Generator.cc

Go to the documentation of this file.

#include "SimG4Core/Generators/interface/Generator.h"
#include "SimG4Core/Generators/interface/HepMCParticle.h"
#include "SimG4Core/Generators/interface/LumiMonitorFilter.h"

#include "SimG4Core/Notification/interface/SimG4Exception.h"

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

#include "HepPDT/ParticleID.hh"

#include "G4Event.hh"

#include "G4HEPEvtParticle.hh"
#include "G4ParticleDefinition.hh"
#include "G4UnitsTable.hh"
#include "G4SystemOfUnits.hh"
#include "G4PhysicalConstants.hh"
#include "G4Log.hh"

using namespace edm;
//using std::cout;
//using std::endl;

Generator::Generator(const ParameterSet & p) : 
  fPCuts(p.getParameter<bool>("ApplyPCuts")),
  fPtransCut(p.getParameter<bool>("ApplyPtransCut")),
  fEtaCuts(p.getParameter<bool>("ApplyEtaCuts")), 
  fPhiCuts(p.getParameter<bool>("ApplyPhiCuts")),
  theMinPhiCut(p.getParameter<double>("MinPhiCut")), // in radians (CMS standard)
  theMaxPhiCut(p.getParameter<double>("MaxPhiCut")),
  theMinEtaCut(p.getParameter<double>("MinEtaCut")),
  theMaxEtaCut(p.getParameter<double>("MaxEtaCut")),
  theMinPCut(p.getParameter<double>("MinPCut")),    // in GeV (CMS standard)
  theMaxPCut(p.getParameter<double>("MaxPCut")),   
  theEtaCutForHector(p.getParameter<double>("EtaCutForHector")),
  verbose(p.getUntrackedParameter<int>("Verbosity",0)),
  fLumiFilter(nullptr),
  evt_(nullptr),
  vtx_(nullptr),
  weight_(0),
  Z_lmin(0),
  Z_lmax(0),
  Z_hector(0),
  pdgFilterSel(false), 
  fPDGFilter(false) 
{
  bool lumi = p.getParameter<bool>("ApplyLumiMonitorCuts");
  if(lumi) { fLumiFilter = new LumiMonitorFilter(); }

  double theRDecLenCut = p.getParameter<double>("RDecLenCut")*cm;
  theDecRCut2 = theRDecLenCut*theRDecLenCut;

  theMinPtCut2 = theMinPCut*theMinPCut;

  double theDecLenCut = p.getParameter<double>("LDecLenCut")*cm;

  pdgFilter.resize(0);
  if ( p.exists("PDGselection") ) {
    pdgFilterSel = (p.getParameter<edm::ParameterSet>("PDGselection")).
                    getParameter<bool>("PDGfilterSel");
    pdgFilter = (p.getParameter<edm::ParameterSet>("PDGselection")).
                    getParameter<std::vector< int > >("PDGfilter");
    if(!pdgFilter.empty()) { 
      fPDGFilter = true; 
      for ( unsigned int ii = 0; ii < pdgFilter.size(); ++ii) {
    if (pdgFilterSel) {
      edm::LogWarning("SimG4CoreGenerator") 
        << " *** Selecting only PDG ID = " << pdgFilter[ii];
    } else {
      edm::LogWarning("SimG4CoreGenerator") 
        << " *** Filtering out PDG ID = " << pdgFilter[ii];
    }
      }
    }
  }

  if(fEtaCuts){
    Z_lmax = theRDecLenCut*((1 - exp(-2*theMaxEtaCut) )/( 2*exp(-theMaxEtaCut)));
    Z_lmin = theRDecLenCut*((1 - exp(-2*theMinEtaCut) )/( 2*exp(-theMinEtaCut)));
  }

