GenParticles2HepMCConverter.cc

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#include "FWCore/Framework/interface/Frameworkfwd.h"
#include "FWCore/Framework/interface/stream/EDProducer.h"

#include "FWCore/Framework/interface/Event.h"
#include "FWCore/Framework/interface/EventSetup.h"
#include "FWCore/Framework/interface/ESHandle.h"
#include "FWCore/Framework/interface/Run.h"
#include "FWCore/Framework/interface/MakerMacros.h"

#include "FWCore/ParameterSet/interface/ParameterSet.h"
#include "FWCore/Utilities/interface/InputTag.h"
#include "DataFormats/Common/interface/Handle.h"

#include "DataFormats/Candidate/interface/CandidateFwd.h"
#include "DataFormats/HepMCCandidate/interface/GenParticleFwd.h"
#include "DataFormats/HepMCCandidate/interface/GenParticle.h"
#include "SimDataFormats/GeneratorProducts/interface/HepMCProduct.h"
#include "SimDataFormats/GeneratorProducts/interface/GenRunInfoProduct.h"
#include "SimDataFormats/GeneratorProducts/interface/GenEventInfoProduct.h"
#include "SimGeneral/HepPDTRecord/interface/ParticleDataTable.h"

#include <iostream>
#include <map>

using namespace std;

class GenParticles2HepMCConverter : public edm::stream::EDProducer<>
{
public:
  explicit GenParticles2HepMCConverter(const edm::ParameterSet& pset);
  ~GenParticles2HepMCConverter() {};

  void produce(edm::Event& event, const edm::EventSetup& eventSetup) override;

private:
  edm::EDGetTokenT<reco::CandidateView> genParticlesToken_;
  edm::EDGetTokenT<GenEventInfoProduct> genEventInfoToken_;
  edm::ESHandle<ParticleDataTable> pTable_;

  std::vector<int> signalParticlePdgIds_;
  const double cmEnergy_;

private:
  inline HepMC::FourVector FourVector(const reco::Candidate::Point& point)
  {
    return HepMC::FourVector(10*point.x(), 10*point.y(), 10*point.z(), 0);
  };

  inline HepMC::FourVector FourVector(const reco::Candidate::LorentzVector& lvec)
  {
    // Avoid negative mass, set minimum m^2 = 0
    return HepMC::FourVector(lvec.px(), lvec.py(), lvec.pz(), std::hypot(lvec.P(), std::max(0., lvec.mass())));
  };


};

GenParticles2HepMCConverter::GenParticles2HepMCConverter(const edm::ParameterSet& pset):
  cmEnergy_(pset.getUntrackedParameter<double>("cmEnergy", 13000)) // dummy value to set incident proton pz for particle gun samples
{
  genParticlesToken_ = consumes<reco::CandidateView>(pset.getParameter<edm::InputTag>("genParticles"));
  genEventInfoToken_ = consumes<GenEventInfoProduct>(pset.getParameter<edm::InputTag>("genEventInfo"));
  signalParticlePdgIds_ = pset.getParameter<std::vector<int>>("signalParticlePdgIds");

  produces<edm::HepMCProduct>("unsmeared");
}

void GenParticles2HepMCConverter::produce(edm::Event& event, const edm::EventSetup& eventSetup)
{
  edm::Handle<reco::CandidateView> genParticlesHandle;
  event.getByToken(genParticlesToken_, genParticlesHandle);

  edm::Handle<GenEventInfoProduct> genEventInfoHandle;
  event.getByToken(genEventInfoToken_, genEventInfoHandle);

  eventSetup.getData(pTable_);

  HepMC::GenEvent* hepmc_event = new HepMC::GenEvent();
  hepmc_event->set_event_number(event.id().event());
  hepmc_event->set_signal_process_id(genEventInfoHandle->signalProcessID());
  hepmc_event->set_event_scale(genEventInfoHandle->qScale());
  hepmc_event->set_alphaQED(genEventInfoHandle->alphaQED());
  hepmc_event->set_alphaQCD(genEventInfoHandle->alphaQCD());

  hepmc_event->weights() = genEventInfoHandle->weights();

  // Set PDF
  const gen::PdfInfo* pdf = genEventInfoHandle->pdf();
  if ( pdf != nullptr ) {
    const int pdf_id1 = pdf->id.first, pdf_id2 = pdf->id.second;
    const double pdf_x1 = pdf->x.first, pdf_x2 = pdf->x.second;
    const double pdf_scalePDF = pdf->scalePDF;
    const double pdf_xPDF1 = pdf->xPDF.first, pdf_xPDF2 = pdf->xPDF.second;
    HepMC::PdfInfo hepmc_pdfInfo(pdf_id1, pdf_id2, pdf_x1, pdf_x2, pdf_scalePDF, pdf_xPDF1, pdf_xPDF2);
    hepmc_event->set_pdf_info(hepmc_pdfInfo);
  }

  // Prepare list of HepMC::GenParticles
  std::map<const reco::Candidate*, HepMC::GenParticle*> genCandToHepMCMap;
  HepMC::GenParticle* hepmc_parton1 = nullptr, * hepmc_parton2 = nullptr;
  std::vector<HepMC::GenParticle*> hepmc_particles;
  const reco::Candidate* parton1 = nullptr, * parton2 = nullptr;
  for ( unsigned int i=0, n=genParticlesHandle->size(); i<n; ++i )
  {
    const reco::Candidate* p = &genParticlesHandle->at(i);
    HepMC::GenParticle* hepmc_particle = new HepMC::GenParticle(FourVector(p->p4()), p->pdgId(), p->status());
    hepmc_particle->suggest_barcode(i+1);

