HLTCalo_TopoCaloClustersMonitor.cxx

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/*
  Copyright (C) 2002-2024 CERN for the benefit of the ATLAS collaboration
*/
 
#include "HLTCalo_TopoCaloClustersMonitor.h"
#include "StoreGate/ReadDecorHandle.h"
#include "LArRecEvent/LArEventBitInfo.h"
#include "AthContainers/ConstAccessor.h"
 
struct clus_kin {
  double et;
  double eta;
  double phi;
  const xAOD::CaloCluster* parent;
};
 
HLTCalo_TopoCaloClustersMonitor::HLTCalo_TopoCaloClustersMonitor( const std::string& name, ISvcLocator* pSvcLocator )
  : AthMonitorAlgorithm(name,pSvcLocator)
{
  declareProperty("HLTContainer", m_HLT_cont_key = "HLT_TopoCaloClustersFS");
  declareProperty("OFFContainer", m_OFF_cont_key = "CaloCalTopoClusters");
  declareProperty("MonGroupName", m_mongroup_name = "TrigCaloMonitor");
  declareProperty("HLTChainsT0", m_hltChainsT0 = "All");
  declareProperty("HLTTypes",  m_HLT_types);
  declareProperty("OFFTypes",  m_OFF_types);
  declareProperty("HLThighET", m_HLT_high_et = 5000.0);
  declareProperty("HLTMinET",  m_HLT_min_et  = -1.0);
  declareProperty("OFFMinET",  m_OFF_min_et  = -1.0);
  declareProperty("MatchType", m_match_types = false);
  declareProperty("DoLC", m_doLC = false);
  declareProperty("MaxDeltaR", m_max_delta_r = 0.04);
}
 
 
HLTCalo_TopoCaloClustersMonitor::~HLTCalo_TopoCaloClustersMonitor() {}
 
 
StatusCode HLTCalo_TopoCaloClustersMonitor::initialize() {
  ATH_CHECK(m_HLT_cont_key.initialize());
  ATH_CHECK(m_OFF_cont_key.initialize());
  ATH_CHECK( m_bunchCrossingKey.initialize());
  ATH_CHECK( m_eventInfoDecorKey.initialize() );
 
  return AthMonitorAlgorithm::initialize();
}
 
 
StatusCode HLTCalo_TopoCaloClustersMonitor::fillHistograms( const EventContext& ctx ) const {
  using namespace Monitored;
 
  // Protect against noise bursts
  SG::ReadHandle<xAOD::EventInfo> thisEvent(GetEventInfo(ctx));
  ATH_CHECK(thisEvent.isValid());
 
  if ( thisEvent->isEventFlagBitSet(xAOD::EventInfo::LAr,LArEventBitInfo::NOISEBURSTVETO))
    return StatusCode::SUCCESS;
  // Get HLT cluster collections
  SG::ReadHandle<xAOD::CaloClusterContainer> hltCluster_readHandle(m_HLT_cont_key, ctx);
  if (! hltCluster_readHandle.isValid() ) {
    ATH_MSG_ERROR("evtStore() does not contain a cluster Collection with key " << m_HLT_cont_key);
    return StatusCode::FAILURE;
  }
 
  // Get OFF cluster collections
  SG::ReadHandle<xAOD::CaloClusterContainer> offCluster_readHandle(m_OFF_cont_key, ctx);
  if (! offCluster_readHandle.isValid() ) {
    ATH_MSG_ERROR("evtStore() does not contain a cluster Collection with key " << m_OFF_cont_key);
    return StatusCode::FAILURE;
  }
 
  // Bunch crossing
  int bcid = ctx.eventID().bunch_crossing_id();
  auto HLT_bc = Monitored::Scalar<int>("HLT_bc",-1);
 
  SG::ReadCondHandle<BunchCrossingCondData> bcidHdl(m_bunchCrossingKey,ctx);
  if (!bcidHdl.isValid()) {
     ATH_MSG_ERROR( "Unable to retrieve BunchCrossing conditions object" );
     return StatusCode::FAILURE;
  }
  const BunchCrossingCondData* bcData=*bcidHdl;
  
  HLT_bc = bcData->distanceFromFront(bcid, BunchCrossingCondData::BunchCrossings);
  // Cache expensive et, eta and phi //
  // calculations for the clusters   //
 
