Problem in generating h(125)->Za->2b2mu Signal for certain mass points

Asked by Aashaq Shah on 2018-11-07

Dear experts,
I am generating a higgs signal h(125)->Za->2b2mu (b--> is b-jet ) using NMSSMHET model. The Z boson is allowed to decay into b-bbar and "a" boson to mu+mu-. Out of the available mass window 1-34 GeV, I tried different mass points for "a" boson like 6, 9, 12, 15, 20, 25, and 30 GeV. When I plot the invariant masses of mu+mu-, it is perfect both at generator level as well as at reconstructed level. However, when I plot invariant mass distribution of b-bbar which should some how peak around 91 GeV (corresponding to Z boson mass), I get it for mass points 30, and 20 GeV only (basically I get a perfect Gaussian as expected). For the lower mass points, I see distributed mass region with mean at around 50 GeV which is very strange. More surprising is that the mass point 9 is fine. In nut shell the problem is observed for mass points 20, 15, 12, 06 and others like 30, 25 and 9 are fine. I cross checked things and it seems everything is perfect. It seems I am clueless now. I would appreciate any possible help/support from the forum here.
Many thanks in advance.

Best,
--Aashaq

Question information

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Last query:
2018-11-07
Last reply:
2018-11-09

Hi,

Which syntax did you use?

Cheers,

Olivier

Aashaq Shah (aashiqphst) said : #2

Hi Olivier,

Thanks for the kind reply.

### h(125)->Za->2b2mu

To tell you that I have prepared input cards and have set Z mass to 91 and a_mass for different values (03, 06, 09, 15, 20, 25, 30).
To be more specific, I am using four cards, that include process_card, run_card, extra models, customized one.

In extra models I use NMSSMHET.zip

In customized card, I set following parameters:
set param_card mass 25 125.0
set param_card mass 23 91.2
set param_card mass 36 20.0

and in the process card I use
import model NMSSMHET --modelname
generate p p > h01 , (h01 > z a01, z > b b~, a01 > mu+ mu-)

Looking at the LHE plots, we see a clear peak for the Higgs boson. However the distribution of m_bb looks a bit strange (see the plot at https://drive.google.com/open?id=1NFvGxGVOJL6kwsCf-TzDja_ni-HUky2I ). For some masses below 25 GeV, we observe outliers in the Z mass distribution. The contribution of the outliers does not follow any specific order. For example we cannot tell if with lower m_a, outliers are more.

However, when I generate h(125)->aa->2b2mu signal with p p > h01 , (h01 > a01, a01, a01 > b b~, a01 > mu+ mu-), I find every thing perfect and expected.

Would you please let me know what we could be missing?

Best,
Aashaq

Hi,

Could you send me those cards/model then?

> However the distribution of m_bb looks a bit strange (see the plot at
> https://drive.google.com/open?id=1NFvGxGVOJL6kwsCf-TzDja_ni-HUky2I ).

It seems that you have a peak at the Z mass but a significant off-shell contribution.
From this syntax:
> generate p p > h01 , (h01 > z a01, z > b b~, a01 > mu+ mu-)

You ask h01 and z and a01 to be onshell (up to 15 times the width if you kept the default)

So the question is also did you set the value of the width correctly for all those particles?

