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HK: Physik der Hadronen und Kerne
HK IV: HV IV
HK IV.1: Hauptvortrag
Dienstag, 21. März 2000, 15:45–16:15, H 04
Nucleon Polarizabilities and Virtual Compton scattering — •Nicole d’Hose — CEA Saclay, DSM/DAPNIA/SPhN, F91191 Gif-sur-Yvette Cedex, France
Virtual Compton scattering, i.e. the exclusive reaction γ* p → γ p with γ* denoting a virtual photon, provides new insights on the internal structure of the proton. Below π0 production threshold, this experiment measures the generalized polarizabilities of the proton as defined by Guichon et al. and Drechsel et al.. These new observables, functions of Q2 enlarge the concept of electric (αE) and magnetic (βM) polarizabilities as defined in Real Compton scattering (Q2=0).
A first dedicated experiment to investigate this reaction was performed with the high resolution spectrometers at the Mainz Microtron MAMI for Q2=0.33 GeV2, covering the energy range of the real photon from 33 to 111 MeV. The measurements of the absolute cross sections and the determination of polarizabilities from the study at different photon energies and from the angular photon distributions will be presented. The results are not well reproduced by constituent quark models, but only by models of the nucleon which takes into account chiral symmetry, an important property of Quantum Chromodynamics Theory.
1P.A.M. Guichon et al., Nucl. Phys. A591 (1995) 606
2D. Drechsel et al., Phys. Rev. C55 (1997) 424, Phys. Rev. C57 (1998) 941