MadGraph5_aMC@NLO

96% veto rate for jet matching in BSM process

Asked by Nathan Mirman

Dear Experts,
I have generated a process which includes direct stop production and 0,1,2,3 ISR jets. When conducting MLM jet matching in Pythia, I get 95.5% events failing the fragmentation cuts. This is with xqcut = 20, qcut = 40.

In my (very limited) experience, I would expect roughly 70% events failing fragmentation cuts, as I've observed in SM ttbar+jets samples with essentially the same configuration that I'm currently using. So, the 95% failure rate that I'm getting now is a bit suspicious.

I was hoping that someone could advise me on whether or not this sounds like an issue, or where to look for a problem if one exists. I'm happy to provide more details, run outputs, etc.

Thank you very much,
Nathan

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Johan Alwall
Solved:
Last query:
Last reply:
Revision history for this message
Johan Alwall (johan-alwall) said : 		#1

Hello Nathan,

Did you generate the DJR plots (i.e., did you have MadAnalysis, td and Root installed on your computer when you ran the matching)? If so, I would recommend to look at those and check that they look smooth. Depending on the mass of the stop, 20 GeV is typically a too low xqcut scale - I would recommend perhaps 50, with QCUT at 70. I would suggest to run with this setting and compare cross sections and DJR plots between the two settings, to check that the results look reasonable.

All the best,
Johan

Revision history for this message
Nathan Mirman (nem46) said : 		#2

Dear Johan,
Thanks for pointing this out. I didn't originally make the DJR plots, but I was able to go back and do several test runs for my process. I limited the number of ISR jets to 2 in order to decrease computation time. It looks like the DJR plots look best at a scale of ~100 GeV, even with a light stop (200 GeV). Does this sound consistent with what you would expect?

Thank you very much,
Nathan

Revision history for this message
Best Johan Alwall (johan-alwall) said : 		#3

Hello Nathan,

The plots shouldn't vary too much for a QCUT scale from, say, 50 to 100 GeV. 100 GeV should be fine for the pt-ordered showers (which require higher matching scale than the virtuality-ordered ones).

All the best,
Johan

Revision history for this message
Nathan Mirman (nem46) said : 		#4

Thanks Johan Alwall, that solved my question.