TruthBornLeptonCollectionMaker.cxx

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
// TruthBornLeptonCollectionMaker.cxx
// Makes a special collection of Born leptons
 
// R/W/D handles
#include "StoreGate/ReadHandle.h"
#include "StoreGate/WriteHandle.h"
#include "StoreGate/ReadDecorHandle.h"
#include "StoreGate/WriteDecorHandle.h"
// My own header file
#include "TruthBornLeptonCollectionMaker.h"
// EDM includes for the particles we need
#include "xAODTruth/TruthParticleContainer.h"
#include "xAODTruth/TruthParticleAuxContainer.h"
// To look up which generator is being used
#include "StoreGate/StoreGateSvc.h"
#include "xAODTruth/TruthMetaDataContainer.h"
#include "AthContainers/ConstAccessor.h"
// STL includes
#include <string>
#include "TruthUtils/HepMCHelpers.h"
 
// Constructor
DerivationFramework::TruthBornLeptonCollectionMaker::TruthBornLeptonCollectionMaker(const std::string& t,
                                const std::string& n,
                                const IInterface* p)
  : base_class(t,n,p)
  , m_metaStore( "MetaDataStore", n )
{
  declareProperty( "MetaDataStore", m_metaStore );
}
 
// Destructor
DerivationFramework::TruthBornLeptonCollectionMaker::~TruthBornLeptonCollectionMaker() {
}
 
// Athena initialize and finalize
StatusCode DerivationFramework::TruthBornLeptonCollectionMaker::initialize()
{
  ATH_MSG_VERBOSE("initialize() ...");
 
   // Input truth particles
   ATH_CHECK( m_particlesKey.initialize() );
   ATH_MSG_INFO("Using " << m_particlesKey.key() << " as the input truth container key");
 
   // ReadDecorHandleKeys
   ATH_CHECK(m_originAccessorKey.initialize());
   ATH_CHECK(m_typeAccessorKey.initialize());
   ATH_CHECK(m_outcomeAccessorKey.initialize());
   ATH_CHECK(m_classificationAccessorKey.initialize());
 
  // Output truth particles
  if (m_collectionName.empty()) {
    ATH_MSG_FATAL("No key provided for the new truth particle collection");
    return StatusCode::FAILURE;
  } else {ATH_MSG_INFO("New truth particle collection key: " << m_collectionName.key() );}
  ATH_CHECK( m_collectionName.initialize());
 
  // Decoration keys - FIXME we should not need to use WriteDecorHandleKeys here.
  ATH_CHECK(m_originDecoratorKey.initialize());
  ATH_CHECK(m_typeDecoratorKey.initialize());
  ATH_CHECK(m_outcomeDecoratorKey.initialize());
  ATH_CHECK(m_classificationDecoratorKey.initialize());
 
  // TODO: needs to be made MT-friendly
  ATH_CHECK( m_metaStore.retrieve() );
 
  return StatusCode::SUCCESS;
}
 
// Selection and collection creation
StatusCode DerivationFramework::TruthBornLeptonCollectionMaker::addBranches() const
{
  // Event context
  const EventContext& ctx = Gaudi::Hive::currentContext();
  
  // Set up for some metadata handling
  static const bool is_sherpa = [this]() {
    bool is_sherpa = false;
    // TODO: needs to be made MT-friendly
    if (m_metaStore->contains<xAOD::TruthMetaDataContainer>("TruthMetaData")){
      // Note that I'd like to get this out of metadata in general, but it seems that the
      // metadata isn't fully available in initialize, and since this is a const function
      // I can only do the retrieve every event, rather than lazy-initializing, since this
      // metadata ought not change during a run
      const xAOD::TruthMetaDataContainer* truthMetaData(nullptr);
      // Shamelessly stolen from the file meta data tool
 
