Thesis Committee Meeting 1

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Thesis Committee Meeting (1)
Measurement of Ax and Az Asymmetries in the
quasi-elastic 3He(e,e'd) reaction
Xiaohui Zhan MIT 11. 14. 2007
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• Physics Motivation
• Theory Introduction
• Experiment Setup and Status

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Physics Motivation

• Achieve a better understanding of the
  ground-state spin structure of 3He nucleus, How
  good it is as the effective polarized neutron
  target?
• Test the state-of-the-art Faddeev calculation and
  gain better understanding of the role of the D
  and S states in 3He ground-state wave function.
• Jlab double polarized measurment E05-102 is a
  good opptunity to access the small components
• Impact all experiments using polarized 3He as the
  polarized neutron target, i. e. A1n, GEn.

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3He ground state

• S spacially symmetric, 90 of averaged WF,
  neutron target
• D generated by tensor component of N-N force,
  8.5
• S mixed-symmetry configuration, 1.5
• Other components negligible, 0.1

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Effective Neutron Polarization in 3He
(J. L. Friar, B. F. Gibson, et al., Phys. Rev. C
42, 2310, 1990 )
Averaging over available world calculations gives
Summary of uncertainties in E99-117, the expected
statistical error of the 11 GeV measurement is
comparable to or even smaller than the error in
Pp and Pn.
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Formalism of the 3He(e,ed)p reaction
Cross-section general form
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Why 3He(e,ed)
Proton pole PWIA
Deuteron pole quasi-deuteron model
Unique isoscalar-isovector interference in
3He(e,ed) sensitivity to S state.
(S. Nagorny, W. Turchinetz, Phys. Lett. B 389
(1996) 429-432)
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Two Independent Faddeev Calculations
Bochum/Krakow Group
Hannover Group

• Faddeev Calculation
• FSI
• AV18 NN Potentail
• Urbana IX 3NF large CPU effort for small effect
• Coulomb Interactions
• Standard MEC
• Charge-Density MEC(sensitive to high momentum
  components)

• Faddeev Calculation
• FSI
• Refit CD Bonn NN Potential (previously used Paris
  NN Potential)
• Delta degrees of freedom used to provide 3NF
• Coulomb Interactions
• Standard MEC
• Relativistic 1-Body Charge Corrections

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Bochum Group Ingredients
Full Faddeev calculations in perpendicular
kinematics, with full wave-function, showing the
dependengce on included ingredients. The 3NF
effect is not negligible, but relatively small.
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Hannover Group Ingredients
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Head-to-Head Comparison

• Different NN potentials along with charge-density
  MEC are presently being investigated.
• Our experiment will help significantly in
  diminishing the differences between these two
  theoretical approaches.

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Bochum/Krakow WF Truncations
Both Bochum/Krakow and Hannover Groups are doing
WF truncation calculations.
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Sensitivity to S'
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Analysis of Proton Events
These new CPU intensive calculations have become
available

• Both (e,ed) and (e,ep) will be detected in
  BigBite.
• Proton asymmetry is not sensitive to S part of
  the WF.

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Experiment configuration
Quasi-elastic electron 2.2GeV
Scattered deuteron 621MeV
target spin parallel or perpendicular to q
Incident electron 2.4GeV
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Hall A Overview
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Beam Polarimetry

• Møller Polarimetry based on the scattering of
  two polarized electrons.

Target polarization (7.950.24) Invasive
measurment 0.5µA Total relative systematic
error 3.4

• Compton Polarimetry measures the process of
  Compton scattering.

Electron beam interacts with circularly polarized
photons. Scattered electron are deflected into an
electron detector and backscattered photons
detected by an electromagnetic calorimeter.
Concurrently measurement total relative
systematic error 1.6
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BigBite Hadron Package

• First used in SRC consists of an auxiliary plane
  and a trigger plane, large momentum (200 900
  MeV) and angular acceptance( 96 msr).

• Modification remove auxiliary plan, accommodate
  the 2-wire chamber assembly.

• Goal exellent discrimination between proton and
  deuteron, and unresolved pion, kaon at low
  momentum region.

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Wire chambers
New frame
SRC frame
Electronics
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BigBite Status
Hardware (Jlab engineerGlasgow)

• Frame design and modification done.
• All PMTs on the trigger plane fixed and re-glued.

Electronics Schematic Design (Bryan Moffit)

• PMTs tested, signal flow diagram done,
  calibration underway.
• Rack setup and cable map done.
• Wire chambers repair underway (on site).
• Wire chamber readout not ready, but will be the
  same as that being used in electron package.
• BigBite analysis package.

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Polarized 3He target

• Spin exchange between optically pumped Rb vapor
  or Rb-K mixture and 3He gas.
• 40cm long sealed glass cell containing 10 atm 3He
  gas.
• Polarization 55, thickness 1022 atoms/cm2.
• With 15 microA beam, polarized luminorsity 1036
  particles/cm2/s.
• Polarization monitored with NMR (nuclear magnetic
  resonance), calibrated by EPR (electron
  paramagnetic resonance) or water NMR
  independently. Total uncertatinty lt4.

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Target Major Upgrades

• The vertical pair of Helmholtz coils were added
  to produce the vertical pumping.

Field mapping was done, BigBite fringe field and
shielding effects have been investigated, the
simulated field gradients are under 20 mG/cm in
the central region (Y. Qiang).

• New oven was designed, light, excellent thermal
  insulation aiming for 250oC, will be installed at
  the end of November.
• New Optics simulation design, software upgrade.
• Production of 20 new cell is underway (WM and
  UVa), 14 done! Maximum polarization 60.

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Target Work List

• NMR, EPR for each new cell.
• Spin filp (transversity, Ay).
• Water calibration.
• Cell characterization cell wall thickness,
  density.

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MCEEP Simulation

• The spin angle of the target will be restricted
  along or perpendicular to the beamline due to the
  optical design. Acceptance effect and statistics
  estimation.
• First round of MCEEP simulation was done, phase
  space weighted by calculated cross-section, but
  only the central kinematics was done.
• Challenge CPU intensive, choose of kinematics.

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Experiment Collaboration





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Thank you!
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