  // prepare HLT clusters
  std::vector<clus_kin> vec_hlt_clusters;
  std::vector<const xAOD::CaloCluster*> accepted_hlt_clusters = ifStepPassed(m_hltChainsT0);
 
  // For monitoring signature specific clusters
   if (accepted_hlt_clusters.size()>0){
    for (const auto* hlt_cluster : accepted_hlt_clusters) {
        auto hlt_clus_et = hlt_cluster->et();
        if (hlt_clus_et < m_HLT_min_et) continue;
 
        bool HLT_type_match = false;
 
        for (unsigned int n = 0; n < m_HLT_types.size(); ++n) {
                if (hlt_cluster->clusterSize() == m_HLT_types[n]) { HLT_type_match = true; break; }
        }
 
    if (!m_HLT_types.empty() && !HLT_type_match) continue;
        vec_hlt_clusters.push_back({hlt_clus_et*0.001, hlt_cluster->eta(), hlt_cluster->phi(), hlt_cluster});
    }
  }
   else{
    for (const auto hlt_cluster : *hltCluster_readHandle) {
        auto hlt_clus_et = hlt_cluster->et();
        if (hlt_clus_et < m_HLT_min_et) continue;
 
        bool HLT_type_match = false;
 
        for (unsigned int n = 0; n < m_HLT_types.size(); ++n) {
                if (hlt_cluster->clusterSize() == m_HLT_types[n]) { HLT_type_match = true; break; }
        }
 
    if (!m_HLT_types.empty() && !HLT_type_match) continue;
        vec_hlt_clusters.push_back({hlt_clus_et*0.001, hlt_cluster->eta(), hlt_cluster->phi(), hlt_cluster});
    }
  }
 
  // prepare OFF clusters
  float off_clus_eta = 0;
  float off_clus_phi = 0;
  float off_clus_et = 0;
  std::vector<clus_kin> vec_off_clusters;
  for (const auto off_cluster : *offCluster_readHandle) {
        if (m_doLC){
      off_clus_et = off_cluster->et();
          off_clus_eta = off_cluster->eta();
          off_clus_phi = off_cluster->phi();
        }
        else{
          off_clus_et = off_cluster->rawE()/std::cosh(std::abs(off_cluster->rawEta()));
          off_clus_eta = off_cluster->rawEta();
          off_clus_phi = off_cluster->rawPhi();
        }
    if (off_clus_et < m_OFF_min_et) continue;
    
    bool OFF_type_match = false;
 
    for (unsigned int n = 0; n < m_OFF_types.size(); ++n) {
        if (off_cluster->clusterSize() == m_OFF_types[n]) { OFF_type_match = true; break; }
    }
 
    if (!m_OFF_types.empty() && !OFF_type_match) continue;
    vec_off_clusters.push_back({off_clus_et*0.001, off_clus_eta, off_clus_phi, off_cluster});
  }
 
  
  // HLT CLUSTERS //
 
  unsigned int n_hlt_clusters = 0;
  unsigned int n_hlt_barrel_high_et_clusters = 0;
  unsigned int n_hlt_clusters_no_match = 0;
  unsigned int n_hlt_clusters_with_match = 0;
 
  // All HLT clusters
  auto HLT_num = Monitored::Scalar<int>("HLT_num",0);
  auto HLT_et = Monitored::Collection("HLT_et", vec_hlt_clusters, &clus_kin::et);
  auto HLT_eta = Monitored::Collection("HLT_eta", vec_hlt_clusters, &clus_kin::eta);
  auto HLT_phi = Monitored::Collection("HLT_phi", vec_hlt_clusters, &clus_kin::phi);
  auto HLT_type = Monitored::Collection("HLT_type", vec_hlt_clusters, []( const clus_kin& clus) { return clus.parent->clusterSize(); } );
  // nCells is a decorated variable not available for older input files
  auto HLT_size = Monitored::Collection("HLT_size", vec_hlt_clusters, []( const clus_kin& clus) {
    static const SG::ConstAccessor<int> nCellsAcc("nCells");
    return nCellsAcc.withDefault(*clus.parent, 0);
  });
  auto HLT_time = Monitored::Collection("HLT_time", vec_hlt_clusters, []( const clus_kin& clus) { return clus.parent->time(); } );
 
