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fastsim::PairProduction Class Reference

Computes the probability for photons to convert into an e+e- pair in the tracker layer. More...

Inheritance diagram for fastsim::PairProduction:
fastsim::InteractionModel

Public Member Functions

void interact (fastsim::Particle &particle, const SimplifiedGeometry &layer, std::vector< std::unique_ptr< fastsim::Particle > > &secondaries, const RandomEngineAndDistribution &random) override
 Perform the interaction. More...
 
 PairProduction (const std::string &name, const edm::ParameterSet &cfg)
 Constructor. More...
 
 ~PairProduction () 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 Member Functions

double gbteth (double ener, double partm, double efrac, const RandomEngineAndDistribution &random) const
 A universal angular distribution. More...
 

Private Attributes

double minPhotonEnergy_
 Cut on minimum energy of photons. More...
 
double Z_
 Atomic number of material (usually silicon Z=14) More...
 

Detailed Description

Computes the probability for photons to convert into an e+e- pair in the tracker layer.

In case, it returns a list of two Secondaries (e+ and e-).

Definition at line 31 of file PairProduction.cc.

Constructor & Destructor Documentation

◆ PairProduction()

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

Constructor.

Definition at line 67 of file PairProduction.cc.

References looper::cfg, minPhotonEnergy_, and Z_.

69  // Set the minimal photon energy for possible conversion
70  minPhotonEnergy_ = cfg.getParameter<double>("photonEnergyCut");
71  // Material properties
72  Z_ = cfg.getParameter<double>("Z");
73 }
double Z_
Atomic number of material (usually silicon Z=14)
Base class for any interaction model between a particle and a tracker layer.
double minPhotonEnergy_
Cut on minimum energy of photons.

◆ ~PairProduction()

fastsim::PairProduction::~PairProduction ( )
inlineoverride

Default destructor.

Definition at line 37 of file PairProduction.cc.

37 { ; };

Member Function Documentation

◆ gbteth()

double fastsim::PairProduction::gbteth ( double  ener,
double  partm,
double  efrac,
const RandomEngineAndDistribution random 
) const
private

A universal angular distribution.

Parameters
ener
partm
efrac
randomThe Random Engine.
Returns
Theta from universal distribution

Definition at line 176 of file PairProduction.cc.

References HLT_2023v12_cff::beta, ztail::d, RandomEngineAndDistribution::flatShoot(), dqm-mbProfile::log, and M_PI.

179  {
180  // Details on implementation here
181  // http://www.dnp.fmph.uniba.sk/cernlib/asdoc/geant_html3/node299.html#GBTETH
182  // http://svn.cern.ch/guest/AliRoot/tags/v3-07-03/GEANT321/gphys/gbteth.F
183 
184  const double alfa = 0.625;
185 
186  const double d = 0.13 * (0.8 + 1.3 / Z_) * (100.0 + (1.0 / ener)) * (1.0 + efrac);
187  const double w1 = 9.0 / (9.0 + d);
188  const double umax = ener * M_PI / partm;
189  double u;
190 
191  do {
192  double beta = (random.flatShoot() <= w1) ? alfa : 3.0 * alfa;
193  u = -std::log(random.flatShoot() * random.flatShoot()) / beta;
194  } while (u >= umax);
195 
196  return u;
197 }
double Z_
Atomic number of material (usually silicon Z=14)
d
Definition: ztail.py:151
#define M_PI
double flatShoot(double xmin=0.0, double xmax=1.0) const

◆ interact()

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

Perform the interaction.

Parameters
particleThe particle that interacts with the matter.
layerThe detector layer that interacts with the particle.
secondariesParticles that are produced in the interaction (if any).
randomThe Random Engine.

Implements fastsim::InteractionModel.

Definition at line 75 of file PairProduction.cc.

References funct::cos(), fastsim::Constants::eMass, RandomEngineAndDistribution::flatShoot(), dqm-mbProfile::log, M_PI, SiStripPI::max, fastsim::Particle::momentum(), fastsim::Particle::pdgId(), fastsim::Particle::position(), funct::sin(), and mathSSE::sqrt().

