BkgElectronClassification.cxx

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
*/
 
#include "DerivationFrameworkEGamma/BkgElectronClassification.h"
#include "StoreGate/ReadDecorHandle.h"
#include "GaudiKernel/EventContext.h"
#include "MCTruthClassifier/IMCTruthClassifier.h"
#include "xAODEgamma/EgammaTruthxAODHelpers.h"
#include "xAODEgamma/Electron.h"
#include "xAODTruth/TruthParticle.h"
#include "TruthUtils/MagicNumbers.h"
#include "TruthUtils/HepMCHelpers.h"
 
namespace DerivationFramework {
 
StatusCode
BkgElectronClassification::initialize()
{
 
  ATH_MSG_DEBUG("Initializing " << name() << "...");
  ATH_CHECK(m_mcTruthClassifier.retrieve());
  ATH_MSG_DEBUG("Retrieved tool " << m_mcTruthClassifier);
 
  ATH_CHECK(m_electronContainer.initialize());
  ATH_CHECK(m_truthContainer.initialize());
  ATH_CHECK(m_electronTruthParticleLink.initialize());
  ATH_CHECK(m_truthPdgId.initialize());
  //
  ATH_CHECK(m_firstEgMotherTruthType.initialize());
  ATH_CHECK(m_firstEgMotherTruthOrigin.initialize());
  ATH_CHECK(m_firstEgMotherTruthClassification.initialize());
  ATH_CHECK(m_firstEgMotherTruthParticleLink.initialize());
  ATH_CHECK(m_firstEgMotherPdgId.initialize());
  //
  ATH_CHECK(m_lastEgMotherTruthType.initialize());
  ATH_CHECK(m_lastEgMotherTruthOrigin.initialize());
  ATH_CHECK(m_lastEgMotherTruthClassification.initialize());
  ATH_CHECK(m_lastEgMotherTruthParticleLink.initialize());
  ATH_CHECK(m_lastEgMotherPdgId.initialize());
 
  ATH_MSG_DEBUG("Initialization successful");
 
  return StatusCode::SUCCESS;
}
 
StatusCode
BkgElectronClassification::addBranches(const EventContext& ctx) const
{
 
  SG::ReadHandle<xAOD::ElectronContainer> electrons{ m_electronContainer, ctx };
  SG::ReadHandle<xAOD::TruthParticleContainer> truthContainer{ m_truthContainer,
                                                               ctx };
 
  // Access for the pre-existing decoration
  SG::ReadDecorHandle<xAOD::ElectronContainer,
                      ElementLink<xAOD::TruthParticleContainer>>
    tPL{ m_electronTruthParticleLink, ctx };
 
  // pdg iD
  SG::WriteDecorHandle<xAOD::ElectronContainer, int> tPdgID(m_truthPdgId, ctx);
  // first mother decorations
  SG::WriteDecorHandle<xAOD::ElectronContainer, int> firstEgMotherTT(
    m_firstEgMotherTruthType, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer, int> firstEgMotherTO(
    m_firstEgMotherTruthOrigin, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer, unsigned int> firstEgMotherTC(
    m_firstEgMotherTruthClassification, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer, int> firstEgMotherPdgID(
    m_firstEgMotherPdgId, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer,
                       ElementLink<xAOD::TruthParticleContainer>>
    firstEgMotherTPL(m_firstEgMotherTruthParticleLink, ctx);
 
  // last mother decorations
  SG::WriteDecorHandle<xAOD::ElectronContainer, int> lastEgMotherTT(
    m_lastEgMotherTruthType, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer, int> lastEgMotherTO(
    m_lastEgMotherTruthOrigin, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer, unsigned int> lastEgMotherTC(
    m_lastEgMotherTruthClassification, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer, int> lastEgMotherPdgID(
    m_lastEgMotherPdgId, ctx);
  SG::WriteDecorHandle<xAOD::ElectronContainer,
                       ElementLink<xAOD::TruthParticleContainer>>
    lastEgMotherTPL(m_lastEgMotherTruthParticleLink, ctx);
  //
 
  for (const xAOD::Electron* el : *electrons) {
    tPdgID(*el) = 0;
    if (tPL.isPresent() && tPL(*el).isValid()) {
      const xAOD::TruthParticle* truthEl = *tPL(*el);
      tPdgID(*el) = truthEl->pdgId();
      // Parents can be removed by truth thinning in e.g cases of Geant4 produced LRT electrons
      // throw a warning in these cases so this is transparent
      if (MC::isElectron(truthEl)) {
        for (size_t p = 0; p < truthEl->nParents(); ++p) {
          if (!truthEl->parent(p)) {
            ATH_MSG_WARNING("Unresolvable truth parent link (ancestry removed by "
                            << "truth thinning) for truth electron with pt "
                            << truthEl->pt() << " MeV");
            break;
          }
        }
      }
    }
    // Use the Helpers for electron from electron or photon
    // Add Extra Decoration from Egamma helpers in case of BkgElectron (Electron
    // coming for a photon) Go back to the first/last electron/photon Generator
    // mother and classify this one
    // First the one entering the Geant4, the first we meet on the way back
    firstEgMotherTT(*el) = 0;
    firstEgMotherTO(*el) = 0;
    firstEgMotherTC(*el) = 0;
    firstEgMotherTPL(*el) = ElementLink<xAOD::TruthParticleContainer>();
    firstEgMotherPdgID(*el) = 0;
    const xAOD::TruthParticle* firstElTruth =
      xAOD::EgammaHelpers::getBkgElectronMother(el, false);
 
    if (firstElTruth) {
      auto res = m_mcTruthClassifier->particleTruthClassifier(firstElTruth, ctx);
      firstEgMotherTT(*el) = res.first;
      firstEgMotherTO(*el) = res.second;
      firstEgMotherTC(*el) = std::get<0>(MCTruthPartClassifier::defOrigOfParticle(firstElTruth)); // See AGENE-2351
      firstEgMotherPdgID(*el) = firstElTruth->pdgId();
      ElementLink<xAOD::TruthParticleContainer> link(
        firstElTruth, *truthContainer, ctx);
      firstEgMotherTPL(*el) = link;
    }
 
    // The last electron / photon we meet on the way back towards the Generator
    // vertex
    lastEgMotherTT(*el) = 0;
    lastEgMotherTO(*el) = 0;
    lastEgMotherTC(*el) = 0;
    lastEgMotherTPL(*el) = ElementLink<xAOD::TruthParticleContainer>();
    lastEgMotherPdgID(*el) = 0;
    const xAOD::TruthParticle* lastElTruth =
      xAOD::EgammaHelpers::getBkgElectronMother(el);
 
    if (lastElTruth) {
      auto res = m_mcTruthClassifier->particleTruthClassifier(lastElTruth, ctx);
      lastEgMotherTT(*el) = res.first;
      lastEgMotherTO(*el) = res.second;
      lastEgMotherTC(*el) = std::get<0>(MCTruthPartClassifier::defOrigOfParticle(lastElTruth)); // See AGENE-2351
      lastEgMotherPdgID(*el) = lastElTruth->pdgId();
      ElementLink<xAOD::TruthParticleContainer> link(
        lastElTruth, *truthContainer, ctx);
      lastEgMotherTPL(*el) = link;
    }
  }
  return StatusCode::SUCCESS;
}
}