Joe Manak and I looked at the hits in the TOF which had no valid TDC information (on either
pmt). Almost all the hits consisted of ADC values just above pedestal, or zeros, and are
eliminated in the offline software as soon as the SC1 bank is filled. The zeros and low ADC
values were split roughly equally.
The zeros are due to overflow hits in the TDC in slot 11. This problem was noticed
previously and was traced to a faulty 82pF capacitor which determines the timeout period of
the TDC. We believe this problem has been fixed.
Of the ADC hits above the sparcification threshold, Approximately 80% fall below 40 ADC
counts. The current sparcification threshold is 30 counts, and the TDC discriminator
threshold corresponds to approximately 35 counts. We propose to raise the sparcification
threshold to 40 counts which keeps it in line with the TDC threshold, so the discriminator
threshold does not need to be changed.
Finally there were a few isolated ADC channels which were very hot and we should deal with
them on an individual basis either by fixing them if possible, adjusting the HV, or finally
increasing the ADC sparcification threshold.
These changes should eliminate approximately 90% of hits which currently get thrown out in
the first pass of the offline.
Elton.