/data/refman/pasoursint/CMSSW_5_3_3/src/TauAnalysis/MCEmbeddingTools/src/ParticleReplacerClass.cc

Go to the documentation of this file.

#include "TauAnalysis/MCEmbeddingTools/interface/ParticleReplacerClass.h"

#include "GeneratorInterface/ExternalDecays/interface/DecayRandomEngine.h"
#include "FWCore/Utilities/interface/RandomNumberGenerator.h"
#include "FWCore/Utilities/interface/Exception.h"

#include "HepMC/IO_HEPEVT.h"

#ifndef TXGIVE
#define TXGIVE txgive_
extern "C" {
  void TXGIVE(const char*,int length);
}
#endif

#ifndef TXGIVE_INIT
#define TXGIVE_INIT txgive_init_
extern "C" {
  void TXGIVE_INIT();
}
#endif

ParticleReplacerClass::ParticleReplacerClass(const edm::ParameterSet& pset, bool verbose):
  ParticleReplacerBase(pset),
  generatorMode_(pset.getParameter<std::string>("generatorMode")),
  tauola_(pset.getParameter< edm::ParameterSet>("TauolaOptions")),
  //tauola_(gen::TauolaInterface::getInstance()),
  printEvent_(verbose),
  outTree(0),
  maxNumberOfAttempts_(pset.getUntrackedParameter<int>("maxNumberOfAttempts", 1000))
{
//      tauola_->setPSet(pset.getParameter< edm::ParameterSet>("TauolaOptions"));
//      using namespace reco;
        using namespace edm;
        using namespace std;

        //HepMC::HEPEVT_Wrapper::set_max_number_entries(4000);
        //HepMC::HEPEVT_Wrapper::set_sizeof_real(8);

        // transformationMode =
        //  0 - no transformation
        //  1 - mumu -> tautau
        transformationMode_ = pset.getUntrackedParameter<int>("transformationMode",1);
        switch (transformationMode_)
        {
                case 0:
                {       
                        LogInfo("Replacer") << "won't do any transformation with the given mumu";
                        break;
                }
                case 1:
                {
                        LogInfo("Replacer") << "will transform mumu into tautau";
                        break;
                }
                case 2:
    {
      LogInfo("Replacer") << "will transform mumu into taunu (as coming from a W boson)";
      break;
    }    
                case 3:
                {
                        LogInfo("Replacer") << "Will transform  mu-nu into tau-nu. No mass correction will be made.";
                        break;
                }
                default:
                {
                        throw cms::Exception("ParticleReplacerClass")  << "Unknown transformation mode!\n";
                        break;
                }
            
        }
        
        // If one wants to use two instances of this module in one
        // configuration file, there might occur some segmentation
        // faults due to the second initialisation of Tauola. This
        // can be prevented by setting noInitialisation to false.
        //          Caution: This option is not tested!
        noInitialisation_ = pset.getUntrackedParameter<bool>("noInitialisation",false);

        motherParticleID_ = pset.getUntrackedParameter<int>("motherParticleID",23);

        // requires the visible decay products of a tau to have a sum transverse momentum
        std::string minVisibleTransverseMomentumLine = pset.getUntrackedParameter<std::string>("minVisibleTransverseMomentum","");

  // fallback for backwards compatibility: If it's a single number then use this as a threshold for both particles
  const char* startptr = minVisibleTransverseMomentumLine.c_str();
  char* endptr;
  double d = strtod(startptr, &endptr);
  if(*endptr == '\0' && endptr != startptr)
  {
                MinVisPtCut cuts[2];
                cuts[0].type_ = cuts[1].type_ = MinVisPtCut::TAU;
    cuts[0].pt_ = cuts[1].pt_ = d;
                cuts[0].index_ = 0; cuts[1].index_ = 1;
                minVisPtCuts_.push_back(std::vector<MinVisPtCut>(cuts, cuts+2));
  }
  else
  {
          // string has new format: parse the minvistransversemomentum string
                for(std::string::size_type prev = 0, pos = 0; prev < minVisibleTransverseMomentumLine.length(); prev = pos + 1)
                {
                        pos = minVisibleTransverseMomentumLine.find(';', prev);
                        if(pos == std::string::npos) pos = minVisibleTransverseMomentumLine.length();

