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

TL;DR

This paper reports a precise measurement of the e+e- to pi+pi- gamma cross section at DAΦNE, deriving the pion form factor and its contribution to the muon g-2 anomaly with reduced systematic uncertainties.

Contribution

It provides a new, more accurate determination of the pion form factor and the two-pion contribution to the muon magnetic anomaly using initial state radiation data.

Findings

Reduced systematic uncertainty in cross section measurement.

Calculated the pion form factor in the specified mass range.

Quantified the two-pion contribution to muon g-2 as (387.2 ± 0.5_stat ± 2.4_exp ± 2.3_th) × 10^{-10}.

Abstract

We have measured the cross section $\sigma(e^+e^-\to\pi^+\pi^-\gamma(\gamma))$ at DA$\Phi$NE, the Frascati \phi-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 $0.592 < M_{\pi\pi} < 0.975$ GeV. For the latter we find $\Delta a^{\pi\pi}_\mu = (387.2\pm0.5_{\rm stat}\pm2.4_{\rm exp}\pm2.3_{\rm th})\times 10^{-10}$