TopDecaySubset.cc

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#include "FWCore/Utilities/interface/EDMException.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"

#include "AnalysisDataFormats/TopObjects/interface/TopGenEvent.h"
#include "TopQuarkAnalysis/TopEventProducers/interface/TopDecaySubset.h"

#include "FWCore/Common/interface/Provenance.h"

TopDecaySubset::TopDecaySubset(const edm::ParameterSet& cfg):
  srcToken_         (consumes<reco::GenParticleCollection>(cfg.getParameter<edm::InputTag>("src"))),
  genEventInfo_srcToken_ (mayConsume < GenEventInfoProduct > (edm::InputTag("generator"))),
  addRadiation_(cfg.getParameter<bool>("addRadiation")),
  showerModel_ (kStart),
  runMode_(kRun1)
{
  // mapping of the corresponding fillMode; see FillMode
  // enumerator of TopDecaySubset for available modes
  std::string mode = cfg.getParameter<std::string>( "fillMode" );
  if(mode=="kME")
    fillMode_=kME;
  else if(mode=="kStable")
    fillMode_=kStable;
  else
    throw cms::Exception("Configuration") << mode << " is not a supported FillMode!\n";

  mode = cfg.getParameter<std::string>( "runMode" );
    if(mode=="Run1")
      runMode_=kRun1;
    else if(mode=="Run2")
        runMode_=kRun2;
    else
      throw cms::Exception("Configuration") << mode << " is not a supported RunMode!\n";

  // produces a set of GenParticles following
  // the decay branch of top quarks to the first level of
  // stable decay products
  produces<reco::GenParticleCollection>();
}

TopDecaySubset::~TopDecaySubset()
{
}

void
TopDecaySubset::produce(edm::Event& event, const edm::EventSetup& setup)
{
  // create target vector
  std::unique_ptr<reco::GenParticleCollection> target( new reco::GenParticleCollection );

  // get source collection
  edm::Handle<reco::GenParticleCollection> src;
  event.getByToken(srcToken_, src);

  // find out what generator we are dealing with
  if (showerModel_ == kStart && runMode_ == kRun2) {
    showerModel_ = checkShowerModel(event);
  }

  // find top quarks in list of input particles
  std::vector<const reco::GenParticle*> tops;
  if(runMode_ == kRun1)
      tops = findTops(*src);
  else
      tops = findPrimalTops(*src);

  // determine shower model (only in first event)
  if(showerModel_==kStart && runMode_ == kRun1)
    showerModel_=checkShowerModel(tops);

  if(showerModel_!=kNone) {
    // check sanity of W bosons
    if (runMode_ == kRun1)
        checkWBosons(tops);
    else {
        // nothing for the moment
    }

    // get ref product from the event
    const reco::GenParticleRefProd ref = event.getRefBeforePut<reco::GenParticleCollection>();
    // clear existing refs
    clearReferences();
    if (runMode_ == kRun1) {
        // fill output
        fillListing(tops, *target);
        // fill references
        fillReferences(ref, *target);
    }
    else {
        std::vector<const reco::GenParticle*> decaying_tops = findDecayingTops(*src);
        // fill output
        fillListing(tops, decaying_tops, *target);
        // fill references
        fillReferences(ref, *target);
    }
  }

  // write vectors to the event
  event.put(std::move(target));
}

std::vector<const reco::GenParticle*>
TopDecaySubset::findTops(const reco::GenParticleCollection& parts)
{
  std::vector<const reco::GenParticle*> tops;
  for(reco::GenParticleCollection::const_iterator t=parts.begin(); t!=parts.end(); ++t){
    if( std::abs(t->pdgId())==TopDecayID::tID && t->status()==TopDecayID::unfrag )
      tops.push_back( &(*t) );
  }
  return tops;
}

std::vector<const reco::GenParticle*> TopDecaySubset::findPrimalTops(
        const reco::GenParticleCollection& parts) {
    std::vector<const reco::GenParticle*> tops;
    for (reco::GenParticleCollection::const_iterator t = parts.begin();
            t != parts.end(); ++t) {
        if (std::abs(t->pdgId()) != TopDecayID::tID)
            continue;

