source: trunk/source/processes/electromagnetic/highenergy/src/G4AnnihiToMuPair.cc@ 1201

Last change on this file since 1201 was 1196, checked in by garnier, 16 years ago

update CVS release candidate geant4.9.3.01
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25//
26//
27// $Id: G4AnnihiToMuPair.cc,v 1.6 2009/11/09 18:24:07 vnivanch Exp $
28// GEANT4 tag $Name: geant4-09-03-cand-01 $
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 CurrentSigma = 0.0;
68 CrossSecFactor = 1.;
69 SetProcessSubType(6);
70
71}
72
73//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
74
75G4AnnihiToMuPair::~G4AnnihiToMuPair() // (empty) destructor
76{ }
77
78//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
79
80G4bool G4AnnihiToMuPair::IsApplicable(const G4ParticleDefinition& particle)
81{
82 return ( &particle == G4Positron::Positron() );
83}
84
85//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
86
87void G4AnnihiToMuPair::BuildPhysicsTable(const G4ParticleDefinition&)
88// Build cross section and mean free path tables
89//here no tables, just calling PrintInfoDefinition
90{
91 CurrentSigma = 0.0;
92 PrintInfoDefinition();
93}
94
95//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
96
97void G4AnnihiToMuPair::SetCrossSecFactor(G4double fac)
98// Set the factor to artificially increase the cross section
99{
100 CrossSecFactor = fac;
101 G4cout << "The cross section for AnnihiToMuPair is artificially "
102 << "increased by the CrossSecFactor=" << CrossSecFactor << G4endl;
103}
104
105//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
106
107G4double G4AnnihiToMuPair::ComputeCrossSectionPerAtom(G4double Epos, G4double Z)
108// Calculates the microscopic cross section in GEANT4 internal units.
109// It gives a good description from threshold to 1000 GeV
110{
111 static const G4double Mmuon = G4MuonPlus::MuonPlus()->GetPDGMass();
112 static const G4double Rmuon = elm_coupling/Mmuon; //classical particle radius
113 static const G4double Sig0 = pi*Rmuon*Rmuon/3.; //constant in crossSection
114
115 G4double CrossSection = 0.;
116 if (Epos < LowestEnergyLimit) return CrossSection;
117
118 G4double xi = LowestEnergyLimit/Epos;
119 G4double SigmaEl = Sig0*xi*(1.+xi/2.)*sqrt(1.-xi); // per electron
120 CrossSection = SigmaEl*Z; // number of electrons per atom
121 return CrossSection;
122}
123
124//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
125
126G4double G4AnnihiToMuPair::CrossSectionPerVolume(G4double PositronEnergy,
127 const G4Material* aMaterial)
128{
129 const G4ElementVector* theElementVector = aMaterial->GetElementVector();
130 const G4double* NbOfAtomsPerVolume = aMaterial->GetVecNbOfAtomsPerVolume();
131
132 G4double SIGMA = 0.0;
133
134 for ( size_t i=0 ; i < aMaterial->GetNumberOfElements() ; ++i )
135 {
136 G4double AtomicZ = (*theElementVector)[i]->GetZ();
137 SIGMA += NbOfAtomsPerVolume[i] *
138 ComputeCrossSectionPerAtom(PositronEnergy,AtomicZ);
139 }
140 return SIGMA;
141}
142
143//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
144
145G4double G4AnnihiToMuPair::GetMeanFreePath(const G4Track& aTrack,
146 G4double, G4ForceCondition*)
147
148// returns the positron mean free path in GEANT4 internal units
149
150{
151 const G4DynamicParticle* aDynamicPositron = aTrack.GetDynamicParticle();
152 G4double PositronEnergy = aDynamicPositron->GetKineticEnergy()
153 +electron_mass_c2;
154 G4Material* aMaterial = aTrack.GetMaterial();
155 CurrentSigma = CrossSectionPerVolume(PositronEnergy, aMaterial);
156
157 // increase the CrossSection by CrossSecFactor (default 1)
158 G4double mfp = DBL_MAX;
159 if(CurrentSigma > DBL_MIN) mfp = 1.0/(CurrentSigma*CrossSecFactor);
160
161 return mfp;
162}
163
164//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
165
