Herbert R. Petry

The Light baryon spectrum in a relativistic quark model with instanton induced quark forces: The Nonstrange baryon spectrum and ground states

Abstract:This is the second of a series of three papers treating light-baryon resonances up to 3 GeV within a relativistically covariant quark model based on the three-fermion Bethe-Salpeter equation with instantaneous two- and three-body forces. In this paper we apply the covariant Salpeter framework (which we developed in the first paper, U. Löring, K. Kretzschmar, B.Ch. Metsch, H.R. Petry, Eur. Phys. J. A 10, 309 (2001)) to specific quark model calculations. Quark confinement is realized by a linearly rising three-body string potential with appropriate spinorial structures in Dirac space. To describe the hyperfine structure of the baryon spectrum we adopt t Hoofts residual interaction based on QCD-instanton effects and demonstrate that the alternative one-gluon exchange is disfavored on phenomenological grounds. Our fully relativistic framework allows to investigate the effects of the full Dirac structures of residual and confinement forces on the structure of the mass spectrum. In the present paper we present a detailed analysis of the complete non-strange-baryon spectrum and show that several prominent features of the nucleon spectrum such as, e.g., the Roper resonance and approximate “parity doublets” can be uniformly explained due to a specific interplay of relativistic effects, the confinement potential and t Hoofts force. The results for the spectrum of strange baryons will be discussed in a subsequent paper, see U. Löring, B.Ch. Metsch, H.R. Petry, this issue, p. 447.

The Light baryon spectrum in a relativistic quark model with instanton induced quark forces: The Strange baryon spectrum

Abstract:This is the third of a series of papers treating light-baryon resonances up to 3 GeV within a relativistically covariant quark model based on the Bethe-Salpeter equation with instantaneous two- and three-body forces. In this last paper we extend our previous work (U. Löring, B.Ch. Metsch, H.R. Petry, this issue, p. 395) on non-strange baryons to a prediction of the complete strange-baryon spectrum and a detailed comparison with experiment. We apply the covariant Salpeter framework, which we developed in the first paper (U. Löring, K. Kretzschmar, B.Ch. Metsch, H.R. Petry, Eur. Phys. J. A 10, 309 (2001)), to the specific quark models introduced in our work published in this issue. Quark confinement is realized by linearly rising three-body string potentials with appropriate Dirac structures; to describe the hyperfine structure of the baryon spectrum we adopt t Hoofts two-quark residual interaction based on QCD instanton effects. The investigation of instanton-induced effects in the baryon mass spectrum plays a central role in this work. We demonstrate that several prominent features of the excited strange mass spectrum, e.g. the low positions of the strange partners of the Roper resonance or the appearance of approximate “parity doublets” in the Λ spectrum, find a natural, uniform explanation in our relativistic quark model with instanton-induced forces.

A relativistic quark model for mesons with an instanton-induced interaction

Abstract:We present new results of a relativistic quark model based on the Bethe-Salpeter equation in its instantaneous approximation. Assuming a linearly rising confinement potential with an appropriate spinorial structure in Dirac space and adopting a residual interaction based on instanton effects, we can compute masses of the light mesons up to highest observed angular momenta with a natural solution of the UA(1) problem. The calculated ground states masses and the radial excitations describe the experimental results well. In this paper, we will also discuss our results concerning numerous meson decay properties. For processes like π+/K+↦e+υeγ and 0-↦γγ at various photon virtualities, we find a good agreement with experimental data. We will also comment on the form factors of the K?3 decay and on the decay constants of the π, K and η mesons. For the sake of completeness, we will furthermore present the electromagnetic form factors of the charged π and K mesons as well as a comparison of the radiative meson decay widths with the most recent experimental data.

Helicity amplitudes and electromagnetic decays of hyperon resonances

Abstract.We present results for the helicity amplitudes of the lowest-lying hyperon resonances Y*, computed within the framework of the Bonn Constituent-Quark model, which is based on the Bethe-Salpeter approach. The seven parameters entering the model were fitted to the best-known baryon masses. Accordingly, the results for the helicity amplitudes are genuine predictions. Some hyperon resonances are seen to couple more strongly to a virtual photon with finite Q2 than to a real photon. Other Y*s, such as the S01(1670) Λ-resonance or the S11(1620) Σ-resonance, couple very strongly to real photons. We present a qualitative argument for predicting the behaviour of the helicity asymmetries of baryon resonances at high Q2.-1

Electric and magnetic form factors of strange baryons

Abstract.Predictions for the electromagnetic form factors of the

The nucleus as a multiquark system

Lambda

Helicity amplitudes of nonstrange baryons in the third and fourth resonance region

,

HELICITY AMPLITUDES AND ELECTROMAGNETIC DECAYS OF STRANGE BARYON RESONANCES

Sigma

Electromagnetic properties of strange baryons in a relativistic quark model

and

Instanton effects in meson spectroscopy

Xi