        bool hasTopMother = false;
        for (unsigned idx = 0; idx < t->numberOfMothers(); ++idx) {
            if (std::abs(t->mother(idx)->pdgId()) == TopDecayID::tID)
                hasTopMother = true;
        }

        if (hasTopMother)  // not a primal top
            continue;
        tops.push_back(&(*t));
    }

    return tops;
}

std::vector<const reco::GenParticle*> TopDecaySubset::findDecayingTops(
        const reco::GenParticleCollection& parts) {
    std::vector<const reco::GenParticle*> tops;
    for (reco::GenParticleCollection::const_iterator t = parts.begin();
            t != parts.end(); ++t) {
        if (std::abs(t->pdgId()) != TopDecayID::tID)
            continue;

        bool hasTopDaughter = false;
        for (unsigned idx = 0; idx < t->numberOfDaughters(); ++idx) {
            if (std::abs(t->daughter(idx)->pdgId()) == TopDecayID::tID)
                hasTopDaughter = true;
        }

        if (hasTopDaughter)  // not a decaying top
            continue;
        tops.push_back(&(*t));
    }

    return tops;
}

const reco::GenParticle* TopDecaySubset::findPrimalW(
        const reco::GenParticle* top) {
    unsigned int w_index = 0;
    for (unsigned idx = 0; idx < top->numberOfDaughters(); ++idx) {
        if (std::abs(top->daughter(idx)->pdgId()) == TopDecayID::WID) {
            w_index = idx;
            break;
        }
    }
    return (reco::GenParticle*)top->daughter(w_index);
}

//const reco::GenParticle* TopDecaySubset::findDecayingW(
//      const reco::GenParticle* top) {
//  const reco::GenParticle* decaying_W = findLastParticleInChain(findPrimalW(top));
//  return findLastParticleInChain(findPrimalW(top));
//}

const reco::GenParticle* TopDecaySubset::findLastParticleInChain(
        const reco::GenParticle* p) {
    int particleID = std::abs(p->pdgId());
    bool containsItself = false;
    unsigned int d_idx = 0;
    for (unsigned idx = 0; idx < p->numberOfDaughters(); ++idx) {
        if (std::abs(p->daughter(idx)->pdgId()) == particleID) {
            containsItself = true;
            d_idx = idx;
        }
    }

    if (!containsItself)
        return p;
    else {
    if (showerModel_ == kPythia){
      // Pythia6 has a weird idea of W bosons (and maybe other particles)
      // W (status == 3) -> q qbar' W. The new W is status 2 and has no daughters
      if(p->status() == 3)
        return p;
    }
    return findLastParticleInChain((reco::GenParticle*)p->daughter(d_idx));
  }


}

TopDecaySubset::ShowerModel
TopDecaySubset::checkShowerModel(const std::vector<const reco::GenParticle*>& tops) const
{
  for(std::vector<const reco::GenParticle*>::const_iterator it=tops.begin(); it!=tops.end(); ++it){
    const reco::GenParticle* top = *it;
    // check for kHerwig type showers: here the status 3 top quark will
    // have a single status 2 top quark as daughter, which has again 3
    // or more status 2 daughters
    if( top->numberOfDaughters()==1){
      if( top->begin()->pdgId()==top->pdgId() && top->begin()->status()==TopDecayID::stable && top->begin()->numberOfDaughters()>1)
    return kHerwig;
    }
    // check for kPythia type showers: here the status 3 top quark will
    // have all decay products and a status 2 top quark as daughters
    // the status 2 top quark will be w/o further daughters
    if( top->numberOfDaughters()>1 ){
      bool containsWBoson=false, containsQuarkDaughter=false;
      for(reco::GenParticle::const_iterator td=top->begin(); td!=top->end(); ++td){
    if( std::abs(td->pdgId ()) <TopDecayID::tID ) containsQuarkDaughter=true;
    if( std::abs(td->pdgId ())==TopDecayID::WID ) containsWBoson=true;
      }
      if(containsQuarkDaughter && containsWBoson)
    return kPythia;
    }
  }
  // if neither Herwig nor Pythia like
  if(tops.empty())
    edm::LogInfo("decayChain")
      << " Failed to find top quarks in decay chain. Will assume that this a \n"
      << " non-top sample and produce an empty decaySubset.\n";
  else
    throw edm::Exception(edm::errors::LogicError,
             " Can not find back any of the supported hadronization models. Models \n"
             " which are supported are:                                            \n"
             " Pythia  LO(+PS): Top(status 3) --> WBoson(status 3), Quark(status 3)\n"
             " Herwig NLO(+PS): Top(status 2) --> Top(status 3) --> Top(status 2)  \n");
  return kNone;
}

