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)x10-10 in the range 0.1<Mππ2<0.85 GeV2, where the theoretical error includes a SU(3) χPT estimate of the uncertainty on photon radiation from the final pions. The discrepancy between the Standard Model evaluation of aμ and the value measured by the Muon g-2 collaboration at BNL is confirmed.