MadGraph5_aMC@NLO

Improved Weizsaecker-Williams Approximation: where is \theta_c?

Asked by Francesca Acanfora

Hi,

I am using version 3.5 of MadGraph. I am simulating a a > resonance and asking lpp1=3, lpp2=-3, i.e. photons coming from electron and positron beam. I ask for pdlabel1=pdlabel2=iww, i.e. the matrix element is integrated with two Improved Weizsaecker-Williams Approx.[hep-ph/9310350] pdfs.

If I go and look into PhotonFlux.f I can actually find the pdf as in formula 20 and the q_max^2 as in formula 25 from the paper but I can not find the q_min^2 as in formula 26. In particular is there a way to provide MadGraph the \theta_c at generation level?

Also, I can see that my results change a lot when varying the dynamical_scale_choice. Up to now the most reasonable choice looks to be around the resonance mass. I am struggling in finding a bijective relation between the MadGraph dynamical_scale_choice and the iww paper, can you help me?

Thank you

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

In our implematation, you provide directly q_min^2 via the choice of factorization scale for that PDF.
This is the reason of the dependence in the dynamical scale choice. You can then use the formula 26 to related the dynamical scale choice to a give value of \theta_c.

Cheers,

Olivier

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