TopDecaySubset::ShowerModel TopDecaySubset::checkShowerModel(
        edm::Event& event) {
    edm::Handle < GenEventInfoProduct > genEvtInfoProduct;
    event.getByToken(genEventInfo_srcToken_, genEvtInfoProduct);

    std::string moduleName = "";
    if (genEvtInfoProduct.isValid()) {
        const edm::Provenance& prov = event.getProvenance(
                genEvtInfoProduct.id());
        moduleName = edm::moduleName(prov);
    }

    ShowerModel shower(kStart);
    if (moduleName.find("Pythia6") != std::string::npos)
        shower = kPythia;
    else if (moduleName.find("Pythia8") != std::string::npos)
        shower = kPythia8;
    else if (moduleName.find("Herwig6") != std::string::npos)
        shower = kHerwig;
    else if (moduleName.find("ThePEG") != std::string::npos)
        // Herwig++
        shower = kHerwig;
    else if (moduleName.find("Sherpa") != std::string::npos)
        shower = kSherpa;
    else
        shower = kNone;
    return shower;
}
void
TopDecaySubset::checkWBosons(std::vector<const reco::GenParticle*>& tops) const
{
  unsigned nTops = tops.size();
  for(std::vector<const reco::GenParticle*>::iterator it=tops.begin(); it!=tops.end();) {
    const reco::GenParticle* top = *it;
    bool isContained=false;
    bool expectedStatus=false;
    if(showerModel_!=kPythia && top->begin()==top->end())
      throw edm::Exception(edm::errors::LogicError,
               "showerModel_!=kPythia && top->begin()==top->end()\n");
    for(reco::GenParticle::const_iterator td=((showerModel_==kPythia) ? top->begin() : top->begin()->begin());
    td!=((showerModel_==kPythia) ? top->end() : top->begin()->end());
    ++td){
      if(std::abs(td->pdgId())==TopDecayID::WID) {
    isContained=true;
    if( ((showerModel_==kPythia) ? td->status()==TopDecayID::unfrag : td->status()==TopDecayID::stable) ) {
      expectedStatus=true;
      break;
    }
      }
    }
    if(!expectedStatus) {
      it=tops.erase(it);
      if(isContained)
    edm::LogInfo("decayChain")
      << " W boson does not have the expected status. This happens, e.g.,      \n"
      << " with MC@NLO in the case of additional ttbar pairs from radiated     \n"
      << " gluons. We hope everything is fine, remove the correspdonding top   \n"
      << " quark from our list since it is not part of the primary ttbar pair  \n"
      << " and try to continue.                                                \n";
    }
    else
      it++;
  }
  if(tops.empty() && nTops!=0)
    throw edm::Exception(edm::errors::LogicError,
             " Did not find a W boson with appropriate status for any of the top   \n"
             " quarks in this event. This means that the hadronization of the W    \n"
             " boson might be screwed up or there is another problem with the      \n"
             " particle listing in this MC sample. Please contact an expert.       \n");
}

void
TopDecaySubset::fillListing(const std::vector<const reco::GenParticle*>& tops, reco::GenParticleCollection& target)
{
  unsigned int statusFlag;
  // determine status flag of the new
  // particle depending on the FillMode
  fillMode_ == kME ? statusFlag=3 : statusFlag=2;

