Par03EMShowerModel Class Reference

Example fast simulation model for EM showers. More...

#include <Doxymodules_parameterisations.h>

Inheritance diagram for Par03EMShowerModel:

Public Member Functions
	Par03EMShowerModel (G4String, G4Region *)
	Par03EMShowerModel (G4String)
	~Par03EMShowerModel ()
virtual G4bool	ModelTrigger (const G4FastTrack &) final
	There are no kinematics constraints. True is returned.
virtual G4bool	IsApplicable (const G4ParticleDefinition &) final
	Model is applicable to electrons, positrons, and photons.
virtual void	DoIt (const G4FastTrack &, G4FastStep &) final
	Take particle out of the full simulation (kill it at the entrance depositing all the energy).
void	Print () const
	Print current settings.
void	SetSigma (const G4double aSigma)
	Set standard deviation of a Gaussian distribution that describes the transverse shower profile.
G4double	GetSigma () const
	Get standard deviation of a Gaussian distribution that describes the transverse shower profile.
void	SetAlpha (const G4double aAlpha)
	Set alpha parameter of a Gamma distribution that describes the longitudinal shower profile.
G4double	GetAlpha () const
	Get alpha parameter of a Gamma distribution that describes the longitudinal shower profile.
void	SetBeta (const G4double aBeta)
	Set beta parameter of a Gamma distribution that describes the longitudinal shower profile.
G4double	GetBeta () const
	Get beta parameter of a Gamma distribution that describes the longitudinal shower profile.
void	SetNbOfHits (const G4int aNumber)
	Set number of (same energy) hits created in the parametrisation.
G4int	GetNbOfHits () const
	Get number of (same energy) hits created in the parametrisation.s.
void	SetLongMaxDepth (const G4double aDepth)
	Set maximum depth of shower created in fast simulation.
G4double	GetLongMaxDepth () const
	Get maximum depth of shower created in fast simulation.

Private Member Functions
G4double	Gamma (G4double x, G4double alpha, G4double beta)
	Gamma distribution.
G4double	Gaussian (G4double x, G4double sigma=1, G4double x0=0)
	Gaussian distribution.

Private Attributes
Par03EMShowerMessenger *	fMessenger
	Messenger for configuration.
std::unique_ptr< G4FastSimHitMaker >	fHitMaker
	Helper class for creation of hits within the sensitive detector.
G4double	fSigma = -1
	Standard deviation of the Gaussian distribution Can be changed with UI command /Par03/fastSim/transverseProfile/sigma <sigma> If sigma is smaller than 0, it will be estimated from the detector material (Moliere radius).
G4double	fAlpha = -1
	Alpha parameter of the Gamma distribution Can be changed with UI command /Par03/fastSim/longitudunalProfile/alpha <alpha> If alpha is smaller than 0, it will be estimated from particle energy and the detector material.
G4double	fBeta = 0.5
	Beta parameter of the Gamma distribution Can be changed with UI command /Par03/fastSim/longitudinalProfile/beta <beta>
G4int	fNbOfHits = 100
	Number of (same energy) hits created by the parametrisation.
G4double	fLongMaxDepth = 30
	Maximum depth of a shower created in fast simulation.

Detailed Description

Example fast simulation model for EM showers.

Parametrisation of electrons, positrons, and gammas. It is triggered if those particles enter the detector so that there is sufficient length for the shower development (max depth, controlled by the UI command).

Parametrisation is based on the PDG chapter on the electromagnetic cascades (chapter 33.5). Longitudinal profile of the shower is described with Gamma distribution, with beta parameter on average equal to 0.5 (default value, Fig. 33.21), and alpha parameter calcluated from the incident particle energy and material of the detector (critical energy) following Eq.(33.36).

