pp> hhtt~ process!

Hi,

> - The command I entered in madgraph was simply: generate p p > h h t t~ . Is it the right way to do it ? (model used is heft).

The heft model is an approximation of the g g > h loop which is valid in the small Q/mt limit.
In your case Q ~ 2mh + 2mt so the limit is certainly wrong.

> - What is the difference between these two commands: ""generate p p > h h t t~"" and ""generate p p > h h t t~ [QCD]"".

The first command performs a LO computation, while the second performs a NLO computation.
the heft model is not NLO ready and except in some very particular case, you can not play with
  ( λ/ λsm) in a meaningfull way at NLO accuracy.

Note that for process without any tree-level diagram, [QCD] will automatically be converted to [noborn=QCD] which is used for loop-induced process (and therefore in those cases, the computation is at LO accuracy)

Cheers,

Olivier

> On 6 Mar 2019, at 11:23, TAIL Saad <email address hidden> wrote:
>
> New question #678998 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/678998
>
> Hello,
>
> I have plotted the cross section for "" p p > h h t t~ "" process versus ( λ/ λsm) - λ is higgs selfcoupling- by changing each time the value of λ. With the increase of the ratio λ/λsm, I got an increasing cross section.
> - A prof of mine mentioned the following: ''sensitivity on the trilinear coupling in ttHH is not very strong: between 0 and 4 the cross section changes by a factor of 2 only''.
> However, in my calculations, for λ/λsm interval of 0 to 4, I found that cross-section changes by a factor higher than 2!
>
> So, my questions:
>
> - The command I entered in madgraph was simply: generate p p > h h t t~ . Is it the right way to do it ? (model used is heft).
> - What is the difference between these two commands: ""generate p p > h h t t~"" and ""generate p p > h h t t~ [QCD]"".
>
> Greetings
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hello,

Thank you for your reply.

Just to make sure I got this straight, so the right way to do it is by
including the loop_sm model instead of heft (with pp> hhtt~ for LO and pp>
hhtt~[QCD]), correct?

Le mer. 6 mars 2019 à 11:43, Olivier Mattelaer <
<email address hidden>> a écrit :

> Your question #678998 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/678998
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Hi,
>
> > - The command I entered in madgraph was simply: generate p p > h h t
> t~ . Is it the right way to do it ? (model used is heft).
>
> The heft model is an approximation of the g g > h loop which is valid in
> the small Q/mt limit.
> In your case Q ~ 2mh + 2mt so the limit is certainly wrong.
>
> > - What is the difference between these two commands: ""generate p p >
> h h t t~"" and ""generate p p > h h t t~ [QCD]"".
>
> The first command performs a LO computation, while the second performs a
> NLO computation.
> the heft model is not NLO ready and except in some very particular case,
> you can not play with
> ( λ/ λsm) in a meaningfull way at NLO accuracy.
>
> Note that for process without any tree-level diagram, [QCD] will
> automatically be converted to [noborn=QCD] which is used for loop-
> induced process (and therefore in those cases, the computation is at LO
> accuracy)
>
>
> Cheers,
>
> Olivier
>
> > On 6 Mar 2019, at 11:23, TAIL Saad <email address hidden>
> wrote:
> >
> > New question #678998 on MadGraph5_aMC@NLO:
> > https://answers.launchpad.net/mg5amcnlo/+question/678998
> >
> > Hello,
> >
> > I have plotted the cross section for "" p p > h h t t~ "" process versus
> ( λ/ λsm) - λ is higgs selfcoupling- by changing each time the value of λ.
> With the increase of the ratio λ/λsm, I got an increasing cross section.
> > - A prof of mine mentioned the following: ''sensitivity on the trilinear
> coupling in ttHH is not very strong: between 0 and 4 the cross section
> changes by a factor of 2 only''.
> > However, in my calculations, for λ/λsm interval of 0 to 4, I found that
> cross-section changes by a factor higher than 2!
> >
> > So, my questions:
> >
> > - The command I entered in madgraph was simply: generate p p > h h t t~
> . Is it the right way to do it ? (model used is heft).
> > - What is the difference between these two commands: ""generate p p > h
> h t t~"" and ""generate p p > h h t t~ [QCD]"".
> >
> > Greetings
> >
> > --
> > You received this question notification because you are an answer
> > contact for MadGraph5_aMC@NLO.
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
>
> https://answers.launchpad.net/mg5amcnlo/+question/678998/+confirm?answer_id=0
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/678998
>
> You received this question notification because you asked the question.
>

