Jet Radius for FxFx Merging

Asked by Zachary Warner on 2020-07-16


I am doing an NLO dijet simulation using madgraph5 and Pythia8. For the jet matching procedure I am using FxFx merging. I would like to do my analysis with the kt-algorithm and the jet cone radius R = 0.4. However, I noticed that when I tried to shower the madgraph generated events Pythia8 gave me a warning saying, " For consistency in the FxFx merging, 'jetradius' has been set to 1.0" even though I had set jetradius = 0.4 in the run_card.dat when generating the events with madgraph. I then read here that FxFx merging expects a jetradius = 1.0.

My question is in regards to whether or not it is possible to produce NLO jets with a R = 0.4 using madgraph and and showering with Pythia8, or is this something that can be taken care of at the analysis level using a jet analysis software like fastjet?

Thank you in advance for your help.

Zach Warner

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MadGraph5_aMC@NLO Edit question
Rikkert Frederix Edit question
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Sorry for the long time before I assigned someone into this.
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Rikkert Frederix (frederix) said :

Dear Zach,

When generating events, the jet radius in the run_card does not define when jet radius you use at the analysis level. Rather, it sets the radius at the level of event generation (before shower is applied). In other words, the jet-radius that FxFx sets to one is the radius needed internally in the matching in order to create a consistent event file. This is independent from the radius you might want to use at the analysis level. The latter you have to define yourself when constructing the analysis.


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