Abstract
The reaction NN → NNπ is studied at low energies within chiral perturbation theory (ChPT). Special emphasis is put on p-wave pion production in different channels of NN → NNπ and Charge Symmetry Breaking (CSB) effects in pn → dπ 0 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 effects at leading order are presented. Based on this calculation we extract the strong contribution to the neutron-proton mass difference.
Highlights
Chiral perturbation theory (ChPT) is a modern framework to systematically investigate low-energy hadronic reactions [1,2]
It was demonstrated that the experimental observables in all these channels can be simultaneously described by adjusting only one low-energy constant contributing at N2LO
It is found that the net contribution of the diagrams at N2LO is of the size predicted by the power counting
Summary
Chiral perturbation theory (ChPT) is a modern framework to systematically investigate low-energy hadronic reactions [1,2]. ChPT is based on the most general effective Lagrangian consistent with the symmetries of QCD. In this approach the pion is associated with the lightest Goldstone boson of the spontaneously broken approximate chiral SU(2) symmetry of QCD. The approach was extended by Weinberg [6] to the low-momentum transfer pion reactions on few nucleon systems. He proposed the so-called hybrid approach which consists of two steps: 1. At any given order they should consist of all possible irreducible graphs
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