KFitV0VertexFitter Class Reference

V0 vertex fitter using KFit. More...

#include <KFitV0VertexFitter.h>

Inheritance diagram for KFitV0VertexFitter:

Public Member Functions
bool	fit (genfit::Track &trackPlus, genfit::Track &trackMinus, const int pdgTrackPlus, const int pdgTrackMinus, genfit::GFRaveVertex &vertex) override
	Fit the V0 vertex. The PDG codes of the daughters are used to compute their energies.
std::string	getName () const override
	Get the name this fitter is registered with in the V0VertexFitterFactory.

Detailed Description

V0 vertex fitter using KFit.

Definition at line 19 of file KFitV0VertexFitter.h.

Member Function Documentation

fit()

bool fit ( genfit::Track & trackPlus, genfit::Track & trackMinus, const int pdgTrackPlus, const int pdgTrackMinus, genfit::GFRaveVertex & vertex )

overridevirtual

Fit the V0 vertex. The PDG codes of the daughters are used to compute their energies.

Implements V0VertexFitter.

Definition at line 103 of file KFitV0VertexFitter.cc.

{
  analysis::VertexFitKFit vertexFit;
  // KFit defaults to KFitConst::kDefaultMagneticField:
  // use instead the same magnetic field used elsewhere in the V0Fitter
  vertexFit.setMagneticField(getMagneticField());
 
  EvtGenDatabasePDG* pdgDB = EvtGenDatabasePDG::Instance();
 
  auto addTrackToFit =
  [&](const genfit::Track & track, const int pdg) {
    const TParticlePDG* particle = pdgDB->GetParticle(pdg);
    if (not particle) {
      B2ERROR("Unknown PDG code of the daughter hypothesis." << LogVar("PDG code", pdg));
      return false;
    }
    TVector3 pos;
    TVector3 mom;
    // KFit needs the 7x7 cov. matrix, not the 6x6 one:
    // in the 6x6 one, correlations with E are missing.
    TMatrixDSym cov6;
    const genfit::MeasuredStateOnPlane state = track.getFittedState();
    state.getPosMomCov(pos, mom, cov6);
    // the mass is used only to complete the energy: the vertex fit itself drops it
    const double mass = particle->Mass();
    const CLHEP::HepLorentzVector clhepMom(mom.X(), mom.Y(), mom.Z(), std::sqrt(mom.Mag2() + mass * mass));
    const HepGeom::Point3D<double> clhepPos(pos.X(), pos.Y(), pos.Z());
    // This is now good for KFit
    const CLHEP::HepSymMatrix clhepCov7 = makeCov7x7(cov6, clhepMom);
    const int charge = track.getFitStatus()->getCharge();
 
    vertexFit.addTrack(clhepMom, clhepPos, clhepCov7, charge);
    return true;
  };
 
  try {
    if (not addTrackToFit(trackPlus, pdgTrackPlus)) return false;
    if (not addTrackToFit(trackMinus, pdgTrackMinus)) return false;
  } catch (...) {
    B2ERROR("Exception during vertex fit.");
    return false;
  }
 
  const bool ok = (vertexFit.doFit() == analysis::KFitError::kNoError);
  if (!ok) return false;
 
  const HepGeom::Point3D<double> posVertex = vertexFit.getVertex();
  const CLHEP::HepSymMatrix covVertex = vertexFit.getVertexError();
  const TVector3 extrapolationTarget(posVertex.x(), posVertex.y(), posVertex.z());
 
  std::vector<genfit::GFRaveTrackParameters*> trackParamsVertex;
  trackParamsVertex.reserve(2);
  for (int i = 0; i <= 1; ++i) {
    const genfit::Track& daughter = i == 0 ? trackPlus : trackMinus;
    // KFit gives back the daughter parameters at the reference point of the track:
    // the momentum there points elsewhere than at the vertex. Transport the daughter
    // to the vertex position with genfit instead.
    TVector3 pos;
    TVector3 mom;
    TMatrixDSym cov6;
    try {
      genfit::MeasuredStateOnPlane daughterState = daughter.getFittedState();
      daughterState.extrapolateToPoint(extrapolationTarget);
      daughterState.getPosMomCov(pos, mom, cov6);
    } catch (...) {
      B2ERROR("Exception while extrapolating a daughter to the fitted vertex.");
      for (auto* trackParams : trackParamsVertex) delete trackParams;
      return false;
    }
    TVectorD state{6};
    state[0] = pos.X();
    state[1] = pos.Y();
    state[2] = pos.Z();
    state[3] = mom.X();
    state[4] = mom.Y();
    state[5] = mom.Z();
    genfit::GFRaveTrackParameters* trackParams = new genfit::GFRaveTrackParameters(nullptr, nullptr, 1, state, cov6, true);
    trackParamsVertex.push_back(trackParams);
  }
  const double ndfVertex = static_cast<double>(vertexFit.getNDF());
  const double chisqVertex = vertexFit.getCHIsq();
 
  vertex = genfit::GFRaveVertex{TVector3{posVertex.x(), posVertex.y(), posVertex.z()}, CLHEPToROOT::getTMatrixDSym(covVertex), trackParamsVertex, ndfVertex, chisqVertex};
 
  return true;
}

getName()

std::string getName ( ) const

inlineoverridevirtual

Get the name this fitter is registered with in the V0VertexFitterFactory.

Implements V0VertexFitter.

Definition at line 29 of file KFitV0VertexFitter.h.

{return "KFit";}

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The documentation for this class was generated from the following files:

• tracking/v0Finding/fitter/include/KFitV0VertexFitter.h
• tracking/v0Finding/fitter/src/KFitV0VertexFitter.cc