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HK: Hadronen und Kerne

HK 11: Structure of Baryons, Mesons II

HK 11.3: Group Report

Monday, March 16, 1998, 14:30–15:00, J

A Relativistic Quark Model for Baryons — •Ulrich L"oring, Klaus Kretzschmar, Bernard Ch. Metsch, and Herbert-R. Petry — Institut für Theoretische Kernphysik, Nu"sallee 14 – 16, D–53115 Bonn

We present a relativistic model for baryons based on the instantaneous 3-quark Bethe-Salpeter equation (Salpeter equation). Conceptionally the approach is very similar to the relativistic treatment of mesons [1] but technically much more involved. Confinement is realized by a stringlike linearly rising 3-quark confinement potential with a suitable spin dependence. Mass splittings between octett and decuplett states are generated by an instanton induced quark-interaction. We show how to treat such 2-particle interactions within the instantaneous 3-quark-Salpeter equation. The field theoretical amplitudes are reduced to the Salpeter form, which still is formally covariant and contains the full Dirac structure with positive and negative energy components, and the resulting Salpeter equation is solved numerically. We computed sofar the mass spectrum for all baryons with light quark flavours (u,d,s) up to 2.5 GeV. The mass spectrum resulting from this calculation is remarkable: Usually in non-relativistic quark models the Roper resonance and its strange partners appear much to high in comparison with the experimentally determined resonance positions and are lowered only when additional interactions (commonly meson dressing effects) are taken into account. In our model this is no longer the case; once the model parameters are fixed to reproduce the correct octett and decuplett ground state masses, the spectrum of the lowest excitations of positive parity is already well described. In addition the Regge trajectorie up to spin J=13/2 fits the experimental data well, showing that our model, which fully respects relativistic covariance is realistic.

[1] Nucl. Phys. A 578 (1994) 418; Nucl. Phys. A 578 (1994) 397