MadGraph5_aMC@NLO

Weight in the Fixed_Order_Analysis files

Asked by Jerry

Hello,

I am using a root analysis file in the FixedOrderAnalysis folder in MG2.4.2 to write the weight ( wgts(1) ) and some additional quantities to a text file that I read out later using my own code to produce histograms. However, I cannot figure out what this weight is. I tried to sum the weights of all the phase space points, expecting that I would obtain the total cross section in pb that is returned by MadGraph at the end of the run. This seems, however, not to be the case.
Therefore I would like to ask you whether you could clarify how this weight is normalised.

Many thanks
Jerry

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Paolo Torrielli Edit question
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Paolo Torrielli (paolo-torrielli) said : 		#1

Dear Jerry,

those weights wgts(1) are associated to the value of the integrand in particular points
of the phase space.
In order to obtain the total cross section, each of them is multiplied by certain phase-space
-dependent factors that take into account the volume of the phase space associated with
each point and the fact that the points are not extracted flatly in the phase space; hence by
summing directly the weights you're not supposed to get the total rate.

Cheers.
Paolo

Revision history for this message
Jerry (jerry7) said : 		#2

Dear Paolo,

Thanks for the answer. Is there a possibility to see what this phase space dependent factors exactely look like? I took a look in the standard reference papaer of a MadGraph but could not find a clue there.

Cheers,
Jerry

Revision history for this message
Paolo Torrielli (paolo-torrielli) said : 		#3

Dear Jerry,

I don’t think this is easy, since it is deeply inside the core code that
performs the integration. You won’t find this information on the manuals.
I personally don’t know precisely what these factors are, probably Rikkert
(who’ll be back soon) could help more.

However, since all this plotting work is done consistently in an automatic
way in the root analyses provided with the code, I guess it would be simpler
to adapt one of the existing analyses to your needs.

Cheers,
Paolo

On 02 Sep 2016, at 13:32, Jerry <email address hidden> wrote:

> Question #374962 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/374962
>
> Status: Answered => Open
>
> Jerry is still having a problem:
> Dear Paolo,
>
> Thanks for the answer. Is there a possibility to see what this phase
> space dependent factors exactely look like? I took a look in the
> standard reference papaer of a MadGraph but could not find a clue there.
>
> Cheers,
> Jerry
>
> --
> You received this question notification because you are subscribed to
> the question.

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