doc/v612/PhaseSpace_8C.html

void PhaseSpace() {
   TLorentzVector target(0.0, 0.0, 0.0, 0.938);
   TLorentzVector beam(0.0, 0.0, .65, .65);
   TLorentzVector W = beam + target;
   //(Momentum, Energy units are Gev/C, GeV)
   Double_t masses[3] = { 0.938, 0.139, 0.139} ;
   TGenPhaseSpace event;
   event.SetDecay(W, 3, masses);
   TH2F *h2 = new TH2F("h2","h2", 50,1.1,1.8, 50,1.1,1.8);
   for (Int_t n=0;n<100000;n++) {
      Double_t weight = event.Generate();
      TLorentzVector *pProton = event.GetDecay(0);
      TLorentzVector *pPip    = event.GetDecay(1);
      TLorentzVector *pPim    = event.GetDecay(2);
      TLorentzVector pPPip = *pProton + *pPip;
      TLorentzVector pPPim = *pProton + *pPim;
      h2->Fill(pPPip.M2() ,pPPim.M2() ,weight);
   }
   h2->Draw();
}