Pileup track using ATLAS pileup card

[Stephen Jiggins]

Dear Authors,

I am trying to generate a sample of pileup only events using custom Pythia8 HepMC2 events. I run the recommended ATLAS_pileup card:

delphes_card_ATLAS_PileUp.tcl

The two datasets used for the sample generation are a soft QCD pileup and a dummy HepMC2 file that contains events with single neutrinos with a pt of exactly 50GeV. The idea is to use the dummy file as a place holder for the hard scatter (yielding no hard scatter inside the data), whilst using the Pythia8 soft QCD sample (formatted into the binary file as per your instructions) to replicate the pileup. At the moment I have configured the pileup profile with the internal poisson distribution set with an average of 38 soft QCD events per hard scatter.

Unfortunately it seems that the run card does not yield events with track information. Any advise on why this is would be greatly appreciated and how to generate a minimum bias equivalent sample with track information would be appreciated.

Kind Regards
Stephen Jiggins

[Pavel Demin]

Could you please provide more details about the commands you are running, the files you are checking, and any other information that would help me understand and reproduce the issue?

If the pileup file contains only soft QCD events, then there may not be any particles in this file with a high enough momentum to pass the track selection cuts. Or maybe all the tracks are removed by the track pile-up subtractor.

[Stephen Jiggins]

Hi Pavel,

Thank you for the quick reply.

I generate a file of 1000 events that contain in each event a neutrino with eta = 0.0 and p_{T} = 50GeV that is generated by ParticleGun (Geant4). This is the hard scatter. This is designed so that we have a dummy hard scatter event on which we can overlay soft QCD events. This file is called:

'single_neutrino_HS.hepmc'

I generate inelastic soft QCD proton-proton collisions using Pythia8 A3 tune. I then merge these into the binary pileup file using:

'./hepmc2pileup MinBias.pileup inelastic_Py8_minbias.hepmc'

Following this I then run the simulation using the command:

./DelphesHepMC2 delphes_card_ATLAS_PileUp.tcl output.root single_neutrino_HS.hepmc

I've attached an example output file from the above run.

Kind Regards

[Pavel Demin]

Thank you for the list of the commands and for the ROOT file. I have checked the ROOT file and it looks OK.

I see that the Track branch is commented out in pileup Tcl files. If it is the Track branch that you are looking for, then try to uncomment line 734 in delphes_card_ATLAS_PileUp.tcl.

[Stephen Jiggins]

Hi Pavel,

Thank you for the details, this does indeed solve my problem.

If I may ask another question:

1) Is there the possibility to have track hits from simulated semi-conductor pixel hits or equivalent tracking elements? If I understand this is not simulated in Delphes as such?
2) Can cells from the calorimeter be included in the output that comprise the clustered calo towers?

Kind Regards