LHE file generated for Pythia

Asked by Antara Sarkar on 2019-05-30

Hi,
I am new to Madgraph and Pythia. I have few questions:
1) I generated higgs from p-p collision in sm : p p > h [QCD]
Then, with the LHE file generated at parton level, I am trying to further decay the higgs to photons in Pythia. However, the photons produced there are found to be very soft and probably not coming from the higgs produced in Madgraph. What could be the reason here? Do I have to change the decay width of higgs in param_card in Madgraph?
2) How to generate two photons from higgs in sm?
3) Also, suppose I generate a process p p > h a and I wish to study the energy distribution of photon produced. What is the syntax for it to be written in the plot_card?
Regards,
Antara

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Last query:
2019-05-31
Last reply:
2019-05-31

Hi,

For the first question, I guess that you did not specify correctly the Higgs decay mode within pythia.
I have however no clue how to do this since I barelly use pythia myself.

2) How to generate two photons from higgs in sm?

I guess that the following paper should help you. It contains a full section on Higgs production/decay within MG5aMC and what feature was added within MG5aMC to be able to handle such cases.
arXiv:1507.00020<http://arXiv.org/abs/arXiv:1507.00020>

3) Also, suppose I generate a process p p > h a and I wish to study the energy distribution of photon produced. What is the syntax for it to be written in the plot_card?
Regards,

Here
1) Energy distribution are not lorentz invariant, so this is typically not a distribution used for hadron collider.
In any case, you then actually to specify which frame you want to use (the typical two choices are the lab frame and the center of mass frame of the partonic process which is a better frame)

2) are you using MadAnalysis4? This code is not supported anymore and doing custom variable is far from trivial. I would suggest to use MAdAalysis5 instead.

Cheers,

Olivier

On 30 May 2019, at 15:32, Antara Sarkar <<email address hidden><mailto:<email address hidden>>> wrote:

New question #681142 on MadGraph5_aMC@NLO:
https://answers.launchpad.net/mg5amcnlo/+question/681142

Hi,
I am new to Madgraph and Pythia. I have few questions:
1) I generated higgs from p-p collision in sm : p p > h [QCD]
Then, with the LHE file generated at parton level, I am trying to further decay the higgs to photons in Pythia. However, the photons produced there are found to be very soft and probably not coming from the higgs produced in Madgraph. What could be the reason here? Do I have to change the decay width of higgs in param_card in Madgraph?
2) How to generate two photons from higgs in sm?
3) Also, suppose I generate a process p p > h a and I wish to study the energy distribution of photon produced. What is the syntax for it to be written in the plot_card?
Regards,
Antara

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Antara Sarkar (antarasarkar) said : #2

Thanks for your response.
For the 1st question, where I generated p p > h [QCD] in Madgraph, I had set the decay width of higgs "auto" in the param_card. Now, with the LHE file obtained here I was trying to decay this higgs to two photons in Pythia. However, there I find that no photon is produced from higgs which is produce in Madgraph. Below is the decay information of higgs from the LHE file. Here, I find no higgs decaying to photons. Then, am I wrong in saying that this is the reason I find no photons from higgs? Also, could you please tell me how to solve this? I wish to study photons produced from the higgs.

