Subject: weirdness explained -- why ST hit width depends on position
From: Bob Nolty (nolty@hep211.cithep.caltech.edu)
Date: Sat Aug 12 2000 - 18:01:53 EDT
Hi --
I got an email from Paolo Bernardini explaining the weird behavior I
pointed out in a recent news item -- and I have new pictures of the
effect; look at
http://www.hep.caltech.edu/macro/protected/notes/wireWidth.ps
http://www.hep.caltech.edu/macro/protected/notes/stripWidth.ps
http://www.hep.caltech.edu/macro/protected/notes/stripWidth.attico.ps
with the usual account and password.
Most strips are perpendicular to what we call the D axis. However,
the attico strips and the strips in planes 1 and 2 of SM1 are oriented
along slightly different axes. This presents a problem for doing
tracking in the D-Z view. The pragmatic solution Bernardini
implemented in DREAM was to compute the entire range of D coordinates
covered by the strip and assign this number as the width of the hit.
In these misaligned planes longer strips have more uncertainty in
their D coordinate than shorter strips.
Bernardini also points out what I had subsequently discovered, that
the width of wire hits also depends on location; he asserts that this
is also because wires are not perfectly perpendicular to the x-axis.
I have not yet understood why this effect leads to exactly the
behavior seen in the figure.
Paolo adds, "Informations are available in MEMOs (10/88 & 1/90) and in
my presentations in general meeting and working group (February 92,
May 1991, October 1991)."
Bob
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