BtoCharmDecayVertexMerger.cc

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// this code is partially taken from BCandidateProducer of L. Wehrli
 
// first revised prototype version for CMSSW 29.Aug.2012
 
#include "FWCore/Framework/interface/stream/EDProducer.h"
#include "FWCore/Framework/interface/Event.h"
#include "FWCore/Framework/interface/MakerMacros.h"
#include "FWCore/Utilities/interface/InputTag.h"
#include "FWCore/ParameterSet/interface/ParameterSet.h"
 
#include "DataFormats/BTauReco/interface/ParticleMasses.h"
#include "DataFormats/Candidate/interface/VertexCompositePtrCandidate.h"
#include "DataFormats/Common/interface/Handle.h"
#include "DataFormats/TrackReco/interface/Track.h"
#include "DataFormats/TrackReco/interface/TrackFwd.h"
#include "DataFormats/VertexReco/interface/Vertex.h"
#include "DataFormats/VertexReco/interface/VertexFwd.h"
#include "RecoVertex/VertexTools/interface/VertexDistance3D.h"
#include "RecoBTag/SecondaryVertex/interface/SecondaryVertex.h"
 
#include "DataFormats/GeometryVector/interface/VectorUtil.h"
 
#include <algorithm>
 
reco::Candidate::LorentzVector vtxP4(const reco::VertexCompositePtrCandidate &vtx) {
  reco::Candidate::LorentzVector sum;
  const std::vector<reco::CandidatePtr> &tracks = vtx.daughterPtrVector();
 
  for (std::vector<reco::CandidatePtr>::const_iterator track = tracks.begin(); track != tracks.end(); ++track) {
    ROOT::Math::LorentzVector<ROOT::Math::PxPyPzM4D<double>> vec;
    vec.SetPx((*track)->px());
    vec.SetPy((*track)->py());
    vec.SetPz((*track)->pz());
    vec.SetM(reco::ParticleMasses::piPlus);
    sum += vec;
  }
  return sum;
}
 
template <typename VTX>
class BtoCharmDecayVertexMergerT : public edm::stream::EDProducer<> {
public:
  BtoCharmDecayVertexMergerT(const edm::ParameterSet &params);
 
  void produce(edm::Event &event, const edm::EventSetup &es) override;
 
  typedef reco::TemplatedSecondaryVertex<VTX> SecondaryVertex;
 
private:
  edm::EDGetTokenT<reco::VertexCollection> token_primaryVertex;
  edm::EDGetTokenT<edm::View<VTX>> token_secondaryVertex;
  reco::Vertex pv;
  // double                                    maxFraction;
  // double                                    minSignificance;
 
  double maxDRForUnique, maxvecSumIMCUTForUnique, minCosPAtomerge, maxPtreltomerge;
 
  // a vertex proxy for sorting using stl
  struct VertexProxy {
    VTX vert;
    double invm;
    size_t ntracks;
  };
 
  // comparison operator for VertexProxy, used in sorting
  friend bool operator<(VertexProxy v1, VertexProxy v2) {
    if (v1.ntracks > 2 && v2.ntracks < 3)
      return true;
    if (v1.ntracks < 3 && v2.ntracks > 2)
      return false;
    return (v1.invm > v2.invm);
  }
 
  VertexProxy buildVertexProxy(const VTX &vtx);
 
  void resolveBtoDchain(std::vector<VertexProxy> &coll, unsigned int i, unsigned int k);
  GlobalVector flightDirection(const reco::Vertex &v1, const reco::Vertex &v2);
  GlobalVector flightDirection(const reco::Vertex &v1, const reco::VertexCompositePtrCandidate &v2);
  GlobalVector flightDirection(const reco::VertexCompositePtrCandidate &v1,
                               const reco::VertexCompositePtrCandidate &v2);
};
 
template <typename VTX>
BtoCharmDecayVertexMergerT<VTX>::BtoCharmDecayVertexMergerT(const edm::ParameterSet &params)
    : token_primaryVertex(consumes<reco::VertexCollection>(params.getParameter<edm::InputTag>("primaryVertices"))),
      token_secondaryVertex(consumes<edm::View<VTX>>(params.getParameter<edm::InputTag>("secondaryVertices"))),
      maxDRForUnique(params.getParameter<double>("maxDRUnique")),
      maxvecSumIMCUTForUnique(params.getParameter<double>("maxvecSumIMifsmallDRUnique")),
      minCosPAtomerge(params.getParameter<double>("minCosPAtomerge")),
      maxPtreltomerge(params.getParameter<double>("maxPtreltomerge"))
// maxFraction(params.getParameter<double>("maxFraction")),
// minSignificance(params.getParameter<double>("minSignificance"))
{
  produces<std::vector<VTX>>();
}
//------------------------------------
template <typename VTX>
void BtoCharmDecayVertexMergerT<VTX>::produce(edm::Event &iEvent, const edm::EventSetup &iSetup) {
  using namespace reco;
  // PV
  edm::Handle<reco::VertexCollection> PVcoll;
  iEvent.getByToken(token_primaryVertex, PVcoll);
 
  if (!PVcoll->empty()) {
    const reco::VertexCollection pvc = *(PVcoll.product());
    pv = pvc[0];
 
