Di-Higgs decays to bb~ aa

Asked by Harshal Kulkarni

Hi,
     I want to generate the process p p > h h at the tree level and then decay the h h pair to h h > b b~ a a using MG5. (I have included the b and b~ quarks in the definition of p). I tried using the syntax p p > h h > b b~ a a, but this only generates the processes with at least one intermediate h in the s-channel, whereas I want to produce both the Higgs and then decay them further. How exactly do I do this?
    Also, if I want to generate the process p p > b b~ a a with no intermediate h h pair, is there a way to do this? I tried setting the mH (mass of the higgs to a very large value, so that the hh intermediate pairs are not produced. Is that alright?

Thanks,
Harshal

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

I would suggest to check the meaning of the two following syntax:
generate p p > h h, h > b b~, h > a a
and
generate p p > b b~ a a $ h

Which might fit (or maybe not) what you want to generate.

Cheers,

Olivier

> On 27 Jun 2021, at 14:01, Harshal Kulkarni <email address hidden> wrote:
>
> New question #697743 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/697743
>
> Hi,
> I want to generate the process p p > h h at the tree level and then decay the h h pair to h h > b b~ a a using MG5. (I have included the b and b~ quarks in the definition of p). I tried using the syntax p p > h h > b b~ a a, but this only generates the processes with at least one intermediate h in the s-channel, whereas I want to produce both the Higgs and then decay them further. How exactly do I do this?
> Also, if I want to generate the process p p > b b~ a a with no intermediate h h pair, is there a way to do this? I tried setting the mH (mass of the higgs to a very large value, so that the hh intermediate pairs are not produced. Is that alright?
>
> Thanks,
> Harshal
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Harshal Kulkarni (hck18ms056) said :
#2

For some reason, MG is not letting me run the process p p > h h, h > b b~ , h > a a. It shows the following error message:
Command "generate p p > h h, h > b b~, h > a a" interrupted with error:
NoDiagramException : No amplitudes generated from process Process: h > a a WEIGHTED=2. Please enter a valid process

And the 2nd process, which I think discards all the Feynman diagrams including the particle h, is also not working. The number of Feynman diagrams that I am getting for the process p p > b b~ a a $ h and p p > b b~ a a are exactly the same, and I can see a couple of diagrams which include the particle h as an intermediate particle.

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said :
#3

Hi,

> NoDiagramException : No amplitudes generated from process Process: h > a a WEIGHTED=2. Please enter a valid process

This depend of the model that you are use. Obviously in the SM, the Higgs does not comple to the photon and that interaction indeed does not exists. You need to have a model where this is added as an effective vertex. (like heft)

> And the 2nd process, which I think discards all the Feynman diagrams
> including the particle h, is also not working.

No this syntax does not discard the diagram, it discard the resonance region.
So this is normal that you have the same number of diagram.

Cheers,

Olivier

> On 27 Jun 2021, at 14:35, Harshal Kulkarni <email address hidden> wrote:
>
> Question #697743 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/697743
>
> Harshal Kulkarni posted a new comment:
> For some reason, MG is not letting me run the process p p > h h, h > b b~ , h > a a. It shows the following error message:
> Command "generate p p > h h, h > b b~, h > a a" interrupted with error:
> NoDiagramException : No amplitudes generated from process Process: h > a a WEIGHTED=2. Please enter a valid process
>
> And the 2nd process, which I think discards all the Feynman diagrams
> including the particle h, is also not working. The number of Feynman
> diagrams that I am getting for the process p p > b b~ a a $ h and p p >
> b b~ a a are exactly the same, and I can see a couple of diagrams which
> include the particle h as an intermediate particle.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Harshal Kulkarni (hck18ms056) said :
#4

Thanks.
Even if the higgs and photons don't couple in the SM, shouldn't there be triangle (fermionic) loop diagrams for the process h > a a? If yes, how to implement that? I tried something like g g > h h [QCD], h > a a [QCD], h > b b~ [QCD] and something similar, but still I am getting some errors.

Thanks, I misunderstood the meaning of the $ symbol with the / in the syntax.

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said :
#5

Hi,

> Even if the higgs and photons don't couple in the SM, shouldn't there be triangle (fermionic) loop diagrams for the process h > a a?

This is not a tree level computation anymore (obviously) and in your question you were mentioning tree-level.

> I tried something like g g > h h [QCD], h > a a [QCD], h > b b~ [QCD] and something similar, but still I am getting some errors.

This is not the same process as the one we discussed before (before we were discussing of b initial state not gluon.
For this one, the best solution is to do the same as for the single higgs production done in this paper:
1507.00020 <https://arxiv.org/abs/1507.00020>
i.e.
generate g g > h h [QCD]
and use madspin (in the heft model and in spinmode=none mode) for the decay of the Higgs.

Cheers,

Olivier

> On 27 Jun 2021, at 16:40, Harshal Kulkarni <email address hidden> wrote:
>
> Question #697743 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/697743
>
> Harshal Kulkarni posted a new comment:
> Thanks.
> Even if the higgs and photons don't couple in the SM, shouldn't there be triangle (fermionic) loop diagrams for the process h > a a? If yes, how to implement that? I tried something like g g > h h [QCD], h > a a [QCD], h > b b~ [QCD] and something similar, but still I am getting some errors.
>
> Thanks, I misunderstood the meaning of the $ symbol with the / in the
> syntax.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Harshal Kulkarni (hck18ms056) said (last edit ):
#6

I generated the process g g > h h [QCD] and imported the .lhe event file in madspin. I didn't understand what you meant by using madspin in the heft model. Can you please elaborate? (I am not able to import any model, using import model " " in madspin)

Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said (last edit ):
#7

Hi,

If you look at this page:
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/MadSpin#Fulllistofoptions

you will see that you can change the model for the decay part compare to the one used for the production.
This is what I was refering to, you can ask to add H> g g and/or h> a a as modeled within the heft model.

Cheers,

Olivier

and by the way here is the patch for have madspin executable python3 compatible;
https://bazaar.launchpad.net/~maddevelopers/mg5amcnlo/LTS_dev/revision/323

Revision history for this message
Harshal Kulkarni (hck18ms056) said :
#8

Thanks Olivier Mattelaer, that solved my question.