geant4

This example checks so-called "spin-frozen" condition There is a good example article hep-ph/0012087v1. This article discusses about how to cancel the muon g-2 precession by applying an electric field.

1. beta is muon velocity,
1. B is an uniform magnetic field and vec{beta}.vec{B}=0, "." means scalar product,
1. Radial electric field (E) in the lab frame and vec{beta}.vec{E}=0,
1. a=(g-2)/2 is muon anomalous magnetic moment.

The required electric field to cancel the g-2 precession is,

E = a*B*light_c*gamma**2*beta

In case of gamma=5 and B=0.24 Tesla, the required electric field is

E = 2 MV/m

"Spin-frozen" happens when spin rotation cycle and muon rotation cycle are same. In this case, both cycles should be 149.5 nsec.

Credit goes to Hiromi Iinuma from KEK.

main()

See main() in field05.cc.

GEOMETRY DEFINITION

As simple world G4Box with a G4ElectroMagneticField \n propagating both spin and momentum (G4EqEMFieldWithSpin) \n with G4ClassicalRK4(fEquation,12) and \n Bz = 0.24tesla; \n Er = 2.113987E+6volt/m;

AN EVENT: THE PRIMARY GENERATOR

Use mu+ G4ParticleGun with Pmu = 517.6*MeV/c \n and aligned spin and momentum direction

PHYSICS

RegisterPhysics(new G4SpinDecayPhysics());
RegisterPhysics(new G4StepLimiterPhysics());

G4SpinDecayPhysics defines muon decay modes with spin,
G4StepLimiterPhysics defines G4StepLimiter and G4UserSpecialCuts.

User Action Classes

F05SteppingAction:

G4Exception when the cosine of the angle between the spin and the momentum is < (1.-1.E-7)

HOW TO START ?

Execute field05 in 'batch' mode from macro files e.g.

% ./field05 field05.in > field.out &

Execute field05 in 'interactive' mode with visualization e.g.

% ./field05
....
Idle> type your commands, for example:
Idle> run/beamOn 1
....