McEventCollectionCnv_p5.cxx

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/*
  Copyright (C) 2002-2025 CERN for the benefit of the ATLAS collaboration
*/
 
// McEventCollectionCnv_p5.cxx
// Implementation file for class McEventCollectionCnv_p5
// Author: S.Binet<binet@cern.ch>
 
// STL includes
#include <utility>
#include <cmath>
#include <cfloat> // for DBL_EPSILON
 
// GeneratorObjectsTPCnv includes
#include "GeneratorObjectsTPCnv/McEventCollectionCnv_p5.h"
#include "HepMcDataPool.h"
#include "GenInterfaces/IHepMCWeightSvc.h"
#include "McEventCollectionCnv_utils.h"
#include "GaudiKernel/ThreadLocalContext.h"
#include "TruthUtils/MagicNumbers.h"
 

// Constructors
 
McEventCollectionCnv_p5::McEventCollectionCnv_p5() :
  Base_t( ),
  m_isPileup(false),m_hepMCWeightSvc("HepMCWeightSvc","McEventCollectionCnv_p5")
{}
 
McEventCollectionCnv_p5::McEventCollectionCnv_p5( const McEventCollectionCnv_p5& rhs ) :
  Base_t( rhs ),
  m_isPileup(false),m_hepMCWeightSvc("HepMCWeightSvc","McEventCollectionCnv_p5")
{}
 
McEventCollectionCnv_p5&
McEventCollectionCnv_p5::operator=( const McEventCollectionCnv_p5& rhs )
{
  if ( this != &rhs ) {
    Base_t::operator=( rhs );
    m_isPileup=rhs.m_isPileup;m_hepMCWeightSvc = rhs.m_hepMCWeightSvc;
  }
  return *this;
}

// Destructor
 
McEventCollectionCnv_p5::~McEventCollectionCnv_p5()
= default;
 
 
void McEventCollectionCnv_p5::persToTrans( const McEventCollection_p5* persObj,
                                           McEventCollection* transObj,
                                           MsgStream& msg )
{
  const EventContext& ctx = Gaudi::Hive::currentContext();
 
  msg << MSG::DEBUG << "Loading McEventCollection from persistent state..."
      << endmsg;
 
  // elements are managed by DataPool
  if (!m_isPileup) {
    transObj->clear(SG::VIEW_ELEMENTS);
  }
  HepMC::DataPool datapools;
  const unsigned int nVertices = persObj->m_genVertices.size();
  datapools.vtx.prepareToAdd(nVertices);
  const unsigned int nParts = persObj->m_genParticles.size();
  datapools.part.prepareToAdd(nParts);
  const unsigned int nEvts = persObj->m_genEvents.size();
  datapools.evt.prepareToAdd(nEvts);
  transObj->reserve( nEvts );
  for ( std::vector<GenEvent_p5>::const_iterator
          itr = persObj->m_genEvents.begin(),
          itrEnd = persObj->m_genEvents.end();
        itr != itrEnd;
        ++itr ) {
    const GenEvent_p5& persEvt = *itr;
    HepMC::GenEvent * genEvt(nullptr);
    if(m_isPileup) {
      genEvt = new HepMC::GenEvent();
    } else {
      genEvt        =  datapools.getGenEvent();
    }
    genEvt->add_attribute (HepMCStr::barcodes, std::make_shared<HepMC::GenEventBarcodes>());
    genEvt->add_attribute(HepMCStr::signal_process_id, std::make_shared<HepMC3::IntAttribute>(persEvt.m_signalProcessId));
    genEvt->set_event_number(persEvt.m_eventNbr);
    genEvt->add_attribute(HepMCStr::mpi, std::make_shared<HepMC3::IntAttribute>(persEvt.m_mpi));
    genEvt->add_attribute(HepMCStr::event_scale, std::make_shared<HepMC3::DoubleAttribute>(persEvt.m_eventScale));
    genEvt->add_attribute(HepMCStr::alphaQCD, std::make_shared<HepMC3::DoubleAttribute>(persEvt.m_alphaQCD));
    genEvt->add_attribute(HepMCStr::alphaQED, std::make_shared<HepMC3::DoubleAttribute>(persEvt.m_alphaQED));
    genEvt->weights()= persEvt.m_weights;
    genEvt->add_attribute(HepMCStr::random_states, std::make_shared<HepMC3::VectorLongIntAttribute>(persEvt.m_randomStates));
 
    genEvt->set_units(static_cast<HepMC3::Units::MomentumUnit>(persEvt.m_momentumUnit),
                      static_cast<HepMC3::Units::LengthUnit>(persEvt.m_lengthUnit));
 
