Nucleon excitation in low energy πN→γγN

The process π+N→2γ+N is investigated at low (50 MeV pion kinetic energy) energies, motivated by (nuclear) experiments in progress. Particular attention is given to contributions of the Δ excitation of the nucleon, which is also included in a computer calculation of the lowest order perturbation theory amplitudes. The Δ amplitudes enhance the calculated rate by 10--25 % typically, a result which is slightly smaller than the Δ contribution to the corresponding single photon process at the same energy