[Sane-analysis] Bigcal Re-Calibration Progresss

[Whitney R. Armstrong]

Hello Everyone,

I wanted to share some results in my refinement of the BigCal calibration from 
pi0s. 

Below you will find plots showing the mass spectrum (above the pi0 mass) from 
two photons (top central plots) for parallel and perpendicular configurations.

In the mass plot you can see a bump near the eta mass (547 MeV). 

Parallel:
http://quarks.temple.edu/~whit/SANE/analysis_main/results/pi0calibration/etamass2-2000_1.png

Perp:
http://quarks.temple.edu/~whit/SANE/analysis_main/results/pi0calibration/etamass2-2000_5.png

Please note the following:

1) Only after recalibrating did the eta mass peak start to show up. This is 
because the mass reconstructino of the eta is most sensitive to the energy 
resolution and less sensitive to the position (due to the larger opening angle 
for the eta compared to the pi0).  

2) The parallel calibration is better than the perpendicular. That is, the perp 
calibration can certainly be improved compared to the parallel, thus the eta 
mass is resolved better for the parallel.

3) The background is much higher than the pi0, therefore, it does not seem 
feasible to directly calibrate (like pi0) using the eta mass peak.  However, 
because the two eta clusters are separated bny large distances (>90 cm), it 
provides a nice confirmation that the opposite sides (eg the top and bottom) 
are calibrated properly against each other. 

4) All previous results were contaminated by the insidious behaviour of the old 
calibration. The top (RCS) energies were shifted higher while the bottom 
(Protvino) was shifted lower (thus producing a nicely centered pi0mass when 
summing over the whole detector). This likely exlains why Anusha consistently 
saw energy differences in the elastics. It also explains (the problem seen long 
ago) that the top appeared to have all the higher energy events compared to the 
bottom.  It would be interesting to look at both of these problems again.

Please let me know if you have any suggestions on how to clean up the eta mass 
spectrum. 

As always, your comments and questions are greatly appreciated. 

Cheers,
Whit