Improved Phase Space Treatment of Massive Multi-Particle Final States
  In this paper the revised Kajantie-Byckling approach and improved phase space sampling techniques for the massive multi-particle final states are presented. The application of the developed procedures to the processes representative for LHC physics indicates the possibility of a substantial simplification of multi-particle phase space sampling while retaining a respectable weight variance reduction and unweighing efficiencies in the event generation process. 
Borut Paul Kersevan, Elzbieta Richter-Was