Measurement of Proton Electromagnetic Form Factors in in the Energy Region 2.00–3.08 GeV
M. Ablikim (Institute of High Energy Physics, Beijing 100049, People’s Republic of China); M. N. Achasov (G.I. Budker Institute of Nuclear Physics SB RAS (BINP), Novosibirsk 630090, Russia); P. Adlarson (Uppsala University, Box 516, SE-75120 Uppsala, Sweden); S. Ahmed (Helmholtz Institute Mainz, Johann-Joachim-Becher-Weg 45, D-55099 Mainz, Germany); M. Albrecht (Bochum Ruhr-University, D-44780 Bochum, Germany); et al - Show all 502 authors
The process of is studied at 22 center-of-mass energy points () from 2.00 to 3.08 GeV, exploiting of data collected with the BESIII detector operating at the BEPCII collider. The Born cross section () of 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 () and the value of the effective (), electric (), and magnetic () form factors are measured by studying the helicity angle of the proton at 16 center-of-mass energy points. and are determined with high accuracy, providing uncertainties comparable to data in the spacelike region, and 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.