HepMCValidationHelper.cc

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#include "Validation/EventGenerator/interface/HepMCValidationHelper.h"
#include "DataFormats/Math/interface/deltaR.h"
#include <iostream>
#include <cassert>
#include <limits>
#include "TLorentzVector.h"

//#define DEBUG_HepMCValidationHelper

namespace HepMCValidationHelper {
  void findFSRPhotons(const std::vector<const HepMC::GenParticle*>& leptons, 
                      const HepMC::GenEvent* all,
                      double deltaRcut,
                      std::vector<const HepMC::GenParticle*>& fsrphotons){

    std::vector<const HepMC::GenParticle*> status1;
    allStatus1(all, status1);
    findFSRPhotons(leptons, status1, deltaRcut, fsrphotons);
  }
  
  void findFSRPhotons(const std::vector<const HepMC::GenParticle*>& leptons,
                      const std::vector<const HepMC::GenParticle*>& all,
                      double deltaRcut,
                      std::vector<const HepMC::GenParticle*>& fsrphotons){
                        
    //find all status 1 photons
    std::vector<const HepMC::GenParticle*> allphotons;
    for (unsigned int i = 0; i < all.size(); ++i){
      if  (all[i]->status()==1 && all[i]->pdg_id()==22) allphotons.push_back(all[i]);
    }

    //loop over the photons and check the distance wrt the leptons
    for (unsigned int ipho = 0; ipho < allphotons.size(); ++ipho){
      bool close = false;
      for (unsigned int ilep = 0; ilep < leptons.size(); ++ilep){
        if (deltaR(allphotons[ipho]->momentum(), leptons[ilep]->momentum()) < deltaRcut){
          close = true;
          break;
        }  
      }
      if (close) fsrphotons.push_back(allphotons[ipho]);
    }
  }

  //returns true if a status 3 particle is a tau or if a status 1 particle is either an electron or a neutrino
  bool isChargedLepton(const HepMC::GenParticle* part){
    int status = part->status();
    unsigned int pdg_id = abs(part->pdg_id());
    if (status == 2) return pdg_id == 15;
    else return status == 1 &&  (pdg_id == 11 || pdg_id == 13 ) ;
  }

  //returns true if a status 1 particle is a neutrino
  bool isNeutrino(const HepMC::GenParticle* part ) {
      int status = part->status();
      unsigned int pdg_id = abs(part->pdg_id());
      return status == 1 &&  (pdg_id == 12 || pdg_id == 14 || pdg_id == 16) ;
  } 

  //returns true is status 3 particle is tau
  bool isTau(const HepMC::GenParticle* part){
    return part->status() == 2 && abs(part->pdg_id()) == 15;
  }
/* 
  void getTaus(const HepMC::GenEvent* all, std::vector<const HepMC::GenParticle*>& taus){
    for (HepMC::GenEvent::particle_const_iterator iter = all->particles_begin(); iter != all->particles_end(); ++iter){
      if (abs((*iter)->pdg_id()) == 15) taus.push_back(*iter);
    }
  }
*/
  // get all status 1 particles
  void allStatus1(const HepMC::GenEvent* all, std::vector<const HepMC::GenParticle*>& status1){
    for (HepMC::GenEvent::particle_const_iterator iter = all->particles_begin(); iter != all->particles_end(); ++iter){
      if ((*iter)->status() == 1) status1.push_back(*iter);
    }
  }

  void allStatus2(const HepMC::GenEvent* all, std::vector<const HepMC::GenParticle*>& status1){
    for (HepMC::GenEvent::particle_const_iterator iter = all->particles_begin(); iter != all->particles_end(); ++iter){
      if ((*iter)->status() == 2) status1.push_back(*iter);
    }
  }

  void allStatus3(const HepMC::GenEvent* all, std::vector<const HepMC::GenParticle*>& status1){
    for (HepMC::GenEvent::particle_const_iterator iter = all->particles_begin(); iter != all->particles_end(); ++iter){
      if ((*iter)->status() == 3) status1.push_back(*iter);
    }
  }

  void findDescendents(const HepMC::GenParticle* a, std::vector<const HepMC::GenParticle*>& descendents){
    HepMC::GenVertex* decayVertex = a->end_vertex();
    if (!decayVertex) return;
    HepMC::GenVertex::particles_out_const_iterator ipart;
    for (ipart = decayVertex->particles_out_const_begin(); ipart != decayVertex->particles_out_const_end(); ++ipart ){
      if ((*ipart)->status() == 1) descendents.push_back(*ipart);
      else findDescendents(*ipart, descendents);
    }
  }

