scale, dsqrt_q2fact1, dsqrt_q2fact2 setup

Asked by SUBHASISH BEHERA on 2021-04-22

Hi,

Greetings!
I was trying to produce some processes at a PROTON (in the +ve z-axis) - ELECTRON collider with different beam energies (E_p=7000, E_e=150 GeV) or I may change E_e value as per requirement.
I wanted to know if I will produce a process with "Higgs" in the final state then what should I set in the following:

(1) when I wanted to set a muf=mur=mass of the higgs (mh=120 taken here) for the fixed scale scenario: what are the changes I should do in the following 7 parameters?

# Renormalization and factorization scales *
#*********************************************************************
  True = fixed_ren_scale ! if .true. use fixed ren scale
  True = fixed_fac_scale ! if .true. use fixed fac scale
  120.0 = scale ! fixed ren scale
  120.0 = dsqrt_q2fact1 ! fixed fact scale for pdf1
  120.0 = dsqrt_q2fact2 ! fixed fact scale for pdf2
  -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices
  1.0 = scalefact ! scale factor for event-by-event scales
#*********************************************************************

(2) when I dont want to set fixed scale: what are the changes I should do in the above 7 parameters?

(3)when I dont want to set fixed scale and I want to produce processes with PROTON - PHOTON (photon from Electron): what are the changes I should do in the above 7 parameters?

If possible please also explain/provide documentations available online.
Thanks in advance!

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SUBHASISH BEHERA
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Hi,

> (1) when I wanted to set a muf=mur=mass of the higgs (mh=120 taken here) for the fixed scale scenario: what are the changes I should do in the following 7 parameters?

Your setup is correct

> (2) when I dont want to set fixed scale: what are the changes I should do in the above 7 parameters?

Then you need
> False = fixed_ren_scale ! if .true. use fixed ren scale
> False = fixed_fac_scale ! if .true. use fixed fac scale

and pick the type of dynamical scale of your choice:
> -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices

You can type "help dynamical_scale_choice" in the question allowing you to edit the cards to see the meaning of all integer value. or see 1507.00020 <https://arxiv.org/abs/1507.00020>

> (3)when I dont want to set fixed scale and I want to produce processes with PROTON - PHOTON (photon from Electron): what are the changes I should do in the above 7 parameters?

The Photon part has to be in fixed scale since this correspond to the unresolve scale of the electron.
So this is typically a scale around a few GeV so for that one you have to set dsqrt_q2fact2 to such value.
The other scale can be dynamical with the same setup as for point2.

Cheers,

Olivier

PS: Note that the behavior for point 3 depends of the version of MG5aMC that you use. So this is for 2.9.3 and 3.1.0

> On 22 Apr 2021, at 08:45, SUBHASISH BEHERA <email address hidden> wrote:
>
> New question #696686 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/696686
>
> Hi,
>
> Greetings!
> I was trying to produce some processes at a PROTON (in the +ve z-axis) - ELECTRON collider with different beam energies (E_p=7000, E_e=150 GeV) or I may change E_e value as per requirement.
> I wanted to know if I will produce a process with "Higgs" in the final state then what should I set in the following:
>
> (1) when I wanted to set a muf=mur=mass of the higgs (mh=120 taken here) for the fixed scale scenario: what are the changes I should do in the following 7 parameters?
>
> # Renormalization and factorization scales *
> #*********************************************************************
> True = fixed_ren_scale ! if .true. use fixed ren scale
> True = fixed_fac_scale ! if .true. use fixed fac scale
> 120.0 = scale ! fixed ren scale
> 120.0 = dsqrt_q2fact1 ! fixed fact scale for pdf1
> 120.0 = dsqrt_q2fact2 ! fixed fact scale for pdf2
> -1 = dynamical_scale_choice ! Choose one of the preselected dynamical choices
> 1.0 = scalefact ! scale factor for event-by-event scales
> #*********************************************************************
>
> (2) when I dont want to set fixed scale: what are the changes I should do in the above 7 parameters?
>
> (3)when I dont want to set fixed scale and I want to produce processes with PROTON - PHOTON (photon from Electron): what are the changes I should do in the above 7 parameters?
>
> If possible please also explain/provide documentations available online.
> Thanks in advance!
>
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear Olivier,

Thanks for the detailed answer!
(3a)Just wanted to ask for "PROTON - PHOTON (photon from Electron)" case:
Can I set "dsqrt_q2fact2 = 2 GeV" or how do you calculate this value for example for E_e=150 GeV?

