G2p Analysis Minutes

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Minutes of the weekly analysis meetings



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