G2p Analysis Minutes

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Minutes of the weekly analysis meetings



Present: JP, Chao, Jie, Pengjia, Min, Kalyan, Melissa
By Phone: Ryan, Ellie, Karl, Vince

Feature Presentations:

  • Melissa
    • Gave an update on packing fraction analysis. In order to combine yields from dummy and production runs, it is necessary to scale
      the radiation lengths to match. The yields are generated using two different radiation thicknesses; one using the length of helium in
      the dummy run, and the length of helium in the production cell. The ratio of these results gives the factor used to scale the radiation
      length of the dummy run to match the radiation length of the production run. The scaling factor from using this method is close to 1.
      Instead of using just the radiation length of helium in the production, the contributions from all materials should be considered, which
      should make the correction larger. She is also planning to update her fitting routine to determine the contamination to the elastic peak.
      Currently, the quasi-elastic peak is fit with a single gaussian, but ideally the fit should account for the helium quasi-elastic, nitrogen
      quasi-elastic, and hydrogen elastic peaks. JP also suggested checking for temperature fluctuations in the target nose, since at these low
      temperatures, small fluctuations could have a large effect on the density of the helium. More details can be seen in her slides here.
  • Ryan
    • Gave an update on his study of the Small Angle GDH nitrogen cross sections. Showed an overview of his method and a summary of the
      saGDH data available. We won't be able to get a ratio of nitrogen/carbon, because the only available carbon data has difference acceptance
      cuts than the nitrogen data. He showed an example of unfolding the data for 2.1GeV at 6 degrees, using the Bosted model for the lowest
      energy spectrum in the unfolding. Karl suggested checking the effect of changing the central energy of the model. To get an experimental,
      unfolded cross section, the difference between the unfolded and radiated interpolated spectrum is applied to the saGDH data. He is using the
      difference method, as opposed to the ratio method, because the cross section gets close to zero at some points. He also discussed his method
      of error propagation. Based on conversations with Vince, he starts with a 6% systematic, and combines this with contributions from the elastic
      tail subtraction and inelastic unfolding. The raw statistical error is scaled using the ratio of the unfolded and inelastic radiated cross sections.
      To tune the Bosted model, he is trying to find one set of parameters that describe the saGDH data. JP pointed out that there is a visible difference
      between the model and data at the quasi-elastic peak. It's possible the 2MeV binning is too fine; Ryan will look at the 10 MeV bin data to see if
      it smooths out the peak. More details can be seen in his slides here.
  • Pengjia
    • Is working on studying the effect of different acceptance cuts on the physics asymmetry. For each variable (x, y, theta, phi), he split the
      distribution into several regions and compared the asymmetry in each region. JP suggested splitting each variable into equal regions statistically
      instead of equal regions in size. For now, the dilution factor can be left out, and can be applied later when dilution factor analysis is complete.
      His slides can be seen here.
  • Chao
    • Gave an update on optics analysis, specifically the y calibration using the target chamber upstream window. Last time he showed a first
      iteration of the calibration using events from only one large hole in the sieve slit. For the second iteration, he included any possible events from
      the target and the aluminum window. In addition, he added a focal plane cut to make it easier to distinguish between the sieve holes. The results
      from the second iteration look pretty good, so for the LHRS calibrations he will stop here for now. The RHRS straight through calibration (with good
      septum) is completed, so he will start on the longitudinal field setting for the RHRS. More details can be seen in his slides here.
  • Jie
    • Gave a quick update on the energy loss model for g2psim. The main update is that the Landau distribution used for the ionization model should
      be Landau(x,ε) instead of Landau(x,4ε). He will give more details next week. His slides can be seen here.

General Discussion:

  • A room has been booked for the collaboration meeting on November 14th. Kalyan will set up a formal registration for the meeting.


