Measurement of the Proton's Electric to Magnetic Form Factor Ratio from {sup 1}H-vector(e-vector,e{sup '}p)

We report the first precision measurement of the proton electric to magnetic form factor ratio from spin-dependent elastic scattering of longitudinally polarized electrons from a polarized hydrogen internal gas target. The measurement was performed at the MIT-Bates South Hall Ring over a range of four-momentum transfer squared Q{sup 2} from 0.15 to 0.65 (GeV/c){sup 2}. Significantly improved results on the proton electric and magnetic form factors are obtained in combination with existing cross-section data on elastic electron-proton scattering in the same Q{sup 2} region.