    //restore weight names from the dedicated svc (which was keeping them in metadata for efficiency)
    if(!genEvt->run_info()) genEvt->set_run_info(std::make_shared<HepMC3::GenRunInfo>());
    genEvt->run_info()->set_weight_names(m_hepMCWeightSvc->weightNameVec(ctx));
    // cross-section restore
 
    if (!persEvt.m_crossSection.empty()) {
      auto cs = std::make_shared<HepMC3::GenCrossSection>();
      const std::vector<double>& xsection = persEvt.m_crossSection;
      genEvt->set_cross_section(cs);
      if( static_cast<bool>(xsection[0]) )
        cs->set_cross_section(xsection[2],xsection[1]);
      else
        cs->set_cross_section(-1.0, -1.0);
    }
 
    // heavyIon restore
    if (!persEvt.m_heavyIon.empty()) {
      auto hi = std::make_shared<HepMC3::GenHeavyIon>();
      const std::vector<float>& hIon = persEvt.m_heavyIon;
      //AV NOTE THE ORDER
      hi->set(
         static_cast<int>(hIon[12]), // Ncoll_hard
         static_cast<int>(hIon[11]), // Npart_proj
         static_cast<int>(hIon[10]), // Npart_targ
         static_cast<int>(hIon[9]), // Ncoll
         static_cast<int>(hIon[8]), // spectator_neutrons
         static_cast<int>(hIon[7]), // spectator_protons
         static_cast<int>(hIon[6]), // N_Nwounded_collisions
         static_cast<int>(hIon[5]), // Nwounded_N_collisions
         static_cast<int>(hIon[4]), // Nwounded_Nwounded_collisions
         hIon[3],                   // impact_parameter
         hIon[2],                  // event_plane_angle
         hIon[1],                  // eccentricity
         hIon[0]         );         // sigma_inel_NN
      genEvt->set_heavy_ion(std::move(hi));
    }
 
 
 
    // pdfinfo restore
    if (!persEvt.m_pdfinfo.empty())
    {
      const std::vector<double>& pdf = persEvt.m_pdfinfo;
      HepMC3::GenPdfInfoPtr pi = std::make_shared<HepMC3::GenPdfInfo>();
      pi->set(static_cast<int>(pdf[8]), // id1
              static_cast<int>(pdf[7]), // id2
              pdf[4],                   // x1
              pdf[3],                   // x2
              pdf[2],                   // scalePDF
              pdf[1],                   // pdf1
              pdf[0],                   // pdf2
              static_cast<int>(pdf[6]), // pdf_id1
              static_cast<int>(pdf[5]));// pdf_id2
      genEvt->set_pdf_info(std::move(pi));
    }
    transObj->push_back( genEvt );
 
    // create a temporary map associating the barcode of an end-vtx to its
    // particle.
    // As not all particles are stable (d'oh!) we take 50% of the number of
    // particles as an initial size of the hash-map (to prevent re-hash)
    ParticlesMap_t partToEndVtx( (persEvt.m_particlesEnd - persEvt.m_particlesBegin)/2 );
    // This is faster than the HepMC::barcode_to_vertex
    std::map<int, HepMC::GenVertexPtr> brc_to_vertex;
 
    // create the vertices
    const unsigned int endVtx = persEvt.m_verticesEnd;
    for ( unsigned int iVtx = persEvt.m_verticesBegin; iVtx != endVtx; ++iVtx ) {
       auto vtx = createGenVertex( *persObj, persObj->m_genVertices[iVtx], partToEndVtx, datapools, genEvt );
       brc_to_vertex[persObj->m_genVertices[iVtx].m_barcode] = std::move(vtx);
    } //> end loop over vertices
 
    // set the signal process vertex
    const int sigProcVtx = persEvt.m_signalProcessVtx;
    if ( sigProcVtx != 0 && brc_to_vertex.count(sigProcVtx) ) {
      HepMC::set_signal_process_vertex(genEvt, brc_to_vertex[sigProcVtx] );
    }
 
