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.
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Received: 25 May 2001 / Accepted: 21 June 2001
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Bernard, V., Kaiser, N. & Meißner, UG. Aspects of near-threshold neutral pion photoproduction off protons. Eur Phys J A 11, 209–216 (2001). https://doi.org/10.1007/s100500170085
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DOI: https://doi.org/10.1007/s100500170085