Transverse profile is in this model approximated by the Gaussian distribution, with the mean along the shower axis (incident particle momentum direction) and the standard deviation calculated from the detector material (Moliere radius). This assumes that EM shower is in 90% contained within a cylinder of radius equal to Moliere radius, and that area below Gaussian distribution from mean-1.645 sigma to mean+1.645 sigma is also equal to 90% of total distribution.

Parameters of both distributions (alpha, beta for Gamma, sigma for Gaussian) can be overwritten by UI commands.

Parametrisation creates N hits of same energy (N can be set by UI command), using rejection sampling to generate position along shower axis from Gamma distribution, and then sampling from uniform and Gaussian distributions to sample phi and radius, respectively. Created hits are deposited in the detector using its readout geometry, using the helper class G4FastSimHitMaker that locates the volume, and calls appropriate sensitive detector class.

PDG Chapter 33: https://pdg.lbl.gov/2019/reviews/rpp2018-rev-passage-particles-matter.pdf

Definition at line 63 of file Doxymodules_parameterisations.h.

Constructor & Destructor Documentation

Par03EMShowerModel() [1/2]

Par03EMShowerModel::Par03EMShowerModel	(	G4String	aModelName,
		G4Region *	aEnvelope
	)

Definition at line 38 of file Par03EMShowerModel.cc.

  : G4VFastSimulationModel(aModelName, aEnvelope)
  , fMessenger(new Par03EMShowerMessenger(this))
  , fHitMaker(new G4FastSimHitMaker)
{}

Par03EMShowerModel() [2/2]

Par03EMShowerModel::Par03EMShowerModel

(

G4String

aModelName

)

Definition at line 46 of file Par03EMShowerModel.cc.

  : G4VFastSimulationModel(aModelName)
  , fMessenger(new Par03EMShowerMessenger(this))
  , fHitMaker(new G4FastSimHitMaker)
{}

~Par03EMShowerModel()

Par03EMShowerModel::~Par03EMShowerModel ( )

default

Member Function Documentation

ModelTrigger()

G4bool Par03EMShowerModel::ModelTrigger ( const G4FastTrack &  aFastTrack )

finalvirtual

There are no kinematics constraints. True is returned.

Definition at line 68 of file Par03EMShowerModel.cc.

{
  // Check energy
  if(aFastTrack.GetPrimaryTrack()->GetKineticEnergy() < 1 * GeV)
  {
    return false;
  }
  // Check length of detector
  // Calculate depth of the detector along shower axis to verify if shower
  // will fit inside. Required max shower depth is defined by fLongMaxDepth, and
  // can be changed with UI command `/Par03/fastSim/longitudinalProfile/maxDepth
  G4double X0 = aFastTrack.GetPrimaryTrack()->GetMaterial()->GetRadlen();
  auto particleDirection     = aFastTrack.GetPrimaryTrackLocalDirection();
  auto particlePosition      = aFastTrack.GetPrimaryTrackLocalPosition();
  G4double detectorDepthInMM = aFastTrack.GetEnvelopeSolid()->DistanceToOut(
    particlePosition, particleDirection);
  G4double detectorDepthInX0 = detectorDepthInMM / X0;
  // check if detector depth is sufficient to create showers
  if(detectorDepthInX0 < fLongMaxDepth)
  {
    return false;
  }
  return true;
}

IsApplicable()

G4bool Par03EMShowerModel::IsApplicable ( const G4ParticleDefinition &  aParticleType )

finalvirtual

Model is applicable to electrons, positrons, and photons.

Definition at line 58 of file Par03EMShowerModel.cc.

{
  return &aParticleType == G4Electron::ElectronDefinition() ||
         &aParticleType == G4Positron::PositronDefinition() ||
         &aParticleType == G4Gamma::GammaDefinition();
}

DoIt()

void Par03EMShowerModel::DoIt ( const G4FastTrack &  aFastTrack, G4FastStep &  aFastStep  )

finalvirtual

Take particle out of the full simulation (kill it at the entrance depositing all the energy).

