Unitary πNN model

An important feature of nuclear reactions at energies accessible to the new facilities at CEBAF and RHIC is pion production. It is important to determine the extent to which these reactions can be described in terms of color-singlet hadronic degrees of freedom. Without such a baseline, any attempt to explore QCD dynamics from such complex processes will be difficult. We are improving our earlier work on the πNN model with the π and Δ degrees of freedom to address this question. Our current focus is to improve the model by taking into account three recent developments: (1) the nonresonant pion production mechanisms were identified in the study of threshold pion production in proton-proton collisions, (2) the short-range NN and NΔ interactions can be calculated from the chiral quark model, and (3) the NN phase shifts analysis was improved and extended to 1.6 GeV. We obtained the first results showing that, by including the nonresonant pion production mechanisms of Lee and Riska, the long-standing problem concerning the NN inelasticities near threshold can be resolved. We are carrying out extensive numerical calculations to quantify the improved πNN model. The resulting model will be used to improve our many investigations of nuclear dynamics involving π and Δ degrees of freedom, as described in the following subsections