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HK: Physik der Hadronen und Kerne

HK 19: Theorie II

HK 19.8: Vortrag

Dienstag, 18. März 2003, 18:00–18:15, D

Signatures of Spontaneous Symmetry Breaking in Compton Scattering off the Proton — •Robert Hildebrandt, Harald W. Grießhammer, and Thomas R. Hemmert — Institute for Theoretical Physics (T39), TU München, Germany

The dynamical nucleon polarizabilities – spin independent as well as spin dependent – can be defined via the multipole expansion of the non-Born amplitudes in nucleon Compton scattering [1, 2]. We present results of Chiral Perturbation Theory with and without explicit Δ(1232) degrees of freedom and compare with a dispersion relation (DR) analysis [2]. We calculate unpolarized differential cross sections for Compton scattering off protons and find excellent agreement with DR and experimental data. Due to the very fast convergence of the multipole expansion, quadrupole contributions are found to be negligibly small. This offers the possibility of directly determining dynamical nucleon polarizabilities from experiment by fitting cross sections with six Compton multipoles.

We demonstrate the strong influence of nucleon spin-polarizabilities even in unpolarized Compton cross sections. In order to further examine the spin structure of the nucleon, we present predictions for polarized nucleon Compton scattering experiments.

Work supported in part by DFG and BMBF.

• [1] H. W. Grießhammer, T. R. Hemmert, Phys. Rev. C 65, 045207 (2002)
• [2] R. Hildebrandt, H. W. Grießhammer, T. R. Hemmert, B. Pasquini,
  [2] preprint TUM-T39-02-05 in preparation