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HK: Hadronen und Kerne

HK 15: Hadronic Probes II, Nucleon-Nucleon Interaction

HK 15.2: Group Report

Monday, March 16, 1998, 17:30–18:00, C

Peripheral Nucleon-Nucleon Phase Shifts and Chiral Symmetry — •Norbert Kaiser², Rolf Brockmann¹, Stefan Gerstendörfer², and Wolfram Weise² — ¹Universität Mainz, Institut für Kernphysik — ²Technische Universität München, Physik Department T39

Within the one loop approximation of baryon chiral perturbation theory we calculate all 1π- and 2π-exchange contributions to the NN-interaction. The phase shifts with orbital angular momentum L≥ 2 and mixing angles with J≥2 are given parameterfree and allow for a test of chiral pion dynamics in the two-nucleon system. In particular we evaluate in closed form the triangle and (planar and crossed) box graphs with single and double Δ(1232)-isobar excitation including the relativistic 1/M-corrections. We find that the Δ-excitation processes alone (when evaluated without any ad hoc ”form factors”) produce enough isoscalar central attraction and reduce the 1π-exchange isovector tensor force by the right amount. Correlated 2π-exchange (two-loop graphs involving the chiral ππ-interaction) give rise to small repulsive corrections. Neither a low mass scalar σ-meson nor a large ρ-meson tensor coupling are needed. Chiral 1π- and 2π-exchange successfully predicts the peripheral NN phase shifts with L≥ 3 in a completely parameterfree fashion. The S-, P- and D-wave phase shifts are sensitive to the (phenomenological) short range NN-interaction. We propose to use the chiral NN phase shifts with L≥3 as input in a future phase shift analysis of the upcoming COSY-data.