lars/geant4
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity
Files
96686e0c8f4994abca7e1ccf08ac315c6d680b1e
geant4/source/processes/electromagnetic/standard/src/G4AnnihiToMuPair.cc
T
Gabriele Cosmo 96686e0c8f Import Geant4 6.0.0 source tree
2016-06-09 10:41:53 +02:00

251 lines
9.4 KiB
C++
Raw Blame History

//
// ********************************************************************
// * DISCLAIMER *
// * *
// * The following disclaimer summarizes all the specific disclaimers *
// * of contributors to this software. The specific disclaimers,which *
// * govern, are listed with their locations in: *
// * http://cern.ch/geant4/license *
// * *
// * Neither the authors of this software system, nor their employing *
// * institutes,nor the agencies providing financial support for this *
// * work make any representation or warranty, express or implied, *
// * regarding this software system or assume any liability for its *
// * use. *
// * *
// * This code implementation is the intellectual property of the *
// * GEANT4 collaboration. *
// * By copying, distributing or modifying the Program (or any work *
// * based on the Program) you indicate your acceptance of this *
// * statement, and all its terms. *
// ********************************************************************
//
//
// $Id: G4AnnihiToMuPair.cc,v 1.2 2003/02/04 11:08:42 maire Exp $
// GEANT4 tag $Name: geant4-06-00 $
//
// ------------ G4AnnihiToMuPair physics process ------
// by H.Burkhardt, S. Kelner and R. Kokoulin, November 2002
// -----------------------------------------------------------------------------
//
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......//
//
// 04.02.03 : cosmetic simplifications (mma)
// 27.01.03 : first implementation (hbu)
//
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
#include "G4AnnihiToMuPair.hh"
#include "G4ios.hh"
#include "Randomize.hh"
#include "G4Positron.hh"
#include "G4MuonPlus.hh"
#include "G4MuonMinus.hh"
#include "G4Material.hh"
#include "G4Step.hh"
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
// constructor
G4AnnihiToMuPair::G4AnnihiToMuPair(const G4String& processName)
: G4VDiscreteProcess (processName)
{
//e+ Energy threshold
const G4double Mu_massc2 = G4MuonPlus::MuonPlus()->GetPDGMass();
LowestEnergyLimit = 2*Mu_massc2*Mu_massc2/electron_mass_c2 - electron_mass_c2;
//modele ok up to 1000 TeV due to neglected Z-interference
HighestEnergyLimit = 1000*TeV;
CrossSecFactor = 1.;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4AnnihiToMuPair::~G4AnnihiToMuPair() // (empty) destructor
{ }
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4bool G4AnnihiToMuPair::IsApplicable(const G4ParticleDefinition& particle)
{
return ( &particle == G4Positron::Positron() );
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
void G4AnnihiToMuPair::BuildPhysicsTable(const G4ParticleDefinition&)
// Build cross section and mean free path tables
//here no tables, just calling PrintInfoDefinition
{
PrintInfoDefinition();
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
void G4AnnihiToMuPair::SetCrossSecFactor(G4double fac)
// Set the factor to artificially increase the cross section
{
CrossSecFactor = fac;
G4cout << "The cross section for AnnihiToMuPair is artificially "
<< "increased by the CrossSecFactor=" << CrossSecFactor << G4endl;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4double G4AnnihiToMuPair::ComputeCrossSectionPerAtom(G4double Epos, G4double Z)
// Calculates the microscopic cross section in GEANT4 internal units.
