New Method for Determining Polarization Standards in Nuclear Reactions

We discuss and apply a general method for measuring the difference of polarization observables from their maximum allowed value. Relatively crude double-scattering experiments determine the proton polarization for 12-MeV $p-{}_{}{}^4{}_{}{}^{}\mathrm{He}$ scattering with an absolute uncertainty of 1 part in 1000. It is anticipated that these concepts can be applied to higher-energy reactions where experiments do not lend themselves easily to precision measurements and where basic symmetries appear more likely to break down.