Matching and Merging in madgraph

Hi,

I would not include the process with:
add process p p > y1 w+ , y1 > u u~
add process p p > y1 w+ , y1 > d d~
add process p p > y1 w+ , y1 > xm xm
add process p p > y1 z , y1 > u u~
add process p p > y1 z , y1 > d d~
add process p p > y1 z , y1 > xm xm
add process p p > y1 a , y1 > u u~
add process p p > y1 a , y1 > d d~
add process p p > y1 a , y1 > xm xm

in this computation since they are not QCD related.
Now for the rest, I would expect that this can be scale related what is the theoretical uncertainty on those numbers?
Did you set ptj and mmjj to 30 when setting ickkw=0? you need to set those value to have a fair comparison in this case.

Cheers,

Olivier

Hi Olivier,

Yes I did set the ptj and mmjj cut to 30 while setting ickkw=0, still my cross-section is less than ickkw=1 case.

>Now for the rest, I would expect that this can be scale related what is the theoretical uncertainty on those numbers?
By the numbers do you mean the scale? I don't quite understand this.

Cheers,
Prashant

Hi Olivier,

I was going through the run of the events, at the end of Pythia shower i get an output like this

Cross-section : 17.2 +- 0.05501 pb
    Nb of events : 10000
    Pythia8 merged cross-sections are:
     > Merging scale = 30 : 8.315 +/- 0.03 [pb]
     > Merging scale = 45 : 8.3546 +/- 0.03 [pb]
     > Merging scale = 60 : 8.3408 +/- 0.03 [pb]
    Notice that because Systematics computation is turned on, the merging did not veto events but modified their weights instead.
    The resulting hepmc/stdhep file should therefore be use with those weights

What does the cross-section 17pb signify ?Is it the total inclusive cross-section for the process or the matched one? I am a bit confused about this.

Thanks,
Prashant

Hi Olivier,

For the above comment I forgot to specify that i have set ickkw=1 and set xqcut to 15 and qcut to 30.

Cheers,
Prashant

Hi,

Yes 17.2 is the sum of the individual cross-section of each multiplicity independently.
Those numbers lack the inclusion of the Sudakov form factor which will make each multiplicity exclusive and remove the double counting. Such Sudakov is performed by Pythia8 via a veto method. And this is why the cross-section after pythia is smaller.

The physical cross-section is the one after pythia8.

Cheers,

Olivier

Dear Olivier,

Thanks a lot for the answer.I still have one small question ,the hepmc file that is generated at the end of the run, does it contain the merged cross-sections? I am trying to run these hepmc files in Rivet-3.1.0 analyses and i see that the generated cross-section is 17.2pb which is not the merged one , so how can i make sure that the physical cross-section after pythia shower is included in my hepmc file.

Thanks,
Prashant

You need to use the weight associated to each event within the analysis otherwise the cross-section (and observables) will be wrong.

Cheers,

Olivier

So can i do this at the level of madgraph or do i need to implement it in Rivet?And where do i get the weight associated to each event?

Cheers,
Prashant

They are inside the hepmc file, Rivet need to take that into account.

Cheers,

Olivier

> On 14 Aug 2020, at 16:10, prashant sundaram <email address hidden> wrote:
>
> Question #692330 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/692330
>
> prashant sundaram posted a new comment:
> So can i do this at the level of madgraph or do i need to implement it
> in Rivet?And where do i get the weight associated to each event?
>
> Cheers,
> Prashant
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.