Monte Carlo Truth

Introduction

One may want to access the truth information from Monte Carlo data in order to compare the truth particles to those from reconstruction. The truth particles in the AOD are in containers just like particles from reconstruction. Most particles types are all together in a single container called SpclMC. Jets are a special case and are in separate truth containers.

These notes will explain the analysis of truth information using the EventView Framework.

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Truth Particle Insertion

Truth particles, like from the SpclMC container, are inserted using the EVTruthParticleInserter. One specifies the type of particle with its PDG code. To save you from having to look up PDG codes, you should import the following Python module.

from PyAnalysisUtils import PDG

Then declare an EVMultipleOutputToolLooper to store truth information in its own EventView.

TruthLooper = EVMultipleOutputToolLooper('TruthLooper',
        EventViewCollectionOutputName = 'TruthEVCollection',
        OutputLevel = WARNING)
theJob += TruthLooper

Then add inserters to that looper. In the arguments for the inserter, you need to specify the PDG code, for example, muons.

TruthLooper += EVTruthParticleInserter('MuonTruthInserter',
        InsertedLabels = ['TrueMuon'],
        pdgCode = [PDG.mu_plus, PDG.mu_minus],
        usePdgCodeSign = True,
        etCut = 2*GeV,
        NoOverlapCheck = True,
        ContainerKey = 'SpclMC' )

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True Tau Jets

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Associators

Now that you have truth particles in their own EventView, you might want to compare those truth particles to particles that you reconstructed.

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-- RyanReece - 28 Feb 2008