The analyzing power $A$ in 28-GeV/c proton-proton elastic scattering was measured with a polarized proton target and a high-intensity unpolarized proton beam at the Brook-haven National Laboratory alternating-gradient synchrotron. The ${P_{\perp }}^2$ range of 2.85 to 5.95 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ was covered with good precision. A small dip of about -3.5% was found near ${P_{\perp }}^2=3.5\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ where a 24-GeV/c CERN experiment had reported a deep dip of about -16% with large errors. In the previously unexplored large-${P_{\perp }}^2$ region near 6 ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ these new large-error points suggest that $A$ may be rising.

• Received 26 August 1983

DOI:https://doi.org/10.1103/PhysRevLett.51.2359