Author: J. V. Allaby

Publisher:

Published: 1965

Total Pages: 17

ISBN-13:

Measurements of the differential cross-section for the reaction gamma + p to pion ( - ) + pion (+) + p have been made at several angles for photon energies in the range 550-1000 MeV, using the Stanford Mark III linear accelerator. The pion( - ) were detected and momentum analyzed using a 90 degree magnetic spectrometer. It was found that the reaction was dominated by the pseudo-2-body photoproduction gamma + p to pion ( - ) + N* (1238) especially near the threshold for this process. At low momenta, the pion( - ) were identified by range. At high momenta (>250 MeV/c), the contaminating electrons were eliminated by using a lead and scintillation-counter sandwich system. The yields of both pion ( - ) and pion (+) off hydrogen were measured and the normalization was obtained by comparing with the known cross-sections for gamma + p to pion (+) + n. Computer calculations of the shapes of the yield curves expected from 2-body and 3-body production enabled the data to be separated into the two possible states gamma + p to pion ( - ) + N* (1238) and gamma + p to pion ( - ) + pion (+) + p. Angular distributions and total cross-sections are presented. (Author).