  for(std::vector<const reco::GenParticle*>::const_iterator it=tops.begin(); it!=tops.end(); ++it){
    const reco::GenParticle* t = *it;
    // if particle is top or anti-top
    std::unique_ptr<reco::GenParticle> topPtr( new reco::GenParticle( t->threeCharge(), p4(it, statusFlag), t->vertex(), t->pdgId(), statusFlag, false ) );
    target.push_back( *topPtr );
    ++motherPartIdx_;
    // keep the top index for the map to manage the daughter refs
    int iTop=motherPartIdx_;
    std::vector<int> topDaughters;
    // define the W boson index (to be set later) for the map to
    // manage the daughter refs
    int iW = 0;
    std::vector<int> wDaughters;
    // sanity check
    if(showerModel_!=kPythia && t->begin()==t->end())
      throw edm::Exception(edm::errors::LogicError,
               "showerModel_!=kPythia && t->begin()==t->end()\n");
    //iterate over top daughters
    for(reco::GenParticle::const_iterator td=((showerModel_==kPythia)?t->begin():t->begin()->begin()); td!=((showerModel_==kPythia)?t->end():t->begin()->end()); ++td){
      if( td->status()==TopDecayID::unfrag && std::abs( td->pdgId() )<=TopDecayID::bID ){
    // if particle is beauty or other quark
    std::unique_ptr<reco::GenParticle> bPtr( new reco::GenParticle( td->threeCharge(), p4( td, statusFlag ), td->vertex(), td->pdgId(), statusFlag, false ) );
    target.push_back( *bPtr );
    // increment & push index of the top daughter
    topDaughters.push_back( ++motherPartIdx_ );
    if(addRadiation_){
      addRadiation(motherPartIdx_,td,target);
    }
      }
      // sanity check
      if(showerModel_!=kPythia && td->begin()==td->end())
    throw edm::Exception(edm::errors::LogicError,
                 "showerModel_!=kPythia && td->begin()==td->end()\n");
      reco::GenParticle::const_iterator buffer = (showerModel_==kPythia)?td:td->begin();
      if( buffer->status()==TopDecayID::unfrag && std::abs( buffer->pdgId() )==TopDecayID::WID ){
    // if particle is a W boson
    std::unique_ptr<reco::GenParticle> wPtr(  new reco::GenParticle( buffer->threeCharge(), p4( buffer, statusFlag), buffer->vertex(), buffer->pdgId(), statusFlag, true ) );
    target.push_back( *wPtr );
    // increment & push index of the top daughter
    topDaughters.push_back( ++motherPartIdx_ );
    // keep the W idx for the map
    iW=motherPartIdx_;
    if(addRadiation_){
      addRadiation(motherPartIdx_,buffer,target);
    }
    if(showerModel_!=kPythia && buffer->begin()==buffer->end())
      throw edm::Exception(edm::errors::LogicError,
                   "showerModel_!=kPythia && buffer->begin()==buffer->end()\n");
    // iterate over W daughters
    for(reco::GenParticle::const_iterator wd=((showerModel_==kPythia)?buffer->begin():buffer->begin()->begin()); wd!=((showerModel_==kPythia)?buffer->end():buffer->begin()->end()); ++wd){
      // make sure the W daughter is of status unfrag and not the W itself
      if( wd->status()==TopDecayID::unfrag && !(std::abs(wd->pdgId())==TopDecayID::WID) ) {
        std::unique_ptr<reco::GenParticle> qPtr( new reco::GenParticle( wd->threeCharge(), p4( wd, statusFlag ), wd->vertex(), wd->pdgId(), statusFlag, false) );
        target.push_back( *qPtr );
        // increment & push index of the top daughter
        wDaughters.push_back( ++motherPartIdx_ );
        if( wd->status()==TopDecayID::unfrag && std::abs( wd->pdgId() )==TopDecayID::tauID ){
          // add tau daughters if the particle is a tau pass
          // the daughter of the tau which is of status 2
          //addDaughters(motherPartIdx_, wd->begin(), target);
          // add tau daughters if the particle is a tau pass
          // the tau itself, which may add a tau daughter of
          // of status 2 to the listing
          addDaughters(motherPartIdx_,wd,target);
        }
      }
    }
      }
      if(addRadiation_ && buffer->status()==TopDecayID::stable && ( buffer->pdgId()==TopDecayID::glueID || std::abs(buffer->pdgId())<TopDecayID::bID)){
    // collect additional radiation from the top
    std::unique_ptr<reco::GenParticle> radPtr( new reco::GenParticle( buffer->threeCharge(), buffer->p4(), buffer->vertex(), buffer->pdgId(), statusFlag, false ) );
    target.push_back( *radPtr );
    // increment & push index of the top daughter
    topDaughters.push_back( ++motherPartIdx_ );
      }
    }
    // add potential sisters of the top quark;
    // only for top to prevent double counting
    if(t->numberOfMothers()>0 && t->pdgId()==TopDecayID::tID){
      for(reco::GenParticle::const_iterator ts = t->mother()->begin(); ts!=t->mother()->end(); ++ts){
    // loop over all daughters of the top mother i.e.
    // the two top quarks and their potential sisters
    if(std::abs(ts->pdgId())!=t->pdgId() && ts->pdgId()!=t->mother()->pdgId()){
      // add all further particles but the two top quarks and potential
      // cases where the mother of the top has itself as daughter
      reco::GenParticle* cand = new reco::GenParticle( ts->threeCharge(), ts->p4(), ts->vertex(), ts->pdgId(), ts->status(), false );
      std::unique_ptr<reco::GenParticle> sPtr( cand );
      target.push_back( *sPtr );
      if(ts->begin()!=ts->end()){
        // in case the sister has daughters increment
        // and add the first generation of daughters
        addDaughters(++motherPartIdx_,ts->begin(),target,false);
      }
    }
      }
    }
    // fill the map for the administration
    // of daughter indices
    refs_[ iTop ] = topDaughters;
    refs_[ iW   ] = wDaughters;
  }
}

