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Forum: Fields: Magnetic and Otherwise
Re: Question Spin tracking of moving muons (Kevin Lynch)
Re: Feedback Re: Spin tracking of moving muons (Gumplinger Peter)
Date: 18 Feb, 2009
From: Tom Roberts <Tom Roberts>

> 3) As for your last question, the missing third term is an oversight. I
> noticed it a little while ago when I went back to Jackson. I made mental
> note to investigate and fix it. Actually, I have no feeling as to when
> this term (size of E field and beta) becomes sizable relative to the
> others. Until now, I only thought of E fields inside drift chambers.
> According to Jackson: "If the particle is relativistic (beta->1), even
> the presence of an electric field causes the longitudinal polarization
> to change only very slowly, at a rate proportional to gamma**(-2) times
> the electric field component perpendicular to v_vector." (I assume you
> are dealing with 'surface muons' - longitudinal polarized muons?)

In a few months I will be interested in simulating polarized muons in a muon cooling channel. This involves RF cavities with electric fields of 10-30 Mega-Volts/meter, perhaps more. There are also magnetic fields up to 30 Tesla, perhaps more. The muon momentum starts 200-600 MeV/c or so, and depending on application remains above ~100 MeV/c or decreases all the way down to zero. So I hope you can implement this without approximation, including terms which might be negligible in some physical situations.

The highly-polarized muons come from forward or backward decays of pions, so they are essentially longitudinally polarized.

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