Measurement of $\sigma(e^+e^-\to \pi^+ \pi^- \gamma)$ and extraction of $\sigma(e^+e^-\to \pi^+\pi^-)$ below 1 {\rm GeV} with the KLOE detector

TL;DR

This paper reports a precise measurement of the $e^+e^- o ext{pion pair}$ cross section below 1 GeV using initial state radiation at the KLOE detector, enabling improved calculations of the muon g-2.

Contribution

The study provides the first extraction of the $e^+e^- o ext{pion pair}$ cross section below 1 GeV from $ ext{e}^+ ext{e}^- o ext{pion pair} ext{gamma}$ data at the $ ext{phi}$ resonance.

Findings

Extracted $ ext{e}^+ ext{e}^- o ext{pion pair}$ cross section in the 0.35-0.95 GeV$^2$ range.

Calculated the pion form factor and hadronic contribution to muon g-2.

Provided data to refine theoretical models of hadronic effects in muon anomalous magnetic moment.

Abstract

We have measured the cross section $\sigma(e^+e^-\to \pi^+\pi^- \gamma)$ at an energy $W=m_\phi=1.02$ GeV with the KLOE detector at the electron-positron collider DA$\Phi$NE. From the dependence of the cross section on the invariant mass of the two-pion system, we extract $\sigma(e^+e^-\to \pi^+\pi^-)$ for the mass range $0.35<s<0.95$ GeV$^2$. From this result, we calculate the pion form factor and the hadronic contribution to the muon anomaly, $a_\mu$.