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.
Average Moller polarization
Compton run number>
Maximum Compton asymmetry
Elapsed time from Moller end to Compton end
-74.2% +/- 0.2%
-6.0% +/- 0.1%
74.5% +/- 0.2%
6.1% +/- 0.1%
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