5 Sep 2014
CMS ATLAS meeting on ssWW
The meeting started with presentation from CMS and ATLAS answering the
questions that were posed prior to the meeting.
Refer to presentation for Q&A: https://indico.cern.ch/event/338764/
In the discussion the following points were raised:
1) Discussion on fiducial volume definition:
CMS uses an extended fiducial phase space with the idea of minimizing different efficiency corrections depending on the model due to jet resolution.
When m(jj) is not flat a model dependence in the extrapolation to low mjj resides.
ATLAS has chosen a volume close to experimental cuts to minimise the extrapolation.
It was agreed that a fiducial phase common to ATLAS and CMS should be defined to allow the combination of results.
ATLAS will make public the migration factors in the fiducial volume and will try to extrapolate to CMS volume.
CMS question on parton level vs clustered jets. ATLAS saw difference, calculation after parton shower.
2) CMS asked about interference calculation, clarified. CMS studies the scale dependence of the interference contribution. The interference term can have different sign in madgraph vs sherpa for some scale choices. ATLAS has not yet studied the interference dependence.
3) Both CMS and ATLAS aim for unfolded spectra, the simplest case being a fiducial volume cross section measurement. Start discussion about common unfolded spectra (variables, binning).
4) aQGC : two different approaches, no conclusion reached, yet.
5) WZ background difference remains puzzling. CMS data driven using WZ+2jets
ATLAS asked whether the b quark component for WZ production is included? CMS need to check.
CMS has b-jet veto with multiple components, including a soft muon top tagger (pt>4GeV).
6) ATLAS asked what is the effect on aQGC limits on the background estimation as non-SM aQGC would alter the 3-lepton control region used for normalization. Effect not checked yet.
7) ATLAS asked about the effect of WZj + 1 jet from pile-up, since CMS used WZ+2parton only. CMS will check the effect.