I do not know,

If you are dominated by the ggh vertex, then certainly not.
This one will not be include at all at LO in that model.
This contribution should technically be a NNLO contribution so it should not be include either
for the NLO computation (even if the loop is displayed as Feynman diagram, it will include only the
the interference of the loop with the associate born matrix-element

I do not know enough the mechanism of production for that process to comment more.
And to be able to advise a strategy.

Cheers,

Olivier

> On 6 Mar 2019, at 12:23, TAIL Saad <email address hidden> wrote:
>
> Question #678998 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/678998
>
> Status: Answered => Open
>
> TAIL Saad is still having a problem:
> Hello,
>
> Thank you for your reply.
>
> Just to make sure I got this straight, so the right way to do it is by
> including the loop_sm model instead of heft (with pp> hhtt~ for LO and pp>
> hhtt~[QCD]), correct?
>
>
> Le mer. 6 mars 2019 à 11:43, Olivier Mattelaer <
> <email address hidden>> a écrit :
>
>> Your question #678998 on MadGraph5_aMC@NLO changed:
>> https://answers.launchpad.net/mg5amcnlo/+question/678998
>>
>> Status: Open => Answered
>>
>> Olivier Mattelaer proposed the following answer:
>> Hi,
>>
>>> - The command I entered in madgraph was simply: generate p p > h h t
>> t~ . Is it the right way to do it ? (model used is heft).
>>
>> The heft model is an approximation of the g g > h loop which is valid in
>> the small Q/mt limit.
>> In your case Q ~ 2mh + 2mt so the limit is certainly wrong.
>>
>>> - What is the difference between these two commands: ""generate p p >
>> h h t t~"" and ""generate p p > h h t t~ [QCD]"".
>>
>> The first command performs a LO computation, while the second performs a
>> NLO computation.
>> the heft model is not NLO ready and except in some very particular case,
>> you can not play with
>> ( λ/ λsm) in a meaningfull way at NLO accuracy.
>>
>> Note that for process without any tree-level diagram, [QCD] will
>> automatically be converted to [noborn=QCD] which is used for loop-
>> induced process (and therefore in those cases, the computation is at LO
>> accuracy)
>>
>>
>> Cheers,
>>
>> Olivier
>>
>>> On 6 Mar 2019, at 11:23, TAIL Saad <email address hidden>
>> wrote:
>>>
>>> New question #678998 on MadGraph5_aMC@NLO:
>>> https://answers.launchpad.net/mg5amcnlo/+question/678998
>>>
>>> Hello,
>>>
>>> I have plotted the cross section for "" p p > h h t t~ "" process versus
>> ( λ/ λsm) - λ is higgs selfcoupling- by changing each time the value of λ.
>> With the increase of the ratio λ/λsm, I got an increasing cross section.
>>> - A prof of mine mentioned the following: ''sensitivity on the trilinear
>> coupling in ttHH is not very strong: between 0 and 4 the cross section
>> changes by a factor of 2 only''.
>>> However, in my calculations, for λ/λsm interval of 0 to 4, I found that
>> cross-section changes by a factor higher than 2!
>>>
>>> So, my questions:
>>>
>>> - The command I entered in madgraph was simply: generate p p > h h t t~
>> . Is it the right way to do it ? (model used is heft).
>>> - What is the difference between these two commands: ""generate p p > h
>> h t t~"" and ""generate p p > h h t t~ [QCD]"".
>>>
>>> Greetings
>>>
>>> --
>>> You received this question notification because you are an answer
>>> contact for MadGraph5_aMC@NLO.
>>
>> --
>> If this answers your question, please go to the following page to let us
>> know that it is solved:
>>
>> https://answers.launchpad.net/mg5amcnlo/+question/678998/+confirm?answer_id=0
>>
>> If you still need help, you can reply to this email or go to the
>> following page to enter your feedback:
>> https://answers.launchpad.net/mg5amcnlo/+question/678998
>>
>> You received this question notification because you asked the question.
>>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.