PFDisplacedVertexCandidateFinder.cc

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#include "RecoParticleFlow/PFTracking/interface/PFDisplacedVertexCandidateFinder.h"

#include "DataFormats/GeometryVector/interface/GlobalVector.h"
#include "DataFormats/TrackReco/interface/Track.h"
#include "DataFormats/VertexReco/interface/Vertex.h"

#include "MagneticField/Engine/interface/MagneticField.h"

using namespace std;
using namespace reco;

//for debug only
//#define PFLOW_DEBUG

PFDisplacedVertexCandidateFinder::PFDisplacedVertexCandidateFinder()
    : vertexCandidates_(new PFDisplacedVertexCandidateCollection),
      dcaCut_(1000),
      primaryVertexCut2_(0.0),
      dcaPInnerHitCut2_(1000.0),
      vertexCandidatesSize_(50),
      theMinimum_(TwoTrackMinimumDistance::SlowMode),
      debug_(false),
      magField_(nullptr) {}

PFDisplacedVertexCandidateFinder::~PFDisplacedVertexCandidateFinder() {
#ifdef PFLOW_DEBUG
  if (debug_)
    cout << "~PFDisplacedVertexCandidateFinder - number of remaining elements: " << eventTracks_.size() << endl;
#endif
}

void PFDisplacedVertexCandidateFinder::setPrimaryVertex(edm::Handle<reco::VertexCollection> mainVertexHandle,
                                                        edm::Handle<reco::BeamSpot> beamSpotHandle) {
  const math::XYZPoint beamSpot = beamSpotHandle.isValid()
                                      ? math::XYZPoint(beamSpotHandle->x0(), beamSpotHandle->y0(), beamSpotHandle->z0())
                                      : math::XYZPoint(0, 0, 0);

  // The primary vertex is taken from the refitted list,
  // if does not exist from the average offline beam spot position
  // if does not exist (0,0,0) is used
  pvtx_ = mainVertexHandle.isValid()
              ? math::XYZPoint(
                    mainVertexHandle->begin()->x(), mainVertexHandle->begin()->y(), mainVertexHandle->begin()->z())
              : beamSpot;
}

// Set the imput collection of tracks and calculate their
// trajectory parameters the Global Trajectory Parameters
void PFDisplacedVertexCandidateFinder::setInput(const edm::Handle<TrackCollection>& trackh,
                                                const MagneticField* magField) {
  magField_ = magField;
  trackMask_.clear();
  trackMask_.resize(trackh->size());
  eventTrackTrajectories_.clear();
  eventTrackTrajectories_.resize(trackh->size());

  for (unsigned i = 0; i < trackMask_.size(); i++)
    trackMask_[i] = true;

  eventTracks_.clear();
  if (trackh.isValid()) {
    for (unsigned i = 0; i < trackh->size(); i++) {
      TrackRef tref(trackh, i);
      TrackBaseRef tbref(tref);

      if (!isSelected(tbref)) {
        trackMask_[i] = false;
        continue;
      }

      const Track* trk = tref.get();
      eventTracks_.push_back(tbref);
      eventTrackTrajectories_[i] = getGlobalTrajectoryParameters(trk);
    }
  }
}

// -------- Main function which find vertices -------- //

void PFDisplacedVertexCandidateFinder::findDisplacedVertexCandidates() {
  if (debug_)
    cout << "========= Start Finding Displaced Vertex Candidates =========" << endl;

  // The vertexCandidates have not been passed to the event, and need to be cleared
  if (vertexCandidates_.get())
    vertexCandidates_->clear();
  else
    vertexCandidates_.reset(new PFDisplacedVertexCandidateCollection);

  vertexCandidates_->reserve(vertexCandidatesSize_);
  for (IE ie = eventTracks_.begin(); ie != eventTracks_.end();) {
    // Run the recursive procedure to find all tracks link together
    // In one blob called Candidate

    PFDisplacedVertexCandidate tempVertexCandidate;

    ie = associate(eventTracks_.end(), ie, tempVertexCandidate);

    // Build remaining links in current block
    if (tempVertexCandidate.isValid()) {
      packLinks(tempVertexCandidate);
      vertexCandidates_->push_back(tempVertexCandidate);
    }
  }

  if (debug_)
    cout << "========= End Finding Displaced Vertex Candidates =========" << endl;
}