  // HLT cut masks
  std::vector<char> vec_hlt_barrel_high_et, vec_hlt_no_off_match, vec_hlt_with_off_match;
  auto HLT_barrel_high_et = Monitored::Collection("HLT_barrel_high_et", vec_hlt_barrel_high_et);
  auto HLT_no_OFF_match = Monitored::Collection("HLT_no_OFF_match", vec_hlt_no_off_match);
  auto HLT_with_OFF_match = Monitored::Collection("HLT_with_OFF_match", vec_hlt_with_off_match);
 
  auto HLT_barrel_high_et_num = Monitored::Scalar<int>("HLT_barrel_high_et_num",0);
  auto HLT_no_OFF_match_num = Monitored::Scalar<int>("HLT_no_OFF_match_num",0);
  auto HLT_with_OFF_match_num = Monitored::Scalar<int>("HLT_with_OFF_match_num",0);
 
  // HLT clusters vs. OFF clusters
  std::vector<float> vec_hlt_vs_off_minimum_delta_r, vec_hlt_vs_off_delta_eta, vec_hlt_vs_off_delta_phi, vec_hlt_vs_off_delta_time, vec_hlt_vs_off_resolution, vec_off_match_et;
 
  auto HLT_matched_fraction = Monitored::Scalar<float>("HLT_matched_fraction", 0.0);
  auto HLT_vs_OFF_minimum_delta_r = Monitored::Collection("HLT_vs_OFF_minimum_delta_r", vec_hlt_vs_off_minimum_delta_r);
  auto HLT_vs_OFF_delta_eta = Monitored::Collection("HLT_vs_OFF_delta_eta", vec_hlt_vs_off_delta_eta);
  auto HLT_vs_OFF_delta_phi = Monitored::Collection("HLT_vs_OFF_delta_phi", vec_hlt_vs_off_delta_phi);
  auto HLT_vs_OFF_delta_time = Monitored::Collection("HLT_vs_OFF_delta_time", vec_hlt_vs_off_delta_time);
  auto HLT_vs_OFF_resolution = Monitored::Collection("HLT_vs_OFF_resolution", vec_hlt_vs_off_resolution);
  auto OFF_match_et = Monitored::Collection("OFF_match_et", vec_off_match_et);
 
  const clus_kin *off_match = nullptr; // For matching
 
  // Loop over HLT clusters
 
  for (const auto& hlt_cluster : vec_hlt_clusters) {
 
    ++n_hlt_clusters;
 
    // high-ET clusters
    if (hlt_cluster.et > (m_HLT_high_et * 0.001) && std::abs(hlt_cluster.eta) < 2.5) {
        ++n_hlt_barrel_high_et_clusters;
        vec_hlt_barrel_high_et.push_back(1);
    }
    else vec_hlt_barrel_high_et.push_back(0);
 
    // matching HLT clusters to OFF clusters
 
    float min_delta_r  = 999999.9;
 
    for (const auto& off_cluster : vec_off_clusters) {
        float delta_r = calculateDeltaR(m_max_delta_r, hlt_cluster.eta, hlt_cluster.phi, off_cluster.eta, off_cluster.phi);
 
        if (delta_r < min_delta_r) {
 
            min_delta_r = delta_r;
            off_match = &off_cluster;
        }
 
    } // End loop over OFF clusters
 
    vec_hlt_vs_off_minimum_delta_r.push_back(min_delta_r);
 
    // No OFF match
    if (min_delta_r >= m_max_delta_r) {
 
        ++n_hlt_clusters_no_match;
 
        vec_off_match_et.push_back(0.);
 
        vec_hlt_vs_off_resolution.push_back(0.);
        vec_hlt_vs_off_delta_eta.push_back(0.);
        vec_hlt_vs_off_delta_phi.push_back(0.);
        vec_hlt_vs_off_delta_time.push_back(0.);
 
        vec_hlt_no_off_match.push_back(1);
        vec_hlt_with_off_match.push_back(0);
    }
 
    // With OFF match
    else {
 
        ++n_hlt_clusters_with_match;
 
        vec_off_match_et.push_back(off_match->et);
 
        vec_hlt_vs_off_resolution.push_back(((off_match->et - hlt_cluster.et) / off_match->et) * 100);
        vec_hlt_vs_off_delta_eta.push_back(off_match->eta - hlt_cluster.eta);
        vec_hlt_vs_off_delta_phi.push_back(calculateDeltaPhi(off_match->phi, hlt_cluster.phi));
        vec_hlt_vs_off_delta_time.push_back(off_match->parent->time() - hlt_cluster.parent->time());
 
        vec_hlt_no_off_match.push_back(0);
        vec_hlt_with_off_match.push_back(1);
    }
 
