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6aa23be5171b125c3363b5a4cfa00a57e524598b
geant4/source/processes/electromagnetic/highenergy/src/G4AnnihiToMuPair.cc
T
Gabriele Cosmo 6aa23be517 Import Geant4 10.5.0.beta source tree
2018-06-29 10:58:11 +02:00

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//
// ********************************************************************
// * License and Disclaimer *
// * *
// * The Geant4 software is copyright of the Copyright Holders of *
// * the Geant4 Collaboration. It is provided under the terms and *
// * conditions of the Geant4 Software License, included in the file *
// * LICENSE and available at http://cern.ch/geant4/license . These *
// * include a list of copyright holders. *
// * *
// * 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. Please see the license in the file LICENSE and URL above *
// * for the full disclaimer and the limitation of liability. *
// * *
// * This code implementation is the result of the scientific and *
// * technical work of the GEANT4 collaboration. *
// * By using, copying, modifying or distributing the software (or *
// * any work based on the software) you agree to acknowledge its *
// * use in resulting scientific publications, and indicate your *
// * acceptance of all terms of the Geant4 Software license. *
// ********************************************************************
//
//
// $Id: G4AnnihiToMuPair.cc 108750 2018-03-02 15:26:50Z gcosmo $
//
// ------------ G4AnnihiToMuPair physics process ------
// by H.Burkhardt, S. Kelner and R. Kokoulin, November 2002
// -----------------------------------------------------------------------------
//
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......//
//
// 27.01.03 : first implementation (hbu)
// 04.02.03 : cosmetic simplifications (mma)
// 25.10.04 : migrade to new interfaces of ParticleChange (vi)
// 28.02.18 : cross section now including SSS threshold factor
//
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
#include "G4AnnihiToMuPair.hh"
#include "G4ios.hh"
#include "Randomize.hh"
#include "G4PhysicalConstants.hh"
#include "G4SystemOfUnits.hh"
#include "G4Positron.hh"
#include "G4MuonPlus.hh"
#include "G4MuonMinus.hh"
#include "G4Material.hh"
#include "G4Step.hh"
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
using namespace std;
G4AnnihiToMuPair::G4AnnihiToMuPair(const G4String& processName,
G4ProcessType type):G4VDiscreteProcess (processName, type)
{
//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;
CurrentSigma = 0.0;
CrossSecFactor = 1.;
SetProcessSubType(6);
}
//....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
{
CurrentSigma = 0.0;
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 = CLHEP::elm_coupling/Mmuon; //classical particle radius
static const G4double Sig0 = CLHEP::pi*Rmuon*Rmuon/3.; //constant in crossSection
static const G4double pia = CLHEP::pi * CLHEP::fine_structure_const; // pi * alphaQED
G4double CrossSection = 0.;
if (Epos < LowestEnergyLimit) return CrossSection;
G4double xi = LowestEnergyLimit/Epos;
G4double piaxi = pia * sqrt(xi);
G4double SigmaEl = Sig0 * xi * (1.+xi/2.) * piaxi;
if( Epos>LowestEnergyLimit+1.e-5 ) SigmaEl /= (1.-std::exp( -piaxi/std::sqrt(1-xi) ));
CrossSection = SigmaEl*Z; // SigmaEl per electron * number of electrons per atom
return CrossSection;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
G4double G4AnnihiToMuPair::CrossSectionPerVolume(G4double PositronEnergy,
const G4Material* aMaterial)
{
const G4ElementVector* theElementVector = aMaterial->GetElementVector();
const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
G4double SIGMA = 0.0;
for ( size_t i=0 ; i < aMaterial->GetNumberOfElements() ; ++i )
{
G4double AtomicZ = (*theElementVector)[i]->GetZ();
SIGMA += NbOfAtomsPerVolume[i] *
ComputeCrossSectionPerAtom(PositronEnergy,AtomicZ);
}
return SIGMA;
}
//....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();
CurrentSigma = CrossSectionPerVolume(PositronEnergy, aMaterial);
// increase the CrossSection by CrossSecFactor (default 1)
G4double mfp = DBL_MAX;
if(CurrentSigma > DBL_MIN) mfp = 1.0/(CurrentSigma*CrossSecFactor);
return mfp;
}
//....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;
// test of cross section
if(CurrentSigma*G4UniformRand() >
CrossSectionPerVolume(Epos, aTrack.GetMaterial()))
{
return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
}
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.; }
// Loop checking, 07-Aug-2015, Vladimir Ivanchenko
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.ProposeEnergy(0.);
aParticleChange.ProposeTrackStatus(fStopAndKill);
return &aParticleChange;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
void G4AnnihiToMuPair::PrintInfoDefinition()
{
G4String comments ="e+e->mu+mu- annihilation, atomic e- at rest, SubType=.";
G4cout << G4endl << GetProcessName() << ": " << comments
<< GetProcessSubType() << G4endl;
G4cout << " threshold at " << LowestEnergyLimit/GeV << " GeV"
<< " good description up to "
<< HighestEnergyLimit/TeV << " TeV for all Z." << G4endl;
}
//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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