    // get the IVF collection
    edm::Handle<edm::View<VTX>> secondaryVertices;
    iEvent.getByToken(token_secondaryVertex, secondaryVertices);
 
    //loop over vertices,  fill into own collection for sorting
    std::vector<VertexProxy> vertexProxyColl;
    for (typename edm::View<VTX>::const_iterator sv = secondaryVertices->begin(); sv != secondaryVertices->end();
         ++sv) {
      vertexProxyColl.push_back(buildVertexProxy(*sv));
    }
 
    // sort the vertices by mass and track multiplicity
    sort(vertexProxyColl.begin(), vertexProxyColl.end());
 
    // loop forward over all vertices
    for (unsigned int iVtx = 0; iVtx < vertexProxyColl.size(); ++iVtx) {
      // nested loop backwards (in order to start from light masses)
      // check all vertices against each other for B->D chain
      for (unsigned int kVtx = vertexProxyColl.size() - 1; kVtx > iVtx; --kVtx) {
        // remove D vertices from the collection and add the tracks to the original one
        resolveBtoDchain(vertexProxyColl, iVtx, kVtx);
      }
    }
 
    // now create new vertex collection and add to event
    auto bvertColl = std::make_unique<std::vector<VTX>>();
    for (typename std::vector<VertexProxy>::const_iterator it = vertexProxyColl.begin(); it != vertexProxyColl.end();
         ++it)
      bvertColl->push_back((*it).vert);
    iEvent.put(std::move(bvertColl));
  } else {
    iEvent.put(std::make_unique<std::vector<VTX>>());
  }
}
//------------------------------------
template <typename VTX>
GlobalVector BtoCharmDecayVertexMergerT<VTX>::flightDirection(const reco::Vertex &v1, const reco::Vertex &v2) {
  return GlobalVector(v2.x() - v1.x(), v2.y() - v1.y(), v2.z() - v1.z());
}
 
template <typename VTX>
GlobalVector BtoCharmDecayVertexMergerT<VTX>::flightDirection(const reco::Vertex &v1,
                                                              const reco::VertexCompositePtrCandidate &v2) {
  return GlobalVector(v2.vertex().x() - v1.x(), v2.vertex().y() - v1.y(), v2.vertex().z() - v1.z());
}
 
template <typename VTX>
GlobalVector BtoCharmDecayVertexMergerT<VTX>::flightDirection(const reco::VertexCompositePtrCandidate &v1,
                                                              const reco::VertexCompositePtrCandidate &v2) {
  return GlobalVector(
      v2.vertex().x() - v1.vertex().x(), v2.vertex().y() - v1.vertex().y(), v2.vertex().z() - v1.vertex().z());
}
//-------------- template specializations --------------------
 
// -------------- buildVertexProxy ----------------
template <>
BtoCharmDecayVertexMergerT<reco::Vertex>::VertexProxy BtoCharmDecayVertexMergerT<reco::Vertex>::buildVertexProxy(
    const reco::Vertex &vtx) {
  VertexProxy vtxProxy = {vtx, vtx.p4().M(), vtx.tracksSize()};
  return vtxProxy;
}
 
template <>
BtoCharmDecayVertexMergerT<reco::VertexCompositePtrCandidate>::VertexProxy
BtoCharmDecayVertexMergerT<reco::VertexCompositePtrCandidate>::buildVertexProxy(
    const reco::VertexCompositePtrCandidate &vtx) {
  VertexProxy vtxProxy = {vtx, vtxP4(vtx).M(), vtx.numberOfSourceCandidatePtrs()};
  return vtxProxy;
}
 
// -------------- resolveBtoDchain ----------------
template <>
void BtoCharmDecayVertexMergerT<reco::Vertex>::resolveBtoDchain(std::vector<VertexProxy> &coll,
                                                                unsigned int i,
                                                                unsigned int k) {
  using namespace reco;
 
  GlobalVector momentum1 = GlobalVector(coll[i].vert.p4().X(), coll[i].vert.p4().Y(), coll[i].vert.p4().Z());
  GlobalVector momentum2 = GlobalVector(coll[k].vert.p4().X(), coll[k].vert.p4().Y(), coll[k].vert.p4().Z());
 
