EnergyLossEstimator Class Reference

Helper struct to provide consistent energy loss estimation throughout the CDC track finding. More...

#include <EnergyLossEstimator.h>

Public Member Functions
	EnergyLossEstimator (double eDensity, double I, double bZ=NAN)
	Constructor from the material properties.
double	getBetheStoppingPower (double p, int pdgCode) const
	Stopping power aka energy loss / arc length.
double	getEnergyLoss (double p, int pdgCode, double arcLength) const
	Calculates the total energy loss after travelling the given distance.
double	getMomentumLossFactor (double p, int pdgCode, double arcLength) const
	Calculates a factor applicable scaling the current momentum to the momentum after traveling given arc length.
double	getLossDist2D (double pt, int pdgCode, double arcLength2D) const
	Calculates a correction term for the two dimensional distance undoing the energy loss after the given arc length.

Static Public Member Functions
static EnergyLossEstimator	forCDC ()
	Create an energy loss estimator with the material properties of the CDC.
static double	getMass (int pdgCode)
	Lookup the mass for the given pdg code.
static int	getCharge (int pdgCode)
	Lookup the charge for the given pdg code.

Private Attributes
double	m_eDensity
	Electron density in mol / cm^3.
double	m_I
	Mean excitation energy in GeV.
double	m_bZ
	B field to be used for the distance translation.

Detailed Description

Helper struct to provide consistent energy loss estimation throughout the CDC track finding.

Definition at line 22 of file EnergyLossEstimator.h.

Constructor & Destructor Documentation

EnergyLossEstimator()

EnergyLossEstimator	(	double	eDensity,
		double	I,
		double	bZ = NAN
	)

Constructor from the material properties.

Parameters

eDensity	Electron density in mol / cm ^ 3, e.g. from Z * density / A
I	Excitation energy (must be given in standard GeV units)
bZ	Mean magentic field in the z direction

Definition at line 121 of file EnergyLossEstimator.cc.

  : m_eDensity(eDensity)
  , m_I(I)
  , m_bZ(bZ)
{
}

Member Function Documentation

forCDC()

EnergyLossEstimator forCDC ( )

static

Create an energy loss estimator with the material properties of the CDC.

Definition at line 28 of file EnergyLossEstimator.cc.

{
 
  // Look up material properties from the Belle2 geometry
  G4Navigator g4Nav;
  G4VPhysicalVolume* g4World = geometry::GeometryManager::getInstance().getTopVolume();
  g4Nav.SetWorldVolume(g4World);
 
  // Choose position well inside the CDC
  double posX = 0;
  double posY = 50;
  double posZ = 0;
 
  G4ThreeVector g4Pos(posX * CLHEP::cm, posY * CLHEP::cm, posZ * CLHEP::cm);
  const G4VPhysicalVolume* g4Volume = g4Nav.LocateGlobalPointAndSetup(g4Pos);
  const G4Material* g4Mat = g4Volume->GetLogicalVolume()->GetMaterial();
 
  double A = 0;
  double Z = 0;
 
  if (g4Mat->GetNumberOfElements() == 1) {
    A = g4Mat->GetA() * CLHEP::mole / CLHEP::g;
    Z = g4Mat->GetZ();
  } else {
    // Calculate weight-averaged A, Z
    for (unsigned i = 0; i < g4Mat->GetNumberOfElements(); ++i) {
      const G4Element* element = (*g4Mat->GetElementVector())[i];
      const double elementA = element->GetA() * CLHEP::mole / CLHEP::g;
      const double elementZ = element->GetZ();
      const double frac = g4Mat->GetFractionVector()[i];
      B2RESULT("Part " << i << " Z=" << elementZ << " A=" << elementA << " (" << frac << ")");
      Z += elementZ * frac;
      A += elementA * frac;
    }
  }
 
  // Make sure to translate to Belle units from the Geant4 / CLHEP units
  // Z has correct units (is unitless)
  const double density = g4Mat->GetDensity() / CLHEP::g * CLHEP::cm3;
  const double radiationLength = g4Mat->GetRadlen() / CLHEP::cm;
  const double mEE = g4Mat->GetIonisation()->GetMeanExcitationEnergy() / CLHEP::GeV;
 
  B2RESULT("Received Z " << Z);
  B2RESULT("Received A " << A);
  B2RESULT("Received density " << density);
  B2RESULT("Received radiation length " << radiationLength);
  B2RESULT("Received mean excitation energy " << mEE);
 
  const double eDensity = Z * density / A;
  B2RESULT("Received electron density " << eDensity);
 
  const double bZ = CDCBFieldUtil::getBFieldZ();
 
  return EnergyLossEstimator(eDensity, mEE, bZ);
}

getBetheStoppingPower()

double getBetheStoppingPower	(	double	p,
		int	pdgCode
	)		const

Stopping power aka energy loss / arc length.