78  {
79  double eGamma = particle.momentum().e();
80  //
81  // only consider photons
82  //
83  if (particle.pdgId() != 22) {
84  return;
85  }
86 
87  double radLengths = layer.getThickness(particle.position(), particle.momentum());
88  //
89  // no material
90  //
91  if (radLengths < 1E-10) {
92  return;
93  }
94 
95  //
96  // The photon has enough energy to create a pair
97  //
98  if (eGamma < minPhotonEnergy_) {
99  return;
100  }
101 
102  //
103  // Probability to convert is 7/9*(dx/X0)
104  //
105  if (-std::log(random.flatShoot()) > (7. / 9.) * radLengths) {
106  return;
107  }
108 
109  double xe = 0;
111  double xm = eMass / eGamma;
112  double weight = 0.;
113 
114  // Generate electron energy between emass and eGamma-emass
115  do {
116  xe = random.flatShoot() * (1. - 2. * xm) + xm;
117  weight = 1. - 4. / 3. * xe * (1. - xe);
118  } while (weight < random.flatShoot());
119 
120  // the electron
121  double eElectron = xe * eGamma;
122  double tElectron = eElectron - eMass;
123  double pElectron = std::sqrt(std::max((eElectron + eMass) * tElectron, 0.));
124 
125  // the positron
126  double ePositron = eGamma - eElectron;
127  double tPositron = ePositron - eMass;
128  double pPositron = std::sqrt((ePositron + eMass) * tPositron);
129 
130  // Generate angles
131  double phi = random.flatShoot() * 2. * M_PI;
132  double sphi = std::sin(phi);
133  double cphi = std::cos(phi);
134 
135  double stheta1, stheta2, ctheta1, ctheta2;
136 
137  if (eElectron > ePositron) {
138  double theta1 = gbteth(eElectron, eMass, xe, random) * eMass / eElectron;
139  stheta1 = std::sin(theta1);
140  ctheta1 = std::cos(theta1);
141  stheta2 = stheta1 * pElectron / pPositron;
142  ctheta2 = std::sqrt(std::max(0., 1.0 - (stheta2 * stheta2)));
143  } else {
144  double theta2 = gbteth(ePositron, eMass, xe, random) * eMass / ePositron;
145  stheta2 = std::sin(theta2);
146  ctheta2 = std::cos(theta2);
147  stheta1 = stheta2 * pPositron / pElectron;
148  ctheta1 = std::sqrt(std::max(0., 1.0 - (stheta1 * stheta1)));
149  }
150 
151  //Rotate to the lab frame
152  double thetaLab = particle.momentum().Theta();
153  double phiLab = particle.momentum().Phi();
154 
155  // Add a electron
156  secondaries.emplace_back(new fastsim::Particle(
157  11,
158  particle.position(),
159  math::XYZTLorentzVector(pElectron * stheta1 * cphi, pElectron * stheta1 * sphi, pElectron * ctheta1, eElectron)));
160  secondaries.back()->momentum() =
161  ROOT::Math::RotationZ(phiLab) * (ROOT::Math::RotationY(thetaLab) * secondaries.back()->momentum());
162 
163  // Add a positron
164  secondaries.emplace_back(new fastsim::Particle(
165  -11,
166  particle.position(),
168  -pPositron * stheta2 * cphi, -pPositron * stheta2 * sphi, pPositron * ctheta2, ePositron)));
169  secondaries.back()->momentum() =
170  ROOT::Math::RotationZ(phiLab) * (ROOT::Math::RotationY(thetaLab) * secondaries.back()->momentum());
171 
172  // The photon converted
173  particle.momentum().SetXYZT(0., 0., 0., 0.);
174 }
Sin< T >::type sin(const T &t)
Definition: Sin.h:22
const math::XYZTLorentzVector & position() const
Return position of the particle.
Definition: Particle.h:140
Definition: weight.py:1
static double constexpr eMass
Electron mass[GeV].
Definition: Constants.h:13
XYZTLorentzVectorD XYZTLorentzVector
Lorentz vector with cylindrical internal representation using pseudorapidity.
Definition: LorentzVector.h:29
T sqrt(T t)
Definition: SSEVec.h:19
Cos< T >::type cos(const T &t)
Definition: Cos.h:22
#define M_PI
int pdgId() const
Return pdgId of the particle.
Definition: Particle.h:134
const math::XYZTLorentzVector & momentum() const
Return momentum of the particle.
Definition: Particle.h:143
double minPhotonEnergy_
Cut on minimum energy of photons.
double gbteth(double ener, double partm, double efrac, const RandomEngineAndDistribution &random) const
A universal angular distribution.
double flatShoot(double xmin=0.0, double xmax=1.0) const
Definition of a generic FastSim Particle which can be propagated through the detector (formerly Parti...
Definition: Particle.h:16

Member Data Documentation

◆ minPhotonEnergy_

double fastsim::PairProduction::minPhotonEnergy_
private

Cut on minimum energy of photons.

Definition at line 62 of file PairProduction.cc.

Referenced by PairProduction().

◆ Z_

double fastsim::PairProduction::Z_
private

Atomic number of material (usually silicon Z=14)

Definition at line 63 of file PairProduction.cc.

Referenced by PairProduction().