TauA1NuConstrainedFitter.cc

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/* From SimpleFits Package
 * Designed an written by
 * author: Ian M. Nugent
 * Humboldt Foundations
 */
#include <functional>
#include <cmath>
#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include "RecoTauTag/ImpactParameter/interface/TauA1NuConstrainedFitter.h"
#include "RecoTauTag/ImpactParameter/interface/PDGInfo.h"
#include <iostream>
 
using namespace tauImpactParameter;
 
TauA1NuConstrainedFitter::TauA1NuConstrainedFitter(unsigned int ambiguity,
                                                   const LorentzVectorParticle& A1,
                                                   const TVector3& PVertex,
                                                   const TMatrixTSym<double>& VertexCov)
    : MultiProngTauSolver(), ambiguity_(ambiguity) {
  TLorentzVector Tau(0, 0, 0, 0);
  //dummy substitution not used later
  TVectorT<double> nu_par(LorentzVectorParticle::NLorentzandVertexPar, 1);
  TMatrixTSym<double> nu_cov(LorentzVectorParticle::NLorentzandVertexPar);
  LorentzVectorParticle Nu(nu_par, nu_cov, PDGInfo::nu_tau, 0.0, A1.bField());
  particles_.push_back(A1);
  particles_.push_back(Nu);
 
  // setup 13 by 13 matrix
  int size = LorentzVectorParticle::NVertex + particles_.size() * LorentzVectorParticle::NLorentzandVertexPar;
  TVectorT<double> inpar(size);
  TMatrixTSym<double> incov(size);
 
  // Get primary vertex information
  if (VertexCov.GetNrows() != LorentzVectorParticle::NVertex)
    return;
  inpar(LorentzVectorParticle::vx) = PVertex.X();
  inpar(LorentzVectorParticle::vy) = PVertex.Y();
  inpar(LorentzVectorParticle::vz) = PVertex.Z();
  for (int i = 0; i < LorentzVectorParticle::NVertex; i++) {
    for (int j = 0; j < LorentzVectorParticle::NVertex; j++)
      incov(i, j) = VertexCov(i, j);
  }
  int A1offset = LorentzVectorParticle::NVertex;
  int Nuoffset = LorentzVectorParticle::NLorentzandVertexPar + LorentzVectorParticle::NVertex;
  for (int i = 0; i < LorentzVectorParticle::NLorentzandVertexPar; i++) {
    inpar(i + A1offset) = A1.parameter(i);
    inpar(i + Nuoffset) = Nu.parameter(i) + 1.0;  // offset by 1 GeV to prevent convergence on first iteration
    for (int j = 0; j < LorentzVectorParticle::NLorentzandVertexPar; j++) {
      incov(i + A1offset, j + A1offset) = A1.covariance(i, j);
      incov(i + Nuoffset, j + Nuoffset) = Nu.covariance(i, j);
    }
  }
 
  exppar.ResizeTo(nexpandedpar, 1);
  exppar = ComputeInitalExpPar(inpar);
  expcov.ResizeTo(nexpandedpar, nexpandedpar);
  expcov = ErrorMatrixPropagator::propagateError(&TauA1NuConstrainedFitter::ComputeInitalExpPar, inpar, incov);
 
  TVectorT<double> PAR_0(npar);
  par_0.ResizeTo(npar);
  cov_0.ResizeTo(npar, npar);
  PAR_0 = ComputeExpParToPar(exppar);
  for (int i = 0; i < npar; i++)
    par_0(i) = PAR_0(i);
  cov_0 = ErrorMatrixPropagator::propagateError(&TauA1NuConstrainedFitter::ComputeExpParToPar, exppar, expcov);
 
  for (int i = 0; i < npar; i++) {
    for (int j = 0; j < npar; j++) {
      cov_0(i, j) = expcov(i, j);
    }
  }
 
