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discussion on LHC / Tevatron combinations of mW
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Maarten presented the validation of the recoil smearing procedure on various distributions. There is a shift in the mT observable between the smeared and the reconstructed level distributions. This seems to be due to a missing correction of the recoil scale. TO DO: implement this correction and rerun the validation
Nansi presented very preliminary results on the combination with Tevatron with first estimation of the Tevatron pdf uncertainties using the approximate smearing available for now. A difference of ~30% is observed and might be explained by the 90% to 68% CL scaling factor used in the PDF uncertainty evaluation. The scaling factor used to scale CT10 in ATLAS is 1.645, however at the Tevatron the scaling factor is 2.15 and derived from the comparison of MSTW2008 68 and 95%CL (the central value is done with CTEQ6.6). This factor is different from 1.645 because of non gaussian uncertainties in the PDF fit. The difference between CTEQ6.6 and MSTW2008 in the central value is quoted to be 6 MeV (as stated in arXiv:1311.0894) but not taken into account in the final uncertainty (therefore to be decorrelated with the 3.8 MeV envelope quoted in ATLAS result from the comparison of various PDF sets).
TO DO: Josh will produce samples pp- 2 TeV and pp 7 TeV with both MSTW2008 68 and 90% to be able to reproduce these numbers.
TO DO: Nansi redo the fits for Tevatron for the fitting range 65-90 GeV (mT) and 32-48 GeV (pTl).
Chris has shown a parametric simulation model, based on the one used for the CDF mW measurement, which gives reasonable estimate of PDFs.
TO DO: Nansi and Chris upload the smearing tools and parameterisations to: https://gitlab.cern.ch/lhcewkwg/lhcewkwg-precisionEW/mwcombinations
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