Measurements of ς electromagnetic form factors in the timelike region using the untagged initial-state radiation technique

The process e+e-→ς+ς¯- is studied from threshold up to 3.04 GeV/c2 via the initial-state radiation technique using data with an integrated luminosity of 12.0 fb-1, collected at center-of-mass energies between 3.773 and 4.258 GeV with the BESIII detector at the BEPCII collider. The pair production cross sections and the effective form factors of ς are measured in eleven ς+ς¯- invariant mass intervals from threshold to 3.04 GeV/c2. The results are consistent with the previous results from Belle and BESIII. Furthermore, the branching fractions of the decays J/ψ→ς+ς¯- and ψ(3686)→ς+ς¯- are determined and the obtained results are consistent with the previous results of BESIII.