KLOE-2 results on hadron physics

Abstract

Two recent precision measurements of the Standard Model parameters using $1.7$ fb$^{-1}$ of $e^+e^-$ data collected with the KLOE detector at DA$\Phi$NE are presented: Dalitz plot distribution for the $\eta \to \pi^+ \pi^- \pi^0$ decay is studied with the world's largest sample of $\sim 4.7 \cdot 10^6$ events from $e^+e^-\to\phi\to\eta\gamma$. The statistical uncertainty of all parameters is improved by a factor of two with respect to the earlier measurements. The data are used as input in dispersive calculations to determine ratio of the light quark masses. Running of the effective QED coupling constant $\alpha(s)$ in the time-like region $0.600<\sqrt s< 0.980$ GeV is studied using the Initial-State Radiation process $e^+e^-\to\mu^+\mu^-\gamma$. More than 5$\sigma$ significance of the hadronic contribution to the running of $\alpha(s)$ is seen, which is the strongest direct evidence achieved in a single measurement. By using the $e^+e^-\to\pi^+\pi^-$ cross section measured by KLOE, the real and imaginary parts of $\alpha(s)$ have been extracted. From a fit of the real part the branching ratio $BR(\omega\to\mu^+\mu^-) =(6.6\pm1.4_{stat}\pm1.7_{syst})\cdot 10^{-5} $ has been determined.