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Forum: Fields: Magnetic and Otherwise
Re: None =?UTF-8?B?QnVnPz8=?= A question of G4EqEMFieldWithSpin.cc (Hiromi Iinuma)
Re: More Re: =?UTF-8?B?QnVnPz8=?= A question of G4EqEMFieldWithSpin.cc (Kevin Lynch)
Date: 05 Nov, 2009
From: Hiromi Iinuma <Hiromi Iinuma>

Dear Kevin,

Hello. Thank you for a reply.
Let me explain what I have done:
1) I checked 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.

Here, I am going to use these parameters:
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. 
This is my expectation from the article hep-ph/0012087v1 and Jackson, 
3rd edition.
(Actually, my Jackson is Japanese version.)

Then I tried to apply proper electromagnetic field and muon momentum in 
GEANT4 simulation.
Although I got correct muon rotation cycle,I did not get correct spin 
rotation cycle.
Therefore I modified "G4EqEMFieldWithSpin.cc" as I wrote in the previous 
e-mail,
and finally I got expected results.
I can show you more detail analysis note as needed.

Best regards,
Hiromi



----- Original Message -----
> 
> *** Discussion title: Fields: Magnetic and Otherwise
> 
> It's possible ... I asked the Geant collaboration to add this code, so
> I'm responsible for any bug is this piece of code. Before 4.9.2.p02, 
the
> whole beta x E terms was missing. I could have screwed it up. It's 
been
> a while since I wrote this, so let me trace back through what I did 
and
> see how the argument went....
> 
> When you say the "simulated spin rotation frequency do not agree with
> the correct frequency from Thomas-BMT equation", did you check that? 
Are
> you sure the C is not hiding somewhere else? Are you sure you're using
> the Maxwell equations in the right units? I cribbed most of the
> equations from Jackson, 2nd edition, and matched them onto the 
existing
> code to try and get the units right.
> 
> I'm not sure I got it all right, but it would be nice to do so before 
I
> need to start relying on my own simulation results :-)
> 
> -------------------------------------------------------------
> Visit this GEANT4 at hypernews.slac.stanford.edu message (to reply or 
unsubscribe) at: 
> http://hypernews.slac.stanford.edu/HyperNews/geant4/get/emfields/161/1.
html 
> 

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1 None: Re: =?UTF-8?B?QnVnPz8=?= A question of G4EqEMFieldWithSpin.cc   (Kevin Lynch - 06 Nov, 2009)
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