Photoproduction ofπ0from Hydrogen near the Second and Third Pion-Nucleon Resonances

Measurements of the differential cross section for the process $\gamma +p\to {\pi }^0+p$ have been made at eight pion center-of-mass angles in the range 51-135° and for incident photon energies from approximately 600-1200 MeV. The bremsstrahlung photon beam used was obtained from the California Institute of Technology electron synchrotron. Both the recoil proton and one $\gamma$ ray from the decay of the ${\pi }^0$ were detected. The incident photon energy was determined by measuring the laboratory angle and time of flight of the recoil proton. The angular distributions obtained indicate that the third pion-nucleon resonance is predominantly a $D\left(\frac{5}{2}\right)$ resonance excited by a magnetic quadrupole transition. It can also be concluded that any contribution to the ${\pi }^0$ photoproduction cross section from a virtual vector-meson exchange process is probably negligible in the region of the second and third pion-nucleon resonances.