TFitParticleMomDev.cc

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// Classname: TFitParticleMomDev
// Author: Jan E. Sundermann, Verena Klose (TU Dresden)      


//________________________________________________________________
// 
// TFitParticleMomDev
// --------------------
//
// Particle with special parametrization of the momentum 4vector and
// free mass (4 free parameters). The parametrization is chosen as
// follows:
//
// p = r*|p|*u_r + theta*u_theta + phi*u_phi
// E(fit) =  Sqrt( |p|^2 + d^2*m^2 )
//
// with u_r = p/|p|
//      u_phi = (u_z x u_r)/|u_z x u_r|
//      u_theta = (u_r x u_phi)/|u_r x u_phi|
//
// The initial parameters values are chosen like (r, theta, phi, d) = (1., 0., 0., 1.)
// corresponding to the measured momentum and mass.
//

#include <iostream>
#include "FWCore/MessageLogger/interface/MessageLogger.h"
#include "PhysicsTools/KinFitter/interface/TFitParticleMomDev.h"
#include "TMath.h"


//----------------
// Constructor --
//----------------
TFitParticleMomDev::TFitParticleMomDev()
  :TAbsFitParticle()  
{
  init(nullptr, nullptr);
}

TFitParticleMomDev::TFitParticleMomDev( const TFitParticleMomDev& fitParticle )
  :TAbsFitParticle( fitParticle.GetName(), fitParticle.GetTitle() )
{

  _nPar = fitParticle._nPar;
  _u1 = fitParticle._u1;
  _u2 = fitParticle._u2;
  _u3 = fitParticle._u3;
  _covMatrix.ResizeTo(  fitParticle._covMatrix );
  _covMatrix = fitParticle._covMatrix;
  _iniparameters.ResizeTo( fitParticle._iniparameters );
  _iniparameters = fitParticle._iniparameters;
  _parameters.ResizeTo( fitParticle._parameters );
  _parameters = fitParticle._parameters;
  _pini = fitParticle._pini;
  _pcurr = fitParticle._pcurr;

}

TFitParticleMomDev::TFitParticleMomDev(TLorentzVector* pini, const TMatrixD* theCovMatrix)
  :TAbsFitParticle()  
{
  init(pini, theCovMatrix);
}

TFitParticleMomDev::TFitParticleMomDev(const TString &name, const TString &title, 
               TLorentzVector* pini, const TMatrixD* theCovMatrix)
  :TAbsFitParticle(name, title)  
{
  init(pini, theCovMatrix);
}

TAbsFitParticle* TFitParticleMomDev::clone( const TString& newname ) const {
  // Returns a copy of itself
  
  TAbsFitParticle* myclone = new TFitParticleMomDev( *this );
  if ( newname.Length() > 0 ) myclone->SetName(newname);
  return myclone;

}

//--------------
// Destructor --
//--------------
TFitParticleMomDev::~TFitParticleMomDev() {

}

//--------------
// Operations --
//--------------
void TFitParticleMomDev::init(TLorentzVector* pini, const TMatrixD* theCovMatrix ) {

  _nPar = 4;
  _iniparameters.ResizeTo(_nPar,1);
  _iniparameters(0,0)=1.;
  _iniparameters(1,0)=0.;
  _iniparameters(2,0)=0.;
  _iniparameters(3,0)=1.;
  _parameters.ResizeTo(_nPar,1);
  _parameters = _iniparameters;
  setIni4Vec(pini);
  setCovMatrix(theCovMatrix);


}

void TFitParticleMomDev::setIni4Vec(const TLorentzVector* pini) {
  // Set the initial 4vector. Will also set the 
  // inital parameter values

  if (pini == nullptr) {

    _u1.SetXYZ(0., 0., 0.);
    _u3.SetXYZ(0., 0., 0.);
    _u2.SetXYZ(0., 0., 0.);
    _pini.SetXYZT(0., 0., 0., 0.);
    _pcurr = _pini;
    
  } else {
    
    _pini = (*pini);
    _pcurr = _pini;

    _u1 = pini->Vect();
    _u1 *= 1./_u1.Mag();
    
