EGammaAmbiguityTool.cxx

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
#include "ElectronPhotonSelectorTools/EGammaAmbiguityTool.h"
 
#include "xAODCaloEvent/CaloCluster.h"
#include "xAODTracking/Vertex.h"
#include "xAODTracking/TrackParticle.h"
 
#include "xAODEgamma/Egamma.h"
#include "xAODEgamma/Electron.h"
#include "xAODEgamma/Photon.h"
#include "xAODEgamma/EgammaContainer.h"
#include "xAODEgamma/ElectronContainer.h"
#include "xAODEgamma/PhotonContainer.h"
 
#include "xAODEgamma/EgammaDefs.h"
#include "xAODEgamma/EgammaxAODHelpers.h"
#include "FourMomUtils/xAODP4Helpers.h"
 
#define CHECK_HITS(EXP)                                                        \
  if (!(EXP)) {                                                                \
    ATH_MSG_WARNING("Failed \"" << #EXP << "\"");                              \
    return false;                                                              \
  }
 
//=============================================================================
// Standard constructor
//=============================================================================
EGammaAmbiguityTool::EGammaAmbiguityTool(const std::string& myname)
  : asg::AsgTool(myname)
{
  declareProperty(
    "minNoSiHits",
    m_MinNoSiHits = 4,
    "Minimum number of silicon hits to be an electron==>not photon for sure");
  declareProperty(
    "minNoPixHits",
    m_MinNoPixHits = 2,
    "Minimum number of Pixel hits to be an electron==>not photon for sure");
  declareProperty("maxEoverPCut",
                  m_maxEoverPCut = 10,
                  "Maximum EoverP , more that this is ambiguous");
  declareProperty(
    "minPCut", m_minPtCut = 2000, "Minimum Pt, less than that is ambiguous");
  declareProperty("maxDeltaR_innermost",
                  m_maxDeltaR_innermost = 40,
                  "Maximum value for Rconv - RfirstHit for Si+Si conversions "
                  "where both tracks have innermost hits");
  declareProperty("noVertexNoInnermostAsAmb",
                  m_noVertexNoInnermostAsAmb = true,
                  "If true classify as ambiguous when there is no vertex and "
                  "no innermost Hits. "
                  "If false classify no vertex as for sure not photon");
  declareProperty("AcceptAmbiguous",
                  m_acceptAmbiguous = true,
                  "When used as a selector accept the ambiguous as default");
}
 
StatusCode EGammaAmbiguityTool::initialize(){
  ATH_MSG_DEBUG("Initializing " << name() << "...");
  return StatusCode::SUCCESS;
}
 
// ====================================================================
// return value: AuthorElectron, AuthorPhoton, AuthorAmbiguous, AuthorUnknown
unsigned int EGammaAmbiguityTool::ambiguityResolve(const xAOD::CaloCluster* cluster,
                                                   const xAOD::Vertex* vx,
                                                   const xAOD::TrackParticle* tp,
                           xAOD::AmbiguityTool::AmbiguityType& type) const{
 
  type=xAOD::AmbiguityTool::unknown;
  // Result should stay the same before after calibration corrections
  double cluster_e = (cluster->clusterSize() != xAOD::CaloCluster::SW_35ele &&
                      cluster->clusterSize() != xAOD::CaloCluster::SW_35gam &&
                      cluster->clusterSize() != xAOD::CaloCluster::SuperCluster)
                       ? cluster->altE()
                       : cluster->e();
 
  //Number of hits from the track
  uint8_t trkPixelHits(0);
  uint8_t trkSiHits(0);
  if (tp && !tp->summaryValue(trkPixelHits,xAOD::numberOfPixelHits)){
    ATH_MSG_WARNING("Could not retrieve number of pixel hits from track");
  }
  if (tp && !tp->summaryValue(trkSiHits, xAOD::numberOfSCTHits)){
    ATH_MSG_WARNING("Could not retrieve number of SCT hits from track");
  }
  trkSiHits += trkPixelHits;
 
