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    User name D. Parno

    Log entry time 21:27:59 on August 25, 2009

    Entry number 285973

    keyword=Compton FADC: Helicity-Correlated Pedestal Shift

    Fig. 1 shows the shift in the FADC pedestal correlated with the helicity bit read out by the TIR. Note that this correlation is with the prompt bit, of course; we expect there to be no correlation with the actual (i.e.) delayed helicity. (We will be checking this.)

    The two (nominally pedestal-subtracted) histograms shown are for a helicity input bit of 0 and a helicity input bit of 1. After a Gaussian fit, the means are 6.52939e+05 +/- 3.06050e+03 (helicity = 0) and 6.39600e+05 +/- 3.06538e+03 (helicity = 1). The shift in the mean is 13,339 which (over 6.6 million samples) corresponds to a pedestal shift of 0.002 FADC channels. This is not large but the error in pedestal subtraction would affect Accumulator 0 asymmetries.

    The run number was 18354.

    A copy of this log entry has been emailed to: gbfranklin@cmu.edu, mfriend@andrew.cmu.edu, souder@jlab.org

    Figure 1