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25 //
26 // Geant4 Class file
27 //
28 // File name: G4PolarizationHelper
29 //
30 // Author: Andreas Schaelicke
31 //
32 // Class Description:
33 // Provides some basic polarization transformation routines.
34
35 #include "G4PolarizationHelper.hh"
36
37 #include "G4PhysicalConstants.hh"
38 #include "G4StokesVector.hh"
39 #include "Randomize.hh"
40
41 G4ThreeVector G4PolarizationHelper::GetFrame(const G4ThreeVector& mom1,
42 const G4ThreeVector& mom2)
43 {
44 G4ThreeVector normal = (mom1.cross(mom2)).unit();
45 return normal;
46 }
47
48 G4ThreeVector G4PolarizationHelper::GetParticleFrameY(const G4ThreeVector& uZ)
49 {
50 if(uZ.x() == 0. && uZ.y() == 0.)
51 {
52 return G4ThreeVector(0., 1., 0.);
53 }
54
55 G4double invPerp = 1. / std::sqrt(sqr(uZ.x()) + sqr(uZ.y()));
56 return G4ThreeVector(-uZ.y() * invPerp, uZ.x() * invPerp, 0);
57 }
58
59 G4ThreeVector G4PolarizationHelper::GetParticleFrameX(const G4ThreeVector& uZ)
60 {
61 if(uZ.x() == 0. && uZ.y() == 0.)
62 {
63 if(uZ.z() >= 0.)
64 return G4ThreeVector(1., 0., 0.);
65 return G4ThreeVector(-1., 0., 0.);
66 }
67
68 G4double perp = std::sqrt(sqr(uZ.x()) + sqr(uZ.y()));
69 G4double invPerp = uZ.z() / perp;
70 return G4ThreeVector(uZ.x() * invPerp, uZ.y() * invPerp, -perp);
71 }
72
73 G4ThreeVector G4PolarizationHelper::GetRandomFrame(const G4ThreeVector& mom1)
74 {
75 G4double phi = 2. * pi * G4UniformRand();
76 G4ThreeVector normal =
77 std::cos(phi) * GetParticleFrameX(mom1) +
78 std::sin(phi) * G4PolarizationHelper::GetParticleFrameY(mom1);
79 return normal;
80 }
81
82 G4ThreeVector G4PolarizationHelper::GetSpinInPRF(const G4ThreeVector& uZ,
83 const G4ThreeVector& spin)
84 {
85 if(uZ.x() == 0. && uZ.y() == 0.)
86 {
87 if(uZ.z() >= 0.)
88 return spin;
89 return G4ThreeVector(-spin.x(), spin.y(), -spin.z());
90 }
91
92 G4double perp = std::sqrt(sqr(uZ.x()) + sqr(uZ.y()));
93 G4double invPerp = 1. / perp;
94
95 G4ThreeVector uX(uZ.x() * uZ.z() * invPerp, uZ.y() * uZ.z() * invPerp, -perp);
96 G4ThreeVector uY(-uZ.y() * invPerp, uZ.x() * invPerp, 0);
97
98 return G4ThreeVector(spin * uX, spin * uY, spin * uZ);
99 }
100
101 void G4PolarizationHelper::TestPolarizationTransformations()
102 {
103 G4double theta = 0.;
104 G4cout << "========================================\n\n";
105 for(G4int i = 0; i <= 10; ++i)
106 {
107 theta = pi * i / 10.;
108 G4ThreeVector zAxis = G4ThreeVector(std::sin(theta), 0., std::cos(theta));
109 if(i == 5)
110 zAxis = G4ThreeVector(1., 0., 0.);
111 if(i == 10)
112 zAxis = G4ThreeVector(0., 0., -1.);
113 G4ThreeVector yAxis = GetParticleFrameY(zAxis);
114
115 G4cout << zAxis << " " << zAxis.mag() << "\n";
116 G4cout << yAxis << " " << yAxis.mag() << "\n";
117 G4ThreeVector xAxis = yAxis.cross(zAxis);
118 G4cout << xAxis << " " << xAxis.mag() << "\n\n";
119 }
120
121 G4cout << "========================================\n\n";
122
123 for(G4int i = 0; i <= 10; ++i)
124 {
125 theta = pi * i / 10.;
126 G4ThreeVector zAxis = G4ThreeVector(0., std::sin(theta), std::cos(theta));
127 if(i == 5)
128 zAxis = G4ThreeVector(0., 1., 0.);
129 if(i == 10)
130 zAxis = G4ThreeVector(0., 0., -1.);
131 G4ThreeVector yAxis = GetParticleFrameY(zAxis);
132
133 G4cout << zAxis << " " << zAxis.mag() << "\n";
134 G4cout << yAxis << " " << yAxis.mag() << "\n";
135 G4ThreeVector xAxis = yAxis.cross(zAxis);
136 G4cout << xAxis << " " << xAxis.mag() << "\n\n";
137
138 G4cout << "spat : " << xAxis * yAxis.cross(zAxis) << "\n\n";
139 }
140 G4cout << "========================================\n\n";
141 }
142
143 void G4PolarizationHelper::TestInteractionFrame()
144 {
145 // check transformation procedure for polarisation transfer
146 // calculation in scattering processes
147 // a) transfer target polarisation in beam particle reference frame (PRF)
148 // b) calc correct asymmetry w.r.t. scattering plane
149 // c) determine incoming polarisation in interaction frame (IF)
150 // d) transfer outgoing polarisation from IF to PRF
151 G4cout << "========================================\n\n";
152
153 G4double theta = 0.;
154
155 G4ThreeVector dir0 = G4ThreeVector(0., 0., 1.);
156 G4ThreeVector dir2 = G4ThreeVector(std::sin(theta), 0., std::cos(theta));
157
158 G4StokesVector pol0 = G4StokesVector::P3;
159 G4StokesVector pol1 = G4StokesVector::P3;
160
161 pol1.rotateUz(dir0);
162
163 G4cout << "========================================\n\n";
164 }
165