Method to exclude duplicated processes

Asked by Sihyun Jeon

Dear Olivier,

I am trying to make WW NLO samples with same flavor lepton decays but wonder if what I am doing would make sense.

So I am doing like below
generate p p > e+ ve w- [QCD] -> [1]
add process p p > e- ve~ w+ [QCD] -> [2]

and in MadSpin
decay w- > e- ve~ -> [3]
decay w+ > e+ ve -> [4]

But this would be problematic when the "e+ ve" from [1] is from onshell W+ since it will give you duplicated contributions from [2] + [4]. Is my guess correct?

[1] + [3] will give you :
(1) onshell w+ & onshell w-
(2) offshell w+ & onshell w-

[2] + [4] will give you :
(3) onshell w+ & onshell w-
(4) onshell w+ & offshell w-

Due to (1) and (3), there is some double countings -> This is my understanding

If my understanding is correct I wonder if this would avoid the double counting issues
generate p p > e+ ve w- $$ w+ [QCD] -> [1]
add process p p > e- ve~ w+ [QCD] -> [2]

and in MadSpin
decay w- > e- ve~ -> [3]
decay w+ > e+ ve -> [4]

Then I expect that [1] would not allow onshell w+ production and thus give you
[1] + [3]
(1) offshell w+ & onshell w-

[2] + [4]
(2) onshell w+ & onshell w-
(3) onshell w+ & offshell w-

Would this be a correct way to remove duplicated onshell w+ and onshell w- contributions?

Regards,
Sihyun.

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Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said :
#1

Hi,

The answer is not trivial, the issue with the $$ syntax is that you might break gauge invariance of the theory.
I do not know if this is the case for this process.
You can do
check p p > e+ ve w- $$ w+, w- > e- ve~
and
check p p > e+ ve w- j $$ w+, w- > e- ve~

to check that.

Independently of that,
I would suggest to simply do
generate p p > e+ ve e- ve~ [QCD]

Cheers,

Olivier

> On 7 Oct 2021, at 14:45, Sihyun Jeon <email address hidden> wrote:
>
> New question #698999 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/698999
>
> Dear Olivier,
>
> I am trying to make WW NLO samples with same flavor lepton decays but wonder if what I am doing would make sense.
>
> So I am doing like below
> generate p p > e+ ve w- [QCD] -> [1]
> add process p p > e- ve~ w+ [QCD] -> [2]
>
> and in MadSpin
> decay w- > e- ve~ -> [3]
> decay w+ > e+ ve -> [4]
>
> But this would be problematic when the "e+ ve" from [1] is from onshell W+ since it will give you duplicated contributions from [2] + [4]. Is my guess correct?
>
> [1] + [3] will give you :
> (1) onshell w+ & onshell w-
> (2) offshell w+ & onshell w-
>
> [2] + [4] will give you :
> (3) onshell w+ & onshell w-
> (4) onshell w+ & offshell w-
>
> Due to (1) and (3), there is some double countings -> This is my understanding
>
>
> If my understanding is correct I wonder if this would avoid the double counting issues
> generate p p > e+ ve w- $$ w+ [QCD] -> [1]
> add process p p > e- ve~ w+ [QCD] -> [2]
>
> and in MadSpin
> decay w- > e- ve~ -> [3]
> decay w+ > e+ ve -> [4]
>
> Then I expect that [1] would not allow onshell w+ production and thus give you
> [1] + [3]
> (1) offshell w+ & onshell w-
>
> [2] + [4]
> (2) onshell w+ & onshell w-
> (3) onshell w+ & offshell w-
>
>
> Would this be a correct way to remove duplicated onshell w+ and onshell w- contributions?
>
> Regards,
> Sihyun.
>
> --
> 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.