questions on pileup corrections

[Sergei Chekanov]

Hello,

I have a few questions related to a pileup subtraction & documentation.

1) Delphes3 has the variable ScalarHT. But the documentation does not say how it was calculated (tracks? towers? pflows?)

2) Is any way to access the information on number of primary vertecies (important for pileup correction)

3) Is it possible to use jet area correction (the code comes with fastjet). I guess, this code should be inserted somewhere where the fastjet algorithm builds jets?

best, Sergei

[Pavel Demin]

1. Here is how ScalarHT calculation is configured by default:

   module Merger ScalarHT {
   # add InputArray InputArray
     add InputArray UniqueObjectFinder/jets
     add InputArray UniqueObjectFinder/electrons
     add InputArray UniqueObjectFinder/photons
     add InputArray MuonIsolation/muons
     set EnergyOutputArray energy
   }
   

   So, by default, it takes unique jets, unique isolated electrons, unique isolated photons and isolated muons as input. This module can be configured to use any other objects to calculate ScalarHT.

2. Currently, no information about primary vertices is stored. I don't see right now how to obtain this information from HepMC files. Your suggestions are more than welcome.

3. In version 3.0.5, we added an example card examples/delphes_card_CMS_PileUp.tcl that demonstrates how to apply the jet area correction. The mains differences w.r.t. the default card are
   • module FastJetFinder Rho that computes per event pile-up contamination (Rho)
   • module JetPileUpSubtractor JetPileUpSubtractor that subtracts the per event pile-up contamination from the jets.
   • all isolation modules also take Rho as input.

There is a wiki page with some instructions and we'll try to update it with more detailed examples:
https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook/PileUp