Measurement of the Proton Form Factor by Studying e⁺e⁻ → pp̅

Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of e⁺e⁻ → pp̅ at 12 center-of-mass energies from 2232.4 to 3671.0 MeV. The corresponding effective electromagnetic form factor of the proton is deduced under the assumption that the electric and magnetic form factors are equal |G(E)| = |G(M)|. In addition, the ratio of electric to magnetic form factors, |G(E)/G(M)|, and |G(M)| are extracted by fitting the polar angle distribution of the proton for the data samples with larger statistics, namely at √s̅ = 2232.4 and 2400.0 MeV and a combined sample at √s̅ = 3050.0, 3060.0 and 3080.0 MeV, respectively. The measured cross sections are in agreement with recent results from BABAR, improving the overall uncertainty by about 30%. |G(E)/G(M)| ratios are close to unity and consistent with BABAR results in the same q^2 region, which indicates the data are consistent with the assumption that |G(E)| = |G(M)| within uncertainties.