Measurement of the beam-helicity asymmetry $I^{\odot }$ in the photoproduction of ${\pi }^0{\pi }^{\pm }$-pairs off protons and off neutrons

Abstract

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions $\mathbf{\gamma }p\to n{\pi }^0{\pi }^{+}$ off free protons and $\mathbf{\gamma }d\to (p)p{\pi }^0{\pi }^{-}$ and $\mathbf{\gamma }d\to (n)n{\pi }^0{\pi }^{+}$ off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4 GeV. Circularly polarized photons were produced from bremsstrahlung of longitudinally polarized electrons and tagged with the Glasgow-Mainz magnetic spectrometer. The charged pions, recoil protons, recoil neutrons, and decay photons from ${\pi }^0$ mesons were detected in the 4$\pi$ electromagnetic calorimeter composed of the Crystal Ball and TAPS detectors. Using a complete kinematic reconstruction of the final state, excellent agreement was found between the results for free and quasi-free protons, suggesting that the quasi-free neutron results are also a close approximation of the free-neutron asymmetries. A comparison of the results to the predictions of the Two-Pion-MAID reaction model shows that the reaction mechanisms are still not well understood, in particular at low incident photon energies in the second nucleon-resonance region.

arXiv commentaccepted for publication in Eur. phys. J. A

References in corpus (38)

• Excited state baryon spectroscopy from lattice QCD
• Studies of Nucleon Resonance Structure in Exclusive Meson Electroproduction
• Study of Non-Strange Baryon Resonances with Meson Photoproduction
• Upgrade of the Glasgow photon tagging spectrometer for Mainz MAMI-C
• A study of the $P_{11}(1440)$ and $D_{13}(1520)$ resonances from CLAS data on $ep\to e^{\prime }{\pi }^{+}{\pi }^{-}{p}^{\prime }$
• Measurement of $ep\to e^{{}^{\prime }}p{\pi }^{+}{\pi }^{-}$ and baryon resonance analysis
• New results on the Roper resonance and the P_{11} partial wave
• Double pion photoproduction on nucleon and deuteron
• Spectrum of hadrons with strangeness
• Quasi-free photoproduction of eta-mesons of the neutron
• Polarization Observables for Two-Pion Production off the Nucleon
• N* and Delta* decays into N pi0 pi0
• Quasi-free photoproduction of eta-mesons off the deuteron
• Study of the reaction $\gamma p\to p{\pi }^0\eta$
• The role of Delta(1700) excitation and rho production in double pion photoproduction
• Beam-Helicity Asymmetries in Double-Charged-Pion Photoproduction on the Proton
• Model Analysis of the $ep\to e{p}^{\prime }{\pi }^{+}{\pi }^{-}$ Electroproduction Reaction on the Proton
• Photoproduction of pi^0 eta on protons and the Delta(1700)D_{33} resonance
• Photoproduction of pions and properties of baryon resonances from a Bonn-Gatchina partial wave analysis
• Photoproduction of mesons off nuclei
• Evidence for a parity doublet Delta(1920)P_{33} and Delta(1940)D_{33}$ from γp\to pπ^0η
• A narrow structure in the excitation function of eta-photoproduction off the neutron
• Extracting the photoproduction cross section off the neutron gn-->pi-p from deuteron data with FSI effects
• Study of the gamma p --> pi0 pi0 p reaction with the Crystal Ball/TAPS at the Mainz
• Photoproduction of pi0pi0 and pi0pi+-pairs off the proton from threshold to the second resonance region
• Beam-Helicity Asymmetries in Double Pion Photoproduction off the Proton
• Radiative pi0 photoproduction on protons in the Delta+(1232) region
• Photoabsorption on a Nucleon in the D_{13} Resonance Energy Region
• Double ${\pi }^0$ Photoproduction off the Proton at Threshold
• Helicity amplitudes for photoexcitation of nucleon resonances off neutrons
• Study of polarization observables in double pion photoproduction on the proton
• Electroproduction of p π^{+} π^{-} off protons at 0.2<Q^{2}<0.6 GeV^{2} and 1.3<W<1.57 GeV with CLAS
• Photoproduction of ${\eta }^{\prime }$-mesons off the deuteron
• Amplitude analysis of gamma n --> pi- p data above 1 GeV
• Measurement of the beam-helicity asymmetry $I^{\odot }$ in the photoproduction of ${\pi }^0$-pairs off the proton and off the neutron
• Quasi-free photoproduction of eta-mesons off 3He nuclei
• First measurement of the circular beam asymmetry in the gamma p --> pi0 eta p reaction
• Helicity asymmetries in double pion photoproduction on the proton

Cited by in corpus (11)

• Light Baryon Spectroscopy
• Photoproduction Reactions and Non-Strange Baryon Spectroscopy
• First measurement of the helicity asymmetry $E$ in $\eta$ photoproduction on the proton
• 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
• 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
• Photoproduction ofeta-pi pairs off nucleons and deuterons
• Photoproduction of {\boldmath{${\pi }^0$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region
• First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons
• 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