PndMvdIdealPidAlgo.cxx

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#include "PndMvdIdealPidAlgo.h"
#include "PndMvdPidCand.h"
//public

void PndMvdIdealPidAlgo::CalcLikelihood(PndMvdPidCand* cand) {
  //computes pid likelihoods for pi, k, p, mu and stores them in the likelihood map
  //with the map key used as pdg id. This is basically done by integrating the
  //respective energy loss distribution within the chosen selector limits

  double weightP;
  double weightK;
  double weightPi;

  double dE=0;
  double dx=0;
  double momentum=0;

  for (Int_t k=0;k<cand->GetMvdHits(); k++) {
    dE+=cand->GetMvdHitdE(k);
    dx+=cand->GetMvdHitdx(k);
    momentum+=cand->GetMvdHitMomentum(k);
  }

  if (dx>0) {
    double energyloss=dE/dx;
    momentum=momentum/cand->GetMvdHits();

    //Proton selector
    if (energyloss>=LowerProtonBoundary(momentum)) {
      weightP=1-fPRemainder;
      weightK=1-LandauIntegral((LowerProtonBoundary(momentum)-LowerBoundary(momentum, fkMass)-fkShift)/fkScale);
      weightPi=1-LandauIntegral((LowerProtonBoundary(momentum)-LowerBoundary(momentum, fpiMass)-fpiShift)/fpiScale);

    //Kaon selector
    } else if (energyloss>=LowerKaonBoundary(momentum)) {
      weightP=fPRemainder;
      weightK=LandauIntegral((LowerProtonBoundary(momentum)-LowerBoundary(momentum, fkMass)-fkShift)/fkScale)
             -fKRemainder;
      weightPi=LandauIntegral((LowerProtonBoundary(momentum)-LowerBoundary(momentum, fpiMass)-fpiShift)/fpiScale)
              -LandauIntegral((LowerKaonBoundary(momentum)-LowerBoundary(momentum, fpiMass)-fpiShift)/fpiScale);

    //Pion selector
    } else if (energyloss>=LowerPionBoundary(momentum)) {
      weightP=0;
      weightK=fKRemainder;
      weightPi=LandauIntegral((LowerKaonBoundary(momentum)-LowerBoundary(momentum, fpiMass)-fpiShift)/fpiScale)
              -fPiRemainder;

    //Electron selector
    } else {
      weightP=0;
      weightK=0;
      weightPi=fPiRemainder;
    }
  } else {
    weightP=1;
    weightK=1;
    weightPi=1;
  }

  //Muons have approximately the same distribution as pions.
  double sum=weightP+weightK+2*weightPi;
  weightP/=sum;
  weightK/=sum;
  weightPi/=sum;

  cand->SetLikelihood(211, weightPi);
  cand->SetLikelihood(2212, weightP);
  cand->SetLikelihood(321, weightK);
  cand->SetLikelihood(13, weightPi);
}

//private

double PndMvdIdealPidAlgo::LowerProtonBoundary(double p) {
  return LowerBoundary(p+0.02, fpMass)-5e-4;
};

double PndMvdIdealPidAlgo::LowerKaonBoundary(double p) {
  return LowerBoundary(p+0.02, fkMass)-3e-4;
};

double PndMvdIdealPidAlgo::LowerPionBoundary(double p) {
  return LowerBoundary(p+0.01, fpiMass)-3e-4;
};


double PndMvdIdealPidAlgo::LowerBoundary(double p, double m) {
//Calculate the lower boundary of the energy loss distribution.

  double sqrfBeta=1/(1+pow(m/p,2));
  return 4.9312e-05 * (log(2*feMass*fc*fc/feb*sqrfBeta/(1-sqrfBeta))-sqrfBeta)/sqrfBeta;
};

double PndMvdIdealPidAlgo::LandauIntegral(double x) {
//compute integral approximation of a Landau-p.d.f from -INF to x
//with expected value 0 and deviation 1. Hard coded numbers have
//been fitted within their respective intervals.

  if (x<-0.8)
  //gauss
    return 0.199785*exp(-pow(x+0.149198,2)*0.769779);
  else if (x<0.5)
    //linear
    return 0.177214*(x+1.61437);
  else
    //power function
    return 1-19.0054*pow(x+5.860003,-1.84611);
}

//[GeV/c**2]
float PndMvdIdealPidAlgo::fpiMass=0.1396;
float PndMvdIdealPidAlgo::fkMass=0.4937;
float PndMvdIdealPidAlgo::fpMass=0.9383;
float PndMvdIdealPidAlgo::feMass=0.511e-3;
//[GeV]
float PndMvdIdealPidAlgo::feb=0.14e-6;
//[m/s]
float PndMvdIdealPidAlgo::fc=2.99792458e8;

//Landau distribution parameters; these parameters have been
//obtained by fitting the Landau-p.d.f on the energy loss shifted
//by the Bethe-Bloch energy loss at momentum >= 0.4 GeV
double PndMvdIdealPidAlgo::fkShift=3.38598e-4;
double PndMvdIdealPidAlgo::fkScale=1.36362e-4;

double PndMvdIdealPidAlgo::fpiShift=3.09159e-4;
double PndMvdIdealPidAlgo::fpiScale=1.58696e-4;

//General remainders of integrals for integrating from -INF to
//below the Bethe-Bloch lower boundary as obtained by MC Simulation
double PndMvdIdealPidAlgo::fPRemainder=0.015;
double PndMvdIdealPidAlgo::fKRemainder=0.01;
double PndMvdIdealPidAlgo::fPiRemainder=0.001;