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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

  • The Crystal Ball at MAMI, TAPS and A2 Collaborations
  • M. Oberle
  • J. Ahrens
  • J. R. M. Annand
  • H. J. Arends
  • K. Bantawa
  • P. A. Bartolome
  • R. Beck
  • V. Bekrenev
  • H. Berghäuser
  • A. Braghieri
  • D. Branford
  • W. J. Briscoe
  • J. Brudvik
  • S. Cherepnya
  • B. Demissie
  • M. Dieterle
  • E. J. Downie
  • P. Drexler
  • L. V. Fil’kov
  • A. Fix
  • D. I. Glazier
  • E. Heid
  • D. Hornidge
  • D. Howdle
  • G. M. Huber
  • O. Jahn
  • I. Jaegle
  • T. C. Jude
  • A. Käser
  • V. L. Kashevarov
  • I. Keshelashvili
  • R. Kondratiev
  • M. Korolija
  • S. P. Kruglov
  • B. Krusche
  • A. Kulbardis
  • V. Lisin
  • K. Livingston
  • I. J. D. MacGregor
  • Y. Maghrbi
  • J. Mancell
  • D. M. Manley
  • Z. Marinides
  • M. Martinez
  • J. C. McGeorge
  • E. McNicoll
  • D. Mekterovic
  • V. Metag
  • S. Micanovic
  • D. G. Middleton
  • A. Mushkarenkov
  • B. M. K. Nefkens
  • A. Nikolaev
  • R. Novotny
  • M. Ostrick
  • B. Oussena
  • P. Pedroni
  • F. Pheron
  • A. Polonski
  • S. N. Prakhov
  • J. Robinson
  • G. Rosner
  • T. Rostomyan
  • S. Schumann
  • M. H. Sikora
  • D. I. Sober
  • A. Starostin
  • I. Supek
  • M. Thiel
  • A. Thomas
  • M. Unverzagt
  • D. P. Watts
  • D. Werthmüller
  • L. Witthauer
  • F. Zehr
Open Access
Regular Article - Experimental Physics

Abstract.

Beam-helicity asymmetries have been measured at the MAMI accelerator in Mainz for the photoproduction of mixed-charge pion pairs in the reactions \( \gamma p\rightarrow n\pi^{0}\pi^{+}\) off free protons and \( \gamma d \rightarrow (p)p\pi^{0}\pi^{-}\) and \( \gamma d\rightarrow (n)n\pi^{0}\pi^{+}\) off quasi-free nucleons bound in the deuteron for incident photon energies up to 1.4GeV. 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.

Keywords

Monte Carlo Resonance Region Charged Pion Incident Photon Energy Free Proton 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© The Author(s) 2014

Authors and Affiliations

  • The Crystal Ball at MAMI, TAPS and A2 Collaborations
  • M. Oberle
    • 1
  • J. Ahrens
    • 2
  • J. R. M. Annand
    • 3
  • H. J. Arends
    • 2
  • K. Bantawa
    • 4
  • P. A. Bartolome
    • 2
  • R. Beck
    • 5
  • V. Bekrenev
    • 6
  • H. Berghäuser
    • 7
  • A. Braghieri
    • 8
  • D. Branford
    • 9
  • W. J. Briscoe
    • 10
  • J. Brudvik
    • 11
  • S. Cherepnya
    • 12
  • B. Demissie
    • 10
  • M. Dieterle
    • 1
  • E. J. Downie
    • 2
    • 3
    • 10
  • P. Drexler
    • 7
  • L. V. Fil’kov
    • 12
  • A. Fix
    • 13
  • D. I. Glazier
    • 9
  • E. Heid
    • 2
  • D. Hornidge
    • 14
  • D. Howdle
    • 3
  • G. M. Huber
    • 15
  • O. Jahn
    • 2
  • I. Jaegle
    • 1
  • T. C. Jude
    • 9
  • A. Käser
    • 1
  • V. L. Kashevarov
    • 12
    • 2
  • I. Keshelashvili
    • 1
  • R. Kondratiev
    • 16
  • M. Korolija
    • 17
  • S. P. Kruglov
    • 6
  • B. Krusche
    • 1
  • A. Kulbardis
    • 6
  • V. Lisin
    • 16
  • K. Livingston
    • 3
  • I. J. D. MacGregor
    • 3
  • Y. Maghrbi
    • 1
  • J. Mancell
    • 3
  • D. M. Manley
    • 4
  • Z. Marinides
    • 10
  • M. Martinez
    • 2
  • J. C. McGeorge
    • 3
  • E. McNicoll
    • 3
  • D. Mekterovic
    • 17
  • V. Metag
    • 7
  • S. Micanovic
    • 17
  • D. G. Middleton
    • 14
  • A. Mushkarenkov
    • 8
  • B. M. K. Nefkens
    • 11
  • A. Nikolaev
    • 5
  • R. Novotny
    • 7
  • M. Ostrick
    • 2
  • B. Oussena
    • 2
    • 10
  • P. Pedroni
    • 8
  • F. Pheron
    • 1
  • A. Polonski
    • 16
  • S. N. Prakhov
    • 11
  • J. Robinson
    • 3
  • G. Rosner
    • 3
  • T. Rostomyan
    • 1
    • 8
  • S. Schumann
    • 2
  • M. H. Sikora
    • 9
  • D. I. Sober
    • 18
  • A. Starostin
    • 11
  • I. Supek
    • 17
  • M. Thiel
    • 7
  • A. Thomas
    • 2
  • M. Unverzagt
    • 2
    • 5
  • D. P. Watts
    • 9
  • D. Werthmüller
    • 1
  • L. Witthauer
    • 1
  • F. Zehr
    • 1
  1. 1.Department of PhysicsUniversity of BaselBaselSwitzerland
  2. 2.Institut für KernphysikUniversity of MainzMainzGermany
  3. 3.School of Physics and AstronomyUniversity of GlasgowGlasgowUK
  4. 4.Kent State UniversityKentUSA
  5. 5.Helmholtz-Institut für Strahlen- und KernphysikUniversity of BonnBonnGermany
  6. 6.Petersburg Nuclear Physics InstituteGatchinaRussia
  7. 7.II. Physikalisches InstitutUniversity of GiessenGiessenGermany
  8. 8.INFN, Sezione di PaviaPaviaItaly
  9. 9.School of PhysicsUniversity of EdinburghEdinburghUK
  10. 10.Center for Nuclear StudiesThe George Washington UniversityWashington, DCUSA
  11. 11.University of California Los AngelesLos AngelesUSA
  12. 12.Lebedev Physical InstituteMoscowRussia
  13. 13.Laboratory of Mathematical PhysicsTomsk Polytechnic UniversityTomskRussia
  14. 14.Mount Allison UniversityNew BrunswickCanada
  15. 15.University of ReginaRegina, SKCanada
  16. 16.Institute for Nuclear ResearchMoscowRussia
  17. 17.Rudjer Boskovic InstituteZagrebCroatia
  18. 18.The Catholic University of AmericaWashington, DCUSA

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