Applying Pythia merging setting doesnt work properly

Asked by Jay Sandesara on 2020-07-01

Hi,

I am trying to generate g g -> 4 lep +0,1,2 jet events using MadGraph+Pythia. To do this, I have to generate each sample individually with MadGraph and run it through Pythia with CKKW-L merging settings applied. I then intend to use them together after proper normalization.

First I generate the lhe events with the following additional settings apart from the standard ones+ mmnl>180:

0 = ickkw
0.0 = drjj
30 = ktdurham
0.4 = parameter

After this, I setup the Pythia card. You can find this and the entire run directory here: https://drive.google.com/drive/folders/1NpI0dlPuhcdSwgHE_P8mpmS3aiM7yhn2?usp=sharing

However as you may see In the log, even though it says that CKKW-L merging is on, I am not getting any vetoed events and the final sample contain any number of jets (3,4,..) even if I set I set nJetMax=1 or 2. I have also set TMS cut to 40.0 and it still doesn't reject any events and I end up getting the same cross section after merging and showering that I got for the initial MadGraph run.

Can you please take a look for what I am doing wrong?

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
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Last query:
2020-07-01
Last reply:
2020-07-01

Hi,

If you have an issue with pythia8, you should contact Pythia8 author.

> he final sample contain any number of jets (3,4,..) even if I set I set nJetMax=1 or 2.

This is normal this parameter indicates to pythia your highest multiplicity sample generated with MG5aMC, such that such sample is handle in a different way (since you do not have double counting with higher sample).

> g g -> 4 lep +0,1,2 jet

Why gluon in the initial state? this is likely to create issue for the matching/merging since you do not include all flavor combination for the initial state

Cheers,

Olivier

Jay Sandesara (jaysandesara) said : #2

Thanks, I will give it a try with full flavor initial states with filters on.

I have one question that might be related to how I am generating events in MadGraph. After the Pythia run I get the following warning:

Warning in Merging::mergeProcessCKKWL: No clusterings found. History incomplete.

Is this related to MadGraph generation. Should I be setting clusinfo=True for this to error to go away?

Can you help with this problem?

Provide an answer of your own, or ask Jay Sandesara for more information if necessary.

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