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Re: back of the envelope



Hi Mark --

  thanks for posting that. I gather you have assumed that there is just a 
uniform scaling in the field everywhere. I would guess that a more likely
problem is that because we do not know the exact locations of the coils,
that the field profile is not what we think it is. In such a scenario, the 
overall scale of the field may well be correct, but the local variations from
that average may not be what we expect. 

   I am not sure how you could access this without calcualting a field map
from coils slightly displaced from where we expect them, and the use that
to generate the events in GEANT. We then reconstruct them with the true
map.  T do this, I would guess that we need to know what sort of errors 
we might have in coil locations and alignment, and then define some sort
of "worst-case scenario" to produce the distorted map.

   However, thanks for starting to look at this.

     Curtis
On Fri February 27 2009, Mark M. Ito wrote:
> Folks,
> 
> At last Monday’s tracking meeting Eugene suggested that someone make an 
> estimate of the position error caused by a mistake in the knowledge of 
> the magnetic field. Here is an example: http://tinyurl.com/btp8jx
> 
> -- Mark
> 



-- 
Professor Curtis A. Meyer        Department of Physics
Phone:  (412) 268-2745          Carnegie Mellon University
Fax:    (412) 681-0648            Pittsburgh PA 15213-3890
cmeyer@ernest.phys.cmu.edu  http://www.curtismeyer.com/