[Frost] tagger sag & phi dependence

[Steffen Strauch]

Dear Sung et al.,

we may or may not have a tagger-sag problem in g9a. I agree with  
Michael that it is important to have all 'known' corrections  
implemented before the kinematic fitter is applied.  The fitter is  
probably not a good tool to correct for 'systematic' errors.  In terms  
of these systematic effects I am still very concerned about the  
azimuthal dependence of the g9a single-pion data.  The variation of  
the measured pi+ momentum from the expected momentum (assuming  
correctly measured pion angles and photon energy) is very large; up to  
10-15 MeV/c within one sector's coverage.

See: http://www.jlab.org/Hall-B/secure/g9/g9_strauch/mtg/20100414.pdf

I wonder if you see such a phi-dependence also in your double-pion  
data or if the many particles in the final state wash out any such  
effect.  We need to address this phi dependence.

All the best,
Steffen