MadGraph5_aMC@NLO

Set ptj or ptb for pp>ttbb processes

Asked by Mar

Hello, I'm generating the process pp>tt~bb~ within the standard model. I'm using "define p = g u u~ c c~ d d~ s s~ b b~". I was changing the transverse momentum of the jets and the bottoms from the run_card.dat. I was expecting the result depends on the ptb, because there are no jets in the process. But what I found is that the results changes with a change in ptj, but if ptb<ptj, then MadGrapgh doesn't care for the ptb, for it gives the same result if ptj is not changed but ptb is.

eg, if ptj=ptb=20 and then I change it to ptj=20 and ptb=10, it gives exactly the same results.

Could it be that MadGraph is including b in the jet so it takes the maximun value between ptj and ptb for pt?

In the same process, if I left everything invariant, but I set
etaj=5
etab=5

and in the next run

etaj=5
etab=2.5

again, the results are exactly the same.

Cheers,

Mar

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Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

This is actually related to another parameter of the card:
maxjetflavor

if that parameter is on 5 then all b-quark have the same cut as the jet and in that case all b related cut are not used in the code.
If that parameter is on 4, then the cut related to the b (ptb/etab/…) are used for b-quark parton
if that parameter is on 3 then the cut related to the b (ptb/etab/…) are used for b and c quark parton

The default run_card written at “output” stage has a value of this parameter which depends on the model that you use.
If your model defines a mass for the b-quark then the default value in the run_card will be 4
Otherwise if the model forces a massless b, then the default value in the run_card will be 5.

This is done in order to have the more coherent behavior (if the b is massless, you can not distinguish it from the other jets)

Cheers,

Olivier

> On Apr 18, 2016, at 16:22, Mar <email address hidden> wrote:
>
> New question #291345 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/291345
>
> Hello, I'm generating the process pp>tt~bb~ within the standard model. I'm using "define p = g u u~ c c~ d d~ s s~ b b~". I was changing the transverse momentum of the jets and the bottoms from the run_card.dat. I was expecting the result depends on the ptb, because there are no jets in the process. But what I found is that the results changes with a change in ptj, but if ptb<ptj, then MadGrapgh doesn't care for the ptb, for it gives the same result if ptj is not changed but ptb is.
>
> eg, if ptj=ptb=20 and then I change it to ptj=20 and ptb=10, it gives exactly the same results.
>
> Could it be that MadGraph is including b in the jet so it takes the maximun value between ptj and ptb for pt?
>
> In the same process, if I left everything invariant, but I set
> etaj=5
> etab=5
>
> and in the next run
>
> etaj=5
> etab=2.5
>
> again, the results are exactly the same.
>
> Cheers,
>
> Mar
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Mar (septembris-forest) said : 		#2

Thanks Olivier Mattelaer, that solved my question.