Present: JP, Chao, Jie, Pengjia, Min, Kalyan, Jixie, Melissa
By Phone: Moshe, Toby, Ryan, Ellie, Karl

Feature Presentations:

  • Toby
    • Gave an update on dilution analysis. His current method involves building the total background yield from dilution runs, which are scaled
      appropriately to match the radiation lengths between runs. To determine the overall systematic uncertainty, contributions come from the
      packing fraction and the scaling factor gamma, which is the radiation length/nucleon scaling factor for scaling carbon dilution runs to
      nitrogen. The scaling parameters alpha and beta, which are determined using simulation with the Bosted model, may also contribute to the
      overall systematic. The results for the dilution factor (for the 3.3 GeV setting) seem reasonable but have a large uncertainty currently. He
      also described a possible new method, which has been used previously for the RSS and SANE experiments. In this method, the yields are
      determined from simulation, where the packing fraction value is an input. In this method, some of the systematics will cancel out in the
      ratio used to determine the dilution factor. The downside to this method is that it requires the ratio of the simulation/data to be
      kinematically independent. JP suggested trying to improve this method to rely less on the model. More details can be seen in his slides here.
  • Min
    • Gave an update on matching focal plane data in SNAKE. Her goal is to match the simulation results and focal plane data at the "virtual
      plane", which is located at the entrance of Q1. This location is chosen so that changes can be applied in the septum region, not at the HRS.
      She showed the comparison of simulation with data for each sieve hole before and after applying the first order fit. There was much discussion
      on how to do the fit; Jixie suggested fixing the parameters a2/b2 to begin with, then tune them during the second iteration and JP suggested
      fitting the offset first. There was also some discussion on how to determine the chi-squared value, specifically whether chi-sqared can be
      minimized in y and phi at the same time, or whether they should be minimized separately. Jixie and Min will discuss this more offline. More
      details can be seen in her slides here.

General Discussion:

  • Based on the results of the poll, November 14th is the best day for a collaboration meeting. Each student will give a summary of analysis

progress (~30 minutes) and there will be time for discussion of thesis topics.


Present: JP, Chao, Jie, Pengjia, Min, Kalyan, Jixie, Melissa
By Phone:Toby, Ryan, Ellie, Karl

Feature Presentations:

  • Pengjia
    • Gave a summary of BPM calibrations for entire experimental run. The best situation for calibrations is for data taken between May 3-7, which
      includes some optics and production data. For runs taken during this time period, the average beam position and angle is 1mm and 1.1 mrad,
      respectively. The biggest uncertainties are seen in data taken between March 29-31 and April 26-30. During March 29-30, both production and
      optics data was taken, and the calibration became worse due to large uncertainty in the pedestal. During April 26-30, only production data was
      taken and the calibration of BPM B had to be done using BPM A and harp data. JP asked how reliable these uncertainties are; Chao said that optics
      data can be used to try to reconstruct the beam position, as a cross check, but he is not sure of the uncertainty of this method. The run-by-run
      uncertainties are available in the mysql database. For next time, he will compile a table of contributions to the systematic uncertainty. More details
      can be seen in his slides here.
  • Ryan
    • Showed a systematic error study for inelastic radiative corrections. He wanted to do a sanity check of his method to unfold/radiatively correct the
      nitrogen data. He started with the Bosted model, which he radiated using SAGDH settings. He then unfolded/radiatively corrected this model, and
      used the result to compare to the original Bosted model. In radiating the model, he didn't average over the scattering angle at all, and used 3MeV as
      the value for Delta-E. To radiatively correct this model, it is not possible to directly unfold the equation to get an experimental Born XS, instead he
      must use an iterative procedure. He showed a comparison of the Bosted model, the radiated model, and the unfolded model. The ratio of the Bosted
      model compared with the radiated-then-unfolded model agree at low nu to ~1-3%. At higher nu the disagreement becomes larger, but it is never
      more than 5%. This is good evidence that his method works, so going forward he will start to unfold the SAGDH data and see if he can tune the Bosted
      model to match the SAGDH data set. More details can be seen in his slides here.

General Discussion:

  • Pengjia will be at JLab for 3 months. We should have another discussion soon about analysis tasks for students as some projects start to finish up.
  • Will we try to have a collaboration meeting in mid November. Kalyan has set up a Doodle Poll to select a date - please respond!


