# From Hadronic Cross Section to the measurement of the Vacuum Polarization at KLOE: a fascinating endeavour

## TL;DR

The paper reviews KLOE's 18-year effort using Initial State Radiation to measure the hadronic cross section and the vacuum polarization, crucial for testing the Standard Model's prediction of the muon g-2 anomaly.

## Contribution

It presents the first direct measurement of the time-like complex running alpha(s) below 1 GeV using ISR data from KLOE, advancing understanding of vacuum polarization effects.

## Key findings

- Precise hadronic cross section measurements below 1 GeV.
- First direct determination of the time-like complex running alpha(s).
- Insights into the muon g-2 discrepancy.

## Abstract

The KLOE experiment at the $\phi-factory$ DA$\Phi$NE in Frascati is the first to have employed Initial State Radiation (ISR) to precisely determine the $e^+e^-\to\pi^+\pi^-(\gamma)$ cross section below 1 GeV. Such a measurement is particularly important to test the Standard Model (SM) calculation for the $(g-2)$ of the muon, where a long standing 3$\sigma$ discrepancy is observed. I will review the ISR activity in KLOE in the last 18 years from the measurement of the hadronic cross section to the first direct determination of the time-like complex running $\alpha(s)$ in the region below 1 GeV.