G2p Analysis Minutes

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Minutes of the weekly analysis meetings



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
  • 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


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.


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 ± 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.


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.


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.


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.


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.


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.


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.

Jan-June 2015


July-Dec 2014


Jan-June 2014


June-Dec 2013


Jan-May 2013


April-Dec 2012


Jan-March 2012


July-Dec 2011


Jan-June 2011