G4ReactionKinematics.cc

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00028 //      CERN Geneva Switzerland
00029 //
00030 //      ------------ G4ReactionDynamics::TwoBody ------
00031 //                     new method TwoBodyScattering
00032 //                   by Christian V"olcker (CERN-Munich), September 1997
00033 //                     E-mail: Christian.Volcker@cern.ch
00034 // ************************************************************
00035 //-----------------------------------------------------------------------------
00036 
00037 #include "G4ReactionKinematics.hh"
00038 #include "G4PhysicalConstants.hh"
00039 
00040 // ************************************************************
00041 void G4ReactionKinematics::TwoBodyScattering(
00042            const G4DynamicParticle* pIn1, const G4DynamicParticle* pIn2,
00043            G4DynamicParticle* pOut1, G4DynamicParticle* pOut2)
00044 // ************************************************************
00045 {           
00046 // initial particles:
00047 
00048 // - total invariant mass
00049    G4LorentzVector sumIn(pIn1->Get4Momentum()+pIn2->Get4Momentum());
00050    G4double invariantMass=sumIn.mag();
00051 
00052 // - beta of center-of-mass system
00053    G4ThreeVector betaCMS=sumIn.boostVector();
00054 
00055 // final particles:
00056 
00057 // - get final particle masses
00058    G4double massOut1=pOut1->GetMass();
00059    G4double massOut2=pOut2->GetMass();
00060 
00061 // - calculate breakup momentum:
00062    G4double breakupMomentum=BreakupMomentum(invariantMass, massOut1, massOut2);
00063 
00064 // - isotropic decay angle
00065    G4double costheta = 2.0*G4UniformRand() - 1.0;
00066    G4double sintheta = std::sqrt(1.0 - costheta*costheta);
00067    G4double phi = 2.0*pi*G4UniformRand();
00068 
00069 // - setup LorentzVectors
00070    G4double pz=costheta*breakupMomentum;
00071    G4double px=sintheta*std::cos(phi)*breakupMomentum;
00072    G4double py=sintheta*std::sin(phi)*breakupMomentum;
00073    
00074    G4double breakupMomentumSquared=breakupMomentum*breakupMomentum;
00075    G4double energy1=std::sqrt(breakupMomentumSquared+massOut1*massOut1);
00076    G4double energy2=std::sqrt(breakupMomentumSquared+massOut2*massOut2);
00077 
00078    G4LorentzVector lorentz1(px, py, pz, energy1);
00079    G4LorentzVector lorentz2(px, py, pz, energy2);
00080 
00081 // - back into lab system
00082 
00083    lorentz1.boost(betaCMS);
00084    lorentz2.boost(betaCMS);
00085 
00086 // fill in new particles:
00087 
00088    pOut1->Set4Momentum(lorentz1);
00089    pOut2->Set4Momentum(lorentz2);
00090 
00091    return;
00092 }

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