    // connect particles to their end vertices
    for (auto & p : partToEndVtx) {
      if ( brc_to_vertex.count(p.second) ) {
        auto decayVtx = brc_to_vertex[p.second];
        decayVtx->add_particle_in( p.first );
      } else {
        msg << MSG::ERROR << "GenParticle points to null end vertex !!" << endmsg;
      }
    }
    // set the beam particles
    const int beamPart1 = persEvt.m_beamParticle1;
    const int beamPart2 = persEvt.m_beamParticle2;
    if (  beamPart1 != 0  &&  beamPart2 != 0 ) {
      genEvt->set_beam_particles(HepMC::barcode_to_particle(genEvt, beamPart1),
                                 HepMC::barcode_to_particle(genEvt, beamPart2));
    }
 
 
  } //> end loop over m_genEvents
 
  msg << MSG::DEBUG << "Loaded McEventCollection from persistent state [OK]"
      << endmsg;
}
 
void McEventCollectionCnv_p5::transToPers( const McEventCollection* transObj,
                                           McEventCollection_p5* persObj,
                                           MsgStream& msg )
{
  const EventContext& ctx = Gaudi::Hive::currentContext();
 
  msg << MSG::DEBUG << "Creating persistent state of McEventCollection..."
      << endmsg;
  persObj->m_genEvents.reserve( transObj->size() );
 
  const std::pair<unsigned int,unsigned int> stats = nbrParticlesAndVertices( transObj );
  persObj->m_genParticles.reserve( stats.first  );
  persObj->m_genVertices.reserve ( stats.second );
 
  const McEventCollection::const_iterator itrEnd = transObj->end();
  for ( McEventCollection::const_iterator itr = transObj->begin();
        itr != itrEnd;
        ++itr ) {
    const unsigned int nPersVtx   = persObj->m_genVertices.size();
    const unsigned int nPersParts = persObj->m_genParticles.size();
    const HepMC::GenEvent* genEvt = *itr;
   //save the weight names to metadata via the HepMCWeightSvc
      if (genEvt->run_info()) {
        if (!genEvt->run_info()->weight_names().empty()) {
          m_hepMCWeightSvc->setWeightNames(  names_to_name_index_map(genEvt->weight_names()), ctx ).ignore();
        } else {
          //AV : This to be decided if one would like to have default names.
          //std::vector<std::string> names{"0"};
          //m_hepMCWeightSvc->setWeightNames( names_to_name_index_map(names), ctx );
        }
      }
 
      auto A_mpi=genEvt->attribute<HepMC3::IntAttribute>(HepMCStr::mpi);
      auto A_signal_process_id=genEvt->attribute<HepMC3::IntAttribute>(HepMCStr::signal_process_id);
      auto A_event_scale=genEvt->attribute<HepMC3::DoubleAttribute>(HepMCStr::event_scale);
      auto A_alphaQCD=genEvt->attribute<HepMC3::DoubleAttribute>(HepMCStr::alphaQCD);
      auto A_alphaQED=genEvt->attribute<HepMC3::DoubleAttribute>(HepMCStr::alphaQED);
      auto signal_process_vertex = HepMC::signal_process_vertex(genEvt);
      auto A_random_states=genEvt->attribute<HepMC3::VectorLongIntAttribute>(HepMCStr::random_states);
      auto beams=genEvt->beams();
      persObj->m_genEvents.
      emplace_back(A_signal_process_id?(A_signal_process_id->value()):-1,
                              genEvt->event_number(),
                              A_mpi?(A_mpi->value()):-1,
                              A_event_scale?(A_event_scale->value()):0.0,
                              A_alphaQCD?(A_alphaQCD->value()):0.0,
                              A_alphaQED?(A_alphaQED->value()):0.0,
                              signal_process_vertex?HepMC::barcode(signal_process_vertex):0,
                              !beams.empty()?HepMC::barcode(beams[0]):0,
                              beams.size()>1?HepMC::barcode(beams[1]):0,
                              genEvt->weights(),
                              A_random_states?(A_random_states->value()):std::vector<long>(),
                              std::vector<double>(),      // cross section
                              std::vector<float>(),       // heavyion
                              std::vector<double>(),      // pdf info
                              genEvt->momentum_unit(),
                              genEvt->length_unit(),
                              nPersVtx,
                              nPersVtx + genEvt->vertices().size(),
                              nPersParts,
                              nPersParts + genEvt->particles().size() );
 