  void removeIsolatedLeptons(const HepMC::GenEvent* all, double deltaRcut, double sumPtCut, std::vector<const HepMC::GenParticle*>& pruned) {
    //get all status 1 particles
    std::vector<const HepMC::GenParticle*> status1;
    allStatus1(all, status1);
    std::vector<const HepMC::GenParticle*> toRemove;
    //loop on all particles and find candidates to be isolated
    for (unsigned int i = 0; i < status1.size(); ++i){
      //if it is a neutrino is a charged lepton (not a tau) this is a candidate to be isolated
      if (isNeutrino(status1[i]) || (isChargedLepton(status1[i]) && !isTau(status1[i]))){
        //list of particles not to be considered in the isolation computation.
        //this includes the particle to be isolated and the fsr photons in case of charged lepton
        std::vector<const HepMC::GenParticle*> leptons;
        leptons.push_back(status1[i]);
        std::vector<const HepMC::GenParticle*> removedForIsolation;
        removedForIsolation.push_back(status1[i]);
        if (isChargedLepton(status1[i])) findFSRPhotons(leptons, status1, deltaRcut, removedForIsolation);
#ifdef  DEBUG_HepMCValidationHelper
        //std::cout << removedForIsolation.size() << " particles to be removed for isolation calculation " << std::endl;
#endif
        //create vector of particles to compute isolation (removing removedForIsolation);
        std::vector<const HepMC::GenParticle*> forIsolation;
        std::vector<const HepMC::GenParticle*>::iterator iiso;
        for (iiso = status1.begin(); iiso != status1.end(); ++iiso){
          std::vector<const HepMC::GenParticle*>::const_iterator iremove;
          bool marked = false;
          for ( iremove = removedForIsolation.begin(); iremove != removedForIsolation.end(); ++iremove){
            if ((*iiso)->barcode() == (*iremove)->barcode()) {
#ifdef  DEBUG_HepMCValidationHelper
              //std::cout << "removing particle " << **iiso << " from the list of particles to compute isolation" << std::endl;
#endif
              marked = true;  
              break;
            }
          }
          if (!marked) forIsolation.push_back(*iiso);
        }
        //now compute isolation
        double sumIso = 0;
        for (iiso = forIsolation.begin(); iiso < forIsolation.end(); ++iiso){
           if (deltaR(leptons.front()->momentum(), (*iiso)->momentum()) < deltaRcut){
              sumIso += (*iiso)->momentum().perp();
           }
        }
        //if isolated remove from the pruned list
        if (sumIso < sumPtCut) {
#ifdef  DEBUG_HepMCValidationHelper
           std::cout << "particle " <<  *status1[i] <<  " is considered isolated, with sumPt " << sumIso << std::endl; 
#endif
           toRemove.insert(toRemove.end(), removedForIsolation.begin(), removedForIsolation.end()); 
        }
#ifdef  DEBUG_HepMCValidationHelper        
        else {
          std::cout << "NOT isolated! " <<  *status1[i] <<  " is considered not isolated, with sumPt " << sumIso << std::endl;
        }
#endif        
      } 
    }
    //at this point we have taken care of the electrons and muons, but pruned could  still contain the decay products of isolated taus, 
    //we want to remove these as well
    std::vector<const HepMC::GenParticle*> status2;
    allStatus2(all, status2);
    std::vector<const HepMC::GenParticle*> taus;
    //getTaus(all, taus);
    for (unsigned int i = 0; i < status2.size(); ++i){
      if (isTau(status2[i])) {
        //check the list we have already for duplicates
        //there use to be duplicates in some generators (sherpa) 
        bool duplicate = false; 
        TLorentzVector taumomentum(status2[i]->momentum().x(), status2[i]->momentum().y(), status2[i]->momentum().z(), status2[i]->momentum().t());
        for (unsigned int j = 0; j < taus.size(); ++j){
          //compare momenta
          TLorentzVector othermomentum(taus[j]->momentum().x(), taus[j]->momentum().y(), taus[j]->momentum().z(), taus[j]->momentum().t());
          othermomentum-=taumomentum;
          if (status2[i]->pdg_id() == taus[j]->pdg_id() &&
              othermomentum.E() < 0.1 &&//std::numeric_limits<float>::epsilon() &&
              othermomentum.P() < 0.1 ){ //std::numeric_limits<float>::epsilon()){
            duplicate = true;
            break;
          }    
        }
        if (!duplicate) taus.push_back(status2[i]);
      }  
    }
    //loop over the taus, find the descendents, remove all these from the list of particles to compute isolation   
    for (unsigned int i = 0; i < taus.size(); ++i){
      std::vector<const HepMC::GenParticle*> taudaughters;
      findDescendents(taus[i], taudaughters);
      assert(taudaughters.size()>0);
      const HepMC::FourVector& taumom = taus[i]->momentum();
      //remove the daughters from the list of particles to compute isolation
      std::vector<const HepMC::GenParticle*> forIsolation;
      std::vector<const HepMC::GenParticle*>::iterator iiso;
      for (iiso = status1.begin(); iiso < status1.end(); ++iiso){
        bool marked = false;
        std::vector<const HepMC::GenParticle*>::const_iterator iremove;
        for ( iremove = taudaughters.begin(); iremove != taudaughters.end(); ++iremove){
          if ((*iiso)->barcode() == (*iremove)->barcode()) {
#ifdef  DEBUG_HepMCValidationHelper
//            std::cout << "removing particle " << **iiso << " from the list of particles to compute isolation because it comes from a tau" << std::endl;
#endif
            marked = true;
            break;
          }
          if (!marked) forIsolation.push_back(*iiso);
        }
      }
      //no compute isolation wrt the status 2 tau direction
      double sumIso = 0;
      for (iiso = forIsolation.begin(); iiso < forIsolation.end(); ++iiso){
         if (deltaR(taumom, (*iiso)->momentum()) < deltaRcut){
            sumIso += (*iiso)->momentum().perp();
         }
      }
      //if isolated remove the tau daughters from the pruned list
      if (sumIso < sumPtCut) {
#ifdef  DEBUG_HepMCValidationHelper
        std::cout << "particle " <<  *taus[i] <<  " is considered isolated, with sumPt " << sumIso << std::endl;
#endif
        toRemove.insert(toRemove.end(), taudaughters.begin(), taudaughters.end());
      }
    }

