→ π + π − ) measurement via radiative return method ∗

The radiative return method [1] (look [2] for a short introduction) is a powerful tool in the measurement of σ(ee → hadrons), crucial for predictions of the hadronic contributions to aμ, the anomalous magnetic moment of the muon, and to the running of the electromagnetic coupling from its value at low energy up to MZ (for recent reviews look [3, 4, 5]). Due to a complicated experimental setup, the use of Monte Carlo (MC) event generators [1, 6, 7, 8, 9], which includes various radiative corrections [10, 11] is indispensable. Some more extensive analysis of that subject can be found also in [12, 13, 14]. The most important hadronic mode, i.e. ππ, is currently measured by KLOE [15, 16, 17, 18], and BaBar [19] by means of radiative return method. This measurement can suffer from a background from the process ee → ππee, as suggested in [20], for at least two reasons: 1. At present KLOE measures only pions (+ missing momenta) in the final state and for that particular measurement there is