Example field05

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,
• 2) B is an uniform magnetic field and vec{beta}.vec{B}=0, "." means scalar product,
• 3) Radial electric field (E) in the lab frame and vec{beta}.vec{E}=0,
• 4) 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.

See also: http://research.kek.jp/people/hiromi/MyHomePage/G-2_work_files/SpinStudyinEMfieldByGeant4.pdf

Credit goes to Hiromi Iinuma from KEK.

Classes Used

main ()

See field05.cc.

GEOMETRY DEFINITION

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

AN EVENT: THE PRIMARY GENERATOR

use mu+ G4ParticleGun with Pmu = 517.6*MeV/c
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.

\section field05_s5 User Action Classes

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

\section field05_s6 HOW TO START ?

 - Execute field05 in 'batch' mode from macro files e.g.
\verbatim
% 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
  ....