    //now actually remove
    pruned.clear();
    for (unsigned int i = 0; i < status1.size(); ++i){
      bool marked = false; 
      std::vector<const HepMC::GenParticle*>::const_iterator iremove;
      for ( iremove = toRemove.begin(); iremove != toRemove.end(); ++iremove){
        if (status1[i]->barcode() == (*iremove)->barcode()){
          marked = true;
          break;
        }
      }
      if (!marked) pruned.push_back(status1[i]);
    }

#ifdef  DEBUG_HepMCValidationHelper    
    std::cout<< "list of remaining particles:" <<std::endl;   
    for (unsigned int i = 0; i < pruned.size(); ++i){
      std::cout << *pruned[i] << std::endl;
    }
#endif    
  } 

  //get all visible status1 particles
  void allVisibleParticles(const HepMC::GenEvent* all, std::vector<const HepMC::GenParticle*>& visible)  {
    std::vector<const HepMC::GenParticle*> status1;
    visible.clear();    
    allStatus1(all, status1);
    for (unsigned int i = 0; i < status1.size(); ++i){
      if (!isNeutrino(status1[i])) visible.push_back(status1[i]);
    }    
  }

  //compute generated met
  TLorentzVector genMet(const HepMC::GenEvent* all, double etamin, double etamax){
    std::vector<const HepMC::GenParticle*> visible;
    allVisibleParticles(all, visible);
    TLorentzVector momsum(0., 0., 0., 0.);  
    for (unsigned int i = 0; i < visible.size(); ++i){
      if (visible[i]->momentum().eta() > etamin && visible[i]->momentum().eta() < etamax) {
        TLorentzVector mom(visible[i]->momentum().x(), visible[i]->momentum().y(), visible[i]->momentum().z(), visible[i]->momentum().t()); 
        momsum += mom;  
      }             
    }
    TLorentzVector met(-momsum.Px(), -momsum.Py(), 0., momsum.Pt());    
    return met; 
  }      
}