  //Check if the vertex is double silicon
  xAOD::EgammaParameters::ConversionType convType(xAOD::EgammaHelpers::conversionType(vx));
  bool vxDoubleSi = (convType == xAOD::EgammaParameters::doubleSi);
 
  // Check if the track particle and the ones associated to the conversion vertex
  // have innermost pixel hits
  bool trkHasInnermostHit = tp && hasInnermostPixelHit(*tp);
  size_t nTrkVxWithInnermostHit{};
  if (vx and vxDoubleSi) nTrkVxWithInnermostHit = nTrkWithInnermostPixelHits(*vx);
 
  //See if the Si+Si conversion shares one track with the electron
  //if not we might have a trident.
  //if yes and the track is not good we definitely matched the conversion as electron.
  bool shareTrack = vx && tp && trkSiHits>=m_MinNoSiHits && vxDoubleSi && isInVertex(*tp, *vx);
 
  //Debug messages
  ATH_MSG_DEBUG("Vertex, SiSi, tracks with innermost pixel hits: "
        << (vx != nullptr) << ", " << vxDoubleSi << ",  " << nTrkVxWithInnermostHit);
  ATH_MSG_DEBUG("Track, Si hits, pixel hits, has innermost pixel hit: "
        << (tp != nullptr) << ", " << (int) trkSiHits << ", " << (int) trkPixelHits
        << " , " <<  (int) trkHasInnermostHit);
  ATH_MSG_DEBUG("Share track : " << shareTrack);
 
  //The Electron collection will NOT contain Photons
  //The Photon collection will NOT contain Electrons
 
  //So for conversions vs electrons better to go to ambiguous
  //except  if we are sure.
 
  //Practically a photon here means definetely not Electron
  //And vice-versa
 
  //Photon ==> Surely not electron
  // - no track
  // - or no track with the minimum requirent hits to be an electron
  // - or Si+Si vertex and
  //    - No pixel
  //    - The electron track is part of the conversion
  // In this case we do not want this to be in Electrons
  if (!tp ||
      trkSiHits<m_MinNoSiHits ||
      (vxDoubleSi && !trkPixelHits && shareTrack)){
    ATH_MSG_DEBUG("Returning Photon");
    type= xAOD::AmbiguityTool::photon;
    return xAOD::EgammaParameters::AuthorPhoton;
  }
 
  // Ambigous due to E/P, Min Pt, pixel hits
  // We are not sure it is a Photon, but is not good enough either to be surely
  // an Electron
  // - E/P >10  or track Pt < 2.0 GeV or no-pixel then Ambiguous
  double track_ep = cluster_e * fabs(tp->qOverP());
 
  if(tp->pt()<m_minPtCut) {
    ATH_MSG_DEBUG("Returning Ambiguous due  min Pt");
    type=xAOD::AmbiguityTool::ambiguousTrackLowPt;
    return xAOD::EgammaParameters::AuthorAmbiguous;
  }
 
  if( track_ep > m_maxEoverPCut) {
    ATH_MSG_DEBUG("Returning Ambiguous due to E over P");
    type=xAOD::AmbiguityTool::ambiguousTrackHighEoverP;
    return xAOD::EgammaParameters::AuthorAmbiguous;
  }
 
 
  if(!trkPixelHits) {
    ATH_MSG_DEBUG("Returning Ambiguous due to  no pixels");
    type=xAOD::AmbiguityTool::ambiguousTrackNoPixel;
    return xAOD::EgammaParameters::AuthorAmbiguous;
  }
 
