München 2006 – wissenschaftliches Programm
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HK: Physik der Hadronen und Kerne
HK 48: Elektromagnetische und Hadronische Sonden
HK 48.2: Gruppenbericht
Donnerstag, 23. März 2006, 17:30–18:00, F
Dispersion Theory and the Low Energy Constants for Pion Photoproduction — •Barbara Pasquini1, Dieter Drechsel2, and Lothar Tiator2 — 1Dipartimento di Fisica Nucleare e Teorica, Universita degli Studi di Pavia and INFN, Sezione di Pavia, Pavia, Italy — 2Institut für Kernphysik, Universität Mainz
The relativistic amplitudes of pion photoproduction are evaluated by dispersion relations at t= const. The imaginary parts of the amplitudes are taken from the MAID model covering the absorption spectrum up to center-of-mass energies W=2.5 GeV. For sub-threshold kinematics the amplitudes are expanded in powers of the two independent variables ν and t related to energy and momentum transfer. Subtraction of the corresponding series for the loop corrections allows one to determine the size of the counterterms of covariant baryon chiral perturbation theory. The proposed continuation of the amplitudes into the unphysical region provides a unique framework to derive the low-energy constants to any given order as well as an estimate of the higher order terms by global properties of the absorption spectrum.