Calculate energy deposited in the detector according to Gamma distribution (along the particle direction) and Gaussian distribution in the transverse direction. Mean of the Gaussian is centred on the shower axis. Create energy deposits on a cylindrical mesh. Parameters of the mesh (size, number of cells) and of the distributions (alpha, beta for Gamma, sigma for Gaussian) can be set with UI commands.

Definition at line 95 of file Par03EMShowerModel.cc.

{
  // Remove particle from further processing by G4
  aFastStep.KillPrimaryTrack();
  aFastStep.ProposePrimaryTrackPathLength(0.0);
  G4double energy = aFastTrack.GetPrimaryTrack()->GetKineticEnergy();
  // No need to create any deposit, it will be handled by this model (and
  // G4FastSimHitMaker that will call the sensitive detector)
  aFastStep.ProposeTotalEnergyDeposited(0);
  auto particlePosition  = aFastTrack.GetPrimaryTrackLocalPosition();
  auto particleDirection = aFastTrack.GetPrimaryTrackLocalDirection();
 
  // Calculate how to create energy deposits
  // Following PDG 33.5 chapter
  // material calculation assumes homogeneous detector (true for Par03 example)
  auto material       = aFastTrack.GetPrimaryTrack()->GetMaterial();
  G4double materialX0 = material->GetRadlen();
  G4double materialZ  = material->GetZ();
  // EC estimation follows PDG fit to solids in Fig. 33.14 (rms 2.2%)
  G4double materialEc = 610 * MeV / (materialZ + 1.24);
  // RM estimation follows PDG Eq. (33.37) (rms 2.2%)
  G4double materialRM = 21.2052 * MeV * materialX0 / materialEc;
  G4double particleY  = energy / materialEc;
  // Estimate shower maximum and alpha parameter of Gamma distribution
  // that describes the longitudinal profile (PDG Eq. (33.35))
  // unless alpha is specified by UI command
  if(fAlpha < 0)
  {
    // from PDG Eq. (33.36)
    G4double particleTmax = std::log(particleY);
    if(aFastTrack.GetPrimaryTrack()->GetParticleDefinition() ==
       G4Gamma::GammaDefinition())
    {
      particleTmax += 0.5;
    }
    else
    {
      particleTmax -= 0.5;
    }
    fAlpha = particleTmax * fBeta + 1;
  }
  // Unless sigma of Gaussian distribution describing the transverse profile
  // is specified by UI command, use value calculated from Moliere Radius
  if(fSigma < 0)
  {
    // 90% of shower is contained within 1 * R_M
    // 1.645 * std dev of Gaussian contains 90%
    fSigma = materialRM / 1.645;
  }
 
  // Calculate rotation matrix along the particle momentum direction
  // It will rotate the shower axes to match the incoming particle direction
  G4RotationMatrix rotMatrix = G4RotationMatrix();
  double particleTheta       = particleDirection.theta();
  double particlePhi         = particleDirection.phi();
  double epsilon             = 1e-3;
  rotMatrix.rotateY(particleTheta);
  // do not use (random) phi if x==y==0
  if(!(std::fabs(particleDirection.x()) < epsilon &&
       std::fabs(particleDirection.y()) < epsilon))
    rotMatrix.rotateZ(particlePhi);
 
  // Create hits
  // First use rejecton sampling to sample from Gamma distribution
  // then get random numbers from uniform distribution for azimuthal angle, and
  // from Gaussian for radius
  G4ThreeVector position;
  G4double gammaMax   = Gamma((fAlpha - 1) / fBeta, fAlpha, fBeta);
  G4int generatedHits = 0;
  while(generatedHits < fNbOfHits)
  {
    G4double random1 = G4UniformRand() * fLongMaxDepth;
    G4double random2 = G4UniformRand() * gammaMax;
    if(Gamma(random1, fAlpha, fBeta) >= random2)
    {
      // Generate corresponding rho (phi) from Gaussian (flat) distribution
      G4double phiPosition = G4UniformRand() * 2 * CLHEP::pi;
      G4double rhoPosition = G4RandGauss::shoot(0, fSigma);
      position             = particlePosition +
                 rotMatrix * G4ThreeVector(rhoPosition * std::sin(phiPosition),
                                           rhoPosition * std::cos(phiPosition),
                                           random1 * materialX0);
      // Create energy deposit in the detector
      // This will call appropriate sensitive detector class
      fHitMaker->make(G4FastHit(position, energy / fNbOfHits), aFastTrack);
      generatedHits++;
    }
  }
}

