Using Jets in Analysis

Now let’s add jets to our analysis. We will apply a calibration, the JVT selection, and cuts on p_T and η before writing their four momenta to the output ntuple.

Schedule jet analysis sequence

Begin by scheduling the jet analysis sequence. Do this by adding the following lines to makeSequence() in MyAnalysisAlgorithms.py near the other object analysis sequences:

    # Include and set up the jet analysis sequence:
    from JetAnalysisAlgorithms.JetAnalysisSequence import makeJetAnalysisSequence
    jetContainer = 'AntiKt4EMPFlowJets'
    jetSequence = makeJetAnalysisSequence( dataType, jetContainer,
                                           runGhostMuonAssociation = True, shallowViewOutput = False )
    jetSequence.configure( inputName = jetContainer,
                           outputName = 'AnaJets_%SYS%' )

    # Add the jet analysis sequence to the job:
    algSeq += jetSequence

This schedules the implementation of jet calibration and systematic uncertainties. It also implements the JVT selection by applying a decoration called jvt_selection.

Schedule jet selection algorithm

Now let’s apply some basic selection criteria for our jets. We want to only select jets with p_T > 50 GeV and |η| < 4.5.

Define the following variables in MyAnalysisAlgorithms.py:

jetMinPt = 50e3 # Minimum pt in MeV
jetMaxEta = 4.5

Put the following lines in makeSequence() after the electron selection algorithm:

    # Include and set up jet selection algorithm:
    selAlgJet = createAlgorithm( 'CP::AsgSelectionAlg', 'UserJetSelectionAlg' )
    addPrivateTool( selAlgJet, 'selectionTool', 'CP::AsgPtEtaSelectionTool' )
    if jetMinPt is not None :
        selAlgJet.selectionTool.minPt = jetMinPt
    if jetMaxEta is not None :
        selAlgJet.selectionTool.maxEta = jetMaxEta
    selAlgJet.selectionDecoration = 'selectPtEta,as_char'
    selAlgJet.particles = 'AnaJets_%SYS%'

    # Add the jet selection algorithm to the job:
    algSeq += selAlgJet

Add a jet summary preselection flag

The jvt_selection decoration requires an additional step to use. To do this, we will add an algorithm that summarizes the jet criteria as a single decoration that we will call preselection. To do this, add the following code to makeSequence() after the object selection algorithms but before return algSeq:

    # Schedule preselection summary algorithms
    preselAlgJet = createAlgorithm( 'CP::AsgSelectionAlg','JetPreelectionAlg' )
    preselAlgJet.preselection = 'selectPtEta,as_char&&jvt_selection'
    preselAlgJet.particles = 'AnaJets_%SYS%'
    preselAlgJet.selectionDecoration = 'preselection,as_char'
    algSeq += preselAlgJet

Apply selection to jets and write to ntuple

Follow the steps for adding electrons to the output, making the necessary modifications for jets. Note that you will need to add xAODJet to CMakeLists.txt and add

#include <xAODJet/JetContainer.h>

to MyxAODAnalysis.cxx.

Instead of applying cuts on baselineSelection_* (which does not exist for jets) and selectPtEta in the loop over jets, simply apply a selection on the preselection decoration.

Rerun to make sure your code is behaving as expected. Once you are happy with the changes, commit and push them.

⭐️ Bonus Exercise

Try running your algorithm using a different AntiKt4 jet container. Check the input file for the container options you have. How does your output change with these new jets?