Present: JP, Kalyan, Min, Jie, Chao, Jixie, Melissa
By Phone:Toby, Ryan

Feature Presentations:

  • Melissa
    • Gave an update on packing fraction analysis. As was suggested previously, the differing radiation lengths between the dummy and production runs
      needed to be accounted for. Following the method previously described by Toby, the he4 cross section was radiated using two different radiation
      thicknesses, one that matched the empty run and one that matched the production run. The ratio of these two cross sections is then used to scale the
      yield from the dummy run. The scaling factor was larger than expected, most likely due to the fact that the "radcor" program was used to radiate the
      he4 cross section, and is not meant for elastic radiative corrections. Using this scaling factor, the value of the packing fraction is 0.432. The uncertainty
      is still large (0.045). This includes a contribution from the difference between the sum and fitting method used to get the area of the peaks. Since the fit
      is only used to determine the level of contamination, JP suggested that it shouldn't be included directly in the uncertainty. He also suggested that, in the
      fit of the production run, using one gaussian peak to fit the the second peak may not be a good approximation, since the second peak contains
      contributions contributions from hydrogen elastic, nitrogen quasi-elastic and helium quai-elastic. More details can be seen in her slides here.
  • Jie
    • Gave an update on the energy loss model used in g2psim. He showed several comparisons of simulation results with data using different ionization
      models. He showed a simulation results using the ionization model from geant4 combined with the bremsstrahlung model from g2psim, compared to
      results using the SAMC energy loss model. There is a shift between the two results, which may result from using the mean value vs the most probable
      value of the distribution. Comparing the simulation results with data, the combination of the SAMC ionization model with the SAMC bremsstrahlung
      model seems to match best with the data. One update from last time, instead of using data from all sieve holes, he cut on just the center sieve hole. He
      showed the step-by-step energy loss process (from SAMC), and tried switching the order to see the effect on the results. JP pointed out that the 3
      middle steps actually happen simultaneously, so breaking them into steps is an approximation. More details can be seen in his slides here.
  • Chao
    • Gave an optics status update, specifically a revision of the y-target calibration. Using the beam position scan isn't ideal; since we only took data at
      dp=0%, the calibration will only work for a small dp range. Jixie results (using geant4) suggest that the upstream window of the target chamber has
      some acceptance by the Q1 entrance. Since they have seen something upstream in the optics data, he will try to use this data to do the y-target
      calibration. This result will be more reliable, as it will take all dp settings into account. He identified the data from the window, and used a vertex cut
      to select them. In each setting, one hole was selected to do the calibration. The calibration result was compared to the known location of the sieve
      hole. There was good agreement, which suggests the method is working. He is currently on figuring out how to check that the data is actually
      coming from the upstream window. More details can be seen in his slides here.


Present: Chao, JP, Jie, Jixie, Kalyan, Melissa
By Phone: Pengjia, Toby, Ryan, Ellie

Feature Presentations:

  • Ryan
    • Gave an update on using SAMC to compare the Bosted model to SAGDH nitrogen cross sections. SAMC can include both energy loss and inelastic
      radiative corrections, which makes it the best comparison to the SAGDH cross sections. However, the radiative corrections take a long time to run,
      so it may not be worthwhile. To test the results of SAMC, he threw 10M events for each momentum setting, but did not turn on energy loss. He
      compared this to his previous method of averaging the Bosted model result over the scattering angle. The ratio of the two methods is close to 1,
      suggesting that both methods give similar results. He also did the same comparison, but first radiating SAMC/angle averaged Bosted model, (see
      slide for equations). There was some discussion on whether this is the proper method to apply these corrections, but it seems that Ryan's method is
      consistent with what was done previously. Of the two methods, Ryan concluded that the SAMC method isn't any better than his previous method, so
      it is not worth the extra time it takes to run. JP suggested checking how much the scattering angle varies over the length of the target; if it is linear,
      than using the average is a good approximation, but this may not be the case. Since there is no SAGDH carbon data that matches our kinematics (that
      has been analyzed), we won't be able to do a comparison of nitrogen/carbon. Ryan plans to nail down the Bosted model so that it can be used instead;
      he will scale the Bosted model to match SAGDH nitrogen data, do the same with the SAGDH carbon data, then use the ratio of these to translate the
      results to our data. More details can be seen in his slides here.


