Neutral pion photoproduction off nucleons revisited |
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Authors: | V. Bernard N. Kaiser Ulf G. Meißner |
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Affiliation: | 1. Centre de Recherches Nucleaires, Physique Theorique, Bat. 40, BP 28, F-67037, Strasbourg Cedex 2, France 4. Laboratoire de Physique Theorique, Institut de Physique 3-5 rue de l’Universite, F-67084, Strasbourg Cedex, France 2. Physik Department T39, Technische Universit?t München, James Franck Stra?e, D-85747, Garching, Germany 3. Institut für Theoretische Kernphysik, Universit?t Bonn, Nussallee 1416, D-53115, Bonn, Germany
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Abstract: | We investigate threshold pion photoproduction in the framework of heavy baryon chiral perturbation theory. We give the expansion of the electric dipole amplitude E 0+ to three orders in μ the ratio of the pion to nucleon mass, and show that it is slowly converging. We argue that this observable is not a good testing ground for the chiral dynamics of QCD. In contrast, we exhibit new and fastly converging low-energy theorems in the P-waves which should be used to constrain the data analysis. We also discuss the importance of polarization observables to accurately pin down certain multipoles and give predictions for the reaction γ n → π0 n. |
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