3-body decay contribution missing in the param_card

Asked by Matt on 2018-01-02

Dear Madgraph staff,

I am dealing with a model containing heavy quarks and interacting with SM particles with both gauge interactions (mediated by the SM vector bosons) and four-fermion contact interactions - six dimensional operator - that I implemented with Feynrules by defining an auxiliary gauge boson with very high mass and by imposing its propagator not to have momentum dependence (i.e. ~ 1/Maux^2).
To calculate the widths of these heavy quarks I set their widths to the value “Auto” as usual, but anyway, after the event generation I see only the two bodies contribution in the updated param_card, even if also the 3 bodies channels are expected to be relevant.
In fact by prompting “compute_width Heavy_quark —body_decay=3” I also see the 3 bodies channels with comparable partial widths to the 2 bodies case.
Is this something I should expect?

Best,
Matt

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2018-01-03
Last query:
2018-01-03
Last reply:
2018-01-02

Hi,

I guess that one of the estimator under estimate the contribution. This is the first time that we observe such behaviour so far.
We did not have any theoretical proof that our two estimator were always over-estimating the contribution.
So looks like you face a case where it is not the case.
I would need to have the model to be able to investigate and try to understand why we face such issue for such model (and then see if it is possible to improve something in this case)

Cheers,

Olivier

> On 2 Jan 2018, at 16:43, Matt <email address hidden> wrote:
>
> New question #662492 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/662492
>
> Dear Madgraph staff,
>
> I am dealing with a model containing heavy quarks and interacting with SM particles with both gauge interactions (mediated by the SM vector bosons) and four-fermion contact interactions - six dimensional operator - that I implemented with Feynrules by defining an auxiliary gauge boson with very high mass and by imposing its propagator not to have momentum dependence (i.e. ~ 1/Maux^2).
> To calculate the widths of these heavy quarks I set their widths to the value “Auto” as usual, but anyway, after the event generation I see only the two bodies contribution in the updated param_card, even if also the 3 bodies channels are expected to be relevant.
> In fact by prompting “compute_width Heavy_quark —body_decay=3” I also see the 3 bodies channels with comparable partial widths to the 2 bodies case.
> Is this something I should expect?
>
> Best,
> Matt
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Matt (elvin.j) said : #2

Hi,

thank you for the answer. I've send you the model to your email.

Cheers,
Matt

Matt (elvin.j) said : #3

Thanks Olivier Mattelaer, that solved my question.