Energy Dependence of Spin Effects inp↑+p↑→p+p

Abstract

We measured the analyzing power A and the spin-spin correlation parameter A/sub n//sub n/, in large-P/sub perpendicular//sup 2/ proton-proton elastic scattering, using a polarized-proton target and the polarized-proton beam at the Brookhaven Alternating-Gradient Synchrotron. We also used our polarimeter to measure A at small P/sub perpendicular//sup 2/ at 13 GeV with good precision and found some deviation from the expected 1/P/sub lab/ behavior. At 18.5 GeV/c we found A/sub n//sub n/ = (-2 +- 16)% at P/sub perpendicular//sup 2/ = 4.7 (GeV/c)/sup 2/. Comparison with lower-energy data from the Argonne Zero-Gradient Synchrotron shows a sharp and surprising energy dependence for A/sub n//sub n/ at large P/sub perpendicular//sup 2/.