Import Geant4 11.0.0.beta source tree

source/processes/electromagnetic/standard/src/G4eplusAnnihilation.cc

@@ -36,6 +36,13 @@
 // Creation date: 02.08.2004
 //
 // Modified by Michel Maire, Vladimir Ivanchenko and Daren Sawkey
+//
+// Introduced Quantum Entanglement  April 2021  John Allison
+// This is activated by /process/em/QuantumEntanglement
+// For e+e- -> gamma gamma, the gammas are "tagged" here
+// and must be "analysed" in a Compton scattering process - see, for
+// example, G4LivermorePolarizedComptonModel. Otherwise entanglement
+// has no effect even if activated.
 
 //
 // -------------------------------------------------------------------
@@ -47,25 +54,31 @@
 #include "G4PhysicalConstants.hh"
 #include "G4MaterialCutsCouple.hh"
 #include "G4Gamma.hh"
+#include "G4Electron.hh"
 #include "G4Positron.hh"
 #include "G4eeToTwoGammaModel.hh"
 #include "G4EmBiasingManager.hh"
+#include "G4EntanglementAuxInfo.hh"
+#include "G4eplusAnnihilationEntanglementClipBoard.hh"
+#include "G4EmParameters.hh"
+#include "G4PhysicsModelCatalog.hh"
 
 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
 
-using namespace std;
-
 G4eplusAnnihilation::G4eplusAnnihilation(const G4String& name)
-  : G4VEmProcess(name), isInitialised(false)
+  : G4VEmProcess(name)
 {
   theGamma = G4Gamma::Gamma();
-  SetIntegral(true);
+  theElectron = G4Electron::Electron();
+  SetCrossSectionType(fEmDecreasing);
   SetBuildTableFlag(false);
   SetStartFromNullFlag(false);
   SetSecondaryParticle(theGamma);
   SetProcessSubType(fAnnihilation);
   enableAtRestDoIt = true;
   mainSecondaries = 2;
+  fEntanglementModelIndex =
+    G4PhysicsModelCatalog::Register("G4GammaGammaEntanglement");
 }
 
 //....oooOO0OOooo........oooOO0OOooo........oooOO0OOooo........oooOO0OOooo....
@@ -95,7 +108,7 @@ void G4eplusAnnihilation::InitialiseProcess(const G4ParticleDefinition*)
 {
   if(!isInitialised) {
     isInitialised = true;
-    if(!EmModel(0)) { SetEmModel(new G4eeToTwoGammaModel()); }
+    if(nullptr == EmModel(0)) { SetEmModel(new G4eeToTwoGammaModel()); }
     EmModel(0)->SetLowEnergyLimit(MinKinEnergy());
     EmModel(0)->SetHighEnergyLimit(MaxKinEnergy());
     AddEmModel(1, EmModel(0));
@@ -128,7 +141,7 @@ G4VParticleChange* G4eplusAnnihilation::AtRestDoIt(const G4Track& track,
   G4double gammaCut = GetGammaEnergyCut();
   model->SampleSecondaries(&secParticles, MaterialCutsCouple(), 
 			   track.GetDynamicParticle(), gammaCut);
- 
+
   G4int num0 = secParticles.size();
 
   // splitting or Russian roulette
@@ -144,8 +157,37 @@ G4VParticleChange* G4eplusAnnihilation::AtRestDoIt(const G4Track& track,
       }
     }
   }
+
   // save secondaries
   G4int num = secParticles.size();
+
+  // Check that entanglement is switched on... (the following flag is
+  // set by /process/em/QuantumEntanglement).
+  G4bool entangled = G4EmParameters::Instance()->QuantumEntanglement();
+  // ...and that we have two gammas with both gammas' energies above
+  // gammaCut (entanglement is only programmed for e+ e- -> gamma gamma).
+  G4bool entangledgammagamma = false;
+  if (entangled) {
+    if (num == 2) {
+      entangledgammagamma = true;
+      for (const auto* p: secParticles) {
+        if (p->GetDefinition() != theGamma ||
+            p->GetKineticEnergy() < gammaCut) {
+          entangledgammagamma = false;
+        }
+      }
+    }
+  }
+
+  // Prepare a shared pointer for psossible use below. If it is used, the
+  // shared pointer is copied into the tracks through G4EntanglementAuxInfo.
+  // This ensures the clip board lasts until both tracks are destroyed.
+  std::shared_ptr<G4eplusAnnihilationEntanglementClipBoard> clipBoard;
+  if (entangledgammagamma) {
+    clipBoard = std::make_shared<G4eplusAnnihilationEntanglementClipBoard>();
+    clipBoard->SetParentParticleDefinition(track.GetDefinition());
+  }
+
   if(num > 0) {
 
     fParticleChange.SetNumberOfSecondaries(num);
@@ -169,6 +211,17 @@ G4VParticleChange* G4eplusAnnihilation::AtRestDoIt(const G4Track& track,
         if (good) { 
           G4Track* t = new G4Track(dp, time, track.GetPosition());
           t->SetTouchableHandle(track.GetTouchableHandle());
+          if (entangledgammagamma) {
+	    // entangledgammagamma is only true when there are only two gammas
+	    // (See code above where entangledgammagamma is calculated.)
+            if (i == 0) { // First gamma
+              clipBoard->SetTrackA(t);
+            } else if (i == 1) {  // Second gamma
+              clipBoard->SetTrackB(t);
+            }
+            t->SetAuxiliaryTrackInformation
+            (fEntanglementModelIndex,new G4EntanglementAuxInfo(clipBoard));
+          }
           if (biasManager) {
             t->SetWeight(weight * biasManager->GetWeight(i));
           } else {