Transcript NN and Few Nucleon Elastic Scattering

3N and 4N Systems
and the Ay Puzzle
Thomas B. Clegg
for TUNL Collaborators
Faculty: Clegg, Karwowski, Ludwig, Tornow
Current graduate students: Arnold, Couture, Daniels, Esterline,
Former experimental colleagues: Brune, Fisher, Katabuchi, Weisel
Theoretical collaborators: Fonseca et al., (Lisbon), Viviani et al. (Pisa)
Hale (LANL)
September 18, 2006
Chiral Dynamics 2006
Outline
• What physics is being investigated?
– Recent theoretical advances
– Theoretical comparisons with data: most are good
– Glaring discrepancies remain: what is their origin?
• New experiments are underway
– Ay in n+p, n+d, and n+3He
– Spin correlation measurements in p+3He
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Chiral Dynamics 2006
Modeling Few-N Scattering
• Start with modern NN potentials
– Nijmegen, CD-Bonn, AV-18
– 3N interaction, e.g. Urbana IX
• Use these to calculate observables in 3N & 4N systems
– Coordinate vs. momentum space descriptions
– “Benchmark calculation for proton-deuteron elastic
scattering observables including the Coulomb interaction,”
A. Deltuva, et al. Phys. Rev. C 71, 064003 (2005)
• 4N system is becoming a fertile ‘theoretical laboratory’
– Lightest system with resonant states and thresholds
– Simplest where systems of isospin T=3/2 can be studied.
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p+d: Benchmark Comparisons
A. Deltuva, et al. Phys. Rev. C 71, 064003 (2005)
dσ/dΩ
Ay
3 MeV
10 MeV
65 MeV
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iT11
Modeling Few-N Scattering
• Start with modern NN potentials
– Nijmegen, CD-Bonn, AV-18
– 3N interaction, e.g. Urbana IX
• Use these to calculate observables in 3N & 4N systems
– Coordinate vs. momentum space descriptions
– “Benchmark calculation for proton-deuteron elastic
scattering observables including the Coulomb interaction,”
A. Deltuva, et al. Phys. Rev. C 71, 064003 (2005)
• 4N system is becoming a fertile ‘theoretical laboratory’
– Lightest system with resonant states and thresholds
– Simplest where systems of isospin T=3/2 can be studied.
September 18, 2006
Chiral Dynamics 2006
Brune et al., Phys Rev C63 (2001) 44013
September 18, 2006
T21
Ayy
– 3N systems: σ, T20, T21, T22
T21
• Excellent agreement also
with some observables
T20
Comparisons with Data
Chiral Dynamics 2006
p+d, 431.3 keV
Comparisons with Data
• Excellent agreement with
some observables
– 4N systems: σ(θ)
p + 3He, 1.0 - 4.0 MeV
Fisher et al, PRC74 (2006) 034001
Fisher et al, PRC74 (2006) 034001
P+ 3He , 1.o-4.0 MeV
B. Fisher et al, PRC74
(2006) 034001
September 18, 2006
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Glaring Discrepancies
The “Ay Puzzle”
• Significant disagreement remains for Ay
– Discrepancy grows with increasing target mass
Barker et al., PRL 48 (1982) 918.
p+p
5.05 MeV
Brune, et al., PR C63, 044013 (2001)
p+d
667 keV
9.05 MeV
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Chiral Dynamics 2006
Fisher et al, PRC74 (2006) 034001
p+3He
1.00 MeV 1.60 MeV
p + 3He Ay Measurements
September 18, 2006
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Comparisons with Data
The “Ay Puzzle”
– Fractional difference is
nearly constant for 3N
systems at low energy
– These differences vanish
above 40 MeV.
[Ay(expt)-Ay(th)] / Ay(expt)
• Differences between experiment and theory with 3NF
persist for several targets and over a significant energy
range
p + 3He
p+d
•
n+do
B Fisher, PRC74 (2006) 034001
Beam Energy (MeV)
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Origin of Discrepancy?
• Are the input NN potentials correct?
• Is the correct 3-nucleon interaction being used?
• Is something being left out of calculations?
Disagreement exists about
the origin of the problem!
