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    User name D. Parno

    Log entry time 23:16:49 on February 20, 2009

    Entry number 262392

    Followups:

    keyword=Compton/Moller Comparison

    I found Compton runs (original DAQ) taken relatively close in time to yesterday's Moller measurement (2/19) as well as to the 2/11 Moller measurement. The polarizations measured by the Moller agreed very well with each other. The Compton is not yet equipped to calculate absolute beam polarizations -- we need either tagged electrons or a detector response function -- but the raw asymmetries can be used as a relative polarization measurement. As the table shows, Compton runs near the Moller measurements agree with each other, which is encouraging. Estimated errors shown are statistical only.
    Date Average Moller polarization Compton run number> Maximum Compton asymmetry Elapsed time from Moller end to Compton end
    19 Feb -74.2% +/- 0.2% 15883 -6.0% +/- 0.1% 4.5 hours
    11 Feb 74.5% +/- 0.2% 15731 6.1% +/- 0.1% 29 hours
    The Compton run after the 2/11 Moller measurement is actually quite some time after (29 hours from end-of-run to end-of-run). This is because the vertical tune in the Compton chicane was not good for most of the day following the Moller measurement; the Compton run reported in the table was taken after a vertical tune. We note that the 11 Feb measurements were taken with the half-wave plate OUT and the 19 Feb measurements were taken with it IN. Both Moller and Compton results flip sign, as expected.

    A copy of this log entry has been emailed to: brads, vasulk, camsonne