    TVector3 uz(0., 0., 1.);
    _u3 = uz.Cross(_u1);
    _u3 *= 1./_u3.Mag();
    
    _u2 = _u3.Cross(_u1);
    _u2 *= 1./_u2.Mag();

  }

  // reset parameters
  _parameters = _iniparameters;

}

TLorentzVector* TFitParticleMomDev::calc4Vec( const TMatrixD* params ) {
  // Calculates a 4vector corresponding to the given
  // parameter values

  if (params == nullptr) {
    return nullptr;
  }

  if ( params->GetNcols() != 1 || params->GetNrows() !=_nPar ) {
    edm::LogError ("WrongMatrixSize")
      << GetName() << "::calc4Vec - Parameter matrix has wrong size.";
    return nullptr;
  }

  Double_t X = _pini.P() * (*params)(0,0) *_u1.X() +
    (*params)(1,0) * _u2.X()+
    (*params)(2,0) * _u3.X();
  Double_t Y = _pini.P() * (*params)(0,0) *_u1.Y() +
    (*params)(1,0) * _u2.Y()+
    (*params)(2,0) * _u3.Y();
  Double_t Z = _pini.P() * (*params)(0,0) *_u1.Z() +
    (*params)(1,0) * _u2.Z()+
    (*params)(2,0) * _u3.Z();
  Double_t E =  TMath::Sqrt( X*X + Y*Y + Z*Z + (*params)(3,0)*(*params)(3,0)*_pini.M2() );

  TLorentzVector* vec = new TLorentzVector( X, Y, Z, E );
  return vec;

}

TMatrixD* TFitParticleMomDev::getDerivative() {
  // returns derivative dP/dy with P=(p,E) and y=(r, theta, phi, d) 
  // the free parameters of the fit. The columns of the matrix contain 
  // (dP/dr, dP/dtheta, dP/dphi, dP/dd).

  TMatrixD* DerivativeMatrix = new TMatrixD(4,4);
  (*DerivativeMatrix) *= 0.;

  //1st column: dP/dr
  (*DerivativeMatrix)(0,0)=_pini.P()*_u1.X();
  (*DerivativeMatrix)(1,0)=_pini.P()*_u1.Y();
  (*DerivativeMatrix)(2,0)=_pini.P()*_u1.Z();
  (*DerivativeMatrix)(3,0)=0.;

  //2nd column: dP/dtheta
  (*DerivativeMatrix)(0,1)=_u2.X();
  (*DerivativeMatrix)(1,1)=_u2.Y();
  (*DerivativeMatrix)(2,1)=_u2.Z();
  (*DerivativeMatrix)(3,1)=0.;

   //3rd column: dP/dphi
  (*DerivativeMatrix)(0,2)=_u3.X();
  (*DerivativeMatrix)(1,2)=_u3.Y();
  (*DerivativeMatrix)(2,2)=_u3.Z();
  (*DerivativeMatrix)(3,2)=0.;

   //4th column: dP/dm
  (*DerivativeMatrix)(0,3)=0.;
  (*DerivativeMatrix)(1,3)=0.;
  (*DerivativeMatrix)(2,3)=0.;
  (*DerivativeMatrix)(3,3)=_pini.M()*_pini.M()*_parameters(3,0)/_pcurr.E();

  return DerivativeMatrix;  
}

TMatrixD* TFitParticleMomDev::transform(const TLorentzVector& vec) {
  // Returns the parameters corresponding to the given 
  // 4vector wrt. to the current base vectors u_r, u_theta, and u_phi

  // construct rotation matrix
  TRotation rot;
  rot.RotateAxes( _u1, _u2, _u3 );
  rot.Invert();

  // rotate vector
  TVector3 vec3( vec.Vect() );
  vec3.Transform( rot );

  // retrieve parameters
  TMatrixD* tparams = new TMatrixD( _nPar, 1 );
  (*tparams)(0,0) = vec3(0)/_pini.P();
  (*tparams)(1,0) = vec3(1);
  (*tparams)(2,0) = vec3(2);
  (*tparams)(3,0) = vec.M()/_pini.M();

  return tparams;

}