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New Experiment: n+p
G. Weisel, et al. , private communication
• New TUNL 12 MeV Ay data being analyzed
• Careful corrections applied
for polarization-dependent
detector efficiencies
Nijmegen
Polynomial Fit
• Goal: Check present 3P N-N
scattering phase shifts
• New data lie significantly below predictions using phases
from the Nijmegen partial wave analysis.
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New Experiment: n+d
G. Weisel, et al. , private communication
16 MeV
• New data being taken to map out the
energy dependence of the discrepancy.
• New TUNL data in energy range
where the ‘Ay puzzle’ disappears.
• Data collection incomplete, and
multiple scattering and finite geometry
corrections have not yet been applied.
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19 MeV
22.5 MeV
30 MeV
New Experiment: n+3He
J. Esterline, et al., private communication
• Data collection underway for Ay
with shielded neutron source
and incident polarized beam
• Goal is high-accuracy measurements
at low energies where p+3He data
were taken by Fisher et al.
• Compare with:
4.05 MeV
– R-matrix calculations of G. Hale
– calculations of A. Fonseca et al. which
use finite range approximation of the
CD-Bonn potential
September 18, 2006
3.14 MeV
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5.54 MeV
New Experiment: p+3He
T. Daniels, et al., private communication
• New data being collected
with recently completed
optically-pumped
polarized 3He target
• New A0y, Ayy, Axx data
between 2 and 6 MeV
Polarized
3He in
Faraday
cup
NMR
Coil
• Plan new phase-shift
analysis of all new and existing data
Detectors
Shielded
Sine-Theta
Coil
Beam
Target
Cell
• Compare with most recent calculations of Viviani et al.
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Chiral Dynamics 2006
Rb-3He Spin-Exchange
Rb
3He
laser
light
I·S
Fermi-contact
hyperfine interaction
Rb
I
S
• Works best for I = ½ noble gases (3He and 129Xe).
• Takes minutes for 129Xe, hours for 3He.
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3He
Polarized 3He Target “Overview”
Katabuchi, et al., Rev. Sci. Instrum. 76, 033503 (2005)
TargetTarget
cell
inside
sine-theta coil
rizer
Optically pumped
Rb spin-exchange
polarizer
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Polarized 3He Target Cell
•
•
•
•
•
September 18, 2006
Pyrex glass cell with Kapton windows
3He pressure ~1 ATM
NMR to monitor 3He target polarization
Calibrate NMR by 4He+3He scattering
Polarization 1/e lifetime ~ 2 hrs
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p+3He: New Axx and Ayy Data
Axx
Ayy
George and Knutson,
PRC 67, 027001 (2003)
• Two existing best-fit PSA solutions provide widely
different p-3He zero-energy scattering lengths.
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Chiral Dynamics 2006
New Narrowed Laser System
• Use external optical cavity with grating to narrow laser
linewidth from 3 nm to 0.3 nm
• More efficient use of light enables higher 3He polarization
Wavelength profile measured behind
optical pumping cell
50 W, 25-diode laser array
Grating
0.3nm FWHM
30 W to optical
pumping cell
September 18, 2006
¼ wave plate
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Hybrid Spin-Exchange Optical Pumping
E. Babcock, et al., “Hybrid Spin-Exchange Optical Pumping of 3He,” PRL 91, 123003 (2003).
Circularly
polarized
laser light
(ħ per
photon)
OP
Polarized
Polarize
Polarize
valence
d
d
electrons of
Rb Rb atoms
K
SE
Polarized 3He
nuclei
alkali-alkali
spin
exchange
• Enables shorter pumping time and higher 3He polarization
• New p+3He scattering measurements with these systems
will begin soon.
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Other Experimental Possibilities?
• n+3He cross section measurements, En< 5 MeV.
• n+3He A0y and spin-correlation measurements
– Requires development of a high-pressure, polarized 3He target
and improved pulsed polarized neutron beam
• n+t, p+t measurements

– Analysis of old LANL A0y measurements in t  p scattering
– Make n+t Ay measurements
– Requires a sealed high-pressure tritium target
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Summary
• Low-energy, few-nucleon scattering:
– is providing the best possible data to resolve current
theoretical issues;
– is supported by a strong community of active theorists;
– is providing stimulating thesis projects for doctoral
students.
• But, what is most important to measure next??
September 18, 2006
Chiral Dynamics 2006
September 18, 2006
Chiral Dynamics 2006