TruthGuidedProtoTrackCreatorTool.cxx

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/*
  Copyright (C) 2002-2026 CERN for the benefit of the ATLAS collaboration
  */
 
#include "src/TruthGuidedProtoTrackCreatorTool.h"
#include "TrkEventPrimitives/ParticleHypothesis.h"
#include "Acts/Surfaces/PerigeeSurface.hpp"
#include "TruthUtils/HepMCHelpers.h"
 
 
ActsTrk::TruthGuidedProtoTrackCreatorTool::TruthGuidedProtoTrackCreatorTool(const std::string& type, 
                                        const std::string& name,
                                        const IInterface* parent)
  : base_class(type,name,parent)
{}
 
StatusCode  ActsTrk::TruthGuidedProtoTrackCreatorTool::initialize()
{
    ATH_CHECK( m_prdMultiTruthCollectionNames.initialize() );
    return StatusCode::SUCCESS;
}
 
StatusCode ActsTrk::TruthGuidedProtoTrackCreatorTool::findProtoTracks(const EventContext& ctx,
                                      const xAOD::PixelClusterContainer & pixelContainer,
                                      const xAOD::StripClusterContainer & stripContainer,
                                      std::vector<ActsTrk::ProtoTrack> & foundProtoTracks ) const {
 
    // Read the PRD information
    std::vector<const PRD_MultiTruthCollection*> prdMultiTruthCollections;        
    prdMultiTruthCollections.reserve(m_prdMultiTruthCollectionNames.size());
    // load the PRD collections from SG
    for(const auto& pmtCollNameIter:m_prdMultiTruthCollectionNames)
    {
     // try to retrieve the PRD multi truth collection
     SG::ReadHandle<PRD_MultiTruthCollection> curColl (pmtCollNameIter, ctx);
     if (!curColl.isValid())
     {
       ATH_MSG_WARNING("Could not retrieve " << pmtCollNameIter << ". Ignoring ... ");
     }
     else
     {
       ATH_MSG_INFO("Added " << pmtCollNameIter << " to collection list for truth track creation.");
       prdMultiTruthCollections.push_back(curColl.cptr());
     }
   }
 
    // create the map for the ine
    std::map<Identifier, HepMC::ConstGenParticlePtr> identToHepMCMap;
    for (auto & PRD_truthCollec: prdMultiTruthCollections )
    {
        // loop over the map and get the identifier, GenParticle relation
        PRD_MultiTruthCollection::const_iterator prdMtCIter  = PRD_truthCollec->begin();
        PRD_MultiTruthCollection::const_iterator prdMtCIterE = PRD_truthCollec->end();
        for ( ; prdMtCIter != prdMtCIterE; ++ prdMtCIter ){
 
            // check if entry exists and if   
            HepMC::ConstGenParticlePtr curGenP       = (*prdMtCIter).second.scptr();
            Identifier                curIdentifier = (*prdMtCIter).first;
 
            // Min pT cut
            if ( curGenP->momentum().perp() < 500. ) continue;
 
 
 
            identToHepMCMap[curIdentifier] = curGenP;
        }
    }
 
    // Now loop over the pixel and strip container and make collectiong
    std::map<HepMC::ConstGenParticlePtr,
            std::vector<const xAOD::UncalibratedMeasurement*>> trackCollections;
 
    for(const auto cluster: pixelContainer)
    {
        // Get the idetifier list for the RDOs
        auto identifierList = cluster->rdoList();
 
        // Loop and push back the cluster in the corresponding trith particle
        for(auto& id_value: identifierList)
        {
            Identifier id(id_value);
            // Found a match, so push it into the track collection
            if(identToHepMCMap.find(id) != identToHepMCMap.end())
            {
                auto truthParticle = identToHepMCMap.at(id);
                trackCollections[truthParticle].emplace_back(cluster);
            }
        }
    }
 
    for(const auto cluster: stripContainer)
    {
        // Get the idetifier list for the RDOs
        auto identifierList = cluster->rdoList();
 
        // Loop and push back the cluster in the corresponding trith particle
        for(auto& id_value: identifierList)
        {
           Identifier id(id_value);
            // Found a match, so push it into the track collection
            if(identToHepMCMap.find(id) != identToHepMCMap.end())
            {
                auto truthParticle = identToHepMCMap.at(id);
                trackCollections[truthParticle].emplace_back(cluster);
            }
        }
    }
 
    for(const auto& var: trackCollections)
    {
        // Skip if we find less than 3 clusters per truth track
        if(var.second.size() < 3) continue;
 
        // Make the intput perigee
        auto inputPerigee = makeDummyParams(var.first);
        ATH_MSG_INFO("Found " << var.second.size() << " clusters for truth partcle "<<var.first);
        foundProtoTracks.push_back({var.second,std::move(inputPerigee)});
    }
 
    // and add to the list (will only make one prototrack per event for now)
 
    return StatusCode::SUCCESS;
}
 
 
std::unique_ptr<Acts::BoundTrackParameters>
ActsTrk::TruthGuidedProtoTrackCreatorTool::makeDummyParams (const HepMC::ConstGenParticlePtr& truthParticle) const{
 
  using namespace Acts::UnitLiterals;
  std::shared_ptr<const Acts::Surface> actsSurface = Acts::Surface::makeShared<Acts::PerigeeSurface>(
        Acts::Vector3(0., 0., 0.));
  Acts::BoundVector params;
 
 
  // No, this is not a physically correct parameter estimate! 
  // We just want a placeholder to point in roughly the expected direction... 
  // A real track finder would do something more reasonable here. 
  params << 0., 0.,
        truthParticle->momentum().phi(), truthParticle->momentum().theta(),
        static_cast<float>(MC::charge(truthParticle)) / (truthParticle->momentum().e()), 0.;
 
 
  // Covariance - let's be honest and say we have no clue ;-) 
  Acts::BoundMatrix cov = Acts::BoundMatrix::Identity();
  cov *= 100000; 
 
  // some ACTS paperwork 
  Trk::ParticleHypothesis hypothesis = Trk::pion;
  float mass = Trk::ParticleMasses::mass[hypothesis] * Acts::UnitConstants::MeV;
  Acts::PdgParticle absPdg = Acts::makeAbsolutePdgParticle(Acts::ePionPlus);
  Acts::ParticleHypothesis actsHypothesis{
    absPdg, mass, static_cast<float>(MC::charge(truthParticle))};
 
  return std::make_unique<Acts::BoundTrackParameters>(actsSurface, params,
                                    cov, actsHypothesis);
 
}