Minutes Jan2014 to June2014

6/25/2014

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

Feature Presentations:

• Melissa:
  • Gave an update on the PbPt check using elastic asymmetries. Proton form factors are used to compute the predicted asymmetry and combined with the
    measured asymmetry to extract the product of f*Pb*Pt. In this case, the measured beam and target polarizations are used as input to extract just the
    dilution factor, as a check of the method. Last time, she used a 1D cut on nu to select events in the hydrogen elastic peak. This time, she used a 2D cut on
    dp vs. scattering angle to better isolate the hydrogen elastic peak. The dilution factor seems large, but more work needs to be done in the determination of
    the scattering angle. A simulation will probably be necessary to understand the dilution factor at the elastic setting. More details can be seen in her slides
    here.

• Chao:
  • Gave an update on optics. By comparing the elements of the reconstruction matrices from different settings, he can provide evidence that the target field
    is being treated correctly. In order to make the matrix elements comparable, some corrections needed to be made with beam position information. Specifically,
    an offset is added to the reference angle when calibrating the matrix, and applied back when the target variables are reconstructed. He also gave a detailed
    explanation of the different coordinate systems at the focal plane. He showed a comparison of replaying the same longitudinal optics run using the first order
    matrix from two different settings. The difference between them is pretty small! Currently he is working on checking the momentum calibration because yield
    spectrum plotted versus nu shows some strange behavior. He is also working on the optics calibration for the RHRS. More details can be seen in his slides
    here.

General Discussion:

• Toby:
  • Pass-3 for the LHRS is completed and the rootfiles are on volatile. They contain updated bpm and optics information. The pass-2 rootfiles for the RHRS are
    also still available on volatile. He and Chao are looking at the yields to check the angle reconstruction.

6/18/2014

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

Feature Presentations:

• Toby:
  • Showed some work on dilution parameterization and scaling. Last time, it was suggested he look at a carbon run without any liquid helium in the nose.
    Unfortunately, the only runs we took like this were at the elastic setting, which can't be compared to the P. Bosted model. Using the "empty" dilution runs,
    he can determine the yield per length of helium, and in turn can use this to determine the yield per length of carbon. He then determine a scaling factor to
    match the yield (normalized by length) to the model. For next time, he will include the density and luminosity in the model, and will show the difference
    between the radiated and unradiated yields. More details can be seen in his slides here.

• Jie:
  • Gave a simulation update. Last time he showed the change in the elastic XS as a function of beam information for various materials. The change is quite
    large, ranging from ~5.6%/mrad for hydrogen to ~11.8%/mrad for nitrogen. To determine the packing fraction and corresponding uncertainty, he is using
    a set of runs including a production run, carbon, dummy, and empty run. The beam position is fairly stable for 3 of the runs, but for the last run (dummy), the
    beam position has shifted. Since the empty/dummy runs are very similar (aluminum contribution is small), he can probably just eliminate the dummy run. He
    showed the extracted packing fraction and resulting uncertainty for two different methods; for the first method the uncertainty is ~17-20%, and for the
    second method the uncertainty is ~32-38%. He also suggested modifying the event generator. The old generator uses a uniform distribution, he proposes that
    the new generator would use a solid angle uniform distribution (so the cross section will be weighted by solid angle). He showed a comparison of the resulting
    target variables theta, phi and dp for the old and new event generators. There were some issues with the "accepted" events, specifically that the accepted events
    in dp were outside the range of the HRS. After much discussion it was determined these are actually "thrown" events, not "accepted" events. It seems the old
    event generator is better suited for the HRS setup. More details can be seen in his slides here.

6/11/2014

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

Feature Presentations:

• Pengjia:
  • Compiled information about the g2p beampackage into a wiki page and uploaded beam information to the mysql DB. Ryan mentioned that some
    runs seem to be missing beam information - Pengjia will look into this. He also finished writing a technote describing the BPM analysis, available
    here. He would appreciate any feedback!

• Ryan:
  • Working on determining the systemic error for the elastic tail subtraction. He determined the cross section from rosetail using 5 different conditions
    (averaging over acceptance and including energy loss, including energy loss but not averaging over the acceptance, etc.) and used the average of the 5
    methods for the central value with the standard deviation as the systematic error. Karl suggested using just the best method to determine the central value.
    He also wanted to try being more aggressive in determining the error for the acceptance correction, using the angular acceptance of the HRS to estimate
    the possible error. These two methods seem to give similar results for the elastic tail subtraction and systematic error, with the largest deviation at higher
    values of W. The largest contributors to the systematic uncertainty are the incident energy loss and averaging over the acceptance. More details can be seen
    in his slides here.

5/28/2014

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

Feature Presentations:

• Jie:
  • Gave an update on simulations, which he is using to understand the effect of variations in beam position on the yield. He did an acceptance study by
    making very narrow cuts on target theta and target dp, and looking at the resulting effect on target phi, both at the event generator and events that were
    detected by the vdc. He used a similar method to look at theta and dp. He also calculated the hydrogen elastic cross section and looked at the relative
    difference compared to the expected cross section versus scattering angle. He found that the cross section changes ~5% per 1mrad shift in scattering angle.
    He also looked at several other materials; helium (~8%/mrad), nitrogen (~13%/mrad) and carbon (~10%/mrad). Next he would like to check the effect of
    multiple scattering events on the yield. More details can be found in his slides here.

