Photoproduction ofeta-pi pairs off nucleons and deuterons

Abstract

Quasi-free photoproduction of $\pi \eta$-pairs has been investigated from threshold up to incident photon energies of 1.4 GeV, respectively up to photon-nucleon invariant masses up to 1.9 GeV. Total cross sections, angular distributions, invariant-mass distributions of the $\pi \eta$ and meson-nucleon pairs, and beam-helicity asymmetries have been measured for the reactions $\gamma p\to p{\pi }^0\eta$, $\gamma n\to n{\pi }^0\eta$, $\gamma p\to n{\pi }^{+}\eta$, and $\gamma n\to p{\pi }^{-}\eta$ from nucleons bound inside the deuteron. For the $\gamma p$ initial state data for free protons have also been analyzed. Finally, the total cross sections for quasi-free production of ${\pi }^0\eta$ pairs from nucleons bound in ${}^3$He nuclei have been investigated in view of final state interaction (FSI) effects. The experiments were performed at the tagged photon beam facility of the Mainz MAMI accelerator using an almost $4\pi$ covering electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. The shapes of all differential cross section data and the asymmetries are very similar for protons and neutrons and agree with the conjecture that the reactions are dominated by the sequential ${\Delta }^{\star }3/2^{-}\to \eta \Delta (1232)\to \pi \eta N$ decay chain, mainly with $\Delta (1700)3/2^{-}$ and $\Delta (1940)3/2^{-}$. The ratios of the magnitude of the total cross sections also agree with this assumption. However, the absolute magnitudes of the cross sections are reduced by FSI effects with respect to free proton data.

accepted for publication in Eur. Phys. J. A

References in corpus (13)

• Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
• New results on the Roper resonance and the P_{11} partial wave
• Quasifree photoproduction of $\eta$ mesons off protons and neutrons
• Evidence for a parity doublet Delta(1920)P_{33} and Delta(1940)D_{33}$ from γp\to pπ^0η
• Study of the gamma p --> pi0 pi0 p reaction with the Crystal Ball/TAPS at the Mainz
• Beam-Helicity Asymmetries in Double Pion Photoproduction off the Proton
• Photoproduction of pi0pi0 and pi0pi+-pairs off the proton from threshold to the second resonance region
• Clues to the nature of the Delta^*(1700) resonance from pion- and photon-induced reactions
• Production of $\eta$ and ${\eta }^{\prime }$ Mesons on Nucleons and Nuclei
• First measurement of the circular beam asymmetry in the gamma p --> pi0 eta p reaction
• Photoproduction of pi0-mesons off neutrons in the nucleon resonance region
• Measurement of the beam-helicity asymmetry $I^{\odot }$ in the photoproduction of ${\pi }^0{\pi }^{\pm }$-pairs off protons and off neutrons
• Polarization observables in ${\pi }^0\eta$-photoproduction on the proton

Cited by in corpus (5)

• Spectroscopy of light $N^{\ast }$ baryons
• First measurement of the polarization observable $E$ and helicity-dependent cross sections in single ${\pi }^0$ photoproduction from quasi-free nucleons
• Observation of a structure in the M${}_{p\eta }$ invariant mass distribution near 1700 MeV/$c^2$ in the $\gamma \mathbf{p}\to \mathbf{p}{\pi }^0\eta$ reaction
• Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons
• Coherent photoproduction of the neutral pion and eta meson on the deuteron at incident energies below 1.15 GeV