 
    //HepMC::GenCrossSection encoding
    if (genEvt->cross_section()) {
      auto cs=genEvt->cross_section();
      GenEvent_p5& persEvt = persObj->m_genEvents.back();
      std::vector<double>& crossSection = persEvt.m_crossSection;
      crossSection.resize(3);
      crossSection[2] = cs->xsec();
      crossSection[1] = cs->xsec_err();
      crossSection[0] = static_cast<double>(cs->is_valid());
      if (crossSection[2] < 0) {
       crossSection[2] = 0.0;
       if (crossSection[1] < 0) {
         crossSection[1] = 0.0;
       }
       crossSection[0] = 0.0;
      }
 
    }
 
    //HepMC::HeavyIon encoding
    if (genEvt->heavy_ion()) {
      auto hi=genEvt->heavy_ion();
      GenEvent_p5& persEvt = persObj->m_genEvents.back();
      std::vector<float>& heavyIon = persEvt.m_heavyIon;
      heavyIon.resize(13);
      heavyIon[12]  = static_cast<float>(hi->Ncoll_hard);
      heavyIon[11]  = static_cast<float>(hi->Npart_proj);
      heavyIon[10]  = static_cast<float>(hi->Npart_targ);
      heavyIon[9]   = static_cast<float>(hi->Ncoll);
      heavyIon[8]   = static_cast<float>(hi->spectator_neutrons);
      heavyIon[7]   = static_cast<float>(hi->spectator_protons);
      heavyIon[6]   = static_cast<float>(hi->N_Nwounded_collisions);
      heavyIon[5]   = static_cast<float>(hi->Nwounded_N_collisions);
      heavyIon[4]   = static_cast<float>(hi->Nwounded_Nwounded_collisions);
      heavyIon[3]   = hi->impact_parameter;
      heavyIon[2]   = hi->event_plane_angle;
      heavyIon[1]   = hi->eccentricity;
      heavyIon[0]   = hi->sigma_inel_NN;
    }
 
    //PdfInfo encoding
    if (genEvt->pdf_info()) {
      auto pi=genEvt->pdf_info();
      GenEvent_p5& persEvt = persObj->m_genEvents.back();
      std::vector<double>& pdfinfo = persEvt.m_pdfinfo;
      pdfinfo.resize(9);
      pdfinfo[8] = static_cast<double>(pi->parton_id[0]);
      pdfinfo[7] = static_cast<double>(pi->parton_id[1]);
      pdfinfo[6] = static_cast<double>(pi->pdf_id[0]);
      pdfinfo[5] = static_cast<double>(pi->pdf_id[1]);
      pdfinfo[4] = pi->x[0];
      pdfinfo[3] = pi->x[1];
      pdfinfo[2] = pi->scale;
      pdfinfo[1] = pi->xf[0];
      pdfinfo[0] = pi->xf[1];
    }
 
    // create vertices
    for (const auto& v: genEvt->vertices()) {
      writeGenVertex( v, *persObj );
    }
 
  } //> end loop over GenEvents
 
  msg << MSG::DEBUG << "Created persistent state of HepMC::GenEvent [OK]" << endmsg;
}
 
 
HepMC::GenVertexPtr
McEventCollectionCnv_p5::createGenVertex( const McEventCollection_p5& persEvt,
                                          const GenVertex_p5& persVtx,
                                          ParticlesMap_t& partToEndVtx, HepMC::DataPool& datapools
                                         ,HepMC::GenEvent* parent
                                          ) const
{
  HepMC::GenVertexPtr vtx(nullptr);
  if(m_isPileup) {
    vtx=HepMC::newGenVertexPtr();
  } else {
    vtx = datapools.getGenVertex();
  }
  if (parent ) parent->add_vertex(vtx);
  vtx->set_position(HepMC::FourVector( persVtx.m_x , persVtx.m_y , persVtx.m_z ,persVtx.m_t ));
  //AV ID cannot be assigned in HepMC3. And its meaning in HepMC2 is not clear.
  int persVtxStatus(persVtx.m_id);
  // GenVertex "status" (id in HepMC2) was not set for some of
  // MC15/MC16 due to a bug in that production release.
  if (persVtxStatus == 0 && HepMC::BarcodeBased::is_simulation_vertex(persVtx.m_barcode)) {
    // Status values for GenVertex objects created during simulation
    // should have been set to 1000 + Geant4 process in the old
    // scheme. Overriding the value to 1000, means that status-based
    // recognition of simulated vertices will work, while still
    // indicating that the process was not set. (ATLASSIM-6901)
    persVtxStatus = 1000;
    }
  vtx->set_status(HepMC::new_vertex_status_from_old(persVtxStatus, persVtx.m_barcode)); // UPDATED STATUS VALUE TO NEW SCHEME
  // cast from std::vector<float> to std::vector<double>
  std::vector<double> weights( persVtx.m_weights.begin(), persVtx.m_weights.end() );
  vtx->add_attribute(HepMCStr::weights,std::make_shared<HepMC3::VectorDoubleAttribute>(weights));
  HepMC::suggest_barcode(vtx,persVtx.m_barcode);
  // handle the in-going (orphans) particles
  const unsigned int nPartsIn = persVtx.m_particlesIn.size();
  for ( unsigned int i = 0; i != nPartsIn; ++i ) {
    createGenParticle( persEvt.m_genParticles[persVtx.m_particlesIn[i]], partToEndVtx, datapools, vtx, false );
  }
 