• Chao:
  • Gave an update on the status of optics analysis. He compared the reconstruction matrix elements for different settings to prove that the target field is
    treated correctly in the analysis. To determine the offset for each setting, the constant term comes from the method used to determine the reference angle.
    If multiple runs are used, the reference angle must be corrected using beam position information. The correction for the 2.2 GeV, longitudinal setting seems
    to be small, which suggests that the method is consistent whether or not the target field is included. The new matrix is ready for the left arm, so we can
    probably start cooking the LHRS data soon. More details can be found in Chao's slides here.

• Toby:
  • Gave an update on dilution analysis. Previously, he calculated a carbon scaling factor using the QFS model. This time, he used the P. Bosted model, which
    which seems to have better agreement with our carbon data at high nu, but shows disagreement at the delta resonance. He first determined a scaling constant
    (alpha), which has an acceptance dependence, to match the PB model to the carbon data. However, this scaling factor does not accurately scale the simulation
    results for helium to our helium data. Using alpha, he can now find the scaling factor to compare nitrogen to carbon. His result of 1.167 is exactly what we would
    expect based on the ratio of nucleons between the two materials. He also showed results for the dilution factor for the 3.3 GeV setting, calculated based on these
    scaling factors. It is a little lower then expected, which could be due to the acceptance scaling factor (alpha). Karl suggested determining alpha by using a helium
    run, or possibly optics runs where the helium was drained from the target nose. More details can be seen in his slides here.

• Min:
  • Wrote a technote on the central scattering angle measurement, which can be seen here. She would appreciate any comments/feedback!

General Discussion:

• There will be no meeting next week due to the Users Group Meeting.

5/21/2014

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

Feature Presentations:

• Melissa:
  • Gave an update on the spread in yields seen in the data. She looked at all the different kinematic settings to determine how many settings have this issue.
    The change in yield seems to be correlated to changes in beam-x; JP suggested this could be due to a drift in the chicane magnet field. Of the 235 total settings
    (with different momentum, material ID or HRS arm), only 27 have a spread in the yields greater than 5%. Of these, 11 have just one bad run. The other 16
    settings that were flagged all had a spread in yields that corresponded to some kind of down time. Karl suggested looking at the settings with only one bad run
    for any kind of pattern, and using comparing yields of settings with problems to the neighboring kinematic settings to see how they match. The material ID
    numbers used here were also added to the mysql database. She also showed a short update on the PbPt check using elastic asymmetries. The raw asymmetry
    was formed with a cut on nu to cut out nitrogen elastic events. Using the predicted asymmetry, beam and target polarization as input, a check of the method
    gives a dilution factor of 0.22. This is in the right ball park, but still needs some work. A 2D cut on dp vs scattering angle would probably be a better way to
    isolate only hydrogen elastic events. More details can be seen in her slides here.

• Ryan:
  • Gave an update on radiative corrections to the elastic peak. The goal is to compute the elastic radiative corrections using nitrogen data from SAGDH, compare
    the cross section from data to that of the model, and look into the effect of energy loss on the elastic tail subtraction. The elastic peak was fit with a Gaussian,
    however, the fit is only constrained by a few data points, so the error bars are large. To look at the energy loss and elastic tail, he looked at how well the Dally fit
    applies to the SAGDH data. At nu just outside of the elastic peak, there should only be elastic radiative tail, so he can use this to qualitatively check how well the
    tail shape matches with the data. The first step is to look at the energy loss correction to the elastic tail. The radiated nitrogen cross section (including energy loss)
    agrees with the Gaussian fit to the elastic peak within 10%. Once the elastic tail is averaged over the angular acceptance, the falling edge appears to agree quite well.
    Finally, to check the variation in the cross section after tail subtraction, the tail is shifted in nu, and then compared to the subtracted cross section with and without
    the shift. More details can be seen in his slides here.

• Pengjia:
  • Gave a summary of the BPM calibrations. There were a total of 9 different settings, each with a different calibration. For each setting, he showed the variance in
    x/y/theta/phi over the course of that period. In the first setting, which contains a set of optics runs, there was a question about the sudden drop in x. It's possible
    this is a result of a beam position scan, but he will have to check the HALOG. He also showed the corresponding uncertainty for the position and angles for each setting
    .There may be a few issues with the estimation of the uncertainty; JP and Pengjia will discuss this more offline. For optics studies, Chao is currently using a different
    method to determine the beam position, but JP suggested that this data should eventually be used as a cross check. More details can be seen in Pengjia's slides here.

5/14/2014

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

Feature Presentations:

• Jie:
  • Gave an update on his study of the relationship between yields and bpm information using simulation. Last time, he showed an acceptance study (both with
    and without the SNAKE model included) comparing the generated and accepted events. JP suggested looking at a wider range of momentum values, instead of
    just elastic events. He also showed the total distribution for the scattering angle at the event generator and for the accepted events, for different values of x. For
    the plot with only accepted events, it was unclear why the distribution is a shift on only one side. He showed a comparison of two dilution runs, and empty and
    dummy run. The data shows that the yields are consistent with each other, as they should be. However, the results of the simulation, using beam information as
    input, suggests that they differ by ~12%. JP suggested that Pengjia should calculate the angle of the beam at the BPM locations, so that the yields can be compared
    to the expected result (based on the nominal beam position), instead of just to each other. The results from simulation for the longitudinal elastic setting also
    disagree with the data, which could be a problem with the phase space used in the simulation. More details can be seen in his slides here.

