# How to remove cartain diagrams in my process?

Asked by Qiji Xin on 2019-07-06

Hi,

I need to remove certain diagrams in my process but I am not sure how to.
There is a tutorial https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-15 but I am not sure how to apply that to my case. So could you please give me some help?

define p d
define j u
generate vm p > mu- mu- mu+ j
displace diagrams

(I am using this definition of p and j to make my question simple.)

Then in the "vm d" diagrams as displayed, how to remove diagrams 4, 5, and 12, which are a photon emited by the initial or final quark then split to a muon pair?

Thanks so much!

## Question information

Language:
English Edit question
Status:
For:
Assignee:
No assignee Edit question
Last query:
2019-07-06
2019-07-06
 Olivier Mattelaer (olivier-mattelaer) said on 2019-07-06: #1

Why keeping 11?
This should break gauge and lorentz invariance to keep it.

Cheers,

Olivier

> On 6 Jul 2019, at 05:47, Qiji Xin <email address hidden> wrote:
>
> New question #681820 on MadGraph5_aMC@NLO:
>
> Hi,
>
> I need to remove certain diagrams in my process but I am not sure how to.
> There is a tutorial https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/FAQ-General-15 but I am not sure how to apply that to my case. So could you please give me some help?
>
> define p d
> define j u
> generate vm p > mu- mu- mu+ j
> displace diagrams
>
> (I am using this definition of p and j to make my question simple.)
>
> Then in the "vm d" diagrams as displayed, how to remove diagrams 4, 5, and 12, which are a photon emited by the initial or final quark then split to a muon pair?
>
> Thanks so much!
>
> --

 Qiji Xin (xinqijisuper) said on 2019-07-06: #2

Dear Olivier,

Ah. Yes. 11 also should be removed.
So in the "vm d" diagrams as displayed, how to remove diagrams 4, 5, and 11, 12, which are a photon emited by the initial or final quark then split to a muon pair?

Thanks so much!

 Olivier Mattelaer (olivier-mattelaer) said on 2019-07-06: #3

Hi,

In this case, I would modify the model to remove the qq~a vertex from the model.

This will allow to use the "check" command to check if the result is still lorentz invariant.

Cheers,

Olivier

> On 6 Jul 2019, at 19:28, Qiji Xin <email address hidden> wrote:
>
> Question #681820 on MadGraph5_aMC@NLO changed:
>
>
> Qiji Xin is still having a problem:
> Dear Olivier,
>
> Ah. Yes. 11 also should be removed.
> So in the "vm d" diagrams as displayed, how to remove diagrams 4, 5, and 11, 12, which are a photon emited by the initial or final quark then split to a muon pair?
>
> Thanks so much!
>
> --

 Qiji Xin (xinqijisuper) said on 2019-07-06: #4

Dear Olivier,

Thanks.
Is there any way to simply use "/" "\$", etc. to remove qq~a vertex?
Or I have to turn to user_filter.py ?
And is there any literature that gives more details how to use user_filter.py ?
Thanks!

 Olivier Mattelaer (olivier-mattelaer) said on 2019-07-06: #5

Hi,

In this case, they are no dedicated syntax for that.
I would NOT use user_filter here. As said above, I would modify the UFO model and remove the associated interaction.
Concerning user_filter. No they are no documentation concerning this possibility (but the FAQ link that you refer above).

We try to discourage user to remove diagram, since this typically lead to a lot of issue (starting by breaking lorentz invariance)

Cheers,

Olivier