Importing ALP model to MadGraph & generating BSM processes, most of the decay widths in parameter_card.dat are set to 0. Why ?

Asked by HH on 2019-09-01

I import ALP_linear_UFO as the model and generate some BSM processes like p p > j j ax using this model (MadGraph versions I used are 2.6.6 and 2.6.5). Then using the command "output targetDirectory", a directory is created. Looking at the Cards/parameter_card.dat file reveals that most of the decay widths are set to zero. As a result, pythia finds no decay channel and showering, hadronization, ... are impossible. How can I overcome this issue?

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2019-09-02
Last query:
2019-09-02
Last reply:
2019-09-02

I you can edit the value within that file and set those to the physical value. If you are in narrow width approximation and without loop induced decay you can set the width to auto. Please read the associated paper to understand what it means

Get Outlook for iOS<https://aka.ms/o0ukef>
________________________________
From: <email address hidden> <email address hidden> on behalf of jack <email address hidden>
Sent: Sunday, September 1, 2019 6:37:33 PM
To: Olivier Mattelaer <email address hidden>
Subject: Re: [Question #683569]: Importing ALP model to MadGraph & generating BSM processes, most of the decay widths in parameter_card.dat are set to 0. Why ?

Question #683569 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/683569

Description changed to:
I import ALP_linear_UFO as the model and generate some BSM processes
like p p > j j ax using this model (MadGraph versions I used are 2.6.6
and 2.6.5). Then using the command "output targetDirectory", a directory
is created. Looking at the Cards/parameter_card.dat file reveals that
most of the decay widths are set to zero. As a result, pythia finds no
decay channel and showering, hadronization, ... are impossible. How can
I overcome this issue?

--
You received this question notification because you are an answer
contact for MadGraph5_aMC@NLO.

HH (hh-madgrapher) said : #2

Thanks for your answer. Since it is to perform LO processes, I will set the
width values to Auto. However another question arises. Setting widths of
the particles listed in param_card to Auto (e.g. set width 21 Auto), MG5
computes only the total widths. Then, if I pass the param_card.dat to
pythia, can pythia perform showering properly using only total widths? I
ask this question because partial widths (or BRs) are essential for pythia
to know.

Thanks in advance

On Sun, Sep 1, 2019, 10:38 PM Olivier Mattelaer <
<email address hidden>> wrote:

> Your question #683569 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/683569
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> I you can edit the value within that file and set those to the physical
> value. If you are in narrow width approximation and without loop induced
> decay you can set the width to auto. Please read the associated paper to
> understand what it means
>
> Get Outlook for iOS<https://aka.ms/o0ukef>
> ________________________________
> From: <email address hidden> <email address hidden> on behalf of jack <
> <email address hidden>>
> Sent: Sunday, September 1, 2019 6:37:33 PM
> To: Olivier Mattelaer <email address hidden>
> Subject: Re: [Question #683569]: Importing ALP model to MadGraph &
> generating BSM processes, most of the decay widths in parameter_card.dat
> are set to 0. Why ?
>
> Question #683569 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/683569
>
> Description changed to:
> I import ALP_linear_UFO as the model and generate some BSM processes
> like p p > j j ax using this model (MadGraph versions I used are 2.6.6
> and 2.6.5). Then using the command "output targetDirectory", a directory
> is created. Looking at the Cards/parameter_card.dat file reveals that
> most of the decay widths are set to zero. As a result, pythia finds no
> decay channel and showering, hadronization, ... are impossible. How can
> I overcome this issue?
>
> --
> 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/683569/+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/683569
>
> You received this question notification because you asked the question.
>

Hi,

> Setting widths of
the particles listed in param_card to Auto (e.g. set width 21 Auto), MG5
computes only the total widths.

This is not True. "Auto" also writes the partial width

Cheers,

Olivier

PS: I hope that "set width 21 Auto" is only an example since having a width for the gluon is a bad idea (and having another particle with pdg 21 is also a bad idea)

Hi,

> Setting widths of
the particles listed in param_card to Auto (e.g. set width 21 Auto), MG5
computes only the total widths.

This is not True. "Auto" also writes the partial width

Cheers,

Olivier

PS: I hope that "set width 21 Auto" is only an example since having a width for the gluon is a bad idea (and having another particle with pdg 21 is also a bad idea)

HH (hh-madgrapher) said : #5

Thanks Olivier Mattelaer, that solved my question.