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0001
0002 =========================================================
0003 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
0004 =========================================================
0005
0006
0007
0008 field05 Example
0009 ---------------
0010
0011 This example checks so-called "spin-frozen" condition
0012 There is a good example article hep-ph/0012087v1.
0013 This article discusses about how to cancel the muon g-2 precession by
0014 applying an electric field.
0015
0016 1) beta is muon velocity,
0017 2) B is an uniform magnetic field and \vec{beta}.\vec{B}=0,
0018 "." means scalar product,
0019 3) Radial electric field (E) in the lab frame and \vec{beta}.\vec{E}=0,
0020 4) a=(g-2)/2 is muon anomalous magnetic moment.
0021
0022 The required electric field to cancel the g-2 precession is,
0023 E=a*B*light_c*gamma**2*beta.
0024
0025 In case of gamma=5 and B=0.24 Tesla, the required electric field is
0026 E=2 MV/m.
0027
0028 "Spin-frozen" happens when spin rotation cycle and muon rotation cycle
0029 are same. In this case, both cycles should be 149.5 nsec.
0030
0031 See also:
0032 http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf
0033
0034
0035 Credit goes to Hiromi Iinuma from KEK.
0036
0037 **************
0038 *Classes Used*
0039 **************
0040
0041 1 - main()
0042
0043 See field05.cc.
0044
0045 2- GEOMETRY DEFINITION
0046
0047 as simple world G4Box with a G4ElectroMagneticField
0048 propagating both spin and momentum (G4EqEMFieldWithSpin)
0049 with G4ClassicalRK4(fEquation,12) and
0050 Bz = 0.24*tesla;
0051 Er = 2.113987E+6*volt/m;
0052
0053 3- AN EVENT: THE PRIMARY GENERATOR
0054
0055 use mu+ G4ParticleGun with Pmu = 517.6*MeV/c
0056 and aligned spin and momentum direction
0057
0058 4- PHYSICS
0059
0060 RegisterPhysics(new G4SpinDecayPhysics());
0061 RegisterPhysics(new G4StepLimiterPhysics());
0062
0063 G4SpinDecayPhysics defines muon decay modes with spin,
0064 G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts.
0065
0066 5- User Action Classes
0067
0068 SteppingAction:
0069 G4Exception when the cosine of the angle between
0070 the spin and the momentum is < (1.-1.E-7)
0071
0072 6- HOW TO START ?
0073
0074 - Execute field05 in 'batch' mode from macro files e.g.
0075 % field05 field05.in > field.out &
0076
0077 - Execute field05 in 'interactive' mode with visualization e.g.
0078 % field05
0079 ....
0080 Idle> type your commands, for example:
0081 Idle> run/beamOn 1
0082 ....
