linearly polarized photon beam?

Hi,

Polarised photon beam are only handle for circular polarisation.

For that you have to use the following information in the run_card:

#*********************************************************************
# Beam polarization from -100 (left-handed) to 100 (right-handed) *
#*********************************************************************
     0.0 = polbeam1 ! beam polarization for beam 1
     0.0 = polbeam2 ! beam polarization for beam 2

This is written for lepton beam but also works for photon.

If you want to have linear polarization for the photon, you have to change the function vxxxxx in the file
Source/DHELAS/aloha_functions.f

and combine the +/- polarization to return the polarization of your choice (then you can use the above parameter if you want to not have 100% polarised beam).

We are currently working quite a lot on polarization so I will see with the other contributor if we want to have a nicer interface for that. But in any case for the moment this is the best that we can do.

Cheers,

Olivier

> On 2 Apr 2019, at 01:08, Y Zhong <email address hidden> wrote:
>
> New question #679708 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/679708
>
> Hi,
>
> I wonder if MG5 can scatter linearly polarized photons with electrons (a e- > a e-) like Whizard did.
>
> https://whizard.hepforge.org/manual/manual006.html#sec159
>
> Thanks very much!
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thanks Olivier! I will try you suggested. Looking forward to your new version!

Best,
Yiming