To extract GEn/GMn, the true "physics" asymmetry must be determined. Since the "raw" asymmetry immediately measured from the data must be corrected for false asymmetry contributions, dilution, and finite acceptance effects.
I recommend that you work through the algebra to understand the correction factors for the asymmetry. Here, I will start with the number of events
N in the positive (+) and negative (-) helicity state and state the final expression.
Aphys = (sigma+ - sigma-) / (sigma+ + sigma-)
while
Araw = (N+ - N-)/(N+ + N-)
and
N+ = sigma+ L+ eta+ + Bck;
likewise for
N-.
What one finds, to first order in the false and true asymmetries, is:
Aphys = 1/D ( Araw - (1 - Q-/Q+ eta-/eta+) )
where
eta is the overall efficiency, and
Q is the accumulated charge for each helicity state.
False Asymmetries
The sources for false asymmetries for GEn are:
- Beam charge asymmetry (more accumulated charge in one helicity state than the other)
- DAQ Livetime asymmetry
- Electronic Livetime asymmetry
- Tracking efficiecy asymmetry
The last three are due generally to the asymmetry in the background pion-production cross-section, which is ~1% for the Kine4 dataset.