Measurements of elastic electron-proton scattering at large momentum transfer.

Measurements of the forward-angle differential cross section for elastic electron-proton scattering were made in the range of momentum transfer from Q2 = 2.9 to 31.3 (GeV/c)2 using an electron beam at the Stanford Linear Accelerator Center. The data span six orders of magnitude in cross section. Combined statistical and systematic uncertainties in the cross section measurements ranged from 3.6% at low Q2 to 19% at high Q2. These data have been used to extract the proton magnetic form factor Gb(Q2) and Dirac form-factor F:(Q2) by using form factor scaling. The logarithmic falloff of Q4F'f expected from leading twist predictions of perturbative quantum chromodynamics (&CD) is consistent with the new data at high Q 2. Some nonperturbative and hybrid calculations also agree with our result 9. 2