High-precision measurement of the analyzing power in large-<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msubsup><mml:mrow><mml:mi mathvariant="italic">P</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">⊥</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msubsup></mml:mrow></mml:math>spin-polarized 24-GeV/<i>c</i>proton-proton elastic scattering

We measured the analyzing power A out to ${\mathit{P}}_{\mathrm{\ensuremath{\perp}}}^{2}$=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 2\ifmmode\times\else\texttimes\fi{}${10}^{11}$ 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 ${\mathit{P}}_{\mathrm{\ensuremath{\perp}}}^{2}$. These precise data confirmed that the one-spin parameter A is nonzero and indeed quite large at high ${\mathit{P}}_{\mathrm{\ensuremath{\perp}}}^{2}$; most theoretical models predict that A should go to zero.