source: trunk/source/processes/electromagnetic/highenergy/src/G4AnnihiToMuPair.cc @ 1315

Last change on this file since 1315 was 1228, checked in by garnier, 14 years ago

update geant4.9.3 tag
File size: 10.0 KB
Line 
1//
2// ********************************************************************
3// * License and Disclaimer                                           *
4// *                                                                  *
5// * The  Geant4 software  is  copyright of the Copyright Holders  of *
6// * the Geant4 Collaboration.  It is provided  under  the terms  and *
7// * conditions of the Geant4 Software License,  included in the file *
8// * LICENSE and available at  http://cern.ch/geant4/license .  These *
9// * include a list of copyright holders.                             *
10// *                                                                  *
11// * Neither the authors of this software system, nor their employing *
12// * institutes,nor the agencies providing financial support for this *
13// * work  make  any representation or  warranty, express or implied, *
14// * regarding  this  software system or assume any liability for its *
15// * use.  Please see the license in the file  LICENSE  and URL above *
16// * for the full disclaimer and the limitation of liability.         *
17// *                                                                  *
18// * This  code  implementation is the result of  the  scientific and *
19// * technical work of the GEANT4 collaboration.                      *
20// * By using,  copying,  modifying or  distributing the software (or *
21// * any work based  on the software)  you  agree  to acknowledge its *
22// * use  in  resulting  scientific  publications,  and indicate your *
23// * acceptance of all terms of the Geant4 Software license.          *
24// ********************************************************************
25//
26//
27// $Id: G4AnnihiToMuPair.cc,v 1.6 2009/11/09 18:24:07 vnivanch Exp $
28// GEANT4 tag $Name: geant4-09-03 $
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......
Note: See TracBrowser for help on using the repository browser.