MadGraph5_aMC@NLO

Analyzing NLO unweighted events

Asked by Mamutjan

Hi,

I wanted to calculate a NLO process on MadGraph and analyze the event file.

I know that in the NLO case we can use the fixed-order-analysis code to get the histograms,
 but I am wondering if we can generate the unweighted NLO events and analyze it via ROOT
 just as what we can do for any LO case where we could generate the unweighted event file and analyze the event file.

How can we generate unweighted NLO events that could be analyzed via ROOT?

Thanks.

Regards,
Mamut

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

At fixed order NLO, the weight of the events are not bounded and it is therefore impossible to generate un-weighted sample.
If you decide to record those weighted sample, you should technically not create LHE file, since those sample are NOT suitable for using a parton-shower (due to the double counting with the parton-shower)

If you are non the non fix-order mode, then both problem are automatically resolved.
Your weights are bounded (so you can generate un-weighted sample) and you do not have double coutinting anymore.
In that mode, we do have a LHE file but it is now parton-shower specific (and the distribution are NOT physical before the parton-shower.

Cheeers,

Olivier

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