  // Electron ==> Surely not Photon
  // - No vertex Matched (and trk has "innermost pixel hits" when
  // m_noVertexNoInnermostAsAmb is true,
  //   othewise ambiguous)
  // - Track with at least the minimum Si and Pixel hits (previous selection for
  // photons/ambiguous)
  // - And has E/P < 10 and Pt > 2.0 GeV (previous for ambiguous)
  // - Or if a vertex exists and:
  //   * is not Si+Si
  //   * is Si+Si but only 1 trk has "innermost pixel hits"
  //   * is Si+Si and both tracks have "innermost pixel hits" but
  //     Rconv - RfirstHit > maxDeltaR_innermost
  // In this case we do not want this to be in Photons
 
  if (!vx) {
    if (trkHasInnermostHit || !m_noVertexNoInnermostAsAmb) {
      ATH_MSG_DEBUG("Returning Electron");
      type = xAOD::AmbiguityTool::electron;
      return xAOD::EgammaParameters::AuthorElectron;
    } else {
      // the true photons falling here are classified as unconverted photons
      // but it may happen that they are late single-track conversions
      // very few true electrons are falling here, since there is no innermost
      // hits
      ATH_MSG_DEBUG("Returning Ambiguous due to no conv vertex and track with "
                    "no innermost hits");
      type = xAOD::AmbiguityTool::ambiguousNoInnermost;
      return xAOD::EgammaParameters::AuthorAmbiguous;
    }
  }
 
  // here we have a conv vertex
  if (trkHasInnermostHit && (!vxDoubleSi || nTrkVxWithInnermostHit == 1 ||
                             !passDeltaR_innermost(*vx))) {
    ATH_MSG_DEBUG("Returning Electron");
    type = xAOD::AmbiguityTool::electron;
    return xAOD::EgammaParameters::AuthorElectron;
  }
 
  // Ambiguous all else, these will go to both electrons and photons
  // A matched Si+Si vertex (where either both or none of the tracks have
  // "innermost pixel hits")
  // and a track with "innermost pixel hits"
  // A non Si+Si vertex matched and a track with no "innermost pixel hits"
 
  //If we have no double si
  //or if the single track p matches the cluster E than the vertex p
  //mark TrackEoverPBetterThanVertexEover.
  //Otherwise maek as TrackEoverPBetterThanVertexEover
  //as the double si vertex is a better match to the cluster E.
  const double track_p = fabs(1.0/tp->qOverP());
  const double vertex_p=xAOD::EgammaHelpers::momentumAtVertex(*vx).mag() ;
  type = !vxDoubleSi || (fabs(track_p - cluster_e) < fabs(vertex_p- cluster_e))?
    xAOD::AmbiguityTool::ambiguousTrackEoverPBetterThanVertexEoverP :
    xAOD::AmbiguityTool::ambiguousVertexEoverPBetterThanTrackEoverP ;
  //end of types
 
  ATH_MSG_DEBUG("Returning Ambiguous");
  return xAOD::EgammaParameters::AuthorAmbiguous;
}
 
unsigned int EGammaAmbiguityTool::ambiguityResolve(const xAOD::CaloCluster* cluster,
                                                   const xAOD::Vertex* vx,
                                                   const xAOD::TrackParticle* tp) const{
 
  xAOD::AmbiguityTool::AmbiguityType type;
  return ambiguityResolve(cluster,
              vx,
              tp,
              type);
 
}
 
 
 
unsigned int EGammaAmbiguityTool::ambiguityResolve(const xAOD::Egamma& egamma) const{
 
    //Fwd and Topo seeded not handled
  if (egamma.author() == xAOD::EgammaParameters::AuthorFwdElectron ||
      egamma.author() == xAOD::EgammaParameters::AuthorCaloTopo35){
    ATH_MSG_DEBUG("Author Fwd of Topo seeded.  Do not do overlap or ambiguity");
    return egamma.author();
  }
 
  //No overlap found so either photon or electron
  if (!egamma.ambiguousObject()){
    ATH_MSG_DEBUG("No overlaping object found");
    return egamma.author();
  }
 
