MadGraph5_aMC@NLO

pp -> hh -> 4b generation with Madgraph 2.3.0

Asked by Biagio Di Micco

Hi,
I'd like to generate the process:

p p > h h > b b~ b b~ with Madgraph 2.3.0 but when I type:

generate p p > h h > b b~ b b~ [QCD]

I get only pp -> h -> 4b.
I also tried with:
generate p p > (h > b b~)(h > b b ~) [QCD]
without success. How can I generate such process?

Thanks,
  Biagio

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
Last query:
Last reply:
Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

I guess that the correct way is to do:
generate g g > h h [QCD]
and then use MadSpin to decay the h in b b~
to have it work, you need to use the option
set spinmode=none in the madspin_card.dat

You can look at the arXiv:1507.00020 for more details on how to handle loop induced processes.

Cheers,

Olivier

On 26 Aug 2015, at 19:41, Biagio Di Micco <email address hidden> wrote:

> New question #270811 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/270811
>
> Hi,
> I'd like to generate the process:
>
> p p > h h > b b~ b b~ with Madgraph 2.3.0 but when I type:
>
> generate p p > h h > b b~ b b~ [QCD]
>
> I get only pp -> h -> 4b.
> I also tried with:
> generate p p > (h > b b~)(h > b b ~) [QCD]
> without success. How can I generate such process?
>
> Thanks,
> Biagio
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Biagio Di Micco (biagio-di-micco) said : 		#2

Hi Olivier,
would this be equivalent to the generation of the full process as above?
I was thinking that there could be problems due to the presence of identical particles in the final state coming from two Higgs boson propagators.

Cheers,
  Biagio

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

Hi Biago,

Clearly the syntax are not equivalent.

generate p p > h > b b~ b b~ [QCD]
is a NLO computation (tree-level + virtual + real contribution)
while
generate g g > h h [QCD]
is a LO process (a loop-induced one)

Those are completely different kind of process with different physics.
If you want the Di-higgs contribution to the process with each of the Higgs decaying to b.
then the second syntax is the correct one (and the only possible way to generate di-higgs in MG5aMC so far —at least i do not see any other—)
For the decay of the Higgs, you can on the other hand decay it independently of MadSpin, by using your favorite parton-shower.
But we do not have any way to have the full 2>4 loop-induced in MG5aMC so far.

Cheers,

Olivier

On 26 Aug 2015, at 23:07, Biagio Di Micco <email address hidden> wrote:

> Question #270811 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/270811
>
> Biagio Di Micco posted a new comment:
> Hi Olivier,
> would this be equivalent to the generation of the full process as above?
> I was thinking that there could be problems due to the presence of identical particles in the final state coming from two Higgs boson propagators.
>
> Cheers,
> Biagio
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Biagio Di Micco (biagio-di-micco) said : 		#4

Thanks Olivier,
I see. My concern was more the handling of identical particle in the final state than the QCD order.
I guess we should have for hh -> bb~ bb~ the same problem we have for
h -> ZZ -> e+e-e+e- compared to h ->ZZ->e+e-mu+mu-.
If I am correct, with this approach it is like to simulate hh -> bb~ cc~.
I wanted to understand if with Madgraph we could evaluate the impact of this approximation.
But I understand that this is still not possible.
Thanks for the answer.

Revision history for this message
Biagio Di Micco (biagio-di-micco) said : 		#5

Thanks Olivier Mattelaer, that solved my question.