Introduction (Work in progress, under construction)

The purpose of this TWiki page is to provide an overview of the current PMG recommendations for rel21 analyses. Links to the PMG subgroups were more informations are available can be found in the table below.


Process-specific uncertainties from Focus Groups
Top WeakBosons JetPhotons

General recommendations

Samples descriptions and references

Information on rescaling to higher-order cross-sections, of existing reweightings, overlap removal procedure

Statistical treatment of modelling uncertainties


XXX Processes

* General things to follow:
  • Nominal samples to be used and known caveats/issues/deficiencies
  • List of uncertainty recipes for different sources (e.g. PDF, ME scales, shower, NLO matching, alternative sample, HF-fractions,...)
  • A collapsable list of evgen datasets for all of the samples needed for the recipes above
  • Link to the relevant Process group twiki or other places were additional documentation is available

Top Processes

Warning: Can't find topic Sandbox.PmgTopProcesses

ttbar (example of what was in the SUSY twiki)

For the ttbar background, the following variations should be considered.

Variation Description
Hard-scatter Compare Powheg+Pythia8 versus aMcAtNlo+Pythia8
Parton showering Compare Powheg+Pythia8 versus Powheg+Herwig7
Radiation (ISR) UP Compare the nominal Powheg+Pythia8 (hdamp=1.5 mtop) with the samples with varied hdamp (hdamp=3 mtop), at the same time dividing by 2 the renormalization and factorization scales and the varying the showering (Var3c Up)
Radiation (ISR) DOWN Compare the nominal Powheg+Pythia8 with the samples obtained doubling the renormalization and factorization scales and the varying the showering (Var3c Down)
Radiation (FSR) The radiation uncertainty quoted previously is mainly covering the ISR component. The FSR components correspond to Var2 variation in Pythia8 and could be relevant for some analysis (for sure b-fragmentation, mass analyses, analyses using substructure of the large-R jets, but everyone should check)
Parton Density Function Nominal Powheg+Pythia8 has been produced with internal reweighting for PDF variations and for PDF error sets

* Notes:

  • MET/HT sliced samples were produced with EVNT-only for aMC@NLO+Pythia8 and Powheg+Herwig7. Powheg+Herwig7 AFII samples are in production ATLMCPROD-5379. See SUSYMC16Samples TWiki for more information.
  • How to retrieve internal weights? See here and/or Calum's instruction.
  • For Rad_UP (ISR), the hdamp variation is included in the alternative samples (410480 and 410482). However, the hdamp variation was found to have a negligible impact (see slides). You can safely ignore it if you normalize the ttbar background in the CR. For the analysis which does not define the ttbar CR, the effect of the hdamp variation should be checked! If the hdamp variation is negligible, the UP/DOWN variations can be retrieved from the nominal samples as internal weights
  • FSR uncertainty (Var2) is usually minor. You can ignore it if the FSR variation is not sensitive to your analysis.
  • For the PDF uncertainty, see TopMCPDFReccommendations TWiki. The PDF uncertainty is usually minor. You could ignore it if the PDF variations are not sensitive to your analysis.
  • If your analysis does not define the CR, make sure to include the cross section uncertainty.
  • The jet pt is known to be mis-modeled due to the top pt mis-modeling. For the extrapolation on the high-pt jet, additional uncertainty should be quoted to cover the data/mc disagreement.
  • See PmgTopProcesses and TopMCSystematicsR21 TWiki pages (and also maybe old TopFocusGroup TWiki page) for more details.

* Samples:

*410470 should NOT be combined with 410472*

*410464 and 410465 to be combined*

*Parton showering*
*410557 and 410558 should be combined*

*Additional radiation (ISR) UP*

*Additional radiation (ISR) DOWN*
 use internal weights of nominal samples

*Additional radiation (FSR)*
 use internal weights of nominal samples

Useful Links

Major updates:
-- KeisukeYoshihara - 2019-03-16

%RESPONSIBLE% SimoneAmoroso
%REVIEW% Never reviewed

-- SimoneAmoroso - 2019-07-03

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Topic revision: r1 - 2019-07-03 - SimoneAmoroso
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