// It gives a good description from threshold to 1000 GeV
{
static const G4double Mmuon = G4MuonPlus::MuonPlus()->GetPDGMass();
static const G4double Rmuon = elm_coupling/Mmuon; //classical particle radius
static const G4double Sig0 = pi*Rmuon*Rmuon/3.; //constant in crossSection
G4double CrossSection = 0.;
if (Epos < LowestEnergyLimit) return CrossSection;
G4double xi = LowestEnergyLimit/Epos;
G4double SigmaEl = Sig0*xi*(1.+xi/2.)*sqrt(1.-xi); // per electron
CrossSection = SigmaEl*Z; // number of electrons per atom
CrossSection *= CrossSecFactor; //increase the CrossSection by (default 1)
return CrossSection;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4double G4AnnihiToMuPair::GetMeanFreePath(const G4Track& aTrack,
G4double, G4ForceCondition*)
// returns the positron mean free path in GEANT4 internal units
{
const G4DynamicParticle* aDynamicPositron = aTrack.GetDynamicParticle();
G4double PositronEnergy = aDynamicPositron->GetKineticEnergy()
+electron_mass_c2;
G4Material* aMaterial = aTrack.GetMaterial();
const G4ElementVector* theElementVector = aMaterial->GetElementVector();
const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
G4double SIGMA = 0 ;
for ( size_t i=0 ; i < aMaterial->GetNumberOfElements() ; i++ )
{
G4double AtomicZ = (*theElementVector)[i]->GetZ();
SIGMA += NbOfAtomsPerVolume[i] *
ComputeCrossSectionPerAtom(PositronEnergy,AtomicZ);
}
return SIGMA > DBL_MIN ? 1./SIGMA : DBL_MAX;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4VParticleChange* G4AnnihiToMuPair::PostStepDoIt(const G4Track& aTrack,
const G4Step& aStep)
//
// generation of e+e- -> mu+mu-
//
{
aParticleChange.Initialize(aTrack);
static const G4double Mele=electron_mass_c2;
static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
// current Positron energy and direction, return if energy too low
const G4DynamicParticle *aDynamicPositron = aTrack.GetDynamicParticle();
G4double Epos = aDynamicPositron->GetKineticEnergy()+Mele;
if (Epos < LowestEnergyLimit)
{ G4cout
<< "error in G4AnnihiToMuPair::PostStepDoIt called with energy below"
" threshold Epos= "
<< Epos << G4endl; // shoud never happen
G4Exception(10);
}
if (Epos < LowestEnergyLimit)
return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
G4ParticleMomentum PositronDirection =
aDynamicPositron->GetMomentumDirection();
G4double xi = LowestEnergyLimit/Epos; // xi is always less than 1,
// goes to 0 at high Epos
// generate cost
//
G4double cost;
do cost = 2.*G4UniformRand()-1.;
while (2.*G4UniformRand() > 1.+xi+cost*cost*(1.-xi) );
//1+cost**2 at high Epos
G4double sint = sqrt(1.-cost*cost);
// generate phi
//
G4double phi=2.*pi*G4UniformRand();
G4double Ecm = sqrt(0.5*Mele*(Epos+Mele));
G4double Pcm = sqrt(Ecm*Ecm-Mmuon*Mmuon);
G4double beta = sqrt((Epos-Mele)/(Epos+Mele));
G4double gamma = Ecm/Mele; // =sqrt((Epos+Mele)/(2.*Mele));
G4double Pt = Pcm*sint;
// energy and momentum of the muons in the Lab
//
G4double EmuPlus = gamma*( Ecm+cost*beta*Pcm);
G4double EmuMinus = gamma*( Ecm-cost*beta*Pcm);
G4double PmuPlusZ = gamma*(beta*Ecm+cost* Pcm);
G4double PmuMinusZ = gamma*(beta*Ecm-cost* Pcm);
G4double PmuPlusX = Pt*cos(phi);
G4double PmuPlusY = Pt*sin(phi);
G4double PmuMinusX =-Pt*cos(phi);
G4double PmuMinusY =-Pt*sin(phi);
// absolute momenta
G4double PmuPlus = sqrt(Pt*Pt+PmuPlusZ *PmuPlusZ );
G4double PmuMinus = sqrt(Pt*Pt+PmuMinusZ*PmuMinusZ);
// mu+ mu- directions for Positron in z-direction
//
G4ThreeVector
MuPlusDirection ( PmuPlusX/PmuPlus, PmuPlusY/PmuPlus, PmuPlusZ/PmuPlus );
G4ThreeVector
MuMinusDirection(PmuMinusX/PmuMinus,PmuMinusY/PmuMinus,PmuMinusZ/PmuMinus);
// rotate to actual Positron direction
//
MuPlusDirection.rotateUz(PositronDirection);
MuMinusDirection.rotateUz(PositronDirection);
aParticleChange.SetNumberOfSecondaries(2);
// create G4DynamicParticle object for the particle1
G4DynamicParticle* aParticle1= new G4DynamicParticle(
G4MuonPlus::MuonPlus(),MuPlusDirection,EmuPlus-Mmuon);
aParticleChange.AddSecondary(aParticle1);
// create G4DynamicParticle object for the particle2
G4DynamicParticle* aParticle2= new G4DynamicParticle(
G4MuonMinus::MuonMinus(),MuMinusDirection,EmuMinus-Mmuon);
aParticleChange.AddSecondary(aParticle2);
// Kill the incident positron
//
aParticleChange.SetMomentumChange( 0., 0., 0. );
aParticleChange.SetEnergyChange(0.);
aParticleChange.SetStatusChange(fStopAndKill);
return &aParticleChange;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
void G4AnnihiToMuPair::PrintInfoDefinition()
{
G4String comments ="e+e->mu+mu- annihilation, atomic e- at rest.\n";
G4cout << G4endl << GetProcessName() << ": " << comments
<< " threshold at " << LowestEnergyLimit/GeV << " GeV"
<< " good description up to "
<< HighestEnergyLimit/TeV << " TeV for all Z." << G4endl;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
Reference in New Issue View Git Blame Copy Permalink