G2p Analysis Minutes

Minutes of the weekly analysis meetings

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Agenda

7/8/2015

Present: JP, Min, Chao, Melissa
By Phone: Toby, Vince

Feature Presentations:

• Pengjia
  • Working on comparing asymmetries determined from MAID to those calculated from
    data; last time he showed a factor of 6 difference between the two results. This
    time, he showed two different methods for calculating the differential XS from the
    virtual photon XS. The first method calculates the differential XS directly from
    the virtual photon XS, and the second method calculates the differential XS using
    F₁, F₂, g₁ and g₂. He also showed two different methods for calculating the
    asymmetry from the virtual photon XS; one method uses A₁ and A₂, while the other
    is calculated from the virtual photon XS. There was a discrepancy between the two
    methods, but he found that there was actually a mistake in one of the equations.
    While the results from the two methods agree with each other, they are still a factor
    of 6 larger than the results from data. More details can be seen in his slides here.

• Toby
  • Showed an update of his scattering angle study for model reconstruction. He is
    using BPM and optics data to determine the scattering angle. He showed an example
    of the calculated scattering angle; JP questioned whether the range was really from
    0-16 deg. Toby pointed out that there really aren't many events at the boundaries,
    the distribution is peaked between 4.5-9 deg. He then uses this scattering angle as
    input for the Bosted model. At low ν the simulation results match reasonably well
    with the data, but the discrepancy starts to become larger as ν increases. He took
    a closer look at the reconstructed scattering angle for each central momentum, and
    found that a second peak is visible for smaller values of p0. If this second peak was
    real, the simulation should recreate the data, so this could suggest a problem with
    the reconstruction. However, Chao pointed out that, for this energy setting, the optics
    calibration is not complete (currently using the longitudinal optics matrix), so the
    reconstructed θ and φ may not be correct yet. For next time, Toby will test this
    analysis using the 1.7 GeV setting, which has calibrated optics. More details can
    be seen in his slides here.

• Melissa
  • Gave a summary of packing fraction analysis. For some settings, the variation in the
    yields (and P_f) is due to a fluctuation in the beam position. This will hopefully be
    resolved by Jie's beam position/acceptance study. For the 2.2 GeV, 2.5T transverse setting
    there is also an issue of a shift in ν between runs. For the 1.1 GeV, 2.5T transverse
    setting, the yields vary depending on the beam current used for each run. JP suggested
    a few things to check as the possible cause for these discrepancies including drift in the
    BCM calibration, anneals of the target material, drift in field (HRS or septum), etc. She
    has posted a technote draft here, feedback would be appreciated. More details can
    be seen in her slides here.

• Min
  • Gave an update on her acceptance study. Last time, she showed that the simulation results
    are more narrow than the data. For this time, she tried cutting on just the center hole,
    and found that the dp distribution from data better matched the simulation. JP suggested
    cutting on each of the different holes individually to determine which hole causes the dp
    distribution to be wider. More details can be seen in her slides here.

• Chao
  • Gave an update on optics analysis, currently checking whether simulation results match
    with data, starting with optics data. First he checked whether the geometry was correct,
    some deviation was found in the recent optics meeting. The position of the BPMs is hard-
    coded into the simulation, and the drifting algorithm is used to drift the electrons
    backward to the BPMs to simulate the readout of BPM A and B. He compared the θ
    distribution before drifting in the target field using a fixed and non-fixed BPM location.
    The results using a fixed BPM match well with the data. He is currently working on
    checking this for all momentum settings, and will follow up with Pengjia about the BPM
    problem. More details can be seen in his slides here.

7/1/2015

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

Feature Presentations:

• Min
  • Gave an update on acceptance studies. She showed a summary table of each energy
    setting and septum configuration. There hasn't been any problems in the 2.2 GeV, 5T
    longitudinal and 1.7 GeV, 2.5T transverse settings, but some settings (2.2 GeV, 2.5T
    transverse, 1.2 GeV, 2.5T transverse and 2.2 GeV, 5T transverse) have a discrepancy
    in the focal plane between data and simulation. She compared the data divided by the
    Mott XS to the simulation results without XS, and found that the simulation results
    of θ and φ are narrower then the data. JP commented that, while including the Mott
    XS might change the shape of the distribution, it shouldn't change the boundary. She
    work on figuring out the cause for this discrepancy before calculating the acceptance.
    More details can be seen in her slides here.

• Pengjia
  • Comparing asymmetries determined from the MAID model to those calculated from data.
    Last time he showed a factor of 6 difference between the two results. He determined the
    scattering angle and Q² by fitting the data and compared them to the quantities calculated
    from MAID. He also showed the results of calculating the quantities g₁, g₂, F₁, F₂, A_L, A_T,
    dXS_L, dXS_T, XS_tot andXS_mott using MAID. He hasn't included radiative corrections in his
    calculations, but this probably won't account for the factor of 6. More details can be seen
    in his slides here.

6/24/2015

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

Feature Presentations:

• Toby
  • Presented some asymmetry plots which Ryan will show in the Chiral Dynamics conference.
    The plots can be seen here. All statistics has been included in these plots along with
    the dilution and the polarizaiton results. The calculated asymmetries is compared with fully
    radiated MAID model. Toby will continue working on the physics asymmetries of all the
    kinematics settings.

• Jie
  • Gave an update on his study of the acceptance. He studied the multiple scattering effect
    of the incoming beam. The standard deviation of this effect is ~0.07mm for position and
    ~0.7mrad for angle. He also studied the influence of the beam position to the acceptance.
    There was a large dependence on y_tg (horizontal direction) but not on x_tg (vertical direction).
    2-D plots shows that the acceptance is not uniform along the vertical direction. JP suggests
    that the horizontal target field may be a reason of this effect. More details can be seen in
    his slides here.