  par.ResizeTo(npar);
  par = par_0;
  cov.ResizeTo(npar, npar);
  cov = cov_0;
}
 
TVectorT<double> TauA1NuConstrainedFitter::ComputeInitalExpPar(const TVectorT<double>& inpar) {
  TVectorT<double> outpar(nexpandedpar);
  int offset = LorentzVectorParticle::NVertex;  // for A1
  TVector3 pv(inpar(LorentzVectorParticle::vx), inpar(LorentzVectorParticle::vy), inpar(LorentzVectorParticle::vz));
  TVector3 sv(inpar(LorentzVectorParticle::vx + offset),
              inpar(LorentzVectorParticle::vy + offset),
              inpar(LorentzVectorParticle::vz + offset));
  TVector3 TauDir = sv - pv;
  outpar(tau_phi) = TauDir.Phi();
  outpar(tau_theta) = TauDir.Theta();
  outpar(a1_px) = inpar(LorentzVectorParticle::px + offset);
  outpar(a1_py) = inpar(LorentzVectorParticle::py + offset);
  outpar(a1_pz) = inpar(LorentzVectorParticle::pz + offset);
  outpar(a1_m) = inpar(LorentzVectorParticle::m + offset);
  outpar(a1_vx) = inpar(LorentzVectorParticle::vx + offset);
  outpar(a1_vy) = inpar(LorentzVectorParticle::vy + offset);
  outpar(a1_vz) = inpar(LorentzVectorParticle::vz + offset);
  offset += LorentzVectorParticle::NLorentzandVertexPar;  // for Nu
  outpar(nu_px) = inpar(LorentzVectorParticle::px + offset);
  outpar(nu_py) = inpar(LorentzVectorParticle::py + offset);
  outpar(nu_pz) = inpar(LorentzVectorParticle::pz + offset);
  return outpar;
}
 
TVectorT<double> TauA1NuConstrainedFitter::ComputeExpParToPar(const TVectorT<double>& inpar) {
  TVectorT<double> outpar(npar);
  for (int i = 0; i < npar; i++) {
    outpar(i) = inpar(i);
  }
  return outpar;
}
 
TVectorT<double> TauA1NuConstrainedFitter::ComputeNuLorentzVectorPar(const TVectorT<double>& inpar) {
  TVectorT<double> outpar(LorentzVectorParticle::NLorentzandVertexPar);
  outpar(LorentzVectorParticle::vx) = inpar(a1_vx);
  outpar(LorentzVectorParticle::vy) = inpar(a1_vy);
  outpar(LorentzVectorParticle::vz) = inpar(a1_vz);
  outpar(LorentzVectorParticle::px) = inpar(nu_px);
  outpar(LorentzVectorParticle::py) = inpar(nu_py);
  outpar(LorentzVectorParticle::pz) = inpar(nu_pz);
  outpar(LorentzVectorParticle::m) = 0;
  return outpar;
}
 
TVectorT<double> TauA1NuConstrainedFitter::ComputeA1LorentzVectorPar(const TVectorT<double>& inpar) {
  TVectorT<double> outpar(LorentzVectorParticle::NLorentzandVertexPar);
  outpar(LorentzVectorParticle::vx) = inpar(a1_vx);
  outpar(LorentzVectorParticle::vy) = inpar(a1_vy);
  outpar(LorentzVectorParticle::vz) = inpar(a1_vz);
  outpar(LorentzVectorParticle::px) = inpar(a1_px);
  outpar(LorentzVectorParticle::py) = inpar(a1_py);
  outpar(LorentzVectorParticle::pz) = inpar(a1_pz);
  outpar(LorentzVectorParticle::m) = inpar(a1_m);
  return outpar;
}
 
TVectorT<double> TauA1NuConstrainedFitter::ComputeMotherLorentzVectorPar(const TVectorT<double>& inpar) {
  TVectorT<double> outpar(LorentzVectorParticle::NLorentzandVertexPar);
  TVectorT<double> nupar = ComputeNuLorentzVectorPar(inpar);
  TVectorT<double> a1par = ComputeA1LorentzVectorPar(inpar);
  for (int i = 0; i < LorentzVectorParticle::NLorentzandVertexPar; i++) {
    if (i < LorentzVectorParticle::NVertex) {
      outpar(i) = a1par(i);
    } else {
      outpar(i) = nupar(i) + a1par(i);
    }
    //if(i==LorentzVectorParticle::m) outpar(i,0)=PDGInfo::tau_mass();
  }
  double nu_px = nupar(LorentzVectorParticle::px);
  double nu_py = nupar(LorentzVectorParticle::py);
  double nu_pz = nupar(LorentzVectorParticle::pz);
  double Enu2 = nu_px * nu_px + nu_py * nu_py + nu_pz * nu_pz;
  double a1_px = a1par(LorentzVectorParticle::px);
  double a1_py = a1par(LorentzVectorParticle::py);
  double a1_pz = a1par(LorentzVectorParticle::pz);
  double a1_m = a1par(LorentzVectorParticle::m);
  double Ea12 = a1_px * a1_px + a1_py * a1_py + a1_pz * a1_pz + a1_m * a1_m;
  double outpar_px = outpar(LorentzVectorParticle::px);
  double outpar_py = outpar(LorentzVectorParticle::py);
  double outpar_pz = outpar(LorentzVectorParticle::pz);
  double P2 = outpar_px * outpar_px + outpar_py * outpar_py + outpar_pz * outpar_pz;
  outpar(LorentzVectorParticle::m) = sqrt(std::fabs(Enu2 + Ea12 + 2 * sqrt(Enu2 * Ea12) - P2));
  return outpar;
}
 