  SecondaryVertex sv1(pv, coll[i].vert, momentum1, true);
  SecondaryVertex sv2(pv, coll[k].vert, momentum2, true);
 
  // find out which one is near and far
  SecondaryVertex svNear = sv1;
  SecondaryVertex svFar = sv2;
  GlobalVector momentumNear = momentum1;
  GlobalVector momentumFar = momentum2;
 
  // swap if it is the other way around
  if (sv1.dist3d().value() >= sv2.dist3d().value()) {
    svNear = sv2;
    svFar = sv1;
    momentumNear = momentum2;
    momentumFar = momentum1;
  }
  GlobalVector nearToFar = flightDirection(svNear, svFar);
  GlobalVector pvToNear = flightDirection(pv, svNear);
  GlobalVector pvToFar = flightDirection(pv, svFar);
 
  double cosPA = nearToFar.dot(momentumFar) / momentumFar.mag() / nearToFar.mag();
  double cosa = pvToNear.dot(momentumFar) / pvToNear.mag() / momentumFar.mag();
  double ptrel = sqrt(1.0 - cosa * cosa) * momentumFar.mag();
 
  double vertexDeltaR = Geom::deltaR(pvToNear, pvToFar);
 
  // create a set of all tracks from both vertices, avoid double counting by using a std::set<>
  std::set<reco::TrackRef> trackrefs;
  // first vertex
  for (reco::Vertex::trackRef_iterator ti = sv1.tracks_begin(); ti != sv1.tracks_end(); ++ti) {
    if (sv1.trackWeight(*ti) > 0.5) {
      reco::TrackRef t = ti->castTo<reco::TrackRef>();
      trackrefs.insert(t);
    }
  }
  // second vertex
  for (reco::Vertex::trackRef_iterator ti = sv2.tracks_begin(); ti != sv2.tracks_end(); ++ti) {
    if (sv2.trackWeight(*ti) > 0.5) {
      reco::TrackRef t = ti->castTo<reco::TrackRef>();
      trackrefs.insert(t);
    }
  }
 
  // now calculate one LorentzVector from the track momenta
  ROOT::Math::LorentzVector<ROOT::Math::PxPyPzM4D<double>> mother;
  for (std::set<reco::TrackRef>::const_iterator it = trackrefs.begin(); it != trackrefs.end(); ++it) {
    ROOT::Math::LorentzVector<ROOT::Math::PxPyPzM4D<double>> temp(
        (*it)->px(), (*it)->py(), (*it)->pz(), ParticleMasses::piPlus);
    mother += temp;
  }
 
  //   check if criteria for merging are fulfilled
  if (vertexDeltaR < maxDRForUnique && mother.M() < maxvecSumIMCUTForUnique && cosPA > minCosPAtomerge &&
      std::abs(ptrel) < maxPtreltomerge) {
    // add tracks of second vertex which are missing to first vertex
    // loop over the second
    bool bFoundDuplicate = false;
    for (reco::Vertex::trackRef_iterator ti = sv2.tracks_begin(); ti != sv2.tracks_end(); ++ti) {
      reco::Vertex::trackRef_iterator it = find(sv1.tracks_begin(), sv1.tracks_end(), *ti);
      if (it == sv1.tracks_end())
        coll[i].vert.add(*ti, sv2.refittedTrack(*ti), sv2.trackWeight(*ti));
      else
        bFoundDuplicate = true;
    }
    // in case a duplicate track is found, need to create the full track list in the vertex from scratch because we need to modify the weight.
    // the weight must be the larger one, otherwise we may have outliers which are not real outliers
 
    if (bFoundDuplicate) {
      // create backup track containers from main vertex
      std::vector<TrackBaseRef> tracks_;
      std::vector<Track> refittedTracks_;
      std::vector<float> weights_;
      for (reco::Vertex::trackRef_iterator it = coll[i].vert.tracks_begin(); it != coll[i].vert.tracks_end(); ++it) {
        tracks_.push_back(*it);
        refittedTracks_.push_back(coll[i].vert.refittedTrack(*it));
        weights_.push_back(coll[i].vert.trackWeight(*it));
      }
      // delete tracks and add all tracks back, and check in which vertex the weight is larger
      coll[i].vert.removeTracks();
      std::vector<Track>::iterator it2 = refittedTracks_.begin();
      std::vector<float>::iterator it3 = weights_.begin();
      for (reco::Vertex::trackRef_iterator it = tracks_.begin(); it != tracks_.end(); ++it, ++it2, ++it3) {
        float weight = *it3;
        float weight2 = sv2.trackWeight(*it);
        Track refittedTrackWithLargerWeight = *it2;
        if (weight2 > weight) {
          weight = weight2;
          refittedTrackWithLargerWeight = sv2.refittedTrack(*it);
        }
        coll[i].vert.add(*it, refittedTrackWithLargerWeight, weight);
      }
    }
 
