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::ProducerBase &producer) 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 35 of file EnergyLoss.cc.

Constructor & Destructor Documentation

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

Constructor.

Definition at line 63 of file EnergyLoss.cc.

References A_, density_, edm::ParameterSet::getParameter(), minMomentum_, radLenInCm_, and Z_.

     : 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");
 }

fastsim::EnergyLoss::~EnergyLoss ( )

inlineoverride

Default destructor.

Definition at line 42 of file EnergyLoss.cc.

References interact(), and random.

42 {;};

Member Function Documentation

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 75 of file EnergyLoss.cc.

References A_, fastsim::Particle::charge(), DEFINE_EDM_PLUGIN, density_, reco::e2, fastsim::Constants::eMass, fastsim::SimplifiedGeometry::getThickness(), LandauFluctuationGenerator::landau(), cmsBatch::log, minMomentum_, fastsim::Particle::momentum(), p2, fastsim::Particle::position(), radLenInCm_, fastsim::Particle::setEnergyDeposit(), mathSSE::sqrt(), theGenerator, and Z_.

Referenced by ~EnergyLoss().

 {
     // 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
     if(newE < particle.momentum().mass()){
         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((newE * newE - m2) / 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);
 }   