Using MET in Analysis

Missing Transverse Energy needs to be calculated separately for each analysis because it is determined by the exact object definitions used. To do this, we first need to define a new type of container that allows the MET tools to use only the objects we want and then the MET sequence is scheduled.

At a minimum, the MET tools require a user-defined jet collection for calculation. Additionally, users can define other object collections to be used in MET calculation, but this is not required. Any energy in the detector that is not associated with user-defined object collections is independently incorporated into the MET calculation.

Schedule MET calculation sequence

Now that we have our selected object containers, it is time to schedule the MET calculation. Add the following lines to the config.yaml file:

# Add MissingET and specify what objects are used in the calculation.
MissingET:
  - containerName: 'AnaMET'
    jets: 'AnaJets'
    electrons: 'AnaElectrons.loose'
    muons: 'AnaMuons.medium'

Here, we specify MET calculation on our input object containers with their appropriate selections.

Write MET information to the ntuple

We need to get the correct instance of MET and then write some information to the ntuple. Since MET is a vector in the transverse plane, it can be represented with only two variables.

The most common representation is the most human-readable and consists of the total MET (a scalar quantity) and the azimuthal angle (φ) of the MET. This allows you to quickly assess the magnitude of the MET and its direction.

To define the scalar and azimuthal angle of the MET, add the following line to the config.yaml file, in the Output block:

Output:
    ...
    # Variables associated with MissingET container
    metVars: []
    ...
    containers:
        ...
        'met_': 'AnaMET'

The metVars are specified separately from the other vars because they are calculated differently from the other vars. Once again, we do not ask for any such additional variables/branches for this ntuple.

Once again, after re-running the code, examine the output ntuple to see branches corresponding to MET information. Commit and push your changes when everything is running correctly.