2000/12/13 by L. Tiator, D. Drechsel, O. Hanstein +4 · 3 citations
Physics and Astronomy · #Neutrino Physics Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions #nucl-th
paper · pdf · doi:10.1016/s0375-9474(01)00835-1
published as Nucl.Phys. A689 (2001) 205-214 · 10 pages LaTeX including 3 figures. Talk given at the XVIIth European conference on Few-Body Problems in Physics, Evora, Portugal, 11 - 16 September 2000; to be published in Nucl.Phys. A
arxiv created 2000/12/13 · openalex publication_date 2001/06/01 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/28
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 Δ(1232) resonance, in particular the E2/M1 ratio REM=(-2.5 +- 0.1) %. For pion electroproduction recent experimental data from Mainz, Bates and JLab for Q2 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 Q2. 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 RSM(0)=(-6.5 +- 0.5) %. At high Q2 the absolute value of the ratio is strongly increasing, a further indication that pQCD is not yet reached.