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HK: Hadronen und Kerne

HK 17: Struktur von Baryonen und Mesonen II

HK 17.3: Gruppenbericht

Montag, 24. März 1997, 18:00–18:30, HS I

Nucleon Formfactors in a covariant Diquark-Quark Model^⋆ — •G. Hellstern, U. Zückert, R. Bäurle, R. Alkofer, and H. Reinhardt — Institut für Theoretische Physik, Auf der Morgenstelle 14, 72076 Tübingen

The nucleon formfactors are calculated in a covariant diquark-quark model. In this approach baryons emerge as relativistic bound states of a 0⁺ diquark and a valence quark interacting through quark exchange.

After solving the corresponding Bethe-Salpeter equation in ladder approximation we couple various external currents to the baryon. In Mandelstam’s formalism we obtain the coupling of the external currents to all constituents of the baryon which are assumed to be confined. Quark and diquark vertex functions are constructed from Ward identities, and therefore gauge invariance and chiral symmetry is respected. The resulting baryonic matrix elements of electromagnetic, axial and pionic currents between nucleon Bethe-Salpeter amplitudes are evaluated in a generalised impulse approximation. Due to the fully relativistic treatment of the bound state it is possible to consider not only spacelike but also timelike formfactors.

Numerical results for the electromagnetic formfactors, the pion-nucleon formfactor as well as the axial formfactor of the nucleon will be presented and discussed.

[*] Supported in part by COSY under contract 41315266.