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User name Parno / Camsonne
Log entry time 16:53:44 on March 2,2009
Entry number 264201
Followups:
- 264328 03/03/09 15:02 D. Parno No change in Compton asymmetry after 2/18 half waveplate switch
- 264363 03/03/09 17:33 brads Linac energies around Feb 28
- 264371 03/03/09 18:13 Parno/Camson Compton asymmetry measurement
The Compton measured a significant drop in beam polarization over the weekend. You can see from the plot that, around Run 16126 (early Saturday afternoon), average polarization falls from around 75% to around 65%. (Please note that these polarization figures are based on an extremely imprecise cross-calibration to the Moller. They're ballpark figures.)
A look at the raw asymmetries (Fig. 2) shows that the asymmetry magnitude drop coincides with the half-waveplate change on Feb. 28. (You can tell because the right and left asymmetries, red and blue, flip sign; the zero asymmetry around Run 16124 is the run during which the flip occurred.)
Our hunch is that this is a real polarization drop; changes to the linac over the weekend would have affected spin precession and hence beam polarization. Tuning mishaps and high background could also have an effect. It will be interesting to look at the beam polarization tomorrow.
(Note: these plots show only photon data. The gaps in the plots correspond to runs taken for electron detector tests, or runs for which the DAQ/analyzer crashed, preventing an asymmetry measurement.)
FIGURE 1
FIGURE 2
