
• Quasifree photoproduction of $\eta$ mesons off protons and neutrons
• Photoproduction of eta-mesons on the deuteron above S11(1535) in the presence of a narrow P11(1670) resonance
• Photoproduction of eta meson within a coupled-channels K-matrix approach
• Evidence for narrow resonant structures at $W\approx 1.68$ and $W\approx 1.72$ GeV in real Compton scattering off the proton

Cited by in corpus (5)

• Light Baryon Spectroscopy
• First measurement of the polarization observable $E$ and helicity-dependent cross sections in single ${\pi }^0$ photoproduction from quasi-free nucleons
• Photo- and electro-production of narrow exotic states: from light quarks to charm and up to bottom
• Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons
• Helicity dependent cross sections for the photoproduction of ${\pi }^0{\pi }^{\pm }$ pairs from quasi-free nucleons