# G2p Analysis Minutes

Minutes of the weekly analysis meetings

## 1/12/2016

Present: Melissa Jixie
By Phone: Jie, Chao, Ryan, Toby, Ellie

Feature Presentations:

• Ryan

Gave an update on his cross-section analysis of the small angle GDH data. yield study using simulation. He is working on the problem that after doing the tail subtraction and running the inelastic Radiative Correction code the fully corrected cross sections go negative at high $\nu$. To solve this, he did a fit on the Nitrogen form factor. During the fitting, two models is considered: the oscillator model and the Fermi Model and the Fermi Model is proved to be better. He will complete the calculation of the elastic tail by using the form factor in a few weeks. More details can be seen in his slides here.

• Toby

Gave an review on the polarization uncertainty estimation. He claimed that the reason of the small uncertainties for the target polarization is because we took large amount of TE for each material. Thus the uncertainty of the calibration constant is reduced by average. Jixie suggests that the error propagation still need to be carefully checked. More details can be seen in his slides here

General Discussion:

• Chao updated his optics technical note.
• There is no meeting next week due to the Hall A collaboration meeting.

## 12/23/2015

Present: Min, Jixie, JP
By Phone: Jie, Chao, Ryan

Feature Presentations:

• Jie

Gave an update on his yield study using simulation. He studied the effect of the raster size cut on the yield. The yield changes with the area of the raster cut size as the prediction but still shows some correlation. He was suggested to study if there is some high order effect which could be corrected. After applied the raster cut, half of the runs with the yield problem could be resolved to a reasonable 3% range. More details can be seen in his slides here.

• Min

Gave an update on her very preliminary calculation results of the asymmetries and structure functions of the 1.7 GeV setting. She applied dilution effects and the radiative correction to the calculation. She also provided a systematic uncertainty estimation. More details can be seen in her slides here.

General Discussion:

• The meeting time will be changed to 10am Tuesday next year.

## 12/16/2015

Present: Min, Jixie, Melissa
By Phone: Jie, Chao, Ryan, Toby, Ellie

Feature Presentations:

• Toby
• Showed updated dilution results for the 2.2 GeV, 5T longitudinal setting, using the
most updated optics matrix. He used a weighted average of the packing fraction
values for material 17; there is some drift in the yields for this setting, and therefore
some drift in the packing fraction. He showed the effect of applying 4 different
acceptance cuts, and found that the structure of the dilution factor was stable. The
dilution factor is very dependent on the packing fraction. The method for dilution
analysis is complete, but until the yield drifts are completely understood (and final
packing fraction values can be extracted), the dilution analysis cannot be finalized.
He also started looking at the transverse setting. Before applying any acceptance cuts,
he found there was already good agreement between the data and the Bosted prediction.
It may not be necessary to apply acceptance cuts at this setting, but it's not clear why
there is no acceptance effect. Ryan suggested that the acceptance effect might be
minimized since the scattering angle is slightly larger for this configuration.More details
can be seen in his slides here.

General Discussion:

• Chao has finished updating the optics databases for all of the LHRS settings. He will
update the DB on ifarm so that Toby can replay the data.

## 12/9/2015

Present: JP, Jixie, Melissa
By Phone: Vince, Jie, Chao, Toby, Ellie, Ryan, Min

Feature Presentations:

• Jie
• Compiled a table summarizing the results from his yields study using simulation. In the
simulation, the beam position and raster size are taken into account. He also simulated
the change in the acceptance from run to run. He found he was able to reproduce the shift
in the yields with simulation for about 50% of the runs. There was some question about the
sign of the beam position, it's possible there is a difference in the definition of the coordinate
systems used by Pengjia and included in the simulation. Jie will double check with Pengjia
to make sure the sign is correct. He is also summarizing his results into a technote.

## 12/2/2015

Present: JP, Min, Melissa
By Phone: Vince, Jie, Chao, Toby, Ellie, Ryan, Karl, Pengjia

Feature Presentations:

• Toby
• Gave an update on his acceptance and yield study using the updated optics database. He
looked at the helium run for one setting in the longitudinal configuration with the smallest p0,
since it is way past the delta the dp distribution should be fairly flat. Without applying any
acceptance cuts, a sawtooth pattern is seen in the data, while the Bosted model prediction is
much flatter. By applying a cut on dp vs phi, he was able to find a region where the dp distribution
matches well with the Bosted prediction. Ellie suggested using a minimization procedure, instead
of selecting the cut by eye, to improve the results further. Karl cautioned that we don't want to bias
our result; we don't necessarily want the distribution to be flat, we just want it to be continuous. JP
commented that it is hard to do this without a full acceptance study; Karl suggested varying phi by
1-2% to see the effect. More details can be seen in his slides here.
• Min
• Showed very preliminary results for asymmetries for the 1.7 GeV setting. She applied loose acceptance
cuts on the focal plane, but will update the results later with cuts on the target plane. She is currently
using a constant value for the dilution factor, and hasn't applied radiative corrections. She will work on
applying these corrections next. More details can be seen in her slides here.
• Pengjia
• Showed the yield spread for different momentum settings, when different sized raster cuts are applied. JP
suggested showing just one momentum setting and showing the effect of the raster cuts for each run. He
also suggested starting with a setting that has stable yields, to confirm that the yields are still stable after
the raster cuts are applied. More details can be seen in his slide here.

