A Measurement of Analyzing Power in 28 Gev/C Proton-Proton Elastic Scattering.

The spin-dependence of proton-proton elastic scattering was studied at 28 GeV/c at the Brookhaven Alternating Gradient Synchrotron (AGS). The AGS unpolarized primary proton beam was scattered from a polarized proton target, and the analyzing power, A, was measured in the P(,(PERP))('2) range of 0.5 to 2.8 (GeV/c)('2). Both final-state protons were detected in coincidence and the asymmetry in the counting rates was measured for the target protons polarized up ((UPARR)) and down ((DARR)). The data show a very interesting structure: the analyzing power has a value of +2.5% near P(,(PERP))('2) = 0.70 (GeV/c)('2) and then sharply dips to about -3% at P(,(PERP))('2) = .8 (GeV/c)('2), which is the position of the break in the elastic differential cross-section at the tail of the diffraction peak. It then steadily rises to 5-6% at 2(GeV/c)('2) and seems to level off up to 2.8(GeV/c)('2).