Generating heavy particles with energy and momentum conservation
  We propose a novel algorithm, called REGGAE, for the generation of momenta of a given sample of particle masses, evenly distributed in Lorentz invariant phase space and obeying energy and momentum conservation. In comparison to other existing algorithms, REGGAE is designed for the use in multiparticle production in hadronic and nuclear collisions where many hadrons are produced and a large part of the available energy is stored in the form of their masses. The algorithm uses a loop simulating multiple collisions which lead to production of configurations with reasonably large weights. 
Michal Meres, Ivan Melo, Boris Tomasik, Vladimir Balek, Vladimir Cerny
nucl-th hep-ph