Measurement of recoil proton polarization in neutral pion phtoproduction at 60 and 90 degrees, using a wire chamber system

Abstract

We measured the recoil proton polarization in the reaction γp --> π°p at the Caltech electron synchrotron at pion CM production angles around 60° and 90°, and photon energies from 0.65 to 1.375 GeV. Recoil protons were momentum-analyzed by a bending magnet along with a counter-wire spark chamber system. The polarization was determined by measuring the left-right asymmetry of p-C scatterings in a carbon plate range chamber. The data acquisition 'Was handled by an on-line PDP-5 computer. Among the 600,000 events taken, approximately 18,000 p-C scattered events survived the kinematics tests and requirements of analyzing power to yield 23 polarization points. The results indicate a strong angular dependence throughout the angular and energy regions covered. They agree very well with earlier results, but with improved statistics and with finer energy binning in the region of overlap. π° photoproduction cross sections in the same kinematical region were also measured in the process. The agreement with known values is excellent. These results are interpreted in the framework of an isobar and partial wave model of π° photoproduction.