Simple question regarding FastJet

Asked by JamesB on 2018-01-17

Hello,

I am working on a p p > h j, h > j j l v process. I am using aMC@NLO to generate LO events. I use PYTHIA8 in the aMC@NLO framework for shower. Then I use the generated .hep file in ./bin/ma5 -R, using the following settings for my attempt at a jet algorithm:

set main.fastsim.package = fastjet
set main.fastsim.algorithm = kt
set main.fastsim.radius = 0.4
set main.fastsim.ptmin = 20.0
set main.fastsim.bjet_id.efficiency = 0.8
set main.outputfile = higgs.lhe
import ~/higgs_lvjj_200/Events/run_01/tag_1_pythia_events.hep
submit

The .lhe output file is essentially the same (now instead of quark and antiquark, it is 2 protons) as data produced after PYTHIA8. My question is, is the above correct? Why is fastjet not really doing anything? Shouldn't all of the gluons and quarks be hadronized? What is the typical output from running fastjet.

I'm also confused because the spectator quarks should hadronize and form jets (but these are not at all considered in this because Madgraph only includes a quark and anti-quark)? Surely this is a fundamental flaw if we're trying to simulate the behaviour in the detector?

Thank you,
James

NOTE, ignore my first 2 comments. I've updated this question accordingly

Question information

Language:
English Edit question
Status:
Solved
For:
MadAnalysis 5 Edit question
Assignee:
Benjamin Fuks Edit question
Solved by:
Benjamin Fuks
Solved:
2018-01-18
Last query:
2018-01-18
Last reply:
2018-01-17

I guess that the tool that you need in your case is MadAnalysis5

Cheers,

Olivier

> On 17 Jan 2018, at 14:12, JamesB <email address hidden> wrote:
>
> New question #663174 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/663174
>
> Hello,
>
> I'm struggling to work out how to run a jet-clustering algorithm on my events generated from Madgraph and Pythia. Can I run an algorithm directly through Madgraph? Or should I use something through Fastjet (3.3.0) with the files produced from Madgraph (ie .lhe or .hep type files?
>
> The events I generated are LO, although I intend to also generate events at NLO.
>
> Thank you,
> James
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

JamesB (jamesb8) said : #2

Dear Oliver,

I can't work out the syntax to use to run fastjet on my lhe output from pythia8.

eg. I've set this:
set main.fastsim.package = fastjet
set main.fastsim.algorithm = kt
set main.fastsim.radius = 0.4
set main.fastsim.ptmin = 20.0
set main.fastsim.bjet_id.efficiency = 0.8

What is the next step to run fastjet on my .lhe file?

Thank you,
James

I'm re-directing you to MA5 author for such type of question.

Cheers,

Olivier

JamesB (jamesb8) said : #4

Note, I've added the following:

set main.fastsim.package = fastjet
set main.fastsim.algorithm = kt
set main.fastsim.radius = 0.4
set main.fastsim.ptmin = 20.0
set main.fastsim.bjet_id.efficiency = 0.8
set main.outputfile = higgs.lhe
import ~/higgs_lvjj_200/Events/run_01/tag_1_pythia_events.lhe
submit

but this just produces a lhe file with the gluons from pythia (and nothing else). No hadronisation is occuring - why is this?

Thanks,
James

Best Benjamin Fuks (fuks) said : #5

Please have a look to the header of the produced LHE file (higgs.lhe). You will see that the meaning of the PDG codes have been modified (21 is here a light jet and not a gluon as we are at the reconstructed level, for instance).

I hope it helps.

Best regards,

Benjamin

JamesB (jamesb8) said : #6

Thanks Benjamin Fuks, that solved my question.