Latest KLOE result on the σ(e+e− → π+π−) and its impact on the muon anomaly

Abstract

The KLOE experiment was the first to exploit Initial State Radiation (ISR) processes to obtain the e+e− → π+π−(γ) cross section below 1 GeV (70% of the leading order contribution to the muon anomaly) publishing two measurements with the photon in the initial state emitted at small angle in 2005 and 2008, and an independent measurement with the photon emitted at large angle in 2011. These measurements were normalized using luminosity from Bhabha. Here, we present the latest KLOE results on e+e− → π+π−(γ) cross section, obtained by the ratio σ(e+e− → π+π−)/σ(e+e− → μ+μ−) measurement for a total integrated luminosity of 239.2 pb−1. The comparison of the present results with with the previous ones performed by KLOE shows a good agreement, while they are in substantially agreement with the other ones obtained by CMD-2, SND and BaBar experiments. From the cross section we extract the pion form factor and the two-pion contribution in the invariant mass range of 592–975 MeV to the muon anomaly confirming the current discrepancy between standard model calculation and experimental measurement.