Photoproduction of Neutral Pions at Energies 500 to 940 Mev

Abstract

The process gamma + p yields pi /sup 0/ + p was studied by detecting recoil protons from a liquid hydrogen target which was bombarded by the bremsstrahlung beam of the California Institute of Technology electron synchrotron. The angle and momentum of the recoil protons were measured by a magnetic spectrometer-three scintillation counter coincidence system. The process was studied between photon laboratory energies of 490 and 940 Mev and between pion center-of-mass angles of 31.5 and 147 deg . Protons which arose from meson pair production were significant at forward laboratory angles. A correction for this contamination is discussed. The results of these measurements show two interesting features. One is that the total cross section, which falls very rapidly above the 3/2 - 3/2 resonance energy near 320 Mev, reaches a minimum at about 600 Mev. and then increases to a broad maximum near 800 or 900 Mev. The other striking feature of the data is that the shape of the angular distribution seems to change rather suddenly near 900 Mev. (auth)