# Setting QED and QCD coupling orders in mg5

Hello,

I would like to ask a clarification on how someone can specify the QED/QCD order in the production.

My understanding is that if nothing is specified, the lowest QED order is considered.

Now I am trying to isolate some high order QED diagrams like the famous

W+W+ EWK production therefore I though about writing something like:

generate p p > e+ mu+ vl vl j j QED=6

(I know that this process alone is not gauge invariant but I assume that this will not be a big problem with the generator).

When looking at the list of diagrams I (surprisingly) see some diagrams with order:

QCD=2, QED=4 ....

Is this expected?

Obviously those diagrams go away if I also requires QCD=0.

The problem with that is that obviously I cannot then use the NLO calculation ([QCD])

since I get the message:

WARNING: Some loop diagrams contributing to this process are discarded because they are not pure (QCD)-perturbation.

Make sure you did not want to include them.

... and obviously the real emission diagrams are not there.

thanks a lot,

Valerio

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- marco zaro Edit question

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