• Chao:
  • Gave an update on optics analysis. He found a linear relationship between the phi-tgt offset (P0000) and beam-x. The fitting result suggests that a 1mm shift in
    beam-x will result in a 1.327 mrad offset in phi. The difference in beam-x is particularly large between the 2.2 GeV and 1.7 GeV settings. To take a closer look at this,
    he looked at focal plane x vs y for a run in each energy setting, and cut on the central hole. He followed a similar procedure for focal plane theta vs phi. From this he
    found that beam-x changes considerably but y and phi (focal plane) do not change as much. Currently, the first iteration of LHRS optics is complete. The reconstruction
    requires two pieces of input; the optics matrix and database of effective beam position. This is complete for the LHRS, and the reconstruction script has been tested
    using the 5T longitudinal setting. Next up is the RHRS. More details can be seen in his slides here.

General Discussion:

• After the next round of replay, a new flag should be created in the mysql to identify "bad" runs that shouldn't be included in future analysis.

5/7/2014

Present: Kalyan, Chao, Jie
By Phone: Toby, Ryan, Ellie, Pengjia, Alexandre

Feature Presentations:

• Pengjia:
  • Gave an update on determining the uncertainty of BPM calibrations. He tested the method to use the rms value for a run range to estimate uncertainty. It was
    calculated for each run before. With this method the uncertainty of theta angle is ~0.0009rad. A method to calculate the uncertainty in auto-gain mode is also
    proposed by him. Several runs with relatively stable beam position were used to get the maximum beam position deviation to replace the pedestal uncertainty.
    The angle uncertainty is ~0.002rad with this method. More details can be found in his slides here.

4/30/2014

Present: Kalyan, Jixie, Jie, Chao
By Phone: Karl, Toby, Ryan, Ellie

Feature Presentations:

• Toby:
  • Gave an update on dilution analysis. Normalized Carbon yields of 2.254 GeV setting was calculated. The yields do not match well, probably because of
    optics. Karl suggested that some acceptance input might fix this problem. Toby also calculated the 3.350 GeV Carbon yields and compared it with Nitrogen QFS
    cross sections to find the scaling factor. Karl suggested to compare the carbon yields with model directly at first. 3.350 GeV dilution factors was also calculated.
    The plot showed a huge jump due to the matching problem of the yields in production data. As the next step, he will run the simulation with P. Bosted model
    and compare with data. Karl suggested that he could use Vince's data for carbon too. More details can be seen in his slides here.

• Chao:
  • Gave an update on optics. He showed a table of the first order matrix results from a new fitting which limit the matrix up to the 2nd order. New matrix elements
    do not show clear dependence of the septum settings, which is different from the previous result. The offset of the theta and phi matrix is still large in the new
    calibration result. He did an extended target correction to remove the theta offset and reduce the high order effect. The correction constants still need to be
    improved. Since the first iteration of LHRS optics is almost done, he also suggested that it is a good time to replay the longitudinal production data and check
    the optics with data. He will work together with Toby to do this. More details can be seen in his slides here.

• Jie:
  • Gave an update on yield results from simulation. He did the simulation again to study the influence of beam position to the yields. An updated HRS transportation
    model with some acceptance cuts was used. However, he still found that the yield would increase when the shift in beam-x became larger. It might be because
    the acceptance cuts of this transportation model still need to be tuned and he will start to work on that. More details can be seen in his slides here.

4/23/2014

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

Feature Presentations:

• Ryan:
  • Working on radiative corrections to the elastic peak. The goal is to determine the elastic radiative corrections for the small angle GDH nitrogen data,
    

then compare the XS results to that of a model. To do this he will need to integrate over the elastic peak in the SAGDH data. For the elastic peak, his
calculations match the results from Mo/Tsai. To find the full strength of the elastic peak, he fit the peak with a Gaussian. However, since there are only
4 points in the fit range, the fit is poorly constrained. JP suggested just summing up the channels in the peak, instead of trying to use a fit. As a "sanity
check", Karl suggested finding the strength of the Born peak, determining the elastic radiative tail, then comparing it to his previously determined
correction for the elastic tail. More details can be seen in Ryan's slides here.

• Melissa:
  • Looked at the spread in yields for production runs in the 2.2 GeV, 2.5T, transverse setting. She showed an example for the setting where p0 = 1.927
    

GeV/c, which had a spread of ~15.2%. However, runs taken with different materials should not be compared to each, as the packing fraction could be
significantly different. For this setting, the yields for material eight seem consistent between runs taken on the left and right HRS. The runs taken with
material 7, which were taken several days later, are considerably lower on the RHRS. She will check other momentum settings for this type of behavior.
Her slides can be seen here.

