External FastJet

[iris]

Hi, I am completely new to this tool. I am using the MG5+Pythia+Delphes package.

I am trying to reproduce some published results using the MDF(mass drop filter) method. What should I do to change the FastJet code inside Delphes? Where can I find the initial code? Seems I need to run Delphes with external FastJet code?

Thanks in advance!

[Pavel Demin]

Hi,

I'm not sure if I understand your questions correctly (for instance, what do you mean by "the initial code"?).

Anyway, there are two possibilities to use a different version of FastJet:

• run Delphes with external FastJet as described in

https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook/ExternalFastJet

• replace FastJet that comes with Delphes by your version of FastJet using update_fastjet.sh:

  cd external
  rm -rf fastjet
  source ../doc/update_fastjet.sh
  

You'll most probably need to slightly modify update_fastjet.sh.

Cheers,

Pavel

[iris]

Thanks!

By "initial code", I mean the code of FastJet used in Delphes since I just want to change a bit rather than rewriting the whole thing.

So anyway I need to install FastJet instead of changing something inside Delphes?

Thank you so much!

[Pavel Demin]

The code of FastJet used in Delphes can be found in the external/fastjet directory. I don't see any problem to change it in place.

When I proposed the two solutions, I thought that you have already a version of FastJet that you want to use with Delphes.

[iris]

Thank you! I should state the question more clearly.

When dealing with the branch "Jet" in Delphes, can I undo the clustering?

To be precise, actually I need to undo the clustering and deal with the subjets. I dont know whether I should change the code in FastJet or analyze the resulting jets in Delphes root file (if so, how to undo the clustering to obtain the subjets?) ?

[iris]

Hello, I found this on web and it is exactly the code I want:

​http://www.lpthe.jussieu.fr/~salam/fastjet/repo/doxygen-3.0alpha3/11-boosted__higgs-new_8cc_source.html

My question is where I should paste it?

[Michele Selvaggi]

Hi,

my suggestion is that have a separate Delphes and FastJet installation.
You have very detailed instructions here for running FastJet using Delphes as an external library here:

https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook/ExternalFastJet

After you did everything explained there, you can then simply modify the examples !ExternalFastJetHepMC.cpp or ExternalFastJetBasic.cpp
by plugging in the fast jet code you mentioned above.

Cheers,
Michele

[Jewel]

Replying to iris:

Hello,

I am doing some event generation using MG5+Pythia+Delphes packages.
Now, I am trying to reproduce higgs invariant mass using mass-dropp tagging method.
How I compile that Fastjet (.cc file) and Delphes root file.
How I reproduce higgs invariant mass plot?
Thanks in advance.

[Michele Selvaggi]

Hi,

you'll have to:

• produce an hepmc file with madGraph
• install standalone Delphes version
• follow instructions here:

https://cp3.irmp.ucl.ac.be/projects/delphes/wiki/WorkBook/ExternalFastJet

This allows you to run Delphes with your own fastjet code.