Münster 2002 – scientific programme

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HK: Physik der Hadronen und Kerne

HK 43: Theory VII

HK 43.2: Group Report

Thursday, March 14, 2002, 16:30–17:00, A

The baryon spectrum in a covariant quark model with instanton-induced forces — •Ulrich Löring, Dirk Merten, Bernard Metsch, Herbert-R. Petry, and Christian Haupt — Institut für Theoretische Kernphysik, Univerität Bonn, Nußallee 14-16, 53115 Bonn

On the basis of the Bethe-Salpeter equation in instantaneous approximation we formulated a relativistic quark model for baryons. Motivated by the success of the non-relativistic quark model, the full quark propagators are replaced by their free forms with constituent quark masses, and the interactions of the quarks are described by unretarded, static potentials. To generate the hyperfine structure of the baryon spectrum we adopt ’t Hooft’s force which is derived from QCD-instanton-effects. This relativistic model allows a very successful description of the complete baryon spectrum up to 3 GeV with spins up to J=15/2. In particular several prominent features such as the linear Regge-trajectories, the low position of the Roper resonance (and its strange counterparts) as well as the striking phenomenon of approximate parity doublets can be uniformly explained. In this respect the specific role of instanton-effects is discussed, and we demonstrate that the alternative one-gluon-exchange, however, is not able to reproduce the excited baryon spectrum correctly.