Matching issues in EWK Vjj + j production

Asked by PedroSilva on 2017-12-21

Dear experts,
i'm trying to generate EWK gamma jj with up to an additional jet in MG5 v2.5.5, with

generate p p > a j j / t t~ h QED=4 QCD=0 @0
add process p p > a j j j / t t~ h QED=4 QCD=1 @1

The run/proc cards can be found here [1]
I then shower the events with Pythia8 using the parameters listed below [2]
and compare the result to a LO production of EWK gamma jj
and get incoherent results as if the matching procedure is also affecting the EWK produced jets.
A set of plots is available here http://cmsdoc.cern.ch/~psilva/EWKVjj/photon_LOvsMLM/
Your advice is very much appreciated.
thanks,
Pedro

--------------------------------------------------------------------------------------

[1] proc card http://cmsdoc.cern.ch/~psilva/EWKVjj/ewkajj_5f_LO_MLM_proc_card.dat
      run card http://cmsdoc.cern.ch/~psilva/EWKVjj/ewkajj_5f_LO_MLM_run_card.dat

[2] Pythia8 matching parameters
JetMatching:setMad = on
JetMatching:scheme = 1
JetMatching:merge = on
JetMatching:jetAlgorithm = 2
JetMatching:etaJetMax = 5.
JetMatching:coneRadius = 1.
JetMatching:slowJetPower = 1
JetMatching:qCut = 20 (xqcut=10)
JetMatching:nQmatch = 5
JetMatching:nJetMax = 1
JetMatching:doShowerKt = off
TimeShower:mMaxGamma = 4.0

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
2017-12-21
Last reply:
2017-12-21

Hi,

Do you have the DJR plot? This are the plot to look at in those case.

Otherwise, I would suggest to double check pythia documentation for
1) JetMatching:setMad = on
since when we make our MG5aMC to pythia interface, we decide to keep this flag to off. (Mainly because it has side effect on Qcut if I remember correctly)

2) JetMatching:nJetMax = 1
For your computation, I would have naively set that parameter to 3. So please check (and contact PY8 author if you are not sure)

Cheers,

Olivier

> On 21 Dec 2017, at 09:33, PedroSilva <email address hidden> wrote:
>
> New question #662037 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/662037
>
> Dear experts,
> i'm trying to generate EWK gamma jj with up to an additional jet in MG5 v2.5.5, with
>
> generate p p > a j j / t t~ h QED=4 QCD=0 @0
> add process p p > a j j j / t t~ h QED=4 QCD=1 @1
>
> The run/proc cards can be found here [1]
> I then shower the events with Pythia8 using the parameters listed below [2]
> and compare the result to a LO production of EWK gamma jj
> and get incoherent results as if the matching procedure is also affecting the EWK produced jets.
> A set of plots is available here http://cmsdoc.cern.ch/~psilva/EWKVjj/photon_LOvsMLM/
> Your advice is very much appreciated.
> thanks,
> Pedro
>
> --------------------------------------------------------------------------------------
>
> [1] proc card http://cmsdoc.cern.ch/~psilva/EWKVjj/ewkajj_5f_LO_MLM_proc_card.dat
> run card http://cmsdoc.cern.ch/~psilva/EWKVjj/ewkajj_5f_LO_MLM_run_card.dat
>
> [2] Pythia8 matching parameters
> JetMatching:setMad = on
> JetMatching:scheme = 1
> JetMatching:merge = on
> JetMatching:jetAlgorithm = 2
> JetMatching:etaJetMax = 5.
> JetMatching:coneRadius = 1.
> JetMatching:slowJetPower = 1
> JetMatching:qCut = 20 (xqcut=10)
> JetMatching:nQmatch = 5
> JetMatching:nJetMax = 1
> JetMatching:doShowerKt = off
> TimeShower:mMaxGamma = 4.0
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

PedroSilva (psilva-3) said : #2

Dear Olivier,
thanks for the fast feedback.
Indeed already changing

JetMatching:setMad = off
JetMatching:nJetMax = 3

improved considerably the situation.
The updated plots are here

http://cmsdoc.cern.ch/~psilva/EWKVjj/photon_LOvsMLM/

I left nJetMax=1 as a cross check - i thought the EWK produced jets would be automatically left out of the matching procedure leaving only up to 1 extra QCD emmission to be matched. I'll follow up with the Pythia8 authors to confirm nJetMax=3 should be used in this case.
Regarding the DJR plot, i don't have it at the moment but i'll try to produce it.

Thanks,
Pedro

One thing that might help as well is to set
> JetMatching:nJetMin = 2

Cheers,

Olivier
> On Dec 21, 2017, at 13:52, PedroSilva <email address hidden> wrote:
>
> Question #662037 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/662037
>
> PedroSilva posted a new comment:
> Dear Olivier,
> thanks for the fast feedback.
> Indeed already changing
>
> JetMatching:setMad = off
> JetMatching:nJetMax = 3
>
> improved considerably the situation.
> The updated plots are here
>
> http://cmsdoc.cern.ch/~psilva/EWKVjj/photon_LOvsMLM/
>
> I left nJetMax=1 as a cross check - i thought the EWK produced jets would be automatically left out of the matching procedure leaving only up to 1 extra QCD emmission to be matched. I'll follow up with the Pythia8 authors to confirm nJetMax=3 should be used in this case.
> Regarding the DJR plot, i don't have it at the moment but i'll try to produce it.
>
> Thanks,
> Pedro
>
> --
> 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 PedroSilva for more information if necessary.

To post a message you must log in.