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    User name johna

    Log entry time 11:11:53 on November13,2001

    Entry number 77136

    This entry is a followup to: 77123

    keyword=double spikes on raw TDC spectra.

    There were double spikes in the past, coming from the singles triggers (T1-T4). As far as I know, they have always been there, but they were probably too small to be seen at the G-, H-, I- kinematics, since the ratio of coincidences (randoms) to singles was so large.

    I think that these come from the T2 and T4 triggers (see next paragraph). This can be checked by doing one detector replay with T2 and T4 not included in the analysis. One can just comment out the 'all trigger types' section of ek/jra_det.kumac, and uncomment the 'coincidence and sray singles' section. If they are all coming from T2/T4, then they should go away when you do this.

    However, while this isn't new, I'm not 100% sure where it comes from. If it were related to singles triggers, it would imply that there was a retiming problem in the TDC (and ADC?) gates. However, since it only occurs for S1, I would guess that they come from T2 and T4, the 'dirty' triggers, and that the second peak corresponds to triggers where only the front plane fires. If the timing in hardware is set up so that S2 sets the timing, then an event with S1 only will have an earlier trigger, and so all
    TDC signals would have a timing offset due to the shift in the trigger timing. Of course since the trigger signal is earlier, I would expect the TDC value to be higher, if they are common start TDCs. If they are common stop, then I think everything makes sense. If someone can check to see if the TDCs are common stop or common start and that the S2 timing is delayed by an extra xx ns (where xx corresponds to the ~200 channel difference in the TDC), then I would say that everything is OK (as long as we aren't losing events in paddle 4, where the main peak is already coming fairly early in the TDC range).