MadGraph5_aMC@NLO

Top decay at NLO-matched in the rest frame of the top

Asked by Andreas Papaefstathiou

I have been trying to generate the top quark decay at NLO in its rest frame via:

generate t > b w+ [QCD]

This works and I get the right diagrams etc., but it seems to disallow changing the fixed_order parameter to OFF for matched event generation via MC@NLO.

Since there are no warnings given, I was wondering if there's a serious technical reason why this is disallowed, and whether it would be possible to circumvent this.

Thanks,
Andreas

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Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Paolo Torrielli Edit question
Solved by:
Andreas Papaefstathiou
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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

I have not study that particular case, but the issue is likely that the Monte-Carlo counter-term and/or the event mapping are not able to handle such cases and therefore we can not correctly remove the double counting with the parton-shower in this case.

Cheers,

Olivier

PS: I assign this the Monte-Carlo counterterm expert if he wants to comment.

Revision history for this message
Paolo Torrielli (paolotorriell) said : 		#2

Hi Andreas!
I agree with Olivier, an issue is that subtracting soft radiation off the top
would need an MC counterterm for a massive initial state, which is currently
not implemented.
Best,
Paolo

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Andreas Papaefstathiou (apapaefs) said : 		#3

That makes sense, thanks very much!