Photoproduction of pi0pi0 and pi0pi+-pairs off the proton from threshold to the second resonance region

Abstract

Precise total cross-sections and invariant-mass distributions have been measured for photoproduction of pion pairs off the proton producing $p{\pi }^0{\pi }^0$ and $n{\pi }^{+}{\pi }^0$ final states from the threshold region up to 800 MeV incident photon energy. Additionally, beam helicity asymmetries have been measured in the second resonance region (550 MeV - 820 MeV). The experiment was performed at the tagged photon beam of the Mainz MAMI accelerator with the Crystal Ball and TAPS detectors combined to give an almost 4$\pi$ solid-angle electromagnetic calorimeter. The results are much more precise than any previous measurements and confirm the chiral perturbation theory predictions for the threshold behavior of these reactions. In the second resonance region, the invariant-mass distributions of meson-meson and meson-nucleon pairs are in reasonable agreement with model predictions, but none of the models reproduce the asymmetries for the mixed-charge channel.

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

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• A narrow structure in the excitation function of eta-photoproduction off the neutron
• Study of the quasi-free $np\to np{\pi }^{+}{\pi }^{-}$ reaction with a deuterium beam at 1.25 GeV/nucleon
• 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
• Photoproduction of pi0-mesons off neutrons in the nucleon resonance region
• Coherent photoproduction of pi^0- and eta-mesons off 7Li
• Measurement of the beam-helicity asymmetry $I^{\odot }$ in the photoproduction of ${\pi }^0{\pi }^{\pm }$-pairs off protons and off neutrons
• 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
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• Photoproduction of {\boldmath{${\pi }^0$}} Mesons off Protons and Neutrons in the Second and Third Nucleon Resonance Region
• 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
• First measurement of helicity-dependent cross sections in pi0-eta photoproduction from quasi-free nucleons
• Minimal complete sets for two pseudoscalar meson photoproduction
• Helicity-dependent cross sections for the photoproduction of ${\pi }^0$ pairs from nucleons
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• Measurement of the beam-helicity asymmetry in photoproduction of ${\pi }^0\eta$ pairs on carbon, aluminum, and lead
• Helicity dependent cross sections for the photoproduction of ${\pi }^0{\pi }^{\pm }$ pairs from quasi-free nucleons
• Quasi-free photoproduction of pion-pairs off protons and neutrons