Top quark initiated processes (6F scheme)

Asked by msadek on 2018-05-27

Hi,

Is it possible to work with 6F scheme in MadGraph? If yes, is it possible to retain the initial state quark mass effect (especially for the top quark!!!)?

Cheers,
Sadek

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msadek
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2018-05-27
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2018-05-27
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2018-05-27

Hi,

I'm not fully sure how much your question makes sense.
What do you call 6F scheme? More exactly how do you expect us to handle the log in that case?

For me 6 flavor means that you need a pdf for the top (from lhapdf) which includes the top as a massless quark (including in the DGLAP evolution) that scheme make sense if muF is much larger than the top mass.
In that definition of 6 flavor, I do not see how you can include top mass effect in initiial state in a consistent way.

This being said, we do not have any test that the initial state is massless when use with a PDF at leading order. So if a PDF is consistently defined for such massive quark, then it should not be a problem for MG5aMC to handle it.

I know that some people are doing exactly that for the 5 flavor and I have seen some paper stating that the theoretical error was (re-)covered/componsated by a better fit of the hadronization model. I doubt that such argument holds for the top mass (but one should check)

So the short answer is: yes it is possible but this is YOUR responsability to check that such results are meaningfull/physical when you introduce the mass.

Cheers,

Olivier

> On 27 May 2018, at 13:08, msadek <email address hidden> wrote:
>
> New question #669703 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/669703
>
> Hi,
>
> Is it possible to work with 6F scheme in MadGraph? If yes, is it possible to retain the initial state quark mass effect (especially for the top quark!!!)?
>
> Cheers,
> Sadek
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

msadek (msadek) said : #2

Dear Olivier,

I mean by 6F with top mass the ACOT scheme as explained in https://arxiv.org/abs/1411.2588.

Thank you very much for your answer

Cheers,
Sadek

Hi,

First that paper is not ACOT but m-ACOT.
Those method are actually not a 6F computation
but multiple flavor computation (with extrapolation between the different flavor computation.

But no this is not supported within our framework right now.
Should be possible to include it but we need to have a volunteer to implement/validate it/ do physics with it.

Cheers,

Olivier

> On 28 May 2018, at 00:08, msadek <email address hidden> wrote:
>
> Question #669703 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/669703
>
> Status: Answered => Solved
>
> msadek confirmed that the question is solved:
> Dear Olivier,
>
> I mean by 6F with top mass the ACOT scheme as explained in
> https://arxiv.org/abs/1411.2588.
>
> Thank you very much for your answer
>
> Cheers,
> Sadek
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.