High-Energy Polarimetry at RHIC

Abstract

We compare a few types of high energy reactions which seem to be practical for polarimetry at RHIC. Coulomb-nuclear interference (CNI) in pp elastic scattering leads to a nearly energy-independent left-right asymmetry A_N(t) at small t. The systematical uncertainty of this method is evaluated to be ~ 10%. The CNI in proton-nucleus elastic scattering is predicted to result in larger values of A_N(t) and occurs at larger momentum transfer than in pp elastic scattering. This energy independent asymmetry can be used for the polarimetry. As an absolute polarimeter one can use elastic pp scattering on a fixed target at large |t| ~ 1 - 1.5 GeV^2, where A_N(t) is reasonably large and nearly energy independent. Although it cannot be reliably calculated, one can calibrate the polarimeter by measuring the polarisation of the recoil protons.