                        std::string sub = minVisibleTransverseMomentumLine.substr(prev, pos - prev);
                        std::vector<MinVisPtCut> cuts;
                        const char* sub_c = sub.c_str();
                        while(*sub_c != '\0')
                        {
                                const char* sep = std::strchr(sub_c, '_');
                                if(sep == NULL) throw cms::Exception("Configuration") << "Minimum transverse parameter string must contain an underscore to separate type from pt threshold" << std::endl;
                                std::string type(sub_c, sep);

                                MinVisPtCut cut;
                                if(type == "elec1") { cut.type_ = MinVisPtCut::ELEC; cut.index_ = 0; }
                                else if(type == "mu1") { cut.type_ = MinVisPtCut::MU; cut.index_ = 0; }
                                else if(type == "had1") { cut.type_ = MinVisPtCut::HAD; cut.index_ = 0; }
                                else if(type == "tau1") { cut.type_ = MinVisPtCut::TAU; cut.index_ = 0; }
                                else if(type == "elec2") { cut.type_ = MinVisPtCut::ELEC; cut.index_ = 1; }
                                else if(type == "mu2") { cut.type_ = MinVisPtCut::MU; cut.index_ = 1; }
                                else if(type == "had2") { cut.type_ = MinVisPtCut::HAD; cut.index_ = 1; }
                                else if(type == "tau2") { cut.type_ = MinVisPtCut::TAU; cut.index_ = 1; }
                                else throw cms::Exception("Configuration") << "'" << type << "' is not a valid type. Allowed values are elec1,mu1,had1,tau1,elec2,mu2,had2,tau2" << std::endl;

                                char* endptr;
                                cut.pt_ = strtod(sep + 1, &endptr);
                                if(endptr == sep + 1) throw cms::Exception("Configuration") << "No pt threshold given" << std::endl;

                                cuts.push_back(cut);
                                sub_c = endptr;
                        }
                minVisPtCuts_.push_back(cuts);
                }
  }

        edm::Service<TFileService> fileService_;
        if(fileService_.isAvailable()) {
          outTree = fileService_->make<TTree>( "event_generation","This tree stores information about the event generation");
          outTree->Branch("attempts",&attempts,"attempts/I");
        }

        edm::Service<RandomNumberGenerator> rng;
        if(!rng.isAvailable()) {
          throw cms::Exception("Configuration")
            << "The RandomNumberProducer module requires the RandomNumberGeneratorService\n"
            "which appears to be absent.  Please add that service to your configuration\n"
            "or remove the modules that require it." << std::endl;
        } 
        // this is a global variable defined in GeneratorInterface/ExternalDecays/src/ExternalDecayDriver.cc
        decayRandomEngine = &rng->getEngine();

        edm::LogInfo("Replacer") << "generatorMode = "<< generatorMode_<< "\n";
        edm::LogInfo("Replacer") << "replacementMode = "<< replacementMode_<< "\n";

        return;
}

ParticleReplacerClass::~ParticleReplacerClass()
{
        // do anything here that needs to be done at desctruction time
        // (e.g. close files, deallocate resources etc.)
}

// ------------ method called to produce the data  ------------
std::auto_ptr<HepMC::GenEvent> ParticleReplacerClass::produce(const reco::MuonCollection& muons, const reco::Vertex *pvtx, const HepMC::GenEvent *genEvt)
{
        using namespace edm;
        using namespace std;
        using namespace HepMC;

        if(pvtx != 0)
          throw cms::Exception("Configuration") << "ParticleReplacerClass does NOT support using primary vertex as the origin for taus" << std::endl;

        HepMC::GenEvent * evt=0;

