# interference ZZjj sample with decay

Asked by Congqiao Li on 2020-02-06

Dear experts,

I am trying to generate QCD-EWK interference sample of ZZjj process, with Z decaying to dileptons. The corresponding QCD and EWK processes are
(QCD) generate p p > z z j j QCD=99 QED=2, z > l+ l-
(EWK) generate p p > z z j j QCD=0 QED=4, z > l+ l-
So the interference process would naturally be
generate p p > z z j j QCD^2==2, z > l+ l-

But this gives an error that "Decay processes cannot specify squared orders constraints."
Therefore I was wondering if there are other workarounds here.
Possible solutions might include
1) generate p p > z > l+ l+ l- l- j j QCD^2==2
2) generate p p > l+ l+ l- l- j j / a QCD^2==2

But they are both not very ideal-- the first case may include dilepton coming from a photon, while the second case excludes every possible photon which is not fully necessary.

Would there be any other solutions to produce this sample? Many thanks for your suggestions in advance.

Best,
Congqiao

## Question information

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Solved by:
Olivier Mattelaer
Solved:
2020-02-07
Last query:
2020-02-07
2020-02-07
 Olivier Mattelaer (olivier-mattelaer) said on 2020-02-06: #1

Hi.

No real solution here.
I would go with using some external code to decay the Z but I'm not sure which one will do this correctly

Cheers,

Olivier

> On 7 Feb 2020, at 00:14, Congqiao Li <email address hidden> wrote:
>
> New question #688566 on MadGraph5_aMC@NLO:
>
> Dear experts,
>
> I am trying to generate QCD-EWK interference sample of ZZjj process, with Z decaying to dileptons. The corresponding QCD and EWK processes are
> (QCD) generate p p > z z j j QCD=99 QED=2, z > l+ l-
> (EWK) generate p p > z z j j QCD=0 QED=4, z > l+ l-
> So the interference process would naturally be
> generate p p > z z j j QCD^2==2, z > l+ l-
>
> But this gives an error that "Decay processes cannot specify squared orders constraints."
> Therefore I was wondering if there are other workarounds here.
> Possible solutions might include
> 1) generate p p > z > l+ l+ l- l- j j QCD^2==2
> 2) generate p p > l+ l+ l- l- j j / a QCD^2==2
>
> But they are both not very ideal-- the first case may include dilepton coming from a photon, while the second case excludes every possible photon which is not fully necessary.
>
> Would there be any other solutions to produce this sample? Many thanks for your suggestions in advance.
>
> Best,
> Congqiao
>
> --

 Congqiao Li (colizz) said on 2020-02-07: #2

Hi Oliver,

Just would like to ask for another possibility. I noticed that for loop process there provides a method to filter user-specified diagrams [1].
Would it be possible also to select the born diagrams, so that we might use the choice (1) above, with some filter applied?

Many thanks!

 Olivier Mattelaer (olivier-mattelaer) said on 2020-02-07: #3

Hi,

We also offer diagram filtering method at tree-level:

But in the case of interference computation this might not be that trivial actually.

Cheers,

Olivier

 Congqiao Li (colizz) said on 2020-02-07: #4

I see. Thank you so much!

 Congqiao Li (colizz) said on 2020-02-07: #5

Thanks Olivier Mattelaer, that solved my question.