Two loops with loop_qcd_qed_sm model

Asked by Duarte Azevedo on 2017-09-14

Hello,

My MG5_aMC experience is moderate and I'm not sure if I can generate the following process:

p p > h , h > a a , (a > b b~ , a > a )

with the loop_qcd_qed_sm model to take care of the loop of H to gamma gamma and possibly add the loop of quarks from the gluon fusion for the H creation. I wanted to do it this way because I want to create samples where I change the coupling Hbb, and compare with events h > b~ b , (b > b a , b > b) where I change the coupling as well.

Is it possible? I'm also having problems just trying to generate p p > h, what could it be?

Best,
Duarte

Question information

Language:
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Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
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Solved by:
Olivier Mattelaer
Solved:
2017-09-15
Last query:
2017-09-15
Last reply:
2017-09-14

Hi,

Since you request for an on-shell Higgs (and without any pt), my first suggestion would be to use the infinite top mass limit effective operator to contract the loop:

import model heft
generate p p > h, h > a > b b~ a

If you want to compute the effect coming from the loop then you should
Follow the example given in arXiv:1507.00020<http://arXiv.org/abs/arXiv:1507.00020>
Where it is explained how
The generation g g > h followed by the decay h > a a is possible when computing the full loop.
In short, you have to use madspin in the special mode introduced in the paper.

In your case, you have to do the decay of the Higgs like
decay h > a > b b~ a [noborn=QED]

Cheers,

Olivier

On 14 Sep 2017, at 15:58, Duarte Azevedo <<email address hidden><mailto:<email address hidden>>> wrote:

New question #658015 on MadGraph5_aMC@NLO:
https://answers.launchpad.net/mg5amcnlo/+question/658015

Hello,

My MG5_aMC experience is moderate and I'm not sure if I can generate the following process:

p p > h , h > a a , (a > b b~ , a > a )

with the loop_qcd_qed_sm model to take care of the loop of H to gamma gamma and possibly add the loop of quarks from the gluon fusion for the H creation. I wanted to do it this way because I want to create samples where I change the coupling Hbb, and compare with events h > b~ b , (b > b a , b > b) where I change the coupling as well.

Is it possible? I'm also having problems just trying to generate p p > h, what could it be?

Best,
Duarte

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Duarte Azevedo (yuhuanknot) said : #2

Thanks Olivier Mattelaer, that solved my question.