    // remove the second vertex from the collection
    coll.erase(coll.begin() + k);
  }
}
 
template <>
void BtoCharmDecayVertexMergerT<reco::VertexCompositePtrCandidate>::resolveBtoDchain(std::vector<VertexProxy> &coll,
                                                                                     unsigned int i,
                                                                                     unsigned int k) {
  using namespace reco;
 
  Candidate::LorentzVector vtx1P4 = vtxP4(coll[i].vert);
  Candidate::LorentzVector vtx2P4 = vtxP4(coll[k].vert);
  GlobalVector momentum1 = GlobalVector(vtx1P4.X(), vtx1P4.Y(), vtx1P4.Z());
  GlobalVector momentum2 = GlobalVector(vtx2P4.X(), vtx2P4.Y(), vtx2P4.Z());
 
  SecondaryVertex sv1(pv, coll[i].vert, momentum1, true);
  SecondaryVertex sv2(pv, coll[k].vert, momentum2, true);
 
  // find out which one is near and far
  SecondaryVertex svNear = sv1;
  SecondaryVertex svFar = sv2;
  GlobalVector momentumNear = momentum1;
  GlobalVector momentumFar = momentum2;
 
  // swap if it is the other way around
  if (sv1.dist3d().value() >= sv2.dist3d().value()) {
    svNear = sv2;
    svFar = sv1;
    momentumNear = momentum2;
    momentumFar = momentum1;
  }
  GlobalVector nearToFar = flightDirection(svNear, svFar);
  GlobalVector pvToNear = flightDirection(pv, svNear);
  GlobalVector pvToFar = flightDirection(pv, svFar);
 
  double cosPA = nearToFar.dot(momentumFar) / momentumFar.mag() / nearToFar.mag();
  double cosa = pvToNear.dot(momentumFar) / pvToNear.mag() / momentumFar.mag();
  double ptrel = sqrt(1.0 - cosa * cosa) * momentumFar.mag();
 
  double vertexDeltaR = Geom::deltaR(pvToNear, pvToFar);
 
  // create a set of all tracks from both vertices, avoid double counting by using a std::set<>
  std::set<reco::CandidatePtr> trackrefs;
  // first vertex
  for (size_t i = 0; i < sv1.numberOfSourceCandidatePtrs(); ++i)
    trackrefs.insert(sv1.daughterPtr(i));
  // second vertex
  for (size_t i = 0; i < sv2.numberOfSourceCandidatePtrs(); ++i)
    trackrefs.insert(sv2.daughterPtr(i));
 
  // now calculate one LorentzVector from the track momenta
  Candidate::LorentzVector mother;
  for (std::set<reco::CandidatePtr>::const_iterator it = trackrefs.begin(); it != trackrefs.end(); ++it) {
    Candidate::LorentzVector temp((*it)->px(), (*it)->py(), (*it)->pz(), ParticleMasses::piPlus);
    mother += temp;
  }
 
  //   check if criteria for merging are fulfilled
  if (vertexDeltaR < maxDRForUnique && mother.M() < maxvecSumIMCUTForUnique && cosPA > minCosPAtomerge &&
      std::abs(ptrel) < maxPtreltomerge) {
    // add tracks of second vertex which are missing to first vertex
    // loop over the second
    const std::vector<reco::CandidatePtr> &tracks1 = sv1.daughterPtrVector();
    const std::vector<reco::CandidatePtr> &tracks2 = sv2.daughterPtrVector();
    for (std::vector<reco::CandidatePtr>::const_iterator ti = tracks2.begin(); ti != tracks2.end(); ++ti) {
      std::vector<reco::CandidatePtr>::const_iterator it = find(tracks1.begin(), tracks1.end(), *ti);
      if (it == tracks1.end()) {
        coll[i].vert.addDaughter(*ti);
        coll[i].vert.setP4((*ti)->p4() + coll[i].vert.p4());
      }
    }
 
    // remove the second vertex from the collection
    coll.erase(coll.begin() + k);
  }
}
 
// define specific instances of the templated BtoCharmDecayVertexMergerT class
typedef BtoCharmDecayVertexMergerT<reco::Vertex> BtoCharmDecayVertexMerger;
typedef BtoCharmDecayVertexMergerT<reco::VertexCompositePtrCandidate> CandidateBtoCharmDecayVertexMerger;
 
// define plugins
DEFINE_FWK_MODULE(BtoCharmDecayVertexMerger);
DEFINE_FWK_MODULE(CandidateBtoCharmDecayVertexMerger);