  // now handle the out-going particles
  const unsigned int nPartsOut = persVtx.m_particlesOut.size();
  for ( unsigned int i = 0; i != nPartsOut; ++i ) {
    createGenParticle( persEvt.m_genParticles[persVtx.m_particlesOut[i]], partToEndVtx, datapools, vtx );
  }
 
  return vtx;
}
 
HepMC::GenParticlePtr
McEventCollectionCnv_p5::createGenParticle( const GenParticle_p5& persPart,
                                            ParticlesMap_t& partToEndVtx, HepMC::DataPool& datapools ,const HepMC::GenVertexPtr& parent, bool add_to_output ) const
{
  HepMC::GenParticlePtr p(nullptr);
    if (m_isPileup) {
    p = HepMC::newGenParticlePtr();
  } else {
    p    = datapools.getGenParticle();
  }
  if (parent) add_to_output?parent->add_particle_out(p):parent->add_particle_in(p);
  p->set_pdg_id(              persPart.m_pdgId);
  p->set_status(HepMC::new_particle_status_from_old(persPart.m_status, persPart.m_barcode)); // UPDATED STATUS VALUE TO NEW SCHEME
  p->add_attribute(HepMCStr::phi,std::make_shared<HepMC3::DoubleAttribute>(persPart.m_phiPolarization));
  p->add_attribute(HepMCStr::theta,std::make_shared<HepMC3::DoubleAttribute>(persPart.m_thetaPolarization));
  HepMC::suggest_barcode(p,persPart.m_barcode);
  p->set_generated_mass(persPart.m_generated_mass);
 
  // Note: do the E calculation in extended (long double) precision.
  // That happens implicitly on x86 with optimization on; saying it
  // explicitly ensures that we get the same results with and without
  // optimization.  (If this is a performance issue for platforms
  // other than x86, one could change to double for those platforms.)
  if ( 0 == persPart.m_recoMethod ) {
    double temp_e = std::sqrt( (long double)(persPart.m_px)*persPart.m_px +
                          (long double)(persPart.m_py)*persPart.m_py +
                          (long double)(persPart.m_pz)*persPart.m_pz +
                          (long double)(persPart.m_m) *persPart.m_m );
      p->set_momentum( HepMC::FourVector(persPart.m_px,persPart.m_py,persPart.m_pz,temp_e));
  } else {
    const int signM2 = ( persPart.m_m >= 0. ? 1 : -1 );
    const double persPart_ene =
      std::sqrt( std::abs((long double)(persPart.m_px)*persPart.m_px +
                (long double)(persPart.m_py)*persPart.m_py +
                (long double)(persPart.m_pz)*persPart.m_pz +
                signM2* (long double)(persPart.m_m)* persPart.m_m));
    const int signEne = ( persPart.m_recoMethod == 1 ? 1 : -1 );
    p->set_momentum(HepMC::FourVector( persPart.m_px,
                       persPart.m_py,
                       persPart.m_pz,
                       signEne * persPart_ene ));
  }
 
