reweight of aMC@NLO events

Asked by Florian Lyonnet

Hi,

I am running some parton level event with aMC@NLO and I have the following question :

In the run_card.dat file I set the number of unweighted events to a given value e.g. 10 000 and when I look in the .lhe.gz file for each event there is a tag <rwgt>. What is this tag for and what does is correspond to ? Are the events really unweighted ?

Thanks a lot for your help.

Cheers,

F.

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MadGraph5_aMC@NLO Edit question
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Solved by:
Stefano Frixione
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Best Stefano Frixione (stefano-frixione) said :
#1

Hi,
yes, the events are unwweighted, as you can see by looking at the third entry
in the line that follows the <event> tag in the LHE file (such entry must be a
constant *up to the sign* in the whole file).
The tag <rwgt> will allow one to compute scale and PDF uncertainties through
reweighting in an exact manner, without the need to re-run. Please check the
aMC@NLO tutorial at:
 https://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=212260
(slides 30 and 31).
Regards, Stefano.

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Florian Lyonnet (dibus2) said :
#2

Thank you for your answer.

Best,

F.

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Florian Lyonnet (dibus2) said :
#3

Thanks Stefano Frixione, that solved my question.