GEpGMpratio by polarization transfer in e^→p →ep^→

The ratio of the proton's elastic electromagnetic form factors, GEpGMp, was obtained by measuring Ptand pl, the transverse and the longitudinal recoil proton polarization, respectively. For elastic e→p →ep→, GEpGMpis proportional to pt/pl Simultaneous measurement of pt/plin a polarimeter provides good control of the systematic uncertainty. The results for the ratio GEpGMpshow a systematic decrease as Q2increases from 0.5 to 3.5GeV2, indicating for the first time a definite difference in the spatial distribution of charge and magnetization currents in the proton. © 2000 The American Physical Society.