Measurement of the proton form factor by studying $e^{+}{e}^{-}\to p\bar{p}$

Abstract

Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of $e^{+}{e}^{-}\to p\bar{p}$ 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 $\sqrt{s}=$ 2232.4 and 2400.0 MeV and a combined sample at $\sqrt{s}$ = 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\%. The $|G_E/G_M|$ 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.

13 pages, 24 figures