Measurement of $σ(e^+e^- \to π^+π^-)$ at DA$Φ$NE with the radiative return

Abstract

The measurement of hadronic cross sections at low centre-of-mass energies is currently attracting much interest because of the rô{}le these measurements play in the theoretical evaluation of the anomalous magnetic moment of the muon. The KLOE experiment at the DA$Φ$NE $ϕ$-factory in Frascati aims to determine the cross section of the dominant contribution $e^{+}e^{-} \to π^{+}π^{-}$ at energies below 1 GeV exploiting the radiative return from the $ϕ$ to the $ρ$ and $ω$ mesons. This method has systematic errors completely different from previous measurements and allows a cross check of existing data in this energy region. The method and results on both the differential cross section for $e^{+}e^{-} \to π^{+}π^{-}γ$ and the total cross section for $e^{+}e^{-} \to π^{+}π^{-}$ are presented.