  } // End loop over HLT clusters
 
  HLT_num = n_hlt_clusters;
  HLT_barrel_high_et_num = n_hlt_barrel_high_et_clusters;
  HLT_no_OFF_match_num = n_hlt_clusters_no_match;
  HLT_with_OFF_match_num = n_hlt_clusters_with_match;
  if (n_hlt_clusters>0) {
    HLT_matched_fraction = static_cast<float>(n_hlt_clusters_with_match) / n_hlt_clusters;
  }
 
  // OFF CLUSTERS //
 
  unsigned int n_off_clusters = 0;
  unsigned int n_off_clusters_no_match = 0;
  unsigned int n_off_clusters_with_match = 0;
 
  // OFF cluster
  std::vector<float> vec_off_et, vec_off_eta, vec_off_phi, vec_off_time;
  std::vector<int> vec_off_type;
 
  auto OFF_num = Monitored::Scalar<int>("OFF_num",0);
  auto OFF_et = Monitored::Collection("OFF_et", vec_off_clusters, &clus_kin::et);
  auto OFF_eta = Monitored::Collection("OFF_eta", vec_off_clusters, &clus_kin::eta);
  auto OFF_phi = Monitored::Collection("OFF_phi", vec_off_clusters, &clus_kin::phi);
  auto OFF_time = Monitored::Collection("OFF_time", vec_off_clusters, []( const clus_kin& clus) { return clus.parent->time(); } );
  auto OFF_type = Monitored::Collection("OFF_type", vec_off_clusters, []( const clus_kin& clus) { return clus.parent->clusterSize(); } );
 
  // cut masks
  std::vector<char> vec_off_no_hlt_match, vec_off_with_hlt_match;
  auto OFF_no_HLT_match = Monitored::Collection("OFF_no_HLT_match", vec_off_no_hlt_match);
  auto OFF_with_HLT_match = Monitored::Collection("OFF_with_HLT_match", vec_off_with_hlt_match);
 
  auto OFF_no_HLT_match_num = Monitored::Scalar<int>("OFF_no_HLT_match_num",0);
  auto OFF_with_HLT_match_num = Monitored::Scalar<int>("OFF_with_HLT_match_num",0);
 
  // OFF clusters vs. HLT clusters
  std::vector<float> vec_off_vs_hlt_minimum_delta_r, vec_off_vs_hlt_delta_eta, vec_off_vs_hlt_delta_phi, vec_off_vs_hlt_delta_time, vec_off_vs_hlt_resolution, vec_hlt_match_et;
 
  auto OFF_matched_fraction = Monitored::Scalar<float>("OFF_matched_fraction", 0.0);
  auto OFF_vs_HLT_minimum_delta_r = Monitored::Collection("OFF_vs_HLT_minimum_delta_r", vec_off_vs_hlt_minimum_delta_r);
  auto OFF_vs_HLT_delta_eta = Monitored::Collection("OFF_vs_HLT_delta_eta", vec_off_vs_hlt_delta_eta);
  auto OFF_vs_HLT_delta_phi = Monitored::Collection("OFF_vs_HLT_delta_phi", vec_off_vs_hlt_delta_phi);
  auto OFF_vs_HLT_delta_time = Monitored::Collection("OFF_vs_HLT_delta_time", vec_off_vs_hlt_delta_time);
  auto OFF_vs_HLT_resolution = Monitored::Collection("OFF_vs_HLT_resolution", vec_off_vs_hlt_resolution);
  auto HLT_match_et = Monitored::Collection("HLT_match_et", vec_hlt_match_et);
 
  const clus_kin *hlt_match = nullptr; // For matching
 
  // Loop over OFF clusters
 
  for (const auto& off_cluster: vec_off_clusters) {
 
    ++n_off_clusters;
 
    // matching OFF clusters to HLT clusters
 
    float min_delta_r  = 999999.9;
 
    for (const auto& hlt_cluster : vec_hlt_clusters) {
 
        float delta_r = calculateDeltaR(m_max_delta_r, off_cluster.eta, off_cluster.phi, hlt_cluster.eta, hlt_cluster.phi);
 
        if (delta_r < min_delta_r) {
 
            min_delta_r = delta_r;
            hlt_match = &hlt_cluster; // avoid HLT double counts?
        }
 
