Spin dependence of high-p/sub perpendicular/2 elastic p-p scattering

We measured dsigma/dt for p/sub arrow-down/ + p/sub arrow-down/ → p + p from P/sub perpendicular/2 = 4.50 to 5.09 (GeV/c)2 at 11.75 GeV/c. We used a 59%-polarized proton beam and a 71%-polarized proton target with both spins oriented perpendicular to the scattering plane. In these large-p/sub perpendicular/2 hard-scattering events, spin effects are very large and the ratio (dsigma/dt)/sub arrow-uparrow-up/:(dsigma/dt)/sub arrow-uparrow-down/ grows rapidly with increasing P/sub perpendicular/2, reaching a value of 4 at 900 (c.m.). Thus, hard elastic scattering, which is presumably due to the direct scattering of the protons' constituents, may only occur when the two incident proton' spins are parallel