MadGraph5_aMC@NLO

di-Higgs production and decay to bb~ and ZZ

Asked by Gavin

Hi!
I was trying to produce di higgs using p p > h h [noborn=QED]. The cross section was at around 14fb of this process. Then I wanted to make the 2 individual higgs decay to Z Z and b b~. I was trying to do it through madspin. But I could not do it successfully. The final errors are like:

Command "launch " interrupted with error:
NoDiagramException : No amplitudes generated from process Process: g/u/c/d/s/u~/c~/d~/s~ g/u/c/d/s/u~/c~/d~/s~ > h h WEIGHTED=8 @1. Please enter a valid process
Please report this bug on https://bugs.launchpad.net/mg5amcnlo

I also tried HEFT model but the cross section came ~O(10^-11 pb). If you guys have any idea of generating these kind of events, please help me.

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

It is possible with MadSpin.

But you have to use a (stupid) mode via the command
set spinmode none

As said above this mode is quite stupid since it does not include spin-correlation and fail to include off-shell effect as well.
SInce both effect are irrelevant in the case of the SM Higgs, it provides a quite accurate description.

Cheers,

Olivier

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Gavin (seeha) said : 		#2

Hi Olivier,

Thanks for this suggestion. But I have another confusion regarding the same thing. This might be very basic but I am still unable to find the actual problem.

After doing ./bin/madevent I was trying to compute widths of SM Higgs (width: 4.961126e-03) which did not match with the actual one and also the BR for h > b b~ came at around 8.677063e-01. I also tried to compute width of h with 3 and 4 body decay also (I don't know whether its right or not!!!), but then the width came with a larger value (~6e-03).

I used loop_qcd_qed_sm-full model to generate events (g g > h h).

Am I doing something wrong? Should I provide the decay width and BRs by hand in parameter card?

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

Hi,

The compute_widths command does not support loop-induced decay which is crucial for the HIggs decay
(in particular in two gluon which impacts the total width)

Otherwise three body decay are required for the Higgs since otherwise you miss the decay in two W/Z.
The 4 body should not contribute at all.

> Am I doing something wrong? Should I provide the decay width and BRs by
> hand in parameter card?

Yes that's the correct way for the Higgs.

Cheers,

Olivier

> On 2 Sep 2018, at 12:47, Gavin <email address hidden> wrote:
>
> Question #673205 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/673205
>
> Gavin posted a new comment:
> Hi Olivier,
>
> Thanks for this suggestion. But I have another confusion regarding the
> same thing. This might be very basic but I am still unable to find the
> actual problem.
>
> After doing ./bin/madevent I was trying to compute widths of SM Higgs
> (width: 4.961126e-03) which did not match with the actual one and also
> the BR for h > b b~ came at around 8.677063e-01. I also tried to compute
> width of h with 3 and 4 body decay also (I don't know whether its right
> or not!!!), but then the width came with a larger value (~6e-03).
>
> I used loop_qcd_qed_sm-full model to generate events (g g > h h).
>
> Am I doing something wrong? Should I provide the decay width and BRs by
> hand in parameter card?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Gavin (seeha) said : 		#4

Thanks