Muon colliders, Monte Carlo and gauge invariance

Abstract

If calculated in the standard way, the cross section for the collision of two unstable particles turns out to diverge. This is because part of such a cross section is proportional to the size of the colliding beams. This effect is called the "linear beam size effect". We present a way of including this linear beam size effect in the usual Monte Carlo integration procedure. Furthermore we discuss the gauge breaking that this may cause.