Precision Small Scattering Angle Measurements of Elastic Proton-Proton Single and Double Spin Analyzing Powers at the RHIC Hydrogen Jet Polarimeter

The Polarized Atomic Hydrogen Gas Jet Target polarimeter is employed by the Relativistic Heavy Ion Collider (RHIC) to measure the absolute polarization of each colliding proton beam. Polarimeter detectors and data acquisition were upgraded in 2015 to increase solid angle, energy range, and energy resolution. These upgrades and advanced systematic error analysis along with improved beam intensity and polarization in RHIC runs 2015 (E_beam=100 GeV ) and 2017 (255 GeV) allowed us to greatly reduce the statistical and systematic uncertainties for elastic spin asymmetries, A_N(t ) and A_NN(t ), in the Coulomb-nuclear interference momentum transfer range 0.0013 <-t <0.018 GeV² . For the first time hadronic single spin-flip r₅ and double spin-flip r₂ amplitude parameters were reliably isolated at these energies and momentum transfers. Measurements at two beam energies enable a separation of Pomeron and Regge pole contributions to r₅(s ) and r₂(s ), indicating that the spin component may persist at high energies.