6/17/2015

Present: JP, Min, Jie, Chao, Melissa
By Phone: Alex, Ryan, Toby, Ellie, Pengjia, Vince

Feature Presentations:

• Ryan
  • Working on inelastic polarized radiative corrections, based on the formalism by Akushevich,
    Ilyichev and Shumeiko. Since there is no polarized proton data yet, he is using models to
    understand the systematic error on the radiative corrections. He used the MAID 2007 model to
    generate the polarized cross sections, and went through the same iterative process he used for
    the unpolarized radiative corrections. To do the systematic study he took the MAID 2007 cross
    sections, radiated them using the POLRAD code, unfolded/radiatively corrected the cross sections,
    then compared them to what he started with; the difference is attributed to systematic error. In
    general, the ratio of unfolded/radiated cross section is close to 1, but there is a jump when Δσ
    crosses zero. JP suggested an alternate method of doing the corrections is the correct on the spin
    up XS and spin down XS separately, since neither will be zero. Ryan will look into this method as
    a cross check. More details can be seen in his slides here.
  • Working on his talk for Chiral Dynamics, he will send out his slides to the collaboration later
    this week.

• Toby
  • Working on fixing the scattering angle dependence on the cross section. His original method
    was to plot the calculated scattering angle, take the central value and plot it versus HRS
    momentum. Fitting this with an exponential function (originally provided by Jixie), he could
    then use the fit parameters in the Bosted model to calculate the cross section. The problem
    with this method is it forces the scattering angle across kinematics to be continuous, but our
    data is not continuous. He generated the model at all scattering angles within a momentum
    setting and combined all resulting models with a weighted average. This causes the model to be
    discontinuous over an energy setting, but this method of generating the model may be necessary
    since the continuous model doesn't represent our data well. JP cautioned that the acceptance
    could have an effect on the scattering angle, so we must be cautious using this data until
    optics/acceptance studies are finalized. More details can be seen in his slides here.

• Min
  • Gave an update on her acceptance study. She divided the data by the Mott cross section before
    comparing it to the simulation results for an empty dilution run (just helium). For the scattering
    angle she is using the survey result, which has an uncertainty of 0.7mrad. JP commented that we must
    be cautious in how we determine the scattering angle, particularly the effect of the septum magnet
    on the angle. For next time, Min will work on tuning the apertures to have better agreement between
    data/simulation. More details can be seen in her slides here.

• Chao
  • Gave a status update on optics, specifically the offset problem he has discussed previously. He
    treats the matrix elements separately and uses the center hole to determine the offset and 2 first
    order matrix elements. He then uses the beam position scan data to determine matrix elements that
    are not related to x_fp and delta scan data to determine the matrix elements related to x_fp.
    However, using the updated matrix (for the 1.7 GeV data) still has a 3mm offset. JP questioned
    whether the effect of the septum is being taken into account properly. Once we understand how to
    treat the septum well, we'll know whether to attribute problems to the septum field, target field,
    etc. Chao will go back and look into the effect of the septum before moving forward on the offset
    problem. More details can be seen in his slides here.

General Discussion:

• The abstract deadline for DNP is July 1st.

6/10/2015

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

Feature Presentations:

• Jie
  • Gave an update on his study of the change in acceptance/yields due to shifts in the
    beam position using simulation. Last time he showed the number of events blocked by
    different components such as the collimators, and magnet entrance/exit planes. He looked
    at the change in acceptance/yields moving along BPM Y and X and found that there was
    not a large dependence on Y, but the dependence on X was significant. In addition,
    removing the Q1 exit plane aperture while moving along BPM X showed a large effect on
    acceptance/yield ratio on the positive x side. He also looked at the effect of extending
    X to +30mm. He found that moving the target ~10mm gives the largest acceptance at the
    Q1 exit endplane. There was some confusion about coordinate definitions, Jie will clear
    this up for next time. More details can be seen in his slides here.

5/27/2015

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

Feature Presentations:

• Pengjia
  • Comparing calculated asymmetries from data to asymmetries calculated from the MAID model.
    He looked at the 2.2 GeV, 5T settings (both longitudinal and transverse) and used a dilution
    factor of 0.15. He needed to scale the MAID model as it was 6X larger than the asymmetries
    calculated from data. He also included a plot of Q² vs W for each setting. JP commented
    that the distribution was a little strange, since Q&sup2 and W are directly correlated the
    distribution shouldn't decrease or stay flat. More details can be seen in his slides here.

• Min
  • Gave an update on acceptance studies, specifically the 3rd septum setting. In this septum
    configuration, the entire second coil is gone. She looked at groups of runs where the beam
    position was stable to determine the uncertainty of the focal plane measurement. She compared
    the y and φ at the center sieve hole at the focal plane determined from data to the SNAKE
    result. The center sieve hole was defined by survey results. JP suggested using the no-target
    field setting as a starting point to determine the offset, then look at the transverse effects.
    More details can be seen in her slides here.

General Discussion:

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

5/20/2015

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

Feature Presentations:

• Pengjia
  • Calculated asymmetries using the MAID model. He used the total cross section output from
    MAID 2007, then summed the cross sections from two channels to extract the asymmetry. He
    calculated the longitudinal/transverse asymmetries and g1,g2,F1 and F2 for several different
    values of Q². Ryan pointed out that the calculated asymmetries cannot be compared directly
    to our data, since our data is not at constant Q², and the MAID model is not radiated. More
    details can be seen in his slides here.