void TauA1NuConstrainedFitter::UpdateExpandedPar() {
  // assumes changes to a1 correlation to vertex is small
  if (par.GetNrows() == npar && cov.GetNrows() == npar && exppar.GetNrows() == npar && expcov.GetNrows() == npar)
    return;
  for (int i = 0; i < npar; i++) {
    exppar(i) = par(i);
    for (int j = 0; j < npar; j++) {
      expcov(i, j) = cov(i, j);
    }
  }
}
 
std::vector<LorentzVectorParticle> TauA1NuConstrainedFitter::getRefitDaughters() {
  std::vector<LorentzVectorParticle> refitParticles;
  UpdateExpandedPar();
  double c(0), b(0);
  for (unsigned int i = 0; i < particles_.size(); i++) {
    c += particles_[i].charge();
    b = particles_[i].bField();
  }
  TVectorT<double> a1 = ComputeA1LorentzVectorPar(exppar);
  TMatrixTSym<double> a1cov =
      ErrorMatrixPropagator::propagateError(&TauA1NuConstrainedFitter::ComputeA1LorentzVectorPar, exppar, expcov);
  refitParticles.push_back(LorentzVectorParticle(a1, a1cov, particles_[0].pdgId(), c, b));
  TVectorT<double> nu = ComputeNuLorentzVectorPar(exppar);
  TMatrixTSym<double> nucov =
      ErrorMatrixPropagator::propagateError(&TauA1NuConstrainedFitter::ComputeNuLorentzVectorPar, exppar, expcov);
  refitParticles.push_back(LorentzVectorParticle(nu, nucov, PDGInfo::nu_tau, 0.0, b));
  return refitParticles;
}
 
LorentzVectorParticle TauA1NuConstrainedFitter::getMother() {
  UpdateExpandedPar();
  double c(0), b(0);
  for (unsigned int i = 0; i < particles_.size(); i++) {
    c += particles_[i].charge();
    b = particles_[i].bField();
  }
  TVectorT<double> m = ComputeMotherLorentzVectorPar(exppar);
  TMatrixTSym<double> mcov =
      ErrorMatrixPropagator::propagateError(&TauA1NuConstrainedFitter::ComputeMotherLorentzVectorPar, exppar, expcov);
  LorentzVectorParticle mymother = LorentzVectorParticle(m, mcov, (int)(-1.0 * std::abs(PDGInfo::tau_minus) * c), c, b);
  return mymother;
}
 
void TauA1NuConstrainedFitter::CovertParToObjects(
    const TVectorD& v, TLorentzVector& a1, TLorentzVector& nu, double& phi, double& theta, TVector3& TauDir) {
  a1 = TLorentzVector(v(a1_px),
                      v(a1_py),
                      v(a1_pz),
                      sqrt(v(a1_m) * v(a1_m) + v(a1_px) * v(a1_px) + v(a1_py) * v(a1_py) + v(a1_pz) * v(a1_pz)));
  nu = TLorentzVector(
      v(nu_px), v(nu_py), v(nu_pz), sqrt(v(nu_px) * v(nu_px) + v(nu_py) * v(nu_py) + v(nu_pz) * v(nu_pz)));
  phi = v(tau_phi);
  theta = v(tau_theta);
  TauDir.SetMagThetaPhi(1.0, theta, phi);
}
 
bool TauA1NuConstrainedFitter::fit() {
  // Check if Tau Direction is unphysical and if nessicary set the starting point to Theta_{GJ-Max}
  TLorentzVector a1(
      par(a1_px),
      par(a1_py),
      par(a1_pz),
      sqrt(par(a1_m) * par(a1_m) + par(a1_px) * par(a1_px) + par(a1_py) * par(a1_py) + par(a1_pz) * par(a1_pz)));
  double phi(par(tau_phi)), theta(par(tau_theta));
  TLorentzVector Tau_plus, Tau_minus, nu_plus, nu_minus;
  TVector3 TauDir(cos(phi) * sin(theta), sin(phi) * sin(theta), cos(theta));
  bool isReal;
  solveByRotation(TauDir, a1, Tau_plus, Tau_minus, nu_plus, nu_minus, isReal);
 
  //check that the do product of the a1 and tau is positive, otherwise there is no information for tau direction -> use zero solution
  if (TauDir.Dot(a1.Vect()) < 0) {
    isReal = false;
  }
 
