Generating WW>Z via EVA approximation

Hi,

If you look at our paper 2111.02442 <https://arxiv.org/abs/2111.02442> (where we implemented and validated the EVA case)
We clearly stated condtions required in order to have EVA as a good approximation.
The main point one is that sqrt(shat) should be larger than 1 TeV.
So for ww>z it does not make sense to use EVA.

After that you are right that we keep both the mass of the W and the Z meaning that this process is not possible.
Now it would be quite weird to remove the mass of the W without removing the mass of the Z (but if you remove both, you will have again kinematical issue.

Cheers,

Olivier

> On 17 May 2024, at 18:20, Hannes Jung <email address hidden> wrote:
>
> New question #815803 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/815803
>
> Hello
>
> I would like to generate a VBF process ww > z via eva approximation (with the aim to do the same for pp processes, once we have the w pdfs inside lhapdf).
> When trying to generate, I get an error:
> ----------------
> Survey return zero cross section.
> Typical reasons are the following:
> 1) A massive s-channel particle has a width set to zero.
> 2) The pdf are zero for at least one of the initial state particles
> or you are using maxjetflavor=4 for initial state b:s.
> 3) The cuts are too strong.
> Please check/correct your param_card and/or your run_card.
> ----------------
> Of course in the process, the w should be virtual, in order to produce the 2->1 process. Is this possible, or are the w's always treated as quasi real, and such a process in not possible kinematically ? Can one treat the w as quasi massless in such an approximation ?
>
> Thanks a lot.
> Best
> Hannes
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

thanks a lot for your answer.
Would on the other hand, a process like the following be reasonable:

generate w+ w- > e+ e- /ve aEW=4

It gives the diagram, I am interested, and it runs (since here the Z is no longer on-mass).

Thanks a lot
Best
Hannes

Hi,

Did you check shat distributions?
I would suggest to ensure that it is not allowed to be too soft:
You can do that via the variable dsqrt_shat in the run_card
(I would suggest to put that value at 1000= 1TeV)

Cheers,

Olivier

> On 18 May 2024, at 06:40, Hannes Jung <email address hidden> wrote:
>
> Question #815803 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/815803
>
> Status: Answered => Open
>
> Hannes Jung is still having a problem:
> Hi Olivier,
>
> thanks a lot for your answer.
> Would on the other hand, a process like the following be reasonable:
>
> generate w+ w- > e+ e- /ve aEW=4
>
> It gives the diagram, I am interested, and it runs (since here the Z is
> no longer on-mass).
>
> Thanks a lot
> Best
> Hannes
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thanks a lot, this is good.
Best
Hannes