    } // End loop over HLT clusters
 
    vec_off_vs_hlt_minimum_delta_r.push_back(min_delta_r);
 
    // No HLT match
    if (min_delta_r >= m_max_delta_r) {
 
        ++n_off_clusters_no_match;
 
        vec_hlt_match_et.push_back(0.);
 
        vec_off_vs_hlt_resolution.push_back(0.);
        vec_off_vs_hlt_delta_eta.push_back(0.);
        vec_off_vs_hlt_delta_phi.push_back(0.);
        vec_off_vs_hlt_delta_time.push_back(0.);
 
        vec_off_no_hlt_match.push_back(1);
        vec_off_with_hlt_match.push_back(0);
    }
    // With HLT match
    else {
 
        ++n_off_clusters_with_match;
 
        vec_hlt_match_et.push_back(hlt_match->et);
 
        vec_off_vs_hlt_resolution.push_back(((off_cluster.et - hlt_match->et) / off_cluster.et) * 100);
        vec_off_vs_hlt_delta_eta.push_back(off_cluster.eta - hlt_match->eta);
        vec_off_vs_hlt_delta_phi.push_back(calculateDeltaPhi(off_cluster.phi, hlt_match->phi));
        vec_off_vs_hlt_delta_time.push_back(off_cluster.parent->time() - hlt_match->parent->time());
 
        vec_off_no_hlt_match.push_back(0);
        vec_off_with_hlt_match.push_back(1);
    }
 
  } // End loop over OFF clusters
 
 
  OFF_num = n_off_clusters;
  OFF_no_HLT_match_num = n_off_clusters_no_match;
  OFF_with_HLT_match_num = n_off_clusters_with_match;
  if (n_off_clusters>0) {
    OFF_matched_fraction = static_cast<float>(n_off_clusters_with_match) / n_off_clusters;
  }
  const std::string chain = m_hltChainsT0;
 
  if(m_hltChainsT0 != "All"){
   if(accepted_hlt_clusters.size()>0){
     ATH_MSG_DEBUG("Filling for : "<<m_hltChainsT0);
    
     fill(m_mongroup_name,
     // HLT clusters
        HLT_num, HLT_et, HLT_eta, HLT_phi, HLT_time, HLT_type, HLT_size, HLT_barrel_high_et_num, HLT_bc,
 
        // HLT cutmasks
        HLT_barrel_high_et, HLT_no_OFF_match, HLT_with_OFF_match,
 
        // OFF clusters
        OFF_num, OFF_et, OFF_eta, OFF_phi, OFF_time, OFF_type,
 
        // OFF cutmasks
        OFF_no_HLT_match, OFF_with_HLT_match,
 
        // HLT matched to OFF
        HLT_matched_fraction, HLT_no_OFF_match_num, HLT_vs_OFF_minimum_delta_r, HLT_with_OFF_match_num,
        OFF_match_et, HLT_vs_OFF_resolution, HLT_vs_OFF_delta_eta, HLT_vs_OFF_delta_phi, HLT_vs_OFF_delta_time,
 
        // OFF matched to HLT
        OFF_matched_fraction, OFF_no_HLT_match_num, OFF_vs_HLT_minimum_delta_r, OFF_with_HLT_match_num,
        HLT_match_et, OFF_vs_HLT_resolution, OFF_vs_HLT_delta_eta, OFF_vs_HLT_delta_phi, OFF_vs_HLT_delta_time
        );
   
   }
   else if(getTrigDecisionTool()->isPassed(m_hltChainsT0)){
     ATH_MSG_DEBUG("Filling for : "<<m_hltChainsT0);
     fill(m_mongroup_name,
     // HLT clusters
        HLT_num, HLT_et, HLT_eta, HLT_phi, HLT_time, HLT_type, HLT_size, HLT_barrel_high_et_num, HLT_bc,
 
        // HLT cutmasks
        HLT_barrel_high_et, HLT_no_OFF_match, HLT_with_OFF_match,
 
