[G8b_run] Tagger Sag

Fri Aug 21 18:24:57 EDT 2009

Chuck, these are all good suggestions from Mike. Would you please:

1. Share your momentum corrections with Mike ASAP?
2. Try the four mini-tests he suggests to firm up your results.
3. Things need to be tweaked until the pulls have mean zero and standard
deviation 1. Until then, there's still work to do.

---BGR

Professor Barry G. Ritchie
Department of Physics
Arizona State University
Tempe, AZ  85287-1504

Telephone: (480) 965-4707
Fax: (480) 965-7954

-----Original Message-----
From: g8b_run-bounces at jlab.org [mailto:g8b_run-bounces at jlab.org] On
Behalf Of Michael Dugger
Sent: Friday, August 21, 2009 3:20 PM
To: Charles Hanretty
Cc: g8b_run at jlab.org
Subject: Re: [G8b_run] Tagger Sag

Chuck and g8b,

Thanks for all your work.

The problem we face is that there has been no real agreement between 
Chuck, Stuart, or me :(

We need some sort of convergence and then everyone needs to use the same

momentum and energy corrections.

My feeling is that a kinematic fitter is most likely to give acceptable 
results for determination of the corrections needed.

I would like to have Chucks momentum correction and see if that helps me

get a better agreement with him on the energy correction.

One comment:
I do not think you can make this statement->
"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."
If this were true, wouldn't a cut on the tails of the distribution be 
equivalent to a confidence level cut? Did you test to see if the center 
changed with change in confidence level cut?

Some questions:

* The title on the plot
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/photonPull_sit04
_WithMomCorrs.gif
says conf cut at 0.001%. Is this true?

* If you correct the photon energies do you get a pull at zero? What is 
the standard deviation of the pull? It looks different than 1. Don't you

need to have all of the pulls close to having a standard deviation = 1. 
Isn't the kinematic fitter very sensitive to having the correct 
covariance matrix?

Chuck, in the name of comparing apples to apples:

* Can you do the same analysis using only amorphous data? It should not 
change the results, but then we would have the same data in common.

* Can you
i) form massX^2 from the reaction

gamma p -> p pi+ pi- X

ii) restrict events to be

-.01 GeV^2 < massX^2 < 0.00385 GeV^2

iii) turn off confidence level cut.

iv) see if your results remain unchanged

If the result remains the same (and it should), than wouldn't this prove

that the confidence level cut is not forcing the energy correction to be

small?

Please correct me if I made any stupid comments or silly questions. We 
need to get this resolved so that we move forward.

Thanks for your time.

Sincerely,
Michael

On Fri, 21 Aug 2009, Charles Hanretty wrote:

> 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
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