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

TL;DR

This study measures the proton's electromagnetic form factors through $e^{+}e^{-} ightarrow par{p}$ collisions at various energies, providing more precise data that supports the assumption $|G_{E}|=|G_{M}|$ and aligns with recent BaBar results.

Contribution

First measurement of the proton form factor via $e^{+}e^{-} ightarrow par{p}$ at multiple energies with improved precision, confirming the ratio $|G_{E}/G_{M}|$ near unity.

Findings

Measured cross sections agree with BaBar results, reducing uncertainty by 30%.

The ratio $|G_{E}/G_{M}|$ is close to unity, supporting the assumption $|G_{E}|=|G_{M}|$.

Results are consistent across different energies and with previous experiments.

Abstract

Using data samples collected with the BESIII detector at the BEPCII collider, we measure the Born cross section of $e^{+}e^{-}\rightarrow p\bar{p}$ 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.