        GenVertex * zvtx = new GenVertex();

        reco::GenParticle * part1=0;
        reco::GenParticle * part2=0;

        std::vector<reco::Particle> particles;  
        switch (transformationMode_)
        {
                case 0: // mumu->mumu
                {
                        if (muons.size()!=2)
                        {
                                LogError("Replacer") << "the decay mode Z->mumu requires exactly two muons, aborting processing";
                                return std::auto_ptr<HepMC::GenEvent>(0);
                        }
        
                        targetParticleMass_  = 0.105658369;
                        targetParticlePdgID_ = 13;
                                
                        reco::Muon muon1 = muons.at(0);
                        reco::Muon muon2 = muons.at(1);
                        reco::Particle tau1(muon1.charge(), muon1.p4(), muon1.vertex(), muon1.pdgId(), 0, true);
                        reco::Particle tau2(muon2.charge(), muon2.p4(), muon2.vertex(), muon2.pdgId(), 0, true);
                        particles.push_back(tau1);
                        particles.push_back(tau2);
                        break;
                } 
                case 1: // mumu->tautau
                {
                        if (muons.size()!=2)
                        {
                                LogError("Replacer") << "the decay mode Z->tautau requires exactly two muons, aborting processing";
                                return std::auto_ptr<HepMC::GenEvent>(0);
                        }

                        targetParticleMass_  = 1.77690;
                        targetParticlePdgID_ = 15;
                        
                        reco::Muon muon1 = muons.at(0);
                        reco::Muon muon2 = muons.at(1);
                        reco::Particle tau1(muon1.charge(), muon1.p4(), muon1.vertex(), muon1.pdgId(), 0, true);
                        reco::Particle tau2(muon2.charge(), muon2.p4(), muon2.vertex(), muon2.pdgId(), 0, true);
                        transformMuMu2TauTau(&tau1, &tau2);
                        particles.push_back(tau1);
                        particles.push_back(tau2);                      
                        break;
                }
    case 2: // mumu->taunu (W boson)
    {
      if (muons.size()!=2)
      {
        LogError("Replacer") << "the decay mode Z->tautau requires exactly two muons, aborting processing";
        return std::auto_ptr<HepMC::GenEvent>(0);
      }

      targetParticleMass_  = 1.77690;
      targetParticlePdgID_ = 15;
      
      reco::Muon muon1 = muons.at(0);
      reco::Muon muon2 = muons.at(1);
      reco::Particle tau1(muon1.charge(), muon1.p4(), muon1.vertex(), muon1.pdgId(), 0, true);
      reco::Particle tau2(muon2.charge(), muon2.p4(), muon2.vertex(), muon2.pdgId(), 0, true);
      transformMuMu2TauNu(&tau1, &tau2);
      particles.push_back(tau1);
      particles.push_back(tau2);                      
      break;
    }  
    case 3: // mu-nu->tau-nu
    {
      if (muons.size()!=2)
      {
        LogError("Replacer") << "transformation mode mu-nu ->tau-nu - wrong input";
        return std::auto_ptr<HepMC::GenEvent>(0);
      }

      targetParticleMass_  = 1.77690;
      targetParticlePdgID_ = 15;
      int targetParticlePdgIDNu_ = 16;
      
      reco::Muon muon1 = muons.at(0);
      reco::Muon::LorentzVector l(muon1.px(), muon1.py(), muon1.pz(), 
                                sqrt(
                                muon1.px()*muon1.px()+
                                muon1.py()*muon1.py()+
                                muon1.pz()*muon1.pz()+targetParticleMass_*targetParticleMass_));

      reco::Particle tau1(muon1.charge(), l, muon1.vertex(), targetParticlePdgID_*std::abs(muon1.pdgId())/muon1.pdgId() 
                                , 0, true
                         );
      tau1.setStatus(1);
      particles.push_back(tau1);

      reco::Muon nu    = muons.at(1);
      reco::Particle nutau( 0, nu.p4(), nu.vertex(), -targetParticlePdgIDNu_*std::abs(muon1.pdgId())/muon1.pdgId(), 0, true);
      nutau.setStatus(1);
      particles.push_back(nutau);
 
      break;
    }  

        }
        
        if (particles.size()==0)
        {
                LogError("Replacer") << "the creation of the new particles failed somehow";     
                return std::auto_ptr<HepMC::GenEvent>(0);
        }
        else
        {
                LogInfo("Replacer") << particles.size() << " particles found, continue processing";
        }

        if (genEvt)
        {
        
                        evt = new HepMC::GenEvent(*genEvt);
        