Parameters

p	absolute momentum
pdgCode

Definition at line 128 of file EnergyLossEstimator.cc.

{
  static const double eMass = getMass(11);
 
  const double M = getMass(pdgCode);
 
  const double E = std::sqrt(p * p + M * M);
  const double gamma = E / M;
  const double beta = p / E;
 
  const double beta2 = beta * beta;
  const double gamma2 = gamma * gamma;
 
  const double Wmax = 2 * eMass * beta2 * gamma2 / (1 + 2 * gamma * eMass / M);
  const double I2 =  m_I * m_I;
 
  static const double K = 0.307075 * Unit::MeV * Unit::cm2;
  const double dEdx = K * m_eDensity / beta2 *
                      (1.0 / 2.0 * std::log(2 * eMass * beta2 * gamma2 * Wmax / I2) - beta2);
  return dEdx;
}

getCharge()

int getCharge ( int  pdgCode )

static

Lookup the charge for the given pdg code.

Definition at line 105 of file EnergyLossEstimator.cc.

{
  if (std::abs(pdgCode) == Const::electron.getPDGCode()) {
    return -sign(pdgCode);
  } else if (std::abs(pdgCode) == Const::muon.getPDGCode()) {
    return -sign(pdgCode);
  } else if (std::abs(pdgCode) == Const::kaon.getPDGCode()) {
    return sign(pdgCode);
  } else if (std::abs(pdgCode) == Const::pion.getPDGCode()) {
    return sign(pdgCode);
  } else if (std::abs(pdgCode) == Const::proton.getPDGCode()) {
    return sign(pdgCode);
  }
  return 0;
}

getEnergyLoss()

double getEnergyLoss	(	double	p,
		int	pdgCode,
		double	arcLength
	)		const

Calculates the total energy loss after travelling the given distance.

Definition at line 150 of file EnergyLossEstimator.cc.

{
  const double dEdx = getBetheStoppingPower(p, pdgCode);
  const double eLoss = arcLength * dEdx;
  return eLoss;
}

getLossDist2D()

double getLossDist2D	(	double	pt,
		int	pdgCode,
		double	arcLength2D
	)		const

Calculates a correction term for the two dimensional distance undoing the energy loss after the given arc length.

Definition at line 170 of file EnergyLossEstimator.cc.

{
  const double eLoss = getEnergyLoss(pt, pdgCode, arcLength2D);
 
  const int q = getCharge(pdgCode);
  const double radius = q * CDCBFieldUtil::absMom2DToBendRadius(pt, m_bZ);;
  return radius * eLoss / (pt - eLoss);
 
  // const double pFactor = getMomentumLossFactor(p, pdgCode, arcLength2D);
  // return radius * (1 / pFactor - 1);
}

getMass()

double getMass ( int  pdgCode )

static

Lookup the mass for the given pdg code.

Definition at line 84 of file EnergyLossEstimator.cc.

{
  if (std::abs(pdgCode) == Const::electron.getPDGCode()) {
    const double electronMass = 0.511 * Unit::MeV;
    return electronMass;
  } else if (std::abs(pdgCode) == Const::muon.getPDGCode()) {
    const double muonMass = 105.658 * Unit::MeV;
    return muonMass;
  } else if (std::abs(pdgCode) == Const::kaon.getPDGCode()) {
    const double kaonMass = 0.493677;
    return kaonMass;
  } else if (std::abs(pdgCode) == Const::pion.getPDGCode()) {
    const double pionMass = 0.13957;
    return pionMass;
  } else if (std::abs(pdgCode) == Const::proton.getPDGCode()) {
    const double protonMass = 0.938272;
    return protonMass;
  }
  return NAN;
}

getMomentumLossFactor()

double getMomentumLossFactor	(	double	p,
		int	pdgCode,
		double	arcLength
	)		const

Calculates a factor applicable scaling the current momentum to the momentum after traveling given arc length.

Definition at line 157 of file EnergyLossEstimator.cc.

{
  const double eLoss = getEnergyLoss(p, pdgCode, arcLength);
  return (p - eLoss) / p;
 
  const double mass = getMass(pdgCode);
 
  const double eBefore = std::sqrt(p * p + mass * mass);
  const double eAfter = eBefore - eLoss;
  const double pAfter = std::sqrt(eAfter * eAfter - mass * mass);
  return pAfter / p;
}

Member Data Documentation

m_bZ

double m_bZ

private

B field to be used for the distance translation.

Definition at line 81 of file EnergyLossEstimator.h.

m_eDensity

double m_eDensity

private

Electron density in mol / cm^3.

Definition at line 75 of file EnergyLossEstimator.h.

m_I

double m_I

private

Mean excitation energy in GeV.

Definition at line 78 of file EnergyLossEstimator.h.

---

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

• tracking/trackFindingCDC/eventdata/utils/include/EnergyLossEstimator.h
• tracking/trackFindingCDC/eventdata/utils/src/EnergyLossEstimator.cc