Isospin breaking in the reaction np --> dpi^0 at threshold
  The model for charge symmetry breaking in the reaction np --> dpi^0 applied earlier around the Delta region is used to calculate the integrated forward-backward asymmetry of the cross section close to threshold. The mixing of the pi and eta mesons appears as strongly dominant at these energies. This contrasts elastic np scattering experiments, where the np mass difference in OPE dominates, or np --> d\pi^0 closer to the Delta region. 
J. A. Niskanen