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Forum: Fast Simulation, Transportation & Others
Re: Question Query: polarized muon decays (Tom Roberts)
Date: 26 Mar, 2012
From: Gumplinger Peter <Gumplinger Peter>

Hi Tom,

Sorry for not replying but I don't monitor this particular Forum. Fred Jones has brought this to my attention. - There are postings in 'Fields: Magnetic and Otherwise' and 'Particles' about tracking spin and defining decays for particles with spin or into spin.

If you use the LXR browser you'd find extended examples where this functionality is exhibited, probably the easiest to learn from is:


with F05PhysicsList showing how to replace the 'standard' decays of pi's and mu's with those required to get polarized muons and their decay. When a muon comes to rest their spin is precessed around the local magn. field for the remainder of the muon's lifetime.

All this functinality is also implemented in Kamil Sedlak's muSR program (at PSI):

We currently have one problem in that muons coming to rest are not re-accelerated along the local E-field:

You wrote to Fred that:

" What is lacking:
 3. the force from grad B on the magnetic moment
 4. polarized muon decays

Geant4 9.5 claims to have implemented #3"

Geant4.9.5 has implemented field tracking in a gravitational field. I don't think I claimed #3(?) However, #4 is certainly implemented, including first order radiative corrections to get the correct e+/e- energy distribution and has been for a long time.

#3 is forthcoming for G4.9.6 and I can send you preliminary code.

Thanks as always for your interesting and illuminating Forum questions, Peter

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