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HK: Physik der Hadronen und Kerne
HK 27: Elektromagnetische und hadronische Proben VI
HK 27.5: Vortrag
Dienstag, 23. März 1999, 18:15–18:30, E
Virtual Compton scattering off the nucleon at low energies and generalized polarizabilities — •B. Pasquini1, D. Drechsel1, A. Metz2, and S. Scherer1 — 1Institut f"ur Kernphysik, Universit"at Mainz, Becherweg 45, D-55099 Mainz — 2Institut f"ur Theoretische Physik, Ruprecht Karls-Universit"at, Philosophenweg 19, D-69120 Heidelberg
Below pion-production threshold, virtual Compton scattering off the nucleon gives access to the generalized polarizabilities [1]. As a consequence of charge conjugation invariance and nucleon crossing symmetry, the ten generalized polarizabilities have to satisfy four constraints [2]. By an explicit calculation we show that these relations are not satisfied in the non-relativistic quark model. We interpret this result by discussing the importance and interplay of the various symmetry properties.
A full determination of the generalized polarizabilities requires unpolarized as well as double polarization experiments. In order to provide estimates of the nucleon structure effects accessible through these reactions, we present predictions of the unpolarized cross section and the double polarization observables [3] in the framework of the linear sigma model [4] and chiral perturbation theory [5].
[1] P.A.M. Guichon, G.Q. Liu, A.W. Thomas, Nucl. Phys. A591, 606 (1995).
[2] D. Drechsel, G. Kn"ochlein, A. Metz and S. Scherer, Phys. Rev. C55, 424 (1997); D. Drechsel, G. Kn"ochlein, A. Yu. Korchin, A. Metz and S. Scherer, Phys. Rev. C58, 1751 (1998).
[3] A. Metz, B. Pasquini and D. Drechsel, Proc. of the second workshop on Electronuclear Physics with Internal Targets and the BLAST detector, MIT, Cambridge, May 28-30, 1998, hep-ph/9808282.
[4] A. Metz and D. Drechsel, Z. Phys. A356, 351 (1996); Z. Phys. A359, 165 (1997).
[5] T.R. Hemmert, B.R. Holstein, G. Kn"ochlein and S. Scherer, Phys. Rev. D55, 2630 (1997); Phys. Rev. Lett. 79, 22 (1997).