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Aspects of near-threshold neutral pion photoproduction off protons

  • V. Bernard
  • N. Kaiser
  • U.-G. Meißner

Abstract:

We investigate near-threshold neutral pion photoproduction off protons to fourth order in heavy-baryon chiral perturbation theory in the light of the new data from MAMI. We show that the unitarity cusp at the secondary π+n threshold is in agreement with expectations from the final-state theorem. We also analyze the fourth-order corrections to the P-wave low-energy theorems and show that potentially large Δ isobar contributions are cancelled by sizeable pion loop effects. This solidifies the parameter-free third-order predictions, which are in good agreement with the data.

PACS. 12.20.Ds Specific calculations – 12.39.Fe Chiral Lagrangians – 25.20.Lj Photoproduction reactions 

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Copyright information

© Società Italiana di Fisica and Springer-Verlag 2001

Authors and Affiliations

  • V. Bernard
    • 1
  • N. Kaiser
    • 2
  • U.-G. Meißner
    • 3
  1. 1.Université Louis Pasteur, Laboratoire de Physique Théorique 3-5, rue de l'Université, F-67084 Strasbourg, FranceFR
  2. 2.Technische Universität München, Physik Department T39 James-Franck-Straße, D-85747 Garching, GermanyDE
  3. 3.Forschungszentrum Jülich, Institut für Kernphysik (Theorie), D-52425 Jülich, GermanyDE

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