MEASUREMENT OF PROTON PROTON ELASTIC SCATTERING IN PURE INITIAL SPIN STATES AT 11.75 GeV/c*

The elastic differential cross section for proton proton scattering at 11.75 GeV/c was measured for the tt, ~, and t~ initial spin states perpendicular to the scattering plane in the range of p~ = 0.6 * 2.2 (GeV/c) ~. The experiment was performed at the Argonne ZGS using a 50~0polarized beam and a 65~ polarized target. We confirmed that the asymmetry parameter, A, decreases with energy in the diffraction peak, but is approximately energy independent at large p~. We found that the spin correlation • 1 . parameter Cnn acquires rather dramatic structure, and at large p± seems to grow with energy. During the past few years the ZGS polarized beam has allowed new and precise measurements of the spin dependence in proton proton elastic scattering, l,~, %4 Recently the polarized beam operated at 11.75 GeV/c allowing the first measurements of pure spin elastic cross sections above 6 GeV/c. We present the results obtained during a one month run in February 1976. The physicists involved in the experiments are: K. Abe, R.C. Fernow, T.A. Mulera, K.M. Terwilliger from the University of Michigan, W. DeBoer from Max Planck Institute Fur Physik, A.D. Krisch*from Niels Bohr Institute, H.E. Miettinen from CERN, J.R. O'Fallon from St. Louis University, and L.G. Ratner from Argonne. The polarized beam was accelerated to 11.75 GeV/c with the internal intensity as high as 7 × 109 per 4.0 sec pulse. The extracted beam intensity was as high as 4 × 109 and averaged about 2.5 × lO @ per pulse. The average polarization for the entire one month run was about PB ~ 47%. We used the Michigan-Argonne PPT V polarized proton target s, which is maintained at O.5°K in a magnetic field of 25 KG and contains beads of propanediol, CsHsO~, doped with K~Cr~OTin a flask ~.13 cm long by 2.9 cm in diameter. The free protons in the propanediol are pumped into a polarized state by the 70 GHz microwaves from a carcinotron tube, using the highly polarized Cr electrons. The proton polarization is measured using a 107 MHz NMR system with signal averaging, which is calibrated against the known thermal equilibrium polarization with a ± 3% precision. The target polarization has been as high as PT = 85%, but the high *Work supported by the U.S. Energy Research and Development Agency + On lea~e from the University of Michigan