nhel and bwcutoff

Asked by Beojan on 2018-06-29

We are studying the h h > b b b~ b~ process and we have a few questions:

1. We use loop_sm to generate the signal with h h > b b b~ b~ [QCD] and sm to generate p p > b b b~ b~ ,p p > j j b b~, and p p > j j j j backgrounds. In the background runcards, nhel defaults to 0 while in the signal runcard it defaults to 1. Do you think this could cause issues, and if so, how should we set nhel?

2. Going back a step, is h h > b b b~ b~ the right way to generate the signal or should we be asking for p p > h h > b b b~ b~?
 Looking at the diagrams, the first seems to work.

3. One interesting set of diagrams is of the form p p > h* > h h. Since the h* is very off-shell, do we need to increase bwcutoff, and would increasing it cause any problems?

Thanks.

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2018-06-29
Last query:
2018-06-29
Last reply:
2018-06-29

hi,

> 1. We use loop_sm to generate the signal with h h > b b b~ b~ [QCD] and sm to generate p p > b b b~ b~ ,p p > j j b b~, and p p > j j j j backgrounds. In the background runcards, nhel defaults to 0 while in the signal runcard it defaults to 1. Do you think this could cause issues, and if so, how should we set nhel?

No that parameter is purely technical and does not affect the physics.
It is advise to set it to one for loop-induced processes and to 0 for other type of process.

> 2. Going back a step, is h h > b b b~ b~ the right way to generate the signal or should we be asking for p p > h h > b b b~ b~?
> Looking at the diagrams, the first seems to work.

Well this depends what you call signal.
> h h > b b b~ b~
means that you are running at a Higgs Factory and looking at the 4 b signal
> h h > b b b~ b~ [QCD]
means that you are running at a Higgs Factory and looking at the 4 b signal at NLO accuracy
> p p > h h > b b b~ b~
means that you are running at proton-proton collision or proton-anti-proton factory.
Now this syntax is actually equivalent to
> p p > h > b b b~ b~
which is likely not what you want.

The typical method for Di-Higss at LHC.
is either
1)
import model heft
generate p p > h h, h > b b~

2)
generate p p > h h [QCD]
output
launch
MadSpin=none # this activate madspin and set the spinmode to none.
decay h > b b~

> 3. One interesting set of diagrams is of the form p p > h* > h h. Since the h* is very off-shell, do we need to increase bwcutoff, and would increasing it cause any problems?

bwcutoff is not doing such kind of cut. It applies cut only if you specify a particule to be onshell (using the comma syntax) or offshell (using the $ syntax).

Cheers,

Olivier

> On 29 Jun 2018, at 14:26, Beojan <email address hidden> wrote:
>
> New question #670546 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/670546
>
> We are studying the h h > b b b~ b~ process and we have a few questions:
>
> 1. We use loop_sm to generate the signal with h h > b b b~ b~ [QCD] and sm to generate p p > b b b~ b~ ,p p > j j b b~, and p p > j j j j backgrounds. In the background runcards, nhel defaults to 0 while in the signal runcard it defaults to 1. Do you think this could cause issues, and if so, how should we set nhel?
>
> 2. Going back a step, is h h > b b b~ b~ the right way to generate the signal or should we be asking for p p > h h > b b b~ b~?
> Looking at the diagrams, the first seems to work.
>
> 3. One interesting set of diagrams is of the form p p > h* > h h. Since the h* is very off-shell, do we need to increase bwcutoff, and would increasing it cause any problems?
>
> Thanks.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Beojan (beojan2) said : #2

Ah, that's interesting.

> generate p p > h h [QCD]
output
launch
MadSpin=none # this activate madspin and set the spinmode to none.
decay h > b b~

Is there a reason we can't do

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

or perhaps the syntax would be

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

This would be the correct syntax

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

But we do not support such type of definition for the moment.

Cheers,

Olivier

> On 29 Jun 2018, at 15:32, Beojan <email address hidden> wrote:
>
> Question #670546 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/670546
>
> Status: Answered => Open
>
> Beojan is still having a problem:
> Ah, that's interesting.
>
>> generate p p > h h [QCD]
> output
> launch
> MadSpin=none # this activate madspin and set the spinmode to none.
> decay h > b b~
>
> Is there a reason we can't do
>
> generate p p > h h [QCD], h > b b~
>
> or perhaps the syntax would be
>
> generate p p > h h, h > b b~ [QCD]
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Beojan (beojan2) said : #4

I see. Thanks.

Beojan (beojan2) said : #5

Thanks Olivier Mattelaer, that solved my question.