$2\gamma$ and $3\gamma$ annihilation as calibration processes for high   energy $e^+ e^-$ colliders
  Born differential cross sections and the lowest-order radiative correction to them are obtained in the kinematics of large-angle final photons emission in high-energy electron-positron annihilation processes. Taking into account possible emission of real soft and hard photons in collinear kinematics we show the validity of the Drell-Yan form of differential cross section with the nonsinglet structure functions of initial leptons. The leading and next-to leading contribution to the cross sections is obtained. The relevant numerical estimations are presented. 
E. Bartos, S. Bakmaev, E. A. Kuraev, M. G. Shatnev, M. Secansky