Recoil Polarization Measurements of the Proton Electromagnetic Form Factor Ratio toQ2=8.5GeV2

Among the most fundamental observables of nucleon structure, electromagnetic form factors are a crucial benchmark for modern calculations describing the strong interaction dynamics of the nucleon’s quark constituents; indeed, recent proton data have attracted intense theoretical interest. In this Letter, we report new measurements of the proton electromagnetic form factor ratio using the recoil polarization method, at momentum transfers $Q^2=5.2$, 6.7, and $8.5{\mathrm{GeV}}^2$. By extending the range of $Q^2$ for which $G_E^p$ is accurately determined by more than 50%, these measurements will provide significant constraints on models of nucleon structure in the nonperturbative regime.