• Jie
  • Investigating the field overlap of the septum and Q1 fields in the SNAKE model. Currently,
    no overlap is assumed between the two fields. He looked at different points in the space
    between the septum and Q1 entrance to check the field from each magnet. Although the Q1
    field goes to zero close to the septum, the septum field extends to the entrance of Q1. The
    current septum field map is too small to cover the full area in the x,z direction, so a larger
    field map is needed. JP also suggested looking at how this will change the particle
    trajectories; Min will work on estimating this for next time. More details can be seen in
    Jie's slides here.

5/13/2015

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

General Discussion:

• Jie posted a draft of a technote on radiation effects in the g2psim package here.

• Toby posted a draft of a technote on dilution analysis here.

Feature Presentations:

• Melissa
  • Looking into packing fraction runs for the 1.1 GeV setting, taken with the short ammonia cell.
    She doubled checked the normalization constants used to calculate the yields and didn't find
    anything strange. She also looked at the s1 and Cherenkov channels for each of the four runs,
    and found some small differences, but this is probably due to the fact that the runs were taken
    at significantly different beam currents. Two of the runs (5197,5198) were taken with a beam
    current of 20nA (compared to 40-50nA that the other runs were taken at), which means the BPMs
    are not reliable for these runs, so the beam position may be significantly different for these
    runs. It's possible there is some effect due to the high rate with a beam current of 40-50 nA
    that is not being accounted for. More details can be seen in her slides here.

5/6/2015

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

Feature Presentations:

• Chao
  • Gave a status update on optics analysis. He found that using the 2.2 GeV 5T longitudinal matrix
    to replay the 1.7 GeV 2.5T transverse data resulted in an overall offset. Because of this, it is
    useful to do a full check of the relation between the reconstructed kinematics and the beam position.
    If there is a correlation between the beam position and reconstructed kinematics, a linear fit will
    be used to determine the correction. The fitting result for φ for the two different settings is added
    directly to the first order matrix element P0000 (constant term). These matrices will be used to
    replay the two data sets, and then the fitting procedure can be applied to improve higher order terms.
    Next he will work on checking other energy settings. More details can be seen in his slides here.

• Min
  • Showed an updated on focal plane matching. For the 2.2 GeV, 0T setting with the "good" septum
    (484816), the data and simulation match well at the focal plane. However, data from the same setting
    but with the target field at 2.5T do not match as well. She tried adjusting the beam position to find
    a better match, but the correction needed was larger than the uncertainty on the beam position, so
    JP suggested looking at the discrepancy starting from the central hole. By adjusting the beam position
    and dipole field, she was able to match data from the central sieve hole to simulation results, within
    uncertainties. Next she will work on fitting the other sieve holes to match the data. More details
    can be seen in her slides here.

4/29/2015

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

Feature Presentations:

• Pengjia
  • Looked at the effect of different raster cuts on the asymmetry. He looked at the 2.2 GeV 5T
    settings, both longitudinal and transverse configurations. First, he placed a cut on the center
    of the raster (50% of total radius), which didn't have a large effect on the asymmetry. He also
    looked at the effect of splitting the beam spot into 4 quadrants; for some asymmetries there was
    a considerable difference between the quadrants. He also found that the yield is larger on the
    left side of the beam spot. More details can be seen in his slides here.

• Melissa
  • Showed the results of packing fraction analysis for the 1.1 GeV setting. There is some
    discrepancy in the yields for some materials, and the ratio of the rate/current is not consistent
    in some cases. She showed the effect of applying acceptance and PID cuts to each run; the
    makes the largest impact is the cut on single track events, which cuts out ~50% of the total
    events in some cases. She will continue trying to figure out the cause of the variance in the
    yields. More details can be seen in her slides here.

4/22/2015

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

Feature Presentations:

• Chao
  • Gave an update on optics analysis. Using data from the single foil target does not provide enough
    constraints for optics analysis, but there are two other methods to additionally constrain the data.
    One way is to look at the relation between the kinematics and beam position for beam position scan
    runs, and the other way is to include data from the aluminum window into the fitting procedure to
    directly correct the reconstruction matrix. The second method is what was tested for this week. To
    improve the fitting routine, he first fits the k=0 matrix elements without the Aluminum window data,
    then fixes the other matrix elements and fits the k=l matrix elements after adding in the aluminum
    data. He found that he couldn't get a good fit using the aluminum window data, even if only the y-fp
    matrix elements are allowed to vary. JP commented that, since y and φ are coupled, they cannot be
    fit separately. It's possible that a higher order polynomial is necessary for the fit. More details
    can be seen in his slides here.

• Toby
  • Put together a summary of the data quality checks on the yields (detailed here), including the
    number of useable runs and percentage of useable statistics in each kinematic setting. Overall, the 5T
    settings look the best, with the exception of the 3.3 GeV setting, which has several settings with yield
    drifts that appear to be unrelated to beam position changes. Karl suggested checking the stability of the
    dipole for settings with bad runs. More details can be seen in his slides here.

General Discussion:

• Pengjia posted a draft of a technote on beam charge measurements here, and would appreciate feedback.

4/15/2015

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

Feature Presentations:

• Jie
  • Gave a simulation update, specifically looking at acceptance and yields. Last time, he used a point
    beam a moved the position from 0-10 in x and y to see the effect on the acceptance and the yields. This
    time, he looked at the acceptance at each endplane using a point beam at (0,0) and (-10,0). One big
    difference is the number of events blocked by the Q1 exit for these two beam positions. He went step by
    step through the simulation to compare the number of events that reach each enplane to the number of
    events that pass through the plane. He found that the shift of the beam position by 1cm caused a drop of
    ~20% in the acceptance. JP and Vince commented that this drop seems too large. It's possible the septum
    is also playing a role in the decreased acceptance, not just Q1. More details can be seen in his slides here

• Melissa
  • Gave an update on packing fraction analysis. She extracted pf values for numerous elastic runs for
    several settings. For settings where there is a drift in the yields, the pf also varies. The most
    variation is seen in the 2.2 GeV, 2.5T setting. The raster size was changed part way through this
    setting, so it may not be possible to compare runs with different rater sizes without first correcting
    for this difference. She will continue working on trying to understand the discrepancies in the yields,
    and finish extracting the values for the 1.1 GeV setting, for the regular and short ammonia cells. More
    details can be seen in her slides here.

