Tonight's shift began with continuing day shift's work on efficiency by
making threshold/voltage changes and software cuts. We ran in to trouble
however and found an abnormally low efficiency for the tested TOF's.
After much investigation it was found that the bottom TOF's were not
having TDC data recorded in amounts comparable to the top tubes. A very
simple trigger was made including only the LTOF1 with an X for the first
Cerenkov box. If any events were to be recorded then data must be getting
through for both tubes. Sure enough, with a high data rate, we saw plenty
of events through this one TOF. Upon running plot_tdc.C we saw that the
top tube saw all of the events but that the bottom saw only a small
fraction. To double check the software, we ran plot_tdc.C and TOFeff.C
again with run 1585 that Tavi took last night. For this run we saw
comparable amounts of data in the top and bottom TOF's. So we did not
have a software problem. We also switched the top and bottom cTOF cables
at the fan-out delays that provide inputs to the TDC's. This time the
bottom had good spectra and the top did not. Therefore it seems that
something upstream of the fan-out delay is causing the problem. After
checking with the scope it was found that the top TDC input precedes the
bottom by about 20 nsec. But again, to our knowledge we did not change
anything that would cause any problems. Investigations continued for
the whole of the shift This is the state of affairs as the graveyard shift
starts. I have spoken to Tavi and he agreed to take the approach
methodically and work one paddle at a time hopefully resolving this and
getting us to production mode.
PK, JS
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