166G4VParticleChange* G4AnnihiToMuPair::PostStepDoIt(const G4Track& aTrack,
167 const G4Step& aStep)
168//
169// generation of e+e- -> mu+mu-
170//
171{
172
173 aParticleChange.Initialize(aTrack);
174 static const G4double Mele=electron_mass_c2;
175 static const G4double Mmuon=G4MuonPlus::MuonPlus()->GetPDGMass();
176
177 // current Positron energy and direction, return if energy too low
178 const G4DynamicParticle *aDynamicPositron = aTrack.GetDynamicParticle();
179 G4double Epos = aDynamicPositron->GetKineticEnergy() + Mele;
180
181 // test of cross section
182 if(CurrentSigma*G4UniformRand() >
183 CrossSectionPerVolume(Epos, aTrack.GetMaterial()))
184 {
185 return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
186 }
187
188 if (Epos < LowestEnergyLimit) {
189 return G4VDiscreteProcess::PostStepDoIt(aTrack,aStep);
190 }
191
192 G4ParticleMomentum PositronDirection =
193 aDynamicPositron->GetMomentumDirection();
194 G4double xi = LowestEnergyLimit/Epos; // xi is always less than 1,
195 // goes to 0 at high Epos
196
197 // generate cost
198 //
199 G4double cost;
200 do cost = 2.*G4UniformRand()-1.;
201 while (2.*G4UniformRand() > 1.+xi+cost*cost*(1.-xi) );
202 //1+cost**2 at high Epos
203 G4double sint = sqrt(1.-cost*cost);
204
205 // generate phi
206 //
207 G4double phi=2.*pi*G4UniformRand();
208
209 G4double Ecm = sqrt(0.5*Mele*(Epos+Mele));
210 G4double Pcm = sqrt(Ecm*Ecm-Mmuon*Mmuon);
211 G4double beta = sqrt((Epos-Mele)/(Epos+Mele));
212 G4double gamma = Ecm/Mele; // =sqrt((Epos+Mele)/(2.*Mele));
213 G4double Pt = Pcm*sint;
214
215 // energy and momentum of the muons in the Lab
216 //
217 G4double EmuPlus = gamma*( Ecm+cost*beta*Pcm);
218 G4double EmuMinus = gamma*( Ecm-cost*beta*Pcm);
219 G4double PmuPlusZ = gamma*(beta*Ecm+cost* Pcm);
220 G4double PmuMinusZ = gamma*(beta*Ecm-cost* Pcm);
221 G4double PmuPlusX = Pt*cos(phi);
222 G4double PmuPlusY = Pt*sin(phi);
223 G4double PmuMinusX =-Pt*cos(phi);
224 G4double PmuMinusY =-Pt*sin(phi);
225 // absolute momenta
226 G4double PmuPlus = sqrt(Pt*Pt+PmuPlusZ *PmuPlusZ );
227 G4double PmuMinus = sqrt(Pt*Pt+PmuMinusZ*PmuMinusZ);
228
229 // mu+ mu- directions for Positron in z-direction
230 //
231 G4ThreeVector
232 MuPlusDirection ( PmuPlusX/PmuPlus, PmuPlusY/PmuPlus, PmuPlusZ/PmuPlus );
233 G4ThreeVector
234 MuMinusDirection(PmuMinusX/PmuMinus,PmuMinusY/PmuMinus,PmuMinusZ/PmuMinus);
235
236 // rotate to actual Positron direction
237 //
238 MuPlusDirection.rotateUz(PositronDirection);
239 MuMinusDirection.rotateUz(PositronDirection);
240
241 aParticleChange.SetNumberOfSecondaries(2);
242 // create G4DynamicParticle object for the particle1
243 G4DynamicParticle* aParticle1= new G4DynamicParticle(
244 G4MuonPlus::MuonPlus(),MuPlusDirection,EmuPlus-Mmuon);
245 aParticleChange.AddSecondary(aParticle1);
246 // create G4DynamicParticle object for the particle2
247 G4DynamicParticle* aParticle2= new G4DynamicParticle(
248 G4MuonMinus::MuonMinus(),MuMinusDirection,EmuMinus-Mmuon);
249 aParticleChange.AddSecondary(aParticle2);
250
251 // Kill the incident positron
252 //
253 aParticleChange.ProposeEnergy(0.);
254 aParticleChange.ProposeTrackStatus(fStopAndKill);
255
256 return &aParticleChange;
257}
258
259//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
260
261void G4AnnihiToMuPair::PrintInfoDefinition()
262{
263 G4String comments ="e+e->mu+mu- annihilation, atomic e- at rest, SubType=.";
264 G4cout << G4endl << GetProcessName() << ": " << comments
265 << GetProcessSubType() << G4endl;
266 G4cout << " threshold at " << LowestEnergyLimit/GeV << " GeV"
267 << " good description up to "
268 << HighestEnergyLimit/TeV << " TeV for all Z." << G4endl;
269}
270
271//....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo......
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