Aod ntuple
This page contains basic prescriptions to get physics objects from the AOD and the AOD-based Root ntuple.
Some comments on quality selection cuts will be added as work progresses.
Electron
There are 3 types of quality cuts you can perform on the electron candidates:
- Cuts based on the
isEMflag - Cuts based on likelihood
- Cuts based on NeuralNet output
The isEM flag uses both calorimeter and tracking information in addition to TRT
information. The flag is a bit field which marks whether the candidate passed or not some safety checks.
The bit field marks the following checks:
// Cluster based egamma
ClusterEtaRange = 0,
ClusterHadronicLeakage = 1,
ClusterMiddleSampling = 2,
ClusterFirstSampling = 3,
// Track based egamma
TrackEtaRange = 8,
TrackHitsA0 = 9,
TrackMatchAndEoP = 10,
TrackTRT = 11
In 9.0.4 there is a problem with TRT simulation so one has to
mask TRT bit to recover the lost efficiency. The variable which combine everything is isEM and it is used as follow:
(*elec)->isEM()
to mask TRT bit you should use: (*elec)->isEM()%16==0
if you use isEM then you will select electrons with an overall eff of about 80% in the barrel but much lower in the crack and endcup.
-alg 2 use likelihood ratio and use the following variable:
energy in different calorimeter sampling, shower shapes in both eta and phi and E/P. No TRT information is used here. You need to access two variables called emweight and pionweight then you can construct the likelihood ratio: defined by: emweight/(emweight+pionweight). Emweight is the product of pdf's for electrons and pionweight is the product of pdf's for pions. In AOD, you use the following code:
ElecEMWeight = elec*->parameter(ElectronParameters::emWeight); ElecPiWeight = elec*->parameter(ElectronParameters::pionWeight);
Then form the variable: X = ElecEMWeight/(ElecEMWeight+ElecPiWeight)
Requiring X > 0.6 will give you more than 90% eff for electrons
-alg 3 use the NeuralNet and use as inputs the same variables used for
likelihood. To use it in AOD you should proceed as follow:
ElecepiNN = elec*->parameter(ElectronParameters::epiNN);
Requiring ElecepiNN > 0.6 will give you about 90% eff for electrons.
However, you should be aware that the ANN was trained in full eta range while the likelihood was computed in 3 bins in eta: barrel, crack and endcup. So I would suggest to use likelihood for now. I am working on improving things but it will not be ready for Rome. For sure using likelihood will give you 90% eff for electrons with a good jet rejection.