Final analysis

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Polarimetry

Compton

87.41 +/- 0.12 (stat) +/- 1.77 (sys) %

Moller

88.92 +/- 0.04 (stat) +/- 1.12 (sys) %

Compton

Mindy's HAPLOG post:

http://ace.phys.virginia.edu:8080/HAPPEX/2582

Final result: 87.41 +/- 0.12 (stat) +/- 1.77 (sys) % (??)

chi^2/NDoF = 1.09 for 13 points over the experiment

Systematic Error

Rel Uncer. (%)
Laser Pol. 0.07 http://ace.phys.virginia.edu:8080/HAPPEX/2530
Gain shift 1.3 email from Megan Friend, see below
Collimator Pos. 0.02 http://ace.phys.virginia.edu:8080/HAPPEX/2568
Nonlinearity 0.3 http://ace.phys.virginia.edu:8080/HAPPEX/2569
Analyzing Power 1.53
TOTAL 2.03

Systematic Error Notes

  • From Megan over gain shift:
I don't think I'm going to be able to get a number for the gain shift
during PREX, although it should scale linearly with signal-background
size. Using the 1% gain shift we saw during HAPPEX (signal+bkg to
background = 122e6 to 53e6), that would give us a 0.8% gain shift for
PREX (signal+bkg to background = 48e6 to 30e6 at 1kHz * 3.3 to convert
to 30Hz). This would give us a change in the final polarization number
of 1.3%, if it's folded into the background subtraction ( which comes
from comparing a background subtraction of
(48e6-30e6*(1.008))/(48e6-30e6) ). So I'd say the possible gain shift
gives you a 1.3% systematic error.
  • From Megan over radiative correction:
I just ran through the PREX data to add in a radiative correction, and I
get that this increases the analyzing power by 0.3% (from 0.01828903 to
0.01834393). This is consistent with what I've seen, so I think it's
safe to add that in there.

There is an increase in analyzing power of 0.3%, which corresponds to a decrease in beam polarization by 0.3%. Therefore, the final analyzing power should multiply by (1+0.003) due to A_real = A_exp * (1+0.3%)

w/o the radiative correction:

analyzing power = 0.01824526 +- 0.00002583 (sta.) +- 0.000279099 (sys.)

w/ the radiative correction:

analyzing power = 0.018299996 +- 0.00002583 (sta.) +- 0.000279099 (sys.)


Moller

http://www.jlab.org/~moller/e02-006.html

Final result weighted average: 88.92 +/- 0.04 (stat) +/- 1.12 (sys) %

(not sure if the systematic is relative or absolute)

Systematic Error

Sasha's report at the Jan 2011 collaboration meeting http://www.jlab.org/~moller/docs/PREX_Col_01_29_2011.pdf

Uncer. (%)
Fe Pol. 0.25
Targ Discrep. 0.5
Targ Saturation 0.3
Analyzing power 0.3
Levchuk 0.5
Targ temp 0.02
Dead time 0.3
Background 0.3
Others 0.5
Current diff 0.3
TOTAL 1.12