Cross section of the SM double Compton process

[Igal]

Dear WO authors,

Recently we have simulated the Standard Model (single) Compton scattering "gamma", "e-" => "gamma", "e-" and the double Compton scattering "gamma", "e-" > "gamma", "gamma", "e-" with WO-2.7.1. The value of the double Compton scattering cross-section disagree with the results shown by Ram and Wang (1971) https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.26.476

Attached please find a plot showing this, where WO stands for Whizard. We also put (after the signature) an example of WO Sandarin script. We used the same photon energy threshold than Ram and Wand (1971): E > 5.11 keV

Thank you very much!

Best,
Igal.

PS: we also tested WO 2.8.0 for 3 different incident photon beam energies and got the same cross-section values than with WO-2.7.1.

model = SM
seed = 5257389
process ae_to_aeee_unpol_eg261keVT0 = "gamma", "e-" => "gamma","e+","e-","e-"
iterations = 8:20000,3:40000
compile
beams = "gamma", "e-"
beams_momentum = 261 keV, 0 MeV
integrate (ae_to_aeee_unpol_eg261keVT0) {cuts = all E > 5.11 keV ["gamma"]}
n_events = 10000
sample_format = lhef
simulate (ae_to_aeee_unpol_eg261keVT0)

[Juergen Reuter (j.r.reuter)]

Updated plot by Igal including another generator.

[Thorsten Ohl (thomega)]

Der Igal,

sorry for taking our time before coming back to this issue.

Ram and Wang have published an erratum

  https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.26.1210

to their original paper

  https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.26.476

In this erratum, they note that the double Compton cross section has to be multiplied by a factor of 1/2. In that cause, the Whizard curve would match Ram and Wang very well.

Thus, we need to know if your curve is taken directly from the original paper or has that factor of 1/2 applied?

Cheers,
-the Whizard Team

[Igal (igjaegle)]

Dear Thorsten and the Whizard Team,

Thank you for coming back to me and pointing me out to the erratum of Ram &
Wang which I was not aware of. I did not apply the 1/2. If I apply the
factor 1/2 correction, there is now a good agreement between WO and R&W
calculation.

[image: image.png]

Thanks, cheers,
 Igal.

On Wed, Nov 20, 2019 at 7:11 AM Thorsten Ohl <email address hidden>
wrote:

> Der Igal,
>
> sorry for taking our time before coming back to this issue.
>
> Ram and Wang have published an erratum
>
> https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.26.1210
>
> to their original paper
>
> https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.26.476
>
> In this erratum, they note that the double Compton cross section has to
> be multiplied by a factor of 1/2. In that cause, the Whizard curve
> would match Ram and Wang very well.
>
> Thus, we need to know if your curve is taken directly from the original
> paper or has that factor of 1/2 applied?
>
> Cheers,
> -the Whizard Team
>
> ** Changed in: whizard
> Status: New => Incomplete
>
> --
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1839654
>
> Title:
> Cross section of the SM double Compton process
>
> Status in WHIZARD:
> Incomplete
>
> Bug description:
> Dear WO authors,
>
> Recently we have simulated the Standard Model (single) Compton
> scattering "gamma", "e-" => "gamma", "e-" and the double Compton
> scattering "gamma", "e-" > "gamma", "gamma", "e-" with WO-2.7.1. The
> value of the double Compton scattering cross-section disagree with the
> results shown by Ram and Wang (1971)
> https://journals.aps.org/prl/pdf/10.1103/PhysRevLett.26.476
>
> Attached please find a plot showing this, where WO stands for Whizard.
> We also put (after the signature) an example of WO Sandarin script. We
> used the same photon energy threshold than Ram and Wand (1971): E >
> 5.11 keV
>
> Thank you very much!
>
> Best,
> Igal.
>
> PS: we also tested WO 2.8.0 for 3 different incident photon beam
> energies and got the same cross-section values than with WO-2.7.1.
>
> model = SM
> seed = 5257389
> process ae_to_aeee_unpol_eg261keVT0 = "gamma", "e-" =>
> "gamma","e+","e-","e-"
> iterations = 8:20000,3:40000
> compile
> beams = "gamma", "e-"
> beams_momentum = 261 keV, 0 MeV
> integrate (ae_to_aeee_unpol_eg261keVT0) {cuts = all E > 5.11 keV
> ["gamma"]}
> n_events = 10000
> sample_format = lhef
> simulate (ae_to_aeee_unpol_eg261keVT0)
>
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/whizard/+bug/1839654/+subscriptions
>

[Thorsten Ohl (thomega)]

Thanks for confirming so promptly!

[Thorsten Ohl (thomega)]

It appears that WHIZARD is spot on!