4/16/2014

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

Feature Presentations:

• Jie:
  • Gave an update on yield results from simulation. He varied the beam position at target center to see the effect on the yields for the elastic peak. He
    found that, as the shift in beam-x became larger, the yield also became larger. JP suggested that this shift is too large; a shift in beam-x of 5mm causes
    the yield to be ~33% larger. Since we have a short target, the shift in x should not affect the scattering angle, at least to first order. It may, however,
    affect the acceptance. It's possible something is not correct in the simulation, Jie will look into this. Since the packing fraction runs for this setting do
    not agree with each other, he tried extracting the packing fraction using a production run taken around the same time as the dilution runs for this setting.
    This way, the beam conditions will be the same for the ammonia/dilution runs. Using two slightly different methods to extract the pf he got results of
    pf=0.583 and pf=0.389. More details can be seen in his slides here.

• Pengjia:
  • Gave an update on determining the uncertainty of BPM calibrations. Included in the calibration constant uncertainty is the harp survey uncertainty, BPMs
    survey uncertainty and the BPM resolution for the calibration runs, with 2Hz filter. Included in the BPM survey uncertainty is the pedestal uncertainty, which
    uses a 2Hz pedestal rms value. The uncertainty caused by the target field is not included. JP commented that this affects the angle more than the position.
    The uncertainty study for the time period in auto-gain mode is not done yet. He is also working on writing up a technote of this analysis. His slides can be
    seen here.

• Min (presented by Chao):
  • Gave a summary of work on transport functions. Looking at all the data, only ~6 production runs in the 2.2 GeV, 2.5T, transverse setting were taken with
    the "good" (484816) septum configuration. The rest of the runs in this setting have the "bad" (403216) septum configuration. The other four settings were
    all taken with the "very bad" (400016) setting. The transport functions are ready to use for all settings except for the 403216 septum configuration. It is not
    clear whether the fitting was done for both the left and right HRS, but Chao will check with Min. More details can be seen in her slides here.

4/9/2014

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

Feature Presentations:

• Melissa:
  • Outlined a procedure for doing a check of the quantity f*Pb*Pt using elastic asymmetries. The prediction for the physics asymmetry can be expressed
    in terms of elastic form factor (details of the formalism can be found in C. Crawford thesis, based on the procedure by Donnelly and Raskin). The
    parameterization for the elastic form factors is taken from the most recent global fit of proton elastic data (J. Arrington et al.). The elastic asymmetries at
    2.2 GeV with 5T magnetic field (both in the longitudinal and transverse configurations) should be large enough for this check. Karl commented that
    detector efficiencies should also be accounted for, and that radiative corrections will need to be included as well. More details can be seen in her slides here.

• Ryan:
  • Working on radiative corrections for the elastic peak. Previously, he has shown results for radiative corrections for the elastic tail, but now is looking
    at corrections for the elastic peak for nitrogen data from Small Angle GDH. The formalism is based on Mo/Tsai, and he is writing the code in c++ from
    scratch. The goal is to be able to compare the XS extracted from data to a model. He gave an overview of the theory explaining the different contributions
    to the overall correction. He still needs to include a calculation of delta-t, which includes the thicknesses of the different materials in the target, and to
    code the "straggling" term. Also, he will work on using a Gaussian fit of SAGDH data to obtain the radiated elastic XS, and will determine the quantity delta-E
    for the SAGDH data. More details can be seen in his slides here.

• Min:
  • Gave an update on transport functions. Previously, she has shown the forward and backward transport functions between the target and focal plane. Now
    she has completed the forward transport functions from the target plane to multiple end-planes along the trajectory of the electron, for the case with the
    "good" septum. She also included a diagram of the side and top down view of the trajectory. She will add this transport function to the g2psim package
    and will next start working on the transport functions for the other septum conditions. She is leaving next week for China, so she will try to have this done
    before she leaves. Her slides can be seen here.

4/2/2014

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

Feature Presentations:

• Chao:
  • Gave an update on optics calibrations. Showed the calibration results for the setting with beam energy of 2.2GeV, 2.5T, transverse target field, and the
    2nd septum setting (40-32-16). The central hole has a small offset in phi, but this is not a problem since the effective phi and theta are determined using
    and event by event simulation. He also showed a table of the first order matrix results, comparing the two septum configurations both with and without
    the target field. The phi matrix elements (P0010 and P0001) for 0T and 2.5T field are comparable, but there is a difference between the different septum
    settings (which makes sense!). The theta matrix elements (T0100) do not change much between the septum settings, since the septum doesn't have a large
    affect on theta. Next he will work on the extended target correction, as the vertical (x) beam position may cause the offset in theta. He will also work on the
    RHRS optics calibrations. More details can be seen in his slides here.

• Toby:
  • Gave an update on dilution analysis. He summarized his method for extracting the dilution factor; first he must define the total background in terms of the
    dilution runs. In order to relate the different dilution runs, a scaling method is used to account for the different radiation lengths of the materials. Also, a
    scaling factor must determined to scale the carbon yield to the nitrogen yield. To determine the radiative tail for the "empty" dilution run, two methods were
    used; using the true radiation length of helium and matching the helium and carbon radiation lengths by extending the helium target length. A ratio is taken
    between the two results and is used to scale the radiation length for the empty dilution run to the carbon run. Karl suggested that the yield from helium does
    not need to scaled in this way - he and Toby will discuss this more offline. He also showed a comparison between simulation and data for the helium yield.
    Currently, he is using Moshe's simulation, which does not include the magnetic field or acceptance. The g2psim package is probably better suited for this study.
    More details can be seen in Toby's slides here.