Print()

void Par03EMShowerModel::Print

(

)

const

Print current settings.

Definition at line 188 of file Par03EMShowerModel.cc.

{
  G4cout << "Par03EMShowerModel: " << G4endl;
  G4cout << "Gaussian distribution (transverse plane): \tmu = 0, sigma = "
         << G4BestUnit(fSigma, "Length") << G4endl;
  if(fSigma < 0)
    G4cout << "Negative sigma value means that it will be recalculated "
              "from the value of the Moliere radius of the detector material, "
              "taking into account that 90% of the area below the Gaussian "
              "distribution (from mu - 1.645 sigma to mu + 1.645 sigma) "
              "corresponds to area within 1 Moliere radius."
           << G4endl;
  G4cout << "Gamma distribution (along shower axis): \talpha = " << fAlpha
         << ", beta = " << fBeta << ", max depth = " << fLongMaxDepth << " X0"
         << G4endl;
  if(fAlpha < 0)
    G4cout << "Negative alpha value means that it will be recalculated "
              "from the critical energy of the detector material, particle "
              "type, and beta parameter.\n alpha = beta * T_max, where T_max = "
              "ln(E/E_C) + C\n where E is particle energy, E_C is critical "
              "energy in the material, and constant C = -0.5 for electrons and "
              "0.5 for photons (Eq. (33.36) from PDG)."
           << G4endl;
  G4cout << "Number of created energy deposits: " << fNbOfHits << G4endl;
}

SetSigma()

void Par03EMShowerModel::SetSigma ( const G4double  aSigma )

inline

Set standard deviation of a Gaussian distribution that describes the transverse shower profile.

Definition at line 94 of file Par03EMShowerModel.hh.

{ fSigma = aSigma; };

GetSigma()

G4double Par03EMShowerModel::GetSigma ( ) const

inline

Get standard deviation of a Gaussian distribution that describes the transverse shower profile.

Definition at line 97 of file Par03EMShowerModel.hh.

{ return fSigma; };

SetAlpha()

void Par03EMShowerModel::SetAlpha ( const G4double  aAlpha )

inline

Set alpha parameter of a Gamma distribution that describes the longitudinal shower profile.

Definition at line 100 of file Par03EMShowerModel.hh.

{ fAlpha = aAlpha; };

GetAlpha()

G4double Par03EMShowerModel::GetAlpha ( ) const

inline

Get alpha parameter of a Gamma distribution that describes the longitudinal shower profile.

Definition at line 103 of file Par03EMShowerModel.hh.

{ return fAlpha; };

SetBeta()

void Par03EMShowerModel::SetBeta ( const G4double  aBeta )

inline

Set beta parameter of a Gamma distribution that describes the longitudinal shower profile.

Definition at line 106 of file Par03EMShowerModel.hh.

{ fBeta = aBeta; };

GetBeta()

G4double Par03EMShowerModel::GetBeta ( ) const

inline

Get beta parameter of a Gamma distribution that describes the longitudinal shower profile.

Definition at line 109 of file Par03EMShowerModel.hh.

{ return fBeta; };

SetNbOfHits()

void Par03EMShowerModel::SetNbOfHits ( const G4int  aNumber )

inline

Set number of (same energy) hits created in the parametrisation.

Definition at line 111 of file Par03EMShowerModel.hh.

