Quasifree photoproduction of $\eta$ mesons off protons and neutrons

Abstract

Differential and total cross sections for the quasifree reactions $\gamma p\to \eta p$ and $\gamma n\to \eta n$ have been determined at the MAMI-C electron accelerator using a liquid deuterium target. Photons were produced via bremsstrahlung from the 1.5 GeV incident electron beam and energy-tagged with the Glasgow photon tagger. Decay photons of the neutral decay modes $\eta \to 2\gamma$ and $\eta \to 3{\pi }^0\to 6\gamma$ and coincident recoil nucleons were detected in a combined setup of the Crystal Ball and the TAPS calorimeters. The $\eta$-production cross sections were measured in coincidence with recoil protons, recoil neutrons, and in an inclusive mode without a condition on recoil nucleons, which allowed a check of the internal consistency of the data. The effects from nuclear Fermi motion were removed by a kinematic reconstruction of the final-state invariant mass and possible nuclear effects on the quasifree cross section were investigated by a comparison of free and quasifree proton data. The results, which represent a significant improvement in statistical quality compared to previous measurements, agree with the known neutron-to-proton cross-section ratio in the peak of the $S_{11}(1535)$ resonance and confirm a peak in the neutron cross section, which is absent for the proton, at a center-of-mass energy $W=(1670\pm 5)$ MeV with an intrinsic width of $\Gamma \approx 30$ MeV.

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• Finite-Energy Sum Rules in Eta Photoproduction off the Nucleon
• Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections
• Cross Section for $\gamma n\to {\pi }^{0}n$ measured at Mainz/A2
• First measurement of the polarization observable $E$ and helicity-dependent cross sections in single ${\pi }^0$ photoproduction from quasi-free nucleons
• Helicity-dependent cross sections and double-polarization observable E in eta photoproduction from quasi-free protons and neutrons
• Role of the $N^{\ast }(1535)$ in the ${\Lambda }_c^{+}\to {\bar{K}}^0\eta p$ decay
• Experimental study of the $\gamma p\to K^0{\Sigma }^{+}$, $\gamma n\to K^0\Lambda$, and $\gamma n\to K^0{\Sigma }^0$ reactions at the Mainz Microtron
• Study of the $\gamma p\to {\pi }^0\eta p$ reaction with the A2 setup at MAMI
• Photoproduction ofeta-pi pairs off nucleons and deuterons
• On the Extraction of Cross Sections for pi0 and eta Photoproduction off Neutrons from Deuteron Data
• Evidence for narrow resonant structures at $W\approx 1.68$ and $W\approx 1.72$ GeV in real Compton scattering off the proton
• Photoproduction of eta mesons from the neutron: cross sections and double polarization observable E
• $K^0\Lambda$ 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
• Comment on "Evidence for narrow resonant structures at $W\approx$ 1.68 GeV and $W\approx$ 1.72 GeV in real Compton scattering off the proton"
• Photoproduction of {\boldmath{${\pi }^0$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region
• Extraction of $\gamma n\to \pi N$ observables from deuteron-target data
• First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons
• Eta and kaon production in a chiral quark model
• Effects of nucleon resonances on $\eta$ photoproduction off the neutron reexamined
• Partial-wave analyses of $\gamma p\to \eta p$ \ and $\gamma n\to \eta n$ using a multichannel framework
• Search for narrow resonances in $\pi p$ elastic scattering from the EPECUR experiment
• Feasibility study of the $K^{+}d\to K^{0}pp$ reaction for the "${\Theta }^{+}$" pentaquark
• Photoproduction of $\eta$ mesons off the proton for $1.2<E_{\gamma }<4.7$ GeV using CLAS at Jefferson Laboratory
• New Narrow $N(1685)$ and $N(1726)$? Remarks on the Interpretation of the Neutron Anomaly as an Interference Phenomenon
• Charged current (anti)neutrino induced eta production off the nucleon
• Possible ${\eta }^{\prime }d$ bound state and its $s$-channel formation in the $\gamma d\to \eta d$ reaction
• 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
• Strangeness Photoproduction on Quasifree Neutrons
• New narrow nucleon resonances $N^{\ast }(1685)$ and $N^{\ast }(1726)$ within the chiral quark-soliton model