Hall A Collaboration Meeting

1
Hall A Collaboration Meeting
2
Main Physics Goals

• General Achieve a better understanding of the
  ground-state spin structure of 3He, i.e. improve
  our understanding of 3He rather than using it as
  an effective neutron target.
• Specific Test state-of-the-art Faddeev
  calculations and use these calculations to gain a
  better understanding of the dynamics and the S'
  and D wave-function components of 3He.

This is accomplished by making precision
measurements of the double polarized 3He(e,e'd)
reaction.

• Impact All experiments using 3He as a
  polarized neutron target.

3
An A1 Example

• Shown are the error bars from a recent Hall A
  polarized 3He experiment PRL 92 (2004) 012004.
• At 12GeV this measurement becomes limited by our
  understanding of 3He.

4
Ground State of 3He

• S spatially symmetric, 90 of spin-averaged WF,
  neutron target
• D generated by tensor component of NN force, 8.5
• S' mixed-symmetry configuration, 1.5

As a function of missing momentum, these
relative contributions can affect the (e,e'N)
reaction differently.
e.g. the NIKHEF D(e,e'p) results PRL 89 (2002)
102302
5
Why detect the quasi-elastic Deuteron?
Unique isoscalar-isovector interference in
3He(e,e'd)
6
Sketch of Experiment
quasi-elastic electron
single arm elastic electron
target spin parallel and perpendicular to q
quasi-elastic deuteron
7
BigBite Spectrometer During SRC Experiment
8
Ingredients of the Theory Calculations
Bochum/Krakov Group
Hannover Group

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

• Faddeev Calculation
• Final State Interactions
• 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

Blue Items are New Since PAC 22
9
Bochum/Krakow Group Ingredients
Q2 fixed by HRS and the missing momentum range
bitten without moving BigBite
10
Hannover Group Ingredients
Q2 fixed by HRS and the missing momentum range
bitten without moving BigBite
11
Head-to-Head Comparison
Hannover Curves Updated From Those Shown In The
Proposal

• Groups are presently working together to
  understand the source(s) of disagreement.
• Different NN potentials along with charge-density
  MEC are presently being investigated.

12
Bochum/Krakow WF Truncations
Both Bochum/Krakow and Hannover Groups are doing
WF truncation calculations.
13
Sensitivity to S'
The same technique as used to extract Form
Factors from asymmetry data.
14
Analysis of Proton Events
These New CPU Intensive Calculations Have Just
Become Available

• both (e,e'p) and (e,e'd) will be detected in
  BigBite
• proton asymmetry is not sensitive to S' part of
  the wave-function

15
Addition of a HAND

• Hall A Neutron Detector
• Fully Assembled And Tested
• DAQ and Cables Available
• A Commitment of Manpower

16
Measurement of GEn by HAND

• Systematics Limited Measurement
• Expected Result is Shown with the Conservative
  Estimate 0.0039

17
Summary Status

• We will take the Benchmark Data at a fixed Q2 in
  (e,e'd) and (e,e'p) simultaneously over a broad
  range of missing momentum that the Bochum/Krakow
  and Hannover groups insist is needed to verify
  their calculations.
• This data will allow significant progress to be
  made on understanding of the three-body system.
• We were approved for 15 PAC days of polarized
  electrons beams.

• Standard HRS
• BigBite and Neutron Detector PMTs need to be
  tested
• Wirechambers same as will be used for d2 and
  Transversity
• 3He system similar to d2 and Transversity

18
Extra Slides
19
NIKHEF Double Asymmetry Deuteron Data
20
Hannover Group WF Truncations