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Re: TDC difference mystery mostly solved



Hi Alex:

Interesting observation.  Since the was no reason to manipulate any of
the BCAL cables for the cosmic ray runs, were the TDC cables also
reversed for the photon runs?

George

>>> Alex Dzierba <dzierba@indiana.edu> 06/22/07 4:53 AM >>>
Dear Friends

In the note that I sent out yesterday titled "BCAL Test
Module - Studies with Cosmic Rays" - referring to Fig 5,
we noted that the North-South TDC difference spectra
showed multiple peaks.  For the cosmic runs where the
trigger paddles were located at z .ne. 0 there is a primary
peak at the 'right' TDC difference and a secondary peak
with the opposite sign.  The 'right' answer is dt=2*z/c where
c is the effective speed of light in the module,
about 16 cm/ns.   For runs at z = -50 and -150 cm there are
smaller additional peaks.

The secondary peaks for all the  z .ne. 0 runs appear to have a
trivial explanation -- the cables for segments 1 and 13 must have
been reversed going into the TDC's.  I determined this by
looking at TDC differences  for modules separately for
events in which more than 90% of the energy is contained
in a single layer.  Segments 1 and 13 are the top and bottom
segments in the first layer (as seen by the photon beam).
In the plots of Figure 5, the ratio of events in the primary
to secondary peaks is approximately 9 to 1 -- consistent with
this conclusion as there are 18 entries per event - corresponding
to the 18 segments.

I am in the process of trying to track down the other
smaller peaks for the z = -50 and -150 cm runs.

Cheers
Alex
-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Alex R. Dzierba
Chancellor's Professor of Physics (Emeritus)
Department of Physics / Indiana U / Bloomington IN 47405 / 812-855-9421
JLab Visiting Fellow
Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 /
757-269-7577
Home Phone: 812-825-4063  Cell:  812-327-1881  Fax: 866-541-1263
http://dustbunny.physics.indiana.edu/~dzierba/
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