G2p Analysis Minutes

Minutes of the weekly analysis meetings

Agenda

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.