Systematic uncertainties

Analyses using a W/Z/H-tagger should consider at least the following uncertainties:

  • Vary Pruned/softdrop jet mass calibration within JMS uncertainty (see above) and calculate impact on signal selection efficiency. If multiple categories for W and Z are used, propagate in this way also the migrations of events between categories into the datacards.
  • Smear Pruned/softdrop jet mass with the measured resolution SF (see above JMR) for the central value, vary within JMR uncertainty (see above) and calculate impact on signal selection efficiency. We recommend using stochastic smearing with the MC resolution provided (See the JetResolution TWiki).
  • Take into account uncertainties on the tau21-selection SF. When using a combination of low purity and high purity categories, propagate the anti-correlations into the datacards (see example from an 8 TeV analysis).
  • Take into account extrapolation uncertainties on the tau21-selection due to propagation to higher momenta (than the pT~200-300 GeV in the reference ttbar sample). Extrapolation uncertainties for a pT W/Z of interest can be estimated from the double ratio of the selection efficiency from Pythia and Herwig samples with pT W/Z of 200 GeV and signal with pT W/Z of interest. These are extracted in the form X * ln(pt/200GeV), where X is given in the following table for PUPPI+SD operating points:
  • Please note that the standard JES and JER uncertainties should be applied to the 4-vector, but the nuisance parameters should be treated as uncorrelated with JMS and JMR.

quantity X
tau21(0.35) HP 8.5%
tau21(0.35) LP 3.9%
tau21(0.55) HP 4.1%
tau21(0.55) LP 2.7%

-- KevinNash - 2017-03-07

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Topic revision: r6 - 2017-03-21 - KevinNash
 
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