    // Assign particle's generated mass from the standard particle data table
    double particleMass;
    if ( pTable_->particle(p->pdgId()) ) particleMass = pTable_->particle(p->pdgId())->mass();
    else particleMass = p->mass();

    hepmc_particle->set_generated_mass(particleMass);

    hepmc_particles.push_back(hepmc_particle);
    genCandToHepMCMap[p] = hepmc_particle;

    // Find incident proton pair
    if ( p->mother() == nullptr and std::abs(p->eta()) > 5 and std::abs(p->pz()) > 1000 ) {
      if ( !parton1 and p->pz() > 0 ) {
        parton1 = p;
        hepmc_parton1 = hepmc_particle;
      }
      else if ( !parton2 and p->pz() < 0 ) {
        parton2 = p;
        hepmc_parton2 = hepmc_particle;
      }
    }
  }

  HepMC::GenVertex* vertex1 = nullptr;
  HepMC::GenVertex* vertex2 = nullptr;
  if ( parton1 == nullptr and parton2 == nullptr ) {
    // Particle gun samples do not have incident partons. Put dummy incident particle and prod vertex
    // Note: leave parton1 and parton2 as nullptr since it is not used anymore after creating hepmc_parton1 and 2
    const reco::Candidate::LorentzVector nullP4(0,0,0,0);
    const reco::Candidate::LorentzVector beamP4(0,0,cmEnergy_/2, cmEnergy_/2);
    vertex1 = new HepMC::GenVertex(FourVector(nullP4));
    vertex2 = new HepMC::GenVertex(FourVector(nullP4));
    hepmc_parton1 =  new HepMC::GenParticle(FourVector(+beamP4), 2212, 4);
    hepmc_parton2 =  new HepMC::GenParticle(FourVector(-beamP4), 2212, 4);
  }
  else {
    // Put incident beam particles : proton -> parton vertex
    vertex1 = new HepMC::GenVertex(FourVector(parton1->vertex()));
    vertex2 = new HepMC::GenVertex(FourVector(parton2->vertex()));
  }
  hepmc_event->add_vertex(vertex1);
  hepmc_event->add_vertex(vertex2);
  vertex1->add_particle_in(hepmc_parton1);
  vertex2->add_particle_in(hepmc_parton2);
  hepmc_event->set_beam_particles(hepmc_parton1, hepmc_parton2);

  // Prepare vertex list
  typedef std::map<const reco::Candidate*, HepMC::GenVertex*> ParticleToVertexMap;
  ParticleToVertexMap particleToVertexMap;
  particleToVertexMap[parton1] = vertex1;
  particleToVertexMap[parton2] = vertex2;
  for ( unsigned int i=0, n=genParticlesHandle->size(); i<n; ++i )
  {
    const reco::Candidate* p = &genParticlesHandle->at(i);
    if ( p == parton1 or p == parton2 ) continue;

    // Connect mother-daughters for the other cases
    for ( unsigned int j=0, nMothers=p->numberOfMothers(); j<nMothers; ++j )
    {
      // Mother-daughter hierarchy defines vertex
      const reco::Candidate* elder = p->mother(j)->daughter(0);
      HepMC::GenVertex* vertex;
      if ( particleToVertexMap.find(elder) == particleToVertexMap.end() )
      {
        vertex = new HepMC::GenVertex(FourVector(elder->vertex()));
        hepmc_event->add_vertex(vertex);
        particleToVertexMap[elder] = vertex;
      }
      else
      {
        vertex = particleToVertexMap[elder];
      }

      // Vertex is found. Now connect each other
      const reco::Candidate* mother = p->mother(j);
      vertex->add_particle_in(genCandToHepMCMap[mother]);
      vertex->add_particle_out(hepmc_particles[i]);
    }
  }

  // Finalize HepMC event record
  bool hasSignalVertex = false;
  if ( !signalParticlePdgIds_.empty() ) {
    // Loop over all vertices to assign the signal vertex, decaying to a signal particle
    for ( auto v = hepmc_event->vertices_begin(); v != hepmc_event->vertices_end(); ++v ) {
      for ( auto p = (*v)->particles_begin(HepMC::children);
            p != (*v)->particles_end(HepMC::children); ++p ) {
        const int pdgId = (*p)->pdg_id();
        if ( std::find(signalParticlePdgIds_.begin(), signalParticlePdgIds_.end(), pdgId) != signalParticlePdgIds_.end() ) {
          hepmc_event->set_signal_process_vertex(*v);
          hasSignalVertex = true;
          break;
        }
      }
      if ( hasSignalVertex ) break;
    }
  }
  // Set the default signal vertex if still not set
  if ( !hasSignalVertex ) hepmc_event->set_signal_process_vertex(*(vertex1->vertices_begin()));

  std::auto_ptr<edm::HepMCProduct> hepmc_product(new edm::HepMCProduct());
  hepmc_product->addHepMCData(hepmc_event);
  event.put(hepmc_product, "unsmeared");

}

DEFINE_FWK_MODULE(GenParticles2HepMCConverter);