  Z_hector = theRDecLenCut*((1 - exp(-2*theEtaCutForHector)) 
                / ( 2*exp(-theEtaCutForHector) ) );

  edm::LogInfo("SimG4CoreGenerator") 
    << " Rdecaycut= " << theRDecLenCut/cm 
    << " cm;  Zdecaycut= " << theDecLenCut/cm 
    << "Z_min= " << Z_lmin/cm << " cm; Z_max= " << Z_lmax 
    << " cm;  Z_hector = " << Z_hector << " cm\n"
    << "ApplyPCuts: " << fPCuts << "  ApplyPtransCut: " << fPtransCut
    << "  ApplyEtaCuts: " << fEtaCuts 
    << "  ApplyPhiCuts: " << fPhiCuts
    << "  ApplyLumiMonitorCuts: " << lumi;
  if(lumi) { fLumiFilter->Describe(); }
}

Generator::~Generator() 
{
  delete fLumiFilter;
}

void Generator::HepMC2G4(const HepMC::GenEvent * evt_orig, G4Event * g4evt)
{

  HepMC::GenEvent *evt=new HepMC::GenEvent(*evt_orig);

  if ( *(evt->vertices_begin()) == nullptr ) {
    throw SimG4Exception("SimG4CoreGenerator: Corrupted Event - GenEvent with no vertex");
  }  
  
  if (!evt->weights().empty()) {

    weight_ = evt->weights()[0] ;
    for (unsigned int iw=1; iw<evt->weights().size(); ++iw) {

      // terminate if the vector of weights contains a zero-weight
      if ( evt->weights()[iw] <= 0 ) break;
      weight_ *= evt->weights()[iw] ;
    }     
  }
  
  if (vtx_ != nullptr) { delete vtx_; }
  vtx_ = new math::XYZTLorentzVector((*(evt->vertices_begin()))->position().x(),
                                     (*(evt->vertices_begin()))->position().y(),
                                     (*(evt->vertices_begin()))->position().z(),
                                     (*(evt->vertices_begin()))->position().t());

  if(verbose > 0) {
    edm::LogInfo("SimG4CoreGenerator") << &evt;
    LogDebug("SimG4CoreGenerator") << "Primary Vertex = (" 
                   << vtx_->x() << "," 
                   << vtx_->y() << ","
                   << vtx_->z() << ")";
  }
    
  unsigned int ng4vtx = 0;

  for(HepMC::GenEvent::vertex_const_iterator vitr= evt->vertices_begin();
      vitr != evt->vertices_end(); ++vitr ) { 

    // loop for vertex, is it a real vertex?
    // Set qvtx to true for any particles that should be propagated by GEANT, i.e.,
    // status 1 particles or
    // status 2 particles that decay outside the beampipe.   
    G4bool qvtx=false;
    HepMC::GenVertex::particle_iterator pitr;
    for (pitr= (*vitr)->particles_begin(HepMC::children);
         pitr != (*vitr)->particles_end(HepMC::children); ++pitr) {

      // For purposes of this function, the status is defined as follows:
      // 1:  particles are not decayed by generator
      // 2:  particles are decayed by generator but need to be propagated by GEANT
      // 3:  particles are decayed by generator but do not need to be propagated by GEANT
      int status = (*pitr)->status();
      if (status > 3 && isExotic(*pitr) && (!(isExoticNonDetectable(*pitr)))) {
        // In Pythia 8, there are many status codes besides 1, 2, 3.
        // By setting the status to 2 for exotic particles, they will be checked:
        // if its decay vertex is outside the beampipe, it will be propagated by GEANT.
    // Some Standard Model particles, e.g., K0, cannot be propagated by GEANT, 
    // so do not change their status code.  
        status = 2;
      }