(4) I have to pass the LHE file to PYTHIA8 (standalone with ep-collision setup) for showering. Will there be any issue (in case of pe- or p gamma- collision) ?

> (3a)Just wanted to ask for "PROTON - PHOTON (photon from Electron)" case:
> Can I set "dsqrt_q2fact2 = 2 GeV" or how do you calculate this value for example for E_e=150 GeV?

The value is linked to the experimental detector (or analysis) that you consider.
i.e. what is the sofest scale on which you will detect the electron ( in energy or pt or ...)

> (4) I have to pass the LHE file to PYTHIA8 (standalone with ep-collision
> setup) for showering. Will there be any issue (in case of pe- or p
> gamma- collision) ?

I do not know about that.... You will likely have to play with some pythia8 internal switch to have the most accurate result.

Cheers,

Olivier

> On 22 Apr 2021, at 12:01, SUBHASISH BEHERA <email address hidden> wrote:
>
> Question #696686 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/696686
>
> Status: Answered => Open
>
> SUBHASISH BEHERA is still having a problem:
> Dear Olivier,
>
> Thanks for the detailed answer!
> (3a)Just wanted to ask for "PROTON - PHOTON (photon from Electron)" case:
> Can I set "dsqrt_q2fact2 = 2 GeV" or how do you calculate this value for example for E_e=150 GeV?
>
> (4) I have to pass the LHE file to PYTHIA8 (standalone with ep-collision
> setup) for showering. Will there be any issue (in case of pe- or p
> gamma- collision) ?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear Olivier,

Many thanks for all suggestions and answer.
Just couple of quick question:
(1) What does EPA stand for in the logger: "Photon from lepton are using fixed scale value of muf [dsqrt_q2fact2] as the cut of the EPA. Looks like you kept the default value (Mz). Is this really the cut-off of the EPA that you want to use?"

(2) As I understood: we need to set "dsqrt_q2fact2=" to be a value <= Max of Energy carried by the photon in the ISR or Bramsstralung process. Is it the case?

Can this be done automatically in MG5 (in future version) when we set the value of "lpp" and "Ebeam" value in the run card?

> (1) What does EPA stand for in the logger: "Photon from lepton are using fixed scale value of muf [dsqrt_q2fact2] as the cut of the EPA. Looks like you kept the default value (Mz). Is this really the cut-off of the EPA that you want to use?"

This is Effective Photon Approximation.

> (2) As I understood: we need to set "dsqrt_q2fact2=" to be a value <=
> Max of Energy carried by the photon in the ISR or Bramsstralung process.
> Is it the case?

Not really, this depend of what you call resolved electron versus un-resolved electron.

> Can this be done automatically in MG5 (in future version) when we set
> the value of "lpp" and "Ebeam" value in the run card?

I do not see how this is possible.

Cheers,

Olivier

> On 22 Apr 2021, at 15:08, SUBHASISH BEHERA <email address hidden> wrote:
>
> Question #696686 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/696686
>
> Status: Answered => Open
>
> SUBHASISH BEHERA is still having a problem:
> Dear Olivier,
>
> Many thanks for all suggestions and answer.
> Just couple of quick question:
> (1) What does EPA stand for in the logger: "Photon from lepton are using fixed scale value of muf [dsqrt_q2fact2] as the cut of the EPA. Looks like you kept the default value (Mz). Is this really the cut-off of the EPA that you want to use?"
>
> (2) As I understood: we need to set "dsqrt_q2fact2=" to be a value <=
> Max of Energy carried by the photon in the ISR or Bramsstralung process.
> Is it the case?
>
> Can this be done automatically in MG5 (in future version) when we set
> the value of "lpp" and "Ebeam" value in the run card?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Dear Olivier,

Many thanks for your answers.