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HK: Physik der Hadronen und Kerne

HK 3: Theorie I

HK 3.3: Group Report

Monday, March 19, 2001, 17:15–17:45, B

Dispersion relations for the virtual Compton scattering and the generalized polarizabilities of the nucleon — •Michael Gorchtein¹, Barbara Pasquini², Dieter Drechsel¹, Andreas Metz³ und Marc Vanderhaeghen¹ — ¹Institut für Kernphysik, Johannes Gutenberg Universität Mainz, Germany — ²ECT*, Trento, Italy — ³Vrije Universiteit, Amsterdam, The Netherlands

A dispersion relation formalism at fixed t and Q² is presented for virtual Compton scattering (VCS) off the nucleon at outgoing photon energies ≤ 500 MeV, which for the first time allows a dispersive evaluation of 4 generalized polarizabilities (GP’s) [1,2,3] at low Q² (up to 1 GeV²). We extend the dispersion theory developed in [4] for real Compton scattering to the case of a virtual initial photon. The dispersion integrals are calculated using a state-of-the-art pion photo- and electroproduction analysis. The dispersion calculation provides a new tool to analyze VCS experiments above pion threshold, thus increasing the accuracy of the extraction of the GP’s from the experimental data. The results are compared to existing data and predictions are given for planned VCS experiments.

[1] P.A.M. Guichon et al., Nucl. Phys. A 591 (1995) 606

[2] P.A.M. Guichon and M. Vanderhaeghen, Prog. Part. Nucl. Phys. 51 (1998) 125

[3] D.Drechsel, G. Knöchlein, A. Metz and S. Scherer, Phys. Rev. C55 (1997) 424

[4] D. Drechsel, M. Gorchtein, B. Pasquini and M. Vanderhaeghen, Phys. Rev. C61 (1999) 015204