• Jie
  • Gave an update on simulations. There is a discrepancy in the yields for the packing fraction runs in the 2.2 GeV, 2.5T transverse setting. The fluctuation in
    yields seems to be correlated to changes in the beam position. He simulated the yields for three different packing fraction runs and varied the average beam
    position and incident angle. While there was some difference seen in the simulated yields as a result of these changes, they did not match the data. That is, the
    run with the smallest yield from the data had the highest simulated yield. He will keep working on this and check his results. More details can be seen in his
    slides here.

• Pengjia
  • Gave an update on determining the uncertainty for the beam position calibrations. The calibration constant uncertainty has contributions from the harp survey
    uncertainty, bpm survey uncertainty (for each calibration run), and the BPM resolution with 2Hz filter. The overall uncertainty for the center position also contains
    BPM survey uncertainty (for each run) and uncertainty due to the pedestal. The uncertainty caused by the target field is not included. He also showed some
    specific uncertainty results for a few different run periods (details can be seen in his slides). For the runs that were taken with the autogain setting (runs taken before
    March 30th), there is no way to get the pedestal uncertainty, so he used one value for all the runs. He is working on writing up the details of this analysis in a
    technote, which he will send out soon. His slides can be found here.

3/26/2014

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

Feature Presentations:

• Melissa:
  • Gave an update on the variance in scattering angle. The discrepancy in yields seems to be correlated to changes in the beam position. She showed
    a couple plots showing the change in the scattering angle an incident angle for a set of runs in the 2.2 GeV, 2.5T setting. Next she will try to understand
    the effect of the change in scattering angle on the yields (using a simulation), and developing a correction for this. Her slides can be seen here.

• Min:
  • Gave an update on the status of optics calibrations. Of the 8 total LHRS settings, 5 are done and 1 is in progress. Min is working on the setting with beam
    energy of 1.7 GeV, 2.5T transverse target field. This setting has the "bad" septum configuration (40-00-16) and a full delta scan on the LHRS. The results of
    the angle and momentum calibration look good. Next she will look at beam position scan data for this setting, then move on to the remaining LHRS settings.
    More details can be seen in her slides here.

• Pengjia:
  • Gave an update on BPM calibrations, specifically the issue of the fluctuating pedestals. He looked at one run, where the pedestal value is different for the first
    and last quarter of the run. If the beam position for these two regions using the pedestal for that region, there is a large discrepancy between the position at
    BPMA and BPMB. If the position is calculated using the same pedestal for both regions (the pedestal for the last quarter of the run), then the discrepancy between
    the two BPMs is much smaller. One possible explanation is that the pedestal fluctuation for this period came from the source after the BPMs receiver amplifier, but
    not before the ADC. Overall, most of the runs now have calibrated beam position information. There are some runs where the happex ADC was saturated, so he
    will have to determine the calibration with the fastbus ADC. He is currently working on determining the uncertainty and writing up this analysis in a technote. More
    details can be seen in his slides here.

3/19/2014

Present: Chao, Jie, Min, Melissa
By Phone: Pengjia, Ellie, Karl

Feature Presentations:

• Chao:
  • Gave an update on status of optics calibrations. He has finished two more settings. The first setting is 1.1 GeV, 2.5T, transverse, with the "worst"
    septum setting. He included a plot of the simulation result showing the effect of the target field. An event by event simulation was used to determine
    the effective theta and phi angles. There is still a small offset in the phi angle for the central hole; this will have to be considered carefully. The
    uncertainty of the dp calibration is of the same order (10^-4) as previous calibration results that have been shown for other energy settings. He has
    also completed the calibration for the 2.2 GeV, 2.5T, transverse setting, this time with the "best" septum setting. Similar results were seen for this setting,
    though the uncertainty in dp is slightly smaller, as the bending effect is not as large for this setting at it is for the 1.1 GeV setting. Of the 8 total optics
    configurations, 5 have been completed and 1 is in progress. The last two settings should be completed in the next couple of weeks, and then it will take
    ~2 weeks to complete the calibrations for the RHRS. More details can be seen in his slides here.

• Jie:
  • Gave an update on including radiative corrections in the simulation package. Last time, there was a question about why the un-radiated distribution (from
    a carbon target) was not symmetric. It appears the value for theta used at the event generator to calculate dp is a uniform distribution, which causes the
    strange shape in the distribution. He described two possible methods to get the final distribution; they are similar but the first method is weighted by the
    elastic Born cross section while the second method is weighted by the radiative cross section. Comparing the two methods, the distributions for dE at the sieve
    show a considerable difference. However, if you compare the distributions for the two methods at the event generator, they are almost the same. It's possible
    that the second method accounts for the energy loss dues to ionization and Bremsstrahlung twice. More details can be seen in Jie's slides here.

3/12/2014

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

Feature Presentations:

• Pengjia:
  • Gave an update about the status of BPM calibrations. He is studying the BPM pedestal value for the run 3600~3900. The typical fluctuation of the
    pedestal value is about 1000 channels. However, Pengjia pointed out that the pedestal value of BPM B changed during some runs (like 3714 and 3732),
    especially for the channel 7 of BPM B. JP suggests that multiple pedestal values can be used in the same run to correct those big jump of pedestal values
    and treat the rest small fluctuations as uncertainty. More details can be seen in his slides here.

General Discussion:

• Jie is working on radiative corrections in the simulation.

