Spin-Spin Interactions in High-p⊥2Elasticp−pScattering

We measured $\frac{d\sigma }{\mathrm{dt}}$ for $p+p\to p+p$ at 11.75 GeV/c using the zero-gradient synchrotron 70% polarized-proton beam and a 65% polarized-proton target. We obtained the spin-orbit asymmetry parameter $A$ and the spin-spin correlation parameter $C_m$ out to ${P_{\perp }}^2=4.2\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$. We found that $A$ drops smoothly towards zero, but that $C_{\mathrm{nn}}$ increases abruptly near ${P_{\perp }}^2=3.6\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$, where the $\exp (-1.4\mathrm{}{P_{\perp }}^2)$ component of elastic scattering becomes dominant. This suggests that large-${P_{\perp }}^2$ "hard" elastic scattering may occur mostly when the two proton spins are parallel.