Measurement of proton electromagnetic form factors in $e^{+}{e}^{-}\to p\bar{p}$ in the energy region 2.00-3.08 GeV

Abstract

The process of $e^{+}{e}^{-}\to p\bar{p}$ is studied at 22 center-of-mass energy points ($\sqrt{s}$) from 2.00 to 3.08 GeV, exploiting 688.5~pb${}^{-1}$ of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section~($\ddot{I}{ƒ}_{p\bar{p}}$) of $e^{+}{e}^{-}\to p\bar{p}$ is measured with the energy-scan technique and it is found to be consistent with previously published data, but with much improved accuracy. In addition, the electromagnetic form-factor ratio ($|G_E/G_M|$) and the value of the effective ($|G_{\mathrm{eff}}|$), electric ($|G_E|$) and magnetic ($|G_M|$) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. $|G_E/G_M|$ and $|G_M|$ are determined with high accuracy, providing uncertainties comparable to data in the space-like region, and $|G_E|$ is measured for the first time. We reach unprecedented accuracy, and precision results in the time-like region provide information to improve our understanding of the proton inner structure and to test theoretical models which depend on non-perturbative Quantum Chromodynamics.