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20 April 2024

» arxiv » nucl-ex/0109013

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Compton Scattering by the Proton using a Large-Acceptance Arrangement
S. Wolf ; V. Lisin ; R. Kondratiev ; A.M. Massone ; G. Galler ; J. Ahrens ; H.-J. Arends ; R. Beck ; M. Camen ; G.P. Capitani ; P. Grabmayr ; F. Härter ; T. Hehl ; P. Jennewein ; K. Kossert ; A.I. L’vov ; C. Molinari ; P. Ottonello ; R.O. Owens ; J. Peise ; I. Preobrajenskij ; S. Proff ; A. Robbiano ; M. Sanzone ; M. Schumacher ; M. Schmitz ; F. Wissmann ;
Date:	19 Sep 2001
Journal:	Eur.Phys.J. A12 (2001) 231-252
Subject:	nucl-ex hep-ex hep-ph
Abstract:	Compton scattering by the proton has been measured using the tagged-photon facility at MAMI (Mainz) and the large-acceptance arrangement LARA. The new data are interpreted in terms of dispersion theory based on the SAID-SM99K parameterization of photo-meson amplitudes. It is found that two-pion exchange in the t-channel is needed for a description of the data in the second resonance region. The data are well represented if this channel is modeled by a single pole with mass parameter m(sigma)=600 MeV. The asymptotic part of the spin dependent amplitude is found to be well represented by pi-0-exchange in the t-channel. A backward spin-polarizability of gamma(pi)=(-37.1+-0.6(stat+syst)+-3.0(model))x10^{-4}fm^4 has been determined from data of the first resonance region below 455 MeV. This value is in a good agreement with predictions of dispersion relations and chiral pertubation theory. From a subset of data between 280 and 360 MeV the resonance pion-photoproduction amplitudes were evaluated leading to a E2/M1 multipole ratio of the p-to-Delta radiative transition of EMR(340 MeV)=(-1.7+-0.4(stat+syst)+-0.2(model))%. It was found that this number is dependent on the parameterization of photo-meson amplitudes. With the MAID2K parameterization an E2/M1 multipole ratio of EMR(340 MeV)=(-2.0+-0.4(stat+syst)+-0.2(model))% is obtained.
Source:	arXiv, nucl-ex/0109013
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