General Discussion:

• Jie will give the g2p update at the Hall A Collaboration meeting in January.

## 11/25/2015

Present: JP, Kalyan, Min, Melissa
By Phone: Vince, Jie, Toby, Ryan, Karl, Chao

Feature Presentations:

• Melissa
• Showed updated "very preliminary" results for g1/g2. She tried to estimate the uncertainty on the
MAID model by comparing it with EG1B data for g1. She looked at the difference between the
model prediction and the EG1B results for their lowest values of Q2, and assigned a constant
uncertainty of 40% on the MAID model. JP suggested breaking the uncertainty up into different
regions, since the data in the delta region matches well with the model prediction but there is a
larger discrepancy for higher W. Karl questioned whether the enhancement in the longitudinal
asymmetry at large W is real, this will have to be considered carefully for the final analysis. More
details can be seen in her slides here.
• Chao
• Gave an update on the issue with the optics database. Toby showed last week that applying a
cut to phi resulted in structure in the dp distribution. Chao scanned the optics matrix to find the
element causing this issue, and found that the x^2 and x^3 elements of the phi tensor were causing
the over-fitting of the matrix. He showed the dp distribution without these two elements and the
unusual structure seen when a cut is placed on phi was gone. JP/Vince commented that it is troubling
that the x^2 dependence is causing a problem. They will discuss is more during the optics meeting.
More details can be seen in Chao's slides here.

## 11/18/2015

Present: Min, JP, Melissa
By Phone: Vince, Jie, Toby, Ryan, Karl, Ellie, Chao

Feature Presentations:

• Toby
• Gave an update on using the newest optics reconstruction matrix. He showed an example of one
run, located way past the delta resonance, so the dp distribution should be fairly flat. He tried
applying the phi cuts he has shown previously to remove acceptance and scattering angle effects,
but making a cut on phi revealed a strange structure in the dp spectrum. He showed the phi vs. dp
reconstruction both at the septum plane (i.e. without target effects) and after being reconstructed
back to the target. The strange structure exists in both distributions, so it is probably not a target
field effect. He is currently working with Chao to resolve this; Chao is doing a comparison of the
old and new databases to determine which element is causing this effect. More details can be seen
in his slides here.
• He has updated the target polarization uncertainties in the mysql. He will send out an email to the
• Pengjia
• Showed the results of a study to check the effect of applying raster cuts on the yield. He showed
several examples of groups of runs where the yield was drifting. In some cases, the raster cuts
got rid of the drift in the yields, or at least made the drift significantly smaller. For one setting, the
raster cut did not resolve the change in yields, so there is likely something else causing the drift.
JP suggested doing some sanity check to confirm that the method works, such as starting with
a setting that has consistent yields and applying the raster cuts to see the effect. More details
can be seen in his slides here.

## 11/11/2015

Present: JP, Melissa
By Phone: Vince, Toby, Ryan, Chao, Min, Karl

Feature Presentations:

• Melissa
• Showed "very preliminary" results for g1/g2. She is using a dilution factor determined from
the Bosted model, and using the average value of the packing fraction for each material. For the
radiative corrections, she is using a model prediction for the asymmetry where the polarized piece
comes from the MAID model and the unpolarized cross section is the Bosted model. The difference
between the model prediction without radiative effects and the model prediction with radiative effects
is used as an additive correction to the asymmetry. There was some concern over the large effect
of the R.C. at high W. Ryan commented that the final R.C will be large, so they will need to be done
very carefully. A cross check with EG1 data will be helpful. In order to match the kinematics of the
longitudinal and transverse settings, she scaled the asymmetry by the ratio of the unpolarized cross
section at the two different kinematic settings. JP commented that this is not valid, and suggested
using model input for the asymmetries, instead of trying to match the kinematics between the data
taken in the longitudinal and transverse settings. Next she will work on updating systematics for the
asymmetries and structure functions. More details can be seen in her slides here.
• Chao
• Gave an update on optics analysis. Comparisons of the data with simulation revealed that there
were offsets in the reconstructed kinematics. This correction could be fixed using a finely-tuned
fitting procedure. The longitudinal setting has already been fixed, today he showed the results
for the 1.7 GeV, transverse setting. He showed the results of doing the calibration; most of the
holes near the center have a difference of less than 0.5 MeV between data and simulation. He is
currently working on finishing the other transverse settings. More details can be found in his
slides here.

