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HK: Hadronen und Kerne
HK 25: Elektromagnetisch wechselwirkende Sonden III
HK 25.2: Gruppenbericht
Dienstag, 25. März 1997, 14:30–15:00, HS G
Pion photo-production and the off-shell behavior of the πN interaction. — •K. Nakayama1,2, Ch. Schütz1, S. Krewald1, J. Speth1,3, and W. Pfeil2 — 1Institut für Kernphysik, Forschungszentrum Jülich, Deutschland — 2Univesity of Georgia, Athens, USA — 3Institut für Physik, Universität Bonn, Deutschland
Pion photo-production for photon incident energies below 500 MeV is investigated within a dynamical model, where the transition amplitude is obtained by solving a coupled channel (πγ + π N) relativistic scattering equation. The basic πN scattering process is modeled within a meson-theoretic formulation, in which the correlated 2π process in the scalar-isoscalar and vector-isovector channels are treated explicitly [1]. The basic pion photo-production mechanisms are derived also within a meson-theoretic model, starting from a chiral-symmetry-motivated effective Lagrangian. The model contains also a phenomenological form factor at each hadronic vertex in order to account for the composite nature of the hadrons.
It is shown that the pion photo-production reaction is extremely sensitive to the hadronic form factors used, and that, in order to reproduce both the πN elastic scattering and photo-production data consistently within our model, one needs extremely soft form factors (corresponding to monopole form factors with a cutoff parameter of the order of Λ = 200−300 MeV). This problem is discussed.
[1] Ch. Schütz, et al., Phys. Rev. C49(1994)2671.