MadGraph5_aMC@NLO

Pdf for elastic and inelastic photons

Asked by Alexa

Hi,

I read some previous solved questions, but I am not sure about two things:

1) If I generate a process with initial photons and in "run_card.dat" I select option 1 for beam type, then this is only for inelastic photons. But if my pdf is "nn23lo1", then it takes into account inelastic and elastic photons (so I understand that semi-elastic also). Is this true? Is this the "total" of all contributions?

2) If I select option 2 for beam type ("photon from proton"), then it is only for elastic photons. But if my pdf is "nn23lo1", it is still giving me only elastic photons, or should I select any other pdf? (and which one?)

Thank you very much,
Alexandra L.

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Olivier Mattelaer
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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Dear Alexandra,

If you set lpp on 1. Then we use ONLY the information from the PDF set.
However each PDF collaboration use different convention for photon pdf.
So you need to check the details for the set that you are interesting in.
NNPDF collaboration include both elastic and inelastic contribution.
(But the error is very very large)

If you set lpp on 2, then you do not not use the PDF set at all, you will have the same result, if you have cteq6l1 as pdf or nn23lo1.
In that case you have only elastic photon [described from theory, so very small error]

Cheers,

Oliver

> On Aug 28, 2016, at 17:46, Alexa <email address hidden> wrote:
>
> New question #369755 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/369755
>
> Hi,
>
> I read some previous solved questions, but I am not sure about two things:
>
> 1) If I generate a process with initial photons and in "run_card.dat" I select option 1 for beam type, then this is only for inelastic photons. But if my pdf is "nn23lo1", then it takes into account inelastic and elastic photons (so I understand that semi-elastic also). Is this true? Is this the "total" of all contributions?
>
> 2) If I select option 2 for beam type ("photon from proton"), then it is only for elastic photons. But if my pdf is "nn23lo1", it is still giving me only elastic photons, or should I select any other pdf? (and which one?)
>
> Thank you very much,
> Alexandra L.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Alexa (alexa-l) said : 		#2

Hi,

Could you give me an advise about a pdf set that doesn't give big errors and includes both elastic and inelastic photons?

Thank you,
Alexandra L.

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#3

I do not think that such Pdf exists.

Cheers,

Olivier

> On Aug 28, 2016, at 19:56, Alexa <email address hidden> wrote:
>
> Question #369755 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/369755
>
> Status: Answered => Open
>
> Alexa is still having a problem:
> Hi,
>
> Could you give me an advise about a pdf set that doesn't give big errors
> and includes both elastic and inelastic photons?
>
> Thank you,
> Alexandra L.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Alexa (alexa-l) said : 		#4

Ok, thank you. I have some questions more:

1) Could you tell me how large is the error in the inclusive case (approximately, so I could have an idea of the %)?
2) If I want only the inelastic case, then I select the option 1 in the beam type, but what pdf should I choose (and if you know how big could be the error, not exactly, but just as a benchmark)?

Or if you could give me a link where I could read more about this.
Thank you very much for your help,
Alexandra L.

Revision history for this message
Best Olivier Mattelaer (olivier-mattelaer) said : 		#5

Hi,

I’m not a PDF expert, so I can not really answer your question.

> 1) Could you tell me how large is the error in the inclusive case (approximately, so I could have an idea of the %)?

For this you just need to with the pdf errorset to know what the error is.
This can be done automatically if you install SysCalc in madgraph (install SysCalc)

> 2) If I want only the inelastic case, then I select the option 1 in the beam type, but what pdf should I choose (and if you know how big could be the error, not exactly, but just as a benchmark)?

I believe that the cteq collaboration release the pdf that you are looking at. Please check on lhapdf wich pdfset have photon included
and go to the associated paper to learn if that include elastic component or not.

> Or if you could give me a link where I could read more about this.

I would suggest to link at the paper of the various collaboration who made such pdf available.

Cheers,

Olivier

> On Aug 28, 2016, at 22:27, Alexa <email address hidden> wrote:
>
> Question #369755 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/369755
>
> Status: Answered => Open
>
> Alexa is still having a problem:
> Ok, thank you. I have some questions more:
>
> 1) Could you tell me how large is the error in the inclusive case (approximately, so I could have an idea of the %)?
> 2) If I want only the inelastic case, then I select the option 1 in the beam type, but what pdf should I choose (and if you know how big could be the error, not exactly, but just as a benchmark)?
>
> Or if you could give me a link where I could read more about this.
> Thank you very much for your help,
> Alexandra L.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Revision history for this message
Alexa (alexa-l) said : 		#6

Thanks Olivier Mattelaer, that solved my question.