-- Main.ccollins - 01 Sep 2005


The Comparator

A utility to allow ATLFAST to be compared and tuned to full simulation using the same generated events.

Main Features

  • User can select which ATLFAST smearing schema to use
  • User can tune ATLFAST smearing to mimic full simulation and reconstruction
  • Outputs of tuning are stored in an AMI database for future use
  • AMI database allows access to all Comparator runs made by all users
  • User can create new smearing schema for ATLFAST
  • Only electrons and muons can be smeared for the moment
    • Photons
    • Jets
    • b-tagging
    • tracks


The Comparator is designed to run using Analysis Object Data (AOD) as input. In the Comparator, an analysis job (currently ComparatorSkeleton) parses the AOD and produces histograms containing full Geant4 information and Atlfast output. The histograms for full/fast output are processed and a value of chi-squared produced, which characterises the degree of difference between the outputs.

The value of chi-squared and the Atlfast smearing parameters are made available to Minuit, which then chooses new values of Atlfast smearing parameters and re-runs the analysis job (AnalysisSkeleton) with these new parameters. In this way, a set of Atlfast smearing parameters is arrived at which mimics the full simulation and reconstruction.

At present, the Comparator only alters the smearing of low luminosity electrons inside Atlfast. Subsequent versions of the Comparator will allow many more quantities to be tuned.

Health warning: A particular parameterisation may only be valid for certain physics samples, or even particular binning of the histograms!

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