# Matching issues in EWK Vjj + j production

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://

Your advice is very much appreciated.

thanks,

Pedro

-------

[1] proc card http://

run card http://

[2] Pythia8 matching parameters

JetMatching:setMad = on

JetMatching:scheme = 1

JetMatching:merge = on

JetMatching:

JetMatching:

JetMatching:

JetMatching:

JetMatching:qCut = 20 (xqcut=10)

JetMatching:nQmatch = 5

JetMatching:nJetMax = 1

JetMatching:

TimeShower:

## Question information

- Language:
- English Edit question

- Status:
- Answered

- Assignee:
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- 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:/

>

> 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://

> Your advice is very much appreciated.

> thanks,

> Pedro

>

> -------

>

> [1] proc card http://

> run card http://

>

> [2] Pythia8 matching parameters

> JetMatching:setMad = on

> JetMatching:scheme = 1

> JetMatching:merge = on

> JetMatching:

> JetMatching:

> JetMatching:

> JetMatching:

> JetMatching:qCut = 20 (xqcut=10)

> JetMatching:nQmatch = 5

> JetMatching:nJetMax = 1

> JetMatching:

> TimeShower:

>

> --

> 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://

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:/

>

> 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://

>

> 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.

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