fastsim::EnergyLoss Class Reference

Implementation of most probable energy loss by ionization in the tracker layers. More...

Inheritance diagram for fastsim::EnergyLoss:

Public Member Functions
	EnergyLoss (const std::string &name, const edm::ParameterSet &cfg)
	Constructor. More...
void	interact (fastsim::Particle &particle, const SimplifiedGeometry &layer, std::vector< std::unique_ptr< fastsim::Particle > > &secondaries, const RandomEngineAndDistribution &random) override
	Perform the interaction. More...
	~EnergyLoss () override
	Default destructor. More...
Public Member Functions inherited from fastsim::InteractionModel
const std::string	getName ()
	Return (unique) name of this interaction. More...
	InteractionModel (std::string name)
	Constructor. More...
virtual void	registerProducts (edm::ProducesCollector) const
	In case interaction produces and stores content in the event (e.g. TrackerSimHits). More...
virtual void	storeProducts (edm::Event &iEvent)
	In case interaction produces and stores content in the event (e.g. TrackerSimHits). More...
virtual	~InteractionModel ()
	Default destructor. More...

Private Attributes
double	A_
	Atomic weight of material (usually silicon A=28.0855) More...
double	density_
	Density of material (usually silicon rho=2.329) More...
double	minMomentum_
	Minimum momentum of incoming (charged) particle. More...
double	radLenInCm_
	Radiation length of material (usually silicon X0=9.360) More...
LandauFluctuationGenerator	theGenerator
	Generator to do Landau fluctuation. More...
double	Z_
	Atomic number of material (usually silicon Z=14) More...

Detailed Description

Implementation of most probable energy loss by ionization in the tracker layers.

Computes the most probable energy loss by ionization from a charged particle in the tracker layer, smears it with Landau fluctuations and returns the particle with modified energy. The deposited energy is assigned with a produced SimHit (if active material hit).

See also

TrackerSimHitProducer

Definition at line 32 of file EnergyLoss.cc.

Constructor & Destructor Documentation

EnergyLoss()

fastsim::EnergyLoss::EnergyLoss	(	const std::string &	name,
		const edm::ParameterSet &	cfg
	)

Constructor.

Definition at line 62 of file EnergyLoss.cc.

    : fastsim::InteractionModel(name), theGenerator(LandauFluctuationGenerator()) {
  // Set the minimal momentum
  minMomentum_ = cfg.getParameter<double>("minMomentumCut");
  // Material properties
  A_ = cfg.getParameter<double>("A");
  Z_ = cfg.getParameter<double>("Z");
  density_ = cfg.getParameter<double>("density");
  radLenInCm_ = cfg.getParameter<double>("radLen");
}

References A_, looper::cfg, density_, minMomentum_, radLenInCm_, and Z_.

~EnergyLoss()

fastsim::EnergyLoss::~EnergyLoss ( )

inlineoverride

Default destructor.

Definition at line 38 of file EnergyLoss.cc.

{ ; };

Member Function Documentation

interact()

void fastsim::EnergyLoss::interact ( fastsim::Particle &  particle, const SimplifiedGeometry &  layer, std::vector< std::unique_ptr< fastsim::Particle > > &  secondaries, const RandomEngineAndDistribution &  random  )

overridevirtual

Perform the interaction.

Parameters

particle	The particle that interacts with the matter.
layer	The detector layer that interacts with the particle.
secondaries	Particles that are produced in the interaction (if any).
random	The Random Engine.

Implements fastsim::InteractionModel.

Definition at line 73 of file EnergyLoss.cc.

