# LbL with lepton beams

Dear experts,

is Light by Light from electron beams available in any model in MG5?

Thank you

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- Last query:
- 2021-02-05

- Last reply:
- 2021-02-05

This has nothing to do with the UFO model right,

But we do have special PDF for photon from electron (or from muon)

You can set the beam to '2" for electron and "3" for muon

Cheers,

Olivier

> On 29 Jan 2021, at 15:05, Patricia Rebello Teles <email address hidden> wrote:

>

> New question #695253 on MadGraph5_aMC@NLO:

> https:/

>

> Dear experts,

>

> is Light by Light from electron beams available in any model in MG5?

>

> Thank you

>

> --

> You received this question notification because you are an answer

> contact for MadGraph5_aMC@NLO.

Hi Olivier,

actually, a a > a a is not accepted using default SM.

NoDiagramException : No amplitudes generated from process

Tried also loop_SM without success. Same diagram exception msg.

since there is a loop, is this loop for aa > aa diagram implemented in any MG5 model?

Cheers Pat

You indeed need a model that can handle electroweak loop if you want to have such loop-induced processes.

You can do this via

import model loop_qcd_qed_sm

generate a a > a a [noborn=QED]

output

launch

set lpp 2

set fixed_scale 5

Cheers,

Olivier

Thank you Olivier. It looks great

Sent from my iPad

> On 29 Jan 2021, at 16:35, Olivier Mattelaer <email address hidden> wrote:

>

> Your question #695253 on MadGraph5_aMC@NLO changed:

> https:/

>

> Status: Open => Answered

>

> Olivier Mattelaer proposed the following answer:

> You indeed need a model that can handle electroweak loop if you want to have such loop-induced processes.

> You can do this via

>

> import model loop_qcd_qed_sm

> generate a a > a a [noborn=QED]

> output

> launch

> set lpp 2

> set fixed_scale 5

>

> Cheers,

>

> Olivier

>

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> You received this question notification because you asked the question.

Hi Olivier

few questions:

1) is there any implementation paper about the loop_qcd_qed_sm model? I would like to understand the model particles "g+,g-", "ghwp, ghwp~" among others.

2) how can I set up the s-quark, c-quark, and b-quark boxes, as well as the muon and tau ones? I am using [virt=QCD QED] but only top u, d quarks appear. How I can assume all particles that have no zero masses to be considered in the loops?

thank you

1) is there any implementation paper about the loop_qcd_qed_sm model? I would like to understand the model particles "g+,g-", "ghwp, ghwp~" among others.

Those are standard gosth. This is likely commented in 1405.0301

2) how can I set up the s-quark, c-quark, and b-quark boxes, as well as the muon and tau ones? I am using [virt=QCD QED] but only top u, d quarks appear. How I can assume all particles that have no zero masses to be considered in the loops?

First s-quark, c-quark and b-quark are massless in that model the same is true for the muon and the tau.

Actually those feynman diagram are present but since they are exactly identical they are not represented.

But you can see that if you forbid loop with electron, you will the digram appearing for the muon.

Cheers,

Olivier

hi Olivier thank you

sorry but where exactly can I find "gosth" related information (what does gosth mean btw) below?

https:/

About (2) how can I forbid loop with electron?

Sorry but I am not familiar with Loop processes (actually it uses Ninja and Collier packages). Is there any MG5 manual with all these details? for instance the definition for the keys noborn, sqrtvirt, virt etc)

Cheers Pat

For the manual, the main reference is the above paper.

except for the "noborn=" which is more recent and has his own paper:

1507.00020.

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