Two-photon physics with GALUGA 2.0 Original Research Article

An extended version of the Monte Carlo program GALUGA is presented for the computation of two-photon production in e+e− collisions. Functions implemented for the five γ*γ* structure functions now include several ansätze of the total hadronic cross section based on the BFKL Pomeron and various Regge-like models. In addition, structure functions for resonance formation are included with full dependence on the two-photon virtualities Q12 and Q22 as given in the constituentquark model. The six lowest-lying resonances of each of the C-even mesons with JP = O−, O+, 1+, 2+ and 2− are provided. The program can also be used to calculate with exact kinematics the effective two-photon luminosity function. Special emphasis is put on a numerically stable evaluation of all variables over the full Q12 range while keeping all dependences on the electron mass and Q12.