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discussion on LHC / Tevatron combinations of mW
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Discussion: LHC/Tevatron combinations of mW
This was the first working meeting to discuss the mW combination between ATLAS and Tevatron experiments. The idea is to combine existing published measurements (without re-analysing to reduce the uncertainties). Two scenarios were discussed: - update the published measurements with a common choice of PDF set - emulate the published measurements using simplified parameterisations to mimic detector effects.
Scenario 1 requires an update of ResBos interfaced to more recent PDF sets: Jan Stark contacted ResBos authors to produce grids with different PDF sets TO DO: check the status. Chris performed studies to show that the PDF uncertainties don’t depend on the tool used to evaluate them and therefore suggests to switch to another computation like MC@nlo or Powheg. TO DO: provide plots to compare 2 different tools for at least one PDF set.
Scenario 2 requires official common parameterisations to be used TO DO: Maarten will create a common repository and Nansi/Chris will share the parameterisations. Preliminary results were shown by Nansi but still need to be updated with the corresponding selection cuts (TO DO). Chris also showed a preliminary 50% correlation using Madgraph NLO.
Few points worth to note:
- No explicit extrapolation uncertainty from pTZ to pTW is quoted in the Tevatron results, therefore there is no correlation with ATLAS for these uncertainties.
- The uncertainty from polarisation coefficients was estimated at the Tevatron and found to be negligible around 0.5 MeV level by comparing the approximate NNLO from Resbos to exact NNLO computations. No correlation is to be considered here as well.
- It was agreed to take the EW uncertainties as fully correlated between the different experiments.
- No pTZ constraint was applied in the PDF uncertainty estimated at the Tevatron.
- It was agreed to show the combination results for different PDF sets (as was done in sin2thetaW public results by ATLAS and CMS).
- It was agreed to use the following PDF sets: CT10, CT14, CTEQ6.6, MMHT and NNPDF3.1.
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