## 11/4/2015

Present: Min, Jixie, Melissa
By Phone: Chao, Vince, Toby, Ryan, Alex, Karl

Feature Presentations:

• Ryan
• Gave an overview of g2p elastic tail and angle reconstruction. The elastic tail is highly sensitive
to the scattering angle, so his goal is to develop a method to include these variations in the elastic
tail subtraction. He started by looking at the simplest case, helium dilution runs. Using his method,
he looked at the elastic tail across a series of different momentum settings, andfound that the tail
was not continuous, which he assumed was due to variations in the scattering angle. He did a pseudo-
simulation using the Bosted model and varying the scattering angle to confirm the "jump" seen in the
elastic tail. However, when he looked at the normalized yields for this same data, he did not see the
same discontinuity. This suggests there might be a problem with the scattering angle reconstruction.
Chao mentioned that the reconstruction code has been updated (at least for the longitudinal setting)
the last replay; he will provide this code to Toby so he can do another replay. Details of the method
and cuts used can be seen in his slides here.
• Jie
• Gave an update on his simulation study to understand the beam dependence on the yields. He used the
beam position and raster size as input to g2psim, and included radiative and acceptance effects. In
general, he found there is a much larger dependence on the beam position using a rastered beam
compared to a point beam. He summarized his results for various different momentum settings and found
that, in some cases, his results matched what we saw in the data, but not in all cases. Vince suggested
testing how much the beam position would need to be changed (for a given momentum setting) to match
the simulation with the data. The details of his study can be found in his slides here, he is also compiling
a technote on this analysis.

## 10/28/2015

Present: JP, Min, Kalyan, Melissa
By Phone: Alexandre, Vince, Jie, Ryan, Toby, Ellie, Karl

Feature Presentations:

• Melissa
• Gave an overview of contributions to the systematic uncertainty for the asymmetry. There are
several contributions which are very small (<0.1%) including the charge asymmetry, livetime
asymmetry and pion contamination. The target polarization uncertainty was surprisingly small.
The values currently listed in the mysql DB for this quantity appear to be incorrect; Toby will
update these values. For the contribution from the dilution factor and radiative corrections, she
assigned 5% as a placeholder until a better estimate could be made. Karl/Ryan commented
that 5% uncertainty on the radiative corrections may be too small, 10-15% would be a better
estimate at this point. The tables shown for the longitudinal and transverse settings represent
an overestimate of the uncertainty; in the long-term this could be looked at more carefully to
decrease the overall systematic uncertainty. More details can be seen in her slides here.

General Discussion:

• There has been a request from the Hall A CC to have an update on g2p at the winter collaboration
meeting. Ellie and Jie are both interested, they will check the dates of the meetings to see if they
are available.

## 10/14/2015

Present: JP, Min, Jixie, Kalyan, Melissa
By Phone: Alexandre, Vince, Jie, Todd, Haiyan, Pengjia, Karl, Toby, Ryan, Xiaochao, Nilanga, Chao

Feature Presentations:

• Karl
• Went over the goals of the collaboration meeting:
• Discuss physics topics for students graduating soon
• Identify major remaining physics topics
• Establish a policy for the release of plots
• Suggested a policy for collaboration release of physics results, including specific requirements
for moving from "very preliminary" to "preliminary" to "final" results. Details can be seen in his
slides here, and they will be circulated to the g2p mailing list with some small modifications.
• Pengjia
• Will be defending next Wednesday (Oct. 21st). He showed a "very preliminary" physics
asymmetry for the 2.2 GeV 5T setting (both longitudinal and transverse) with a comparison to
a radiated model prediction. He used this result to extract a preliminary value for g1 and g2,
using the Bosted model as input for the cross section. This result does not include radiative
corrections. More details can be seen in his slides here.
• Min
• Showed an overview of status of acceptance study; the overall goal is to match the simulation
results to the data, so that the simulation can be used to calculate the acceptance. She
described the various attempts to correct the simulation results to match the data. Adjusting the
apertures based on optics data works well, but the other two methods (adjusting the apertures
based on dilution data and adjusting the acceptance cuts after removing the Mott XS from the
data) only work well around the target run. In addition, the simulated yield has a different shape
than the data, so the simulation must be adjusted to match this. She will go through this process
again once Chao is finished with the optics correction. She is planning to graduate next January,
and would like to include a cross section difference for one kinematic setting in her thesis. More
details can be seen in her slides here.
• Melissa
• Gave an overview of packing fraction analysis. Of the 5 total settings there are 3 that are reasonably
stable with some small drifts in yields, and 2 settings that have larger problems. During the 2.2 GeV,
2.5T setting the raster size was changed, which could possibly be corrected by applying a cut on
the center of the raster. The 1.1 GeV setting has large variations in the elastic yields; some of these
runs were taken at low currents (8-20nA), so the beam position information is not reliable. She also
showed the results of a pion asymmetry study. Although the pion asymmetry is very large, the
residual pion contamination after PID cuts are applied is very small, so the correction is not large.
She has scheduled her defense for December 4th, and would like to include a preliminary result
for g1,g2 in her thesis. To include a fully corrected result she will need preliminary radiative
corrections and dilution results, which she will work with Ryan and Toby to get. More details can
be seen in her slides here.
• Toby
• Showed a preliminary dilution value that he had shown previously, and described several issues
with the result. These issues include that the model assumes a constant scattering angle, and does
not include some acceptance effects that are seen in the data. He has been working on correcting
these issues by incorporating a scattering angle from data into the model and applying acceptance
cuts to the data to remove acceptance effects. He showed the result of applying the acceptance cut
across all kinematics for the 5T longitudinal setting; including the acceptance cut gets rid of some of
the strange structure seen in the yields, such as the sawtooth pattern seen at high nu. The downside
of this method is that the acceptance cut causes a large loss in statistics. He is currently working on
trying to re-incorporate some of the lost statistics from the acceptance cut. More details can be seen
in his slides here.
• Jie
• Gave an update on his study using simulation to understand the drifts in yields. He looked at several
momentum settings in the 2.2 GeV, 2.5T setting that had variation in the yields. He varied the beam
position along the horizontal and vertical directions using both a point beam and rastered beam. He
generated a table summarizing the results using a Monte Carlo method, cross checking with averaged
acceptance. His results were similar to his previous test using only the Bosted model; some results
agree with what was seen in the data, some have the opposite sign. He will write up his method and
results in a technote. He is planning to graduate in summer of 2016. More details can be seen in his
slides here.
• Chao
• Gave an update on optics analysis. Comparisons of simulation with data revealed that the
reconstructed kinematics have some offset. A correction was added to the reconstructed kinematics
(vs beam position) and he is currently working on merging this correction into the database with a
finely tuned fitting procedure. The problem is that the horizontal beam position shifts the dp
reconstruction. He showed the results of applying the new optics matrix which corrects for this shift.
He will apply this method to all kinematic settings and study the uncertainty of the optics. Once this
is done he will write a NIM paper for g2p optics. He plans to graduate in February/March and would
like to include the cross section difference for one or two settings with tuned acceptance and model
inputs to obtain a physics result. More details can be seen in his slides here.
• Ryan
• Since the last collaboration meeting he has improved the model tuning procedure by using an
automated procedure instead of tuning the model by hand. He has tested this using carbon data
from the UVa database and will run it for nitrogen data once he has updated saGDH N2 cross
sections from Vince. He also updated the systematic error study for inelastic unpolarized radiative
corrections by separating the integration/iteration error from the interpolation error. He has the
polarized radiative correction code running, and has completed a systematic uncertainty study on
the inelastic radiative corrections. He is also working on evaluating physics quantities using models,
specifically the hyperfine splitting calculation. He plans to graduate in summer/fall of 2016 and would
like to include full radiative corrections on g2p polarized cross sections in his thesis. More details can
be seen in his slides here.

