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.

References in corpus (11)

• 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
• Measurement of eta photoproduction on the proton from threshold to 1500 MeV
• Measurement of the beam asymmetry in eta-photoproduction off the proton
• Quasi-free photoproduction of eta-mesons of the neutron
• eta-photoproduction in the resonance energy region
• Photoproduction of eta-mesons on the deuteron above S11(1535) in the presence of a narrow P11(1670) resonance
• Photoproduction of $\eta$ mesons off neutrons from a deuteron target
• Photoproduction of eta meson within a coupled-channels K-matrix approach
• Photoproduction of pi0-mesons off neutrons in the nucleon resonance region

Cited by in corpus (9)

• Light Baryon Spectroscopy
• Insight into the narrow structure in {\boldmath{$\eta$}}-photoproduction on the neutron from helicity dependent cross sections
• First measurement of the polarization observable $E$ and helicity-dependent cross sections in single ${\pi }^0$ photoproduction from quasi-free nucleons
• Photoproduction ofeta-pi pairs off nucleons and deuterons
• 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 off the proton for $1.2<E_{\gamma }<4.7$ GeV using CLAS at Jefferson Laboratory
• Charged current (anti)neutrino induced eta production off the nucleon
• 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