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=====  How to access truth particles =====

Truth particle record inside Delphes3 ROOT files (GenParticle) was slimmed to reduce the file size. We slim was done on the truth HEPMC level, before entering the Delphes3 reconstruction.

The following truth particles are removed from the HEPMC record:

  * All gluons (PID=21)
  * All light quarks (pid=1,2,3)
  * All particles with pT<0.05 GeV
  * All particles with |eta|>5
  * All unstable particles but:
  * Keep Z,W,b,t, Zprime or any exotic particle under study



Such slimming is applied for the pileup HEPMC record, before mixing with signal events. This reduces the output file size by 50%.
Plus slim program marks pile-up final state particles (see below).

====== How to identify particles from pile up in the truth record? ======

We run a modified Delphes3 which assumes that all particles with  |status|=1 are stable.

Final-state particles with status=1 are from signal event. Particles with status=-1 are from pileups.
If you build a jet using truth particles and interested in the signal jet only, use status=1.