General Discussion:

• Important to do cross checks of results between students (ex. asymmetries)
• Must be careful to include details of any physics results (whether radiative corrections are included,
dilution factor, model input instead of data, etc.)

## 9/30/2015

Present: JP, Kalyan, Jixie, Min
By Phone: Pengjia, Toby, Ryan, Vince, Jie, Chao, Karl

Feature Presentations:

• Toby
• Showed an update on his acceptance/dilution study. He continued with the study of the cuts on the
reconstructed θ vs φ distribution at the target. He scanned several different θ vs φ cuts to see how
the acceptance effects the scattering angle and resulting yields. It turns out the small angle region is
influenced by the acceptance a lot but the center region gives a good agreement to the model. He
also loosed the center cut to θ ~ ± 40 mrad and φ ~ ± 10 mrad, the data still agreed with the model.
He then recalculated the dilution factor for 2.254 GeV longitudinal setting. More details on his
acceptance cuts and method can be found in his slides here.

## 9/23/2015

Present: JP, Kalyan, Min, Melissa
By Phone: Pengjia, Toby, Ryan, Vince, Jie, Chao, Karl

Feature Presentations:

• Pengjia
• Showed the structure of his code to create a radiated model of the MAID and Bosted
models, based on Ryan's radiative correction work. He showed the breakdown of the
different components to the radiated model (internal, external and elastic tail). He used
the radiated model to calculate an asymmetry and cross section differences, which he
compared with data. Finally, he combined asymmetries calculated from data with the
Bosted model cross section to calculate a value for g1 and g2, which he compared
with values of g1/g2 determined using the MAID model. More details can be seen in
his slides here.
• Min
• Gave an update on acceptance studies. Last time, she found that by adjusting the
apertures in the simulation she could match the data/simulation results for dp (for one
momentum setting). She tested this method for other momentum settings and found
that it did not work as well. She also showed a comparison of the yield spectrum for
helium runs in the 1.7 GeV setting; the shape of the two distributions are quite
different, which might suggest that the model deviates significantly form the data. In
the simulated results she saw several "bumps" in the yield, which correspond to the
location of resonances. She will update these results when the optics corrections are
complete. More details can be seen in her slides here.