                        for ( GenEvent::vertex_iterator p = evt->vertices_begin(); p != evt->vertices_end(); p++ ) 
                        {
                                GenVertex * vtx=(*p);
                                
                                if ( vtx->particles_out_size()<=0 || vtx->particles_in_size()<=0)
                                        continue;
                                
                                bool temp_muon1=false,temp_muon2=false,temp_z=false;
                                for (GenVertex::particles_out_const_iterator it = vtx->particles_out_const_begin(); it!=vtx->particles_out_const_end(); it++)
                                {
                                        if ((*it)->pdg_id()==13) temp_muon1=true;
                                        if ((*it)->pdg_id()==-13) temp_muon2=true;
                                        if ((*it)->pdg_id()==23) temp_z=true;
                                }
        
                                int mother_pdg=(*vtx->particles_in_const_begin())->pdg_id();
        
                                if ((vtx->particles_out_size()==2 && vtx->particles_in_size()>0 
                                        && mother_pdg == 23  
                                        && temp_muon1
                                        && temp_muon2)
                                || (vtx->particles_out_size()>2 && vtx->particles_in_size()>0 
                                        && mother_pdg == 23
                                        && temp_muon1 && temp_muon2 && temp_z ))
                                {
                                        zvtx=*p;
                                }
                        }

                        cleanEvent(evt, zvtx);

                        // prevent a decay of existing particles
                        // this is due to a bug in the PythiaInterface that should be fixed in newer versions
                        for (GenEvent::particle_iterator it=evt->particles_begin();it!=evt->particles_end();it++)
                                (*it)->set_status(0);

                        for (std::vector<reco::Particle>::const_iterator it=particles.begin();it!=particles.end();it++)
                        {
                                zvtx->add_particle_out(new HepMC::GenParticle((FourVector)it->p4(), it->pdgId(), 1, Flow(), Polarization(0,0)));
                        }
        }
        // new product with tau decays
        else
        {
                reco::Particle::LorentzVector mother_particle_p4;
                for (std::vector<reco::Particle>::const_iterator it=particles.begin();it!=particles.end();it++)
                        mother_particle_p4+=it->p4();

                reco::Particle::Point production_point = particles.begin()->vertex();

                GenVertex* startVtx = new GenVertex(FourVector(production_point.x()*10,production_point.y()*10,production_point.z()*10,0));
                startVtx->add_particle_in( new GenParticle( FourVector(0,0,7000,7000), 2212, 3 ) );
                startVtx->add_particle_in( new GenParticle( FourVector(0,0,-7000,7000), 2212, 3 ) );

                GenVertex * decayvtx = new GenVertex(FourVector(production_point.x()*10,production_point.y()*10,production_point.z()*10,0));
                HepMC::GenParticle * mother_particle = new HepMC::GenParticle((FourVector)mother_particle_p4, motherParticleID_, (generatorMode_=="Pythia" ? 3 : 2), Flow(), Polarization(0,0));
                if (transformationMode_ == 3) {
                  //std::cout << "Overriding mother particle id\n" << std::endl;
                  int muPDG = particles.begin()->pdgId();
                  int id = -24*muPDG/std::abs(muPDG);
                  mother_particle->set_pdg_id(id);
                }

                startVtx->add_particle_out(mother_particle);
                decayvtx->add_particle_in(mother_particle);
                evt = new HepMC::GenEvent();
                for (std::vector<reco::Particle>::const_iterator it=particles.begin();it!=particles.end();it++)
                {
                        //std::cout << "XXX" << it->p4().pt() << " " << it->pdgId() << std::endl;
                        decayvtx->add_particle_out(new HepMC::GenParticle((FourVector)it->p4(), it->pdgId(), 1, Flow(), Polarization(0,0)));                    
                }

                evt->add_vertex(startVtx);
                evt->add_vertex(decayvtx);
        }
        repairBarcodes(evt);
        
