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Recent developments in the dynamical and unitary isobar models for pion electromagnetic production

Shin Nan Yang·Guan Yeu Chen·S. S. Kamalov·D. Drechsel·L. Tiator
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Abstract

gamma N->Delta transition form factors and threshold pi^0 photo- and electroproduction are studied with the new version of MAID and a dynamical model. By re-analyzing the recent Jlab data on p(e,e'p) pi^0 at Q^2 = 2.8 and 4.0 (GeV/c)^2, we find that the hadronic helicity conservation is not yet observed in this region of Q^2. The extracted R_{EM}, starting from a small and negative value at the real photon point, actually exhibits a clear tendency to cross zero and change sign as Q^2 increases, while the absolute value of R_{SM} is strongly increasing. Our analysis indicates that A_{1/2} and S_{1/2}, but not A_{3/2}, starts exhibiting the pQCD scaling behavior at about Q^2 = 2.5 (GeV/c)^2. For the pi^0 photo- and electroproduction near threshold, results obtained within the dynamical model with the use of a meson-exchange pi N model for the final state interaction are in as good agreement with the data as ChPT.

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Shin Nan Yang, Guan Yeu Chen, S. S. Kamalov, D. Drechsel, L. Tiator. 2001-06-13. Recent developments in the dynamical and unitary isobar models for pion electromagnetic production. https://doi.org/10.1142/9789812810878_0011

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