Present: Chao, Kalyan, Jie, Min, JP, Jixie, Melissa
By Phone: Pengjia, Toby, Ryan, Ellie, Karl, Alexandre

Feature Presentations:

  • Toby
    • Gave an update on dilution analysis. His previous method for scaling carbon data to the Bosted nitrogen model had some issues; it left a large gap
      at the delta resonance, the yield was not continuous at higher values of nu (which is most likely an acceptance issue), and he assumed a constant
      scaling factor in nu. In his updated method, he ran the Bosted simulation for both carbon and nitrogen, and used the ratio between the two models
      as a bin-by-bin scaling factor for carbon. He also showed a method for matching the radiation lengths of the different materials. To match the
      radiation lengths of two different targets, for example carbon and production, he produces two radiated carbon models. The first has the radiation
      length of the carbon target, while the second uses the radiation length of the production target. The ratio of these two models is the scaling factor to
      matchthe radiation length of carbon to production. JP suggested building both radiation lengths into the model, to make the process one step versus
      two. Toby will look into the difference in results for the two methods. The preliminary results for the dilution factor are smaller than expected, but he
      is still working on determining the uncertainty. More details can be seen in his slides here.
  • Min
    • Working on matching focal plane data to SNAKE. To accomplish this, she first divides the transport functions into two steps; the target to the virtual
      plane, then the virtual plane to the focal plane. She focused on tuning the functions that included contributions from the septum field, and worked on
      aligning the center sieve hole. The results look good, so for next time she will work on aligning the other sieve holes. More details can be seen in her
      slides here.
  • Jie
    • Gave an update on the energy loss model. Last time he showed a comparison of the ionization models used in geant4 and SAMC. This time, he looked
      at how internal and external Bremsstrahlung are included in SAMC and the g2psim package. Ryan suggested looking at the size of the contribution from
      internal/external Bremsstrahlung to the overall energy loss, as he found it was much smaller than the contribution from ionization. Jie showed a comparison
      between data and simulation including two different ionization models; in one case (geant4 model) the simulation was too narrow compared to the data, in
      the other case (SAMC model), the simulation was wider than the data. Jixie suggested to only look at the data from one sieve hole when comparing with
      simulation, as opposed to all the sieve holes. More details can be seen in Jie's slides here.


Present: Min, JP, Jie, Jixie, Melissa
By Phone: Moshe, Pengjia, Toby, Ryan, Ellie, Karl, Alexandre

Feature Presentations:

  • Moshe
    • Gave an update on dilution analysis with GEp data. GEp needs an accurate dilution factor in the hydrogen-elastic region, which is tough to achieve
      since there is little data and few good models for nitrogen and helium in the quasi-elastic region. One solution is to use small angle GDH data and
      extrapolate to different kinematics. The second solution is to use carbon data, if it is possible to scale the carbon data to nitrogen in the quasi-elastic
      setting. He showed results from simulation comparing carbon, nitrogen and helium. In the Bosted model, the quasi-elastic region of carbon and
      nitrogen are scaleable, while in the QFS model, carbon, nitrogen and helium are all scaleable. In the elastic region, he scaled carbon and nitrogen data
      to the same number of elastic events. With both models, this made a good match at the quasi-elastic region. Following this same procedure for
      comparing helium and nitrogen, however, did not give a good match in the quasi-elastic region. Based on his simulation, the contribution from helium
      is relatively small in both models. More details can be seen in his slides here.
  • Melissa
    • Gave an update on extracting the packing fraction using data. She updated her previous method, which included input from simulation, to include
      only production/dilution runs. This method assumes a uniform acceptance throughout the target cell, which can be corrected for once the acceptance
      analysis is complete. Toby pointed out that helium and nitrogen have different radiation lengths, which will need to be accounted for. The resulting
      value for the packing fraction agrees with the expectation, but with a large uncertainty (~10%). She will work on reducing this uncertainty, as well as
      extracting the packing fraction for other materials/settings. More details can be seen in her slides here.
  • Ryan
    • Gave an update on using SAMC to generate nitrogen cross sections. He got the version of SAMC setup for SAGDH experimental conditions from Vince,
      and used the Bosted model as the cross section model. An advantage of using SAMC is that it can include energy loss corrections and inelastic radiative
      corrections. This will probably allow for the best comparison between the Bosted model and SAGDH nitrogen cross sections. However, the radiative
      take a long time to run, so it may not be worthwhile. For next time, he will work on comparing the SAMC results for the XS with his method for averaging
      the cross section over the acceptance as well as the SAMC radiative corrections with his method of radiative corrections. More details can be seen his
      slides here.


