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User name X. Zheng
Log entry time 19:21:46 on November11,2009
Entry number 299007
keyword=PVDIS DAQ - Left arm cherenkov ADC wrap over and discriminator cut histogramIt was noticed that the GC cut on the left arm is not as clean as for the right arm. Below the first plot shows L.cer.asum_c without cut (black) vs. with GC fbTDC cut (red). The GC fbTDC is triggered by the output of a discriminator whose input is the hardware-summed GC. It's expected that the red histogram should show a clean cut somewhere, and reject fully the pions near channel zero, but the data show otherwise. A tighter cut on fbTDC reduces the pion peak by a factor of 2-3, but the pion contamination is still large.
The right arm data does not show this problem. There are two differences between the left and right arms:
1) Left arm has much higher electron rate (215kHz) than right arm (18kHz), and the pion rate (24kHz) is lower than right arm (~55kHz).
2) I noticed the ADC for left arm GC still have overflow/wrapover, see the second plot. However, I am not sure this explains fully the pion contamination since the total # of events in the overflow region, summed over all 10 ADCs, is much less than the pion contamination seen in the first figure.
FIGURE 1
FIGURE 2
