MadGraph5_aMC@NLO

same particle with different decay

Asked by teddym

Hi
      I would to calculate the process p p > t t h, get one t decay hadron the other leptonic
    so I define tt = t t~, bb = b b~, ll = l- l+, vv = vl vl~, ww = w- w+
   and generate p p > tt tt h QED=99 QCD=99, ( tt > bb ww, ww > j j ), ( tt > bb ww, ww > ll vv), h > b b~
    cross section: 37.25fb

   Further I check the process:
        generate p p > t t~ h QED=99 QCD=99, ( t > b w+, w+ > j j ), ( t~ > b~ w-, w- > l- vl~ ), h > b b~
   add process p p > t t~ h QED=99 QCD=99, ( t > b w+, w+ > l+ vl ), ( t~ > b~ w-, w- > j j ), h > b b~
   cross section: 74.42fb

 It's almost 2times the first case.
 Do I use wrong syntax in the first case, so the MG5 only let the first tt decay hadronic and the second tt decay leptonic?

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teddym (niepanchongsheng) said : 		#1

And Further both w-boson are on-shell , right? and the higgs is also on-shell right?

Thanks very much!

Teddy

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#2

Hi Teddy,

Indeed we never think about such case for the decay syntax. and indeed if you look at the diagrams, the top is always associate to the hadronic decay.

> And Further both w-boson are on-shell , right? and the higgs is also
> on-shell right?

Yes they are. This means that the invariant mass of that particles is on shell up to N times the value of the associated width.
The value of N is a parameter that you can adjust in the run_card (this is bwcutoff)

Cheers,

Olivier

On Nov 21, 2013, at 3:21 AM, teddym <email address hidden> wrote:

> Question #239570 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/239570
>
> teddym gave more information on the question:
> And Further both w-boson are on-shell , right? and the higgs is also
> on-shell right?
>
>
> Thanks very much!
>
> Teddy
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Revision history for this message
teddym (niepanchongsheng) said : 		#3

Hi Olivier
    Thanks for your answers
   Further, if I got two Z-boson in one process, and I want to have one decay hadronic and the other decay leptonic(no matter which one), such as
    p p > b b~ z z, z > j j, z > l- l+
   is this syntax right? or I need to add process p p > b b~ z z, z > l- l+, z > j j ?

For the bwcutoff, if I set N to be very large, does this means that it would involve almost off-shell particle, such as in the above process, if I set N=1000, the z-boson may be off-shell?

Thanks very much

Teddy

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#4

Hi teddym,

> Further, if I got two Z-boson in one process, and I want to have one decay hadronic and the other decay leptonic(no matter which one), such as
> p p > b b~ z z, z > j j, z > l- l+
> is this syntax right? or I need to add process p p > b b~ z z, z > l- l+, z > j j ?

the syntax is right, you don't have to add the second one.

> For the bwcutoff, if I set N to be very large, does this means that it
> would involve almost off-shell particle, such as in the above process,
> if I set N=1000, the z-boson may be off-shell?

Then yes, you include off-shell Z boson.
Such off-shell contribution have then very huge systematical (theoretical) error since you completely forget about the photon interference.

Cheers,

Olivier

On Nov 21, 2013, at 2:26 PM, teddym <email address hidden> wrote:

> Question #239570 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/239570
>
> Status: Answered => Open
>
> teddym is still having a problem:
> Hi Olivier
> Thanks for your answers
> Further, if I got two Z-boson in one process, and I want to have one decay hadronic and the other decay leptonic(no matter which one), such as
> p p > b b~ z z, z > j j, z > l- l+
> is this syntax right? or I need to add process p p > b b~ z z, z > l- l+, z > j j ?
>
> For the bwcutoff, if I set N to be very large, does this means that it
> would involve almost off-shell particle, such as in the above process,
> if I set N=1000, the z-boson may be off-shell?
>
> Thanks very much
>
> Teddy
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

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