Hi Don-
	I am going to ask that an attempt be made to reduce the residual field
to less than the present 300G.  At this time, I don't know what value we
can achieve.  It will can cost considerable time and money to get the
field down to a very small value.  Therefore, it would be useful to have
an estimate of the necessary limit on the field.

			nate

Donald Koetke wrote:
> 
> 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/
> >
> >

-- 

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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