Measurement of proton electromagnetic form factors in the time-like region using initial state radiation at BESIII

Understand

The electromagnetic process $e^{+}e^{-}\to p\bar{p}$ is studied with the initial-state-radiation technique using 7.5 fb$^{-1}$ of data collected by the BESIII experiment at seven energy points from 3.773 to 4.600 GeV.

• The Born cross section and the effective form factor of the proton are measured from the production threshold to 3.0 GeV/$c^{2}$ using the $p\bar{p}$ invariant-mass spectrum.
• The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.