Helicity dependence of the γ→p→→nπ+π0 reaction in the second resonance region

Abstract The helicity dependence of the total cross section for the γ → p → → n π + π 0 reaction has been measured for the first time at incident photon energies from 400 to 800 MeV. The measurement was performed with the large acceptance detector DAPHNE at the tagged photon beam facility of the MAMI accelerator in Mainz. This channel is found to be excited predominantly when the photon and proton have a parallel spin orientation, due to the intermediate production of the D 13 resonance.