      if (m_metaStore->retrieve(truthMetaData).isSuccess() && !truthMetaData->empty()){
        // Let's just be super sure...
        const std::string gens = truthMetaData->at(0)->generators();
        is_sherpa = (gens.find("sherpa")==std::string::npos &&
                     gens.find("Sherpa")==std::string::npos &&
                     gens.find("SHERPA")==std::string::npos) ? false : true;
      } // Seems to be the only sure way...
      else {
        ATH_MSG_WARNING("Found xAODTruthMetaDataContainer empty! Configuring to be NOT Sherpa.");
      }
      ATH_MSG_INFO("From metadata configured: Sherpa? " << is_sherpa);
    } 
    else {
      ATH_MSG_WARNING("Could not find metadata container in storegate; assuming NOT Sherpa");
    }
    return is_sherpa;
  }();
 
  // Retrieve truth collections
  SG::ReadHandle<xAOD::TruthParticleContainer> truthParticles(m_particlesKey,ctx);    
  if (!truthParticles.isValid()) {        
    ATH_MSG_ERROR("Couldn't retrieve TruthParticle collection with name " << m_particlesKey);        
    return StatusCode::FAILURE;    
  }
 
  // Create the new particle containers and WriteHandles
  SG::WriteHandle<xAOD::TruthParticleContainer> newParticlesWriteHandle(m_collectionName, ctx);
  ATH_CHECK(newParticlesWriteHandle.record(std::make_unique<xAOD::TruthParticleContainer>(),
                                           std::make_unique<xAOD::TruthParticleAuxContainer>()));
  ATH_MSG_DEBUG( "Recorded new TruthParticleContainer with key: " << (m_collectionName.key()));
 
  // Set up decorators
  SG::WriteDecorHandle<xAOD::TruthParticleContainer, unsigned int > originDecorator(m_originDecoratorKey, ctx);
  SG::WriteDecorHandle<xAOD::TruthParticleContainer, unsigned int > typeDecorator(m_typeDecoratorKey, ctx);
  SG::WriteDecorHandle<xAOD::TruthParticleContainer, unsigned int > outcomeDecorator(m_outcomeDecoratorKey, ctx);
  SG::WriteDecorHandle<xAOD::TruthParticleContainer, unsigned int > classificationDecorator(m_classificationDecoratorKey, ctx);
 
  SG::ReadDecorHandle<xAOD::TruthParticleContainer, unsigned int > originAccessor(m_originAccessorKey, ctx);
  SG::ReadDecorHandle<xAOD::TruthParticleContainer, unsigned int > typeAccessor(m_typeAccessorKey, ctx);
  SG::ReadDecorHandle<xAOD::TruthParticleContainer, unsigned int > outcomeAccessor(m_outcomeAccessorKey, ctx);
  SG::ReadDecorHandle<xAOD::TruthParticleContainer, unsigned int > classificationAccessor(m_classificationAccessorKey, ctx);
 
  // add relevant particles to new collection
  for (unsigned int i=0; i<truthParticles->size(); ++i) {
    // Grab the particle
    const xAOD::TruthParticle* theParticle = (*truthParticles)[i];
    if (!theParticle) continue; // Protection against null pointers
    if (!theParticle->isLepton()) continue; // Only include leptons!
 
