Proton elastic form factor ratios to Q2=3.5GeV2 by polarization transfer

The ratio of the proton elastic electromagnetic form factors, GEp/GMp, was obtained by measuring Pt and P, the transverse and longitudinal recoil proton polarization components, respectively, for the elastic e→p→ep→ reaction in the four-momentum transfer squared range of 0.5 to 3.5GeV2. In the single-photon exchange approximation, GEp/GMp is directly proportional to Pt/P. The simultaneous measurement of Pt and P in a polarimeter reduces systematic uncertainties. The results for GEp/GMp show a systematic decrease with increasing Q2, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. The data have been reanalyzed and their systematic uncertainties have become significantly smaller than those reported previously. © 2005 The American Physical Society.