  // Overlap found. define the electron and the photon
  const xAOD::Electron* electron = static_cast<const xAOD::Electron*>(
    egamma.type() == xAOD::Type::Electron ? &egamma : egamma.ambiguousObject());
  const xAOD::Photon* photon = static_cast<const xAOD::Photon*>(
    egamma.type() == xAOD::Type::Photon ? &egamma : egamma.ambiguousObject());
 
  //Error if cannot define any of them
  if (!electron || !photon){
    ATH_MSG_WARNING("Could not cast to electron and/or photon");
    return egamma.author();
  }
 
  //pass the proper input to the ambiguity resolve method
  xAOD::AmbiguityTool::AmbiguityType type;
  unsigned int result = ambiguityResolve(electron->caloCluster(),
                     photon->vertex(),
                     electron->trackParticle(),
                     type);
  ATH_MSG_DEBUG("Performed ambiguity resolution, resulting type is: "<< type);
  return result;
}
 
bool EGammaAmbiguityTool::accept( const xAOD::Egamma& egamma) const{
  unsigned int author = ambiguityResolve(egamma);
 
  if (author == xAOD::EgammaParameters::AuthorFwdElectron ||
      author == xAOD::EgammaParameters::AuthorCaloTopo35){
    return true;
  }
 
  if (m_acceptAmbiguous && author == xAOD::EgammaParameters::AuthorAmbiguous){
    return true;
  }
 
 return (author == (egamma.type() == xAOD::Type::Electron ?
             xAOD::EgammaParameters::AuthorElectron : xAOD::EgammaParameters::AuthorPhoton) );
}
 
bool EGammaAmbiguityTool::hasInnermostPixelHit(const xAOD::TrackParticle& tp) const
{
  uint8_t trkExpectHit(0);
  uint8_t trkNhits(0);
  CHECK_HITS( tp.summaryValue(trkNhits,xAOD::numberOfInnermostPixelLayerHits) );
  if (trkNhits) {return true;}
 
  CHECK_HITS( tp.summaryValue(trkExpectHit,xAOD::expectInnermostPixelLayerHit) );
  if (trkExpectHit) {return false;}
 
  CHECK_HITS( tp.summaryValue(trkNhits,xAOD::numberOfNextToInnermostPixelLayerHits) );
  if (trkNhits) {return true;}
 
  CHECK_HITS( tp.summaryValue(trkExpectHit,xAOD::expectNextToInnermostPixelLayerHit) );
  if (trkExpectHit) {return false;}
 
  CHECK_HITS( tp.summaryValue(trkNhits,xAOD::numberOfPixelHits) );
  return (trkNhits >= m_MinNoPixHits);
}
 
size_t EGammaAmbiguityTool::nTrkWithInnermostPixelHits(const xAOD::Vertex& vx) const{
  size_t n = 0;
  for (size_t i = 0; i < vx.nTrackParticles(); ++i){
    const xAOD::TrackParticle *tp = vx.trackParticle(i);
    if (!tp) {ATH_MSG_WARNING("Null pointer to track particle in vertex");}
    else if (hasInnermostPixelHit(*tp)) {++n;}
  }
  return n;
}
 
bool EGammaAmbiguityTool::isInVertex(const xAOD::TrackParticle& trk, const xAOD::Vertex& vx) const{
  for (size_t i = 0; i < vx.nTrackParticles(); ++i){
    const xAOD::TrackParticle *tp = vx.trackParticle(i);
    if (!tp) {ATH_MSG_WARNING("Null pointer to track particle in vertex");}
    if (tp == &trk) {return true;}
  }
  return false;
}
 
bool EGammaAmbiguityTool::passDeltaR_innermost(const xAOD::Vertex& vx) const
{
  static const SG::AuxElement::Accessor<float> minRfirstHitAcc("minRfirstHit");
  if (not minRfirstHitAcc.isAvailable(vx)) {
    ATH_MSG_WARNING("minRfirstHit not available");
    return false;
  }
  return xAOD::EgammaHelpers::conversionRadius(&vx) - minRfirstHitAcc(vx) < m_maxDeltaR_innermost;
}