  The Relativistic Heavy Ion Collider at Brookhaven National Laboratory
provides polarized proton beams for the investigation of the nucleon spin
structure. For polarimetry, carbon-proton and proton-proton scattering is used
in the Coulomb nuclear interference region at small momentum transfer ($-t$).
Fast polarization measurements of each beam are carried out with carbon fiber
targets at several times during an accelerator store. A polarized hydrogen gas
jet target is needed for absolute normalization over multiple stores, while the
target polarization is constantly monitored in a Breit-Rabi polarimeter. In
2005, the jet polarimeter has been used with both RHIC beams. We present
results from the jet polarimeter including a detailed analysis of background
contributions to asymmetries and to the beam polarization.