• Ryan
  • Gave an update on radiative corrections. He took a closer look at the systematic error on the
    inelastic radiative corrections, which are different now that he has removed the interpolation from the
    unfolding procedure. He replaced the interpolation with a direct call to the Bosted Model. Comparing
    the two methods, he found that they are consistent with each other. The interpolation will be the
    largest contribution to the systematic error. He also wanted to test if there was a faster way to
    radiate a model. There are two ways to do the integration within the Stein equation, Romberg or Simpson
    integration. The Romberg method is more accurate, but takes longer. The results from using both methods
    to radiation the Bosted model are nearly identical, but the Simpson method is orders of magnitude faster,
    particularly for finer ν binning. Next he will work on setting up polarized radiative corrections.
    More details can be seen in his slides here.

• Toby
  • Gave an updated on dilution analysis. He showed a central fit to the scattering angle compared to the
    model prediction done by Jixie. This is used to scale the angle between different run types, such as
    scaling carbon dilution to nitrogen production. Since the optics isn't complete yet, this scattering angle
    is just a place holder until we better understand the scattering angle. At large ν, the dilution factor
    (and packing fraction) starts to drop off, which he thought could be due to a problem with the scattering
    angle correction. JP commented that this might not be the case, since this is a ratio, but due to the fact
    that at low Q squared the DIS cross section is small. This will probably result in a large statistical
    uncertainty on the dilution factor. Next Toby will extract the dilution factor for the 1.1 GeV and 1.7 GeV
    settings, and finish writing a technote on this analysis. More details can be seen in his slides here.

4/8/2015

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

Feature Presentations:

• Chao
  • Gave an update on optics analysis. Previously he showed that there is an issue with the horizontal beam
    position changing the dp reconstruction. Since there aren't enough constraints to do the reconstruction, it
    is necessary to do a full check of the relations between the beam position and the reconstructed kinematics.
    He looked at delta scan runs and beam position scans to check the correlation between the beam position
    and reconstructed variables. To correct for these effects, he used a linear fit to determine a correction factor
    for θ, φ and dp. To test this method he used a production run, and placed cuts on the raster pattern in
    different areas around the center of the beam spot. While the "old" reconstructed dp variable shifted based
    on the location of the cut, the "corrected" dp variable was stable. Next he will work on applying this method
    to other settings. More details can be seen in his slides here.

4/1/2015

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

Feature Presentations:

• Melissa
  • Gave an update on packing fraction analysis. She started extracting the pf for the 2.5T settings, but the biggest
    lingering issue is the discrepancy seen in the yields for elastic pf/production runs. Several suggestions were made
    to check for a possible problem, such as the septum field drifting over time, looking at the raster pattern, and
    checking the scalar rates and normalization values (specifically the charge). More details can be seen in her slides here.

• Ryan
  • Gave an update on automated model tuning for determining the carbon/nitrogen cross section ratio. Previously, the
    tune was optimized in the order dip-region, inelastic, quasielastic. For this time he swapped the order to inelastic,
    quasielastic, dip-region. The final overall tune represents an average of each settings parameters. He found that
    the best average reduced chi-squared was found after the second iteration, and the fit is good to within 10%. Next
    he will look at saGDH nitrogen data, but is waiting on updated cross sections from Vince. More details can be seen
    in his slides here.

• Min
  • Gave an update on acceptance studies. Last time she compared the data from a delta scan in the 2.2 GeV, 2.5T
    setting (with good septum) with simulation results and found some differences. This time she adjusted the beam
    position in the simulation to match the data, which was quite different from the original beam position. Kalyan
    suggested looking at just the center hole of the sieve slit to determine the offset. It seems the offset is seen
    in the data, but the simulation shifts the events in the opposite direction. Min/Chao have a plan to check each
    part of the simulation, and Pengjia will check the beam position calibration for this setting. More details can
    be seen in her slides here.

• Jie
  • Gave a simulation update, specifically checking the target center compared to the position given by the BPM at
    the target. His goal was to test if the target was centered, whether the BPM could have an offset? Or if the
    target was centered and the BPM position was correct, could the raster size be scaled incorrectly? Looking at
    several runs he saw a shift of 1cm in the target center. However, as the runs were at different energy settings,
    the beam position wouldn't necessarily be the same. Kalyan suggested looking at the carbon hole runs nearest to
    these runs as a check. For next time he will focus on simulating the shifts we see in the yields. More details
    can be seen in his slides here.

3/25/2015

Present: Jie, Min, Vince, JP, Chao
By Phone: Ryan, Karl, Toby, Alexandre, Pengjia

Feature Presentations:

• Jie
  • Gave an update on simulation package. The elastic radiation tail include soft photon contribution is compared with
    the result from the predication calculated using Mo/Tsai. The tail matches at ΔE~6MeV. He also looked at the effect
    of the beam position on the acceptance. The simulation covers the full angle acceptance to test the aperture cut
    in the SNAKE model. The simulation shows that φ acceptance has large correlation with the horizontal beam position.
    JP suggests the aperture setting in the model may be not sufficient to represent the real situation. Chao suggests
    that to use the simulation to determine which aperture stops most particles. More details can be seen in his slides here.