    if (is_sherpa) {
      // For Sherpa, skip is not status 11
      if (MC::isPhysical(theParticle)) continue;
      // Sherpa may have two sets of status == 11 leptons. Here we take the first set.
      // To do so, we check the first status == 11 leptons, 
      //   check that it has a child a parent barecode corresponding the the lepton's uniqueID
      // If so, then save this parent uniqueID and skip all status 11 leptons with this parent uniqueID.
      bool has_parent_of_same_flavour = false;
      if (theParticle->prodVtx())
      for (size_t p = 0; p < theParticle->prodVtx()->nIncomingParticles(); ++p){
          if (theParticle->parent(p)->pdg_id() == theParticle->pdg_id()) has_parent_of_same_flavour = true;
      }
      if (has_parent_of_same_flavour) continue;
    } else {
      // Some generators, look for leptons  coming from vertices with other leptons
      bool physical = false, has_V = false;
      if (!MC::isPhysical(theParticle) && theParticle->hasProdVtx()){
        const xAOD::TruthVertex * prod = theParticle->prodVtx();
        // Look for other leptons in the production vertex and check if those are physical
        for (size_t p = 0; p < prod->nOutgoingParticles(); ++p){
          if (prod->outgoingParticle(p) && prod->outgoingParticle(p)->isLepton() && MC::isPhysical(prod->outgoingParticle(p))){
              physical = true; 
              break;
            }
          }
          // See if there was a boson going *into* the vertex
        for (size_t p = 0; p < prod->nIncomingParticles(); ++p){
          if (prod->incomingParticle(p) && (prod->incomingParticle(p)->isZ() || prod->incomingParticle(p)->isW() || prod->incomingParticle(p)->isHiggs()) ){
            has_V = true;  // Found a vector boson
            break;
          }
        } 
      }
 
      // Now we have all the information for the special case of V->l(born) l(bare) l(born) l(bare)
      // AV: The comment above, most likely is related to the case when the event is passed to PHOTOS with an option to keep 
      // the "documentation" particles, i.e. particles before the photon emission. 
      // These particles in PHOTOS are attached to the same vertex, but have different status, e.g. 3. 
      // The momentum conservation, is, of course, violated.  
      if ( !(physical && has_V && !MC::isPhysical(theParticle)) && !MC::Pythia8::isConditionB(theParticle)){
        // Skip if it has no boson parent, or has no descendent that is a bare lepton
        if (!hasBareDescendent( theParticle ) ) continue;
        const xAOD::TruthVertex * prod = theParticle->prodVtx();
        if (!prod) continue;
        if (prod->nIncomingParticles() < 1) continue;
        size_t bad_parent = 0;
        for (size_t p = 0; p < prod->nIncomingParticles(); ++p){
          if (!theParticle->parent(p)) { bad_parent++; continue;}
          if (!theParticle->parent(p)->isZ() && !theParticle->parent(p)->isW() && !theParticle->parent(p)->isHiggs()) bad_parent++;
        }
        if (bad_parent != 0) continue;
 
      }
    } // End of treatment for generators that are not Sherpa
 
    // Add this particle to the new collection
    xAOD::TruthParticle* xTruthParticle = new xAOD::TruthParticle();
    newParticlesWriteHandle->push_back( xTruthParticle );
    // Fill with numerical content
    *xTruthParticle=*theParticle;
    // Copy over the decorations if they are available
    typeDecorator(*xTruthParticle) = typeAccessor.withDefault(*theParticle, 0);
    originDecorator(*xTruthParticle) = originAccessor.withDefault(*theParticle, 0);
    outcomeDecorator(*xTruthParticle) = outcomeAccessor.withDefault(*theParticle, 0);
    classificationDecorator(*xTruthParticle) = classificationAccessor.withDefault(*theParticle, 0);
  } // Loop over all particles
 
  return StatusCode::SUCCESS;
}
 
// Find out if a particle has a bare descendent
bool DerivationFramework::TruthBornLeptonCollectionMaker::hasBareDescendent( const xAOD::TruthParticle* p ) const
{
  // Null pointer check
  if (!p) return false;
  // If we hit a bare descendent, then we're a winnner
  if (p->isLepton() && MC::isStable(p) ) return true;
  // Otherwise look through all the children
  for (size_t c=0;c<p->nChildren();++c){
    if (!p->child(c)) continue; // Null pointer protection
    if (p->pdgId()!=p->child(c)->pdgId()) continue; // Different particle child
    if (hasBareDescendent( p->child(c) )) return true;
  }
  // No luck -- this branch is a dead end
  return false;
}