It can be very useful to let Gauss write out MCParticles in the Generation directly (without the detector simulation), which then can be analysed. This can be achieved the following way:

gtos = GenerationToSimulation()
gtos.SkipGeant = True
gs = GaudiSequencer("GenMonitor")
MCTruthStream = OutputStream("MCTruthStream")
MCTruthStream.ItemList += [ "/Event/Gen#1", "/Event/Gen/HepMCEvents#1", "/Event/MC#1", "/Event/MC/Header#1", "/Event/MC/Particles#1", "/Event/MC/Vertices#1" ]
MCTruthStream.Output = "DATAFILE='MCTruth.sim' TYP='POOL_ROOTTREE' OPT='RECREATE'"
gs.Members += [ SimInit(), gtos, MCTruthStream ]

The root file can then be run over with an MCTupleTool in DaVinci (with certain restrictions, i.e. only tools which only access 4-vectors will run…)