{ fNbOfHits = aNumber; };

GetNbOfHits()

G4int Par03EMShowerModel::GetNbOfHits ( ) const

inline

Get number of (same energy) hits created in the parametrisation.s.

Definition at line 113 of file Par03EMShowerModel.hh.

{ return fNbOfHits; };

SetLongMaxDepth()

void Par03EMShowerModel::SetLongMaxDepth ( const G4double  aDepth )

inline

Set maximum depth of shower created in fast simulation.

It is expressed in units of radiaton length.

Definition at line 116 of file Par03EMShowerModel.hh.

  {
    fLongMaxDepth = aDepth;
  };

GetLongMaxDepth()

G4double Par03EMShowerModel::GetLongMaxDepth ( ) const

inline

Get maximum depth of shower created in fast simulation.

It is expressed in units of radiaton length.

Definition at line 122 of file Par03EMShowerModel.hh.

{ return fLongMaxDepth; };

Gamma()

G4double Par03EMShowerModel::Gamma ( G4double  x, G4double  alpha, G4double  beta  )

inlineprivate

Gamma distribution.

Definition at line 126 of file Par03EMShowerModel.hh.

  {
    return (std::pow(beta, alpha) / std::tgamma(alpha) * std::pow(x, alpha - 1) *
            std::exp(-beta * x));
  }

Gaussian()

G4double Par03EMShowerModel::Gaussian ( G4double  x, G4double  sigma = 1, G4double  x0 = 0  )

inlineprivate

Gaussian distribution.

Definition at line 132 of file Par03EMShowerModel.hh.

  {
    G4double tmp = (x - x0) / sigma;
    return (1.0 / (std::sqrt(2 * CLHEP::pi) * sigma)) * std::exp(-tmp * tmp / 2);
  }

Member Data Documentation

fMessenger

Par03EMShowerMessenger* Par03EMShowerModel::fMessenger

private

Messenger for configuration.

Definition at line 140 of file Par03EMShowerModel.hh.

fHitMaker

std::unique_ptr<G4FastSimHitMaker> Par03EMShowerModel::fHitMaker

private

Helper class for creation of hits within the sensitive detector.

Definition at line 142 of file Par03EMShowerModel.hh.

fSigma

G4double Par03EMShowerModel::fSigma = -1

private

Standard deviation of the Gaussian distribution Can be changed with UI command /Par03/fastSim/transverseProfile/sigma <sigma> If sigma is smaller than 0, it will be estimated from the detector material (Moliere radius).

Definition at line 148 of file Par03EMShowerModel.hh.

fAlpha

G4double Par03EMShowerModel::fAlpha = -1

private

Alpha parameter of the Gamma distribution Can be changed with UI command /Par03/fastSim/longitudunalProfile/alpha <alpha> If alpha is smaller than 0, it will be estimated from particle energy and the detector material.

Definition at line 154 of file Par03EMShowerModel.hh.

fBeta

G4double Par03EMShowerModel::fBeta = 0.5

private

Beta parameter of the Gamma distribution Can be changed with UI command /Par03/fastSim/longitudinalProfile/beta <beta>

Definition at line 158 of file Par03EMShowerModel.hh.

fNbOfHits

G4int Par03EMShowerModel::fNbOfHits = 100

private

Number of (same energy) hits created by the parametrisation.

Can be changed with UI command /Par03/fastSim/numberOfHits <number>

Definition at line 161 of file Par03EMShowerModel.hh.

fLongMaxDepth

G4double Par03EMShowerModel::fLongMaxDepth = 30

private

Maximum depth of a shower created in fast simulation.

It is expressed in units of radiation length. Can be changed with UI command /Par03/fastSim/longitudinalProfile/maxDepth <depth>

Definition at line 165 of file Par03EMShowerModel.hh.

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

• .doxygen/Doxymodules_parameterisations.h
• extended/parameterisations/Par03/include/Par03EMShowerModel.hh
• extended/parameterisations/Par03/src/Par03EMShowerModel.cc