Measurement of sigma(e + e- ---> pi+ pi- gamma(gamma)) and the dipion contribution to the muon anomaly with the KLOE detector.

We have measured the cross section σ(e+e− → pi+pi−>γ(γ)) at DAΦNE, the Frascati φ–factory, using events with initial state radiation photons emitted at small angle and inclusive of final state radiation. We present the analysis of a new data set corresponding to an integrated luminosity of 240 pb−1. We have achieved a reduced systematic uncertainty with respect to previously published KLOE results. From the cross section we obtain the pion form factor and the contribution to the muon magnetic anomaly from two-pion states in the mass range 0.592 < Mππ < 0.975 GeV. For the latter we find ∆pipiaμ=(387.2±0.5stat±2.4exp±2.3th)×10−10.