• Chao
  • Gave an update on the optics calibration. As Jie points out before, the reconstructed dp does not agree with the
    prediction very well when horizontal beam position changes. The beam position scan runs are used to fit a correction
    to the dp reconstruction matrix. The correction could correct the dp reconstruction result for optics runs. However, the
    reason of this correction is still not clear. After discussion, the suggestion is to add the correction back to the dp matrix
    and redo the fit of higher order terms. More details can be seen in his slides here.

• Toby
  • Gave an update on dilution study. He showed dilution results for all completed settings. The tech note of the dilution
    study is in progress. He also mentioned an alternative way to calculate the packing fraction. The method only works in
    DIS region but a 0th order polynomial fit at large ν can be used to find the packing fraction everywhere. All packing
    fractions seem about 5-10% larger than typical values. More details can be seen in his slides here.

• Pengjia
  • Presented some preliminary results of asymmetry and yield for RHRS. He compared the right arm asymmetry and yield
    with left arm for two kinematic settings. The asymmetry results agree quite well but the yields has some deviation for
    the 2.2GeV, 5T longitudinal field setting, perhaps caused by acceptance effect. More details can be seen in his slides here.

3/18/2015

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

Feature Presentations:

• Melissa
  • Gave an update on packing fraction analysis. For each setting, she tried to identify ammonia runs that could
    be used for the analysis, ideally runs that were taken in close proximity to the dilution (dummy/empty) runs, or
    at least where the beam position is similar. In addition, the fitting routine (to understand the level of
    contamination from the 2nd peak) was adjusted for each energy setting. The 2.2 GeV, 5T settings (longitudinal
    and transverse) have ammonia runs taken close in time to the runs to helium. The 1.7 GeV setting has some
    variation in the ammonia yields, but they are not too large. The 1.2 GeV energy setting has significant variation
    in the elastic yields; she will look more into these runs to see if there is an obvious reason for the variation.
    She also showed the fit results for the different energy settings; JP suggested checking the hydrogen fit, as it
    seems a bit wide. More details can be seen in her slides here.

• Ryan
  • Working on an automated model tune, which will be used to determine the ratio of carbon to nitrogen for dilution
    analysis. Last time, he showed an automated tune of the Bosted model, which assumed that the quasi-elastic and
    inelastic channels are independent one another and can be optimized independently. The caveat to this is that the
    tune is only valid in the Q² range and for the target type of the input data. For this time, he updated the
    automated tune procedure to include an adjustment for the "dip" region. The Bosted model parametrization of the
    dip region is a Gaussian that is calculated as part of the inelastic channel. Including the dip region improves the fit
    to carbon data for each individual setting, however the overall fit it worse. JP suggested that fitting the dip region
    first may be the problem; Ryan will try to swapping the order of the fitting routine to see if it improves the fit.
    More details can be seen in his slides here.

• Min
  • Gave an update on her acceptance study. To improve the simulation, she included data from the windows into the
    calibration and updated the results for the delta scan runs. This new function was applied to both horizontal and
    vertical beam scan runs. This improved the agreement between the data and simulation, especially for the horizontal
    beam scan run. She also looked at beam scan runs with the target field on, this time adding an additional constant
    on y and φ. For the fit of the focal plane, JP cautioned not to use too high-order of a fit, as it can become
    non-physical. For next time, she will adjust the fitting function. More details can be seen in her slides here.

• Pengjia
  • Looked at the effect of raster cuts on the yield. He looked at several kinematic settings with consistent yields
    and a applied a raster cut with a diameter of 6mm. He found that applying the raster cut had a negative effect;
    meaning the spread in the yields became larger after the cut was applied. He also showed the x and y positions at
    BPM A and B for each set of runs. In some cases, the x-position at BPMA is stable, but it varies at BPMB, which
    could be the source of the variation in the calculated scattering angle. It may be more useful to do a relative
    study, (similar to what Jie has shown previously) for individual runs than trying to compare separate runs. More
    details can be seen in his slides here.

3/11/2015

Present: Chao, Jie, Min, JP, Melissa
By Phone: Vince, Toby, Ryan, Karl, Alexandre

Feature Presentations:

• Jie
  • Working on updating the energy loss model in the simulation package. Previously it was found that the energy loss
    model in g2psim does not match the prediction calculated using the Mo/Tsai formulation. He found that the soft photon
    contribution was missing. This term could have a large contribution, up to 20%. He also looked at the effect of
    changing the scattering angle on the dp distribution. Over an 80mrad change in the scattering angle, he saw only a
    ~0.16% change in the dp distribution. He also looked at 5 different areas of the beam spot, to see how the dp changed
    in that region. The simulation results show no change in the dp distribution in the different regions, but the data
    shows that the dp distribution shifts as you move around the beam spot. More details can be seen in his slides here.

General Discussion:

• Ryan sent around an abstract for the upcoming Chiral Dynamics workshop, comments are appreciated.
• JP sent around the latest version of Pengjia's BPM paper, feedback is appreciated.

3/4/2015

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

Feature Presentations:

• Toby
  • Gave an update on dilution analysis. He finished tuning the Bosted model in order to obtain cross section ratios used
    for radiation length matching for dilution runs (for example, scaling a helium run to match the radiation length of a carbon
    run). He showed the calculated background over the full kinematic range for the 2.2 GeV, 5T, Transverse setting. The
    dilution factor can then be extracted using the ratio of the background yield to the total yield. Eventually he will be able
    to update the dilution factor using material specific packing fraction values (when they are ready), and an improved tune
    of the XS model. Next he will work on other settings and compiling a technote. More details can be seen in his slides here.

