Köln 2004 – wissenschaftliches Programm

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HK: Physik der Hadronen und Kerne

HK 38: Electromagnetic and Hadronic Probes VI

HK 38.2: Gruppenbericht

Donnerstag, 11. März 2004, 14:00–14:30, B

Two-Pion Decay of Resonances and the Reaction π N→ππ N — •Sonja Schneider and Siegfried Krewald — Institut für Kernphysik, Forschungszentrum Jülich, D-52425 Jülich

The understanding of the spectrum and the decay properties of baryons is essential to our understanding of QCD in the non-perturbative regime. We focus on the investigation of the two-pion decay of the low-lying N^⋆ resonances, especially the Roper Resonance P₁₁(1440), in the reaction π N → ππ N.

To describe pion-induced two-pion production on the proton, we start from a resonance exchange model similar to the model of Oset and Vicente-Vacas[1] with contributions from the excitation of the Δ isobar and the N^⋆ resonances P₁₁(1440), D₁₃(1520) and S₁₁(1535).

A calculation at Born level already leads to reasonable agreement with the available data. Only the angular distributions are not well reproduced – for π⁺p→ π⁺π⁺n and π⁻p→ π⁰π⁰ n they even have the opposite curvature. The simple tree-level model can be improved by the inclusion of initial and final state interaction. Such effects can be included for the pole contributions in a relatively simple way. The results we obtain with this improved model will be discussed.

[1] E. Oset and M.J. Vicente-Vacas, Nucl. Phys. A446, 584 (2000).