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analysis: add initial draft for 2015 taus (#102)
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@katilp
katilp authored May 6, 2022
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Expand Up @@ -12,69 +12,110 @@ In some physics analyses, the misidentification of electrons or muons as τh can

## Tau 4-vector information

An example of an EDAnalyzer tau information is available in the [TauAnalyzer](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2012/PhysObjectExtractor/src/TauAnalyzer.cc) of the Physics Object Extractor Tool (POET). The following header files needed for accessing tau information are included:
=== "Run 1 Data"

An example of an EDAnalyzer tau information is available in the [TauAnalyzer](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2012/PhysObjectExtractor/src/TauAnalyzer.cc) of the Physics Object Extractor Tool (POET). The following header files needed for accessing tau information are included:

``` cpp
//classes to extract tau information
#include "DataFormats/TauReco/interface/PFTau.h"
#include "DataFormats/TauReco/interface/PFTauFwd.h"
#include "DataFormats/TauReco/interface/PFTauDiscriminator.h"
```

In [TauAnalyzer.cc](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2012/PhysObjectExtractor/src/TauAnalyzer.cc), the tau four-vector elements are accessed as shown below.

``` cpp
Handle<reco::PFTauCollection> mytaus;
iEvent.getByLabel(tauInput, mytaus);

[...]

for (reco::PFTauCollection::const_iterator itTau=mytaus->begin(); itTau!=mytaus->end(); ++itTau){
if (itTau->pt() > tau_min_pt) {
tau_e.push_back(itTau->energy());
tau_pt.push_back(itTau->pt());
tau_px.push_back(itTau->px());
tau_py.push_back(itTau->py());
tau_pz.push_back(itTau->pz());
tau_eta.push_back(itTau->eta());
tau_phi.push_back(itTau->phi());

[...]
}
```

=== "Run 2 Data"

An example of an EDAnalyzer tau information is available in the [TauAnalyzer](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2015MiniAOD/PhysObjectExtractor/src/TauAnalyzer.cc) of the Physics Object Extractor Tool (POET). The following header file needed for accessing tau information is included:

``` cpp
//class to extract tau information
#include "DataFormats/PatCandidates/interface/Tau.h"
```

In [TauAnalyzer.cc](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2015MiniAOD/PhysObjectExtractor/src/TauAnalyzer.cc), the tau four-vector elements are accessed from the `pat::tau` collection as shown below.

``` cpp
Handle<pat::TauCollection> taus;
iEvent.getByToken(tauToken_, taus);
[...]

for (const pat::Tau &tau : *taus)
{
tau_e.push_back(tau.energy());
tau_pt.push_back(tau.pt());
tau_px.push_back(tau.px());
tau_py.push_back(tau.py());
tau_pz.push_back(tau.pz());
tau_eta.push_back(tau.eta());
tau_phi.push_back(tau.phi());

[...]
}
```

with `tauToken_` defined as a member of the `TauAnalyzer` class and its value read from the [configuration file](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2015MiniAOD/PhysObjectExtractor/python/poet_cfg.py).

``` cpp
//classes to extract tau information
#include "DataFormats/TauReco/interface/PFTau.h"
#include "DataFormats/TauReco/interface/PFTauFwd.h"
#include "DataFormats/TauReco/interface/PFTauDiscriminator.h"
```
## Tau identification

In [TauAnalyzer.cc](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2012/PhysObjectExtractor/src/TauAnalyzer.cc), the tau four-vector elements are accessed as shown below.
=== "Run 1 Data"

``` cpp
Handle<reco::PFTauCollection> mytaus;
iEvent.getByLabel(tauInput, mytaus);
The identification of taus relies almost entirely on pre-computed algorithms to determine the quality of the tau reconstruction and the decay type. Since this object is not stable and has several decay modes, different combinations of identification and isolation algorithms are used across different analyses. The [Tau tagging CMS WorkBook page](https://twiki.cern.ch/twiki/bin/view/CMSPublic/WorkBookPFTauTagging#Legacy_Tau_ID_Run_I) provides a large table of available algorithms.

[...]
In contrast to the muon object, tau algorithm results are typically saved in the AOD files as their own PFTauDisciminator collections, rather than as part of the tau object class. As shown in [TauAnalyzer.cc](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2012/PhysObjectExtractor/src/TauAnalyzer.cc), these collections can be accessed with the following impressively long label names:

for (reco::PFTauCollection::const_iterator itTau=mytaus->begin(); itTau!=mytaus->end(); ++itTau){
if (itTau->pt() > tau_min_pt) {
tau_e.push_back(itTau->energy());
tau_pt.push_back(itTau->pt());
tau_px.push_back(itTau->px());
tau_py.push_back(itTau->py());
tau_pz.push_back(itTau->pz());
tau_eta.push_back(itTau->eta());
tau_phi.push_back(itTau->phi());
```cpp
Handle<reco::PFTauDiscriminator> tausLooseIso, tausVLooseIso, tausMediumIso, tausTightIso,
tausTightEleRej, tausTightMuonRej, tausDecayMode, tausRawIso;

