Measurements of the electromagnetic form factor of the Proton at JLab

Punjabi, Vina; Perdrisat, Charles; Collaboration, Jefferson Lab Hall A; Collaboration, GEp-III

Measurements of the electromagnetic form factor of the Proton at JLab

Authors

Punjabi, Vina

Perdrisat, Charles

Collaboration, Jefferson Lab Hall A

Collaboration, GEp-III

Description

The ratio of the proton's elastic electromagnetic form factors $G_{Ep}/G_{Mp}$ was obtained by measuring $P_{t}$ and $P_{\ell}$, the transverse and longitudinal recoil proton polarization, respectively. For the elastic reaction $\vec e p \to e\vec p$, $G_{Ep}/G_{Mp}$ is proportional to $P_t/P_{\ell}$. The simultaneous measurement of $P_{t}$ and $P_{\ell}$ in a polarimeter reduces systematic uncertainties. The results for the ratio $G_{Ep}/G_{Mp}$ measured in Hall A so far show a systematic decrease with increasing $Q^2$, indicating for the first time a definite difference in the distribution of charge and magnetization in the proton. Together these experiments cover the Q$^{2}$- range of 0.5 to 5.6 GeV$^{2}$. A new experiment is currently being prepared, to extend the Q$^2$-range to 9 GeV$^2$ in Hall C.
10 pages, 6 figures, presented at Xth International Seminar on Electromagnetic Interactions of Nuclei at Low and Medium Energies, INP, RAS, Moscow, 16-18 April, 2003, will appear in the proceedings