GEp/GMpRatio by Polarization Transfer ine→p→ep→

The ratio of the proton's elastic electromagnetic form factors, $G_{E_p}{/G}_{M_p}$, was obtained by measuring $P_t$ and $P_{\ell }$, the transverse and the longitudinal recoil proton polarization, respectively. For elastic $\overrightarrow{e}p\to e\overrightarrow{p}$, $G_{E_p}{/G}_{M_p}$ is proportional to $P_t{/P}_{\ell }$. Simultaneous measurement of $P_t$ and $P_{\ell }$ in a polarimeter provides good control of the systematic uncertainty. The results for the ratio $G_{E_p}{/G}_{M_p}$ show a systematic decrease as $Q^2$ increases from 0.5 to $3.5{\mathrm{GeV}}^2$, indicating for the first time a definite difference in the spatial distribution of charge and magnetization currents in the proton.