void TopDecaySubset::fillListing(
        const std::vector<const reco::GenParticle*>& primalTops,
        const std::vector<const reco::GenParticle*>& decayingTops,
        reco::GenParticleCollection& target) {
  std::vector<const reco::GenParticle*>::const_iterator top_start;
  std::vector<const reco::GenParticle*>::const_iterator top_end;
  if (fillMode_ == kME) {
    top_start = primalTops.begin();
    top_end = primalTops.end();
  } else {
    top_start = decayingTops.begin();
    top_end = decayingTops.end();
  }
    for (std::vector<const reco::GenParticle*>::const_iterator it =
        top_start; it != top_end; ++it) {
        const reco::GenParticle* t = *it;
        // summation might happen here
        std::unique_ptr < reco::GenParticle
                > topPtr(
                        new reco::GenParticle(t->threeCharge(), t->p4(),
                                t->vertex(), t->pdgId(), t->status(), false));
        target.push_back(*topPtr);
        ++motherPartIdx_;

        // keep the top index for the map to manage the daughter refs
        int iTop = motherPartIdx_;
        std::vector<int> topDaughters;
        // define the W boson index (to be set later) for the map to
        // manage the daughter refs
        int iW = 0;
        std::vector<int> wDaughters;
        const reco::GenParticle* final_top = findLastParticleInChain(t);

        //iterate over top daughters
        for (reco::GenParticle::const_iterator td = final_top->begin();
                td != final_top->end(); ++td) {
            if (std::abs(td->pdgId()) <= TopDecayID::bID) {
                // if particle is beauty or other quark
                std::unique_ptr < reco::GenParticle
                        > qPtr(
                                new reco::GenParticle(td->threeCharge(),
                                        td->p4(), td->vertex(), td->pdgId(),
                                        td->status(), false));
                target.push_back(*qPtr);
                // increment & push index of the top daughter
                topDaughters.push_back(++motherPartIdx_);
                if (addRadiation_) {
                    // for radation to be added we first need to
                    // pick the last quark in the MC chain
                    const reco::GenParticle* last_q = findLastParticleInChain(
                            (reco::GenParticle*) &*td);
                    addRadiation(motherPartIdx_, last_q, target);
                }
            } else if (std::abs(td->pdgId()) == TopDecayID::WID) {
                // ladies and gentleman, we have a W boson
                std::unique_ptr < reco::GenParticle
                        > WPtr(
                                new reco::GenParticle(td->threeCharge(),
                                        td->p4(), td->vertex(), td->pdgId(),
                                        td->status(), false));
                target.push_back(*WPtr);
                // increment & push index of the top daughter
                topDaughters.push_back(++motherPartIdx_);
                iW = motherPartIdx_;

