1. software offline tutorial, CERN, Dec 7 th 2009 1 Electrons and photons in ATHENA Frédéric DERUE – LPNHE Paris ATLAS offline software tutorial Detectors involved inner detector : track reconstruction, particle-id in TRT LAr EM calorimeter : cell, clusters + shower shapes for particle-id hadronic calorimeter : for leakage and isolation requirements Three reconstruction algorithms standard egamma algorithm – cluster-based for | η |<2.5 “softe” - track-based for | η |<2.5 forward electrons for | η |>2.5 – no inner detector information Several analysis algorithms dedicated for electrons and photons : e.g conversion recovery

2. software offline tutorial, CERN, Dec 7 th 2009 2 Software location Software information all packages under Reconstruction/egamma main algorithms in Reconstruction/egamma/egammaRec python/egammaGetter.py, src/egammaBuilder.cxx python/softeGetter.py, src/softeBuilder.cxx python/forwardGetter.py, src/forwardBuilder.cxx main analysis algorithms in Reconstruction/egamma/egammaAnalysis PhotonAnalysisAlgs ElectronAnalysisAlgs

3. software offline tutorial, CERN, Dec 7 th 2009 3 egamma algorithms Standard reconstruction procedure seeded by clusters reconstructed in LAr EM by a sliding window (SW) algorithm NB: details of SW reconstruction have changed/improved since CSC notes cluster-track matching procedure NB: details have changed/improved since CSC notes cluster-conversion matching procedure Definition of objects cluster+track : electron cluster+ no track : non-converted photon cluster+conversion : converted photon A word on softe uses tracks as input with high preselection cuts to minimize fakes If track is same as the one used by standard algo then keep standard object essentially useful for ET<5 GeV apart “this”, objects or identification is the same as for standard a A word on forward electrons uses topo clusters, no inner detector dedicated identification A certain overlap (few %) exist between electrons and converted photons

4. software offline tutorial, CERN, Dec 7 th 2009 4 cluster-size and calibration Cluster size electrons : 3*7 in barrel, 5*5 in end-caps non-converted photons : 3*5 in barrel, 5*5 in end-caps converted photons : 3*7 in barrel, 5*5 in end-caps Calibration different corrections are applied for electrons/photons for position and energy measurements There are different calorimeter calibrations, cluster sizes, and identification variables and cuts used for electrons and photons: if the user reassigns the type of the object in analysis, the user needs to properly correct for this. Tools are available to do this.

5. software offline tutorial, CERN, Dec 7 th 2009 5 four-momentum I4Momentum base class to keep 4-momentum doxygen documentation http://tinyurl.com/6h2o23 Combination since 15.3.0 the energy of the four-momentum is a combination of the calorimeter and tracker measurement since rel 15.5 for photons energy is only from calo

6. software offline tutorial, CERN, Dec 7 th 2009 6 egamma object CaloCluster calorimeter information available for all objects Link to a TrackParticle tracking information useful only for electrons Link to a VxCandidate vertex information available for converted electrons – in the PhotonContainer egDetail additional reconstructed information available for all objects PID particle identification available for all objects

7. software offline tutorial, CERN, Dec 7 th 2009 7 What's on AOD Three containers available in StoreGate ElectronAODContainer PhotonAODContainer egDetailsAODContainer Links to other containers TrackParticle, CaloCluster, VxCandidate information is sufficient for the user to be able to redo some basic PID Documentation https://twiki.cern.ch/twiki/bin/view/AtlasProtected/EgammaAOD 7 7

8. software offline tutorial, CERN, Dec 7 th 2009 8 Cluster information CaloCluster object reconstructed E, px, py, pz position eta, phi Recalibration of clusters https://twiki.cern.ch/twiki/bin/view/AtlasProtected/EgammaAODRender egDetails object called EMShower contains most of the detailed calorimeter information describe shower shapes define detailed cuts for identification purpose

9. software offline tutorial, CERN, Dec 7 th 2009 9 Tracking information Pointer to the Trk::Track with which the particle was created Tracks associated to electron can be refitted at AOD level Also contains charge Trk::FitQuality DefiningParameters() For electrons this is the Trk::Perigee – useful for vertex fitting

10. software offline tutorial, CERN, Dec 7 th 2009 10 VxCandidate Used to create conversions Single track and double track conversions possible Contains position of the vertex VxTrackAtVertex(s) that make the vertex from which you can obtain the corresponding TrackParticle

11. software offline tutorial, CERN, Dec 7 th 2009 11 egDetail EMShower calorimeter information isolation, leakage EMTrackMatch track to calorimeter matching information e.g Dh, Dh at each of the sampling layers EMConvert conversion matchin variable able to obtain a full Trk::VxCandidate EMBremFit results from CaloBremFit e.g brem radius, improved pT EMTrackFit able to obtain full Trk::Perigee parameters EMFourMomErrors

12. software offline tutorial, CERN, Dec 7 th 2009 12 electron pid - IsEM Multivariate techniques are available but not discussed here (eg. Log Likelihood, Boosted Decision Trees, H-matrix, Neural Nets, …). These techniques will be commissioned after the cut-based electron id has been validated with early data. Only certified variables will be used. Multivariate techniques are available but not discussed here (eg. Log Likelihood, Boosted Decision Trees, H-matrix, Neural Nets, …). These techniques will be commissioned after the cut-based electron id has been validated with early data. Only certified variables will be used. Default method used in electron identification A basic series of cuts based on: shower shape properties in different compartments of the calorimeter combination of ID and Calo Loose - Calorimeter only information hadronic Leakage, Shower Shape (middle layers only of EM cal) excellent ID efficiency, low BG rejection Medium - Adds tracking information basic Track quality cuts more detailed Calorimeter Cuts increased jet rejection efficiency by a factor 3-4 while reducing ID efficiency by 10% Tight - Using all information available b-layer hit requirement,TRT High Threshold hit information strongest background rejection but lowest ID efficiency ISO - For isolated electrons provides tighter calorimeter cuts TRT - For non-isolated electrons (from heavy quark decay) tighter TRT PID

13. software offline tutorial, CERN, Dec 7 th 2009 13 photon pid - IsEM Default method used in photon identification A basic series of cuts based on: shower shape properties in different compartments of the calorimeter different cuts for converted and non converted photons Loose - Calorimeter only information hadronic Leakage, Shower Shape (middle layers only of EM cal) excellent ID efficiency, low BG rejection Tight - Using all information available use information from the strips in particular strongest background rejection but lowest ID efficiency ISO - For isolated photons provides tighter calorimeter cuts Multivariate techniques are available but not discussed here (eg. Log Likelihood, Boosted Decision Trees, H-matrix, Neural Nets, …). These techniques will be commissioned after the cut-based photon id has been validated with early data. Only certified variables will be used. Multivariate techniques are available but not discussed here (eg. Log Likelihood, Boosted Decision Trees, H-matrix, Neural Nets, …). These techniques will be commissioned after the cut-based photon id has been validated with early data. Only certified variables will be used.

14. software offline tutorial, CERN, Dec 7 th 2009 14 More information egamma twiki: https://twiki.cern.ch/twiki/bin/view/AtlasProtected/ElectronGamma egamma CSC notes: http://cdsweb.cern.ch/record/1119939 egamma hypernews https://hypernews.cern.ch/HyperNews/Atlas/get/EGammaWG.html