PFDisplacedVertexCandidateFinder::IE PFDisplacedVertexCandidateFinder::associate(
    IE last, IE next, PFDisplacedVertexCandidate& tempVertexCandidate) {
#ifdef PFLOW_DEBUG
  if (debug_)
    cout << "== Start the association procedure ==" << endl;
#endif

  if (last != eventTracks_.end()) {
    double dist = -1;
    GlobalPoint P(0, 0, 0);
    PFDisplacedVertexCandidate::VertexLinkTest linktest;
    link((*last), (*next), dist, P, linktest);

    if (dist < -0.5) {
#ifdef PFLOW_DEBUG
      if (debug_)
        cout << "link failed" << endl;
#endif
      return ++next;  // association failed
    } else {
      // add next element to the current pflowblock
      tempVertexCandidate.addElement((*next));
      trackMask_[(*next).key()] = false;
#ifdef PFLOW_DEBUG
      if (debug_)
        cout << "link parameters "
             << " *next = " << (*next).key() << " *last = " << (*last).key() << "  dist = " << dist
             << " P.x = " << P.x() << " P.y = " << P.y() << " P.z = " << P.z() << endl;
#endif
    }
  } else {
    // add next element to this eflowblock
#ifdef PFLOW_DEBUG
    if (debug_)
      cout << "adding to block element " << (*next).key() << endl;
#endif
    tempVertexCandidate.addElement((*next));
    trackMask_[(*next).key()] = false;
  }

  // recursive call: associate next and other unused elements
#ifdef PFLOW_DEBUG
  if (debug_) {
    for (unsigned i = 0; i < trackMask_.size(); i++)
      cout << " Mask[" << i << "] = " << trackMask_[i];
    cout << "" << endl;
  }
#endif

  for (IE ie = eventTracks_.begin(); ie != eventTracks_.end();) {
    if (ie == last || ie == next) {
      ++ie;
      continue;
    }

    // *ie already included to a block
    if (!trackMask_[(*ie).key()]) {
      ++ie;
      continue;
    }

#ifdef PFLOW_DEBUG
    if (debug_)
      cout << "calling associate " << (*next).key() << " & " << (*ie).key() << endl;
#endif
    ie = associate(next, ie, tempVertexCandidate);
  }

#ifdef PFLOW_DEBUG
  if (debug_) {
    cout << "**** removing element " << endl;
  }
#endif

  IE iteratorToNextFreeElement = eventTracks_.erase(next);

#ifdef PFLOW_DEBUG
  if (debug_)
    cout << "== End the association procedure ==" << endl;
#endif

  return iteratorToNextFreeElement;
}

void PFDisplacedVertexCandidateFinder::link(const TrackBaseRef& el1,
                                            const TrackBaseRef& el2,
                                            double& dist,
                                            GlobalPoint& P,
                                            PFDisplacedVertexCandidate::VertexLinkTest& vertexLinkTest) {
  if (fabs(el1->eta() - el2->eta()) > 1) {
    dist = -1;
    return;
  }
  if (el1->pt() > 2 && el2->pt() > 2 && fabs(el1->phi() - el2->phi()) > 1) {
    dist = -1;
    return;
  }

  const GlobalTrajectoryParameters& gt1 = eventTrackTrajectories_[el1.key()];
  const GlobalTrajectoryParameters& gt2 = eventTrackTrajectories_[el2.key()];

  // Closest approach
  theMinimum_.calculate(gt1, gt2);

  // Fill the parameters
  dist = theMinimum_.distance();
  P = theMinimum_.crossingPoint();

  vertexLinkTest = PFDisplacedVertexCandidate::LINKTEST_DCA;  //rechit by default

  // Check if the link test fails
  if (dist > dcaCut_) {
    dist = -1;
    return;
  }

  // Check if the closses approach point is too close to the primary vertex/beam pipe
  double rho2 = P.x() * P.x() + P.y() * P.y();

  if (rho2 < primaryVertexCut2_) {
    dist = -1;
    return;
  }

  // Check if the closses approach point is out of range of the tracker

  double tob_rho_limit2 = 10000;
  double tec_z_limit = 270;

  if (rho2 > tob_rho_limit2) {
    dist = -1;
    return;
  }
  if (fabs(P.z()) > tec_z_limit) {
    dist = -1;
    return;
  }

  return;

  /*
  // Check if the inner hit of one of the tracks is not too far away from the vertex
  double dx = el1->innerPosition().x()-P.x();
  double dy = el1->innerPosition().y()-P.y();
  double dz = el1->innerPosition().z()-P.z();
  double dist2 = dx*dx+dy*dy+dz*dz; 

  if (dist2 > dcaPInnerHitCut2_) {
    dist = -1; 
    if (debug_) cout << "track " << el1.key() << " dist to vertex " << sqrt(dist2) << endl; 
    return;
  }

  dx = el2->innerPosition().x()-P.x();
  dy = el2->innerPosition().y()-P.y();
  dz = el2->innerPosition().z()-P.z();
  dist2 = dx*dx+dy*dy+dz*dz; 

  if (dist2 > dcaPInnerHitCut2_) {
    dist = -1; 
    if (debug_) cout << "track " << el2.key() << " dist to vertex " << sqrt(dist2) << endl; 
    return;
  }
  */
}