General Discussion:

• We would like to schedule another collaboration meeting in the near future. The
meeting is tentatively scheduled for Wednesday October 14th during our usual meeting
time (10am-12pm).
• The purpose of the meeting is to:
• Discuss student thesis topics (particularly any updates from the last
collaboration meeting)
• Establish a procedure for presentation/release of collaboration plots/results
• Each student should prepare a few slides (~5 minutes) to show analysis progress

## 9/16/2015

Present: Min, JP, Jixie, Melissa
By Phone: Vince, Jie, Chao, Pengjia, Alex, Ryan, Toby, Ellie

Feature Presentations:

• Jie
• Gave an update on his simulation study using MUDIFI. Last time he showed that he uses a
least square fit to go from endplane to endplane. For the g2p simulation, it's used to go from
(x,y,θ,φ,dp) in the target plane to (x,y,θ,φ,dp) in the focal plane. SNAKE produces (x,y,θ,φ,dp)
data in both planes and a polynomial function can be used to determine the relationship
between the two planes. First the maximum power for each variable is determined, symmetries
are included (if applicable), then the priority of each function must be determined. A Gram-
Schmidt transformation is used to do the minimization, and the final step is to decide whether
to accept the function fi. JP/Vince asked how the priority for each function is chosen, since the
choice could introduce some ordering dependence. Since we don't have enough data to
constrain, JP suggested introducing some physics. He also suggested getting rid of dp in the
focal plane (since it is really just dp in the target plane) so that there is one less dimension to
fit. More details can be seen in Jie's slides here.
• Ryan
• Gave an update on evaluating physics quantities using models. His goal was to do a
comparison of the hyperfine splitting calculation in C. Carlson's 2006/2008 paper using MAID
and Hall B models. Previously he showed a comparison using the Hall B model, where he saw
good agreement between his calculation and Carlson's result. For this time he also did a
comparison using the MAID model. There is a large difference between the two models for the
value of the integrand of Δ2, over the full range of Q2. JP suggested comparing the value of g2
between the two models, instead of Δ2. More details can be seen in his slides here.

General Discussion:

• Toby
• Last time he showed a comparison between data and cross sections calculated using the
Bosted model (seen here). The model was not continuous for one momentum setting. It
turns out the BPM was not recording for that setting, so he re-calculated the XS using
values for θ and φ from surrounding runs and found that the result was now consistent with
the neighboring momentum settings. He also played around with the acceptance cuts he
showed, and found a region using the "extreme cut" where the sawtooth pattern go away
and the yields become flat.

## 9/9/2015

Present: Min, JP, Jixie, Melissa
By Phone: Vince, Jie, Chao, Ryan, Toby, Karl

Feature Presentations:

• Jie
• Gave an overview of his simulation study using SNAKE and MUDIFI. Using SNAKE, the
idea is to trace the particle trajectory in a series of free boxes, then an endplane can be
defined within the free boxes to determine the trajectory from endplane to endplane. In
g2psim this will be used to trace the trajectory between the sieve plane and the focal
plane. There are two important issues to consider, the magnetic field in the free boxes,
and the transportation method between the two endplanes. A Runge-Kutta method is
used for the transportation, and an adaptive method (which changes with field size and
gradient) is used to determine the step size. For the magnetic field, a 3D Tosca field
map is used for the septum, and an analytic model is used for the spectrometer magnets.
He also described the method for choosing the transportation function to determine the
25 matrix terms for each kinematic variable (up to 4th order). JP asked how to determine
which order is more important, and cautioned to be careful not to over fit the data. He and
Jie will discuss this more offline. More details can be seen in his slides here.
• Chao
• Gave an optics status update. The current problem is that changes in the horizontal beam
position changes the dp reconstruction. This was fixed by applying a linear correction in
BPM-x and BPM-y to θ, φ and dp. Applying this correction made the data/simulation
agree, but it is still necessary to understand the correction. Using dp scan data with beam
position scan data still leaves an offset in θ and φ. He also tried two other methods to do
the calibration. Method 1 uses the central hole to determine a constant offset, uses the
horizontal beam position scan data to determine all the matrix elements related to y, and
uses dp scan runs to fit the additional matrix elements. Method 2 uses beam position
scan data to determine the matrix elements that are not related to xfp. Neither of these
methods works very well, even when the fitting order of the matrix elements are adjusted.
He will continue to check more fitting procedures. More details can be found in his slides
here.
• Pengjia
• Gave an update on comparing asymmetries from data/models for the 2.2 GeV, 5T
longitudinal setting. He first radiated the Bosted model XS; he showed the break down of
the different radiative corrections including the elastic tail (internal and external) and the
radiative effects from inelastic scattering. He showed a comparison with Ryan's results
which had good agreement, though there is some deviation when he used different proton
form factors (provided by Moshe). In order to compare the asymmetry result with data, he
needs to do the radiative corrections for the polarized MAID model, which he will continue
to work on. More details can be seen in his slides here.

## 9/2/2015

Present: JP, Min, Kalyan, Melissa
By Phone: Vince, Alex, Jie, Chao, Ryan, Toby, Ellie, Karl

Feature Presentations:

• Melissa
• Gave an update on determining the correction to asymmetries for pion contamination.
Previously, she used the 2.2 GeV, 5T longitudinal setting as an example, for this time
she used the transverse configuration, as it has the largest pion contamination. She
modified her method for differentiating between electrons and pions; previously she
identified pions as events that do not trigger the Cherenkov, this time she used a cut
below the single photo electron peak to select pions. JP suggested using stricter cuts
for selecting pions when determining the pion asymmetry, to make sure it is a clean
sample. Although this setting has a large pion contamination, the number of pion
events that remain after lead glass cuts are applied is low, so the overall correction
is very small. More details can be seen in her slides here.
• Min
• Gave an update on acceptance tuning. She looked at results from the 1.7 GeV setting
and found that the height of the peaks is different between data and simulation for
different holes in the sieve slit. Looking at the θ vs φ distribution, she noticed on the
positive θ side there were fewer holes in simulation than in data, and on the negative
θ side there were more holes in simulation compared to data. She tried adjusting the
aperture cuts by changing the physical location of the Q1, Q2 and septum planes to
uncover events that were previously blocked. After the adjustment, the data/simulation
results agreed much better. She showed a similar procedure for a dilution run and was
able to see better agreement between data/simulation after the aperture adjustments
were made. JP/Vince suggested being cautious when adjusting the aperture cuts, as
the apertures should be well defined already. They suggested adjusting things that are
less well known first, such as the septum field. More details can be seen in her slides
here.
• Ryan
• Working on generating physics quantities using models to eventually compare with data.
So far, he has incorporated the MAID2007 and Hall B models. He calculated the
hyperfine splitting quantities Δ1 and Δ2 using the Hall B EG1 model and compared them
to the results in C. Carlson's 2006 paper. His results agreed very well, he only saw a
small deviation for Δ2 in the lowest Q2 range. To check that nothing strange was going
on in the low Q2 range, he calculated Δ2 for various small ranges around zero, to ensure
that the integration method is well behaved. The Carlson paper also includes calculations
using the Simula model, he would like to do a check of this method as well, but is unsure
where to find the Simula model. Since he was able to reproduce the hyperfine splitting
result, he is confident in his calculation method; it should be straightforward to calculate
other spin structure function integrals. More details on his method can be found in his
slides here.
• Toby
• Showed an update on his acceptance/scattering angle study. He applied cuts of varying
strictness on the reconstructed θ vs φ distribution at the target. He then calculated the
real scattering angle before/after scattering for each cut. Using these scattering angles
as inputs for the Bosted model he was able to calculate the XS and compare it to data.
He showed the comparison between data/Bosted model for each acceptance cut. He
hoped that the more extreme acceptance cuts on the data would flatten the yield
distribution, but it actually just enhanced the sawtooth pattern. JP questioned why the
Bosted prediction for one momentum bin (the green one) was so much lower than the
neighboring ones. Toby said the only input that goes into the model is the scattering angle,
so it must be considerably different for this momentum setting. He also commented that
the model prediction is scaled to match the data, so the scaling enhances the jump in
the model. More details on his acceptance cuts and method can be found in his slides
here.

## 8/26/2015

Present: Jixie, Alex, Min, Kalyan, JP, Chao, Melissa
By Phone: Vince, Jie, Ryan, Toby, Karl

Feature Presentations:

• Chao
• Gave an update on optics studies. Previously, he showed a comparison between optics data
and simulation where he cut on individual sieve holes. For this week, he included a cut on y
and dp that he didn't include previously. In the plot of θ vs y, JP pointed out that there were
additional tails on some sieve holes, Chao says these tails go away when the φ cut is
included. He showed a 2D plot of θ vs φ, along with the 1D projection of these variables. JP
commented that the data is more smeared out than the simulation, so it is difficult to compare
data with simulation results. It's possible that some of the smearing comes from events that
punch through the sieve slit and are not being cut out (the simulation currently assumes these
events are stopped by the sieve). Looking at the center hole, the data/simulation agree
reasonably well, but the agreement gets worse for holes on the edge of the sieve slit. Chao
will continue to look into this. More details can be seen in his slides here.
• He also mentioned that ~1 month ago he reported a problem with the BPM simulation.
He found it was actually a problem with the simulation itself, which has now been updated
to correct the problem.

General Discussion:

• Pengjia has submitted his BPM NIM paper.

## 8/19/2015

Present: Chao, Jie, Min, Jixie, Kalyan, Melissa
By Phone: Vince, Ryan, Toby, Karl, Pengjia

Feature Presentations:

• Melissa
• Showed a method for determining the correction to asymmetries for pion contamination. The
measured asymmetry can be written in terms of the electron and pion asymmetries, multiplied
by the fraction of events of that particle. To differentiate between electrons and pions, a cut is
made on events that trigger the Cherenkov detector (electrons) and events that do not trigger
the Cherenkov (pions). Kalyan commented that this method of selecting pions may be too blind,
and suggested making a 2D cut on E/p vs Cherenkov instead. To determine the fraction of
electrons/pions, "good event" cuts are applied (loose acceptance cuts, single track events and
pion rejector cuts) and the number of electrons/pions that survive the cuts are counted. Although
the pion asymmetry is much larger than the electron asymmetry, the number of residual pions
is very small, so the overall correction is small. For this example the 2.2 GeV, 5T longitudinal
setting was used, but the correction may be larger for the 5T transverse settings, which she
will do next. More details can be seen in her slides here.
• Min
• Gave an update on acceptance studies. She used the 1.7 GeV, 2.5T setting (with 3rd septum
configuration) to test the acceptance cuts using the yield ratio of data to simulation. She
showed a plot of target θ vs φ for both data and simulation, and applied a graphical cut to get
rid of events on the edges. Looking at the resulting 1D plots shows reasonable agreement
between θ and φ. Vince pointed out that there seems to be some additional structure in the
dp distribution, and suggested expanding the δ cut out to &pm; 4% to see if there is more
hidden structure. Min said she has seen this in other settings as well and will look into it. She
also tried adjusting the cuts on θ, φ and δ and looked at how the ratio of yields from data/
simulation changed; the ratio starts to drop off as the cuts get wider. Next she will work on
calculating the yields using W bins. More details can be seen in her slides here.