• Ryan
  • Working on a method to automate model tuning for the QFS and Bosted models. For dilution analysis it is necessary
    to scale carbon data as a replacement for nitrogen yields. Since there is no nitrogen and carbon cross sections available
    from the same experiment, it is necessary to use to model tune of saGDH data for nitrogen, and a model tune of data
    from UVa archives for carbon. Previously, this tuning was done "by hand", with a reduced χ² to determine the
    quality of the fit. A problem with this method is that it could result in inconsistent results for different people tuning the
    same data set; an automated method could solve this problem. JP commented that a possible problem with an automated
    method is that the physics is simplified. He showed results for tuning the Bosted model to carbon data, next he will work
    on saGDH data, and then will repeat the procedure for the QFS model. More details, including a description of the code
    structure, can be seen in his slides here.

• Melissa
  • Gave an update on packing fraction analysis. Previously, she described an update to her method to include cross section
    input. Elastic form factor models were used to determine the cross section ratio σN/σHe. To obtain radiated cross sections
    two methods were used. First, using the g2psim energy loss model, and second, using the Mo/Tsai formalism to calculate
    the correction to the elastic peak. There is a discrepancy between these methods, specifically that the results suggest that
    the correction is smaller than it should be. This will have to be resolved to get an accurate value for the cross section ratio.
    She is also working on fitting the data for dilution and production runs for other energy settings to extract packing fraction
    values for other materials. More details can be seen in her slides here.

• Min
  • Gave an update on her acceptance study. Last time she found that the focal plane variables for production runs didn't
    match well with the simulation. Production runs have a rastered beam, as opposed to the point beam used in optics
    calibration runs, so this effect must be corrected for. For this week, she looked at events at the target window in the focal
    plane, and used these events to improve the fitting at the virtual plane. She also looked at events from the carbon foil at
    the focal plane, and saw a reasonable match. Next she will work on further improving the fitting and incorporating the
    results into g2psim. More details can be seen in her slides here.

2/25/2015

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

Feature Presentations:

• Jie
  • Working on understanding the yield drifts due to changes in the beam position. He used beam position information
    as input to the simulation, and applied loose acceptance cuts to determine the yield. He looked at several momentum
    settings that had a drift in yields >3% in the 1.7 and 1.1 GeV energy settings. In general he found that the effect was
    opposite of what is seen in the data. JP suggested doing the study independent of data, so as not to bias the results,
    and to show the dependence of the yield on each parameter (x,y,θ,φ) individually. He also suggested checking to
    make sure the acceptance effects are included properly, as it is difficult to get them to agree at the boundaries. Jie will
    keep working on this, and will start working on the septum SNAKE model for the 403216 septum configuration. More
    details can be seen in his slides here.

• Pengjia
  • Trying to determine if applying a raster cut to the data will fix the spread in yields. The difficulty is in determining
    the total charge after this cut is applied. To determine the charge, he used the calibrated charge info from both the
    happex and fastbus, and applied the same raster cut to each. He was then able to use the happex raster cut info to
    get the charge from the happex bcm. JP pointed out that, since the happex and fastbus aren't synchronized, this
    method may only work if the beam is stable, so it is important to quantify an uncertainty on the charge. He suggested
    trying this method again with a much smaller raster cut, so that whatever effect this method will be magnified. Pengjia
    will first look at a setting where the yields are stable to see the effect of this cut, then will move on to settings that have
    issues. The raster cut library and testcode is available on the work disk, see his slides here for more details.

• Chao
  • Posted the draft of a technote on target field mapping here. Any comments would be appreciated!

2/18/2015

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

Feature Presentations:

• Min
  • Gave an update on her acceptance study. She showed a comparison of simulation results with data from a production
    run. As was suggested previously, she expanded the acceptance range when generating events. She found that the
    focal plane variables still don't match very well. One possibility is that the production runs have a raster beam, but the
    optics runs she had looked at previously used a point beam, so this effect needs to be corrected for somehow. More
    details can be seen in her slides here.

General Discussion:

• Chao mentioned that a problem was found in the most recent BPM package, and it may have caused a problem
  in the replay. Toby will discuss this with Pengjia offline.

2/11/2015

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

Feature Presentations:

• Toby
  • Gave an update on dilution analysis. The dilution factor is define as one minus the ratio of background yield over
    total yield. The background yield includes contributions from nitrogen, helium and the foil endcap on the target cell.
    To extract the dilution factor he must tune the Bosted model (for helium and carbon) to match cross section data,
    radiate the simulation results and take ratios to obtain necessary scaling constants, and then apply these scaling
    constants to calculate the background yield. For tuning the Bosted model, he is currently using cross section data
    from the UVa quasi-elastic database. The kinematics do not match ours exactly, but this will work until g2p cross
    sections are available. He used a χ-squared minimization routine to determine the scaling factor for each kinematic.
    He also showed the resulting cross sections ratios, which are used to determine the scaling factors α, β and γ.
    Next he will apply the cross section ratios to yields from dilution runs to calculate the background yields and dilution
    factor for the 2.2 GeV, 5T transverse setting, after which he will move on to other settings. More details can be seen
    in his slides here.

2/4/2015

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

Feature Presentations:

• Chao
  • Gave a status update on optics analysis. For the 2.2 GeV, 5T settings (longitudinal and transverse) there was
    limited optics data taken. Instead, the 1.7 GeV optics matrix matrix was used for this setting, with a 0th order
    correction for the longitudinal setting, and a 1st order correction for the transverse setting. He showed the
    longitudinal setting as an example, applying the 1.7 GeV matrix and including the 0th order correction to center
    the sieve holes. JP commented that, if the offset is large, there may be higher order effects to consider. There
    are no optics runs for the 3.3 GeV setting, so he plans to use g2psim to determine the optics matrix. He is
    working on an optics technote, and a technote summarizing the last target field measurement. More details can
    be seen in his slides here.

