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The E2/M1 and C2/M1 ratios and form factors in N -> Delta transitions | | L. Tiator
; D. Drechsel
; O. Hanstein
; S.S. Kamalov
; S.N. Yang
; | | Date: |
13 Dec 2000 | | Journal: | Nucl.Phys. A689 (2001) 205-214 | | Subject: | nucl-th | | Abstract: | A partial wave analysis of pion photoproduction has been obtained in the framework of fixed-t dispersion relations valid from threshold up to 500 MeV. In the resonance region we have precisely determined the electromagnetic properties of the Delta(1232) resonance, in particular the E2/M1 ratio R_{EM}=(-2.5 +- 0.1) %. For pion electroproduction recent experimental data from Mainz, Bates and JLab for Q^2 up to 4.0 (GeV/c)^2 have been analyzed with two different models, an isobar model (MAID) and a dynamical model. The E2/M1 ratios extracted with these two models show, starting from a small and negative value at the real photon point, a clear tendency to cross zero, and become positive with increasing Q^2. This is a possible indication of a very slow approach toward the pQCD region. The C2/M1 ratio near the photon point is found as R_{SM}(0)=(-6.5 +- 0.5) %. At high Q^2 the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached. | | Source: | arXiv, nucl-th/0012046 | | Services: | Forum | Review | PDF | Favorites | |
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