Different Crosssection for a particular process in IDM

Hi,

I do not see a problem, your cross-section is proportional to 1/\Gamma_h+**2, so if you change the value of the width, you should change the value of the cross-section.

Cheers,

Olivier

On 13 Apr 2015, at 08:16, shibasipu <email address hidden> wrote:

> New question #265094 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/265094
>
> Hello Madgraph Team,
> I am generating a process in the context of Inert Doublet Model (IDM)i.e. p p > h+ h- , ( h+ > w+ h2) , ( h- > w- h2 ) at CM energy 14 TeV. For this I am using an UFO model which is available at Feynrules website. For a particular set of parameters, I am getting the crosssection value = 0.0189fb. But when I am fixing "Auto" option for charged Higgs decay width in the param card , I am getting the crossection value = 0.8964fb. I am little bit confused with the above two values. or Is it obvious since I am using "Auto" option ?
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

thanks Oliver for your quick reply. It would be better if you tell what is the meaning of fixing "Auto" option in param card in comparison to without "Auto" option (i.e. inbuilt one ).

Regards,
Shiba

Sure.

In short, we compute the LO value of the width for your benchmark point.
For more information about the hypothesis, please read: arXiv:1402.1178

Cheers,

Olivier

On 13 Apr 2015, at 13:12, shibasipu <email address hidden> wrote:

> Question #265094 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/265094
>
> Status: Answered => Open
>
> shibasipu is still having a problem:
> thanks Oliver for your quick reply. It would be better if you tell
> what is the meaning of fixing "Auto" option in param card in comparison
> to without "Auto" option (i.e. inbuilt one ).
>
>
>
> Regards,
> Shiba
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

thank you very much. Still I am struggling to find out the BR(H+ > W+ h2) in this model (Inert Doublet Model). Actually for this, I am going in the following way. Firstly, I am generating all possible 2 body and 3 body decay processes of H+ for a particular set of parameters. Then in the newly generated param card, it lists all the Brs of above processes. The resulting BR value of H+ > w+ h2 is not matching with those available in literature. My concern is whether I also have to generate off-shell decay mode of H+ ?

Regards,
Shiba

Dear Shiba,

This procedures that you describe is exactly what is done with the “Auto” mode.
Did you check that the value returned in that case matched the literature?

The fact to include simultaneously 2 and 3 body decay is not trivial since you need to avoid double counting
and at the same time, you need to include the off-shell contribution which is possible to do by hand but error prone.

Cheers,

Olivier

On 14 Apr 2015, at 20:06, shibasipu <email address hidden> wrote:

> Question #265094 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/265094
>
> Status: Answered => Open
>
> shibasipu is still having a problem:
> thank you very much. Still I am struggling to find out the BR(H+ > W+
> h2) in this model (Inert Doublet Model). Actually for this, I am going
> in the following way. Firstly, I am generating all possible 2 body and 3
> body decay processes of H+ for a particular set of parameters. Then in
> the newly generated param card, it lists all the Brs of above processes.
> The resulting BR value of H+ > w+ h2 is not matching with those
> available in literature. My concern is whether I also have to generate
> off-shell decay mode of H+ ?
>
>
>
> Regards,
> Shiba
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

thanks a lot. Still I am trying to figure out the above mentioned problem. But Can I do in an alternative way ? i.e.

> generate h+ > all all
> add process h+ > all all all ( for all allowed 2 and 3 body decay assuming off-shell decays contributes less)

From this , I can findout BR(H+ >W+ h2) for a particular parameter set . Am I going in the right direction ?

Regards,
Shiba

Hi,

>> generate h+ > all all
>> add process h+ > all all all ( for all allowed 2 and 3 body decay assuming off-shell decays contributes less)

No this is wrong, because you have double counting

For example you have
h+ > w+ h2
but you also have
h+ > w+ h2, h2 > b b~ (which is part of the contribution of h+ > w+ b b~)

So clearly your total width is wrong and your BR as well.