• Chao is working on optics calibration of 1.1GeV and will compare the result with longitudinal optics.

3/5/2014

Present: JP, Kalyan, Vince, Jie, Min, Chao, Jixie, Melissa
By Phone: Pengjia

Feature Presentations:

• Jie:
  • Gave an update on including radiative corrections in simulation. Included a list of definitions for all the terminology and different processes used
    in the calculations. He showed a comparison of using the peak approximation versus the exact calculation for the NH3 target using two different
    radiation lengths. For small values of nu, there isn't a large difference between the methods. He also showed a comparison of using the exact
    calculation method for two different radiation lengths (0.1/0.03), both with and without the multi-photon correction. Without the correction, the ratio
    is pretty flat, but including the correction causes the ratio to drop for smaller values of nu. He included a plot of the total radiative corrections for the
    carbon target (internal and external), and a plot showing the the carbon cross section with and without corrections. It's unclear why the uncorrected
    cross section is not symmetric; it appears to already have some energy loss. Jie will check this and will also include detector resolution and acceptance,
    which aren't included in these plots. More details can be seen in his slides here.

• Chao:
  • Gave an update on longitudinal optics. He took a closer look at the BPM x fluctuation during the course of a run; it seems the beam position is
    slowly fluctuating over the course of the run. He described the method for matrix calibration; the matrix elements are calibrated by the open angle of
    2 different sieve holes with respect to the scattering point. The fluctuation in the beam position will slightly influence the calibration. The matrix
    calibration can be calculated using geometry relations, so he simulated several different beam positions and calculated the open angle; the results
    showed that the change in angle due to the beam position is small. JP suggested that he should look at the absolute value of the sieve holes, instead
    of the difference between them. He also showed a comparison of the first order matrix for the cases with and without the target field. The theta offset is
    large, which is due to the bend from the target field. JP asked about the effect on the left septum after the right septum broke; according to simulation
    there is ~10% effect. More details can be seen in his slides here.

General Discussion:

• Pengjia is working on checking the pedestals for all periods for BPM calibrations. The change in pedestals seems to be random. There also seems
  to be an effect where changes in current affect the BPMS. Pengjia says this effect seems to be random, but he will show more details on this next time.

2/26/2014

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

Feature Presentations:

• Melissa:
  • Gave a short update on the inconsistency in the yields. There seems to be a correlation between beam position and yield; for p0 = 2.072 GeV/c
    (2.5GeV beam, 2.5T magnetic field) setting, an ~8% drop in yields can be seen when the beam position changes ~3mm in X and ~2mm in Y. She
    also tested the effect of applying different raster cuts, in case the shift in beam caused scraping. The raster cuts did not help to make the yields
    agree. JP suggested that, due to our small scattering angle, a change in beam position can have a significant change in the kinematics. She will
    look more into this, and look at the corresponding effect on the RHRS. Her slides can be seen here.

• Min:
  • Gave an update on the pointing uncertainty. Previously, she used the carbon ground state and first excited state to determine the uncertainty.
    A landau-gaussian convolution fit was used to fit the two peaks and determine the uncertainty. JP cautioned against using fits in Root, as they
    can be unreliable. Min will take a closer look at this and the determination of the uncertainty. Using this method gives a d-theta of ~0.2mr, which
    is within the requirement. She also showed another method to calculate the uncertainty, using the difference in energy between two nuclei (carbon
    and helium), this time using a Monte Carlo simulation to determine the beam offset. The beam position at the target looks identical for both carbon
    and helium, though JP suggested only using one "blob" (the "blobs" arise from drift in the beam position during the run) in order to get better
    resolution. If only survey results are used, the value for d-theta is ~0.7mr. More details can be seen in Min's slides here.

• Pengjia:
  • Gave an overview of status of BPM calibrations. The beampackage tools have been updated, he has dumped all the raw BPM data from volatile
    rootfiles to a data pool and have saved all calculated positions to disk. Students can now insert this information into their own rootfiles. He is
    calculating the uncertainty for each run and checking for any weird changes in beam position. His results will be published on the ELOG when he
    is done. A database containing the average position for each run is built along with a script to access the information. He showed global plots
    of the beam position for every run at BPMA, BPMB and the target. He also showed a global plot of pedestal values for the entire run period. Some
    pedestal runs were taken with out any current (real pedestal runs), while some were taken during long beam trips. Currently, he uses the pedestal
    closest in time to each production run as the pedestal value, but JP suggested breaking them up by setting instead. Pengjia is still working on how to
    estimate the uncertainty for the pedestal value. More details can be seen in his slides here.

General Discussion:

• Moshe has his simulation ready, but needs optics calibrations! JP suggested using straight thru optics results for now.

2/19/2014

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

Feature Presentations:

• Jie:
  • Gave an update on his work to determine the packing fraction using simulation. He is working on updating his simulation to include radiative
    corrections. He is including a correction for the straggling effect, which arises due to "real" bremsstrahlung and ionization. He showed a comparison
    between the peak-approximation method and the exact calculation, for a carbon foil. They agree within 1%, but the difference would probably be
    larger for a (thicker) ammonia target. He also showed the simulated result for the radiative tail in the carbon target, which suggests that the "internal"
    contribution is larger than the "external contribution, except at small values of nu. Finally, he showed the effect of the multi-photon radiation correction,
    which is fairly large at small values of nu. He is still working on optimizing the code. More details can be seen in his slides here.
    

