Elastic Scattering of Polarized Electrons by Polarized Protons

We report on a new type of high-energy electron-proton scattering experiment in which longitudinally polarized electrons are scattered from longitudinally polarized protons. The asymmetry in elastic scattering at $Q^2=0.765\mathrm{}$ ${(\mathrm{G}\mathrm{e}\mathrm{V}/\mathit{c})}^2$ was measured; our result agrees with the theoretical asymmetry and determines the sign of $\frac{G_E}{G_M}$ to be positive.