Measurement of Proton Electromagnetic Form Factors in e(+) e(-) -> p(p)over-bar in the Energy Region 2.00-3.08 GeV

Abstract

The process of e(+)e(-) -> p (p) over bar is studied at 22 center-of-mass energy points (root 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 (sigma(p (p) over bar)) of e(+)e(-) -> p (p) over bar 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 electro-magnetic form-factor ratio (vertical bar G(E)/G(M)vertical bar) and the value of the effective (vertical bar G(eff)vertical bar), electric (vertical bar G(E)vertical bar), and magnetic (vertical bar G(M)vertical bar) form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. vertical bar G(E)/G(M)vertical bar and vertical bar G(M)vertical bar are determined with high accuracy, providing uncertainties comparable to data in the spacelike region, and vertical bar G(E)vertical bar is measured for the first time. We reach unprecedented accuracy, and precision results in the timelike region provide information to improve our understanding of the proton inner structure and to test theoretical models which depend on nonperturbative quantum chromodynamics.