Isobar-width effects in the coupling of nucleon to isobar channels

The investigation of the effects of isobar coupling to two-nucleon channels has been extended to include additional physical features. A new code discretizes the mass distribution of the isobar widths and treats each mass as a separate channel. This allows the treatment of width in the presence of coupling by transition potentials, in addition to the previously permitted boundary coupling. It also produces the S-matrix components required to describe the many-body final-state distributions. When indicated by the one-pion-exchange coupling strength new isobar channels are included. The new results for nucleon-nucleon scattering fit the data better, starting from more realistic models. The observed 1D2 and 3F3 structures are well understood as coupled-channel effects, without exotic-quark contributions. The existence of a structure in the 3P0 channel depends on the amount of inelasticity, which differs among the phase shift solutions. The energy dependence seen in recent analyses, of the 3P2 phase shift near T/sub L/ = 800 MeV, is shown to be a consequence of the isobar channel coupling. Improved models obtained for the 1S0 and 3S1-3D1 channels are being developed. They are important to accurately extrapolate those phases to higher energies where six-quark effects are expected