BSM Processes with tree + loop diagrams

Asked by Ilaria Brivio on 2020-06-19

Dear authors,

I am trying to generate g g > z z with an NLO UFO that contains a BSM particle X, such that the process happens at 1-loop in the SM (via boxes plus the Higgs diagram ) and at tree level in the BSM contribution gg > X > zz.

I was wondering if there is any way to include both classes of diagrams in the same event generation.
and if yes, is there any chance of isolating the interference term between BSM tree and NLO SM?

The BSM couplings have an interaction order NP but no QCD or QED.

So far I have verified that I can produce
* BSM tree alone with g g > z z NP=2
* SM 1-loop alone with g g > z z NP=0 [QCD]
* SM + BSM 1-loop only, with g g > z z QED=2 NP=2 [noborn=QCD]
* BSM tree + BSM 1-loop + SM NLO with real emissions, but without SM boxes and Higgs contributions, with g g > z z NP=2 [QCD]
  however, the event generation of this process crashes due to poles not canceling

I have also looked at the twiki page https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LoopInducedTimesTree
I implemented the modifications needed, patched my model with prepare_model_for_loopInducedXTrees and in ths way I was able to isolate the interference between BSM and SM at pure 1-loop, via
g g > z z BKG_NP=2 NP=2 QED=2 QCD=2 [noborn=QCD BKG_NP] BKG_NP^2==2

still, I wasn't able to figure out a syntax that can give me BSM tree + SM 1 loop diagrams without extra jets.

Is this really impossible in MG, or am I missing something?

Thank you very much in advance!
Ilaria

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Ilaria Brivio
Solved:
2020-06-19
Last query:
2020-06-19
Last reply:
2020-06-19

Indeed this is not possible.
You can likely modify this hack to make it work:
https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LoopInducedTimesTree <https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LoopInducedTimesTree>

But I do not support such hack of the code.

Cheers,

Olivier

> On 19 Jun 2020, at 11:35, Ilaria Brivio <email address hidden> wrote:
>
> New question #691402 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/691402
>
> Dear authors,
>
> I am trying to generate g g > z z with an NLO UFO that contains a BSM particle X, such that the process happens at 1-loop in the SM (via boxes plus the Higgs diagram ) and at tree level in the BSM contribution gg > X > zz.
>
> I was wondering if there is any way to include both classes of diagrams in the same event generation.
> and if yes, is there any chance of isolating the interference term between BSM tree and NLO SM?
>
> The BSM couplings have an interaction order NP but no QCD or QED.
>
> So far I have verified that I can produce
> * BSM tree alone with g g > z z NP=2
> * SM 1-loop alone with g g > z z NP=0 [QCD]
> * SM + BSM 1-loop only, with g g > z z QED=2 NP=2 [noborn=QCD]
> * BSM tree + BSM 1-loop + SM NLO with real emissions, but without SM boxes and Higgs contributions, with g g > z z NP=2 [QCD]
> however, the event generation of this process crashes due to poles not canceling
>
> I have also looked at the twiki page https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/LoopInducedTimesTree
> I implemented the modifications needed, patched my model with prepare_model_for_loopInducedXTrees and in ths way I was able to isolate the interference between BSM and SM at pure 1-loop, via
> g g > z z BKG_NP=2 NP=2 QED=2 QCD=2 [noborn=QCD BKG_NP] BKG_NP^2==2
>
> still, I wasn't able to figure out a syntax that can give me BSM tree + SM 1 loop diagrams without extra jets.
>
> Is this really impossible in MG, or am I missing something?
>
> Thank you very much in advance!
> Ilaria
>
>
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Ilaria Brivio (ilariab) said : #2

Hi Olivier,

thanks for the quick reply.

I am totally fine with taking responsibility for the hack. ;)

It's not completely clear to me how to make it work though. I have tried already but it seems I can't get the set of diagrams I need.
Does it work with any interaction order in principle? Do I need to have tree-level counterterms for the BSM vertices? In that case that might be the issue, cause the BSM part is not renormalized in the UFO (it's an eft at LO)

Thanks again!
Ilaria

Hi,

I do not know the details of such hack.
But if your are able to compute the interference term with the associated model,
you should be able to compute other terms (I guess)

> It's not completely clear to me how to make it work though.

We are at the same level here. I have no clue how to do it

Cheers,

Olivier

> On 19 Jun 2020, at 12:11, Ilaria Brivio <email address hidden> wrote:
>
> Question #691402 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/691402
>
> Status: Answered => Open
>
> Ilaria Brivio is still having a problem:
> Hi Olivier,
>
> thanks for the quick reply.
>
> I am totally fine with taking responsibility for the hack. ;)
>
> It's not completely clear to me how to make it work though. I have tried already but it seems I can't get the set of diagrams I need.
> Does it work with any interaction order in principle? Do I need to have tree-level counterterms for the BSM vertices? In that case that might be the issue, cause the BSM part is not renormalized in the UFO (it's an eft at LO)
>
> Thanks again!
> Ilaria
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Ilaria Brivio (ilariab) said : #4

Hi,

it's ok, that makes sense. I'll see if I can get it to work then.

Thanks again!
Ilaria