[Frost] FROST intial Tagger Sag study

[Charles Hanretty]

Dear FROSTies,

I hope I'm not crossing any lines here in giving my two cents (hopefully 
I've also correctly interpreted the emails):
When Mike and I were studying the Tagger Sag seen in g8b data, I too used 
the photon energy returned by the kinematic fitter as E_measured. Where 
Sung and I differ is that he does not yet have momentum corrections for 
g9a which do affect the fitted photon energy.* The effect of the momentum 
corrections (at least my momentum corrections) on the mean value of the 
photon energy pull has shown itself to be present and real but rather 
small. 
I would then agree with Mike that one cannot prove the absence of a 
Tagger Sag problem using the FSU fitter with g9a data in its present form 
(no mom corrs). As "gray" as this might make my stance, I would also agree 
that the results Sung showed hint that the Tagger Sag was taken care of in 
the cooking.

What I'm saying here is that Sung's results with respect to the Tagger Sag 
are more of a hint that the photon corrections were applied in the cooking 
than proof that it has been taken care of. In order to prove that the 
Tagger Sag has been corrected Sung would indeed have to finalize his 
momentum corrections (and if someone was still unconvinced, the covariance 
matrix errors). It looks promising that you all will have nothing to worry 
about in term of Tagger Sag but I wouldn't start ordering the party 
supplies just yet. :)

I think a plot of [E_calc - E_meas] v E_meas (what I used) or [E_calc - 
E_meas]/E_mea v E_meas would be a better way to look at the data than
E_calc/E_meas v E_meas.

* -> Sung currently does also not have covariance matrix errors for g9a 
but is using my g8b errors which seem to be not that bad for g9a, he will 
be determining his own at a later date.

-Charles Hanretty