Acceleration of polarized protons to 22 GeV/cand the measurement of spin-spin effects inp↑+p↑→p+p

Accelerating polarized protons to 22 GeV/c at the Brookhaven Alternating Gradient Synchro- tron required both extensive hardware modifications and a difficult commissioning process. We had to overcome 45 strong depolarizing resonances to maintain polarization up to 22 GeV/c in this strong-focusing synchrotron. At 18.5 GeV/c we measured the analyzing power A and the spin-spin correlation parameter $A_{\mathrm{nn}}$ in large- $P_{\perp }^2$ proton-proton elastic scattering, using the polarized proton beam and a polarized proton target. We also obtained a high-precision measurement of A at $P_{\perp }^2$=0.3 (GeV/c${)}^2$ at 13.3 GeV/c. At 18.5 GeV/c we found that $A_{\mathrm{nn}}$=(-2±16)% at $P_{\perp }^2$=4.7 (GeV/c${)}^2$, where it was about 60% near 12 GeV at the Argonne Zero Gradient Synchrotron. This sharp change suggests that spin-spin forces may have a strong and unexpected energy dependence at high $P_{\perp }^2$.