Measurements of single and double spin asymmetry in pp elastic scattering in the CNI region with a polarized atomic hydrogen gas jet target

Precise measurements of the single spin asymmetry A_N, and the double spin asymmetry A_NN, in proton-proton (pp) elastic scattering in the region of four-momentum transfer squared 0.001<-t<0.032(GeV/c)² have been performed using a polarized atomic hydrogen gas jet target and the Relativistic Heavy Ion Collider (RHIC) polarized proton beam. We present measurements of A_N and A_NN at center-of-mass energies s=6.8 and 13.7 GeV. These spin-dependent observables are sensitive to the poorly known hadronic spin-dependent amplitudes. Comparing A_N at different energies, a s dependence of the hadronic single spin-flip amplitude is suggested. A hadronic double spin-flip amplitude from the A_NN data is consistent with zero within a 2-σ level. We also present Δσ_T, estimated from the measured A_NN data. The results for Δσ_T are consistent with zero. Our results provide significant constraints toward a comprehensive understanding of the reaction mechanism for pp elastic scattering.