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.

accepted for publication in Eur. phys. J. A

References in corpus (11)

• 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 $ep\to e^{\prime }{\pi }^{+}{\pi }^{-}{p}^{\prime }$
• New results on the Roper resonance and the P_{11} partial wave
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• Model Analysis of the $ep\to e{p}^{\prime }{\pi }^{+}{\pi }^{-}$ Electroproduction Reaction on the Proton
• 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
• 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
• First measurement of the circular beam asymmetry in the gamma p --> pi0 eta p reaction

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
• Photoproduction ofeta-pi pairs off nucleons and deuterons
• 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