## 8/12/2015

Present: Jie, Chao, Kalyan, Min, Jixie, Melissa
By Phone: Pengjia, Ryan, Toby, Karl, Ellie, Alex

Feature Presentations:

• Chao
• Gave an update on optics studies. Previously, Min has shown comparisons of data/simulation
where she looked at different columns of sieve holes. Chao continued this study by cutting on
individual sieve holes. Looking at the center sieve hole, the φ distribution looks reasonable, but
the θ distribution has some issues. Specifically, the data is wider on the left side (negative θ)
than the simulation. He showed results for several sieve holes, including one that was in the
row as the center hole, but in the farthest column on the left side of the sieve slit. In this case
the θ distribution had similar width for both data and simulation, but the height of the simulation
distribution was larger. This may suggest that something is wrong with the acceptance in the
simulation. The problem with θ seems to be systematic; for most of the sieve holes there are
more events on the left side of the data than in the simulation. Kalyan asked whether the
thickness of the sieve slit was taken into account, Chao says it was included in the simulation
and optimizer. Jixie suggested comparing the dp distributions for each sieve hole. More details
can be seen in Chao's slides here.

## 7/29/2015

Present: Chao, Min, JP, Melissa
By Phone: Alex, Pengjia

Feature Presentations:

• Min
• Gave an update on acceptance studies. Previously, Chao showed a correction for the beam
position in g2psim. Min checked this correction by looking at optics runs. On the data she
applied a cut on dp (to select elastic events) and on the focal plane (to get rid of junk
events). On the simulation, only an aperture cut was applied. She compared the data and
simulation results for θ and φ both before and after drifting from the sieve slit to the target.
The effect of the target field on θ is not very large, though there is a shift down in angle.
However, the shape of the θ distribution is different between data and simulation. The
effect of the target field on φ is significant; it's not clear why this is the case. To try to
determine the reason for the discrepancies, she applied a cut along each column of sieve
slit holes in φ and compared the data and simulation results for θ,φ and dp. Column 2
seems to have the best agreement (for dp), columns 1 and 2 have a shift while columns
3-6 have a difference in width. Chao suggested also cutting along each row of sieve slit
holes to better study the effect of the drift on φ. Min will work on identifying the differences
between data and simulation, specifically whether the boundaries are different between
the two. More details can be seen in her slides here.

## 7/22/2015

Present: JP, Min, Jixie, Melissa
By Phone: Alex, Ryan, Toby, Ellie, Karl, Pengjia

Feature Presentations:

• Melissa
• Showed various checks for packing fraction runs that have large discrepancies, including
beam position, beam energy, spectrometer central momentum setting, septum current, and
the location of anneals. For both the 2.2 and 1.1 GeV settings, there are significant shifts in
the x and y beam position (2mm or more). She showed the average and standard deviation
of epics readings for the LHRS septum current for each run. For several runs, there are small
number of epics readings that drift from the average current. It's not clear if this is the
current is actually changing or if it is a readout problem. She will look into the yield vs time
to try to determine this. JP suggested making a raster cut on the center of the beam to get
rid of any potential scraping. Pengjia says there is a way to cut on raster size, but there will
be an additional BPM uncertainty. Melissa will discuss this more offline with Pengjia. More
details can be seen in her slides here.
• Pengjia
• Gave an update on calculating asymmetries/cross sections using the MAID model. This time,
he used the Bosted model to get the unpolarized cross sections for the proton. Using unradiated
cross section models, he still saw a factor of 6 difference when compared with data. Ryan also
calculated asymmetries using unradiated models, and the results were consistent with Pengjia's,
so it seems the radiative effects contribute significantly to the factor of 6 difference. More
details can be seen in his slides here.

## 7/15/2015

Present: JP, Min, Chao, Jixie, Melissa
By Phone: Ryan, Toby, Ellie, Karl, Vince, Pengjia

Feature Presentations:

• Chao
• Doing a check of simulation/data results for the 2.2 GeV, longitudinal setting in order
to check that the optics calibration matrix will work for all momentum settings (not
just elastic). He showed a comparison for several different momentum settings.
Vince suggested simulating more events, since the statistics start to drop off for
lower momentum settings. In general, the data is broader then the result from
simulation. In the θ distribution, the "tails" seen in the data are not symmetric. JP
suggested carefully selecting cuts to remove any background from the data to
ensure a good comparison with simulation. More details can be seen in his
slides here.
• Pengjia
• More discussion on Pengjia's slides from last week. Pengjia has seen a factor of
six difference between his asymmetry calculated from data compared to the
asymmetry determined using the MAID model. Ryan did not see this factor of six
in his study, but in addition to using radiated XS models, he is using a combination
of the Bosted and MAID models (Pengjia is using just the MAID model). Karl
commented that the XS from MAID is not very good for our kinematics. Pengjia
also showed an estimated NH3 XS. JP commented that it was surprising that the
delta peak wasn't visible. Pengjia will look into this for next time.

