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HK: Hadronen und Kerne

HK 37: Hadronic Probes IV, Interaction of Pions

HK 37.3: Gruppenbericht

Dienstag, 17. März 1998, 18:00–18:30, C

The reaction π N→ π π N at Low Energies in Chiral Perturbation Theory — •Norbert Kaiser², Véronique Bernard¹, and Ulf-G. Meißner³ — ¹Univ. Louis Pasteur, Strasbourg, France — ²Technische Universität München, Physik Department T39 — ³FZ Jülich, IKP (Th)

We investigate the reaction π N → ππ N for pion kinetic energies below 400 MeV within the framework of chiral perturbation theory. We derive new chiral low energy theorems for the two threshold amplitudes D_1,2. Corrections from pion loops turn out to be small for the threshold amplitudes. We establish a relation between the ππ N threshold amplitudes and the ππ S-wave scattering lengths consistent with chiral symmetry. Above threshold we perform a tree level calculation including the terms from the second order chiral Lagrangian with five low energy constants fixed from elastic π N scattering. Despite the simplicity of the approach most of the existing data for total and differential cross section as well as angular correlation functions are well reproduced. In particular our chiral prediction agrees with the new TRIUMF data for π⁻ p → π⁻ π⁺ n close to threshold.

[1] V. Bernard, N. Kaiser and Ulf-G. Meißner, Phys. Lett. B332 (1994) 415; Nucl. Phys. B457 (1995) 147; Nucl. Phys. A619 (1997) 261.