VBF and photon fusion

Asked by Gang Li on 2019-06-27

Hi,

I want to generate a pair of doubly-charged Higgs bosons (h++, h--) at the LHC in the vector boson fusion processes, including photon, W and Z boson-fusion subprocesses.

As I know, if I need the subprocess with only photon fusion, I could do as "a a > h++ h-- " including elastic and inelastic scattering. But I want to include all the fusion subprocesses, namely photon-photon fusion, W boson-W boson fusion, photon-W boson, and so on.

So if I generates events in p p > j j h++ h--. I checked that all Feynman diagrams are included. It is weird that even if I did not impose any cut there was no colliear divergence appearing. So I would like to ask if p p > j j h++ h-- included the contributions from photon fusion?

Besides I found the cross section of p p > j j h++ h-- is unreasonble large even if I impose cuts ptj > 10 GeV. I am not sure what has happened.

I used pdf "nn23lo1" and MG5_aMC_v2_6_5 and MG5_aMC_v2_4_3. I could provide model file for validation if needed.

Thanks very much.

Gang

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
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Last query:
2019-06-28
Last reply:
2019-06-28

Hi,

So if I generates events in p p > j j h++ h--. I checked that all Feynman diagrams are included. It is weird that even if I did not impose any cut there was no colliear divergence appearing. So I would like to ask if p p > j j h++ h-- included the contributions from photon fusion?

This certainly does not include the elastic scattering but it does include the inelastic scattering if you see the associate Feynman Diagram. (but it is possible --actually likely-- that your syntax does not include it.

Besides I found the cross section of p p > j j h++ h-- is unreasonble large even if I impose cuts ptj > 10 GeV. I am not sure what has happened.

This might be the sign of divergence actually or that some width are wrongly set.

Cheers,

Olivier

Gang Li (ligangpku) said : #2

Hi Olivier,

thanks for your prompt reply.

I could generate 10000 events of p p > j j h++ h-- without any cut rapidly. Then I guessed no divergence appeared. Since you said p p > j j h++ h-- includes inelastic scattering of photons. Do you mean that there is no divergence in inelastic scattering of initial photons and not necessary to impose a cut on jet pt?

Thanks.

Gang

Hi,

> Since you said p p > j j
> h++ h-- includes inelastic scattering of photons.

I did not say that. I said that it is unlikely to be included, but if you see it you have it.

> Do you mean that there
> is no divergence in inelastic scattering of initial photons and not
> necessary to impose a cut on jet pt?

Well in this case, you do not have initial photon, only intermediate photon.
and you have an automatic cut linked to the dynamical scale choice (at 4 GeV^2).
which can act as a regulator. For the rest, I do not know your process in order to be able to claim anything)

Cheers,

Olivier

> On 27 Jun 2019, at 16:52, Gang Li <email address hidden> wrote:
>
> Question #681649 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/681649
>
> Status: Answered => Open
>
> Gang Li is still having a problem:
> Hi Olivier,
>
> thanks for your prompt reply.
>
> I could generate 10000 events of p p > j j h++ h-- without any cut
> rapidly. Then I guessed no divergence appeared. Since you said p p > j j
> h++ h-- includes inelastic scattering of photons. Do you mean that there
> is no divergence in inelastic scattering of initial photons and not
> necessary to impose a cut on jet pt?
>
> Thanks.
>
> Gang
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Gang Li (ligangpku) said : #4

Hi Olivier,

thanks very much.

> and you have an automatic cut linked to the dynamical scale choice (at 4 GeV^2).
which can act as a regulator

Is it possible to change the "dynamic scale choice"?

Best,
Gang

Sure this is a parameter of the run_card.

Cheers,

Olivier

> On 28 Jun 2019, at 16:42, Gang Li <email address hidden> wrote:
>
> Question #681649 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/681649
>
> Status: Answered => Open
>
> Gang Li is still having a problem:
> Hi Olivier,
>
> thanks very much.
>
>> and you have an automatic cut linked to the dynamical scale choice (at 4 GeV^2).
> which can act as a regulator
>
> Is it possible to change the "dynamic scale choice"?
>
> Best,
> Gang
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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