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

Abstract

We have measured the cross section sigma(e+ e- -> pi+ pi- gamma) at DAFNE, the Frascati phi-factory, using events with initial state radiation photons emitted at small angle andinclusive of final state radiation. We present the analysis of a newdata set corresponding to an integrated luminosity of 240 pb(-1). Wehave achieved a reduced systematic uncertainty with respect topreviously published KLOE results. From the cross section we obtain thepion form factor and the contribution to the muon magnetic anomaly fromtwo-pion states in the mass range 0.592 < M pi pi < 0.975 GeV. For the latter we find Delta(pi pi)_a(mu) = (387.2 +/- 0.5(stat) +/- 2.4(exp)+/- 2.3(th)) x 10^(-10).