source: trunk/source/processes/electromagnetic/highenergy/src/G4AnnihiToMuPair.cc @ 1007

Last change on this file since 1007 was 1007, checked in by garnier, 15 years ago

update to geant4.9.2
File size: 9.7 KB
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27// $Id: G4AnnihiToMuPair.cc,v 1.5 2008/10/16 14:29:48 vnivanch Exp $
28// GEANT4 tag $Name: geant4-09-02 $
29//
30//         ------------ G4AnnihiToMuPair physics process ------
31//         by H.Burkhardt, S. Kelner and R. Kokoulin, November 2002
32// -----------------------------------------------------------------------------
33//
34//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......//
35//
36// 27.01.03 : first implementation (hbu)
37// 04.02.03 : cosmetic simplifications (mma)
38// 25.10.04 : migrade to new interfaces of ParticleChange (vi)
39//
40//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
41
42#include "G4AnnihiToMuPair.hh"
43
44#include "G4ios.hh"
45#include "Randomize.hh"
46
47#include "G4Positron.hh"
48#include "G4MuonPlus.hh"
49#include "G4MuonMinus.hh"
50#include "G4Material.hh"
51#include "G4Step.hh"
52
53//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
54
55using namespace std;
56
57G4AnnihiToMuPair::G4AnnihiToMuPair(const G4String& processName,
58    G4ProcessType type):G4VDiscreteProcess (processName, type)
59{
60 //e+ Energy threshold
61 const G4double Mu_massc2 = G4MuonPlus::MuonPlus()->GetPDGMass();
62 LowestEnergyLimit  = 2*Mu_massc2*Mu_massc2/electron_mass_c2 - electron_mass_c2;
63 
64 //modele ok up to 1000 TeV due to neglected Z-interference
65 HighestEnergyLimit = 1000*TeV;
66 
67 CrossSecFactor = 1.;
68 SetProcessSubType(6);
69
70}
71
72//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
73
74G4AnnihiToMuPair::~G4AnnihiToMuPair() // (empty) destructor
75{ }
76
77//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
78
79G4bool G4AnnihiToMuPair::IsApplicable(const G4ParticleDefinition& particle)
80{
81  return ( &particle == G4Positron::Positron() );
82}
83
84//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
85
86void G4AnnihiToMuPair::BuildPhysicsTable(const G4ParticleDefinition&)
87// Build cross section and mean free path tables
88//here no tables, just calling PrintInfoDefinition
89{
90   PrintInfoDefinition();
91}
92
93//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
94
95void G4AnnihiToMuPair::SetCrossSecFactor(G4double fac)
96// Set the factor to artificially increase the cross section
97{ 
98  CrossSecFactor = fac;
99  G4cout << "The cross section for AnnihiToMuPair is artificially "
100         << "increased by the CrossSecFactor=" << CrossSecFactor << G4endl;
101}
102
103//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
104
105G4double G4AnnihiToMuPair::ComputeCrossSectionPerAtom(G4double Epos, G4double Z)
106// Calculates the microscopic cross section in GEANT4 internal units.
107// It gives a good description from threshold to 1000 GeV
108{
109  static const G4double Mmuon = G4MuonPlus::MuonPlus()->GetPDGMass();
110  static const G4double Rmuon = elm_coupling/Mmuon; //classical particle radius
111  static const G4double Sig0  = pi*Rmuon*Rmuon/3.;  //constant in crossSection
112
113  G4double CrossSection = 0.;
114  if (Epos < LowestEnergyLimit) return CrossSection;
115   
116  G4double xi = LowestEnergyLimit/Epos;
117  G4double SigmaEl = Sig0*xi*(1.+xi/2.)*sqrt(1.-xi); // per electron
118  CrossSection = SigmaEl*Z;         // number of electrons per atom
119  CrossSection *= CrossSecFactor;   //increase the CrossSection by  (default 1)
120  return CrossSection;
121}
122
123//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
124
125G4double G4AnnihiToMuPair::GetMeanFreePath(const G4Track& aTrack,
126                                           G4double, G4ForceCondition*)
127
128// returns the positron mean free path in GEANT4 internal units
129
130{
131  const G4DynamicParticle* aDynamicPositron = aTrack.GetDynamicParticle();
132  G4double PositronEnergy = aDynamicPositron->GetKineticEnergy()
133                                              +electron_mass_c2;
134  G4Material* aMaterial = aTrack.GetMaterial();
135  const G4ElementVector* theElementVector = aMaterial->GetElementVector();
136  const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
137
138  G4double SIGMA = 0 ;
139
140  for ( size_t i=0 ; i < aMaterial->GetNumberOfElements() ; i++ )
141  {
142    G4double AtomicZ = (*theElementVector)[i]->GetZ();
