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LHC EWK working group multiboson discussion
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Europe/Zurich
4/3-006 - TH Conference Room (CERN)
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Description
Dedicate to discussion of ZZ measurements
- the mass window differences between ATLAS and CMS is about 1.6% → keep the mass windows as they are
- ATLAS uses dynamic scale for the scale uncertainty
*** Action items
- For the ZZ cross-section summary plot in the total phase space
- plan to centralize the plot making within the LHC EWK group and assign one contributor from each experiments to be reponsible for the ploting scripts.
- start with the plotting macro from CMS shown in the meeting (Kenneth Long needs to clean his code before it can be used)
- nontrivial to agree on exact presentations and configurations, therefore the plotting script should allow fexibility in 1) whether or not to include Tevatron results; 2) different configurations of theoretical predictions (NLO/NNLO, PDF, QCD scales, precision, EWK contribution)
- tighter mass windows has less gamma* contribution → it’s suggested to add this contribution to the caption in the future
- discrepancy in the Z mass window choice can not be resolved at the time being, difference in the prediction can be only 1-2%; plan to show the predictions using one of the mass window definitions in the summary, and the measurements stay as they are. In the caption, we mention explicitly what mass window is used and also give the definition of another mass window. The sentence can look like “The theoretical predictions and all EXP-A measurements are performed in the dilepton mass range YY-ZZ GeV. All EXP-B measurements are in the mass window AA–BB GeV. The smaller mass window is estimated to cause a XX% reduction in the measured cross section”. Need to decide which mass window to use in the plot though
- agreed to update such plots whenever there is a new measurement; since the summary plot do not include combination of results, we hope in principle no approving procedure is needed; however, each update of the plot will be discussed and reviewed in the LHC EWK meeting
- For the fiducial cross-section summary plot
- a plot of the ratio of data / prediction seems trivial to make, even in the case fiducial definitions are different between experiments.
- ATLAS style can be used (Vasiliki and Yusheng will provide the ATLAS plotting code)
- need to adapt a common calculation for the fiducial xs prediction; initial plan to choose Matrix calculation with one set of PDF and scales, though the PDF and scales are to be fixed.
- centralize the data cards used to produce the theoretical prediction so that the prediction can be produced with different theoretical configurations easily
- For the m(4l) unfolding
- CMS plans to adapt the 8 TeV ATLAS binning in their upcoming 13 TeV publication, and ATLAS also agreed to at least report the unfolding results using the 8 TeV binning in the next publication. The experiment can do their results with other binning as well.
- Discrepancies in the fiducial definitions may not be resolved soon, given that each definition may be well motivated by the detector acceptance. However a common fiducial region which is slightly more inclusive than the definitions in either experiment can be defined to compare unfolding results between ATLAS and CMS and eventually merge them. Further discussion could be organized in the future.
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