Complete lowest-order calculations for four-lepton final states in electron-positron collisions

We present a Monte Carlo procedure which enables us to calculate exact cross sections for processes such as e+e− → e+e−e+e−, e+e− → e+e−μ+μ−, e+e− → μ+μ−μ+μ−, e+e− → μ+μ−τ+τ−. In particular, attention is paid to the calculation of the complete matrix element squared including all interferences and all masses and to the method by which unweighted events are generated. This scheme can also be used to calculate cross sections for e+e− → e+e− qq or e+e− → μ+μ−qq.