Egamma Isolation for 31X

Complete: 5

The easier way to use egamma isolations in CMSSW (>= 3.1) is to access directly to the pre-computed values in the Electron and Photon objects. The Electron object for example implements the follwoing methods:

const IsolationVariables & dr03IsolationVariables()
const IsolationVariables & dr04IsolationVariables()
to retrieve the default values computed in the cones of 0.3 and 0.4. The IsolationVariables struct is defined as follows:
struct IsolationVariables
     {
      float tkSumPt ;                // track iso deposit with electron footprint removed
      float ecalRecHitSumEt ;        // ecal iso deposit with electron footprint removed
      float hcalDepth1TowerSumEt ;   // hcal depht 1 iso deposit with electron footprint removed
      float hcalDepth2TowerSumEt ;   // hcal depht 2 iso deposit with electron footprint removed
      IsolationVariables()
       : tkSumPt(0.), ecalRecHitSumEt(0.), hcalDepth1TowerSumEt(0.), hcalDepth2TowerSumEt(0.)
       {}
     } ;

Direct access to the deposits is implemented as well:

    float dr03TkSumPt() 
    float dr03EcalRecHitSumEt() const { return dr03_.ecalRecHitSumEt ; }
    float dr03HcalDepth1TowerSumEt() const { return dr03_.hcalDepth1TowerSumEt ; }
....
Analogous methods have been defined also for Photons.

In any case if you need to change the default parameters and compute the sums again there are two complementary ways which give identical results and both produce a edm::ValueMap keyed to the electron containing the appropriate isolation. It can either be made in one step using the EgammaElectronTowerIsolationProducer in RecoEgamma/EgammaIsolationAlgos/plugins straight from the CMS.CaloTowers or the CMS.CaloTowers can be first converted into IsoDeposits and then later made into isolation values by CandIsolatorFromDeposits in CMS.PhysicsTools/IsolationAlgos/plugins/. The following example is for the IsoDeposits way as that is what is used by the PAT. The IsoDeposits used to make the HCAL isolations are produced using the EgammaTowerExtractor module in RecoEgamma/EgammaIsolationAlgos/plugins. There is a configuration parameter known as hcalDepth which controls which effective depth of the hcal is used for the isolation. hcalDepth can have 3 values:

  • -1 : all depths (default)
  • 1 : depth 1
  • 2 : depth 2
The IsoDeposits are then made into isolation values in the normal way using the CandIsolatorFromDeposits. The configuration to make the IsoDeposits for electrons can be found here and the configuration to produce the isolation values from the IsoDeposits can be found here.

The sequence to run the egamma isolation values using the IsoDeposit intermediary step is found in RecoEgamma.EgammaIsolationAlgos.egammaIsolationSequencePAT_cff. This will define a sequence egammaIsolationSequencePAT which should be added to your path.

Responsible: MatthewLeBourgeois

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Topic revision: r1 - 2009-07-14 - MatthewLeBourgeois
 
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