        HepMC::GenEvent * retevt = 0;
        HepMC::GenEvent * tempevt = 0;

        int nr_of_trials=0;

        unsigned int cntVisPt_all = 0;
        unsigned int cntVisPt_pass = 0;
        
        HepMC::IO_HEPEVT conv;
        for (int i = 0; i<maxNumberOfAttempts_; i++)
        {
                ++cntVisPt_all;
                if (generatorMode_ == "Pythia") // Pythia
                {
                        LogError("Replacer") << "Pythia is currently not supported!";
                        return std::auto_ptr<HepMC::GenEvent>(evt);
                }

                if (generatorMode_ == "Tauola") // TAUOLA
                {
                        conv.write_event(evt);
                        tempevt=tauola_.decay(evt);
                }

                if (testEvent(tempevt))
                {
                        if (retevt==0) {
                          retevt=tempevt;
                        } else {
                          delete tempevt; 
                        }
                        ++cntVisPt_pass;
                } else {
                  delete tempevt;
                }
        }
        eventWeight = (double)cntVisPt_pass / (double)cntVisPt_all;
        std::cout << /*minVisibleTransverseMomentum_ <<*/ " " << cntVisPt_pass << "\t" << cntVisPt_all << "\n";
        if (!retevt)
        {
                LogError("Replacer") << "failed to create an event which satisfies the minimum visible transverse momentum cuts ";
                attempts=-1;
                eventWeight=0;
                if(outTree) outTree->Fill();
                return std::auto_ptr<HepMC::GenEvent>(0);
        }
        attempts=nr_of_trials;
        if(outTree) outTree->Fill();    

        // recover the status codes
        if (replacementMode_==0)
        {
                for (GenEvent::particle_iterator it=retevt->particles_begin();it!=retevt->particles_end();it++)
                {
                        if ((*it)->end_vertex())
                                (*it)->set_status(2);
                        else
                                (*it)->set_status(1);
                }
        }

        std::auto_ptr<HepMC::GenEvent> ret(retevt);

        if (printEvent_)
                retevt->print(std::cout);

        delete part1;
        delete part2;
        delete zvtx;
        delete evt;
        return ret;
}

// ------------ method called once each job just before starting event loop  ------------
void ParticleReplacerClass::beginRun(edm::Run& iRun,const edm::EventSetup& iSetup)
{
        tauola_.init(iSetup);
}

// ------------ method called once each job just after ending the event loop  ------------
void 
ParticleReplacerClass::endJob()
{
        tauola_.statistics();
}

bool ParticleReplacerClass::testEvent(HepMC::GenEvent * evt)
{
        using namespace HepMC;
        using namespace edm;
        
        if (minVisPtCuts_.empty()) //ibleTransverseMomentum_<=0)
                return true;

  std::vector<double> mus;
  std::vector<double> elecs;
  std::vector<double> hads;
  std::vector<double> taus;

  for (GenEvent::particle_iterator it=evt->particles_begin();it!=evt->particles_end();it++)
        {
                if (abs((*it)->pdg_id())==15 && (*it)->end_vertex())
    {
        FourVector vis_mom();
        math::PtEtaPhiMLorentzVector visible_momentum;
        std::queue<const GenParticle *> decaying_particles;
                        decaying_particles.push(*it);
                        int t=0;
      enum { ELEC, MU, HAD } type = HAD;
                        while(!decaying_particles.empty() && (++t < 30))
                        {
                                const GenParticle * front = decaying_particles.front();
                decaying_particles.pop();