# PDG Width
DECAY 25 6.505493e-03
# BR NDA ID1 ID2 ...
   8.286536e-01 2 -5 5 # 0.00539080019422
   3.977408e-02 2 -15 15 # 0.000258749999021
   1.998158e-02 3 -2 1 24 # 0.000129990028819
   1.998158e-02 3 -4 3 24 # 0.000129990028819
   1.980634e-02 3 -24 -1 2 # 0.000128850006226
   1.980634e-02 3 -24 -3 4 # 0.000128850006226
   6.645461e-03 3 -12 11 24 # 4.32320000173e-05
   6.645461e-03 3 -14 13 24 # 4.32320000173e-05
   6.578057e-03 3 -24 -11 12 # 4.27935037671e-05
   6.578057e-03 3 -24 -13 14 # 4.27935037671e-05
   6.524025e-03 3 -16 15 24 # 4.24419989693e-05
   6.513265e-03 3 -24 -15 16 # 4.23719998646e-05
   1.957807e-03 3 -1 1 23 # 1.27364997339e-05
   1.957807e-03 3 -3 3 23 # 1.27364997339e-05
   1.570673e-03 3 -5 5 23 # 1.02180022068e-05
   1.532244e-03 3 -2 2 23 # 9.96800261629e-06
   1.532244e-03 3 -4 4 23 # 9.96800261629e-06
   8.815115e-04 3 -12 12 23 # 5.73466689267e-06
   8.815115e-04 3 -14 14 23 # 5.73466689267e-06
   8.815115e-04 3 -16 16 23 # 5.73466689267e-06
   4.465611e-04 3 -11 11 23 # 2.90510011012e-06
   4.465611e-04 3 -13 13 23 # 2.90510011012e-06
   4.237496e-04 3 -15 15 23 # 2.75670005655e-06

Regards,
Antara

Hi,

You can NOT use the width set to "Auto" for the Higgs since this mode does NOT include loop-induced decay. So you do not include h to two gluon which is not negligeable and therefore your total-width (and relative BR are wrong). This is also why you do not have any line for the higgs decaying into two photons.

My advise here would be to follow the above paper and do the decay of the Higgs within MG5aMC
via the MadSpin package.

Cheers,

Olivier

> On 31 May 2019, at 10:13, Antara Sarkar <email address hidden> wrote:
>
> Question #681142 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/681142
>
> Status: Answered => Open
>
> Antara Sarkar is still having a problem:
> Thanks for your response.
> For the 1st question, where I generated p p > h [QCD] in Madgraph, I had set the decay width of higgs "auto" in the param_card. Now, with the LHE file obtained here I was trying to decay this higgs to two photons in Pythia. However, there I find that no photon is produced from higgs which is produce in Madgraph. Below is the decay information of higgs from the LHE file. Here, I find no higgs decaying to photons. Then, am I wrong in saying that this is the reason I find no photons from higgs? Also, could you please tell me how to solve this? I wish to study photons produced from the higgs.
>
> # PDG Width
> DECAY 25 6.505493e-03
> # BR NDA ID1 ID2 ...
> 8.286536e-01 2 -5 5 # 0.00539080019422
> 3.977408e-02 2 -15 15 # 0.000258749999021
> 1.998158e-02 3 -2 1 24 # 0.000129990028819
> 1.998158e-02 3 -4 3 24 # 0.000129990028819
> 1.980634e-02 3 -24 -1 2 # 0.000128850006226
> 1.980634e-02 3 -24 -3 4 # 0.000128850006226
> 6.645461e-03 3 -12 11 24 # 4.32320000173e-05
> 6.645461e-03 3 -14 13 24 # 4.32320000173e-05
> 6.578057e-03 3 -24 -11 12 # 4.27935037671e-05
> 6.578057e-03 3 -24 -13 14 # 4.27935037671e-05
> 6.524025e-03 3 -16 15 24 # 4.24419989693e-05
> 6.513265e-03 3 -24 -15 16 # 4.23719998646e-05
> 1.957807e-03 3 -1 1 23 # 1.27364997339e-05
> 1.957807e-03 3 -3 3 23 # 1.27364997339e-05
> 1.570673e-03 3 -5 5 23 # 1.02180022068e-05
> 1.532244e-03 3 -2 2 23 # 9.96800261629e-06
> 1.532244e-03 3 -4 4 23 # 9.96800261629e-06
> 8.815115e-04 3 -12 12 23 # 5.73466689267e-06
> 8.815115e-04 3 -14 14 23 # 5.73466689267e-06
> 8.815115e-04 3 -16 16 23 # 5.73466689267e-06
> 4.465611e-04 3 -11 11 23 # 2.90510011012e-06
> 4.465611e-04 3 -13 13 23 # 2.90510011012e-06
> 4.237496e-04 3 -15 15 23 # 2.75670005655e-06
>
> Regards,
> Antara
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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