Neutral and charged pion production in the S-matrix approach
  The S-matrix approach is applied to charged and neutral pion production in pp collisions, in which the spin/isospin channels filter differently the rescattering mechanism. The chiral perturbation theory rescattering amplitude is employed. The contributions from the single-nucleon, Z-diagrams and Delta-isobar mechanisms are also included. For the reactions investigated, the convergence of the partial wave series is quite satisfactory and J=0 is enough to describe the data close to threshold. 
V. Malafaia, M. T. Pena and J. Adam Jr