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    User name X. Zheng

    Log entry time 12:03:53 on November 13, 2009

    Entry number 299524

    This entry is a followup to: 299374

    keyword=PVDIS DAQ background study - a possible answer to part 1

    Yi Qiang reminded me that the ADC gate of the spectrometer DAQ is only about 400ns wide. So anything coming outside the gate will not have their signal amplitudes in any detector correctly recorded by ADC. THis may explain well why all "background" defined in the previous entry show up near (0,0) in the lead glass spectrum, and near zero in the Cherenkov spectrum. In fact, all fbTDC spectrum shown in the previous entry, when with the "background cut" applied, shows a clear gap between channel 280 and ~1180, or about 450ns.

    If this is the case, then the so called "background" are not backgrounds at all. They could be good electron triggers but only show up without correct ADC information. Below are 3 figures which may support this theory, from run 4972.

    Figure 1. PS vs. SH for gr 4 (here I chose gr4 instead of gr2 to gain more statistics), with a loose cut of fbTDC gr4 EN trigger of >-500. Note: =-500 means no signal.

    Figure 2. same as Figure 1, but with a tight cut of fbTDC gr4 EN trigger between 300 and 1100. This roughly correspond to the gap seen in fbTDC of the previous entry, and could potentially be the ADC gate.

    Figure 3. Cerenkov ADC sum for gr4 EN trigger > -500 (black) vs. between 300 and 1100 (red).

    As can be seen, using a tight fbTDC cut the "background" in both PS vs. SH and Cherenkov is gone.

    Suggestion for future analysis: If you want to have meaningful ADC information, should use a ~400ns fbTDC cut. Since channel 280 is where the "background" is starting to be seen, probablly (280,1080) is a good cut to use.

    A copy of this log entry has been emailed to: rom,pkpan,dwang,deng,yqiang,kkumar,rsubedi

    Figure 1

    Figure 2

    Figure 3