[...]
}
```
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByDecayModeFinding"),tausDecayMode);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByRawCombinedIsolationDBSumPtCorr"), tausRawIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByVLooseCombinedIsolationDBSumPtCorr"), tausVLooseIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByLooseCombinedIsolationDBSumPtCorr"), tausLooseIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByMediumCombinedIsolationDBSumPtCorr"), tausMediumIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByTightCombinedIsolationDBSumPtCorr"), tausTightIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByTightElectronRejection"), tausTightEleRej);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByTightMuonRejection"), tausTightMuonRej);
```

## Tau identification
The tau discriminator collections act as pairs, containing the index of the tau and the value of the discriminant for that tau. Note that the arrays are filled by calls to the individual discriminant objects, but referencing the vector index of the tau in the main tau collection.

``` cpp
const auto idx = itTau - mytaus->begin();
tau_iddecaymode.push_back(tausDecayMode->operator[](idx).second);
tau_idisoraw.push_back(tausRawIso->operator[](idx).second);
tau_idisovloose.push_back(tausVLooseIso->operator[](idx).second);
tau_idisoloose.push_back(tausLooseIso->operator[](idx).second);
tau_idisomedium.push_back(tausMediumIso->operator[](idx).second);
tau_idisotight.push_back(tausTightIso->operator[](idx).second);
tau_idantieletight.push_back(tausTightEleRej->operator[](idx).second);
tau_idantimutight.push_back(tausTightMuonRej->operator[](idx).second);
```

The recommendations for applying these discriminators are summarizes in the [Tau identification nutshell recipe](https://twiki.cern.ch/twiki/bin/view/CMSPublic/NutShellRecipeFor5312AndNewer).

=== "Run 2 Data"

The identification of taus relies almost entirely on pre-computed algorithms to determine the quality of the tau reconstruction and the decay type. Since this object is not stable and has several decay modes, different combinations of identification and isolation algorithms are used across different analyses. The [Tau tagging CMS WorkBook page](https://twiki.cern.ch/twiki/bin/view/CMSPublic/WorkBookPFTauTagging#Legacy_Tau_ID_Run_I) provides a large table of available algorithms.

In contrast to the muon object, tau algorithm results are typically saved in the AOD files as their own PFTauDisciminator collections, rather than as part of the tau object class. As shown in [TauAnalyzer.cc](https://github.com/cms-opendata-analyses/PhysObjectExtractorTool/blob/2012/PhysObjectExtractor/src/TauAnalyzer.cc), these collections can be accessed with the following impressively long label names:

```cpp
Handle<reco::PFTauDiscriminator> tausLooseIso, tausVLooseIso, tausMediumIso, tausTightIso,
tausTightEleRej, tausTightMuonRej, tausDecayMode, tausRawIso;

iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByDecayModeFinding"),tausDecayMode);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByRawCombinedIsolationDBSumPtCorr"), tausRawIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByVLooseCombinedIsolationDBSumPtCorr"), tausVLooseIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByLooseCombinedIsolationDBSumPtCorr"), tausLooseIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByMediumCombinedIsolationDBSumPtCorr"), tausMediumIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByTightCombinedIsolationDBSumPtCorr"), tausTightIso);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByTightElectronRejection"), tausTightEleRej);
iEvent.getByLabel(InputTag("hpsPFTauDiscriminationByTightMuonRejection"), tausTightMuonRej);
```

The tau discriminator collections act as pairs, containing the index of the tau and the value of the discriminant for that tau. Note that the arrays are filled by calls to the individual discriminant objects, but referencing the vector index of the tau in the main tau collection.

``` cpp
const auto idx = itTau - mytaus->begin();
tau_iddecaymode.push_back(tausDecayMode->operator[](idx).second);
tau_idisoraw.push_back(tausRawIso->operator[](idx).second);
tau_idisovloose.push_back(tausVLooseIso->operator[](idx).second);
tau_idisoloose.push_back(tausLooseIso->operator[](idx).second);
tau_idisomedium.push_back(tausMediumIso->operator[](idx).second);
tau_idisotight.push_back(tausTightIso->operator[](idx).second);
tau_idantieletight.push_back(tausTightEleRej->operator[](idx).second);
tau_idantimutight.push_back(tausTightMuonRej->operator[](idx).second);
```

The recommendations for applying these discriminators are summarizes in the [Tau identification nutshell recipe](https://twiki.cern.ch/twiki/bin/view/CMSPublic/NutShellRecipeFor5312AndNewer).
!!! Note "To do"
- to complete once POET 2015MiniAOD branch TauAnalyzer has been validated

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