[G8b_run] Tagger Sag

[Charles Hanretty]

Hello All,
     During our last g8b meeting Mike showed some plots regarding the tagger 
sag.  I was asked to recreate this plot to verify what Mike saw. I've been 
working on this for the past few days and have some plots to share.  I have a 
few more plots than what Mike showed I did this to verify my verification. :)

My process:

STEP 1) Make 2 plots by running over one full run for each coherent edge energy 
(a total of 121 data files).

http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueDivEmeas_v_Emeas_ForSlicing.gif
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueMinusEmeas_v_Emeas_ForSlicing.gif

Both of these histos are TH2F's, produced by running over the data files. I 
defined Etrue as the photon energy coming out of the kinematic fitter and Emeas 
as the photon energy as taken from either the GPID or TAGR bank.  For the plot 
to be filled with these values, the event must be a ppippim final state
and pass a fit to no missing particle (energy & momentum conservation) 
with a confidence level of >10%.
EtrueDivEmeas_v_Emeas_ForSlicing: x-axis-> 0.8-5 GeV, 168 bins
                                   y-axis-> 0.998-1.002, 40 bins
EtrueMinusEmeas_v_Emeas_ForSlicing: x-axis->0.8-5 GeV, 168 bins
                                     y-axis->-0.0024-0.0024, 40 bins

STEP 2) Use the FitSlicesY() function to slice the *_ForSlicing histos 
(above) along the x-axis, one slice per bin, and fit each slice to a gaussian. This
function also makes a histogram containing the mean values of the gaussian
fits, bin by bin:

http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueDivEmeas_v_Emeas_SlicedFitMeanValues.gif
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueMinusEmeas_v_Emeas_SlicedFitMeanValues.gif

      The structure that Mike showed in the meeting is clearly seen again 
in the *_SlicedMeanFitValues.gif plots (good!).  However, as you all have
probably already noticed, my y-scale is much much smaller.  This goes back
to the original histograms (the ones made in STEP 1-> *_ForSlicing.gif). 
I first tried using the exact same scale and binning as Mike and I got this:
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueMinusEmeas_v_Emeas_MikeRange.gif

      You'll notice that the plot looks like a strip with sharp edges. These 
edges are a result of my use of a confidence level cut, if I were to not
use a fitter, I would have a larger spread like what Mike has (this 
confidence level cut only allows for events where Etrue and Emeas are 
close). Therefore I had to "zoom in" on the y-axis in order carry this process
out and the result of this "zooming" is the EtrueMinusEmeas_v_Emeas_ForSlicing.gif
plot.  The projection of this plot onto the y-axis is indeed a Gaussian as the
confidence level cut only cuts off the tails of the distribution and does not
affect the peak position.

      I am assuming that Mike is using ELoss and Stuart's momentum corrections
when he generates these plots.  Since Eloss is the same for everyone and I have
my own momentum corrections (that I made using the kinematic fitter, fitting to 
a ppippim() final state), I decided to produce the 
*_SlicedMeanFitValues.gif plots with the inclusion and exclusion of (my) 
momentum corrections to see the effect these corrections have (also to cover 
all my bases).  The two distributions you see on these plots are with and 
w/o momentum corrections (the upper is without, the lower is with).  The use of
momentum corrections does not affect the scale of the y-axis, but only 
moves the distribution closer to zero (for subtractions) or closer to one 
(for the division).

Photon Pulls for a fit to gamma p -> p pip pim ()
with MomCorrs:
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/photonPull_sit04_WithMomCorrs.gif
without MomCorrs:
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/photonPull_sit04_NoMomCorrs.gif

      Although these pulls are not at zero, they are symmetric.  The shifts from 
zero are indicative of a systematic error and improve once I include my 
momentum corrections.  If you look at the effect my momCorrs have on the 
*_SlicedMeanFitValues plots, you see that they only shift the distribution and 
have no real effect on the y-axis.  I would argue that if I were to get all of 
my pulls to exactly zero (an "in a perfect world" senario), then the 
distribution would only shift down some more but the general shape would 
be unaffected.
Reminder: A pull is the difference between the true value (the value from the 
fitter) and the measured value (the value found in the data) normalized
to the error of that particular measurement. A pull centered at zero 
indicates that the systematic errors for that particular variable are 
negligible.

      To summarize: I have seen the same structure in my plots that Mike showed 
at our last g8b meeting using two appraoches.  Where he and I differ is in the 
scale of the y-axis.  It seems that this difference in scale
arises from my use of a kinematic fitter and also a cut on the confidence level 
for the fit whereas Mike used some iterative routine (not saying that Mike's 
routine is garbage).  If I were to not use a fitter then I would
have a spread in my *_ForSlicing plots similar to that seen in Mike's plots. 
My use of a fitter forces me to "zoom in" on the y-axis if I ever hope to slice 
the histogram and fit the slices.  This shrinking of scale carries through to 
the *_SlicedFitMeanValues plots and forces the amplitude of the distribution 
shape to be much smaller.  The important thing is I see the same shape.

-Chuck