InvariantMassFromVertex.cc

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#include "RecoVertex/VertexTools/interface/InvariantMassFromVertex.h"
#include "FWCore/MessageLogger/interface/MessageLogger.h"

InvariantMassFromVertex::LorentzVector InvariantMassFromVertex::p4(const CachingVertex<5>& vertex,
                                                                   const double mass) const {
  return p4(vertex, std::vector<double>(vertex.tracks().size(), mass));
}

InvariantMassFromVertex::LorentzVector InvariantMassFromVertex::p4(const CachingVertex<5>& vertex,
                                                                   const std::vector<double>& masses) const {
  LorentzVector totalP4;

  // Check that tkToTkCovarianceIsAvailable
  if (!vertex.tkToTkCovarianceIsAvailable()) {
    LogDebug("InvariantMassFromVertex") << "Fit failed: vertex has not been smoothed\n";
    return totalP4;
  }

  if (vertex.tracks().size() != masses.size()) {
    LogDebug("InvariantMassFromVertex") << "Vector of masses does not have the same size as tracks in vertex\n";
    return totalP4;
  }

  std::vector<RefCountedVertexTrack> refTracks = vertex.tracks();
  std::vector<RefCountedVertexTrack>::const_iterator i_s = refTracks.begin();
  std::vector<double>::const_iterator i_m = masses.begin();

  for (; i_s != refTracks.end() && i_m != masses.end(); ++i_s, ++i_m) {
    GlobalVector momentum = (**i_s).refittedState()->freeTrajectoryState().momentum();
    totalP4 += LorentzVector(momentum.x(), momentum.y(), momentum.z(), *i_m);
  }
  return totalP4;
}

GlobalVector InvariantMassFromVertex::momentum(const CachingVertex<5>& vertex) const {
  GlobalVector momentum_;

  // Check that tkToTkCovarianceIsAvailable
  if (!vertex.tkToTkCovarianceIsAvailable()) {
    LogDebug("InvariantMassFromVertex") << "Fit failed: vertex has not been smoothed\n";
    return momentum_;
  }

  std::vector<RefCountedVertexTrack> refTracks = vertex.tracks();
  std::vector<RefCountedVertexTrack>::const_iterator i_s = refTracks.begin();

  for (; i_s != refTracks.end(); ++i_s) {
    momentum_ += (**i_s).refittedState()->freeTrajectoryState().momentum();
  }
  return momentum_;
}

Measurement1D InvariantMassFromVertex::invariantMass(const CachingVertex<5>& vertex, const double mass) const {
  return invariantMass(vertex, std::vector<double>(vertex.tracks().size(), mass));
}

Measurement1D InvariantMassFromVertex::invariantMass(const CachingVertex<5>& vertex,
                                                     const std::vector<double>& masses) const {
  // Check that tkToTkCovarianceIsAvailable
  if (!vertex.tkToTkCovarianceIsAvailable()) {
    LogDebug("InvariantMassFromVertex") << "Fit failed: vertex has not been smoothed\n";
    return Measurement1D(0., 0.);
  }
  if (vertex.tracks().size() != masses.size()) {
    LogDebug("InvariantMassFromVertex") << "Vector of masses does not have the same size as tracks in vertex\n";
    return Measurement1D(0., 0.);
  }

  LorentzVector totalP4 = p4(vertex, masses);
  double u = uncertainty(totalP4, vertex, masses);
  // std::cout << u<<std::endl;
  return Measurement1D(totalP4.M(), u);
}

//method returning the full covariance matrix
//of new born kinematic particle
double InvariantMassFromVertex::uncertainty(const LorentzVector& totalP4,
                                            const CachingVertex<5>& vertex,
                                            const std::vector<double>& masses) const {
  std::vector<RefCountedVertexTrack> refTracks = vertex.tracks();
  int size = refTracks.size();
  AlgebraicMatrix cov(3 * size, 3 * size);
  AlgebraicMatrix jac(1, 3 * size);

  double energy_total = totalP4.E();

  std::vector<RefCountedVertexTrack>::const_iterator rt_i = refTracks.begin();
  std::vector<double>::const_iterator i_m = masses.begin();

  int i_int = 0;
  for (; rt_i != refTracks.end() && i_m != masses.end(); ++rt_i, ++i_m) {
    double a;
    AlgebraicVector5 param = (**rt_i).refittedState()->parameters();  // rho, theta, phi,tr_im, z_im
    double rho = param[0];
    double theta = param[1];
    double phi = param[2];
    double mass = *i_m;

    if ((**rt_i).linearizedTrack()->charge() != 0) {
      a = -(**rt_i).refittedState()->freeTrajectoryState().parameters().magneticFieldInInverseGeV(vertex.position()).z() *
          (**rt_i).refittedState()->freeTrajectoryState().parameters().charge();
      if (a == 0.)
        throw cms::Exception("InvariantMassFromVertex", "Field is 0");
    } else {
      a = 1;
    }

    double energy_local = sqrt(a * a / (rho * rho) * (1 + 1 / (tan(theta) * tan(theta))) + mass * mass);

    jac(1, i_int * 3 + 1) = (-(energy_total / energy_local * a * a / (rho * rho * rho * sin(theta) * sin(theta))) +
                             totalP4.X() * a / (rho * rho) * cos(phi) + totalP4.Y() * a / (rho * rho) * sin(phi) +
                             totalP4.Z() * a / (rho * rho * tan(theta))) /
                            totalP4.M();  //dm / drho

    jac(1, i_int * 3 + 2) =
        (-(energy_total / energy_local * a * a / (rho * rho * sin(theta) * sin(theta) * tan(theta))) +
         totalP4.Z() * a / (rho * sin(theta) * sin(theta))) /
        totalP4.M();  //dm d theta

    jac(1, i_int * 3 + 3) = (totalP4.X() * sin(phi) - totalP4.Y() * cos(phi)) * a / (rho * totalP4.M());  //dm/dphi

    // momentum corellatons: diagonal elements of the matrix
    cov.sub(i_int * 3 + 1, i_int * 3 + 1, asHepMatrix<6>((**rt_i).fullCovariance()).sub(4, 6));

    //off diagonal elements: track momentum - track momentum corellations

    int j_int = 0;
    for (std::vector<RefCountedVertexTrack>::const_iterator rt_j = refTracks.begin(); rt_j != refTracks.end(); rt_j++) {
      if (i_int < j_int) {
        AlgebraicMatrix i_k_cov_m = asHepMatrix<3, 3>(vertex.tkToTkCovariance((*rt_i), (*rt_j)));
        cov.sub(i_int * 3 + 1, j_int * 3 + 1, i_k_cov_m);
        cov.sub(j_int * 3 + 1, i_int * 3 + 1, i_k_cov_m.T());
      }
      j_int++;
    }
    i_int++;
  }
  //   std::cout<<"jac"<<jac<<std::endl;
  //   std::cout<<"cov"<<cov<<std::endl;
  //   std::cout << "final result"<<(jac*cov*jac.T())<<std::endl;

  return sqrt((jac * cov * jac.T())(1, 1));
}