                // next are the daughers of our W boson
        // for Pythia 6 this is wrong as the last W has no daughters at all!
        // instead the status 3 W has 3 daughters: q qbar' and W (WTF??!)
                const reco::GenParticle* decaying_W = findLastParticleInChain(
                        (reco::GenParticle*) &*td);
                for (reco::GenParticle::const_iterator wd = decaying_W->begin();
                        wd != decaying_W->end(); ++wd) {
                    if (!(std::abs(wd->pdgId()) == TopDecayID::WID)) {
                        std::unique_ptr < reco::GenParticle
                                > qPtr(
                                        new reco::GenParticle(wd->threeCharge(),
                                                wd->p4(), wd->vertex(),
                                                wd->pdgId(), wd->status(),
                                                false));
                        target.push_back(*qPtr);
                        // increment & push index of the top daughter
                        wDaughters.push_back(++motherPartIdx_);
                        const reco::GenParticle* last_q = findLastParticleInChain(
                                                    (reco::GenParticle*) &*wd);
                        addRadiation(motherPartIdx_, last_q, target);
                        if (std::abs(wd->pdgId()) == TopDecayID::tauID) {
                            // add tau daughters
                            // currently it adds k-mesons etc as well, which
                            // is not what we want.
                            addDaughters(motherPartIdx_, wd, target);
                        }
                    }
                }

            } else {
        if(addRadiation_ && ( td->pdgId()==TopDecayID::glueID ||
            std::abs(td->pdgId())<TopDecayID::bID)){
          // collect additional radiation from the top
          std::unique_ptr<reco::GenParticle> radPtr(
            new reco::GenParticle( td->threeCharge(),
            td->p4(), td->vertex(), td->pdgId(), td->status(), false ) );
          target.push_back( *radPtr );
        }
                //other top daughters like Zq for FCNC
        // for pythia 6 many gluons end up here
                //std::cout << "other top daughters: to be implemented"
                //      << std::endl;
            }
        }

        // fill the map for the administration
        // of daughter indices
        refs_[iTop] = topDaughters;
        refs_[iW] = wDaughters;
    }
}

reco::Particle::LorentzVector
TopDecaySubset::p4(const std::vector<const reco::GenParticle*>::const_iterator top, int statusFlag)
{
  // calculate the four vector for top/anti-top quarks from
  // the W boson and the b quark plain or including all
  // additional radiation depending on switch 'plain'
  if(statusFlag==TopDecayID::unfrag){
    // return 4 momentum as it is
    return (*top)->p4();
  }
  reco::Particle::LorentzVector vec;
  for(reco::GenParticle::const_iterator p=(*top)->begin(); p!=(*top)->end(); ++p){
    if( p->status() == TopDecayID::unfrag ){
      // descend by one level for each
      // status 3 particle on the way
      vec+=p4( p, statusFlag );
    }
    else{
      if( std::abs((*top)->pdgId())==TopDecayID::WID ){
    // in case of a W boson skip the status
    // 2 particle to prevent double counting
    if( std::abs(p->pdgId())!=TopDecayID::WID )
      vec+=p->p4();
      }
      else{
    // add all four vectors for each stable
    // particle (status 1 or 2) on the way
    vec+=p->p4();
    if( vec.mass()-(*top)->mass()>0 ){
      // continue adding up gluons and qqbar pairs on the top
      // line untill the nominal top mass is reached; then
      // break in order to prevent picking up virtualities
      break;
    }
      }
    }
  }
  return vec;
}

reco::Particle::LorentzVector
TopDecaySubset::p4(const reco::GenParticle::const_iterator part, int statusFlag)
{
  // calculate the four vector for all top daughters from
  // their daughters including additional radiation
  if(statusFlag==TopDecayID::unfrag){
    // return 4 momentum as it is
    return part->p4();
  }
  reco::Particle::LorentzVector vec;
  for(reco::GenParticle::const_iterator p=part->begin(); p!=part->end(); ++p){
    if( p->status()<=TopDecayID::stable && std::abs(p->pdgId ())==TopDecayID::WID){
      vec=p->p4();
    }
    else{
      if(p->status()<=TopDecayID::stable){
    // sum up the p4 of all stable particles
    // (of status 1 or 2)
    vec+=p->p4();
      }
      else{
    if( p->status()==TopDecayID::unfrag){
      // if the particle is unfragmented (i.e.
      // status 3) descend by one level
      vec+=p4(p, statusFlag);
    }
      }
    }
  }
  return vec;
}

