# G2p Analysis Minutes

Minutes of the weekly analysis meetings

## Contents

- 1 11/4/2015
- 2 10/28/2015
- 3 10/14/2015
- 4 9/30/2015
- 5 9/23/2015
- 6 9/16/2015
- 7 9/9/2015
- 8 9/2/2015
- 9 8/26/2015
- 10 8/19/2015
- 11 8/12/2015
- 12 7/29/2015
- 13 7/22/2015
- 14 7/15/2015
- 15 7/8/2015
- 16 7/1/2015
- 17 Jan-June 2015
- 18 July-Dec 2014
- 19 Jan-June 2014
- 20 June-Dec 2013
- 21 Jan-May 2013
- 22 April-Dec 2012
- 23 Jan-March 2012
- 24 July-Dec 2011
- 25 Jan-June 2011

## 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.

- Gave an overview of g2p elastic tail and angle reconstruction. The elastic tail is highly sensitive

- 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.

- Gave an update on his simulation study to understand the beam dependence on the yields. He used the

## 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.

- Gave an overview of contributions to the systematic uncertainty for the asymmetry. There are

**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.

- Went over the goals of the collaboration meeting:

- 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.

- Will be defending next Wednesday (Oct. 21st). He showed a "very preliminary" physics

- 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.

- Showed an overview of status of acceptance study; the overall goal is to match the simulation

- 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.

- Gave an overview of packing fraction analysis. Of the 5 total settings there are 3 that are reasonably

- 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.

- Showed a preliminary dilution value that he had shown previously, and described several issues

- 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.

- Gave an update on his study using simulation to understand the drifts in yields. He looked at several

- 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.

- Gave an update on optics analysis. Comparisons of simulation with data revealed that the

- 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.

- Since the last collaboration meeting he has improved the model tuning procedure by using an

**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.

- Showed an update on his acceptance/dilution study. He continued with the study of the cuts on the

## 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.

- Showed the structure of his code to create a radiated model of the MAID and Bosted

- 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.

- Gave an update on acceptance studies. Last time, she found that by adjusting the

**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

- Discuss student thesis topics (particularly any updates from the last
- 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 f_{i}. 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.

- Gave an update on his simulation study using MUDIFI. Last time he showed that he uses a

- 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 Δ_{2}, over the full range of Q^{2}. JP suggested comparing the value of g2

between the two models, instead of Δ_{2}. More details can be seen in his slides here.

- Gave an update on evaluating physics quantities using models. His goal was to do a

**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.

- Last time he showed a comparison between data and cross sections calculated using the

## 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.

- Gave an overview of his simulation study using SNAKE and MUDIFI. Using SNAKE, the

- 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 x_{fp}. 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.

- Gave an optics status update. The current problem is that changes in the horizontal beam

- 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.

- Gave an update on comparing asymmetries from data/models for the 2.2 GeV, 5T

## 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.

- Gave an update on determining the correction to asymmetries for pion contamination.

- 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.

- Gave an update on acceptance tuning. She looked at results from the 1.7 GeV setting

- 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 Q^{2}range. To check that nothing strange was going

on in the low Q^{2}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.

- Working on generating physics quantities using models to eventually compare with data.

- 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.

- Showed an update on his acceptance/scattering angle study. He applied cuts of varying

## 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.

- Gave an update on optics studies. Previously, he showed a comparison between optics data

**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.

- Showed a method for determining the correction to asymmetries for pion contamination. The

- 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 ± 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.

- Gave an update on acceptance studies. She used the 1.7 GeV, 2.5T setting (with 3rd septum

## 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.

- Gave an update on optics studies. Previously, Min has shown comparisons of data/simulation

## 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.

- Gave an update on acceptance studies. Previously, Chao showed a correction for the beam

## 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.

- Showed various checks for packing fraction runs that have large discrepancies, including

- 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.

- Gave an update on calculating asymmetries/cross sections using the MAID model. This time,

## 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.

- Doing a check of simulation/data results for the 2.2 GeV, longitudinal setting in order

- 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.

- More discussion on Pengjia's slides from last week. Pengjia has seen a factor of

## 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

F_{1}, F_{2}, g_{1}and g_{2}. He also showed two different methods for calculating the

asymmetry from the virtual photon XS; one method uses A_{1}and A_{2}, 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.

- Working on comparing asymmetries determined from MAID to those calculated from

- 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.

- Showed an update of his scattering angle study for model reconstruction. He is

- Melissa
- Gave a summary of packing fraction analysis. For some settings, the variation in the

yields (and P_{f}) 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.

- Gave a summary of packing fraction analysis. For some settings, the variation in the

- 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.

- Gave an update on her acceptance study. Last time, she showed that the simulation results

- 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.

- Gave an update on optics analysis, currently checking whether simulation results match

## 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.

- Gave an update on acceptance studies. She showed a summary table of each energy

- 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 Q^{2}by fitting the data and compared them to the quantities calculated

from MAID. He also showed the results of calculating the quantities g_{1}, g_{2}, F_{1}, F_{2}, A_{L}, A_{T},

dXS_{L}, dXS_{T}, XS_{tot}andXS_{mott}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.

- Comparing asymmetries determined from the MAID model to those calculated from data.