2014
DOI: 10.1140/epja/i2014-14054-5
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Measurement of the beam-helicity asymmetry I⊙ in the photoproduction of $ \pi^{0}$ $ \pi^{\pm}$ pairs off protons and off neutrons

Abstract: Abstract. Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions γp → nπ 0 π + off free protons and γd → (p)pπ 0 π − and γd → (n)nπ 0 π + 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, rec… Show more

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Cited by 21 publications
(45 citation statements)
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“…The data analysis was based on the methods developed for the reaction identification of meson pairs (ππ and πη) described in detail in [7,23,24,27,28] for measurements with unpolarized liquid deuterium targets. The treatment of the unpolarized background from 'heavy' nuclei (carbon, oxygen), present in the butanol target, is described in [33,34,37] for photoproduction of η and π 0 mesons.…”
Section: Discussionmentioning
confidence: 99%
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“…The data analysis was based on the methods developed for the reaction identification of meson pairs (ππ and πη) described in detail in [7,23,24,27,28] for measurements with unpolarized liquid deuterium targets. The treatment of the unpolarized background from 'heavy' nuclei (carbon, oxygen), present in the butanol target, is described in [33,34,37] for photoproduction of η and π 0 mesons.…”
Section: Discussionmentioning
confidence: 99%
“…However, polarization observables seem to be effected in a completely different way. We have previously tested this for the polarization observable I ⊙ measured with a circularly polarized photon beam on unpolarized target for the production of meson pairs [24,27,28]. No significant effects were found for ππ and πη pairs.…”
Section: Complications For Quasi-free Production Off Bound Nucleonsmentioning
confidence: 99%
“…This property for c 1 does not occur for the other coefficients and was also observed for double-pion production in reference [52]. In order to fully make sense of the results shown, a better theoretical understanding of the reactions is needed.…”
Section: Discussionmentioning
confidence: 52%
“…The beam-helicity asymmetry, I , arising from a circularly polarized photon beam, can be chosen to be an independent quantity yielding to a component of the eight complex amplitudes mentioned. This particular observable has previously been studied for double pion photoproduction in references [49,50,52,56] up to center-of-mass energy W < 2.3 GeV. The region with W > 2.3 GeV was previously unexplored, but beam-helicity asymmetry measurements in this region are shown in this chapter.…”
Section: Discussionmentioning
confidence: 85%
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