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G4GDecay3.cc
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26 // $Id$
27 //
28 // File: G4GDecay3.cc
29 // Author: Dennis Wright (SLAC)
30 // Date: 19 April 2013
31 //
32 // Description: three-body phase space momentum generator based on
33 // GDECA3 of Geant3
34 //
35 // 20130620 Address Coverity #51433, initializing all data members
36 // 20141201 Fix error message text to show correct class name
37 // 20150608 M. Kelsey -- Label all while loops as terminating.
38 
39 #include "G4GDecay3.hh"
40 #include "G4PhysicalConstants.hh"
41 #include "Randomize.hh"
42 
43 G4GDecay3::G4GDecay3(const G4double& pMass, const G4double& dMass0,
44  const G4double& dMass1, const G4double& dMass2)
45  : loopMax(100), parentMass(pMass), mDaughter0(dMass0), mDaughter1(dMass1),
46  mDaughter2(dMass2), pDaughter0(0.), pDaughter1(0.), pDaughter2(0.) {;}
47 
48 
49 G4bool G4GDecay3::CalculateMomentumMagnitudes()
50 {
51  G4int looper = 0;
52  G4bool status;
53 
54  G4double rndm;
55  G4double rndm1;
56  G4double rndm2;
57 
58  G4double momentummax;
59  G4double momentumsum;
61 
62  G4double availableE = parentMass - mDaughter0 - mDaughter1 - mDaughter2;
63  do { /* Loop checking 08.06.2015 MHK */
64  rndm1 = G4UniformRand();
65  rndm2 = G4UniformRand();
66  if (rndm2 > rndm1) {
67  // keep randoms in descending order
68  rndm = rndm1;
69  rndm1 = rndm2;
70  rndm2 = rndm;
71  }
72  momentummax = 0.0;
73  momentumsum = 0.0;
74 
75  // daughter 0
76  energy = rndm2*availableE;
77  pDaughter0 = std::sqrt(energy*energy + 2.0*energy*mDaughter0);
78  if (pDaughter0 > momentummax) momentummax = pDaughter0;
79  momentumsum += pDaughter0;
80 
81  // daughter 1
82  energy = (1.-rndm1)*availableE;
83  pDaughter1 = std::sqrt(energy*energy + 2.0*energy*mDaughter1);
84  if (pDaughter1 > momentummax) momentummax = pDaughter1;
85  momentumsum += pDaughter1;
86 
87  // daughter 2
88  energy = (rndm1-rndm2)*availableE;
89  pDaughter2 = std::sqrt(energy*energy + 2.0*energy*mDaughter2);
90  if (pDaughter2 > momentummax) momentummax = pDaughter2;
91  momentumsum += pDaughter2;
92  looper++;
93  status = looper < loopMax;
94  } while ((momentummax > momentumsum - momentummax) && status);
95 
96  return status;
97 }
98 
99 
100 std::vector<G4ThreeVector> G4GDecay3::GetThreeBodyMomenta()
101 {
102 
103  std::vector<G4ThreeVector> pVect;
104 
105  if (CalculateMomentumMagnitudes() ) {
106 
107  // Calculate directions
108  G4double costheta = 2.*G4UniformRand()-1.;
109  G4double sintheta = std::sqrt((1.0-costheta)*(1.0+costheta));
110  G4double phi = twopi*G4UniformRand();
111  G4double sinphi = std::sin(phi);
112  G4double cosphi = std::cos(phi);
113  G4ThreeVector direction0(sintheta*cosphi, sintheta*sinphi, costheta);
114 
115  G4double costhetan = (pDaughter1*pDaughter1 - pDaughter2*pDaughter2
116  - pDaughter0*pDaughter0)/(2.0*pDaughter2*pDaughter0);
117  G4double sinthetan = std::sqrt((1.0-costhetan)*(1.0+costhetan));
118  G4double phin = twopi*G4UniformRand();
119  G4double sinphin = std::sin(phin);
120  G4double cosphin = std::cos(phin);
121  G4ThreeVector direction2;
122  direction2.setX(sinthetan*cosphin*costheta*cosphi -
123  sinthetan*sinphin*sinphi + costhetan*sintheta*cosphi);
124  direction2.setY(sinthetan*cosphin*costheta*sinphi +
125  sinthetan*sinphin*cosphi + costhetan*sintheta*sinphi);
126  direction2.setZ(-sinthetan*cosphin*sintheta + costhetan*costheta);
127 
128  // Return momentum vectors
129  pVect.push_back(pDaughter0*direction0);
130  pVect.push_back(-direction0*pDaughter0 - direction2*pDaughter2);
131  pVect.push_back(pDaughter2*direction2);
132 
133  } else {
134  G4cerr << "G4GDecay3::GetThreeBodyMomenta: " << loopMax
135  << " or more loops in momentum magnitude calculation " << G4endl;
136  }
137 
138  return pVect;
139 }
140 
std::vector< G4ThreeVector > GetThreeBodyMomenta()
Definition: G4GDecay3.cc:100
int G4int
Definition: G4Types.hh:78
void setY(double)
void setZ(double)
void setX(double)
static constexpr double twopi
Definition: G4SIunits.hh:76
#define G4UniformRand()
Definition: Randomize.hh:97
bool G4bool
Definition: G4Types.hh:79
G4double energy(const ThreeVector &p, const G4double m)
#define G4endl
Definition: G4ios.hh:61
double G4double
Definition: G4Types.hh:76
G4GLOB_DLL std::ostream G4cerr