• Min
  • Gave an update on her acceptance study. For this time, she improved the fitting at the virtual plane (for both
    x/y and , and θ/φ) and projected the results onto the focal plane. The corrections on the forward transport
    function were incorporated into g2psim. For the reverse transport function, the fit was done using all dp scan runs.
    The simulation does not match with the data at the edges; this is due to the boundary conditions in the simulation.
    Min will try expanding the boundary to see if it better matches the data. More details can be seen in her slides here.

• Melissa
  • Updated the data quality check for the 2.2 GeV, 2.5T setting to include RHRS runs. In general the problem
    settings on the RHRS are consistent with the LHRS. She also gave an update on the packing fraction analysis;
    there was a problem in the previous definition of the packing fraction. The updated method requires some input
    from cross section models. The resulting packing fraction is slightly larger than the result from the previous
    method. Next she will work on extracting packing fraction values for other settings. More details can be seen
    in her slides here.

• Jie
  • Calculated the energy loss using two methods; using his energy loss model (Monte Carlo, step by step), and
    using a radiated cross section model (from Stein). He used a fixed initial energy and fixed scattering angle for
    a carbon target, and didn't apply any acceptance cuts. He compared the dp spectra for the two methods and
    found that his energy loss model agrees well with the radiation model. Next he will work on a full simulation
    for a beam dependence study (once the acceptance is ready). More details can be seen here.

General Discussion:

• Starting next week we will change the meeting start time to 9:30am.

1/28/2015

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

Feature Presentations:

• Ryan
  • Gave an update on data quality checks for the 1.1 GeV setting. He found that the spread in yields ranges
    from 0.01% - 6.1%, with an average of ~2%. For this setting we also took runs on a short target cell (material
    14). For settings with a large spread, there was a correlation between beam drift and yield drift. Overall, this
    setting seems ok. Next he will move back to working on polarized radiative corrections. More details can be
    in his slides here, and a detailed summary
    of the data quality check can be seen here.

• Pengjia
  • Gave an update on data quality checks for the 1.7 GeV setting. For settings with a large spread in yields,
    he looked at the correlation with the calculated scattering angle. He found that in some cases the change in
    yield was proportional to the change in scattering angle, but for some settings it was inverse proportional.
    He also showed an example of a setting where the yield was drifting, but there was no change in the scattering
    angle. He tried applying raster cuts to see the effect on the yield, but first needs to find a way to calculate the
    charge while including the raster cut. There was some discussion how this could be done; it may be possible to
    use the Happex DAQ, as it is triggered by helicity. More details can be seen in his slides here.

General Discussion:

• Toby will start replaying RHRS runs today, hopefully they will be done by the end of the week.

1/21/2015

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

Feature Presentations:

• Melissa
  • Gave a summary of data quality checks for the 2.2 GeV, 2.5T, transverse setting. There are several momentum
    settings with a significant spread (>2%) in the yields. In most cases, the spread in yields seems to be correlated
    with a change in beam position, which often corresponds to beam down time during the run period. Examples of
    problem settings can be seen in her slides here, and a summary of all settings is available here.

• Chao
  • Gave an update on the status of optics for the RHRS. For the longitudinal and transverse settings at 5T, only a
    few optics runs were taken, so the plan is to use the 1.7 GeV optics matrix for these settings. He also included a
    summary of the RMS value of each kinematic variable (δ, θ and φ) for each setting, and commented that
    the RMS value for y_tg is around 3-4mm, but this is a rough estimation as the fitting is not as good for this variable.
    Next he will test 2.5T transverse optics matrix on the 5T settings to see if it works. His slides are available here.
  • The simulation package has been updated to cover the RHRS and include some upstream geometries. The most
    recent version of g2psim is available through github here: https://github.com/asymmetry/g2psim

• Min
  • Gave an update on her acceptance study. For this time, she combined all dp scan runs in order to do the
    corrections at the virtual plane, which was then projected onto the focal plane. The agreement at the virtual
    plane looks good, but there is still some disagreement at the focal plane. Next she will fit the reverse transport
    functions and compare target plane variables. More details are available in her slides here.

1/14/2015

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

Feature Presentations:

• Jie
  • Gave an update on the dp simulation, specifically trying to understand why the simulation result for elastic dp was
    narrower than the data. Comparing the data (with just PID cuts) to the simulation result (using full acceptance, and
    a raster diameter of 2cm), the simulation is narrower than the data. However, if he applies acceptance cuts to the data
    and simulation, and uses a beam size of 4mm (which matches with the data), the results show a better match between
    data and simulation. He also tried dividing the beam spot into 5 different zones, and looked at the resulting dp
    distribution for each. He did see a shift in the central value of dp between zones, however this shift was not seen in the
    simulation. He also compared the shift in θ and φ for the 5 zones. JP commented that the θ distribution in
    the data is symmetric and centered around zero, while the simulation result is not. It is possible that this is due to the
    fact that Jie is using the old SNAKE model; he will get the updated version from Min and see if it makes a difference.
    More details can be see in his slides here.

• Pengjia
  • Posted his false asymmetry results to the ELOG.
  • Working on data quality check for the 1.7 GeV, 2.5T setting. It looks like the spread in yields in some settings is
    strongly dependent on the scattering angle. JP suggested looking at beam position or other raw variables, since the
    scattering angle is a calculated value and depends on optics. It seems most settings with problems correspond to a
    break in time when the runs were taken, which may suggest a problem with the spectrometer. Pengjia will look into
    this next. More details can be seen in his slides here.

