Difference between revisions of "G2p Analysis Minutes"

Revision as of 19:05, 5 February 2014

Minutes of the weekly analysis meetings

Agenda

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.

June-Dec 2013

Minutes_June2013_to_Dec2013

Jan-May 2013

Minutes_Jan2013_to_May2013

April-Dec 2012

Minutes_Apr2012_to_Dec2012

Jan-March 2012

Minutes_Jan2012_to_Mar2012

July-Dec 2011

Minutes_July2011_to_Dec_2011

Jan-June 2011

Minutes_Jan2011_to_June_2011