An absolute polarimeter for high energy protons

A study of the spin asymmetries for polarized elastic proton-proton collisions in the electromagnetic hadronic interference [Coulomb nuclear interference (CNI)] region of momentum transfer provides a method of self-calibration of proton polarization. The method can be extended to non-identical spin half scattering so that, in principle, the polarization of a proton may be obtained through an analysis of its elastic collision with a different polarized particle, ${}^{3}\mathrm{He},$ for instance. Sufficiently large CNI spin asymmetries provide enough information to facilitate the evaluation of nearly all the helicity amplitudes at small t as well as the polarization of both initial spin half fermions. Thus it can serve equally well as a polarimeter for ${}^{3}\mathrm{He}.$