Electron Reconstruction Software IS UNDER WORK

Complete:

Goals of this page

This page introduces the basics of electron reconstruction, shows how to run reconstruction modules so to produce standard electrons, and briefly discuss the content of the resulting output file. Some related topics are:

• Electron reconstruction physics.
• GSF electron objects.
• Standard sequence for electron reconstruction.
• Standalone ECAL clustering.
• How to analyse those electrons (in analysis workbook).

• This page for release 2_2_10.
• This page for release 2_1_0.

Introduction

The physical aspects of electron reconstruction are detailed here. Below is a short introduction to the reconstruction process.

Electrons are built starting from clusters in ECAL. Electron track seeds are built matching superclusters with hits from the standard trajectory seeds. This matching takes advantage of the fact that the energy-weighted average impact point of the electron and its bremstrahlung photons is precisely where a non-radiating track would have impacted the ECAL. The position measured by the supercluster can thus be used to predict the position of hits in the pixel detector. Since most of the material of the tracker lies after the pixel layers, most of the electrons have not radiated significantly before them and most photon conversion takes place after them. So matching hits are given by most electrons and by few photons. This seeding strategy is complemented by a tracker driven approach to cover cases of very low pT electrons and non isolated electrons.

The seeds are then used to trigger the track finding. The track fit is performed using a Gaussian Sum Filter (GSF), which allows the track to be reconstructed right out to the ECAL surface, despite kinks due to radiated bremsstrahlung. The electron object contains edm::Refs to both the track and the supercluster. The four-vector is obtained by combining information from the track and SuperCluster weighted according to measurement uncertainties.

Set up your Environment

Fisrtly prepare your runtime environment (shown for release 3_1_2):

    scram project CMSSW CMSSW_3_1_2
    cd CMSSW_3_1_2/src
    cmsenv
    addpkg RecoEgamma/EgammaElectronProducers
    cd RecoEgamma/EgammaElectronProducers/test

For more general and/or detailed information, see also:

• Full instructions
• Summary for every login session
• Access modules from the CVS repository.

Run standard electron reconstruction OBSOLETE

The config file recHitsToPixelMatchGsfElectrons_cfg.py shows how to reconstruct standard electrons (GsfElectron) starting from RecHits, which are assumed to already exist in the input sample. Let's examine this example a little further.

The maxEvents parameter is used to define the number of events to be processed, in this case 1000. The next part specifies the input files, in this case a release validation sample of particle gun back-to-back electrons with pT in the range 5 to 100 GeV, generated with CMSSW_1_6_0. Any sample containing RecHits generated with CMSSW_1_6_X can be used here. Such samples can be found using DBS2.

    source = PoolSource {
        untracked vstring fileNames = {
            '/store/RelVal/2007/9/19/RelVal-RelValDiElectron_Pt_5_100-1190216041/0003/14286614-5467-DC11-B1E9-000423D99996.root',
            '/store/RelVal/2007/9/19/RelVal-RelValDiElectron_Pt_5_100-1190216041/0003/1E0674DB-0567-DC11-B7FE-000423D94AA8.root'
        }
    }

The following specifies the output filename, in this case pixelMatchGsfElectrons.root, and the event content to be stored, in this case, the RECOSIM content:

    include "Configuration/EventContent/data/EventContent.cff"    
    module RECO = PoolOutputModule {
        untracked string fileName = 'pixelMatchGsfelectrons.root'
        using RECOSIMEventContent
    }

The next 2 lines are standard includes for running reconstruction. Using FakeConditions means that no conditions data (alignment and calibration coefficients) are read from the conditions database.

    include "Configuration/StandardSequences/data/FakeConditions.cff"
    include "Configuration/StandardSequences/data/Reconstruction.cff"

Next, the path is defined, which specifies the sequences of modules which will be run. In this case, the sequences run are:

• ecalClusteringSequence, defined in ecalClusteringSequence.cff: Standalone ECAL reconstruction strting from EcalRecHits: BasicClusters, SuperClusters and PreshowerClusters.
• pixelMatchGsfElectronSequence, defined in pixelMatchGsfElectronSequence.cff: Reconstructs electrons by matching pixel hits to a SuperCluster and using them to seed GSF tracking.

    path p = { ecalClusteringSequence, pixelMatchGsfElectronSequence }

Once you have customized the config file (you must at least provide the list of input files), you can run the reconstruction simply typing:

    cmsRun recHitsToPixelMatchGsfElectrons_cfg.py

Inspect the result

Open the file pixelMatchGsfElectrons.root in a TBrowser and browse the contents:

Collections ending with __Rec were already in the events that were read in. The collections reconstructed in the example end with __electrons, the name of the process in the first line of recHitsToPixelMatchGsfElectrons.cfg

The newly constructed electron objects are in the collection:

   recoPixelMatchGsfElectrons_pixelMatchGsfElectrons__electrons

   recoGsfTracks_pixelMatchGsfFitBarrel__electrons
   recoGsfTracks_pixelMatchGsfFitEndcap__electrons

   recoSuperClusters_correctedHybridSuperClusters__electrons
   recoSuperClusters_correctedEndcapSuperClustersWithPreshower__electrons

Error and warning categories

All errors and warnings issued by electron reconstruction software are classified both in the general category GsfElectronAlgo and a in some more detailed category, as listed below.

Review status

Responsible: DavidChamont