The radiative return offers the unique possibility for a measurement of the
cross section of electron–positron annihilation into hadrons over a wide range
of energies. The large luminosity of present phi- and B-factories easily
compensates for the additional factor of alpha due to the emission of a hard
photon. Final states with photons at large angles can be easily identified. The
rate for events with collinear photons, however, is enhanced by a large
logarithm and allows, in particular at lower energies, for a complementary
measurement.
The Monte Carlo generator PHOKHARA, which includes next to leading order
corrections from virtual and real photon emission, has been extended from large
photon angles into the collinear region, using recent results for the virtual
corrections. In addition, the present version includes final state radiation
for muon and pion pair production and final states with four pions.
Implications for the experimental analysis at three typical energies, 1.02, 4
and 10.6 GeV, are presented: the magnitude of these new corrections is studied,
possibilities for the separation of initial and final state radiation are
proposed, and the differences with respect to the previous treatment based on
structure functions are investigated.