G2p Analysis Minutes

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.