                                if (!front->end_vertex())
                                {
                                        int pdgId=abs(front->pdg_id());
                                        if (pdgId>10 && pdgId!=12 && pdgId!=14 && pdgId!=16)
                                                visible_momentum+=(math::PtEtaPhiMLorentzVector)front->momentum();

          if(pdgId == 11) type = ELEC;
          if(pdgId == 13) type = MU;
                                }
                                else
                                {
                                        GenVertex * temp_vert = front->end_vertex();
                                        for (GenVertex::particles_out_const_iterator it2=temp_vert->particles_out_const_begin();it2!=temp_vert->particles_out_const_end();it2++)
                                                decaying_particles.push((*it2));
                                }
        }

      double vis_pt = visible_momentum.pt();
      taus.push_back(vis_pt);
      if(type == MU) mus.push_back(vis_pt);
      if(type == ELEC) elecs.push_back(vis_pt);
      if(type == HAD) hads.push_back(vis_pt);
                }
        }

  std::sort(taus.begin(), taus.end(), std::greater<double>());
  std::sort(elecs.begin(), elecs.end(), std::greater<double>());
  std::sort(mus.begin(), mus.end(), std::greater<double>());
  std::sort(hads.begin(), hads.end(), std::greater<double>());

  for(std::vector<std::vector<MinVisPtCut> >::const_iterator iter = minVisPtCuts_.begin(); iter != minVisPtCuts_.end(); ++iter)
  {
    std::vector<MinVisPtCut>::const_iterator iter2;
    for(iter2 = iter->begin(); iter2 != iter->end(); ++iter2)
    {
      std::vector<double>* collection;
      switch(iter2->type_)
      {
      case MinVisPtCut::ELEC: collection = &elecs; break;
      case MinVisPtCut::MU: collection = &mus; break;
      case MinVisPtCut::HAD: collection = &hads; break;
      case MinVisPtCut::TAU: collection = &taus; break;
      default: assert(false); break;
      }

      // subcut fail
      if(iter2->index_ >= collection->size() || (*collection)[iter2->index_] < iter2->pt_)
        break;
    }

    // no subcut failed: This cut passed
    if(iter2 == iter->end())
      return true;
  }

  LogInfo("Replacer") << "refusing the event as the sum of the visible transverse momenta is too small\n";
        return false;
}

void ParticleReplacerClass::cleanEvent(HepMC::GenEvent * evt, HepMC::GenVertex * vtx)
{
        using namespace HepMC;
        using namespace std;
        using namespace edm;
        using namespace reco;

        stack<HepMC::GenParticle *> deleteParticle;
        
        stack<GenVertex *> deleteVertex;
        stack<GenVertex *> queueVertex;

        if (vtx->particles_out_size()>0)
        {
                for (GenVertex::particles_out_const_iterator it=vtx->particles_out_const_begin();it!=vtx->particles_out_const_end();it++)
                {
                        deleteParticle.push(*it);
                        if ((*it)->end_vertex())
                                queueVertex.push((*it)->end_vertex());
                }
        }

        while (!queueVertex.empty())
        {
                GenVertex * temp_vtx=queueVertex.top();
                if (temp_vtx->particles_out_size()>0)
                {
                        for (GenVertex::particles_out_const_iterator it=temp_vtx->particles_out_const_begin();it!=temp_vtx->particles_out_const_end();it++)
                        {
                                if ((*it)->end_vertex())
                                        queueVertex.push((*it)->end_vertex());
                        }
                        delete temp_vtx;
                }
                deleteVertex.push(queueVertex.top());
                queueVertex.pop();
        }
        
        while (!deleteVertex.empty())
        {
                evt->remove_vertex(deleteVertex.top());
                deleteVertex.pop();
        }

        while (!deleteParticle.empty())
        {
                delete vtx->remove_particle(deleteParticle.top());
                deleteParticle.pop();
        }

        while (!deleteVertex.empty())
                deleteVertex.pop();
        while (!queueVertex.empty())
                queueVertex.pop();

        repairBarcodes(evt);
}

void ParticleReplacerClass::repairBarcodes(HepMC::GenEvent * evt)
{
        using namespace HepMC;