  // setup flow
  std::vector<int> flows;
  const unsigned int nFlow = persPart.m_flow.size();
  for ( unsigned int iFlow= 0; iFlow != nFlow; ++iFlow ) {
  flows.push_back(persPart.m_flow[iFlow].second );
  }
  //We construct it here as vector w/o gaps.
  p->add_attribute(HepMCStr::flows, std::make_shared<HepMC3::VectorIntAttribute>(flows));
 
  if ( persPart.m_endVtx != 0 ) {
    partToEndVtx[p] = persPart.m_endVtx;
  }
 
  return p;
}
 
void McEventCollectionCnv_p5::writeGenVertex( const HepMC::ConstGenVertexPtr& vtx,
                                              McEventCollection_p5& persEvt )
{
  const HepMC::FourVector& position = vtx->position();
  auto A_weights=vtx->attribute<HepMC3::VectorDoubleAttribute>(HepMCStr::weights);
  auto A_barcode=vtx->attribute<HepMC3::IntAttribute>(HepMCStr::barcode);
  std::vector<float> weights;
  if (A_weights) {
    auto weights_d = A_weights->value();
    for (auto& w: weights_d) weights.push_back(w);
  }
  persEvt.m_genVertices.emplace_back( position.x(),
                                                position.y(),
                                                position.z(),
                                                position.t(),
                                                HepMC::old_vertex_status_from_new(vtx->status()), // REVERTED STATUS VALUE TO OLD SCHEME
                                                weights.begin(),
                                                weights.end(),
                                                A_barcode?(A_barcode->value()):vtx->id() );
  GenVertex_p5& persVtx = persEvt.m_genVertices.back();
 
  // we write only the orphans in-coming particles and beams
  persVtx.m_particlesIn.reserve(vtx->particles_in().size());
  for (const auto& p: vtx->particles_in()) {
    if ( !p->production_vertex() || p->production_vertex()->id() == 0 ) {
      persVtx.m_particlesIn.push_back( writeGenParticle( p, persEvt ) );
    }
  }
 
  persVtx.m_particlesOut.reserve(vtx->particles_out().size());
  for (const auto& p: vtx->particles_out()) {
    persVtx.m_particlesOut.push_back( writeGenParticle( p, persEvt ) );
  }
 
  }
 
int McEventCollectionCnv_p5::writeGenParticle( const HepMC::ConstGenParticlePtr& p,
                                               McEventCollection_p5& persEvt )
{
  const HepMC::FourVector mom = p->momentum();
  const double ene = mom.e();
  const double m2  = mom.m2();
 
  // Definitions of Bool isTimeLilike, isSpacelike and isLightlike according to HepLorentzVector definition
  const bool useP2M2 = !(m2 > 0) &&   // !isTimelike
    (m2 < 0) &&   //  isSpacelike
    !(std::abs(m2) < 2.0*DBL_EPSILON*ene*ene); // !isLightlike
    auto A_flows=p->attribute<HepMC3::VectorIntAttribute>(HepMCStr::flows);
    auto A_phi=p->attribute<HepMC3::DoubleAttribute>(HepMCStr::phi);
    auto A_theta=p->attribute<HepMC3::DoubleAttribute>(HepMCStr::theta);
 
  const short recoMethod = ( !useP2M2 ? 0: ( ene >= 0.? 1: 2 ) );
  persEvt.m_genParticles.
    emplace_back( mom.px(),
                               mom.py(),
                               mom.pz(),
                               mom.m(),
                               p->pdg_id(),
                               HepMC::old_particle_status_from_new(p->status()), // REVERTED STATUS VALUE TO OLD SCHEME
                               A_flows?(A_flows->value().size()):0,
                               A_theta?(A_theta->value()):0.0,
                               A_phi?(A_phi->value()):0.0,
                               p->production_vertex()? HepMC::barcode(p->production_vertex()):0,
                               p->end_vertex()? HepMC::barcode(p->end_vertex()):0,
                               HepMC::barcode(p),
                               p->generated_mass(),
                               recoMethod );
 
  std::vector< std::pair<int,int> > flow_hepmc2;
  if(A_flows) flow_hepmc2=vector_to_vector_int_int(A_flows->value());
  persEvt.m_genParticles.back().m_flow.assign( flow_hepmc2.begin(),flow_hepmc2.end() );
 
  // we return the index of the particle in the big vector of particles
  // (contained by the persistent GenEvent)
  return (persEvt.m_genParticles.size() - 1);
 
}
 
void McEventCollectionCnv_p5::setPileup() {
  m_isPileup = true;
}