Absolute measurement of thep+panalyzing power at 183 MeV

The analyzing power Ay for p+p elastic scattering at θlab=8.64^∘{}±{}0.07^∘{} (θcms=18.1^∘{}) and at a bombarding energy of 183.1±{}0.4 MeV has been determined to be Ay=0.2122±{}0.0017. The error includes statistics, systematic uncertainties, and the uncertainty in bombarding energy and angle. This measurement represents a calibration standard for polarized beams in this energy range. The absolute scale for the measurement has been obtained by comparison with p+C elastic scattering at the same energy at an angle where Ay is very nearly unity.