• Ryan:
  • Gave an update on the work he's been doing on the radiative corrections for small angle GDH data. At our kinematics (2.1GeV, 6deg), the cross section
    has a strong dependence on the scattering angle, which means the cross section could vary greatly over the entire angular acceptance. The code used to
    produce the elastic radiative tail uses one central scattering angle, so angular acceptance needs to be corrected for. He broke up the acceptance into a grid
    in theta and phi bins, calculated the elastic tail at different angles across the acceptance, and averaged the results. The difference in the cross section using
    the central scattering angle vs. using the average of the reconstructed scattering angles is about 20-25%. He will do a comparison of carbon/nitrogen data
    for 3.7 GeV once he gets the nitrogen data from Vince. He is also writing up a technote documenting this work. More details can be found in his slides here.

• Chao:
  • Gave an update on the status of optics calibration. A program (g2prec) is written to read in L.gold.* (effective angles) and Lrb.tgt_0_* (bpm) type
    variables as input for projection and drifting functions in the simulation package to calculate the final reconstructed variables. It will be configured by the
    database to deal with different kinematic settings, and will write L.rec.* type variables into the final rootfiles as the final reconstructed scattering angle and
    and momentum. He also showed a diagram depicting the structure of the "do_replay" script, which will be automated to insert all necessary information
    into the final rootfiles. He is currently working on determining the calibration matrix for the 9 different optics settings, which can probably be completed in
    ~1 month, though the uncertainties will take longer. His slides can be found here.

2/12/2014

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

Feature Presentations:

• Melissa:
  • Showed a summary of checks she's done to try to understand the discrepancy in yields for packing fraction runs. Many different tests were
    done testing the cuts (acceptance, PID and raster) as well as checking the multitrack efficiency and comparing the first and second half of each run.
    JP pointed out a few odd things that should be resolved (such as the "spikes" in the reconstructed phi variable, events above the good electrons in
    leadglass 2D plot, etc.) The difference in yields is still not clear, but it's possible that a Moller measurement that was taken between runs 3503 and
    3574 could have altered the beam conditions. She will discuss with Pengjia to see if the Moller measurement had a large effect on beam position.
    More details can be seen in her slides here.

• Min:
  • Showed an update on her pointing study to determine the central scattering angle. She showed the details of calculating the uncertainty in the
    scattering angle using survey results. She used the assumption that z and x are the same for both theta1 and theta2, which JP warned could in be
    incorrect. Looking at the results for the left and right HRS, the results from pointing and survey agree for the LHRS, but not for the RHRS. The pointing
    uncertainty is different for left and right HRS; this is determined using the difference in the carbon ground state and first excited state, compared to
    the nominal value. Min is currently writing up the details of the pointing study so far. More details can be seen in her slides here.

• Pengjia:
  • Gave an update on the status of BPM calibrations. He is working on the calibration for the optics run near 3185, but unfortunately there are no straight
    through calibrations with div=2. The closest calibration is from 3/6 with div=3. Looking at the results for run 3185 using this calibration gives a beam
    position of -0.84mm(X) and 2.39mm(Y) at the target. Chao's fitting result for this run was -3.5mm(X). JP asked how much a change in beam position of
    3mm would affect the central angle calibration. Pengjia will try to get the calibration as good as possible, then summarize his work and determine the
    uncertainty for the beam position. Also, he will compile a table of all beam condition changed throughout the run. His slides can be seen here.

2/05/2014

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

Feature Presentations:

• Toby:
  • Working on dilution analysis. Gave an explanation of his method to determine the background yield in terms of the dilution runs (carbon,
    empty, dummy). He also needed to create a scaling factor to relate the carbon runs to the nitrogen background. Using Moshe's nitrogen
    simulation he was able to scale the carbon production data (with the "empty" run yield subtracted out) to match the nitrogen yield. He made
    a graphical cut on the carbon and empty dilution to isolate the elastic/quasi-elastic channels so that each channel could be scaled separately.
    He can then use these scaling factors to determine the overall background yield. The current scaling factors result in a background contribution
    that is much too large; the yield is greater than the yield for a production run. This is most likely due to the fact that Toby currently doesn't
    include any radiative corrections, which he will include in his method for next time. The details of his method can be seen in his slides here.

• Chao:
  • Gave an update on the status of optics calibrations. He is currently working on longitudinal optics for the 2.2 GeV, 5T setting, since Min will
    need this for her pointing study. He first used a simulation to show the effect of the longitudinal field, setting the beam position to the average
    value of the BPM readout. The beam positions actually vary slightly between different optics runs, so he had to approximate the beam position for
    "bunches" of 5000 events. An event by event simulation was used to calculate the effective theta and phi angle. The calibration looks pretty good
    for this setting. The calibration tool kit, which combines the optimizer and the simulation, is almost finalized. He is currently working on updating
    the reconstruction script to calculate the kinematic variables. More details can be seen in Chao's slides here.

