A precise new KLOE measurement of $|F_\pi|^2$ with ISR events and determination of $\pi\pi$ contribution to $a_\mu$ for $0.592 < M_{\pi\pi} < 0.975$ GeV

TL;DR

This paper presents a highly precise measurement of the pion form factor using ISR events at KLOE, refining the $1$ contribution to the muon anomalous magnetic moment and confirming existing discrepancies with the Standard Model.

Contribution

It introduces a new precise measurement of the pion form factor with reduced errors, improving the accuracy of the $1$ contribution to $a_1$ and confirming previous findings.

Findings

Reduced statistical and systematic errors in $a_1$ measurement

Results consistent with previous KLOE measurements

Supports the discrepancy between Standard Model and experimental $a_1$

Abstract

The KLOE experiment at the DA$\Phi$NE $\phi$-factory has performed a new precise measurement of the pion form factor using Initial State Radiation events, with photons emitted at small polar angle. Results based on an integrated luminosity of 240 pb$^{-1}$ and extraction of the $\pi\pi$ contribution to $a_\mu$ in the mass range $0.35< M^2_{\pi\pi}<0.95$ GeV$^2$ are presented. The new value of $a^{\pi\pi}_\mu$ has smaller (30%) statistical and systematic error and is consistent with the KLOE published value (confirming the current disagreement between the standard model prediction for $a_\mu$ and the measured value).