Generation of A/H, including interference with the SM, at NLO

Asked by Yoav Afik

Dear Experts,

I have a question regarding the generation of p p > t t~ with A/H at NLO.
I was wondering if it's possible to generate the signal+interference (S+I) part separately from the SM background (B) at NLO.
I was following the model at:
http://feynrules.irmp.ucl.ac.be/wiki/AHttbarNLO

In case it is possible, I would appreciate if you can let me know what is the correct command. I think it should be something like:
generate p p > t t~ QCD=2 QED=1 EFT=1 [QCD] EFT^2 > 0
But I would like to confirm.

Best,

Yoav.

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Olivier Mattelaer (olivier-mattelaer) said :
#1

Hi,

I do not know the model, neither which interference term you want to look at.
but indeed for interference you need to use the syntax
A^2==X
The "^2" means that the restriction applies at the diagram square level and not at the diagram level.
"==" select a given value for that parameter.

where A is either QCD,QED for the sm, and can be anything for the BSM part.
The value of X is also model dependent for EFT many model count the power in the EFT scale
and in that case you need
EFT^2==2
but some model will count the coupling and in that case you need
EFT^2==1
You need to check model documentation (or check with model author)

Now computing interference alone is NOT advise since
1) The phase-space integrator is not optimised for such type of mode (i.e. expect slow code and potentially wrong convergence of the integrator --in other words bias--)
2) In some cases, you can not use such sample of events as starting point of the parton-shower (and I doubt that this is tested at NLO --we do for sure at LO--)

So be very carefull (i.e. run many validation for such type of run)

Cheers,

Olivier

> On 10 Nov 2021, at 15:30, Yoav Afik <email address hidden> wrote:
>
> New question #699425 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/699425
>
> Dear Experts,
>
> I have a question regarding the generation of p p > t t~ with A/H at NLO.
> I was wondering if it's possible to generate the signal+interference (S+I) part separately from the SM background (B) at NLO.
> I was following the model at:
> http://feynrules.irmp.ucl.ac.be/wiki/AHttbarNLO
>
> In case it is possible, I would appreciate if you can let me know what is the correct command. I think it should be something like:
> generate p p > t t~ QCD=2 QED=1 EFT=1 [QCD] EFT^2 > 0
> But I would like to confirm.
>
> Best,
>
> Yoav.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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Yoav Afik (yoavafik) said :
#2

Hi Olivier,

Thanks for the feedback.
In the case I noted there is an extra scalar or pseudo-scalar (A/H) which couples to top quarks. Therefore, for t t~ production there are in general two terms:
1. Interference term of the A/H with the SM.
2. A "pure resonance" production of t t~ via A/H.

I understand from your response it's not recommended to generate 1 alone, but now I wonder if it would be OK to generate 1+2 together.

Best,

Yoav.

Revision history for this message
Yoav Afik (yoavafik) said :
#3

Hi Olivier,

The is a kind reminder I'm still waiting for your response.

Best,

Yoav.

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said :
#4

It is certainly less problematic.
Now if the interference are larger than the resonance, you actually do not solve the problem per say.

Cheers,

Olivier

Revision history for this message
Yoav Afik (yoavafik) said :
#5

Thanks Olivier!

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