EWK diboson production

Hi Philipp,

> 1.) While I am able to produce some (e.g. the WW > H > ZZ) of the diagrams, I cannot figure out the syntax for the other diagrams, in particular the second and third. What does the syntax for those processes look like?

The correct syntax is
“generate p p > j j Z Z QCD=0” to have the full EWK production,
“generate p p > j j Z Z QED=2” to have the QCD production
“generate p p > j j Z Z QCD=2” to have the full QCD+EWK production

The possibility to have only the interference term and/or other combinaison are not yet in the release but are accessible as alpha version:
https://code.launchpad.net/~maddevelopers/mg5amcnlo/MG5_aMC_splitOrders_MadEvent/+merge/208742

> 3.) There is the issue of interference terms between the EWK and QCD diagrams and I have read on some conference slides that the interference between the two is <5% level. Is it a valid procedure to estimate the impact of the neglected interference by comparing the sum of EWK+QCD with the unconstrained simulation of ZZ production? Are there traps/dangers in this procedure due to breaking of unitary?

Yes this is the correct way to measure the impact of the interference. I don’t see any trouble with the breaking of unitarity. Especially if one of the matrix-element square breaks the unitary bound (which will not happen at LHC) then the interference will simply be large (a nd negative) since it needs to restore the unitary bound.

Cheers,

Olivier

On Apr 25, 2014, at 4:56 PM, Philipp Pigard <email address hidden> wrote:

> New question #247651 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/247651
>
> Hello,
>
> I am trying to use MG5 2.1.1 to generate samples for the EWK production of dibosons (ZZ in particular, e.g. http://imageshack.com/a/img836/7673/ez4t.jpg).
>
> 1.) While I am able to produce some (e.g. the WW > H > ZZ) of the diagrams, I cannot figure out the syntax for the other diagrams, in particular the second and third. What does the syntax for those processes look like?
>
> 2.) In more general terms, I am wondering how one can "split" the total ZZ cross section into an EWK and QCD part in MG5, since I'll need to remove the EWK ZZ production when I generate the QCD background.
>
> 3.) There is the issue of interference terms between the EWK and QCD diagrams and I have read on some conference slides that the interference between the two is <5% level. Is it a valid procedure to estimate the impact of the neglected interference by comparing the sum of EWK+QCD with the unconstrained simulation of ZZ production? Are there traps/dangers in this procedure due to breaking of unitary?
>
> The above are only partly related to MG5 per se, but any help on these issues (links to theory papers/presentations) would be much appreciated
>
> Thanks
> Philipp
>
>
>
>
>
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