[Clas12_verystrange] xi polarization uncertainty plot

[Lei Guo]

Somehow my email is not going through. Maybe it's because of the  
attachment.

The plots are at

www.jlab.org/Hall-B/secure/g12/lguo/xipol/

I generated the polarization uncertainties for the xi-, using what  
Mike gave me (which are the counts of xi- as a function of Egamma, and  
angles in the cm frame). I did a simple exercise, assuming the  
polarization being 10% or 30%, and estimated the statistical  
uncertainty.

The formula I used was P=(-2/alpha)(Npos-Nneg)/(Npos+Nneg). What Mike  
gave me was the Ntot=Npos+Nneg in each bin. I assume the Npos and Nneg  
was measured independently without correlation. Then it can be shown  
that
the error was |dP|=(2/alpha)*sqrt(Npos*Nneg*Ntot)/(Ntot**2).

The results are in the two attached plots. The first one xipolErr.pdf  
are for all energy bins. The second one xipolErrEg8250.pdf is for the  
Egamma=8.25GeV bin.

Please let me know if you notice anything wrong, and have suggestions  
for improvement.

Thanks a lot!

Lei