        // OFF clusters
        OFF_num, OFF_et, OFF_eta, OFF_phi, OFF_time, OFF_type,
 
        // OFF cutmasks
        OFF_no_HLT_match, OFF_with_HLT_match,
 
        // HLT matched to OFF
        HLT_matched_fraction, HLT_no_OFF_match_num, HLT_vs_OFF_minimum_delta_r, HLT_with_OFF_match_num,
        OFF_match_et, HLT_vs_OFF_resolution, HLT_vs_OFF_delta_eta, HLT_vs_OFF_delta_phi, HLT_vs_OFF_delta_time,
 
        // OFF matched to HLT
        OFF_matched_fraction, OFF_no_HLT_match_num, OFF_vs_HLT_minimum_delta_r, OFF_with_HLT_match_num,
        HLT_match_et, OFF_vs_HLT_resolution, OFF_vs_HLT_delta_eta, OFF_vs_HLT_delta_phi, OFF_vs_HLT_delta_time
        );
    }
   }
   else {
    ATH_MSG_DEBUG("Filling for : "<<m_hltChainsT0);
     fill(m_mongroup_name,
     // HLT clusters
        HLT_num, HLT_et, HLT_eta, HLT_phi, HLT_time, HLT_type, HLT_size, HLT_barrel_high_et_num, HLT_bc,
 
        // HLT cutmasks
        HLT_barrel_high_et, HLT_no_OFF_match, HLT_with_OFF_match,
 
        // OFF clusters
        OFF_num, OFF_et, OFF_eta, OFF_phi, OFF_time, OFF_type,
 
        // OFF cutmasks
        OFF_no_HLT_match, OFF_with_HLT_match,
 
        // HLT matched to OFF
        HLT_matched_fraction, HLT_no_OFF_match_num, HLT_vs_OFF_minimum_delta_r, HLT_with_OFF_match_num,
        OFF_match_et, HLT_vs_OFF_resolution, HLT_vs_OFF_delta_eta, HLT_vs_OFF_delta_phi, HLT_vs_OFF_delta_time,
 
        // OFF matched to HLT
        OFF_matched_fraction, OFF_no_HLT_match_num, OFF_vs_HLT_minimum_delta_r, OFF_with_HLT_match_num,
        HLT_match_et, OFF_vs_HLT_resolution, OFF_vs_HLT_delta_eta, OFF_vs_HLT_delta_phi, OFF_vs_HLT_delta_time
        );
 
  }
  return StatusCode::SUCCESS;
}
 
 
float HLTCalo_TopoCaloClustersMonitor::calculateDeltaR( float max_deltar, float eta_1, float phi_1, float eta_2, float phi_2 ) const {
  // reject the match as early as possible to avoid the expensive delta r calculation
  if (std::abs(eta_1-eta_2) > max_deltar) return 99.9;
  double DeltaPhi = calculateDeltaPhi(phi_1, phi_2);
  if (DeltaPhi > max_deltar) return 99.9;
  return sqrt( ((eta_1-eta_2)*(eta_1-eta_2)) + (DeltaPhi*DeltaPhi) );
}
 
float HLTCalo_TopoCaloClustersMonitor::calculateDeltaPhi( float phi_1, float phi_2 ) const {
  return std::abs( std::abs( std::abs( phi_1 - phi_2 ) - TMath::Pi() ) - TMath::Pi() );
}
 
std::vector<const xAOD::CaloCluster*> HLTCalo_TopoCaloClustersMonitor::ifStepPassed(const std::string& chain) const{
  Trig::FeatureRequestDescriptor featureRequestDescriptor;
  featureRequestDescriptor.setChainGroup(chain);
  featureRequestDescriptor.setCondition(TrigDefs::includeFailedDecisions);
  std::vector<TrigCompositeUtils::LinkInfo<xAOD::CaloClusterContainer>> fVec = getTrigDecisionTool()->features<xAOD::CaloClusterContainer>(featureRequestDescriptor);
  std::vector<const xAOD::CaloCluster*> clustersToMonitorForChain;
  for (const TrigCompositeUtils::LinkInfo<xAOD::CaloClusterContainer>& f : fVec) {
     if (f.state == TrigCompositeUtils::ActiveState::ACTIVE) {
       clustersToMonitorForChain.push_back( *(f.link) );
    }
  }
  ATH_MSG_DEBUG("clustersToMonitorForChain.size(): "<<clustersToMonitorForChain.size());
  for(auto &p: clustersToMonitorForChain) 
    ATH_MSG_DEBUG("clustersToMonitorForChain->et(): "<<p->et());
  return clustersToMonitorForChain;
}