Gabriele Cosmo
80 lines
2.0 KiB
Markdown
80 lines
2.0 KiB
Markdown
\page Examplefield05 Example field05
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This example checks so-called "spin-frozen" condition
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There is a good example article hep-ph/0012087v1.
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This article discusses about how to cancel the muon g-2 precession by
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applying an electric field.
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- 1) beta is muon velocity,
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- 2) B is an uniform magnetic field and vec{beta}.vec{B}=0,
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"." means scalar product,
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- 3) Radial electric field (E) in the lab frame and vec{beta}.vec{E}=0,
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- 4) a=(g-2)/2 is muon anomalous magnetic moment.
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The required electric field to cancel the g-2 precession is,
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```cpp
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E = a*B*light_c*gamma**2*beta
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```
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In case of gamma=5 and B=0.24 Tesla, the required electric field is
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```cpp
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E = 2 MV/m
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```
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"Spin-frozen" happens when spin rotation cycle and muon rotation cycle
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are same. In this case, both cycles should be 149.5 nsec.
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See also:
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http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf
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Credit goes to Hiromi Iinuma from KEK.
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## main()
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See main() in field05.cc.
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## GEOMETRY DEFINITION
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As simple world G4Box with a G4ElectroMagneticField \n
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propagating both spin and momentum (G4EqEMFieldWithSpin) \n
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with G4ClassicalRK4(fEquation,12) and \n
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Bz = 0.24*tesla; \n
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Er = 2.113987E+6*volt/m;
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## AN EVENT: THE PRIMARY GENERATOR
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Use mu+ G4ParticleGun with Pmu = 517.6*MeV/c \n
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and aligned spin and momentum direction
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## PHYSICS
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```cpp
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RegisterPhysics(new G4SpinDecayPhysics());
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RegisterPhysics(new G4StepLimiterPhysics());
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```
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- G4SpinDecayPhysics defines muon decay modes with spin,
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- G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts.
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## User Action Classes
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- F05SteppingAction:
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G4Exception when the cosine of the angle between
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the spin and the momentum is < (1.-1.E-7)
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## HOW TO START ?
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- Execute field05 in 'batch' mode from macro files e.g.
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```
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% ./field05 field05.in > field.out &
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```
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- Execute field05 in 'interactive' mode with visualization e.g.
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```
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% ./field05
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....
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Idle> type your commands, for example:
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Idle> run/beamOn 1
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....
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``` |