Present: Kalyan, Min, JP, Jie, Jixie Melissa
By Phone: Toby, Ryan, Ellie, Karl, Pengjia, Moshe, Alexandre

Feature Presentations:

  • Jie
    • Gave an update on the energy loss model being used in the g2psim package. Previously, he showed a discrepancy in the delta when comparing
      data with simulation results. He was able to better match the data with simulation by using a different ionization model. The old ionization model
      (taken from Geant 4) used a continuous energy loss, with fluctuations, below an energy threshold. Above the threshold, the energy loss is simulated
      by the explicit secondary particles. The updated ionization model (taken from SAMC) assumes the probability distribution of energy loss by ionization
      is a Landau distribution. He showed a comparison of the energy loss from ionization for g2psim and the SAMC model. If g2psim includes continuous
      energy loss, but not delta-ray production, it does not match with the model. But, if g2psim includes 1 delta-ray production along with continuous energy
      loss, it agrees much better with the model. More details can be seen in his slides here.
  • Min
    • Gave an update on her acceptance study. Last time, she showed that there is some discrepancy between the peaks (in delta, theta and phi variables),
      between data and simulation. She showed comparisons of the data and simulation with the "true" locations, and a sanity check of the transport functions,
      which seem to fit our requirements for the resolution. There was some discussion about whether or not the exit/entrance windows (made of kapton and
      titanium) were included in the energy loss model. Jie says they are both included right after the sieve slit. In the simulation, Min modified the VDC resolution
      to be 0 and made the x-tg inputs the same, and saw good agreement between the data and simulation. However, when the VDC resolution was included back
      in, she again saw a discrepancy between the data and simulation. For next time, she will also include focal plane variables. More details can be seen in her
      slides here.
  • Jixie
    • Simulated optics events scattering from the target chamber window to see if they make it to the focal plane. He used a 1cm raster with no target field, and
      found that events originating from the target chamber entrance window do indeed make it to the focal plane. The ratio of events from the chamber window to
      events from the target is 3.6%. More details can be seen in his slides here.


Present: Kalyan, Min, JP, Jixie Melissa
By Phone: Pengjia, Moshe, Alexandre, Chao

Feature Presentations:

  • Melissa
    • Gave an update on packing fraction analysis. In her current method to extract the packing fraction, the g2psim package is used to determine a value
      for the cross section of different materials (nitrogen, hydrogen and helium). She showed an updated comparison of the simulation with data. The results
      look better, but there are still some problems (simulation needs to be weighted by cross section, for example). There were also some questions raised
      about the fitting routine used to fit the data; the Landau-Gaussian convolution fit does a good job of fitting the elastic peak, but not the radiative tail. Once
      radiative corrections are included, the values of Ax (normalization factor used in packing fraction equation) will most likely change; the contribution from
      Nitrogen should be larger. A suggestion was made to not use cross sections from simulation as input, but rather just use yields from data instead. She will
      try this for next time. More details can be seen in her slides here.
  • Pengjia
    • Posted yields calculated from pass-3 rootfiles to the ELog. The unusual shape seen in some cases is most likely due to acceptance. There is still a
      discrepancy in the yields between different runs for some settings.


Present: Min, JP, Jie, Jixie, Melissa
By Phone: Chao, Toby, Ryan, Ellie, Pengjia, Alexandre, Karl

Feature Presentations:

  • Min
    • Gave an update on acceptance studies. In the simulation, the events are generated uniformly over the area of the raster, so she did a study to check
      the beam distribution for the data. Within the raster pattern, she divided each event by the XS (which was calculated event by event using the Bosted
      model). By doing this, the 2D plot of the raster pattern appears to be uniform. She also showed the corresponding 1D plots of beam x and beam y;
      the beam y distribution appears to be flat while the beam x distribution has a slope on the left side. She also used the same procedure, but divided by
      the Mott cross section, and saw similar results.
    • Also showed a comparison between data and simulation for a 2.2 GeV optics run with 0T target field. Last time, she showed a discrepancy between the
      two. For this time, she updated the simulation to include a different ionization model and used the same energy loss used in optics calibrations. Using the
      updated simulation, there is much better agreement between data and simulation. JP commented that we should make sure we understand where the
      discrepancy came from in order to choose the best model, not just choosing the one that matches the data best, so as not to introduce bias to the analysis.
      For next time, Jie will show a comparison of the two models. More details can be seen in Min's slides here.
  • Ryan
    • Gave an update on his comparison of the nitrogen XS from SAGDH data with the Bosted model. The raw XS results from SAGDH now include a multi-track
      analysis study. To find the best scaling factor to match the data with the model, he uses a reduced chi-squared method. Vince gave him the results of an
      elastic tail Monte Carlo used to simulate the acceptance, which also includes the "punch through" correction. Although this can't be compared to older SAGDH
      nitrogen analysis (since the acceptance cuts have changed), but he can use the results to compare Vince's method to his. He found that his method is consistent
      with the Monte Carlo results, and the small difference (which is a maximum of 5% in the tail), is only ~1% difference in the subtracted XS. He showed the
      comparison of the XS from data with the Bosted for all the SADGH kinematics; each setting has a different scaling factor and shift in nu. The shift in nu is quite
      large (6-16 MeV). To understand the energy shift, Karl suggested trying to reproduce the shift with a change in scattering angle. JP also suggested making the
      outgoing thickness of the cell a parameter, as a small change could have a large effect. There was a question of what was included in the radiating of the Bosted
      model; for next time he will show a comparison of the model before and after radiation. He will also work on full inelastic radiative corrections for the SAGDH data
      so that he can extract the Born XS, which can then be compared to the Bosted model. More details can be seen in his slides here.


