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1
2 =========================================================
3 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
4 =========================================================
5
6
7
8 field05 Example
9 ---------------
10
11 This example checks so-called "spin-frozen" condition
12 There is a good example article hep-ph/0012087v1.
13 This article discusses about how to cancel the muon g-2 precession by
14 applying an electric field.
15
16 1) beta is muon velocity,
17 2) B is an uniform magnetic field and \vec{beta}.\vec{B}=0,
18 "." means scalar product,
19 3) Radial electric field (E) in the lab frame and \vec{beta}.\vec{E}=0,
20 4) a=(g-2)/2 is muon anomalous magnetic moment.
21
22 The required electric field to cancel the g-2 precession is,
23 E=a*B*light_c*gamma**2*beta.
24
25 In case of gamma=5 and B=0.24 Tesla, the required electric field is
26 E=2 MV/m.
27
28 "Spin-frozen" happens when spin rotation cycle and muon rotation cycle
29 are same. In this case, both cycles should be 149.5 nsec.
30
31 See also:
32 http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf
33
34
35 Credit goes to Hiromi Iinuma from KEK.
36
37 **************
38 *Classes Used*
39 **************
40
41 1 - main()
42
43 See field05.cc.
44
45 2- GEOMETRY DEFINITION
46
47 as simple world G4Box with a G4ElectroMagneticField
48 propagating both spin and momentum (G4EqEMFieldWithSpin)
49 with G4ClassicalRK4(fEquation,12) and
50 Bz = 0.24*tesla;
51 Er = 2.113987E+6*volt/m;
52
53 3- AN EVENT: THE PRIMARY GENERATOR
54
55 use mu+ G4ParticleGun with Pmu = 517.6*MeV/c
56 and aligned spin and momentum direction
57
58 4- PHYSICS
59
60 RegisterPhysics(new G4SpinDecayPhysics());
61 RegisterPhysics(new G4StepLimiterPhysics());
62
63 G4SpinDecayPhysics defines muon decay modes with spin,
64 G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts.
65
66 5- User Action Classes
67
68 SteppingAction:
69 G4Exception when the cosine of the angle between
70 the spin and the momentum is < (1.-1.E-7)
71
72 6- HOW TO START ?
73
74 - Execute field05 in 'batch' mode from macro files e.g.
75 % field05 field05.in > field.out &
76
77 - Execute field05 in 'interactive' mode with visualization e.g.
78 % field05
79 ....
80 Idle> type your commands, for example:
81 Idle> run/beamOn 1
82 ....
