[BLAST_TOF] Wednesday, end of day shift

From: Adrian T Sindile (asindile@cisunix.unh.edu)
Date: Wed Sep 11 2002 - 20:56:17 EDT


Hi, TOF experts!
Today started with a gray mood - not only did we see 70% efficiency for
the TOFs the day before, we also had lost bottom signals (TDCs) for some
of the TOFs.
Chris and I tried to analyze runs taken by Tavi over night - all of them
were garbage - "unknown event type" etc. This was due to the problems CODA
had, as reported by Karen (a process hanging!?)...
Not following suggestions of going into the D-tunnel (which I do not avoid
just because of the heat - I also avoid when I really think the problem is
not there, or I really can't solve it) I suggested maybe stuff got screwed
up during the yesterday trip to the D-tunnel (when Karen and myself tried
to make things better). I made this suggestion after tracking down what
run was the first to get messed up.
To make a long story short, after Karen performed her magic (I did not
understand all the details, I will look carefully at her emails when I am
not so tired) I took the following runs, with the follwing results for
LTOF#1 (the only one we could test, due to the present setup):

1631 99.18% LTOF#1 CFD thresh=20.9mV
1632 99.01% thresh=31mV
1633 99.00% thresh=41mV

As you can see, even raising the CFD thresholds for LTOF#1 to 41 mV
(following John's idea) did not affect the efficiency! By this, I think we
proved we are safe (we still have to prove this for as many TOFs as
possible).

Thinking that the first and the last two TOFs (and their corresponding
"sandwiches") are being missed because of the start counter's coverage, I
put the start counter in X mode, relying just on a double coincidence
between the small paddle and the Cerenkov box.

Run 1636 showed no better result with the start counter in X mode.

Karen then proceeded to shortened TDC cables, in order to make things even
safer (timingwise) - during her access to the South Hall and the D-tunnel
I attended the software meeting held by Tim.

Before doing anything else, Doug put the field on but we realized we
cannot use it, as it kills small paddles' and start counter's PMTs (they
are not shielded).
We powered the coils down, took another run: 1640 efficiency = 71%!!!!!!
Thresholds for LTOF#1 were still 41 mV.

As I was reaching the end of the shift, I updated Pete and told him
that the drop in efficiency for the last run was probably due again to the
timing change Karen tried (as she tried to improve things).
I suggested Karen be contacted immediately so that we do not waste time
again - then results reproduced and paddles moved to the next TOFs (which
was my goal for the shift - cut short by the timing problem towards the
end of the shift).

Adrian

-------------------------------
Adrian Sindile
Research Assistant
Nuclear Physics Group
University of New Hampshire
phone: (603)862-1691
FAX: (603)862-2998
email: asindile@alberti.unh.edu
http://einstein.unh.edu/~adrian/



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