MadGraph5_aMC@NLO

Photon pdf interface to LHAPDF

Asked by Florian Lyonnet

Hi,

I am using photon PDF via LHAPDF in MG5 and something is bothering me. When I look into the Source/PDF/pdf_lhapdf.f
the evolution of the photon pdf is done via the call to the lhapdf routine

evolvePDFphoton(...,photon)

I believe, according to the web page of LHAPDF that this returns x times pdfofphoton. However, unlike for the other partons the photon pdf is not divided by x .

Can you confirm that this x factor is accounted for properly somewhere else in the code ?

When I calculate some photon initiated process with MG5 and compare with some personal implementation I have a factor of ten difference. The results are identical when dividing by x the photon pdf .

Let me also know if I should create a bug report associated to this problem.

Thank you in advance,

Best,

Florian Lyonnet

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MadGraph5_aMC@NLO Edit question
Assignee:
marco zaro Edit question
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marco zaro
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Best marco zaro (marco-zaro) said : 		#1

Hi Florian,
indeed, the fact that we don't divide the photon pdf by x is an error.
I will fix it so that in the new release it should be working fine.
Thanks for letting us know this!

Cheers,

Marco

Revision history for this message
Florian Lyonnet (dibus2) said : 		#2

Thanks marco zaro, that solved my question.

Revision history for this message
marco zaro (marco-zaro) said : 		#3

Hi Florian,
I realized the fix i did was not correct, as it can lead to segfaults.
Can you please have a look at the new push in 2.1.2?
Many thanks,

Marco

Revision history for this message
Florian Lyonnet (dibus2) said : 		#4

Hi marco,

of course I could but I don't know the procedure to get the latest push ?

F.

On 19 Jun 2014, at 13:26, marco zaro wrote:

> Your question #250015 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/250015
>
> marco zaro posted a new comment:
> Hi Florian,
> I realized the fix i did was not correct, as it can lead to segfaults.
> Can you please have a look at the new push in 2.1.2?
> Many thanks,
>
> Marco
>
> --
> You received this question notification because you asked the question.

Revision history for this message
marco zaro (marco-zaro) said : 		#5

If you got the branch using bzr branch, you simply type
bzr pull

Cheers,

Marco
On 19 Jun 2014, at 13:32, Florian Lyonnet <email address hidden> wrote:

> Question #250015 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/250015
>
> Florian Lyonnet posted a new comment:
> Hi marco,
>
> of course I could but I don't know the procedure to get the latest push
> ?
>
> F.
>
> On 19 Jun 2014, at 13:26, marco zaro wrote:
>
>> Your question #250015 on MadGraph5_aMC@NLO changed:
>> https://answers.launchpad.net/mg5amcnlo/+question/250015
>>
>> marco zaro posted a new comment:
>> Hi Florian,
>> I realized the fix i did was not correct, as it can lead to segfaults.
>> Can you please have a look at the new push in 2.1.2?
>> Many thanks,
>>
>> Marco
>>
>> --
>> You received this question notification because you asked the question.
>
> --
> You received this question notification because you are a direct
> subscriber of the question.