143    SIGMA += NbOfAtomsPerVolume[i] *
144      ComputeCrossSectionPerAtom(PositronEnergy,AtomicZ);
145  }
146  return SIGMA > DBL_MIN ? 1./SIGMA : DBL_MAX;
147}
148
149//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
150
151G4VParticleChange* G4AnnihiToMuPair::PostStepDoIt(const G4Track& aTrack,
152                                                  const G4Step&  aStep)
153//
154// generation of e+e- -> mu+mu-
155//
156{
157
158  aParticleChange.Initialize(aTrack);
159  static const G4double Mele=electron_mass_c2;
160  static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
161
162  // current Positron energy and direction, return if energy too low
163  const G4DynamicParticle *aDynamicPositron = aTrack.GetDynamicParticle();
164  G4double Epos = aDynamicPositron->GetKineticEnergy()+Mele;
165
166 if (Epos < LowestEnergyLimit)
167  { G4cout
168        << "error in G4AnnihiToMuPair::PostStepDoIt called with energy below"
169           " threshold Epos= "
170        << Epos << G4endl;       // shoud never happen
171        G4Exception(10);
172  }
173
174  if (Epos < LowestEnergyLimit)
175     return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
176
177  G4ParticleMomentum PositronDirection = 
178                                       aDynamicPositron->GetMomentumDirection();
179  G4double xi = LowestEnergyLimit/Epos; // xi is always less than 1,
180                                        // goes to 0 at high Epos
181
182  // generate cost
183  //
184  G4double cost;
185  do cost = 2.*G4UniformRand()-1.;
186  while (2.*G4UniformRand() > 1.+xi+cost*cost*(1.-xi) ); 
187                                                       //1+cost**2 at high Epos
188  G4double sint = sqrt(1.-cost*cost);
189
190  // generate phi
191  //
192  G4double phi=2.*pi*G4UniformRand();
193
194  G4double Ecm   = sqrt(0.5*Mele*(Epos+Mele));
195  G4double Pcm   = sqrt(Ecm*Ecm-Mmuon*Mmuon);
196  G4double beta  = sqrt((Epos-Mele)/(Epos+Mele));
197  G4double gamma = Ecm/Mele;                    // =sqrt((Epos+Mele)/(2.*Mele));
198  G4double Pt    = Pcm*sint;
199 
200  // energy and momentum of the muons in the Lab
201  //
202  G4double EmuPlus   = gamma*(     Ecm+cost*beta*Pcm);
203  G4double EmuMinus  = gamma*(     Ecm-cost*beta*Pcm);
204  G4double PmuPlusZ  = gamma*(beta*Ecm+cost*     Pcm);
205  G4double PmuMinusZ = gamma*(beta*Ecm-cost*     Pcm);
206  G4double PmuPlusX  = Pt*cos(phi);
207  G4double PmuPlusY  = Pt*sin(phi);
208  G4double PmuMinusX =-Pt*cos(phi);
209  G4double PmuMinusY =-Pt*sin(phi);
210  // absolute momenta
211  G4double PmuPlus  = sqrt(Pt*Pt+PmuPlusZ *PmuPlusZ );
212  G4double PmuMinus = sqrt(Pt*Pt+PmuMinusZ*PmuMinusZ);
213
214  // mu+ mu- directions for Positron in z-direction
215  //
216  G4ThreeVector
217    MuPlusDirection ( PmuPlusX/PmuPlus, PmuPlusY/PmuPlus,  PmuPlusZ/PmuPlus  );
218  G4ThreeVector
219    MuMinusDirection(PmuMinusX/PmuMinus,PmuMinusY/PmuMinus,PmuMinusZ/PmuMinus);
220
221  // rotate to actual Positron direction
222  //
223  MuPlusDirection.rotateUz(PositronDirection);
224  MuMinusDirection.rotateUz(PositronDirection);
225
226  aParticleChange.SetNumberOfSecondaries(2);
227  // create G4DynamicParticle object for the particle1
228  G4DynamicParticle* aParticle1= new G4DynamicParticle(
229                         G4MuonPlus::MuonPlus(),MuPlusDirection,EmuPlus-Mmuon);
230  aParticleChange.AddSecondary(aParticle1);
231  // create G4DynamicParticle object for the particle2
232  G4DynamicParticle* aParticle2= new G4DynamicParticle(
233                     G4MuonMinus::MuonMinus(),MuMinusDirection,EmuMinus-Mmuon);
234  aParticleChange.AddSecondary(aParticle2);
235
236  // Kill the incident positron
237  //
238  aParticleChange.ProposeEnergy(0.); 
239  aParticleChange.ProposeTrackStatus(fStopAndKill);
240
241  return &aParticleChange;
242}
243
244//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
245
246void G4AnnihiToMuPair::PrintInfoDefinition()
247{
248  G4String comments ="e+e->mu+mu- annihilation, atomic e- at rest, SubType=.";
249  G4cout << G4endl << GetProcessName() << ":  " << comments
250         << GetProcessSubType() << G4endl;
251  G4cout << "        threshold at " << LowestEnergyLimit/GeV << " GeV"
252         << " good description up to "
253         << HighestEnergyLimit/TeV << " TeV for all Z." << G4endl;
254}
255
256//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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