// Build up a matrix of all the links between different tracks in
// In the Candidate
void PFDisplacedVertexCandidateFinder::packLinks(PFDisplacedVertexCandidate& vertexCandidate) {
  const vector<TrackBaseRef>& els = vertexCandidate.elements();

  //First Loop: update all link data
  for (unsigned i1 = 0; i1 < els.size(); i1++) {
    for (unsigned i2 = i1 + 1; i2 < els.size(); i2++) {
      // no reflexive link
      if (i1 == i2)
        continue;

      double dist = -1;
      GlobalPoint P(0, 0, 0);
      PFDisplacedVertexCandidate::VertexLinkTest linktest;

      link(els[i1], els[i2], dist, P, linktest);

#ifdef PFLOW_DEBUG
      if (debug_)
        cout << "Setting link between elements " << i1 << " key " << els[i1].key() << " and " << i2 << " key "
             << els[i2].key() << " of dist =" << dist << " computed from link test " << linktest << endl;
#endif

      if (dist > -0.5)
        vertexCandidate.setLink(i1, i2, dist, P, linktest);
    }
  }
}

// --------------- TOOLS -------------- //

// This tool is a copy from VZeroFinder
GlobalTrajectoryParameters PFDisplacedVertexCandidateFinder::getGlobalTrajectoryParameters(const Track* track) const {
  const GlobalPoint position(track->vx(), track->vy(), track->vz());

  const GlobalVector momentum(track->momentum().x(), track->momentum().y(), track->momentum().z());

  GlobalTrajectoryParameters gtp(position, momentum, track->charge(), magField_);

  return gtp;
}

// This tool allow to pre-select the track for the displaced vertex finder
bool PFDisplacedVertexCandidateFinder::goodPtResolution(const TrackBaseRef& trackref) const {
  double nChi2 = trackref->normalizedChi2();
  double pt = trackref->pt();
  double dpt = trackref->ptError();
  double dxy = trackref->dxy(pvtx_);

  double pt_error = dpt / pt * 100;

  if (debug_)
    cout << " PFDisplacedVertexFinder: PFrecTrack->Track Pt= " << pt << " dPt/Pt = " << pt_error
         << "% nChi2 = " << nChi2 << endl;
  if (nChi2 > nChi2_max_ || pt < pt_min_) {
    if (debug_)
      cout << " PFBlockAlgo: skip badly measured or low pt track"
           << " nChi2_cut = " << 5 << " pt_cut = " << 0.2 << endl;
    return false;
  }
  //  cout << "dxy = " << dxy << endl;
  if (fabs(dxy) < dxy_ && pt < pt_min_prim_)
    return false;
  //  if (fabs(dxy) < 0.2 && pt < 0.8) return false;

  return true;
}

ostream& operator<<(std::ostream& out, const PFDisplacedVertexCandidateFinder& a) {
  if (!out)
    return out;

  out << "====== Particle Flow Block Algorithm ======= ";
  out << endl;
  out << "number of unassociated elements : " << a.eventTracks_.size() << endl;
  out << endl;

  out << " Tracks selection based on " << std::endl;
  out << " pvtx_ = " << a.pvtx_ << std::endl;
  out << " fabs(dxy) < " << a.dxy_ << " and pt < " << a.pt_min_prim_ << std::endl;
  out << " nChi2 < " << a.nChi2_max_ << " and pt < " << a.pt_min_ << std::endl;

  out << endl;

  for (PFDisplacedVertexCandidateFinder::IEC ie = a.eventTracks_.begin(); ie != a.eventTracks_.end(); ie++) {
    double pt = (*ie).get()->pt();

    math::XYZPoint Pi = (*ie).get()->innerPosition();
    math::XYZPoint Po = (*ie).get()->outerPosition();

    double innermost_radius = sqrt(Pi.x() * Pi.x() + Pi.y() * Pi.y() + Pi.z() * Pi.z());
    double outermost_radius = sqrt(Po.x() * Po.x() + Po.y() * Po.y() + Po.z() * Po.z());
    double innermost_rho = sqrt(Pi.x() * Pi.x() + Pi.y() * Pi.y());
    double outermost_rho = sqrt(Po.x() * Po.x() + Po.y() * Po.y());

    out << "ie = " << (*ie).key() << " pt = " << pt << " innermost hit radius = " << innermost_radius
        << " rho = " << innermost_rho << " outermost hit radius = " << outermost_radius << " rho = " << outermost_rho
        << endl;
  }

  const std::unique_ptr<reco::PFDisplacedVertexCandidateCollection>& vertexCandidates = std::move(a.vertexCandidates());

  if (!vertexCandidates.get()) {
    out << "vertexCandidates already transfered" << endl;
  } else {
    out << "number of vertexCandidates : " << vertexCandidates->size() << endl;
    out << endl;

    for (PFDisplacedVertexCandidateFinder::IBC ib = vertexCandidates->begin(); ib != vertexCandidates->end(); ib++)
      ib->Dump();
  }

  return out;
}