There are several MC tests we intend to do to ascertain how best
to treat possible residual B-field effects when doing alignments.

We will generate MC runs with different, small residual B-fields and fit
straight lines to these tracks.  We will then -

-- Examine the effect on the chisquare for these fits as a function of
   the strength of the residual B-field, and,

-- Perform a complete alignment exercise to see how the overall plane-
   by-plane alignments are affected by these small B-fields, and thereby
   attempt to ascertain the sensitivity of the alignment to these small
   B-fields.

It seems prudent to do these tests before worrying about the possibility
of having to fit helices to tracks in these small fields for purposes
of alignment.

Cheers!
Don & Shirvel

---------------------------------
Donald D. Koetke
Department of Physics & Astronomy
Valparaiso University
219-464-5377 (Voice)
219-464-5489 (FAX)
donald.koetke@valpo.edu
www.physics.valpo.edu

On Sat, 3 Nov 2001, Nate Rodning wrote:

> Date: Sat, 03 Nov 2001 08:13:42 -0800
> From: Nate Rodning 
> To: e614-align@Phys.UAlberta.CA, e614-s3@Phys.UAlberta.CA
> Cc: Carl Gagliardi 
> Subject: residual field
>
> One way to guess the effect of a residual field on our data is to note
> that our sensitivity to the 2T field is at about 1/10,000.  That is, we
> are sensitive to 2G.
>
> Therefore, for Michel positrons, we need a field less than about 2G if
> we want to say we have "field off".
>
> The situation for beam pions at 120 MeV/c is not vastly different.
> P-perp is somewhat smaller, so perhaps our sensitivity is greater.  In
> any case, 300G residual field sounds very big.
>
> Can someone make a more reliable estimate of the effect of a residual
> field on our apparent resolution?
>
> Perhaps we need to do alignments by tracking helices in a small field,
> rather than assuming zero field.
>
> 			nate
>
> --
>
> Nathan Rodning
> Professor of Physics, University of Alberta
> **** 2001/02 at TRIUMF:  (604) 222-7549
> **** TRIUMF Fax:  (604) 222-1074
> -----------------------------------
> Alberta: (780) 492-3862  /  Fax:  (780) 492-0714
> http://www.thehungersite.com/
>
>

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