The reaction 2 H (γ,π0)np in the threshold region Original Research Article

Neutral pion photoproduction on the deuteron in the inelastic channel is studied in the threshold region from 142 to 160 MeV. The calculation is based on the use of the diagrammatic approach. Contributions from the pole diagrams, one-loop diagrams both with n – p and π – N rescattering as well as two-loop diagrams with simultaneous inclusion of these rescattering mechanisms are taken into account. We have found a reasonable agreement with a very simple calculation by J.C. Bergstrom et al. [Phys. Rev. C 57 (1998) 3203]. It is shown that the `effectiveʹ electric dipole deuteron amplitude View the MathML source is negative in agreement with a prediction of ChPT. We conclude that a deviation of about 20% from a ChPT prediction for View the MathML source discovered in an experiment on coherent π0 photoproduction off the deuteron cannot be attributed to inadequate estimates of inelastic channel contributions. We suggest that π – N rescattering is responsible for the deviation of the free-nucleon View the MathML source threshold amplitude from the value measured in that experiment.