Münster 2002 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 9: Poster Session: Theory

HK 9.1: Poster

Dienstag, 12. März 2002, 10:30–12:45, Foyer Chemie

Dispersive Effects in Nucleon Polarisabilities Observed in Deuteron Compton Scattering — •Harald W. Grießhammer — Institut für Theoretische Physik (T39), TU München, D-85747 Garching — ECT*, Villa Tambosi, I-38050 Villazzano (Trento), Italy

A formalism to extract the dynamical nucleon polarisabilities defined via a multipole expansion of the structure amplitudes in nucleon Compton scattering was developed in [1]. In contradistinction to the static polarisabilities, dynamical polarisabilities gauge the response of the internal degrees of freedom of a composed object to an external, real photon field of arbitrary energy. Being energy dependent, they contain information about dispersive effects induced by internal relaxation mechanisms, baryonic resonances and meson production thresholds of the nucleon.

As the iso-scalar dynamical polarisabilities are directly accessible in low energy deuteron Compton scattering, their energy dependence is discussed especially in the light of the SAL data at ω=91 MeV which suggest a magnetic dipole polarisability five times bigger than values from extractions at zero energy. At those energies, dynamical effects are however large and cannot be mimicked by taking only the slopes of the polarisabilities at zero energy into account. An analysis using dynamical polarisabilities from either Heavy Baryon Chiral Perturbation Theory including the Δ(1232) as dynamical degree of freedom or using dispersion theory predicts however values in agreement with experiment at all energies. We comment on recent data from Lund at ω≈ 50 MeV.

Supported in part by DFG under grant GR 1887/1-2 and by BMBF.

[1.] H.W. Grießhammer and T.R. Hemmert: nucl-th/0110006.