Precise measurement of the e + e − → π + π − (γ) cross section with the initial state radiation method at BABAR

We present a precise BABAR measurement on the cross section of the process e + e − → π + π − (γ) from threshold to an energy of 3 GeV with the initial state radiation (ISR) technique, using 232 fb −1 of data collected with the BABAR detector at e + e − center-of-mass energies near 10.58 GeV. The ISR luminosity is determined from a study of the leptonic process e + e − → μ + μ − γ(γ). The leading-order hadronic contribution to the muon magnetic anomaly calculated using the ππ cross section measured from threshold to 1.8 GeV is (514.1 ± 2.2(stat) ±3.1(syst)) × 10 −10 .