Log entry time 23:47:44 on November 12, 2009

Entry number 299374

Followups:

• 299524 11/13/09 12:03 X. Zheng PVDIS DAQ background study - a possible answer to part 1

Figure 1: Group 2 Preshower vs. Shower sum with cut on fbTDC of gr2 EN triggers. Here we clearly see the threshold on the sum, shown as the red line. However, there are events below the red line, which are the background we need to understand. (Note, before we only noticed this background when plotting the global trigger, but in fact it is there even for individual group triggers.)

Figure 2: fbTDC histogram for gr2: Total shower (top), Preshower (middle), and EN trigger (bottom), for all events in Figure 1.

Figure 3: fbTDC histogram for gr2: Total shower (top), Preshower (middle), and EN trigger (bottom), for events below (2*PS+SH<1500) in Figure 2. This cut selects events (much) below the red line. Interestingly, all of them show up about 200ns (400 channels) after the main trigger peak in Figure 2.

Figure 4: similar plot as Figure 1, but this time is for R.ps.asum_c vs. R.sh.asum_c, i.e., sum of all Preshower and Shower ADCs. Here, again we see a relatively clear threshold on the sum (red line), and some background below it. In addition, we also see some pileup events way above the electron "blob", which are potentially electron-electron pileups. Since this is not seen in Figure 1, it means it should be 2 electrons in two different groups.

Figure 5: this is fbTDC of electron VETO signal. After the main trigger peak, it is evenly distributed in time, both within and outside 200ns of the main trigger.

Figure 6: fbTDC of global electron narrow EN trigger, for all events in Fig.4 (top), and events below the red line in Figure 4 (bottom). Again, backgrounds appear only after ~200ns of the main trigger.

Figure 7: These are R.cer.asum_c for background events in gr2 triggers (top), and the global EN triggers (bottom). Clearly, they should not have passed the gas cherenkov threshold.

These are merely observations and further investigations are needed to understand these backgrounds. They do not seem to be electron-pion accidental coincidences, since the timing of the background clearly is not the same as the main electron trigger. Why do they happen only >200ns after the main triggers? And do they come in all the time, but we do not see them in fbTDC histograms because of the fbTDC range (down to only channel -500)? Also, from all histograms these events should not have passed any of the 3 PID cuts (Preshower, Shower, and Cerenkov), so why do they show up?

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

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