pileup studies

[Sergei Chekanov]

Hello,

I have a technical question related to the current snowmass activity. We have HEPMC records which contain signal+pileup events. How can we propagate information into the Delphes output and tell which truth particle comes from pileup, and which come from the signal event? For example, I can set "status=-1" (stable particle from pileup) in HEPMC, but then Delphes should understand abs(status)=1 as stable particle (not only status==1) when doing smearing and building jets. Then I should see "status=-1" in ROOT output and use such particles for my studies (like building truth jets without pileup effect)

best, Sergei

best, Sergei

[Pavel Demin]

Hello Sergei,

What Delphes version are you using?

In Delphes-3.0.5, we added GenParticle::IsPU parameter that can be set to 1 for pile-up particles.

Your method would also work with minimal modifications of the HepMC reader code.

In both cases, you'll need to modify the HepMCConverter::AnalyzeParticle method in readers/DelphesHepMC.cpp.

You can replace

  if(fStatus == 1 && pdgParticle->Stable())
  {
    fStableParticleOutputArray->Add(candidate);
  }

with

  if(TMath::Abs(fStatus) == 1 && pdgParticle->Stable())
  {
    fStableParticleOutputArray->Add(candidate);
  }

or something similar.