Generation of QCD inclusive multijet events in pp collision

Asked by suman on 2018-08-15

Hi all,
I want to generate QCD multijet event with MLM jet matching for PP collision. For this purpose I am going to used following step
with SM
generate p p > j j

in run_card

ptj_bias = bias_module
{'ptj_bias_target_ptj': 7000.0, 'ptj_bias_enhancement_power': 4.0} = bias_parameters
ickkw=1
xqcut =20
maxjetflavor=5

in pythia_card
!pythia_card_for merging
Beams:setProductionScalesFromLHEF=on
Beams:frameType=4

JetMatching:setMad = on
!JetMatching:doMerge = ickkw,
!JetMatching:qCut = xqcut,
!JetMatching:nQmatch = maxjetflavor,
!JetMatching:clFact = alpsfact.

JetMatching:scheme = 1 #1 for madgraph
JetMatching:merge = on
JetMatching:jetAlgorithm = 2 #2 for Slowjet
JetMatching:etaJetMax = 5
JetMatching:coneRadius = 1.0
JetMatching:slowJetPower = 1
JetMatching:nJetMax = 2
JetMatching:doShowerKt = off

but still there is miss match with the desire. The Pt distribution is underestimate than the PYTHIA8 generation and data.

Here I use independent PYTHIA8 generation with bellow setting

  pythia.readString("HardQCD:all = on"); //
  pythia.readString("PhaseSpace:pTHatMin = 15");
  pythia.readString("PhaseSpace:pTHatMax = 7000.0");
  pythia.readString("PhaseSpace:bias2Selection = on");
  pythia.readString("PhaseSpace:bias2SelectionPow = 4.0");
  pythia.readString("Beams:eCM = 13000.");

so please suggest me if the above madgraph setting is right for comparison with the PYTHIA8 generation as stated bellow setting?
or I have to try any different combination matching of jet ?

Thanks in advance.

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
suman
Solved:
2018-08-15
Last query:
2018-08-15
Last reply:
2018-08-15

You need to have more than one multiplicity for mlm.

Please use
 generate p p > j j
Add process p p > j j j
 And so on for up to the number of jet that you want

Cheers

Olivier

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________________________________
From: <email address hidden> <email address hidden> on behalf of suman <email address hidden>
Sent: Wednesday, August 15, 2018 7:52:51 AM
To: Olivier Mattelaer
Subject: [Question #672282]: Generation of QCD inclusive multijet events in pp collision

New question #672282 on MadGraph5_aMC@NLO:
https://answers.launchpad.net/mg5amcnlo/+question/672282

Hi all,
I want to generate QCD multijet event with MLM jet matching for PP collision. For this purpose I am going to used following step
with SM
generate p p > j j

in run_card

ptj_bias = bias_module
{'ptj_bias_target_ptj': 7000.0, 'ptj_bias_enhancement_power': 4.0} = bias_parameters
ickkw=1
xqcut =20
maxjetflavor=5

in pythia_card
!pythia_card_for merging
Beams:setProductionScalesFromLHEF=on
Beams:frameType=4

JetMatching:setMad = on
!JetMatching:doMerge = ickkw,
!JetMatching:qCut = xqcut,
!JetMatching:nQmatch = maxjetflavor,
!JetMatching:clFact = alpsfact.

JetMatching:scheme = 1 #1 for madgraph
JetMatching:merge = on
JetMatching:jetAlgorithm = 2 #2 for Slowjet
JetMatching:etaJetMax = 5
JetMatching:coneRadius = 1.0
JetMatching:slowJetPower = 1
JetMatching:nJetMax = 2
JetMatching:doShowerKt = off

but still there is miss match with the desire. The Pt distribution is underestimate than the PYTHIA8 generation and data.

Here I use independent PYTHIA8 generation with bellow setting

  pythia.readString("HardQCD:all = on"); //
  pythia.readString("PhaseSpace:pTHatMin = 15");
  pythia.readString("PhaseSpace:pTHatMax = 7000.0");
  pythia.readString("PhaseSpace:bias2Selection = on");
  pythia.readString("PhaseSpace:bias2SelectionPow = 4.0");
  pythia.readString("Beams:eCM = 13000.");

so please suggest me if the above madgraph setting is right for comparison with the PYTHIA8 generation as stated bellow setting?
or I have to try any different combination matching of jet ?

Thanks in advance.

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

suman (sumanmg5) said : #2

Thanks olivier, for the quick answer.

I understand that for MLM
I will use p p > j j
        add process p p > j j j
        and so on.

But Here I have three more queries ;
1. what is the maximum number of additional jet should I add?
 I like to mention that here I am try to generate only LO order matching MC sample with pythia8.2

2.What will be the JetMatching:nJetMax value for this differnet jet addition in p p > j j process in showering card pythia_card.dat ?

3. What will be the treatment when I will go for NLO order generation ? i.e. p p > j j [QCD]

Thanks and Regards,

Hi,

> 1. what is the maximum number of additional jet should I add?
> I like to mention that here I am try to generate only LO order matching MC sample with pythia8.2

That's first depend of the observable that you are looking for.
And second on how much cpu time you have available for the computation (the complexity grows more than factorially)

> 2.What will be the JetMatching:nJetMax value for this differnet jet
> addition in p p > j j process in showering card pythia_card.dat ?

For this process
> JetMatching:nJetMin
should be on 2
and
> JetMatching:nJetMax
should be set according to the highest multiplicity sample.
If you use our interface this one is set automatically.
but if you stop at 3 jet then you have to set it to 3,
if you stop at 4 jets, then you have to set it at 4 (and so on)

> 3. What will be the treatment when I will go for NLO order generation ?
> i.e. p p > j j [QCD]

MLM is only LO,
the closest equivalent is FxFx for NLO, but that method does not support di-jet production.
Another possibility is to use UNLOPS, but I have no experience in that one.

Cheers,

Olivier

> On 15 Aug 2018, at 10:09, suman <email address hidden> wrote:
>
> Question #672282 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/672282
>
> Status: Answered => Open
>
> suman is still having a problem:
> Thanks olivier, for the quick answer.
>
> I understand that for MLM
> I will use p p > j j
> add process p p > j j j
> and so on.
>
> But Here I have three more queries ;
> 1. what is the maximum number of additional jet should I add?
> I like to mention that here I am try to generate only LO order matching MC sample with pythia8.2
>
> 2.What will be the JetMatching:nJetMax value for this differnet jet
> addition in p p > j j process in showering card pythia_card.dat ?
>
> 3. What will be the treatment when I will go for NLO order generation ?
> i.e. p p > j j [QCD]
>
> Thanks and Regards,
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

suman (sumanmg5) said : #4

Thanks Olivier for all the answer.
It will help me a lots since I am new with madgraph. Thanks again.

Best regards ,