      // Particles which are not decayed by generator
      if (status == 1) {
        qvtx = true;
        if (verbose > 2) LogDebug("SimG4CoreGenerator") 
      << "GenVertex barcode = " << (*vitr)->barcode() 
      << " selected for GenParticle barcode = " << (*pitr)->barcode();
        break;
      }  
      // The selection is made considering if the partcile with status = 2 
      // have the end_vertex with a radius greater than the radius of beampipe 
      // cylinder (no requirement on the Z of the vertex is applyed).
      else if (status == 2) {
        if ( (*pitr)->end_vertex() != nullptr  ) { 
          double xx = (*pitr)->end_vertex()->position().x();
          double yy = (*pitr)->end_vertex()->position().y();
          double r_dd = xx*xx+yy*yy;
          if (r_dd > theDecRCut2) {
            qvtx = true;
            if (verbose > 2) LogDebug("SimG4CoreGenerator") 
          << "GenVertex barcode = " << (*vitr)->barcode() 
          << " selected for GenParticle barcode = " 
          << (*pitr)->barcode() << " radius = " << std::sqrt(r_dd);
            break;
          }
        } else {
      // particles with status 2 without end_vertex are 
      // equivalent to stable
      qvtx = true;
    }
      }
    }

    // if this vertex is inside fiductial volume inside the beam pipe
    // and has no long-lived secondary the vertex is not saved 
    if (!qvtx) {
      continue;
    }
    
    double x1 = (*vitr)->position().x()*mm;
    double y1 = (*vitr)->position().y()*mm;
    double z1 = (*vitr)->position().z()*mm;
    double t1 = (*vitr)->position().t()*mm/c_light;

    G4PrimaryVertex* g4vtx = new G4PrimaryVertex(x1, y1, z1, t1);

    for (pitr= (*vitr)->particles_begin(HepMC::children);
         pitr != (*vitr)->particles_end(HepMC::children); ++pitr){

      // Filter on allowed particle species if required      
      if (fPDGFilter) {
        std::vector<int>::iterator it = find(pdgFilter.begin(),pdgFilter.end(),
                         (*pitr)->pdg_id()); 
        if ( (it != pdgFilter.end() && !pdgFilterSel) 
         || ( it == pdgFilter.end() && pdgFilterSel ) ) {
          if (verbose > 2) LogDebug("SimG4CoreGenerator") 
        << "Skip GenParticle barcode = " << (*pitr)->barcode() 
        << " PDG Id = " << (*pitr)->pdg_id();
          continue;
        }
      }

      double x2 = 0.0;
      double y2 = 0.0;
      double z2 = 0.0;
      double decay_length = 0.0;
      int status = (*pitr)->status();

      if (status > 3 && isExotic(*pitr) && (!(isExoticNonDetectable(*pitr))) ) {
    status = 2;
      }

      // check the status, 2 has end point with decay defined by generator
      if (1 == status || 2 == status) {

        // this particle has decayed but have no vertex
    // it is an exotic case
        if ( !(*pitr)->end_vertex() ) { 
          status = 1; 
    } else {
          x2 = (*pitr)->end_vertex()->position().x();
          y2 = (*pitr)->end_vertex()->position().y();
          z2 = (*pitr)->end_vertex()->position().z();
      decay_length = 
          std::sqrt((x2-x1)*(x2-x1)+(y2-y1)*(y2-y1)+(z2-z1)*(z2-z1));
    }
      } 

      bool toBeAdded = false;
      double px = (*pitr)->momentum().px();
      double py = (*pitr)->momentum().py();
      double pz = (*pitr)->momentum().pz();
      double ptot = std::sqrt(px*px + py*py + pz*pz);
      math::XYZTLorentzVector p(px, py, pz, (*pitr)->momentum().e());
      
      double ximpact = x1;
      double yimpact = y1;
      double zimpact = z1;

      // protection against numerical problems for extremely low momenta
      // compute impact point at transition to Hector
      const double minTan = 1.e-20;
      if(fabs(z1) < Z_hector && fabs(pz) >= minTan*ptot) {
        if(pz > 0.0) { zimpact =  Z_hector; }
    else         { zimpact = -Z_hector; }
        double del = (zimpact - z1)/pz;
        ximpact += del*px;
        yimpact += del*py;
      }
      double rimpact2 = ximpact*ximpact + yimpact*yimpact;
      
      if (verbose > 2) LogDebug("SimG4CoreGenerator") 
    << "Processing GenParticle barcode= " << (*pitr)->barcode() 
    << " pdg= " << (*pitr)-> pdg_id()
    << " status= " << (*pitr)->status() 
    << " st= " << status 
    << " rimpact(cm)= " << std::sqrt(rimpact2)/cm
    << " zimpact(cm)= " << zimpact/cm
    << " ptot(GeV)= " << ptot
    << " pz(GeV)= " << pz;

