POLARIZATION MEASUREMENTS ON THE RECOIL PROTON FROM PION (O) PHOTOPRODUCTION

Abstract : The polarization of the recoil proton in pion(o) photoproduction off hydrogen has been measured for photons in the range 500-1000 MeV, using the Stanford Mark III linear accelerator. Protons were detected at an angle b and momentum analyzed using a 90 degree magnetic spectrometer. The scattered protons were detected by two counter telescopes placed symmetrically to left and right of the carbon target and making angles = C with respect to the direction of a proton emerging from the spectrometer. The measured asymmetry was obtained from the usual formula: e = L-R/L+R and the proton polarization P(b) was then obtained by substituting the known carbon analyzing power A(c) in the equation e(b,c) = (P(b) A(c). Using parity conservation it can be shown that P(b) = -P(b). Thus the running time was equally divided between measurements with the spectrometer at +b and -b. This technique enabled residual artificial asymmetries to be removed, since these do not change sign when b becomes -b. Preliminary results are presented and compared to existing data from various laboratories. (Author)