## 7/8/2015

Present: JP, Min, Chao, Melissa
By Phone: Toby, Vince

Feature Presentations:

• Pengjia
• Working on comparing asymmetries determined from MAID to those calculated from
data; last time he showed a factor of 6 difference between the two results. This
time, he showed two different methods for calculating the differential XS from the
virtual photon XS. The first method calculates the differential XS directly from
the virtual photon XS, and the second method calculates the differential XS using
F1, F2, g1 and g2. He also showed two different methods for calculating the
asymmetry from the virtual photon XS; one method uses A1 and A2, while the other
is calculated from the virtual photon XS. There was a discrepancy between the two
methods, but he found that there was actually a mistake in one of the equations.
While the results from the two methods agree with each other, they are still a factor
of 6 larger than the results from data. More details can be seen in his slides here.
• Toby
• Showed an update of his scattering angle study for model reconstruction. He is
using BPM and optics data to determine the scattering angle. He showed an example
of the calculated scattering angle; JP questioned whether the range was really from
0-16 deg. Toby pointed out that there really aren't many events at the boundaries,
the distribution is peaked between 4.5-9 deg. He then uses this scattering angle as
input for the Bosted model. At low ν the simulation results match reasonably well
with the data, but the discrepancy starts to become larger as ν increases. He took
a closer look at the reconstructed scattering angle for each central momentum, and
found that a second peak is visible for smaller values of p0. If this second peak was
real, the simulation should recreate the data, so this could suggest a problem with
the reconstruction. However, Chao pointed out that, for this energy setting, the optics
calibration is not complete (currently using the longitudinal optics matrix), so the
reconstructed θ and φ may not be correct yet. For next time, Toby will test this
analysis using the 1.7 GeV setting, which has calibrated optics. More details can
be seen in his slides here.
• Melissa
• Gave a summary of packing fraction analysis. For some settings, the variation in the
yields (and Pf) is due to a fluctuation in the beam position. This will hopefully be
resolved by Jie's beam position/acceptance study. For the 2.2 GeV, 2.5T transverse setting
there is also an issue of a shift in ν between runs. For the 1.1 GeV, 2.5T transverse
setting, the yields vary depending on the beam current used for each run. JP suggested
a few things to check as the possible cause for these discrepancies including drift in the
BCM calibration, anneals of the target material, drift in field (HRS or septum), etc. She
has posted a technote draft here, feedback would be appreciated. More details can be seen in her slides here.
• Min
• Gave an update on her acceptance study. Last time, she showed that the simulation results
are more narrow than the data. For this time, she tried cutting on just the center hole,
and found that the dp distribution from data better matched the simulation. JP suggested
cutting on each of the different holes individually to determine which hole causes the dp
distribution to be wider. More details can be seen in her slides here.
• Chao
• Gave an update on optics analysis, currently checking whether simulation results match
with data, starting with optics data. First he checked whether the geometry was correct,
some deviation was found in the recent optics meeting. The position of the BPMs is hard-
coded into the simulation, and the drifting algorithm is used to drift the electrons
backward to the BPMs to simulate the readout of BPM A and B. He compared the θ
distribution before drifting in the target field using a fixed and non-fixed BPM location.
The results using a fixed BPM match well with the data. He is currently working on
checking this for all momentum settings, and will follow up with Pengjia about the BPM
problem. More details can be seen in his slides here.

## 7/1/2015

Present: Chao, Vince, Jie, JP, Min, Melissa
By Phone: Pengjia

Feature Presentations:

• Min
• Gave an update on acceptance studies. She showed a summary table of each energy
setting and septum configuration. There hasn't been any problems in the 2.2 GeV, 5T
longitudinal and 1.7 GeV, 2.5T transverse settings, but some settings (2.2 GeV, 2.5T
transverse, 1.2 GeV, 2.5T transverse and 2.2 GeV, 5T transverse) have a discrepancy
in the focal plane between data and simulation. She compared the data divided by the
Mott XS to the simulation results without XS, and found that the simulation results
of θ and φ are narrower then the data. JP commented that, while including the Mott
XS might change the shape of the distribution, it shouldn't change the boundary. She
work on figuring out the cause for this discrepancy before calculating the acceptance.
More details can be seen in her slides here.
• Pengjia
• Comparing asymmetries determined from the MAID model to those calculated from data.
Last time he showed a factor of 6 difference between the two results. He determined the
scattering angle and Q2 by fitting the data and compared them to the quantities calculated
from MAID. He also showed the results of calculating the quantities g1, g2, F1, F2, AL, AT,
dXSL, dXST, XStot andXSmott using MAID. He hasn't included radiative corrections in his
calculations, but this probably won't account for the factor of 6. More details can be seen
in his slides here.