madgraph+shower

Asked by HuanyuBi on 2018-12-21

Dear experts,

I want to study the parton shower effect on p p > z z h [QCD]. So I generate the events in the following. There are two options that I don't know how to set.

generate p p > z z h [QCD]
output pp-zzh-test
launch
/=================================================================================\
| 1. Type of perturbative computation order = NLO |
| 2. No MC@[N]LO matching / event generation fixed_order = OFF |
| 3. Shower the generated events shower = PYTHIA8 |
| 4. Decay onshell particles madspin = OFF |
| 5. Add weights to events for new hypp. reweight = OFF |
| 6. Run MadAnalysis5 on the events generated madanalysis = OFF |
\=================================================================================/
enter

Then, in the run_card.dat there is a ickkw option, and I don't know which one is suitable for my current study.
#***********************************************************************
# ickkw parameter: *
# 0: No merging *
# 3: FxFx Merging - WARNING! Applies merging only at the hard-event *
# level. After showering an MLM-type merging should be applied as *
# well. See http://amcatnlo.cern.ch/FxFx_merging.htm for details. *
# 4: UNLOPS merging (with pythia8 only). No interface from within *
# MG5_aMC available, but available in Pythia8. *
# -1: NNLL+NLO jet-veto computation. See arxiv:1412.8408 [hep-ph]. *
#***********************************************************************
0 = ickkw

In the shower_card.dat, how to correctly set these two options.
# FxFx merging parameters !ONLY FOR PYTHIA8!
#***********************************************************************
Qcut = -1.0 # Merging scale
njmax = 0 # Maximal multiplicity in the merging
#***********************************************************************

Thanks!

Huanyu Bi

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
2018-12-22
Last reply:
2018-12-22

From the information that I see in your mail.
I would say that one correct option is to keep ickkw=0
and the two others parameter are then fine as well.

Now I do not know how you will handle those samples. If you want to merge those with other samples generated with
p p > z z h j [QCD]
Then obviously the above choice is not appropriate.

Cheers,

Olivier

HuanyuBi (bihuanyu) said : #2

Dear Olivier,
Thank you for your answer. I don't plan to merge pp>zzh [QCD] with pp>zzhj. I have another problem.
I want to compare some differential distribution, e.g, the transverse momentum of higgs (PT(h1)) before and after parton shower. I use ma5
>ma5
>import event.lhe.gz
>plot PT(h1) 100 0 400 [logY]
>submit
then I get the PT(h1) before shower. To get the transverse momentum of higgs after shower, I type
>ma5
>import events_PYTHIA8_0.hepmc.gz
>plot PT(h1) 100 0 400 [logY interstate]
>plot PT(h1[1]) 100 0 400 [logY interstate]
>submit
The question is that the two distributions after shower, i.e., PT(h1) and PT(h1[1]), are different in shape, and the integral cross section of PT(h1) after shower is much bigger than that of PT(h1) before shower and that of PT(h1[1]) after shower, i.e., sigma(PT(h1))_NLO+PS >> sigma(PT(h1))_fNLO~sigma(PT(h1[1]))_NLO+PS.
So I want to know which step is wrong, and which differential distribution after shower ( PT(h1) or PT(h1[1]) ) is correct to compare with the distribution before shower.

Thank you very much!

Sincerely yours,

Huanyu Bi

At2018-12-22 04:03:05,Olivier Mattelaer<email address hidden>wrote:
> Your question #676961 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/676961
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> >From the information that I see in your mail.
> I would say that one correct option is to keep ickkw=0
> and the two others parameter are then fine as well.
>
> Now I do not know how you will handle those samples. If you want to merge those with other samples generated with
> p p > z z h j [QCD]
> Then obviously the above choice is not appropriate.
>
> Cheers,
>
> Olivier
>
> --
> 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/676961/+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/676961
>
> You received this question notification because you asked the question.

Hi,

Distribution "before PS" in NLO+PS are not physical and therefore should be used with caution.
So the typical comparison is between NLO+PS (with MC@NLO formalism) compare to fix-order NLO.
(which is not the same as "before PS" due to the MC@NLO substraction scheme removing double counting)

> The question is that the two distributions after shower, i.e., PT(h1) and PT(h1[1]), are different in shape,

This you should ask the MG5aMC author. This means that you have more than one Higgs plotted in your sample.

> and the integral cross section of PT(h1) after shower is much bigger than that of PT(h1) before shower and that of PT(h1[1]) after shower, i.e., sigma(PT(h1))_NLO+PS >> sigma(PT(h1))_fNLO~sigma(PT(h1[1]))_NLO+PS.

This is just because you have more than one Higgs entering the plot per-events.

Cheers,

Olivier

> On 22 Dec 2018, at 10:27, HuanyuBi <email address hidden> wrote:
>
> Question #676961 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/676961
>
> Status: Answered => Open
>
> HuanyuBi is still having a problem:
> Dear Olivier,
> Thank you for your answer. I don't plan to merge pp>zzh [QCD] with pp>zzhj. I have another problem.
> I want to compare some differential distribution, e.g, the transverse momentum of higgs (PT(h1)) before and after parton shower. I use ma5
>> ma5
>> import event.lhe.gz
>> plot PT(h1) 100 0 400 [logY]
>> submit
> then I get the PT(h1) before shower. To get the transverse momentum of higgs after shower, I type
>> ma5
>> import events_PYTHIA8_0.hepmc.gz
>> plot PT(h1) 100 0 400 [logY interstate]
>> plot PT(h1[1]) 100 0 400 [logY interstate]
>> submit
> The question is that the two distributions after shower, i.e., PT(h1) and PT(h1[1]), are different in shape, and the integral cross section of PT(h1) after shower is much bigger than that of PT(h1) before shower and that of PT(h1[1]) after shower, i.e., sigma(PT(h1))_NLO+PS >> sigma(PT(h1))_fNLO~sigma(PT(h1[1]))_NLO+PS.
> So I want to know which step is wrong, and which differential distribution after shower ( PT(h1) or PT(h1[1]) ) is correct to compare with the distribution before shower.
>
> Thank you very much!
>
> Sincerely yours,
>
> Huanyu Bi
>
> At2018-12-22 04:03:05,Olivier Mattelaer<email address hidden>wrote:
>> Your question #676961 on MadGraph5_aMC@NLO changed:
>> https://answers.launchpad.net/mg5amcnlo/+question/676961
>>
>> Status: Open => Answered
>>
>> Olivier Mattelaer proposed the following answer:
>>> From the information that I see in your mail.
>> I would say that one correct option is to keep ickkw=0
>> and the two others parameter are then fine as well.
>>
>> Now I do not know how you will handle those samples. If you want to merge those with other samples generated with
>> p p > z z h j [QCD]
>> Then obviously the above choice is not appropriate.
>>
>> Cheers,
>>
>> Olivier
>>
>> --
>> 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/676961/+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/676961
>>
>> You received this question notification because you asked the question.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Can you help with this problem?

Provide an answer of your own, or ask HuanyuBi for more information if necessary.

To post a message you must log in.