void
TopDecaySubset::addRadiation(int& idx, const reco::GenParticle::const_iterator part, reco::GenParticleCollection& target)
{
  std::vector<int> daughters;
  int idxBuffer = idx;
  for(reco::GenParticle::const_iterator daughter=part->begin(); daughter!=part->end(); ++daughter){
    if(daughter->status()<=TopDecayID::stable && daughter->pdgId()!=part->pdgId()){
      // skip comment lines and make sure that
      // the particle is not double counted as
      // daughter of itself
      std::unique_ptr<reco::GenParticle> ptr(  new reco::GenParticle( daughter->threeCharge(), daughter->p4(), daughter->vertex(), daughter->pdgId(), daughter->status(), false) );
      target.push_back( *ptr );
      daughters.push_back( ++idx ); //push index of daughter
    }
  }
  if(!daughters.empty()) {
    refs_[ idxBuffer ] = daughters;
  }
}

void TopDecaySubset::addRadiation(int& idx, const reco::GenParticle* part,
        reco::GenParticleCollection& target) {
    std::vector<int> daughters;
    int idxBuffer = idx;
    for (reco::GenParticle::const_iterator daughter = part->begin();
            daughter != part->end(); ++daughter) {
        // either pick daughters as long as they are different
        // to the initial particle
        if (daughter->pdgId() != part->pdgId()) {
            std::unique_ptr < reco::GenParticle
                    > ptr(
                            new reco::GenParticle(daughter->threeCharge(),
                                    daughter->p4(), daughter->vertex(),
                                    daughter->pdgId(), daughter->status(),
                                    false));
            target.push_back(*ptr);
            daughters.push_back(++idx); //push index of daughter
        }
    }
    if (!daughters.empty()) {
        refs_[idxBuffer] = daughters;
    }
}

void
TopDecaySubset::addDaughters(int& idx, const reco::GenParticle::const_iterator part, reco::GenParticleCollection& target, bool recursive)
{
  std::vector<int> daughters;
  int idxBuffer = idx;
  for(reco::GenParticle::const_iterator daughter=part->begin(); daughter!=part->end(); ++daughter){
      std::unique_ptr<reco::GenParticle> ptr( new reco::GenParticle( daughter->threeCharge(), daughter->p4(), daughter->vertex(), daughter->pdgId(), daughter->status(), false) );
      target.push_back( *ptr );
      // increment & push index of daughter
      daughters.push_back( ++idx );
      // continue recursively if desired
      if(recursive){
    addDaughters(idx,daughter,target);
      }
  }
  if(!daughters.empty()) {
    refs_[ idxBuffer ] = daughters;
  }
}

void
TopDecaySubset::clearReferences()
{
  // clear vector of references
  refs_.clear();
  // set idx for mother particles to a start value
  // of -1 (the first entry will raise it to 0)
  motherPartIdx_=-1;
}

void
TopDecaySubset::fillReferences(const reco::GenParticleRefProd& ref, reco::GenParticleCollection& sel)
{
  int idx=0;
  for(reco::GenParticleCollection::iterator p=sel.begin(); p!=sel.end(); ++p, ++idx){
    //find daughter reference vectors in refs_ and add daughters
    std::map<int, std::vector<int> >::const_iterator daughters=refs_.find( idx );
    if( daughters!=refs_.end() ){
      for(std::vector<int>::const_iterator daughter = daughters->second.begin();
      daughter!=daughters->second.end(); ++daughter){
    reco::GenParticle* part = dynamic_cast<reco::GenParticle* > (&(*p));
    if(part == nullptr){
     throw edm::Exception( edm::errors::InvalidReference, "Not a GenParticle" );
    }
    part->addDaughter( reco::GenParticleRef(ref, *daughter) );
    sel[*daughter].addMother( reco::GenParticleRef(ref, idx) );
      }
    }
  }
}