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    User name R. Michaels

    Log entry time 16:28:54 on July 2,2010

    Entry number 329461

    This entry is a followup to: 329213

    keyword=comments on coincidence measurements

    This log entry tries to anticipate the TDC spectrum we'll
    be looking at for finding coincidences. I don't think anyone
    has thought about this.

    An early activity will be to find true e- pi+ coincidences to
    verify the timing setup.

    We'll be looking at the "trigger flags".

    Triggers are defined in halog 329213 and 329311

    Triggers were plugged into a TDC to make trigger flags,
    see halog 329275

    What we may see is shown in fig 1 for the trigger on the two
    spectrometers.

    Since we aligned all the triggers at the trigger supervisor, it's
    not obvious which one will define the timing for the true coinc-
    dences. If we aligned perfectly, then the time gap "TG" in fig 1
    would be zero. I expect TG to be between 0 and 10 nsec. The
    "true coincidence" peak will be bigger or smaller depending on
    the signal-to-background ratio.

    Note, there are variations on this. In the "scope picture", B
    could be earlier than A. This means that A defines the coincidence
    timing. This would reverse the roles. The common stop for the TDC
    comes from whatever made the timing at the TS.

    Realized later:
    Also, this picture assumed that ps1 = ps3 = ps4 = 1.
    In the more common case where ps1 and ps3 are large, the self-timing
    peak will occur on the left side for each of T1 and T3.

    Anyway, we'll have fun sorting out what the peaks mean.


    FIGURE 1