      // Particles of status 1 trasnported along the beam pipe for forward 
      // detectors (HECTOR) always pass to Geant4 without cuts 
      if( 1 == status && 
      fabs(zimpact) >= Z_hector && rimpact2 <= theDecRCut2) {
        toBeAdded = true;
        if ( verbose > 2 ) LogDebug("SimG4CoreGenerator") 
      << "GenParticle barcode = " << (*pitr)->barcode() 
      << " passed case 3";
      } else {

    // Standard case: particles not decayed by the generator
    if(1 == status && 
           (fabs(zimpact) < Z_hector || rimpact2 > theDecRCut2)) {

      // Ptot cut for all particles
      if (fPCuts && (ptot < theMinPCut || ptot > theMaxPCut)) {
            continue;
      }
      // phi cut is applied mainly for particle gun
      if (fPhiCuts) {
        double phi = p.phi();
        if(phi < theMinPhiCut || phi  > theMaxPhiCut) {
          continue;
        }
      }
      // eta cut is applied if position of the decay
      // is within vacuum chamber and limited in Z
      if(fEtaCuts) {

        // eta cut
        double xi = x1;
        double yi = y1;
        double zi = z1;

        // can be propagated along Z
        if(fabs(pz) >= minTan*ptot) {
          if((zi >= Z_lmax) & (pz < 0.0)) {
        zi = Z_lmax;
          } else if((zi <= Z_lmin) & (pz > 0.0)) {
        zi = Z_lmin;
          } else {
        if(pz > 0) { zi = Z_lmax; }
        else { zi = Z_lmin; }
          }
          double del = (zi - z1)/pz;
          xi += del*px;
          yi += del*py;
        }
        // check eta cut
        if((zi >= Z_lmin) & (zi <= Z_lmax) 
           & (xi*xi + yi*yi < theDecRCut2)) {
          continue;
        }
      }
      if(fLumiFilter && !fLumiFilter->isGoodForLumiMonitor(*pitr)) 
        { continue; }
      toBeAdded = true;
      if ( verbose > 2 ) LogDebug("SimG4CoreGenerator") 
        << "GenParticle barcode = " << (*pitr)->barcode() 
        << " passed case 1";

      // Decay chain outside the fiducial cylinder defined by theRDecLenCut
      // are used for Geant4 tracking with predefined decay channel
      // In the case of decay in vacuum particle is not tracked by Geant4
    } else if(2 == status &&
          x2*x2 + y2*y2 >= theDecRCut2 && fabs(z2) < Z_hector) {

      toBeAdded = true;
      if ( verbose > 2 ) LogDebug("SimG4CoreGenerator") 
        << "GenParticle barcode = " << (*pitr)->barcode() 
        << " passed case 2" 
        << " decay_length(cm)= " << decay_length/cm;
    }
      }
      if(toBeAdded){
        G4int pdgcode= (*pitr)-> pdg_id();
        G4PrimaryParticle* g4prim= 
          new G4PrimaryParticle(pdgcode, px*GeV, py*GeV, pz*GeV);
        
        if ( g4prim->GetG4code() != nullptr ){ 
          g4prim->SetMass( g4prim->GetG4code()->GetPDGMass() );
          double charge = g4prim->GetG4code()->GetPDGCharge();

      // apply Pt cut
      if (fPtransCut && 
          0.0 != charge && px*px + py*py < theMinPtCut2) {
            delete g4prim;
            continue;
      }
          g4prim->SetCharge(charge);  
        }

