MadGraph5_aMC@NLO

cross section calculations

Asked by Sihyun Jeon

Hi MG team,

I am trying to generate WW diboson sample by following command line

(1)generate p p > w+ w-

I did not require any more decays from w boson.

As far as I know,

(2)generate p p > z > w+ w-

only generates z mediated s channel w+ w- decays.

So I thought cross section from (1) should be bigger than (2) since (1) includes p p > a > w+ w- and t-channel.

However, (1) is about 70 pb and (2) is about 300 pb.

Is this some mistake I made? I don't understand why the result is like this.
(I haven't changed very much from the default runcard)

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
Last query:
Last reply:
Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

This is because the two diagrams have negative interference.
It actually does not make sense to request only (2) in this case.
This is why I strongly discourage this syntax in my tutorial.

Cheers,

Olivier

> On 21 Sep 2017, at 10:12, Sihyun Jeon <email address hidden> wrote:
>
> New question #658434 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/658434
>
> Hi MG team,
>
> I am trying to generate WW diboson sample by following command line
>
> (1)generate p p > w+ w-
>
> I did not require any more decays from w boson.
>
> As far as I know,
>
> (2)generate p p > z > w+ w-
>
> only generates z mediated s channel w+ w- decays.
>
>
>
> So I thought cross section from (1) should be bigger than (2) since (1) includes p p > a > w+ w- and t-channel.
>
> However, (1) is about 70 pb and (2) is about 300 pb.
>
>
> Is this some mistake I made? I don't understand why the result is like this.
> (I haven't changed very much from the default runcard)
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Sihyun Jeon (shjeon) said : 		#2

Thanks Olivier Mattelaer, that solved my question.