#include <PairProductionSimulator.h>

Inheritance diagram for PairProductionSimulator:

Public Member Functions
	PairProductionSimulator (double photonEnergyCut)
	Constructor. More...

	~PairProductionSimulator () override
	Default Destructor. More...

Public Member Functions inherited from MaterialEffectsSimulator
RHEP_const_iter	beginDaughters () const
	Returns const iterator to the beginning of the daughters list. More...

int	closestDaughterId ()
	The id of the closest charged daughter (filled for nuclear interactions only) More...

double	eMass () const
	Electron mass in GeV/c2. More...

RHEP_const_iter	endDaughters () const
	Returns const iterator to the end of the daughters list. More...

double	excitE () const
	Mean excitation energy (in GeV) More...

	MaterialEffectsSimulator (double A=28.0855, double Z=14.0000, double density=2.329, double radLen=9.360)

unsigned	nDaughters () const
	Returns the number of daughters. More...

XYZVector	orthogonal (const XYZVector &) const
	A vector orthogonal to another one (because it's not in XYZTLorentzVector) More...

double	radLenIncm () const
	One radiation length in cm. More...

double	rho () const
	Density in g/cm3. More...

virtual void	save ()
	Used by NuclearInteractionSimulator to save last sampled event. More...

void	setNormalVector (const GlobalVector &normal)
	Sets the vector normal to the surface traversed. More...

double	theA () const
	A. More...

double	theZ () const
	Z. More...

void	updateState (ParticlePropagator &myTrack, double radlen, RandomEngineAndDistribution const *)
	Compute the material effect (calls the sub class) More...

virtual	~MaterialEffectsSimulator ()

Private Member Functions
void	compute (ParticlePropagator &Particle, RandomEngineAndDistribution const *) override
	Generate an e+e- pair according to the probability that it happens. More...

double	gbteth (double ener, double partm, double efrac, RandomEngineAndDistribution const *)
	A universal angular distribution - still from GEANT. More...

Private Attributes
double	photonEnergy
	The minimal photon energy for possible conversion. More...

Additional Inherited Members
Public Types inherited from MaterialEffectsSimulator
typedef std::vector< RawParticle >::const_iterator	RHEP_const_iter

Protected Attributes inherited from MaterialEffectsSimulator
std::vector< RawParticle >	_theUpdatedState

double	A

double	density

double	radLen

double	radLengths

int	theClosestChargedDaughterId

GlobalVector	theNormalVector

double	Z

Detailed Description

Definition at line 24 of file PairProductionSimulator.h.

Constructor & Destructor Documentation

◆ PairProductionSimulator()

PairProductionSimulator::PairProductionSimulator ( double photonEnergyCut )

Constructor.

Definition at line 7 of file PairProductionSimulator.cc.

References SiStripPI::max, photonEnergy, and fastSimProducer_cff::photonEnergyCut.

                                                                        {
   // Set the minimal photon energy for possible conversion
   photonEnergy = std::max(0.100, photonEnergyCut);
 }

◆ ~PairProductionSimulator()

PairProductionSimulator::~PairProductionSimulator ( )

inlineoverride

Default Destructor.

Definition at line 30 of file PairProductionSimulator.h.

30 {}

Member Function Documentation

◆ compute()

void PairProductionSimulator::compute	(	ParticlePropagator &	Particle,
		RandomEngineAndDistribution const *	random
	)

overrideprivatevirtual

Generate an e+e- pair according to the probability that it happens.

Implements MaterialEffectsSimulator.

Definition at line 12 of file PairProductionSimulator.cc.

References MaterialEffectsSimulator::_theUpdatedState, funct::cos(), MaterialEffectsSimulator::eMass(), RandomEngineAndDistribution::flatShoot(), gbteth(), dqm-mbProfile::log, M_PI, makeParticle(), SiStripPI::max, phi, photonEnergy, MaterialEffectsSimulator::radLengths, funct::sin(), and mathSSE::sqrt().

