High-precision measurement of the analyzing power in large-Pperpendicular2 spin-polarized 24-GeV/c proton-proton elastic scattering

We measured the analyzing power A out to Pperpendicular2=7.1 (GeV/c)2 with high precision by scattering a 24-GeV/c unpolarized proton beam from the new University of Michigan polarized proton target; the target's 1-W cooling power allowed a beam intensity of more than 2x1011 protons per pulse. This high beam intensity together with the unexpectedly high average target polarization of about 85% allowed unusually accurate measurements of A at large Pperpendicular2. These precise data confirmed that the one-spin parameter A is nonzero and indeed quite large at high Pperpendicular2; most theoretical models predict that A should go to zero