• Toby
  • Gave an update on his yield drift study for the 3.3 GeV setting. For this time, he looked at the target field (central
    NMR value) over the 2.34 GeV momentum setting, a period of about 6 hours. While there are some jumps in the signal,
    there isn't a consistent drift like is seen in the yields. However, there is a period where the signal jumps significantly; he
    will look into a possible cause for this. He also looked at the scaler BCM counts and trigger rates for these runs. There
    was no noticeable drift in the scaler rates, but the beam current was not stable during this time.. He also computed the
    "scaler yield" by dividing the total triggers by the BCM counts and saw a drift similar to what is seen in the normalized
    standard yield. Previous to these runs being taken, there was a flood in the hall resulting in a power outage. It's possible
    that the drifting is a result of systems not being stable while these runs were taken. More details can be seen in his
    slides here.

• Ryan
  • Working on a data quality check for the 1.1 GeV, 2.5T setting. In general the setting looks pretty good; the maximum
    spread is 10% and the minimum is 0.01%, with an average of ~2% spread. Fewer runs were taken in this setting, and the
    runs were taken consecutively, resulting in smaller spreads overall. In addition, there was data taken at this setting at
    3 different momentum settings, all looking at elastic, and all on the same material. Next he will try to determine the
    problem for the settings with a large spread (~10%). More details can be seen in his slides here.

1/7/2015

Present: Chao, Jie, JP, Min, Kalyan, Jixie, Melissa
By Phone: Yunxiu, Vince, Pengjia, Toby, Ryan, Ellie, Karl, Todd, Nilanga, Haiyan

Feature Presentations:

Each student gave a short update on their analysis projects since the last collaboration meeting on November 14th:

• Melissa
  • Method for packing fraction analysis is complete; the packing fraction values for each material still need to be
    extracted. This will probably take ~1 week, but the yield discrepancies need to be understood before it can be
    completed. She is also working on data quality checks for yields, specifically the 2.2 GeV, 2.5T setting. After these
    projects are complete she will work on the PbPt check using elastic asymmetries. More details can be seen in her
    slides here.

• Toby
  • Focusing on data quality checks of yields for production runs. He has completed the 2.2 GeV 5T settings, both
    longitudinal and transverse, and the 3.3 GeV setting. The 2.2 GeV 5T settings have few problems, but the 3.3 GeV
    has many momentum settings where the yields drift over time. He sees a similar drift in the left and right arm data.
    He is still trying to figure out the cause for the drift. In addition, he is working on tuning the Bosted model to helium
    and carbon dilution runs to simulate the background for dilution analysis, with a goal of finishing the dilution analysis
    by mid-march. More details can be seen in his slides here.
  • Information on data quality checks can be found on the wiki here.

• Jie
  • Looked at the effect of changing the scattering angle on the cross section for carbon, nitrogen, helium and hydrogen.
    This may help explain the discrepancy we see in the yields, but is problem not the only cause. He is also working on
    finishing the dp simulation, which should be done soon, and will begin working with Min to learn more about the acceptance
    study. More details can be seen in his slides here.

• Chao
  • Gave an update on the status of optics analysis. He is finishing up the 2nd iteration of the optics calibration; the LHRS
    is complete and the RHRS has one setting to go (1.158 GeV). For the 2.2 GeV, 5T, transverse setting, there is no full
    dp scan, so the longitudinal data taken at that energy setting will be used. Once the 2nd iteration of the calibration is
    complete, he and Min will compile a technote on the optics study. He has also modified the geometry part of the g2psim
    package to make it more configurable. More details can be seen in his slides here.

• Min
  • Working on the acceptance study. In the focal plane, there seems to be good agreement between simulation and data.
    In the target plane, in the θ vs φ plot, there seems to be a shift in φ for all dp settings; it seems to be a linear
    correlation with dp. Next she will work on a correction for φ-target vs dp and compare target plane variables. To finish the
    good septum, straight through setting it will probably take 1-2 months, then an additional 1-2 months for the other 2 septum
    settings. More details can be see in her slides here.

• Ryan
  • He has completed a draft for a PRC paper on unpolarized He3 cross section data. He still needs to complete the He3 radiative
    correction analysis for saGDH, but is waiting on updated nitrogen cross sections for saGDH. He is also working on the carbon/
    nitrogen ratio for saGDH, but is waiting on updated analysis from Vince before continuing. He is also working on data quality
    checks for production runs for the 1.1 GeV setting, and is starting to look into polarized radiative corrections. More details can
    be seen in his slides here.

• Pengjia
  • Calculated the false asymmetry by comparing the asymmetry before and after applying detector cuts. He found the false
    asymmetry to be small; less than 200 ppm for all energy settings. He's also working on a data quality check for the 1.7 GeV
    data set. More details can be seen in his slides here.

General Discussion:

• Yields stability/overall data quality check is the main issue at this time.
• Progress of acceptance study looks good, but could become an analysis bottleneck.

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Jan-June 2015

Minutes_Jan2015_to_June2015

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July-Dec 2014

Minutes_July2014_to_Dec2014

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Jan-June 2014

Minutes_Jan2014_to_June2014

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June-Dec 2013

Minutes_June2013_to_Dec2013

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Jan-May 2013

Minutes_Jan2013_to_May2013

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April-Dec 2012

Minutes_Apr2012_to_Dec2012

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Jan-March 2012

Minutes_Jan2012_to_Mar2012

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July-Dec 2011

Minutes_July2011_to_Dec_2011

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Minutes_Jan2011_to_June_2011

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