Difference between revisions of "G2p Analysis Minutes"

Revision as of 10:50, 18 November 2015

Minutes of the weekly analysis meetings

Agenda

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 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.

• 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 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.

• 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 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.

• 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, 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.

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