ar X iv : 0 81 2 . 19 39 v 1 [ he p - ph ] 1 0 D ec 2 00 8 Status of PHOKHARA ∗

The basis of the radiative return method, proposed in [1], is an observation that one can extract the hadronic cross section (ee → hadrons) from the measurement of the cross section of the reaction ee → hadrons + photons, where the photons are emitted from the initial leptons. This is possible due to the factorization dσ(ee → hadrons + γISR) = H(Q, θγ)dσ(e e → hadrons)(s = Q), where the function H is fully calculable within QED and Q is the invariant mass of the hadronic system. The radiative return method has been used by meson factories DAPHNE, BaBar and BELLE and allows for the measurement of the hadronic cross section from the nominal energy of these experiments down to the production threshold. The traditional way of measuring of the hadronic cross section via the energy scan needs dedicated experiments, while using the radiative return one can profit from the existing meson factories. The smaller cross section of the radiative process (by a factor of α/π as compared to the process without photons emission) has to be compensated by higher luminosities of factories. To obtain the hadronic cross section using the radiative return method in a realistic experimental situation, one needs a Monte Carlo event generator of the measured process. To provide such a tool to the experimental groups PHOKHARA event generator was constructed. The construc-