        // repair the barcodes
        int max_barc=0;
        for (GenEvent::vertex_iterator it=evt->vertices_begin();it!=evt->vertices_end();it++)
                while (!(*it)->suggest_barcode(-1*(++max_barc)))
                        ;

        max_barc=0;
        for (GenEvent::particle_iterator it=evt->particles_begin();it!=evt->particles_end();it++)
                while (!(*it)->suggest_barcode(++max_barc))
                        ;
}

void ParticleReplacerClass::transformMuMu2TauTau(reco::Particle * muon1, reco::Particle * muon2)
{
        using namespace edm;
        using namespace reco;
        using namespace std;
        
        reco::Particle::LorentzVector muon1_momentum = muon1->p4();
        reco::Particle::LorentzVector muon2_momentum =  muon2->p4();
        reco::Particle::LorentzVector z_momentum = muon1_momentum + muon2_momentum;

        ROOT::Math::Boost booster(z_momentum.BoostToCM());
        ROOT::Math::Boost invbooster(booster.Inverse());
        
        reco::Particle::LorentzVector Zb = booster(z_momentum);

        reco::Particle::LorentzVector muon1b = booster(muon1_momentum);
        reco::Particle::LorentzVector muon2b = booster(muon2_momentum);
        
        double tau_mass2 = targetParticleMass_*targetParticleMass_;

        double muonxb_mom2 = muon1b.x()*muon1b.x() + muon1b.y()*muon1b.y() + muon1b.z() * muon1b.z();
        double tauxb_mom2 = 0.25 * Zb.t() * Zb.t() - tau_mass2;

        float scaling1 = sqrt(tauxb_mom2 / muonxb_mom2);
        float scaling2 = scaling1;

        float tauEnergy= Zb.t() / 2.;

        if (tauEnergy*tauEnergy<tau_mass2)
                return;
        
        reco::Particle::LorentzVector tau1b_mom = reco::Particle::LorentzVector(scaling1*muon1b.x(),scaling1*muon1b.y(),scaling1*muon1b.z(),tauEnergy);
        reco::Particle::LorentzVector tau2b_mom = reco::Particle::LorentzVector(scaling2*muon2b.x(),scaling2*muon2b.y(),scaling2*muon2b.z(),tauEnergy);

        reco::Particle::LorentzVector tau1_mom = (invbooster(tau1b_mom));
        reco::Particle::LorentzVector tau2_mom = (invbooster(tau2b_mom));
        
        // some additional checks
        // the following tests guarantee a deviation of less
        // than 0.1% for the following values of the original
        // muons and the placed taus
        //      invariant mass
        //      transverse momentum
        assert(std::abs((muon1_momentum+muon2_momentum).mass()-(tau1_mom+tau2_mom).mass())/(muon1_momentum+muon2_momentum).mass()<0.001);
        assert(std::abs((muon1_momentum+muon2_momentum).pt()-(tau1_mom+tau2_mom).pt())/(muon1_momentum+muon2_momentum).pt()<0.001);

        muon1->setP4(tau1_mom);
        muon2->setP4(tau2_mom);

        muon1->setPdgId(targetParticlePdgID_*muon1->pdgId()/abs(muon1->pdgId()));
        muon2->setPdgId(targetParticlePdgID_*muon2->pdgId()/abs(muon2->pdgId()));

        muon1->setStatus(1);
        muon2->setStatus(1);

        return;
}
void ParticleReplacerClass::transformMuMu2TauNu(reco::Particle * part1, reco::Particle * part2)
{
        using namespace edm;
        using namespace reco;
        using namespace std;

        reco::Particle::LorentzVector muon1_momentum = part1->p4();
        reco::Particle::LorentzVector muon2_momentum =  part2->p4();
        reco::Particle::LorentzVector z_momentum = muon1_momentum + muon2_momentum;