Cheers,

Olivier

> On 8 Nov 2018, at 14:27, Aashaq Shah <email address hidden> wrote:
>
> Question #675999 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/675999
>
> Aashaq Shah posted a new comment:
> Hi Olivier,
>
> Thanks for the kind reply.
>
> ### h(125)->Za->2b2mu
>
> To tell you that I have prepared input cards and have set Z mass to 91 and a_mass for different values (03, 06, 09, 15, 20, 25, 30).
> To be more specific, I am using four cards, that include process_card, run_card, extra models, customized one.
>
> In extra models I use NMSSMHET.zip
>
> In customized card, I set following parameters:
> set param_card mass 25 125.0
> set param_card mass 23 91.2
> set param_card mass 36 20.0
>
> and in the process card I use
> import model NMSSMHET --modelname
> generate p p > h01 , (h01 > z a01, z > b b~, a01 > mu+ mu-)
>
> Looking at the LHE plots, we see a clear peak for the Higgs boson.
> However the distribution of m_bb looks a bit strange (see the plot at
> https://drive.google.com/open?id=1NFvGxGVOJL6kwsCf-TzDja_ni-HUky2I ).
> For some masses below 25 GeV, we observe outliers in the Z mass
> distribution. The contribution of the outliers does not follow any
> specific order. For example we cannot tell if with lower m_a, outliers
> are more.
>
> However, when I generate h(125)->aa->2b2mu signal with p p > h01 , (h01
>> a01, a01, a01 > b b~, a01 > mu+ mu-), I find every thing perfect and
> expected.
>
> Would you please let me know what we could be missing?
>
>
> Best,
> Aashaq
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Aashaq Shah (aashiqphst) said : #4

Hi Olivier,

Thanks for the explanation. To let you know, we kept things default except setting the mass of Z and a.

Please find the cards for a_mass =9 GeV at github repo: https://github.com/aashaqshah/Higgs_Za_2b2m_Cards/tree/master

Now, If we want to force Z-boson exclusively On-Shell., how are we going to move ahead?

Many thanks once again.

Best,
Aashaq

Hi,

1) wget http://exotichiggs.physics.sunysb.edu/web/wopr/NMSSMHET.zip
fails with error 404

2) Your github does not contain the full param-card only the modification to the default card.
(which probably means that you put inconsitent width but except that i can not comment).

3) If you want to keep the Z exactly onshell, the only option is to use MadSpin either in spinmode set to
"none" (no spin-correlation and Z exactly onshell) or with spinmode set to "onshell" (spin-correlation but Z exaclyt onshell). You can not handle the decay inside the "main" part of MG5aMC for such approximation.

Cheers,

Olivier

On 9 Nov 2018, at 11:08, Aashaq Shah <<email address hidden><mailto:<email address hidden>>> wrote:

Question #675999 on MadGraph5_aMC@NLO changed:
https://answers.launchpad.net/mg5amcnlo/+question/675999

Aashaq Shah posted a new comment:

Hi Olivier,

Thanks for the explanation. To let you know, we kept things default
except setting the mass of Z and a.

Please find the cards for a_mass =9 GeV at github repo:
https://github.com/aashaqshah/Higgs_Za_2b2m_Cards/tree/master

Now, If we want to force Z-boson exclusively On-Shell., how are we going
to move ahead?

Many thanks once again.

Best,
Aashaq

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

Aashaq Shah (aashiqphst) said : #6

Hi Olivier,

Thanks for the suggestions. I will try with the your suggestions and will get back to this thread with the outcome.

Instead of doing wget, please find the model here https://cms-project-generators.web.cern.ch/cms-project-generators/ and see if you can manually download it.

Best,
Aashaq

Looks like the Z width is set to 0 in your model.
massive Particles with zero width will lead to instabilitty if they are on a resonance s-channel with decay.
(which is inconsistent with the zero width assumptions).

So you have to modify your model in order to allow the model to include the correct Z-width.

Cheers,

Olivier

On 9 Nov 2018, at 11:43, Aashaq Shah <<email address hidden><mailto:<email address hidden>>> wrote:

 https://cms-project-<https://cms-project-/>
generators.web.cern.ch/cms-project-generators/<http://generators.web.cern.ch/cms-project-generators/>

Aashaq Shah (aashiqphst) said : #8

Hi,

I just realized that the model page I shared has excess only to CMS people and not sure if you could download it.
Here again, I have uploaded it to google drive and please find it at https://drive.google.com/open?id=1Y2cYICW1HfOByzYtOgDeQr9eLnyoXrjt

I will see if things can be fixed. Thanks a lot for the prompt replies and discussion.

Best,
Aashaq

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