Scanning of the $ee\rightarrow \pi\pi$ cross-section below 1 GeV by radiative events with untagged photon

Abstract.

We discuss an inclusive approach to the measurement of the $e^+e^-\rightarrow \pi^+\pi^-$ cross-section by the radiative return method without photon tagging. The essential part of this approach is the choice of rules for event selection which provide rejection of events with 3 (or more) pions and decrease the final-state radiation background. The radiative corrections to the initial-state radiation process are computed for DA$\Phi$NE conditions, using the quasi-real electron approximation for both, the cross-section and the underlying kinematics. The two cases of restricted and unrestricted pion phase space are considered. Some numerical calculations illustrate our analytical results.