Distinguising leptonic jets from hadronic jets

[James]

Hello,

I have created parton level events with Madgraph and showered them with Pythia8. Next I have performed jet clustering and detector effects using Delphes (with delphes_card_ATLAS.tcl)

My question is based on the output after Delphes:
How can I distinguish leptonic jets from hadronic jets (my events have both: WW > lvqq)? In the ROOT file I am using I can't work out how to distinguish them.

Also, I want to specify a minimum delta(R) between the lepton and a jet, but I have no idea how to set this condition.

Basically, I believe I have a ROOT file in a useful form for my analysis, but I am unable to extract leptonic/hadronic jets from this as required. I am new to this so the more basic the explanation the better!

Thank you for your help,
James

[Michele Selvaggi]

Hi,

you can read the ROOT files with macros such as those in the examples directory.
For instance:

root -l examples/Example1.C'("delphes_output.root")'

In your case you'll have to perform a nested loop over GenParticle and Jets, take the 4-vector (these are TLorentzVector) of each and build the deltaR with the relevant method:

​https://root.cern.ch/root/html602/TLorentzVector.html

[James]

Hello,

Thank you for your answer. I don't have GenParticle in the ROOT file. I think I'm confused over the following issue:

Do electrons/muons get reconstructed as jets and placed in the Jet branch, or is their information post detector simulation found elsewhere - ie in the Electron/Muon branches? When I loop through the Electron/Muon branches only some of the events have any entries, whereas every event as them - what is occurring here? For example, when I look at the Particle branch there are high PT leptons in every event, but not in the Electron/Muon branches.

Also, wouldn't it be simpler just to use eta and phi of the jets/leptons to set the condition delta(R) > 0.4? Is there something wrong with this method?

Thank you!
James

[Michele Selvaggi]

Sorry the collection is called Particle.

Do electrons/muons get reconstructed as jets and placed in the Jet branch, or is their information post detector simulation found elsewhere - ie in the Electron/Muon? branches?

non islated ele/mu wil be present in jets. Isolated one are not.

For example, when I look at the Particle branch there are high PT leptons in every event, but not in the Electron/Muon? branches.

Particle branch contains every particle pre-detector simulation.

Also, wouldn't it be simpler just to use eta and phi of the jets/leptons to set the condition delta(R) > 0.4? Is there something wrong with this method?

I would loop over Particle , find the W's, make sure they produced leptonic decays/hadronic and match the information with jets.
To loop over Particles have a look at Example5.C. If you need to access jet contituents have a look at Example3.C

[James]

Thank you very much mselvaggi - this is very informative for me.

One query:

"I would loop over Particle , find the W's, make sure they produced leptonic decays/hadronic and match the information with jets."

I am able to find the decay products of the W bosons, but don't know how to then determine which jets these correspond to. I can't see any useful information in the Jet Branch of my ROOT file. Do you have any suggestions?

Thanks again,
James

[Michele Selvaggi]

Well once you have the the P4 of the Gen W's daughters you can simply loop over reconstructed jets and match with a DR criterion (ie using the P4 of the jet). Otherwise you could get more sophisticated and match leptons from the W decay products and loop over jet constituents and see if you find a match. In Example3 you can see how to loop over jet consts, as well as how to access the genparticle reference for every recosntructed object, including that of constituents.

[James]

Thank you very much. I have this working as desired now.

As for the information about the neutrinos, what do you suggest is the best way to get their information? Simply use the MissingET branch? Or does Delphes reconstruct the neutrinos as jets too, and therefore I can use the same method as for the leptons?

[Michele Selvaggi]

For reco objects neutrinos are taken into account as missing energy, and they are not part of jets.
At gen level you have access to neutrinos in the same way as you access other leptons by looking at the pdg code.

[usernew]

Replying to mselvaggi:

Sorry the collection is called Particle.

Do electrons/muons get reconstructed as jets and placed in the Jet branch, or is their information post detector simulation found elsewhere - ie in the Electron/Muon? branches?

non islated ele/mu wil be present in jets. Isolated one are not.

For example, when I look at the Particle branch there are high PT leptons in every event, but not in the Electron/Muon? branches.

Particle branch contains every particle pre-detector simulation.

Also, wouldn't it be simpler just to use eta and phi of the jets/leptons to set the condition delta(R) > 0.4? Is there something wrong with this method?

I would loop over Particle , find the W's, make sure they produced leptonic decays/hadronic and match the information with jets.
To loop over Particles have a look at Example5.C. If you need to access jet contituents have a look at Example3.C

How would you find the W's? Is there an example?