    // V.I. do not use SetWeight but the same code
        // value of the code compute inside TrackWithHistory        
        //g4prim->SetWeight( 10000*(*vpitr)->barcode() ) ;
        setGenId( g4prim, (*pitr)->barcode() );

        if (2 == status) {
          particleAssignDaughters(g4prim,
                  (HepMC::GenParticle *) *pitr, decay_length);
    }
        if ( verbose > 1 ) g4prim->Print();
        g4vtx->SetPrimary(g4prim);
      }
    }

    if ( verbose > 1 ) g4vtx->Print();
    g4evt->AddPrimaryVertex(g4vtx);
    ++ng4vtx;
  }
  
  // Add a protection for completely empty events (produced by LHCTransport): 
  // add a dummy vertex with no particle attached to it
  if ( ng4vtx == 0 ) {
    G4PrimaryVertex* g4vtx = new G4PrimaryVertex(0.0, 0.0, 0.0, 0.0);
    if ( verbose > 1 ) g4vtx->Print();
    g4evt->AddPrimaryVertex(g4vtx);
  }

  delete evt;
}

void Generator::particleAssignDaughters( G4PrimaryParticle* g4p, 
                     HepMC::GenParticle* vp, 
                     double decaylength)
{
  if ( verbose > 1 ) {
    LogDebug("SimG4CoreGenerator") 
      << "Special case of long decay length \n" 
      << "Assign daughters with to mother with decaylength=" 
      << decaylength/cm << " cm";
  }
  math::XYZTLorentzVector p(vp->momentum().px(), vp->momentum().py(), 
                vp->momentum().pz(), vp->momentum().e());

  // defined preassigned decay time
  double proper_time = decaylength/(p.Beta()*p.Gamma()*c_light);
  g4p->SetProperTime(proper_time); 

  if( verbose > 2 ) {
    LogDebug("SimG4CoreGenerator") <<" px= "<< p.px()
                   <<" py= "<< p.py()
                   <<" pz= "<< p.pz()
                   <<" e= " <<  p.e()
                   <<" beta= "<< p.Beta()
                   <<" gamma= " << p.Gamma()
                   <<" Proper time= " <<proper_time/ns <<" ns";
  }

  // the particle will decay after the same length if it 
  // has not interacted before
  double x1 = vp->end_vertex()->position().x();
  double y1 = vp->end_vertex()->position().y();
  double z1 = vp->end_vertex()->position().z();

  for (HepMC::GenVertex::particle_iterator 
         vpdec= vp->end_vertex()->particles_begin(HepMC::children);
       vpdec != vp->end_vertex()->particles_end(HepMC::children); ++vpdec) {
    
    //transform decay products such that in the rest frame of mother
    math::XYZTLorentzVector pdec((*vpdec)->momentum().px(),
                                 (*vpdec)->momentum().py(),
                                 (*vpdec)->momentum().pz(),
                                 (*vpdec)->momentum().e());

    // children should only be taken into account once
    G4PrimaryParticle * g4daught= 
      new G4PrimaryParticle((*vpdec)->pdg_id(), pdec.x()*GeV, 
                pdec.y()*GeV, pdec.z()*GeV);

    if ( g4daught->GetG4code() != nullptr )
      { 
        g4daught->SetMass( g4daught->GetG4code()->GetPDGMass() ) ;
        g4daught->SetCharge( g4daught->GetG4code()->GetPDGCharge() ) ;  
      }

