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Separated cross-sections in \pi^{0}_{} electroproduction at threshold at Q2 = 0.05GeV2/c2 |
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| Authors: | M Weis P Bartsch D Baumann J Bermuth A M Bernstein K Bohinc R Böhm M Ding M O Distler I Ewald J M Friedrich J Friedrich M Kahrau M Kohl K W Krygier A Liesenfeld H Merkel P Merle U Müller R Neuhausen M M Pavan Th Pospischil M Potokar G Rosner H Schmieden M Seimetz S Širca A Wagner Th Walcher |
| Institution: | 1. Institut für Kernphysik, Johannes Gutenberg-Universit?t Mainz, D-55099, Mainz, Germany 2. Institut für Physik, Johannes Gutenberg-Universit?t Mainz, D-55099, Mainz, Germany 3. Laboratory for Nuclear Science, Massachusetts Institute of Technology, 02139, Cambridge, MA, USA 4. Jo?ef Stefan Institute, SI-1001, Ljubljana, Slovenia 5. Institut für Kernphysik, Technische Universit?t Darmstadt, D-64289, Darmstadt, Germany 6. Department of Physics, University of Ljubljana, SI-1000, Ljubljana, Slovenia |
| Abstract: | The differential cross-sections σ0 = σT + εσL , σLT , and σTT of  electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value
of the photon four-momentum transfer of Q
2 = 0.05 GeV2/c2 and a center-of-mass angle of θ = 90° . By an additional out-of-plane measurement with polarized electrons σLT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the  threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory
(HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological
model and are in good agreement with the dynamical model DMT. |
| Keywords: | PACS" target="_blank">PACS 25 30 Rw Electroproduction reactions 13 60 Le Meson production |
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