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

摘要

The electromagnetic processe+e?→ppˉis studied with the initial-state-radiation technique using 7.5 fb?1of 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/c2using theppˉinvariant-mass spectrum. The ratio of electric and magnetic form factors of the proton is determined from the analysis of the proton-helicity angular distribution.