Present: JP, Melissa
By Phone: Toby, Ryan, Ellie, Pengjia, Alexandre

Feature Presentations:

  • Toby
    • Gave an update on dilution analysis. Last time, he showed a comparison of yields from data with the prediction from the Bosted model, and then
      scaled the model by computing an "acceptance factor". This time, he did the same thing for the 2.2 GeV settings, but found that the same acceptance
      factor did not work for all energy settings, due to the fact that the scattering angle is different for each energy setting. Since the scattering angle is
      dependent on nu, the acceptance factor will have to be momentum dependent. He showed plots of the scattering angle vs nu for the 3.3 and 2.2 GeV
      settings, and fit the distribution with an exponential function (see Jixie's elog post 49 for more details). The parameters from the fit can then be used
      to calculate the scattering angle for each momentum value in the Bosted model. This method looks promising, but there appears to be a suppression
      of the delta in our data that does not match with simulation. From this, he will be able to extract a rough value for the dilution factor, which should be
      available soon. More details can be seen in his slides here.


Present: Jie, Min, Jixie, Melissa
By Phone: Toby, Ryan, Ellie, Karl, Pengjia

Feature Presentations:

  • Min
    • Working on an acceptance study for the 1st and 3rd septum settings. For looking at data from optics runs, she applies focal plane and target cuts to
      get rid of junk events and select only elastic events. For this time, she updated the beam cut to match what Chao used for the optics calibrations. For
      the simulation, elastic events are generated according to the beam position in the cut. For the dilution run (empty run), the procedure is similar, but she
      applies a target plane graphical cut on the data instead of a focal plane cut. To simulate the empty run, she used the same target plane cuts that were
      applied to the data, but generated events in an ellipse. For both the optics and dilution runs, the theta and phi variables agree reasonably well, but there
      is a discrepancy in the dp variable. For next time, she will look into this discrepancy as well as look at the other settings. More details can be seen in her
      slides here.
  • Ryan
    • Showed a comparison of the Bosted Model with SAGDH data. He generated the nitrogen cross section using the Bosted model for each of the SAGDH
      kinematics, then he can radiate the model for each reconstructed scattering angle, within acceptance. In order to compare to SAGDH data, he averaged
      over the scattering angles. Previously, he tried to determine a single scaling factor for all the kinematic settings, this time he chose different scaling
      factors for each setting to best match the data. For each setting, he found that averaging over the scattering angle decreases the scaling factor by about
      5%. Karl suggested using another data set to compare, possibly using our data to extract the carbon cross section. For the future, he will consider the
      effect of the punch through from the collimators, which effectively increases the radiation length. He will also look at the SAGDH data for
      two settings that he hasn't looked at before (9deg/2234 MeV and 9deg/3319 MeV), among other things. More details can be seen in his slides here.
  • Jie
    • Gave an update on packing fraction analysis. Last time, he used runs from the 2nd septum setting (40-32-16). Since the SNAKE model is not quite
      ready for this setting yet, this time he analyzed a set of runs from the 2.2 GeV, 5T, longitudinal setting, which uses the 3rd septum setting (40-00-16).
      He applied a 2D graphical cut to select elastic events, though Karl pointed out that this isn't a 100% pure elastic sample, as there could be a tail underneath
      the peak. Using this set of runs, he determined the packing fraction to be 0.51, with an uncertainty of 7.6%. The largest contribution to this uncertainty
      comes from the uncertainty of the absolute beam position. Ellie suggested showing a comparison of the XS models (that are used as input) to data to test
      how well they match, which Jie will work on for next time. More details can be seen in his slides here.

