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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