MadGraph5_aMC@NLO

single top t-channel production and decay

Asked by Nicolas Chanon

Dear experts,
I am trying to generate single top t-channel production and decay.

For production only, I would do something like:
import model sm-no_b_mass
generate p p > t j $$ w+ w-

For including also the decay, without setting a narrow-width for the top:
import model sm-no_b_mass
generate p p > b l+ vl j $$w+ w- QCD=0 QED=4

It seems not to be the correct way, I obtain very small cross section with the latter, probably linked to the use of $$w+ w- forbidding diagrams in the decay.
Another way I see is to force to have a b-quark in the initial state, but it seems to miss some of the diagrams.
Which syntax is best suited?

Cheers,
Nicolas

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

I do not know enough what kind of diagram you want/do not want in order to help you here.
Indeed setting $$ w+ w- is bad here since this will forbid also the W present in the decay.

> Another way I see is to force to have a b-quark in the initial state, but it seems to miss some of the diagrams.

Which diagrams that you want is missing with that syntax?

Cheers,

Olivier

> On 17 Jan 2020, at 10:45, Nicolas Chanon <email address hidden> wrote:
>
> generate p p > b l+ vl j $$w+ w- QCD=0 QED=4

Revision history for this message
Nicolas Chanon (nicolaschanon) said : 		#2

Hi Olivier,

For the following three runs I am using
import model sm-no_b_mass

So with $$ ww syntax:
generate p p > b l+ vl j $$ w+ w- QCD=0 QED=4
add process p p > b~ l- vl~ j $$ w+ w- QCD=0 QED=4
0.00376873 pb

With narrow width:
generate p p > t j $$ w+ w- , t > b l+ vl
add process p p > t~ j $$ w+ w- , t~ > b~ l- vl~
38.627 pb

And with b at the initial state:
generate p b > t j , t > b l+ vl
add process b p > t j, t > b l+ vl
add process p b~ > t~ j , t~ > b~ l- vl~
add process b~ p > t~ j , t~ > b~ l- vl~
31.946 pb

I am not sure what I might be missing, any idea?

Cheers,
Nicolas

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#3

Hi Nicolas,

> I am not sure what I might be missing, any idea?

What is your question (in other word what do you think you are missing)

Cheers,

Olivier

> On 6 Feb 2020, at 15:28, Nicolas Chanon <email address hidden> wrote:
>
> Question #688066 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/688066
>
> Status: Answered => Open
>
> Nicolas Chanon is still having a problem:
> Hi Olivier,
>
> For the following three runs I am using
> import model sm-no_b_mass
>
> So with $$ ww syntax:
> generate p p > b l+ vl j $$ w+ w- QCD=0 QED=4
> add process p p > b~ l- vl~ j $$ w+ w- QCD=0 QED=4
> 0.00376873 pb
>
> With narrow width:
> generate p p > t j $$ w+ w- , t > b l+ vl
> add process p p > t~ j $$ w+ w- , t~ > b~ l- vl~
> 38.627 pb
>
> And with b at the initial state:
> generate p b > t j , t > b l+ vl
> add process b p > t j, t > b l+ vl
> add process p b~ > t~ j , t~ > b~ l- vl~
> add process b~ p > t~ j , t~ > b~ l- vl~
> 31.946 pb
>
> I am not sure what I might be missing, any idea?
>
> Cheers,
> Nicolas
>
> --
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