• Jie:
  • Working on updating the simulation package to include radiative corrections. There are two pieces to the correction; the radiation effect and the
    straggling effect. The radiation effect includes the contribution from the dynamical effect (Bremstrahlung), which Jie has approximated as two
    external radiator lengths. Ryan suggested just doing the full internal calculation, as it doesn't require much extra computing power. Since our target
    thickness is ~0.03, the straggling effect is significant. He showed the simulated yields for the elastic nitrogen peak with and without the radiative
    corrections, but neglected to include the radiative tail, which he will include this for next time. He also looked at the simulated yields using the actual
    beam positions for the packing fraction runs 3503, 3574 and 3864. The yields agree within 4.5%, meaning that the differences in beam position is not
    what is causing the discrepancy in the yields of the packing fraction runs. Jie's slides can be seen here.

1/24/2014

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

Feature Presentations:

• Melissa:
  • Gave an update on packing fraction analysis. Compared the x/y beam positions for the four packing fraction runs for material 7; one
    run (3727) has unreliable beam position information, but the other 3 runs seem fairly consistent. There is still a large discrepancy in the
    yield for one run (3503). This is the earliest run taken; she will go through the logbook to look for any condition changes that could cause
    this discrepancy. The results for the packing fraction for the other 3 runs seem fairly consistent, but lower than expected. More details can
    be seen here.

• Pengjia:
  • Gave an overview of his calibration method; the raw signal received in the antenna is compared to the recorded ADC value, and the
    linear region is fit. This can then be rewritten using a diff/sum value and the nonlinearity corrected for. The position is then calibrated
    using data from harp scans. Some of the calibrations were used for runs with different currents, assuming that the beam position
    didn't change for these runs, which JP suggested was a dangerous assumption to make. There were several periods where the pedestal
    was different between the calibration and production runs. This fluctuating pedestal could change the resulting beam position by ~2mm.
    For next time, Pengjia will summarize the assumptions made for these calibrations so the uncertainty can be assessed for each one. More
    details of his calibration method can be seen in his slides here.

• Min:
  • Gave an update on the pointing study to determine the central scattering angle. She showed the equation for elastic scattering
    (which includes energy loss); she will look at the difference in the scattered energy for two different nuclei. She included two different
    methods for calculating the pointing uncertainty. The first method uses the carbon-12 ground state and first excited state, and gave
    a result for d-theta/theta <1%. JP suggested Min will probably need to combine left and right data to get the precision we need. The
    second method combines various uncertainties (from survey, beam_x, etc.) and uses 2 different scattering angles; one including the
    z-offset and one without. Using just one scattering angle to compute d-theta gives an uncertainty of ~2mr, using the quotient of the
    two scattering angles gives an uncertainty of ~0.2mr, and using the difference of the two angles gives an uncertainty of ~0.04mr. She
    still needs to include input for the incoming beam angle, and include the uncertainty from energy loss. More details can be seen in her
    slides here.

General Discussion:

• Ryan:
  • Working through Rosetail to understand radiative correction calculations/code.

• Toby:
  • Looking at scaling carbon data to nitrogen for dilution analysis.

• Chao:
  • Working on longitudinal optics calibration.

1/15/2014

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

Feature Presentations:

• Jie:
  • Gave an update on using the simulation package to determine the packing fraction. He showed multiple methods for extracting
    the packing fraction, which account for different contributions to the overall yield. He used the g2psim package to get relative cross
    sections for each contributing material. Next he will work on including the radiative corrections to the elastic peak and include the
    calibrated beam position information (once it is ready). Details for the methods used can be seen is his slides here.

1/8/2014

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

Feature Presentations:

• Melissa:
  • Gave a short update on yields for packing fraction runs. For one run (3864), the ungated livetime is significantly different then
    the helicity-gated livetime. Using the average of the helicity gated LT values for the normalization makes this run agree better with
    other packing fraction runs (3574 and 3727). She will check the beam position for these runs to see if this could have a large effect
    on the yields. Her slides can be seen here.

• Chao
  • Gave an update on the simulation package. Previously, the real theta and phi were not determined event by event, but for an entire
    run. Since we know the position of the reaction point and the sieve hole, and the momentum of the electron, it is possible to use a
    bisection method to determine the real theta and phi for each event. With this update it will be easier to determine the calibration for
    different dp settings. Next he will work on finishing the optics calibration for the first setting with the target field. His slides can be
    seen here.

• Min
  • Gave an update on pointing analysis. The calculation was done using the March 14th calibration, using a carbon foil in liquid helium.
    Using the carbon-12 ground state and first excited state to do the calibration of d(delta-E'), the results for the LHRS (4.40MeV) and
    RHRS (4.42 MeV) agreed within the uncertainty with the nominal value (4.44MeV). However, including other uncertainties (survey and
    beam x), add up to ~0.11 deg uncertainty in the scattering angle. She concluded that using the carbon foil in LHe is not ideal for a
    pointing study. Next she will try CH2 run in longitudinal target field setting, once the optics calibration is complete for this setting. Her
    slides can be seen here.

• Pengjia
  • Gave an update on the status of the BPM calibrations. He has finalized the calibrations for data taken from April 11th to May 18th,
    which includes three different BPM gain settings. For settings before April 11th, the process is more complicated (larger pedestals,
    auto-gain), but he will try to finalize the calibrations soon. He will provide a technote of his procedures and results. More details can
    be seen here.

General Discussion:

• If any students are interested in giving a talk at the APS April Meeting, please circulate an abstract to the group. The deadline for
  abstract submission is this Friday, January 10th.