    // V.I. do not use SetWeight but the same code
    // value of the code compute inside TrackWithHistory        
    setGenId( g4daught, (*vpdec)->barcode() );

    if ( verbose > 2 ) LogDebug("SimG4CoreGenerator") 
      <<"Assigning a "<< (*vpdec)->pdg_id()
      <<" as daughter of a " << vp->pdg_id();
    if ( (*vpdec)->status() == 2 && (*vpdec)->end_vertex() != nullptr) 
      {
        double x2 = (*vpdec)->end_vertex()->position().x();
        double y2 = (*vpdec)->end_vertex()->position().y();
        double z2 = (*vpdec)->end_vertex()->position().z();
        double dd = std::sqrt((x1-x2)*(x1-x2)+(y1-y2)*(y1-y2)+(z1-z2)*(z1-z2));
        particleAssignDaughters(g4daught,*vpdec,dd);
      }
    (*vpdec)->set_status(1000+(*vpdec)->status()); 
    g4p->SetDaughter(g4daught);

    if ( verbose > 1 ) g4daught->Print();
  }
}

// Used for non-beam particles
bool Generator::particlePassesPrimaryCuts(const G4ThreeVector& p) const 
{
  bool flag = true;
  double ptot = p.mag();
  if (fPCuts && (ptot < theMinPCut*GeV || ptot > theMaxPCut*GeV)) {
    flag = false;
  } 
  if (fEtaCuts && flag) {
    double pz = p.z();
    if(ptot < pz + 1.e-10) { 
      flag = false;

    } else {
      double eta = 0.5*G4Log((ptot + pz)/(ptot - pz));
      if(eta < theMinEtaCut || eta > theMaxEtaCut) {
    flag = false;
      }
    }
  }
  if (fPhiCuts && flag) {
    double phi = p.phi();
    if(phi < theMinPhiCut || phi > theMaxPhiCut) {
      flag = false;
    }
  }
  
  if ( verbose > 2 ) LogDebug("SimG4CoreGenerator") 
    << "Generator ptot(GeV)= " << ptot/GeV << " eta= " << p.eta() 
    << "  phi= " << p.phi() << " Flag= " << flag;

  return flag;
}

bool Generator::isExotic(HepMC::GenParticle* p) const
{
  int pdgid = abs(p->pdg_id());  
  if ((pdgid >= 1000000 && pdgid <  4000000) || // SUSY, R-hadron, and technicolor particles
      pdgid == 17 || // 4th generation lepton 
      pdgid == 34 || // W-prime
      pdgid == 37)   // charged Higgs
    {
    return true;
  } 

  return false;
}

bool Generator::isExoticNonDetectable(HepMC::GenParticle* p) const
{
  int pdgid = abs(p->pdg_id());  
  HepPDT::ParticleID pid(p->pdg_id());
  int charge = pid.threeCharge();
  if ((charge==0) && (pdgid >= 1000000 && pdgid <  1000040)) // SUSY 
    {
    return true;
  } 

  return false;
}



void Generator::nonBeamEvent2G4(const HepMC::GenEvent * evt, G4Event * g4evt) 
{
  int i = 0; 
  for(HepMC::GenEvent::particle_const_iterator it = evt->particles_begin(); 
      it != evt->particles_end(); ++it ) {
    ++i;
    HepMC::GenParticle * gp = (*it);    
    int g_status = gp->status();
    // storing only particle with status == 1   
    if (g_status == 1) {
      int g_id = gp->pdg_id();      
      G4PrimaryParticle * g4p = 
    new G4PrimaryParticle(g_id,gp->momentum().px()*GeV,
                  gp->momentum().py()*GeV,
                  gp->momentum().pz()*GeV);
      if (g4p->GetG4code() != nullptr) { 
    g4p->SetMass(g4p->GetG4code()->GetPDGMass());
    g4p->SetCharge(g4p->GetG4code()->GetPDGCharge());
      }
      setGenId(g4p,i);
      if (particlePassesPrimaryCuts(g4p->GetMomentum())) {
    G4PrimaryVertex * v = 
      new G4PrimaryVertex(gp->production_vertex()->position().x()*mm,
                  gp->production_vertex()->position().y()*mm,
                  gp->production_vertex()->position().z()*mm,
                  gp->production_vertex()->position().t()*mm/c_light);
    v->SetPrimary(g4p);
    g4evt->AddPrimaryVertex(v);
    if(verbose > 0) { v->Print(); }

      } else {
    delete g4p;
      }
    }
  } // end loop on HepMC particles
}