Measurement of the cross section for γd → π0d in a backward region

A primitive motivation of the present work is to look for an experimental evidence of the dibaryon resonances of isospin one, because an effect of the dibaryon resonances is expected to appear in the behavior of differential cross sections for the reaction γd → π0d at large angles. The report present differential cross sections for the reaction γd → π0d in the kinematical region Eγ = 500 to 1000 MeV and θc.m. = 90 deg to 156 deg. The experimental data are compared with cross sections calculated by a constituent model. Diagrams are shown which can interprete the dynamical properties of the above reaction in the photon energy region Eγ = 500 to 750 MeV. The elementary processes occuring on the nucleon inside the deuteron are well approximated by phenomenological amplitudes obtained on-shell; the Metcalf-Walker amplitudes for γN → πN and the phase-shift amplitudes for πN → πN. To describe the deuteron state, a deuteron wave function based on the Paris potential may be used. Then the observed data are well reproduced within the experimental accuracy. Consequently it is argued that cross section at large angles are described almost entirely by the double-scattering term. Within the experimental accuracy there are no positive indication for the possible existence of the dibaryon resonances of a mass around 2.5 GeV. In the energy region Eγ = 750 to 1000 MeV, any significant structure is found in the observed results. This implies that the reaction γd → π0d occurs through a mechanism similar to that an Eγ greater than 750 MeV. (Nogami, K.)