                                                                                                              {
   double eGamma = Particle.particle().e();
 
   // The photon has enough energy to create a pair
   if (eGamma >= photonEnergy) {
     // This is a simple version (a la PDG) of a photon conversion generator.
     // It replaces the buggy GEANT3 -> C++ former version.
     // Author : Patrick Janot - 7-Jan-2004
 
     // Probability to convert is 7/9*(dx/X0)
     if (-std::log(random->flatShoot()) <= (7. / 9.) * radLengths) {
       double xe = 0;
       double xm = eMass() / eGamma;
       double weight = 0.;
 
       // Generate electron energy between emass and eGamma-emass
       do {
         xe = random->flatShoot() * (1. - 2. * xm) + xm;
         weight = 1. - 4. / 3. * xe * (1. - xe);
       } while (weight < random->flatShoot());
 
       double eElectron = xe * eGamma;
       double tElectron = eElectron - eMass();
       double pElectron = std::sqrt(std::max((eElectron + eMass()) * tElectron, 0.));
 
       double ePositron = eGamma - eElectron;
       double tPositron = ePositron - eMass();
       double pPositron = std::sqrt((ePositron + eMass()) * tPositron);
 
       // Generate angles
       double phi = random->flatShoot() * 2. * M_PI;
       double sphi = std::sin(phi);
       double cphi = std::cos(phi);
 
       double stheta1, stheta2, ctheta1, ctheta2;
 
       if (eElectron > ePositron) {
         double theta1 = gbteth(eElectron, eMass(), xe, random) * eMass() / eElectron;
         stheta1 = std::sin(theta1);
         ctheta1 = std::cos(theta1);
         stheta2 = stheta1 * pElectron / pPositron;
         ctheta2 = std::sqrt(std::max(0., 1.0 - (stheta2 * stheta2)));
       } else {
         double theta2 = gbteth(ePositron, eMass(), xe, random) * eMass() / ePositron;
         stheta2 = std::sin(theta2);
         ctheta2 = std::cos(theta2);
         stheta1 = stheta2 * pPositron / pElectron;
         ctheta1 = std::sqrt(std::max(0., 1.0 - (stheta1 * stheta1)));
       }
 
       double chi = Particle.particle().theta();
       double psi = Particle.particle().phi();
       RawParticle::RotationZ rotZ(psi);
       RawParticle::RotationY rotY(chi);
 
       _theUpdatedState.reserve(2);
       _theUpdatedState.clear();
 
       // The electron
       _theUpdatedState.emplace_back(makeParticle(
           Particle.particleDataTable(),
           +11,
           XYZTLorentzVector(pElectron * stheta1 * cphi, pElectron * stheta1 * sphi, pElectron * ctheta1, eElectron)));
       _theUpdatedState[0].rotate(rotY);
       _theUpdatedState[0].rotate(rotZ);
 
       // The positron
       _theUpdatedState.emplace_back(makeParticle(
           Particle.particleDataTable(),
           -11,
           XYZTLorentzVector(-pPositron * stheta2 * cphi, -pPositron * stheta2 * sphi, pPositron * ctheta2, ePositron)));
       _theUpdatedState[1].rotate(rotY);
       _theUpdatedState[1].rotate(rotZ);
     }
   }
 }

◆ gbteth()

double PairProductionSimulator::gbteth	(	double	ener,
		double	partm,
		double	efrac,
		RandomEngineAndDistribution const *	random
	)

private

A universal angular distribution - still from GEANT.

Definition at line 89 of file PairProductionSimulator.cc.

References HLT_2022v12_cff::beta, ztail::d, RandomEngineAndDistribution::flatShoot(), dqm-mbProfile::log, M_PI, and MaterialEffectsSimulator::theZ().

Referenced by compute().

                                                                                   {
   const double alfa = 0.625;
 
   double d = 0.13 * (0.8 + 1.3 / theZ()) * (100.0 + (1.0 / ener)) * (1.0 + efrac);
   double w1 = 9.0 / (9.0 + d);
   double umax = ener * M_PI / partm;
   double u;
 
   do {
     double beta;
     if (random->flatShoot() <= w1)
       beta = alfa;
     else
       beta = 3.0 * alfa;
     u = -(std::log(random->flatShoot() * random->flatShoot())) / beta;
   } while (u >= umax);
 
   return u;
 }

Member Data Documentation

◆ photonEnergy

double PairProductionSimulator::photonEnergy

private

The minimal photon energy for possible conversion.

Definition at line 34 of file PairProductionSimulator.h.

Referenced by compute(), PairProductionSimulator(), and Jet.Jet::photonEnergyFraction().

Public Member Functions

Private Member Functions

Private Attributes

Additional Inherited Members