A STUDY OF PI-NUCLEON S-WAVE RESONANCES AND THE ETA-NUCLEON INTERACTION

We study the nature of the S-wave resonances N(1535) and N(1650) concerning their couplings with the eta-N channel. These resonances are usually interpreted as spatially excited states of constituent quarks with the intrinsic spin 1/2 and 3/2 .In this paper, we introduce an N*-isobar model for the pi-T N and eta-N interactions so as to study the properties of the resonances by using the above two quark-model wave functions with pure intrinsic spin states for the isobars. The dynamical coupling of the isobars to pi-N and eta-N channels are described by the meson-quark coupling. We find that the cooperative effect of the couplings with mesons and the tensor interaction among quarks is important for the mixing of the intrinsic spins. The physical states of the resonances are strongy mixed states of the isobars. This mixture enhances (suppresses) the coupling strength of the N(1535) (N(1650)) to eta-N and reproduces the energy dependence of the pi--p --> eta-n reaction cross section including the peak region.