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    User name X. Zheng

    Log entry time 22:40:42 on November 6,2009

    Entry number 297915

    keyword=PVDIS DAQ - left arm PRL1,2 spectrum and possible swapping

    Used run 25269 to study the left arm DAQ performance. Because most of lead glass blocks have gain-matched, the ADC spectrum look much better than yesterday. Applying cut on the fbTDC channels provide evidence that the discriminators are working. As shown in Fig. 1.

    The only problem here is that the PVDIS DAQ is designed to cut on the Total shower (PRL1+PRL2), and PRL1 alone, to isolate electrons. But the histogram with cut on Preshower fbTDC cut shows instead a sharp cut on the PRL2 sum. Interesting thing is, the spectrometer ADCs are NOT swapped between PRL1 and PRL2, as shown in Fig.2.

    In Fig.1, the top left plot shows group 1 PRL1 vs. PRL2 spectrum w/o cut. The top right shows the one with Total shower cut, which shows expected behavior. The bottom left plot shows the histogram with Preshower cut, which shows UNEXPECTED behavior (instead of a horizontal cut, it shows a vertical cut). All other groups show similar behavior.

    A separate observation from Fig.1: The Total shower cut is effectively on PS+SH, not on PS*2+SH as seen on the right arm. Also, the current threshold on Total shower seems to be a little high, should decrease from channel 1700 to 1500, or from -100mV to -88mV. The preshower (or Shower) cut is in ADC channel 500, which is the right value if applied on layer 1.

    To see if the two layers are swapped in cabling, Fig.2 shows PRL1.asum_c vs. PRL2.asum_c, w/o cut (top left), with Cerenkov ADC sum >500 cut (top right), and with Cerenkov ADC sum <1 cut (bottom left). The top right and bottom left show typical electron and pion distribution similar to many previous experiments. Clearly PRL1 and PRL2 are NOT swapped in spectrometer ADCs.

    Possible explanations:
    (1) There is double-swapping in cabling: From lead glass PMTs to PVDIS DAQ, then from PVDIS DAQ back to HRS ADCs; This way, the cut on preshower in the PVDIS DAQ will turns out to cut on Shower instead;

    (2) There is no problem in cabling, but the PVDIS DAQ is installed/cabeled wrong. Instead of cutting on Preshower, we instead cut on Shower.

    Both seem impossible, but we will investigate these during tomorrow's access.

    FIGURE 1

    FIGURE 2