        ROOT::Math::Boost booster(z_momentum.BoostToCM());
        ROOT::Math::Boost invbooster(booster.Inverse());

        reco::Particle::LorentzVector Zb = booster(z_momentum);

        const double breitWignerWidth_Z = 2.4952;
        const double breitWignerWidth_W = 2.141;
        const double knownMass_W = 80.398;
        const double knownMass_Z = 91.1876;
                      
        double Wb_mass = ( Zb.mass() - knownMass_Z ) * ( breitWignerWidth_W / breitWignerWidth_Z ) + knownMass_W;
        std::cout << "Wb_mass: " << Wb_mass << "\n";

        reco::Particle::LorentzVector muon1b = booster(muon1_momentum);
        reco::Particle::LorentzVector muon2b = booster(muon2_momentum);

        double tau_mass2 = targetParticleMass_*targetParticleMass_;

        double muonxb_mom2 = muon1b.x()*muon1b.x() + muon1b.y()*muon1b.y() + muon1b.z() * muon1b.z();
        double tauxb_mom2 = 0.25 * Zb.t() * Zb.t() - tau_mass2;

        float scaling1 = sqrt(tauxb_mom2 / muonxb_mom2) * Wb_mass/Zb.mass();
        float scaling2 = scaling1;

        float tauEnergy= Zb.t() / 2.;

        if (tauEnergy*tauEnergy<tau_mass2)
                      return;

        reco::Particle::LorentzVector tau1b_mom = reco::Particle::LorentzVector(scaling1*muon1b.x(),scaling1*muon1b.y(),scaling1*muon1b.z(),tauEnergy* Wb_mass/Zb.mass());
        reco::Particle::LorentzVector tau2b_mom = reco::Particle::LorentzVector(scaling2*muon2b.x(),scaling2*muon2b.y(),scaling2*muon2b.z(),tauEnergy* Wb_mass/Zb.mass());

        std::cout << "muon1b_momentum: " << muon1b << "\n";
        std::cout << "muon2b_momentum: " << muon2b << "\n";

        std::cout << "tau1b_momentum: " << tau1b_mom << "\n";
        std::cout << "tau2b_momentum: " << tau2b_mom << "\n";

        std::cout << "zb_momentum: " << Zb << "\n";
        std::cout << "wb_momentum: " << (tau1b_mom+tau2b_mom) << "\n";
                              
        // some checks
        // the following test guarantees a deviation
        // of less than 0.1% for phi and theta for the
        // original muons and the placed taus
        // (in the centre-of-mass system of the z boson)
        assert((muon1b.phi()-tau1b_mom.phi())/muon1b.phi()<0.001);
        assert((muon2b.phi()-tau2b_mom.phi())/muon2b.phi()<0.001);
        assert((muon1b.theta()-tau1b_mom.theta())/muon1b.theta()<0.001);
        assert((muon2b.theta()-tau2b_mom.theta())/muon2b.theta()<0.001);        

        reco::Particle::LorentzVector tau1_mom = (invbooster(tau1b_mom));
        reco::Particle::LorentzVector tau2_mom = (invbooster(tau2b_mom));

        // some additional checks
        // the following tests guarantee a deviation of less
        // than 0.1% for the following values of the original
        // muons and the placed taus
        //      invariant mass
        //      transverse momentum
        //assert(((muon1_momentum+muon1_momentum).mass()-(tau1_mom+tau2_mom).mass())/(muon1_momentum+muon1_momentum).mass()<0.001);
        //assert(((muon1_momentum+muon2_momentum).pt()-(tau1_mom+tau2_mom).pt())/(muon1_momentum+muon1_momentum).pt()<0.001);

        part1->setP4(tau1_mom);
        part2->setP4(tau2_mom);

        part1->setPdgId(15*part1->pdgId()/abs(part1->pdgId()));
        part2->setPdgId(16*part2->pdgId()/abs(part2->pdgId()));

        part1->setStatus(1);
        part2->setStatus(1);

        return;
}


//define this as a plug-in
//DEFINE_FWK_MODULE(Replacer);