[G8b_run] links for today's meeting.
Ken Livingston
k.livingston at physics.gla.ac.uk
Thu Sep 3 11:44:20 EDT 2009
Hi All,
Here are some links for the meeting, cut and pasted from previous emails.
Emails are below:
Mike's tagger sag links
The g1c CMU energy correction plot (figure 9 on page 12):
http://www1.jlab.org/ul/Physics/Hall-B/clas/public/2004-017.pdf
compares well to the ASU iterative routine
http://www.jlab.org/Hall-B/secure/g8b/ASU/egCorr/g1cEgCorr.gif
Chuck's Links
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueMinusEmeas_v_Emeas_FitMeans_BothConfCuts.gif
The second plot again has two taggerSag distributions. The bottom one is
the original dist (the one using a conf lvl cut of 10%) and the top one is
the distribution made using the mm2 cuts that were suggested by Mike.
The effect of this mm2 cut is almost exactly the same as the effect from
making a conf lvl cut of 0.1%:
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueMinusEmeas_v_Emeas_ConfCutAndMM2Cut.gif
Mike's recent email
g8b run group,
Chuck: Nice job :)
The run group should come to an agreement as to the energy and momentum
corrections. It would be best if we all used the same corrections and had
some sort of documentation to point to.
My feeling is that a kinematic fitting routine should give the best
results for this sort of study. Since replacing the confidence level cut
with a missing mass cut does not change the results in any real meaningful
way, the selection of events due to confidence level does not appear to
be very important in the end analysis. As long as the pull distributions
look good, I feel comfortable going with Chuck's results.
Assuming that I read the plots correctly, Chuck's results suggest that the
photon energies in the range of interest (0.9 to 2.0 GeV) are within 0.3
MeV ! If this is the case, we do not need to worry about the photon energy
correction and we state the width of an eid as being the uncertainty in
the photon energy.
Question: Should meet next week to discuss this?
Take care,
Michael
Chuck's emails:
Hello all,
Here is my momentum correction function and array again. You can find
it at:
/u/home/hanretty/rootbeer2.1/NTuple_code/corrected_proton_mom.cc
the array needed can be found at:
/u/home/hanretty/rootbeer2.1/NTuple_code/mom_corr_array.pro
The function requires you to give it the proton's 4-vec as it
comes from the data file, no corrections should be made to this 4-vec
prior to the call to the function. This 4-vec is used to find the correct
bin in momentum, theta, and phi and the appropiate correction factor. The
function also needs a 3-vec vertex position and the run number. The 3-vec
and run number are needed to apply the ELoss package to the 4-vector both
before the corrections are applied and after. This function does not
apply ELoss twice to the same 4-vector though. ELoss is first applied to
the 4-vec so the binning can be determined. The correction factors are
then applied to the (raw) 4-vec components and the momCorred 4-vec then
has ELoss applied to it. The function then returns the corrected
4-vec.
I have also made some plots for tht tagger sag using a different
confidence level cut and also the suggested mm2 cut. The first of the
two plots I'd like to share show the taggerSag distributions using a conf
lvl cut of 10% and 0.1%. In the histo, the lower distribution comes from
using a conf lvl cut of 10% while the upper comes from using a conf lvl
cut of 0.1%. The low points of the two distributions are almost the same
but the "humps" of the distribution using the lower conf lvl cut are more
pronounced:
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueMinusEmeas_v_Emeas_FitMeans_BothConfCuts.gif
The second plot again has two taggerSag distributions. The bottom one is
the original dist (the one using a conf lvl cut of 10%) and the top one is
the distribution made using the mm2 cuts that were suggested by Mike.
The effect of this mm2 cut is almost exactly the same as the effect from
making a conf lvl cut of 0.1%:
http://hadron.physics.fsu.edu/~hanretty/Files/TaggerSag/EtrueMinusEmeas_v_Emeas_ConfCutAndMM2Cut.gif
-Chuck
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
Mike's earlier email.
Dear g8b collaborators,
Stuart showed an energy dependence in the photon energy correction (for
g8b data) that was not a simple multiplicative factor. I decided to verify
Stuart's results. I found that there is an energy dependence in the photon
energy correction that is not a simple multiplicative factor. It appears
that the tagger sag correction applied to g8b data was not sufficient.
The method I had been using previously (massX2 vs. incident photon
energy) can not be used to determine an energy correction that is
different from a common multiplicative factor. Therefore, I am now using
an iterative routine that capitalizes on the overdetermined reaction
gamma p -> p pi+ pi- (as is standard in this type of study). This
iterative routine has been successfully tested against the known energy
correction obtained by the CMU group for the g1c data set.
The g1c CMU energy correction plot (figure 9 on page 12):
http://www1.jlab.org/ul/Physics/Hall-B/clas/public/2004-017.pdf
compares well to the ASU iterative routine
http://www.jlab.org/Hall-B/secure/g8b/ASU/egCorr/g1cEgCorr.gif
The CMU energy correction has one free parameter. This parameter is an
offset to the fractional photon energy (E_gamma/E_e). For g8b data, in
addition to the standard CMU energy correction, I have included a term
that is a simple multiplicative factor:
energy_correction -> CMU_correction + E_gamma*multiplicative_factor
The result of this 2 parameter fit can be found at
http://www.jlab.org/Hall-B/secure/g8b/ASU/egCorr/g8bEgCorr.gif
The three bump structure of the tagger sag is clearly seen.
The fit results:
multiplicative factor = -0.00351(6)
offset = 0.00134(3)
The function is very simple and a FORTRAN version of the g8b photon
energy correction can be found at
http://www.jlab.org/Hall-B/secure/g8b/ASU/egCorr/cmuErgCor.f
I have decided not to produce a stack of slides fully describing the steps
taken to obtain the results shown in this email. Instead, I will write a
CLAS note that can be easily referenced from analysis notes. I hope to
have the note completed in the next week or two.
Sincerely,
Michael
--
=======================================================
Ken Livingston
Dept. of Physics & Astronomy, Tel: +44 141 330 6428
University of Glasgow, Fax: +44 141 330 5889
Glasgow G12 8QQ.
Scotland. UK.
=======================================================
More information about the G8b_run
mailing list