Cheers,

Olivier

On 15 Apr 2015, at 14:26, shibasipu <email address hidden> wrote:

> Question #265094 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/265094
>
> Status: Answered => Open
>
> shibasipu is still having a problem:
> thanks a lot. Still I am trying to figure out the above mentioned
> problem. But Can I do in an alternative way ? i.e.
>
>> generate h+ > all all
>> add process h+ > all all all ( for all allowed 2 and 3 body decay assuming off-shell decays contributes less)
>
>> From this , I can findout BR(H+ >W+ h2) for a particular parameter set
> . Am I going in the right direction ?
>
>
> Regards,
> Shiba
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

No , in this model h2 > b b~ decay is not possible because h2 , h3 , h+ are odd under Z_2 symmetry. All SM fields are even under Z_2 symmetry. Additional info is h2 or h3 can be candidate of dark matter depending on mass. So one of them will not decay at all.

Hope, this info. will help.

Regards,
Shiba

Dear Shiba,

Ok my example is wrong, and since I do not know your model, I’m not sure that i can make example which makes sense.

A second case where you can have error with your syntax, is the inclusion of radiation
for example you will have
h+ > h2 w+
and
h+ > h2 w+ a
The second being a correction NLO that should not be include in the computation of the three body decay.

Cheers,

Olivier

On 15 Apr 2015, at 17:56, shibasipu <email address hidden> wrote:

> Question #265094 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/265094
>
> Status: Answered => Open
>
> shibasipu is still having a problem:
> No , in this model h2 > b b~ decay is not possible because h2 , h3 , h+
> are odd under Z_2 symmetry. All SM fields are even under Z_2 symmetry.
> Additional info is h2 or h3 can be candidate of dark matter depending on
> mass. So one of them will not decay at all.
>
> Hope, this info. will help.
>
>
>
> Regards,
> Shiba
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

thanks Oliver for your quick helps. Now I crosschecked some of the results available in literature.

Hello Oliver,
                 Another mismatch in the value of the cross section ! I am considering the following benchmark point in this model(Inert Doublet Model)

m_H+ = 80 , m_h2 = 65 , m_h3 = 73. I got the BR(H+ > W+^* h2> j j h2) = 0.72 and BR(H+ > W+^* h2 > l+ vl h2) = 0.24 and total decay width of H+ = 6.8008 * 10^-7 for the above mentioned parameter set. Now I also calculated the cross section of p p > H+ w- h2 at root S = 14 TeV with the above parameter set which equals to 5.990 fb.

But Cross section of ( p p > H+ w- h2 , (H+ > j j h2)) at 14 TeV (with the above parameter set and \Gamma_H+ = 6.8008*10^-7) = 2.332*10^-2 fb. As per my understanding, it should match to Cross-section of (p p > H+ w- h2) * BR(H+ > W+^* h2> j j h2). But here it is not matching , the later value returns to 5.990 * 0.72 = 4.3128.

Hope, you will understand the confusion .

Regards,
Shiba

Hi,

Did you look at the following FAQ:
https://answers.launchpad.net/mg5amcnlo/+faq/2442

Cheers,

Olivier

On 21 Apr 2015, at 15:46, shibasipu <email address hidden> wrote:

> Question #265094 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/265094
>
> Status: Solved => Open
>
> shibasipu is still having a problem:
> Hello Oliver,
> Another mismatch in the value of the cross section ! I am considering the following benchmark point in this model(Inert Doublet Model)
>
> m_H+ = 80 , m_h2 = 65 , m_h3 = 73. I got the BR(H+ > W+^* h2> j j h2)
> = 0.72 and BR(H+ > W+^* h2 > l+ vl h2) = 0.24 and total decay width of
> H+ = 6.8008 * 10^-7 for the above mentioned parameter set. Now I also
> calculated the cross section of p p > H+ w- h2 at root S = 14 TeV with
> the above parameter set which equals to 5.990 fb.
>
> But Cross section of ( p p > H+ w- h2 , (H+ > j j h2)) at 14 TeV (with
> the above parameter set and \Gamma_H+ = 6.8008*10^-7) = 2.332*10^-2 fb.
> As per my understanding, it should match to Cross-section of (p p > H+
> w- h2) * BR(H+ > W+^* h2> j j h2). But here it is not matching , the
> later value returns to 5.990 * 0.72 = 4.3128.
>
> Hope, you will understand the confusion .
>
> Regards,
> Shiba
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hello Oliver,
                     After fixing set cut_decays on False on the run_card, I am able to get rid of my previous query.
Thanks for your help.

Regards,
Shiba