Difference between revisions of "G2p Analysis Minutes"

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*Ryan
 
*Ryan
**Since the last collaboration meeting he has improved the model tuning procedure by using an automated <br>procedure instead of tuning the model by hand.  He has tested this using carbon data from the UVa database <br>and will run it for nitrogen data once he has updated saGDH N2 cross sections from Vince. He also updated <br>the systematic error study for inelastic unpolarized radiative corrections by separating the integration/<br>iteration error from the interpolation error.  He has the polarized radiative correction code running, and <br>has completed a systematic uncertainty study on the inelastic radiative corrections.  He is also working <br>on evaluating physics quantities using models, specifically the hyperfine splitting calculation.  He plans <br>to graduate in summer/fall of 2016 and would like to include full radiative corrections on g2p polarized <br>cross sections in his thesis.  More details can be seen in his slides [https://userweb.jlab.org/~rbziel/Weekly_Meetings/g2p_101315.pdf here].
+
**Since the last collaboration meeting he has improved the model tuning procedure by using an <br>automated procedure instead of tuning the model by hand.  He has tested this using carbon data <br>from the UVa database and will run it for nitrogen data once he has updated saGDH N2 cross <br>sections from Vince. He also updated the systematic error study for inelastic unpolarized radiative <br>corrections by separating the integration/iteration error from the interpolation error.  He has the <br>polarized radiative correction code running, and has completed a systematic uncertainty study on <br>the inelastic radiative corrections.  He is also working on evaluating physics quantities using models, <br>specifically the hyperfine splitting calculation.  He plans to graduate in summer/fall of 2016 and would <br>like to include full radiative corrections on g2p polarized cross sections in his thesis.  More details can<br> be seen in his slides [https://userweb.jlab.org/~rbziel/Weekly_Meetings/g2p_101315.pdf here].
  
  

Revision as of 08:21, 15 October 2015

Minutes of the weekly analysis meetings


Agenda

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.



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