Precision measurement of $\sigma(e^+e^-\rightarrow\pi^+\pi^-\gamma)/\sigma(e^+e^-\rightarrow \mu^+\mu^-\gamma)$ and determination of the $\pi^+\pi^-$ contribution to the muon anomaly with the KLOE detector

TL;DR

This paper reports a precise measurement of the ratio of cross sections for e+e- to pi+pi- gamma and mu+mu- gamma, leading to an improved determination of the pion contribution to the muon g-2 anomaly, confirming existing discrepancies.

Contribution

It provides a new, highly precise measurement of the pion form factor and the two-pion contribution to the muon anomaly using the KLOE detector, refining previous estimates.

Findings

Confirmed the discrepancy between Standard Model and experimental muon g-2.

Measured the pion form factor with high precision.

Determined the two-pion contribution to muon anomaly as (385.1 ± 1.1_stat ± 2.7_sys+theo) × 10^{-10}.

Abstract

We have measured the ratio $\sigma(e^+e^-\rightarrow\pi^+\pi^-\gamma)/\sigma(e^+e^-\rightarrow \mu^+\mu^-\gamma)$, with the KLOE detector at DA$\Phi$NE for a total integrated luminosity of $\sim$ 240 pb$^{-1}$. From this ratio we obtain the cross section $\sigma(e^+e^-\rightarrow\pi^+\pi^-)$. From the cross section we determine the pion form factor $|F_\pi|^2$ and the two-pion contribution to the muon anomaly $a_\mu$ for $0.592<M_{\pi\pi}<0.975$ GeV, $\Delta^{\pi\pi} a_\mu$= $({\rm 385.1\pm1.1_{stat}\pm2.7_{sys+theo}})\times10^{-10}$. This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement of the muon anomaly.