  //case 1: is real then solve analytically
  if (isReal && (ambiguity_ == plus || ambiguity_ == minus)) {
    // popogate errors
    TVectorT<double> par_tmp = TauA1NuConstrainedFitter::SolveAmbiguityAnalytically(par, ambiguity_);
    cov = ErrorMatrixPropagator::propagateError(
        std::bind(TauA1NuConstrainedFitter::SolveAmbiguityAnalytically, std::placeholders::_1, ambiguity_), par, cov_0);
    for (int i = 0; i < npar; i++)
      par(i) = par_tmp(i);
    return true;
  }
  // case 2 is in unphsyical region - rotate and substitue \theta_{GJ} with \theta_{GJ}^{Max} and then solve analytically
  else if (!isReal && ambiguity_ == zero) {
    TVectorT<double> par_tmp = TauA1NuConstrainedFitter::SolveAmbiguityAnalyticallywithRot(par, ambiguity_);
    cov = ErrorMatrixPropagator::propagateError(
        std::bind(TauA1NuConstrainedFitter::SolveAmbiguityAnalyticallywithRot, std::placeholders::_1, ambiguity_),
        par,
        cov_0);
    for (int i = 0; i < npar; i++)
      par(i) = par_tmp(i);
    return true;
  }
  return false;
}
 
TVectorT<double> TauA1NuConstrainedFitter::SolveAmbiguityAnalytically(const TVectorT<double>& inpar, unsigned int amb) {
  // Solve equation quadratic equation
  TVectorT<double> outpar(inpar.GetNrows());
  TLorentzVector a1, nu;
  double phi(0), theta(0);
  TVector3 TauDir;
  CovertParToObjects(inpar, a1, nu, phi, theta, TauDir);
  TLorentzVector a1_d = a1;
  TLorentzVector nu_d = nu;
  TLorentzVector Tau_plus, Tau_minus, nu_plus, nu_minus;
  bool isReal;
  solveByRotation(TauDir, a1_d, Tau_plus, Tau_minus, nu_plus, nu_minus, isReal, true);
  if (amb == plus)
    nu = nu_plus;
  else
    nu = nu_minus;
  for (int i = 0; i < outpar.GetNrows(); i++) {
    outpar(i) = inpar(i);
  }
  outpar(nu_px) = nu.Px();
  outpar(nu_py) = nu.Py();
  outpar(nu_pz) = nu.Pz();
  return outpar;
}
 
TVectorT<double> TauA1NuConstrainedFitter::SolveAmbiguityAnalyticallywithRot(const TVectorT<double>& inpar,
                                                                             unsigned int ambiguity) {
  // Rotate and subsitute \theta_{GJ} with \theta_{GJ}^{Max} - assumes uncertianty on thata and phi of the a1 or small compared to the tau direction.
  TVectorT<double> outpar(inpar.GetNrows());
  TLorentzVector a1, nu;
  double phi(0), theta(0);
  TVector3 TauDir;
  CovertParToObjects(inpar, a1, nu, phi, theta, TauDir);
  double theta_a1(a1.Theta()), phi_a1(a1.Phi()), theta_GJMax(thetaGJMax(a1));
  TauDir.RotateZ(-phi_a1);
  TauDir.RotateY(-theta_a1);
  double phiprime(TauDir.Phi());
  TauDir = TVector3(sin(theta_GJMax) * cos(phiprime), sin(theta_GJMax) * sin(phiprime), cos(theta_GJMax));
  TauDir.RotateY(theta_a1);
  TauDir.RotateZ(phi_a1);
  for (int i = 0; i < outpar.GetNrows(); i++)
    outpar(i) = inpar(i);
  outpar(tau_phi) = TauDir.Phi();
  outpar(tau_theta) = TauDir.Theta();
  return SolveAmbiguityAnalytically(outpar, ambiguity);
}
 
// Return the significance of the rotation when the tau direction is in the unphysical region
double TauA1NuConstrainedFitter::getTauRotationSignificance() {
  TVectorT<double> par_tmp = TauA1NuConstrainedFitter::TauRot(par);
  TMatrixTSym<double> cov_tmp = ErrorMatrixPropagator::propagateError(&TauA1NuConstrainedFitter::TauRot, par, cov_0);
  if (!(cov_tmp(0, 0) > 0))
    return -999;  // return invalid value if the covariance is unphysical (safety flag)
  if (par_tmp(0) > 0)
    return par_tmp(0) / sqrt(cov_tmp(0, 0));  // return the significance if the value is in the unphysical region
  return 0;  // reutrn 0 for the rotation significance if the tau is in the physical region
}
 
TVectorT<double> TauA1NuConstrainedFitter::TauRot(const TVectorT<double>& inpar) {
  TVectorT<double> outpar(1);
  TLorentzVector a1, nu;
  double phi(0), theta(0);
  TVector3 TauDir;
  CovertParToObjects(inpar, a1, nu, phi, theta, TauDir);
  double theta_a1(a1.Theta()), phi_a1(a1.Phi()), theta_GJMax(thetaGJMax(a1));
  TauDir.RotateZ(-phi_a1);
  TauDir.RotateY(-theta_a1);
  outpar(0) = (TauDir.Theta() - theta_GJMax);
  return outpar;
}