Measurement of proton--proton elastic scattering in pure initial spin states

Using the Argonne ZGS polarized proton beam and a polarized proton target, we have measured the elastic p-p differential cross sections sigma(uu), sigma(ud) = sigma(du) and sigma(dd) in pure initial spin states, with spins perpendicular to the scattering plane. The measurements were made at p/sub lab/ = 6 GeV/c over the four-momentum transfer squared range absolute value t = 0.53 → 2.83 (GeV/c)2. The cross sections were found to have different t-dependences and were unequal by up to a factor of two. The three independent cross sections can be expressed in terms of the spin-averaged cross section [sigma], the asymmetry parameter A and the spin correlation parameter C/sub nn/. C/sub nn/ was found to be positive over the t-range covered by the experiment and comparable to A in magnitude within the diffraction peak