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None Problems with transportation with spin 

Forum: Fast Simulation, Transportation & Others
Date: 15 Mar, 2012
From: Tom Roberts <Tom Roberts>

I am trying to track electrons and muons with spin in Geant4 9.5. I followed the prescription in the application developer's guide section 4.3.3. When muons go around in circles in a uniform B field, their polarization vector does indeed precess (initial polarization=[0,0,1] when headed in the +z direction).

But there are several problems:

1. The G4Track global time is not updated. This is surely a bug. When I use
   G4EqMagElectricField the track time is updated normally (but of course the
   track's polarization is zeroed).

2. The magnetic moment anomaly is set in G4Mag_SpinEqRhs, not in
   G4ParticleDefinition. This is a peculiar design decision which puts a
   rather complicated burden on developers (maintain a table of the anomalous
   magnetic moments for all particles, and set it in PreUserTrackingAction()).

3. The constructor of G4Mag_SpinEqRhs takes a G4MagneticField, not a
   G4ElectroMagneticField. As a result, the particles do not see any electric
   field -- neither spin nor momentum are changed by an E field.

4. According to the application developer's guide for 9.5, G4Transportation
   now has EnableUseMagneticMoment(). Calling this function does not seem to
   work: for a 2 MeV/c mu+ traveling along +z, with spin along +y, and in a 
   1000 tesla/meter B field gradient along +y (By=y in units tesla and mm),
   the track is not deflected.

I can live with item 2, but I need to get the others fixed. Suggestions?

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1 None: Re: Problems with transportation with spin   (Tom Roberts - 15 Mar, 2012)
2 None: Re: Problems with transportation with spin   (Tom Roberts - 20 Mar, 2012)
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