Measurement of σ(e+e−→π+π−) from threshold to 0.85 GeV2 using initial state radiation with the KLOE detector

We have measured the cross section of the radiative process e+e−→π+π−γ with the KLOE detector at the Frascati ϕ-factory DAΦNE, from events taken at a CM energy W=1 GeV. Initial state radiation allows us to obtain the cross section for e+e−→π+π−, the pion form factor |Fπ|2 and the dipion contribution to the muon magnetic moment anomaly, Δaμππ=(478.5±2.0stat±5.0syst±4.5th)×10−10 in the range 0.1