/afs/cern.ch/work/a/aaltunda/public/www/CMSSW_6_2_5/src/CommonTools/CandAlgos/plugins/ParticleDecayProducer.cc

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// user include files
#include "FWCore/Framework/interface/Frameworkfwd.h"
#include "FWCore/Framework/interface/EDProducer.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/Utilities/interface/InputTag.h"
#include <vector>

class ParticleDecayProducer : public edm::EDProducer {
 public:
  explicit ParticleDecayProducer(const edm::ParameterSet&);
  ~ParticleDecayProducer();

 private:
  virtual void produce(edm::Event&, const edm::EventSetup&);
  edm::InputTag genCandidates_;
  int motherPdgId_;
  std::vector<int> daughtersPdgId_;
  std::string decayChain_;
  std::vector<std::string> valias;
};

// Candidate handling
#include "DataFormats/Candidate/interface/Candidate.h"
#include "DataFormats/Candidate/interface/CandMatchMap.h"
#include "DataFormats/Common/interface/AssociationVector.h"
#include "CommonTools/Utils/interface/PtComparator.h"
#include "FWCore/Framework/interface/Event.h"
#include <sstream>
using namespace edm;
using namespace std;
using namespace reco;

// constructors
ParticleDecayProducer::ParticleDecayProducer(const edm::ParameterSet& iConfig) :
  genCandidates_(iConfig.getParameter<InputTag>("src")),
  motherPdgId_(iConfig.getParameter<int>("motherPdgId")),
  daughtersPdgId_(iConfig.getParameter<vector<int> >("daughtersPdgId")),
  decayChain_(iConfig.getParameter<std::string>("decayChain")) {
  string alias;
  produces<CandidateCollection >(alias = decayChain_+ "Mother").setBranchAlias(alias);
  for (unsigned int j = 0; j < daughtersPdgId_.size(); ++ j) {
    ostringstream index,collection;
    index << j;
    collection << decayChain_ << "Lepton" << index.str();
    valias.push_back(collection.str());
    produces<CandidateCollection >(valias.at(j)).setBranchAlias( valias.at(j) );
  }
}

// destructor
ParticleDecayProducer::~ParticleDecayProducer() {
}

void ParticleDecayProducer::produce(edm::Event& iEvent, const edm::EventSetup& iSetup) {
  // get gen particle candidates
  edm::Handle<CandidateCollection> genCandidatesCollection;
  iEvent.getByLabel(genCandidates_, genCandidatesCollection);

  auto_ptr<CandidateCollection> mothercands(new CandidateCollection);
  auto_ptr<CandidateCollection> daughterscands(new CandidateCollection);
  size_t daughtersize = daughtersPdgId_.size();
  for( CandidateCollection::const_iterator p = genCandidatesCollection->begin();p != genCandidatesCollection->end(); ++ p ) {
    if (p->pdgId() == motherPdgId_  && p->status() == 3){
      mothercands->push_back(p->clone());
      size_t ndau = p->numberOfDaughters();
      for(size_t i = 0; i < ndau; ++ i){
        for (size_t j = 0; j < daughtersize; ++j){
          if (p->daughter(i)->pdgId()==daughtersPdgId_[j] && p->daughter(i)->status()==3){
            daughterscands->push_back(p->daughter(i)->clone());
          }
        }
      }      
    }
  }

  iEvent.put(mothercands, decayChain_ + "Mother");
  daughterscands->sort(GreaterByPt<reco::Candidate>());
  
  for (unsigned int row = 0; row < daughtersize; ++ row ){
    auto_ptr<CandidateCollection> leptonscands_(new CandidateCollection);
    leptonscands_->push_back((daughterscands->begin()+row)->clone());
    iEvent.put(leptonscands_, valias.at(row));
  }
}

#include "FWCore/Framework/interface/MakerMacros.h"

DEFINE_FWK_MODULE( ParticleDecayProducer );