Hey! I am doing some tree level calculations of production of four final leptons and have some trouble with the kinematics. Does anybody know any good references where to read up a bit this topic and/or good variables/frames to use in order for the description to be as easy as possible? My problem is to choose a frame/variables where I can find a resonably simple description of the matrix element and also solve the phase-space integrals. A typical process would be e+ e- --> gamma --> W+ W- --> e+ e- anti-v v Thanks alot!