TWOGEN—a simple Monte Carlo generator for two-photon reactions

TWOGEN samples the transverse-transverse luminosity function for real and virtual photons, then weights events with any user-supplied cross section σTT(γγ → X) in a “hit or miss” sampling, using a simple method to avoid the singularity at the minimum electron angle ϑmin=0. Events within defined kinematic limits are accepted and the corresponding cross section is estimated, together with the effective luminosity of the run. Functions implemented for σTT include the production cross sections for lepton pairs, for the formation of narrow resonances and for hadron production in tagged, deep inelastic scattering. A comparison is made with an existing Monte Carlo generator and a simple analytic approximation.