Final state interactions in strong two-body baryon decays

Abstract

In the first part of this thesis, masses and strong decay widths of non-strange baryon resonances are described in the framework of a covariant quark model. The model is based on the solutions of the Bethe-Salpeter equation, considered in instantaneous approximation and with effective free-quark propagators. Here, the underlying quark interactions are parameterized by a confinement potential with an appropriate spin structure, supplemented by a residual spin- and flavor-dependent potential motivated by instanton effects. In such an approach the strong decays of baryon resonances can be described in a parameter-free calculation, by applying the Mandelstam formalism in lowest-order of perturbation theory.<br /> Whereas the resulting mass spectrum accounts for most of the features observed experimentally, the theoretical decay widths are generally to small when compared to the data. In this context, the aim of this work is to investigate corrections from final state rescattering to these lowest-order results for strong decays. For this purpose we limit the scope of our investigation to the decays of low-lying N and Δresonances into the πN, πΔ and ηN channels. Accordingly, in the second part of the thesis we implement a model for coupled-channel interactions involving these two-body states, and then employ the resulting amplitudes to dress the strong decay vertices from the quark model and re-evaluate the corresponding decay widths. <br /> It was found, that this method does not improve the quark-model results for strong baryon decays. After inclusion of final state interactions, the decay widths into πN and ηN are roughly the same while those into πΔ are even smaller than before. Such results indicate that the problem lies in the assumptions introduced in the quark model. Accordingly, we suggest a possible modification of the framework: We conjecture that by employing full quark propagators – also taken in instantaneous approximation – instead of the effective free-quark propagators utilized before, one would obtain different results for strong baryon decays as depicted in the present approach.