                                                                              {
  // Reset the energy deposit in the layer
  particle.setEnergyDeposit(0);
 
  //
  // no material
  //
  double radLengths = layer.getThickness(particle.position(), particle.momentum());
  if (radLengths < 1E-10) {
    return;
  }
 
  //
  // only charged particles
  //
  if (particle.charge() == 0) {
    return;
  }
 
  //
  // minimum momentum
  //
  double p2 = particle.momentum().Vect().Mag2();
  if (p2 < minMomentum_ * minMomentum_) {
    return;
  }
 
  // Mean excitation energy (in GeV)
  double excitE = 12.5E-9 * Z_;
 
  // The thickness in cm
  double thick = radLengths * radLenInCm_;
 
  // This is a simple version (a la PDG) of a dE/dx generator.
  // It replaces the buggy GEANT3 -> C++ former version.
  // Author : Patrick Janot - 8-Jan-2004
 
  double m2 = particle.momentum().mass() * particle.momentum().mass();
  double e2 = p2 + m2;
 
  double beta2 = p2 / e2;
  double gama2 = e2 / m2;
 
  double charge2 = particle.charge() * particle.charge();
 
  // Energy loss spread in GeV
  double eSpread = 0.1536E-3 * charge2 * (Z_ / A_) * density_ * thick / beta2;
 
  // Most probable energy loss (from the integrated Bethe-Bloch equation)
  double mostProbableLoss =
      eSpread * (log(2. * fastsim::Constants::eMass * beta2 * gama2 * eSpread / (excitE * excitE)) - beta2 + 0.200);
 
  // Generate the energy loss with Landau fluctuations
  double dedx = mostProbableLoss + eSpread * theGenerator.landau(&random);
 
  // Compute the new energy and momentum
  double newE = particle.momentum().e() - dedx;
 
  // Particle is stopped
  double eDiff2 = newE * newE - m2;
  if (eDiff2 < 0) {
    particle.momentum().SetXYZT(0., 0., 0., 0.);
    // The energy is deposited in the detector
    // Assigned with SimHit (if active layer) -> see TrackerSimHitProducer
    particle.setEnergyDeposit(particle.momentum().e() - particle.momentum().mass());
    return;
  }
 
  // Relative change in momentum
  double fac = std::sqrt(eDiff2 / p2);
 
  // The energy is deposited in the detector
  // Assigned with SimHit (if active layer) -> see TrackerSimHitProducer
  particle.setEnergyDeposit(dedx);
 
  // Update the momentum
  particle.momentum().SetXYZT(
      particle.momentum().Px() * fac, particle.momentum().Py() * fac, particle.momentum().Pz() * fac, newE);
}

References fastsim::Particle::charge(), fastsim::Constants::eMass, phase1PixelTopology::layer, dqm-mbProfile::log, fastsim::Particle::momentum(), p2, fastsim::Particle::position(), fastsim::Particle::setEnergyDeposit(), and mathSSE::sqrt().

Member Data Documentation

A_

double fastsim::EnergyLoss::A_

private

Atomic weight of material (usually silicon A=28.0855)

Definition at line 57 of file EnergyLoss.cc.

Referenced by EnergyLoss().

density_

double fastsim::EnergyLoss::density_

private

Density of material (usually silicon rho=2.329)

Definition at line 55 of file EnergyLoss.cc.

Referenced by EnergyLoss().

minMomentum_

double fastsim::EnergyLoss::minMomentum_

private

Minimum momentum of incoming (charged) particle.

Definition at line 54 of file EnergyLoss.cc.

Referenced by EnergyLoss().

radLenInCm_

double fastsim::EnergyLoss::radLenInCm_

private

Radiation length of material (usually silicon X0=9.360)

Definition at line 56 of file EnergyLoss.cc.

Referenced by EnergyLoss().

theGenerator

LandauFluctuationGenerator fastsim::EnergyLoss::theGenerator

private

Generator to do Landau fluctuation.

Definition at line 53 of file EnergyLoss.cc.

Z_

double fastsim::EnergyLoss::Z_

private

Atomic number of material (usually silicon Z=14)

Definition at line 58 of file EnergyLoss.cc.

Referenced by EnergyLoss().