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28 March 2024
 
  » arxiv » nucl-th/0106027

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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 ;
Date 13 Jun 2001
Subject nucl-th
Abstractgamma 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.
Source arXiv, nucl-th/0106027
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