Pion Form Factor at BESIII

At BESIII, we measured the cross section of e+e−→π+π− in the energy range between 600 and 900 MeV/c2 with a 2.93 fb−1 data set taken at the center-of-mass energy 3.773 GeV. The initial state radiation technique is used, and the total systematic uncertainty is estimated to be 0.9%. The squared form factor |Fπ|2 is extracted, and comparisons are made with results from both KLOE and BaBar. The two-pion contribution to the hadronic vacuum polarization contribution to (g−2)μ is calculated to be aμππ,LO(600−900MeV/c2)=(368.2±2.5stat.±3.3syst.)⋅10−10.