Low-energy π NN system

The reaction NN → NNπ is studied at low energies within chiral perturbation theory (ChPT). Special emphasis is put on p-wave pion production in di erent channels of NN → NNπ and Charge Symmetry Breaking (CSB) e ects in pn → dπ0 recently measured at TRIUMF. A very good agreement of the p-wave amplitudes with experimental observables demonstrates the applicability of ChPT to these reactions regardless the large momentum transfer. The results of a complete calculation of CSB e ects at leading order are presented. Based on this calculation we extract the strong contribution to the neutron-proton mass di erence.