General Discussion:

  • Ryan and Toby have circulated their abstracts for the GRC. Please provide feedback!


Present: Jie, Min, Melissa
By Phone: Toby, Ryan, Ellie, Karl, Pengjia

Feature Presentations:

  • Melissa
    • Showed updates to her method to extract the packing fraction. Biggest change is that the input for cross sections for the various materials will be
      determined using g2psim. Also, different runs, which have consistent beam position information, were used for the analysis. To test the conditions of
      the simulation, she showed a comparison between simulation and data for a helium dilution run. The parameters of the simulation will need to be
      adjusted, as there is a clear discrepancy between the simulation and data. Using the updated values for the XS, the value for the packing fraction
      increases slightly, but will likely change as the simulation results are improved. More details can be seen in her slides here.


Present: Kalyan, JP, Chao, Jie, Min, Jixie, Melissa
By Phone: Toby, Ryan, Ellie, Karl, Pengjia, Alexandre

Feature Presentations:

  • Min
    • Working on an acceptance study for the 3rd ("very bad") septum configuration, using a Monte-Carlo simulation. She started with optics and dilution runs,
      since they have a simple target. Loose cuts were applied to throw away junk events, and to select elastic events. She showed a comparison of simulation vs
      data; for the 1.7 GeV setting (empty cell run), the simulation results are smaller than the data, but for the 2.2 GeV setting, the simulation is larger than the data.
      Also, the shape
      of the phi distributions from simulation do not match the data. JP suggested this could be a result of the momentum calibration or energy
      loss being slightly off. For next time, she will look at a setting with the "good" septum configuration. Also, she will look into the delta discrepancy for the elastic
      setting and will work on tuning the apertures for theta/phi matching (boundary matching). Additionally, the simulation needs to be updated to reflect the true
      shape of the beam, which is elliptical, not circular. More details can be seen in her slides here.
  • Jie
    • Gave an update on simulations. Last time he showed an update to the event generator. This time, he wanted to check the difference in the phase space
      density. He showed a comparison of the density function vs theta for two different values of phi-target; the difference between them was very small. He also
      showed an update of the packing fraction uncertainty. He determined the relative uncertainty to be 7.19% for a 1mrad shift in the scattering angle. He showed
      the beam information for the 3 runs being used in the packing fraction calculation (a production, dummy and carbon run), and the beam position seemed
      consistent for all 3 runs. JP expressed concern that this beam position calibration is too good, and doesn't reflect the actual beam conditions. For next time,
      Jie will show the beam position event by event. More details can be seen in his slides here.
  • Ryan
    • Showed a comparison of small angle GDH data with the P. Bosted model. He generated a nitrogen cross section using the Bosted model, then inelastically
      radiated it so that it could be compared with the SAGDH data (the SAGDH data already has the elastic tail subtracted). He showed comparisons for several
      different energy settings, in all cases the Bosted XS had been scaled down by 30%. For next time, he will check the effect of averaging over the scattering angle;
      the Bosted model is calculated at one scattering angle, while the SAGDH data is broken up into multiple bins. He will also repeat this study using QFS and do full
      inelastic radiative corrections on the SAGDH data in order to extract the Born cross section. More details can be seen in his slides here.
  • Toby
    • Gave an update on dilution analysis. Last time there was a question about using the radiated vs unradiated Bosted model, this time he showed a comparison
      of the two. He also updated his method to extract the dilution factor. The number of counts is defined in terms of the acceptance, luminosity, cross section and
      time. This way, the yield scales by the acceptance, which can be assumed to be the same for each run. The yield from carbon (and helium) can be calculated using
      dilution runs, which can then be related to a cross section using the P. Bosted model. Using the acceptance scaling factor, he can relate the nitrogen and carbon
      yields. Using the data from the 3.3 GeV setting, the scaling factor ("a") that relates carbon to nitrogen is 1.17, but this may need to be adjusted regions (quasi-
      elastic, delta, beyond the delta, etc.) More details can be seen in his slides here.

Jan-June 2014


June-Dec 2013


Jan-May 2013


April-Dec 2012


Jan-March 2012


July-Dec 2011


Jan-June 2011