9 May 2014 
LHC EWK di-boson meeting

Steven presented the combination status of ZZ 7 TeV between ATLAS and CMS.
The reproduction of limits with each others framework including full systematics yields differences
in the few percent level. This is suspected to be due to difference in nuisance parameter constraints,
i.e. truncated Gaussian vs log-normal PDF’s.

AI: Compare results with no systematics.
AI: ATLAS to implement log-normal PDF’s.
AI: CMS sum-up all the uncertainties for log-normal to compare.

The aim is to reach a 1% level of agreement before we go ahead with combination.

A procedure to reduce the number of nuisance parameters used by ATLAS was presented. CMS
will try this procedure.

The proposal to make the combination result public in the form of a LHC-EWK-WG report was supported.

It was decided to use EFT of neutral couplings in a future combination, not for the 7TeV or 8 TeV combination. We may recast in EFT also at 7 or 8 TeV, since EFT parameters are simple linear combination of the TGC parameters.

It was suggested to start a parallel effort to arrive at a common (ATLAS+CMS) EFT parameterisation,
and also to look in common setting etc. for generators.

AI: need to identify person-power to work on this.

The next meeting will be in 4 weeks, i.e. 6th June.